Bug Summary

File:lib/Transforms/Utils/SimplifyCFG.cpp
Warning:line 2329, column 27
Called C++ object pointer is null

Annotated Source Code

1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Peephole optimize the CFG.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/ADT/APInt.h"
15#include "llvm/ADT/ArrayRef.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/Optional.h"
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/ADT/SetOperations.h"
20#include "llvm/ADT/SetVector.h"
21#include "llvm/ADT/SmallPtrSet.h"
22#include "llvm/ADT/SmallSet.h"
23#include "llvm/ADT/SmallVector.h"
24#include "llvm/ADT/Statistic.h"
25#include "llvm/Analysis/AssumptionCache.h"
26#include "llvm/Analysis/ConstantFolding.h"
27#include "llvm/Analysis/EHPersonalities.h"
28#include "llvm/Analysis/InstructionSimplify.h"
29#include "llvm/Analysis/TargetTransformInfo.h"
30#include "llvm/Analysis/ValueTracking.h"
31#include "llvm/IR/BasicBlock.h"
32#include "llvm/IR/CFG.h"
33#include "llvm/IR/CallSite.h"
34#include "llvm/IR/Constant.h"
35#include "llvm/IR/ConstantRange.h"
36#include "llvm/IR/Constants.h"
37#include "llvm/IR/DataLayout.h"
38#include "llvm/IR/DebugInfo.h"
39#include "llvm/IR/DerivedTypes.h"
40#include "llvm/IR/GlobalValue.h"
41#include "llvm/IR/GlobalVariable.h"
42#include "llvm/IR/IRBuilder.h"
43#include "llvm/IR/InstrTypes.h"
44#include "llvm/IR/Instruction.h"
45#include "llvm/IR/Instructions.h"
46#include "llvm/IR/IntrinsicInst.h"
47#include "llvm/IR/Intrinsics.h"
48#include "llvm/IR/LLVMContext.h"
49#include "llvm/IR/MDBuilder.h"
50#include "llvm/IR/Metadata.h"
51#include "llvm/IR/Module.h"
52#include "llvm/IR/NoFolder.h"
53#include "llvm/IR/Operator.h"
54#include "llvm/IR/PatternMatch.h"
55#include "llvm/IR/Type.h"
56#include "llvm/IR/User.h"
57#include "llvm/IR/Value.h"
58#include "llvm/Support/Casting.h"
59#include "llvm/Support/CommandLine.h"
60#include "llvm/Support/Debug.h"
61#include "llvm/Support/ErrorHandling.h"
62#include "llvm/Support/KnownBits.h"
63#include "llvm/Support/MathExtras.h"
64#include "llvm/Support/raw_ostream.h"
65#include "llvm/Transforms/Utils/BasicBlockUtils.h"
66#include "llvm/Transforms/Utils/Local.h"
67#include "llvm/Transforms/Utils/ValueMapper.h"
68#include <algorithm>
69#include <cassert>
70#include <climits>
71#include <cstddef>
72#include <cstdint>
73#include <iterator>
74#include <map>
75#include <set>
76#include <utility>
77#include <vector>
78
79using namespace llvm;
80using namespace PatternMatch;
81
82#define DEBUG_TYPE"simplifycfg" "simplifycfg"
83
84// Chosen as 2 so as to be cheap, but still to have enough power to fold
85// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
86// To catch this, we need to fold a compare and a select, hence '2' being the
87// minimum reasonable default.
88static cl::opt<unsigned> PHINodeFoldingThreshold(
89 "phi-node-folding-threshold", cl::Hidden, cl::init(2),
90 cl::desc(
91 "Control the amount of phi node folding to perform (default = 2)"));
92
93static cl::opt<bool> DupRet(
94 "simplifycfg-dup-ret", cl::Hidden, cl::init(false),
95 cl::desc("Duplicate return instructions into unconditional branches"));
96
97static cl::opt<bool>
98 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
99 cl::desc("Sink common instructions down to the end block"));
100
101static cl::opt<bool> HoistCondStores(
102 "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
103 cl::desc("Hoist conditional stores if an unconditional store precedes"));
104
105static cl::opt<bool> MergeCondStores(
106 "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
107 cl::desc("Hoist conditional stores even if an unconditional store does not "
108 "precede - hoist multiple conditional stores into a single "
109 "predicated store"));
110
111static cl::opt<bool> MergeCondStoresAggressively(
112 "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
113 cl::desc("When merging conditional stores, do so even if the resultant "
114 "basic blocks are unlikely to be if-converted as a result"));
115
116static cl::opt<bool> SpeculateOneExpensiveInst(
117 "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
118 cl::desc("Allow exactly one expensive instruction to be speculatively "
119 "executed"));
120
121static cl::opt<unsigned> MaxSpeculationDepth(
122 "max-speculation-depth", cl::Hidden, cl::init(10),
123 cl::desc("Limit maximum recursion depth when calculating costs of "
124 "speculatively executed instructions"));
125
126STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps")static llvm::Statistic NumBitMaps = {"simplifycfg", "NumBitMaps"
, "Number of switch instructions turned into bitmaps", {0}, false
}
;
127STATISTIC(NumLinearMaps,static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, false}
128 "Number of switch instructions turned into linear mapping")static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, false}
;
129STATISTIC(NumLookupTables,static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, false}
130 "Number of switch instructions turned into lookup tables")static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, false}
;
131STATISTIC(static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, false}
132 NumLookupTablesHoles,static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, false}
133 "Number of switch instructions turned into lookup tables (holes checked)")static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, false}
;
134STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares")static llvm::Statistic NumTableCmpReuses = {"simplifycfg", "NumTableCmpReuses"
, "Number of reused switch table lookup compares", {0}, false
}
;
135STATISTIC(NumSinkCommons,static llvm::Statistic NumSinkCommons = {"simplifycfg", "NumSinkCommons"
, "Number of common instructions sunk down to the end block",
{0}, false}
136 "Number of common instructions sunk down to the end block")static llvm::Statistic NumSinkCommons = {"simplifycfg", "NumSinkCommons"
, "Number of common instructions sunk down to the end block",
{0}, false}
;
137STATISTIC(NumSpeculations, "Number of speculative executed instructions")static llvm::Statistic NumSpeculations = {"simplifycfg", "NumSpeculations"
, "Number of speculative executed instructions", {0}, false}
;
138
139namespace {
140
141// The first field contains the value that the switch produces when a certain
142// case group is selected, and the second field is a vector containing the
143// cases composing the case group.
144typedef SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>
145 SwitchCaseResultVectorTy;
146// The first field contains the phi node that generates a result of the switch
147// and the second field contains the value generated for a certain case in the
148// switch for that PHI.
149typedef SmallVector<std::pair<PHINode *, Constant *>, 4> SwitchCaseResultsTy;
150
151/// ValueEqualityComparisonCase - Represents a case of a switch.
152struct ValueEqualityComparisonCase {
153 ConstantInt *Value;
154 BasicBlock *Dest;
155
156 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
157 : Value(Value), Dest(Dest) {}
158
159 bool operator<(ValueEqualityComparisonCase RHS) const {
160 // Comparing pointers is ok as we only rely on the order for uniquing.
161 return Value < RHS.Value;
162 }
163
164 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
165};
166
167class SimplifyCFGOpt {
168 const TargetTransformInfo &TTI;
169 const DataLayout &DL;
170 unsigned BonusInstThreshold;
171 AssumptionCache *AC;
172 SmallPtrSetImpl<BasicBlock *> *LoopHeaders;
173 // See comments in SimplifyCFGOpt::SimplifySwitch.
174 bool LateSimplifyCFG;
175 Value *isValueEqualityComparison(TerminatorInst *TI);
176 BasicBlock *GetValueEqualityComparisonCases(
177 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases);
178 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
179 BasicBlock *Pred,
180 IRBuilder<> &Builder);
181 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
182 IRBuilder<> &Builder);
183
184 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
185 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
186 bool SimplifySingleResume(ResumeInst *RI);
187 bool SimplifyCommonResume(ResumeInst *RI);
188 bool SimplifyCleanupReturn(CleanupReturnInst *RI);
189 bool SimplifyUnreachable(UnreachableInst *UI);
190 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
191 bool SimplifyIndirectBr(IndirectBrInst *IBI);
192 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
193 bool SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
194
195public:
196 SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
197 unsigned BonusInstThreshold, AssumptionCache *AC,
198 SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
199 bool LateSimplifyCFG)
200 : TTI(TTI), DL(DL), BonusInstThreshold(BonusInstThreshold), AC(AC),
201 LoopHeaders(LoopHeaders), LateSimplifyCFG(LateSimplifyCFG) {}
202
203 bool run(BasicBlock *BB);
204};
205
206} // end anonymous namespace
207
208/// Return true if it is safe to merge these two
209/// terminator instructions together.
210static bool
211SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2,
212 SmallSetVector<BasicBlock *, 4> *FailBlocks = nullptr) {
213 if (SI1 == SI2)
214 return false; // Can't merge with self!
215
216 // It is not safe to merge these two switch instructions if they have a common
217 // successor, and if that successor has a PHI node, and if *that* PHI node has
218 // conflicting incoming values from the two switch blocks.
219 BasicBlock *SI1BB = SI1->getParent();
220 BasicBlock *SI2BB = SI2->getParent();
221
222 SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
223 bool Fail = false;
224 for (BasicBlock *Succ : successors(SI2BB))
225 if (SI1Succs.count(Succ))
226 for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
227 PHINode *PN = cast<PHINode>(BBI);
228 if (PN->getIncomingValueForBlock(SI1BB) !=
229 PN->getIncomingValueForBlock(SI2BB)) {
230 if (FailBlocks)
231 FailBlocks->insert(Succ);
232 Fail = true;
233 }
234 }
235
236 return !Fail;
237}
238
239/// Return true if it is safe and profitable to merge these two terminator
240/// instructions together, where SI1 is an unconditional branch. PhiNodes will
241/// store all PHI nodes in common successors.
242static bool
243isProfitableToFoldUnconditional(BranchInst *SI1, BranchInst *SI2,
244 Instruction *Cond,
245 SmallVectorImpl<PHINode *> &PhiNodes) {
246 if (SI1 == SI2)
247 return false; // Can't merge with self!
248 assert(SI1->isUnconditional() && SI2->isConditional())((SI1->isUnconditional() && SI2->isConditional(
)) ? static_cast<void> (0) : __assert_fail ("SI1->isUnconditional() && SI2->isConditional()"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 248, __PRETTY_FUNCTION__))
;
249
250 // We fold the unconditional branch if we can easily update all PHI nodes in
251 // common successors:
252 // 1> We have a constant incoming value for the conditional branch;
253 // 2> We have "Cond" as the incoming value for the unconditional branch;
254 // 3> SI2->getCondition() and Cond have same operands.
255 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
256 if (!Ci2)
257 return false;
258 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
259 Cond->getOperand(1) == Ci2->getOperand(1)) &&
260 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
261 Cond->getOperand(1) == Ci2->getOperand(0)))
262 return false;
263
264 BasicBlock *SI1BB = SI1->getParent();
265 BasicBlock *SI2BB = SI2->getParent();
266 SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
267 for (BasicBlock *Succ : successors(SI2BB))
268 if (SI1Succs.count(Succ))
269 for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
270 PHINode *PN = cast<PHINode>(BBI);
271 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
272 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
273 return false;
274 PhiNodes.push_back(PN);
275 }
276 return true;
277}
278
279/// Update PHI nodes in Succ to indicate that there will now be entries in it
280/// from the 'NewPred' block. The values that will be flowing into the PHI nodes
281/// will be the same as those coming in from ExistPred, an existing predecessor
282/// of Succ.
283static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
284 BasicBlock *ExistPred) {
285 if (!isa<PHINode>(Succ->begin()))
286 return; // Quick exit if nothing to do
287
288 PHINode *PN;
289 for (BasicBlock::iterator I = Succ->begin(); (PN = dyn_cast<PHINode>(I)); ++I)
290 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
291}
292
293/// Compute an abstract "cost" of speculating the given instruction,
294/// which is assumed to be safe to speculate. TCC_Free means cheap,
295/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
296/// expensive.
297static unsigned ComputeSpeculationCost(const User *I,
298 const TargetTransformInfo &TTI) {
299 assert(isSafeToSpeculativelyExecute(I) &&((isSafeToSpeculativelyExecute(I) && "Instruction is not safe to speculatively execute!"
) ? static_cast<void> (0) : __assert_fail ("isSafeToSpeculativelyExecute(I) && \"Instruction is not safe to speculatively execute!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 300, __PRETTY_FUNCTION__))
300 "Instruction is not safe to speculatively execute!")((isSafeToSpeculativelyExecute(I) && "Instruction is not safe to speculatively execute!"
) ? static_cast<void> (0) : __assert_fail ("isSafeToSpeculativelyExecute(I) && \"Instruction is not safe to speculatively execute!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 300, __PRETTY_FUNCTION__))
;
301 return TTI.getUserCost(I);
302}
303
304/// If we have a merge point of an "if condition" as accepted above,
305/// return true if the specified value dominates the block. We
306/// don't handle the true generality of domination here, just a special case
307/// which works well enough for us.
308///
309/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
310/// see if V (which must be an instruction) and its recursive operands
311/// that do not dominate BB have a combined cost lower than CostRemaining and
312/// are non-trapping. If both are true, the instruction is inserted into the
313/// set and true is returned.
314///
315/// The cost for most non-trapping instructions is defined as 1 except for
316/// Select whose cost is 2.
317///
318/// After this function returns, CostRemaining is decreased by the cost of
319/// V plus its non-dominating operands. If that cost is greater than
320/// CostRemaining, false is returned and CostRemaining is undefined.
321static bool DominatesMergePoint(Value *V, BasicBlock *BB,
322 SmallPtrSetImpl<Instruction *> *AggressiveInsts,
323 unsigned &CostRemaining,
324 const TargetTransformInfo &TTI,
325 unsigned Depth = 0) {
326 // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
327 // so limit the recursion depth.
328 // TODO: While this recursion limit does prevent pathological behavior, it
329 // would be better to track visited instructions to avoid cycles.
330 if (Depth == MaxSpeculationDepth)
331 return false;
332
333 Instruction *I = dyn_cast<Instruction>(V);
334 if (!I) {
335 // Non-instructions all dominate instructions, but not all constantexprs
336 // can be executed unconditionally.
337 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
338 if (C->canTrap())
339 return false;
340 return true;
341 }
342 BasicBlock *PBB = I->getParent();
343
344 // We don't want to allow weird loops that might have the "if condition" in
345 // the bottom of this block.
346 if (PBB == BB)
347 return false;
348
349 // If this instruction is defined in a block that contains an unconditional
350 // branch to BB, then it must be in the 'conditional' part of the "if
351 // statement". If not, it definitely dominates the region.
352 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
353 if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
354 return true;
355
356 // If we aren't allowing aggressive promotion anymore, then don't consider
357 // instructions in the 'if region'.
358 if (!AggressiveInsts)
359 return false;
360
361 // If we have seen this instruction before, don't count it again.
362 if (AggressiveInsts->count(I))
363 return true;
364
365 // Okay, it looks like the instruction IS in the "condition". Check to
366 // see if it's a cheap instruction to unconditionally compute, and if it
367 // only uses stuff defined outside of the condition. If so, hoist it out.
368 if (!isSafeToSpeculativelyExecute(I))
369 return false;
370
371 unsigned Cost = ComputeSpeculationCost(I, TTI);
372
373 // Allow exactly one instruction to be speculated regardless of its cost
374 // (as long as it is safe to do so).
375 // This is intended to flatten the CFG even if the instruction is a division
376 // or other expensive operation. The speculation of an expensive instruction
377 // is expected to be undone in CodeGenPrepare if the speculation has not
378 // enabled further IR optimizations.
379 if (Cost > CostRemaining &&
380 (!SpeculateOneExpensiveInst || !AggressiveInsts->empty() || Depth > 0))
381 return false;
382
383 // Avoid unsigned wrap.
384 CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
385
386 // Okay, we can only really hoist these out if their operands do
387 // not take us over the cost threshold.
388 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
389 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
390 Depth + 1))
391 return false;
392 // Okay, it's safe to do this! Remember this instruction.
393 AggressiveInsts->insert(I);
394 return true;
395}
396
397/// Extract ConstantInt from value, looking through IntToPtr
398/// and PointerNullValue. Return NULL if value is not a constant int.
399static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
400 // Normal constant int.
401 ConstantInt *CI = dyn_cast<ConstantInt>(V);
402 if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
403 return CI;
404
405 // This is some kind of pointer constant. Turn it into a pointer-sized
406 // ConstantInt if possible.
407 IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
408
409 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
410 if (isa<ConstantPointerNull>(V))
411 return ConstantInt::get(PtrTy, 0);
412
413 // IntToPtr const int.
414 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
415 if (CE->getOpcode() == Instruction::IntToPtr)
416 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
417 // The constant is very likely to have the right type already.
418 if (CI->getType() == PtrTy)
419 return CI;
420 else
421 return cast<ConstantInt>(
422 ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
423 }
424 return nullptr;
425}
426
427namespace {
428
429/// Given a chain of or (||) or and (&&) comparison of a value against a
430/// constant, this will try to recover the information required for a switch
431/// structure.
432/// It will depth-first traverse the chain of comparison, seeking for patterns
433/// like %a == 12 or %a < 4 and combine them to produce a set of integer
434/// representing the different cases for the switch.
435/// Note that if the chain is composed of '||' it will build the set of elements
436/// that matches the comparisons (i.e. any of this value validate the chain)
437/// while for a chain of '&&' it will build the set elements that make the test
438/// fail.
439struct ConstantComparesGatherer {
440 const DataLayout &DL;
441 Value *CompValue; /// Value found for the switch comparison
442 Value *Extra; /// Extra clause to be checked before the switch
443 SmallVector<ConstantInt *, 8> Vals; /// Set of integers to match in switch
444 unsigned UsedICmps; /// Number of comparisons matched in the and/or chain
445
446 /// Construct and compute the result for the comparison instruction Cond
447 ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL)
448 : DL(DL), CompValue(nullptr), Extra(nullptr), UsedICmps(0) {
449 gather(Cond);
450 }
451
452 /// Prevent copy
453 ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
454 ConstantComparesGatherer &
455 operator=(const ConstantComparesGatherer &) = delete;
456
457private:
458 /// Try to set the current value used for the comparison, it succeeds only if
459 /// it wasn't set before or if the new value is the same as the old one
460 bool setValueOnce(Value *NewVal) {
461 if (CompValue && CompValue != NewVal)
462 return false;
463 CompValue = NewVal;
464 return (CompValue != nullptr);
465 }
466
467 /// Try to match Instruction "I" as a comparison against a constant and
468 /// populates the array Vals with the set of values that match (or do not
469 /// match depending on isEQ).
470 /// Return false on failure. On success, the Value the comparison matched
471 /// against is placed in CompValue.
472 /// If CompValue is already set, the function is expected to fail if a match
473 /// is found but the value compared to is different.
474 bool matchInstruction(Instruction *I, bool isEQ) {
475 // If this is an icmp against a constant, handle this as one of the cases.
476 ICmpInst *ICI;
477 ConstantInt *C;
478 if (!((ICI = dyn_cast<ICmpInst>(I)) &&
479 (C = GetConstantInt(I->getOperand(1), DL)))) {
480 return false;
481 }
482
483 Value *RHSVal;
484 const APInt *RHSC;
485
486 // Pattern match a special case
487 // (x & ~2^z) == y --> x == y || x == y|2^z
488 // This undoes a transformation done by instcombine to fuse 2 compares.
489 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) {
490
491 // It's a little bit hard to see why the following transformations are
492 // correct. Here is a CVC3 program to verify them for 64-bit values:
493
494 /*
495 ONE : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
496 x : BITVECTOR(64);
497 y : BITVECTOR(64);
498 z : BITVECTOR(64);
499 mask : BITVECTOR(64) = BVSHL(ONE, z);
500 QUERY( (y & ~mask = y) =>
501 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
502 );
503 QUERY( (y | mask = y) =>
504 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
505 );
506 */
507
508 // Please note that each pattern must be a dual implication (<--> or
509 // iff). One directional implication can create spurious matches. If the
510 // implication is only one-way, an unsatisfiable condition on the left
511 // side can imply a satisfiable condition on the right side. Dual
512 // implication ensures that satisfiable conditions are transformed to
513 // other satisfiable conditions and unsatisfiable conditions are
514 // transformed to other unsatisfiable conditions.
515
516 // Here is a concrete example of a unsatisfiable condition on the left
517 // implying a satisfiable condition on the right:
518 //
519 // mask = (1 << z)
520 // (x & ~mask) == y --> (x == y || x == (y | mask))
521 //
522 // Substituting y = 3, z = 0 yields:
523 // (x & -2) == 3 --> (x == 3 || x == 2)
524
525 // Pattern match a special case:
526 /*
527 QUERY( (y & ~mask = y) =>
528 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
529 );
530 */
531 if (match(ICI->getOperand(0),
532 m_And(m_Value(RHSVal), m_APInt(RHSC)))) {
533 APInt Mask = ~*RHSC;
534 if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) {
535 // If we already have a value for the switch, it has to match!
536 if (!setValueOnce(RHSVal))
537 return false;
538
539 Vals.push_back(C);
540 Vals.push_back(
541 ConstantInt::get(C->getContext(),
542 C->getValue() | Mask));
543 UsedICmps++;
544 return true;
545 }
546 }
547
548 // Pattern match a special case:
549 /*
550 QUERY( (y | mask = y) =>
551 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
552 );
553 */
554 if (match(ICI->getOperand(0),
555 m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
556 APInt Mask = *RHSC;
557 if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
558 // If we already have a value for the switch, it has to match!
559 if (!setValueOnce(RHSVal))
560 return false;
561
562 Vals.push_back(C);
563 Vals.push_back(ConstantInt::get(C->getContext(),
564 C->getValue() & ~Mask));
565 UsedICmps++;
566 return true;
567 }
568 }
569
570 // If we already have a value for the switch, it has to match!
571 if (!setValueOnce(ICI->getOperand(0)))
572 return false;
573
574 UsedICmps++;
575 Vals.push_back(C);
576 return ICI->getOperand(0);
577 }
578
579 // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
580 ConstantRange Span = ConstantRange::makeAllowedICmpRegion(
581 ICI->getPredicate(), C->getValue());
582
583 // Shift the range if the compare is fed by an add. This is the range
584 // compare idiom as emitted by instcombine.
585 Value *CandidateVal = I->getOperand(0);
586 if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) {
587 Span = Span.subtract(*RHSC);
588 CandidateVal = RHSVal;
589 }
590
591 // If this is an and/!= check, then we are looking to build the set of
592 // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
593 // x != 0 && x != 1.
594 if (!isEQ)
595 Span = Span.inverse();
596
597 // If there are a ton of values, we don't want to make a ginormous switch.
598 if (Span.isSizeLargerThan(8) || Span.isEmptySet()) {
599 return false;
600 }
601
602 // If we already have a value for the switch, it has to match!
603 if (!setValueOnce(CandidateVal))
604 return false;
605
606 // Add all values from the range to the set
607 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
608 Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
609
610 UsedICmps++;
611 return true;
612 }
613
614 /// Given a potentially 'or'd or 'and'd together collection of icmp
615 /// eq/ne/lt/gt instructions that compare a value against a constant, extract
616 /// the value being compared, and stick the list constants into the Vals
617 /// vector.
618 /// One "Extra" case is allowed to differ from the other.
619 void gather(Value *V) {
620 Instruction *I = dyn_cast<Instruction>(V);
621 bool isEQ = (I->getOpcode() == Instruction::Or);
622
623 // Keep a stack (SmallVector for efficiency) for depth-first traversal
624 SmallVector<Value *, 8> DFT;
625 SmallPtrSet<Value *, 8> Visited;
626
627 // Initialize
628 Visited.insert(V);
629 DFT.push_back(V);
630
631 while (!DFT.empty()) {
632 V = DFT.pop_back_val();
633
634 if (Instruction *I = dyn_cast<Instruction>(V)) {
635 // If it is a || (or && depending on isEQ), process the operands.
636 if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
637 if (Visited.insert(I->getOperand(1)).second)
638 DFT.push_back(I->getOperand(1));
639 if (Visited.insert(I->getOperand(0)).second)
640 DFT.push_back(I->getOperand(0));
641 continue;
642 }
643
644 // Try to match the current instruction
645 if (matchInstruction(I, isEQ))
646 // Match succeed, continue the loop
647 continue;
648 }
649
650 // One element of the sequence of || (or &&) could not be match as a
651 // comparison against the same value as the others.
652 // We allow only one "Extra" case to be checked before the switch
653 if (!Extra) {
654 Extra = V;
655 continue;
656 }
657 // Failed to parse a proper sequence, abort now
658 CompValue = nullptr;
659 break;
660 }
661 }
662};
663
664} // end anonymous namespace
665
666static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
667 Instruction *Cond = nullptr;
668 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
669 Cond = dyn_cast<Instruction>(SI->getCondition());
670 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
671 if (BI->isConditional())
672 Cond = dyn_cast<Instruction>(BI->getCondition());
673 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
674 Cond = dyn_cast<Instruction>(IBI->getAddress());
675 }
676
677 TI->eraseFromParent();
678 if (Cond)
679 RecursivelyDeleteTriviallyDeadInstructions(Cond);
680}
681
682/// Return true if the specified terminator checks
683/// to see if a value is equal to constant integer value.
684Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
685 Value *CV = nullptr;
686 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
687 // Do not permit merging of large switch instructions into their
688 // predecessors unless there is only one predecessor.
689 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
690 pred_end(SI->getParent())) <=
691 128)
692 CV = SI->getCondition();
693 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
694 if (BI->isConditional() && BI->getCondition()->hasOneUse())
695 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
696 if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
697 CV = ICI->getOperand(0);
698 }
699
700 // Unwrap any lossless ptrtoint cast.
701 if (CV) {
702 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
703 Value *Ptr = PTII->getPointerOperand();
704 if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
705 CV = Ptr;
706 }
707 }
708 return CV;
709}
710
711/// Given a value comparison instruction,
712/// decode all of the 'cases' that it represents and return the 'default' block.
713BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases(
714 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases) {
715 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
716 Cases.reserve(SI->getNumCases());
717 for (auto Case : SI->cases())
718 Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(),
719 Case.getCaseSuccessor()));
720 return SI->getDefaultDest();
721 }
722
723 BranchInst *BI = cast<BranchInst>(TI);
724 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
725 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
726 Cases.push_back(ValueEqualityComparisonCase(
727 GetConstantInt(ICI->getOperand(1), DL), Succ));
728 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
729}
730
731/// Given a vector of bb/value pairs, remove any entries
732/// in the list that match the specified block.
733static void
734EliminateBlockCases(BasicBlock *BB,
735 std::vector<ValueEqualityComparisonCase> &Cases) {
736 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
737}
738
739/// Return true if there are any keys in C1 that exist in C2 as well.
740static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
741 std::vector<ValueEqualityComparisonCase> &C2) {
742 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
743
744 // Make V1 be smaller than V2.
745 if (V1->size() > V2->size())
746 std::swap(V1, V2);
747
748 if (V1->empty())
749 return false;
750 if (V1->size() == 1) {
751 // Just scan V2.
752 ConstantInt *TheVal = (*V1)[0].Value;
753 for (unsigned i = 0, e = V2->size(); i != e; ++i)
754 if (TheVal == (*V2)[i].Value)
755 return true;
756 }
757
758 // Otherwise, just sort both lists and compare element by element.
759 array_pod_sort(V1->begin(), V1->end());
760 array_pod_sort(V2->begin(), V2->end());
761 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
762 while (i1 != e1 && i2 != e2) {
763 if ((*V1)[i1].Value == (*V2)[i2].Value)
764 return true;
765 if ((*V1)[i1].Value < (*V2)[i2].Value)
766 ++i1;
767 else
768 ++i2;
769 }
770 return false;
771}
772
773/// If TI is known to be a terminator instruction and its block is known to
774/// only have a single predecessor block, check to see if that predecessor is
775/// also a value comparison with the same value, and if that comparison
776/// determines the outcome of this comparison. If so, simplify TI. This does a
777/// very limited form of jump threading.
778bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
779 TerminatorInst *TI, BasicBlock *Pred, IRBuilder<> &Builder) {
780 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
781 if (!PredVal)
782 return false; // Not a value comparison in predecessor.
783
784 Value *ThisVal = isValueEqualityComparison(TI);
785 assert(ThisVal && "This isn't a value comparison!!")((ThisVal && "This isn't a value comparison!!") ? static_cast
<void> (0) : __assert_fail ("ThisVal && \"This isn't a value comparison!!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 785, __PRETTY_FUNCTION__))
;
786 if (ThisVal != PredVal)
787 return false; // Different predicates.
788
789 // TODO: Preserve branch weight metadata, similarly to how
790 // FoldValueComparisonIntoPredecessors preserves it.
791
792 // Find out information about when control will move from Pred to TI's block.
793 std::vector<ValueEqualityComparisonCase> PredCases;
794 BasicBlock *PredDef =
795 GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases);
796 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
797
798 // Find information about how control leaves this block.
799 std::vector<ValueEqualityComparisonCase> ThisCases;
800 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
801 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
802
803 // If TI's block is the default block from Pred's comparison, potentially
804 // simplify TI based on this knowledge.
805 if (PredDef == TI->getParent()) {
806 // If we are here, we know that the value is none of those cases listed in
807 // PredCases. If there are any cases in ThisCases that are in PredCases, we
808 // can simplify TI.
809 if (!ValuesOverlap(PredCases, ThisCases))
810 return false;
811
812 if (isa<BranchInst>(TI)) {
813 // Okay, one of the successors of this condbr is dead. Convert it to a
814 // uncond br.
815 assert(ThisCases.size() == 1 && "Branch can only have one case!")((ThisCases.size() == 1 && "Branch can only have one case!"
) ? static_cast<void> (0) : __assert_fail ("ThisCases.size() == 1 && \"Branch can only have one case!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 815, __PRETTY_FUNCTION__))
;
816 // Insert the new branch.
817 Instruction *NI = Builder.CreateBr(ThisDef);
818 (void)NI;
819
820 // Remove PHI node entries for the dead edge.
821 ThisCases[0].Dest->removePredecessor(TI->getParent());
822
823 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
824 << "Through successor TI: " << *TI << "Leaving: " << *NIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
825 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
826
827 EraseTerminatorInstAndDCECond(TI);
828 return true;
829 }
830
831 SwitchInst *SI = cast<SwitchInst>(TI);
832 // Okay, TI has cases that are statically dead, prune them away.
833 SmallPtrSet<Constant *, 16> DeadCases;
834 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
835 DeadCases.insert(PredCases[i].Value);
836
837 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI; } } while (false)
838 << "Through successor TI: " << *TI)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI; } } while (false)
;
839
840 // Collect branch weights into a vector.
841 SmallVector<uint32_t, 8> Weights;
842 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
843 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
844 if (HasWeight)
845 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
846 ++MD_i) {
847 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
848 Weights.push_back(CI->getValue().getZExtValue());
849 }
850 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
851 --i;
852 if (DeadCases.count(i->getCaseValue())) {
853 if (HasWeight) {
854 std::swap(Weights[i->getCaseIndex() + 1], Weights.back());
855 Weights.pop_back();
856 }
857 i->getCaseSuccessor()->removePredecessor(TI->getParent());
858 SI->removeCase(i);
859 }
860 }
861 if (HasWeight && Weights.size() >= 2)
862 SI->setMetadata(LLVMContext::MD_prof,
863 MDBuilder(SI->getParent()->getContext())
864 .createBranchWeights(Weights));
865
866 DEBUG(dbgs() << "Leaving: " << *TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Leaving: " << *TI <<
"\n"; } } while (false)
;
867 return true;
868 }
869
870 // Otherwise, TI's block must correspond to some matched value. Find out
871 // which value (or set of values) this is.
872 ConstantInt *TIV = nullptr;
873 BasicBlock *TIBB = TI->getParent();
874 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
875 if (PredCases[i].Dest == TIBB) {
876 if (TIV)
877 return false; // Cannot handle multiple values coming to this block.
878 TIV = PredCases[i].Value;
879 }
880 assert(TIV && "No edge from pred to succ?")((TIV && "No edge from pred to succ?") ? static_cast<
void> (0) : __assert_fail ("TIV && \"No edge from pred to succ?\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 880, __PRETTY_FUNCTION__))
;
881
882 // Okay, we found the one constant that our value can be if we get into TI's
883 // BB. Find out which successor will unconditionally be branched to.
884 BasicBlock *TheRealDest = nullptr;
885 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
886 if (ThisCases[i].Value == TIV) {
887 TheRealDest = ThisCases[i].Dest;
888 break;
889 }
890
891 // If not handled by any explicit cases, it is handled by the default case.
892 if (!TheRealDest)
893 TheRealDest = ThisDef;
894
895 // Remove PHI node entries for dead edges.
896 BasicBlock *CheckEdge = TheRealDest;
897 for (BasicBlock *Succ : successors(TIBB))
898 if (Succ != CheckEdge)
899 Succ->removePredecessor(TIBB);
900 else
901 CheckEdge = nullptr;
902
903 // Insert the new branch.
904 Instruction *NI = Builder.CreateBr(TheRealDest);
905 (void)NI;
906
907 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
908 << "Through successor TI: " << *TI << "Leaving: " << *NIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
909 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
910
911 EraseTerminatorInstAndDCECond(TI);
912 return true;
913}
914
915namespace {
916
917/// This class implements a stable ordering of constant
918/// integers that does not depend on their address. This is important for
919/// applications that sort ConstantInt's to ensure uniqueness.
920struct ConstantIntOrdering {
921 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
922 return LHS->getValue().ult(RHS->getValue());
923 }
924};
925
926} // end anonymous namespace
927
928static int ConstantIntSortPredicate(ConstantInt *const *P1,
929 ConstantInt *const *P2) {
930 const ConstantInt *LHS = *P1;
931 const ConstantInt *RHS = *P2;
932 if (LHS == RHS)
933 return 0;
934 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
935}
936
937static inline bool HasBranchWeights(const Instruction *I) {
938 MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
939 if (ProfMD && ProfMD->getOperand(0))
940 if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
941 return MDS->getString().equals("branch_weights");
942
943 return false;
944}
945
946/// Get Weights of a given TerminatorInst, the default weight is at the front
947/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
948/// metadata.
949static void GetBranchWeights(TerminatorInst *TI,
950 SmallVectorImpl<uint64_t> &Weights) {
951 MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
952 assert(MD)((MD) ? static_cast<void> (0) : __assert_fail ("MD", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 952, __PRETTY_FUNCTION__))
;
953 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
954 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
955 Weights.push_back(CI->getValue().getZExtValue());
956 }
957
958 // If TI is a conditional eq, the default case is the false case,
959 // and the corresponding branch-weight data is at index 2. We swap the
960 // default weight to be the first entry.
961 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
962 assert(Weights.size() == 2)((Weights.size() == 2) ? static_cast<void> (0) : __assert_fail
("Weights.size() == 2", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 962, __PRETTY_FUNCTION__))
;
963 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
964 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
965 std::swap(Weights.front(), Weights.back());
966 }
967}
968
969/// Keep halving the weights until all can fit in uint32_t.
970static void FitWeights(MutableArrayRef<uint64_t> Weights) {
971 uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
972 if (Max > UINT_MAX(2147483647 *2U +1U)) {
973 unsigned Offset = 32 - countLeadingZeros(Max);
974 for (uint64_t &I : Weights)
975 I >>= Offset;
976 }
977}
978
979/// The specified terminator is a value equality comparison instruction
980/// (either a switch or a branch on "X == c").
981/// See if any of the predecessors of the terminator block are value comparisons
982/// on the same value. If so, and if safe to do so, fold them together.
983bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
984 IRBuilder<> &Builder) {
985 BasicBlock *BB = TI->getParent();
986 Value *CV = isValueEqualityComparison(TI); // CondVal
987 assert(CV && "Not a comparison?")((CV && "Not a comparison?") ? static_cast<void>
(0) : __assert_fail ("CV && \"Not a comparison?\"", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 987, __PRETTY_FUNCTION__))
;
988 bool Changed = false;
989
990 SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
991 while (!Preds.empty()) {
992 BasicBlock *Pred = Preds.pop_back_val();
993
994 // See if the predecessor is a comparison with the same value.
995 TerminatorInst *PTI = Pred->getTerminator();
996 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
997
998 if (PCV == CV && TI != PTI) {
999 SmallSetVector<BasicBlock*, 4> FailBlocks;
1000 if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) {
1001 for (auto *Succ : FailBlocks) {
1002 if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split"))
1003 return false;
1004 }
1005 }
1006
1007 // Figure out which 'cases' to copy from SI to PSI.
1008 std::vector<ValueEqualityComparisonCase> BBCases;
1009 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
1010
1011 std::vector<ValueEqualityComparisonCase> PredCases;
1012 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
1013
1014 // Based on whether the default edge from PTI goes to BB or not, fill in
1015 // PredCases and PredDefault with the new switch cases we would like to
1016 // build.
1017 SmallVector<BasicBlock *, 8> NewSuccessors;
1018
1019 // Update the branch weight metadata along the way
1020 SmallVector<uint64_t, 8> Weights;
1021 bool PredHasWeights = HasBranchWeights(PTI);
1022 bool SuccHasWeights = HasBranchWeights(TI);
1023
1024 if (PredHasWeights) {
1025 GetBranchWeights(PTI, Weights);
1026 // branch-weight metadata is inconsistent here.
1027 if (Weights.size() != 1 + PredCases.size())
1028 PredHasWeights = SuccHasWeights = false;
1029 } else if (SuccHasWeights)
1030 // If there are no predecessor weights but there are successor weights,
1031 // populate Weights with 1, which will later be scaled to the sum of
1032 // successor's weights
1033 Weights.assign(1 + PredCases.size(), 1);
1034
1035 SmallVector<uint64_t, 8> SuccWeights;
1036 if (SuccHasWeights) {
1037 GetBranchWeights(TI, SuccWeights);
1038 // branch-weight metadata is inconsistent here.
1039 if (SuccWeights.size() != 1 + BBCases.size())
1040 PredHasWeights = SuccHasWeights = false;
1041 } else if (PredHasWeights)
1042 SuccWeights.assign(1 + BBCases.size(), 1);
1043
1044 if (PredDefault == BB) {
1045 // If this is the default destination from PTI, only the edges in TI
1046 // that don't occur in PTI, or that branch to BB will be activated.
1047 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1048 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1049 if (PredCases[i].Dest != BB)
1050 PTIHandled.insert(PredCases[i].Value);
1051 else {
1052 // The default destination is BB, we don't need explicit targets.
1053 std::swap(PredCases[i], PredCases.back());
1054
1055 if (PredHasWeights || SuccHasWeights) {
1056 // Increase weight for the default case.
1057 Weights[0] += Weights[i + 1];
1058 std::swap(Weights[i + 1], Weights.back());
1059 Weights.pop_back();
1060 }
1061
1062 PredCases.pop_back();
1063 --i;
1064 --e;
1065 }
1066
1067 // Reconstruct the new switch statement we will be building.
1068 if (PredDefault != BBDefault) {
1069 PredDefault->removePredecessor(Pred);
1070 PredDefault = BBDefault;
1071 NewSuccessors.push_back(BBDefault);
1072 }
1073
1074 unsigned CasesFromPred = Weights.size();
1075 uint64_t ValidTotalSuccWeight = 0;
1076 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1077 if (!PTIHandled.count(BBCases[i].Value) &&
1078 BBCases[i].Dest != BBDefault) {
1079 PredCases.push_back(BBCases[i]);
1080 NewSuccessors.push_back(BBCases[i].Dest);
1081 if (SuccHasWeights || PredHasWeights) {
1082 // The default weight is at index 0, so weight for the ith case
1083 // should be at index i+1. Scale the cases from successor by
1084 // PredDefaultWeight (Weights[0]).
1085 Weights.push_back(Weights[0] * SuccWeights[i + 1]);
1086 ValidTotalSuccWeight += SuccWeights[i + 1];
1087 }
1088 }
1089
1090 if (SuccHasWeights || PredHasWeights) {
1091 ValidTotalSuccWeight += SuccWeights[0];
1092 // Scale the cases from predecessor by ValidTotalSuccWeight.
1093 for (unsigned i = 1; i < CasesFromPred; ++i)
1094 Weights[i] *= ValidTotalSuccWeight;
1095 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
1096 Weights[0] *= SuccWeights[0];
1097 }
1098 } else {
1099 // If this is not the default destination from PSI, only the edges
1100 // in SI that occur in PSI with a destination of BB will be
1101 // activated.
1102 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1103 std::map<ConstantInt *, uint64_t> WeightsForHandled;
1104 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1105 if (PredCases[i].Dest == BB) {
1106 PTIHandled.insert(PredCases[i].Value);
1107
1108 if (PredHasWeights || SuccHasWeights) {
1109 WeightsForHandled[PredCases[i].Value] = Weights[i + 1];
1110 std::swap(Weights[i + 1], Weights.back());
1111 Weights.pop_back();
1112 }
1113
1114 std::swap(PredCases[i], PredCases.back());
1115 PredCases.pop_back();
1116 --i;
1117 --e;
1118 }
1119
1120 // Okay, now we know which constants were sent to BB from the
1121 // predecessor. Figure out where they will all go now.
1122 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1123 if (PTIHandled.count(BBCases[i].Value)) {
1124 // If this is one we are capable of getting...
1125 if (PredHasWeights || SuccHasWeights)
1126 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
1127 PredCases.push_back(BBCases[i]);
1128 NewSuccessors.push_back(BBCases[i].Dest);
1129 PTIHandled.erase(
1130 BBCases[i].Value); // This constant is taken care of
1131 }
1132
1133 // If there are any constants vectored to BB that TI doesn't handle,
1134 // they must go to the default destination of TI.
1135 for (ConstantInt *I : PTIHandled) {
1136 if (PredHasWeights || SuccHasWeights)
1137 Weights.push_back(WeightsForHandled[I]);
1138 PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault));
1139 NewSuccessors.push_back(BBDefault);
1140 }
1141 }
1142
1143 // Okay, at this point, we know which new successor Pred will get. Make
1144 // sure we update the number of entries in the PHI nodes for these
1145 // successors.
1146 for (BasicBlock *NewSuccessor : NewSuccessors)
1147 AddPredecessorToBlock(NewSuccessor, Pred, BB);
1148
1149 Builder.SetInsertPoint(PTI);
1150 // Convert pointer to int before we switch.
1151 if (CV->getType()->isPointerTy()) {
1152 CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()),
1153 "magicptr");
1154 }
1155
1156 // Now that the successors are updated, create the new Switch instruction.
1157 SwitchInst *NewSI =
1158 Builder.CreateSwitch(CV, PredDefault, PredCases.size());
1159 NewSI->setDebugLoc(PTI->getDebugLoc());
1160 for (ValueEqualityComparisonCase &V : PredCases)
1161 NewSI->addCase(V.Value, V.Dest);
1162
1163 if (PredHasWeights || SuccHasWeights) {
1164 // Halve the weights if any of them cannot fit in an uint32_t
1165 FitWeights(Weights);
1166
1167 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1168
1169 NewSI->setMetadata(
1170 LLVMContext::MD_prof,
1171 MDBuilder(BB->getContext()).createBranchWeights(MDWeights));
1172 }
1173
1174 EraseTerminatorInstAndDCECond(PTI);
1175
1176 // Okay, last check. If BB is still a successor of PSI, then we must
1177 // have an infinite loop case. If so, add an infinitely looping block
1178 // to handle the case to preserve the behavior of the code.
1179 BasicBlock *InfLoopBlock = nullptr;
1180 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1181 if (NewSI->getSuccessor(i) == BB) {
1182 if (!InfLoopBlock) {
1183 // Insert it at the end of the function, because it's either code,
1184 // or it won't matter if it's hot. :)
1185 InfLoopBlock = BasicBlock::Create(BB->getContext(), "infloop",
1186 BB->getParent());
1187 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1188 }
1189 NewSI->setSuccessor(i, InfLoopBlock);
1190 }
1191
1192 Changed = true;
1193 }
1194 }
1195 return Changed;
1196}
1197
1198// If we would need to insert a select that uses the value of this invoke
1199// (comments in HoistThenElseCodeToIf explain why we would need to do this), we
1200// can't hoist the invoke, as there is nowhere to put the select in this case.
1201static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1202 Instruction *I1, Instruction *I2) {
1203 for (BasicBlock *Succ : successors(BB1)) {
1204 PHINode *PN;
1205 for (BasicBlock::iterator BBI = Succ->begin();
1206 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1207 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1208 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1209 if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
1210 return false;
1211 }
1212 }
1213 }
1214 return true;
1215}
1216
1217static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
1218
1219/// Given a conditional branch that goes to BB1 and BB2, hoist any common code
1220/// in the two blocks up into the branch block. The caller of this function
1221/// guarantees that BI's block dominates BB1 and BB2.
1222static bool HoistThenElseCodeToIf(BranchInst *BI,
1223 const TargetTransformInfo &TTI) {
1224 // This does very trivial matching, with limited scanning, to find identical
1225 // instructions in the two blocks. In particular, we don't want to get into
1226 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1227 // such, we currently just scan for obviously identical instructions in an
1228 // identical order.
1229 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1230 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1231
1232 BasicBlock::iterator BB1_Itr = BB1->begin();
1233 BasicBlock::iterator BB2_Itr = BB2->begin();
1234
1235 Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
1236 // Skip debug info if it is not identical.
1237 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1238 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1239 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1240 while (isa<DbgInfoIntrinsic>(I1))
1241 I1 = &*BB1_Itr++;
1242 while (isa<DbgInfoIntrinsic>(I2))
1243 I2 = &*BB2_Itr++;
1244 }
1245 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1246 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1247 return false;
1248
1249 BasicBlock *BIParent = BI->getParent();
1250
1251 bool Changed = false;
1252 do {
1253 // If we are hoisting the terminator instruction, don't move one (making a
1254 // broken BB), instead clone it, and remove BI.
1255 if (isa<TerminatorInst>(I1))
1256 goto HoistTerminator;
1257
1258 if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
1259 return Changed;
1260
1261 // For a normal instruction, we just move one to right before the branch,
1262 // then replace all uses of the other with the first. Finally, we remove
1263 // the now redundant second instruction.
1264 BIParent->getInstList().splice(BI->getIterator(), BB1->getInstList(), I1);
1265 if (!I2->use_empty())
1266 I2->replaceAllUsesWith(I1);
1267 I1->andIRFlags(I2);
1268 unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
1269 LLVMContext::MD_range,
1270 LLVMContext::MD_fpmath,
1271 LLVMContext::MD_invariant_load,
1272 LLVMContext::MD_nonnull,
1273 LLVMContext::MD_invariant_group,
1274 LLVMContext::MD_align,
1275 LLVMContext::MD_dereferenceable,
1276 LLVMContext::MD_dereferenceable_or_null,
1277 LLVMContext::MD_mem_parallel_loop_access};
1278 combineMetadata(I1, I2, KnownIDs);
1279
1280 // I1 and I2 are being combined into a single instruction. Its debug
1281 // location is the merged locations of the original instructions.
1282 if (!isa<CallInst>(I1))
1283 I1->setDebugLoc(
1284 DILocation::getMergedLocation(I1->getDebugLoc(), I2->getDebugLoc()));
1285
1286 I2->eraseFromParent();
1287 Changed = true;
1288
1289 I1 = &*BB1_Itr++;
1290 I2 = &*BB2_Itr++;
1291 // Skip debug info if it is not identical.
1292 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1293 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1294 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1295 while (isa<DbgInfoIntrinsic>(I1))
1296 I1 = &*BB1_Itr++;
1297 while (isa<DbgInfoIntrinsic>(I2))
1298 I2 = &*BB2_Itr++;
1299 }
1300 } while (I1->isIdenticalToWhenDefined(I2));
1301
1302 return true;
1303
1304HoistTerminator:
1305 // It may not be possible to hoist an invoke.
1306 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1307 return Changed;
1308
1309 for (BasicBlock *Succ : successors(BB1)) {
1310 PHINode *PN;
1311 for (BasicBlock::iterator BBI = Succ->begin();
1312 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1313 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1314 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1315 if (BB1V == BB2V)
1316 continue;
1317
1318 // Check for passingValueIsAlwaysUndefined here because we would rather
1319 // eliminate undefined control flow then converting it to a select.
1320 if (passingValueIsAlwaysUndefined(BB1V, PN) ||
1321 passingValueIsAlwaysUndefined(BB2V, PN))
1322 return Changed;
1323
1324 if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1325 return Changed;
1326 if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1327 return Changed;
1328 }
1329 }
1330
1331 // Okay, it is safe to hoist the terminator.
1332 Instruction *NT = I1->clone();
1333 BIParent->getInstList().insert(BI->getIterator(), NT);
1334 if (!NT->getType()->isVoidTy()) {
1335 I1->replaceAllUsesWith(NT);
1336 I2->replaceAllUsesWith(NT);
1337 NT->takeName(I1);
1338 }
1339
1340 IRBuilder<NoFolder> Builder(NT);
1341 // Hoisting one of the terminators from our successor is a great thing.
1342 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1343 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1344 // nodes, so we insert select instruction to compute the final result.
1345 std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
1346 for (BasicBlock *Succ : successors(BB1)) {
1347 PHINode *PN;
1348 for (BasicBlock::iterator BBI = Succ->begin();
1349 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1350 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1351 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1352 if (BB1V == BB2V)
1353 continue;
1354
1355 // These values do not agree. Insert a select instruction before NT
1356 // that determines the right value.
1357 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1358 if (!SI)
1359 SI = cast<SelectInst>(
1360 Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1361 BB1V->getName() + "." + BB2V->getName(), BI));
1362
1363 // Make the PHI node use the select for all incoming values for BB1/BB2
1364 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1365 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1366 PN->setIncomingValue(i, SI);
1367 }
1368 }
1369
1370 // Update any PHI nodes in our new successors.
1371 for (BasicBlock *Succ : successors(BB1))
1372 AddPredecessorToBlock(Succ, BIParent, BB1);
1373
1374 EraseTerminatorInstAndDCECond(BI);
1375 return true;
1376}
1377
1378// All instructions in Insts belong to different blocks that all unconditionally
1379// branch to a common successor. Analyze each instruction and return true if it
1380// would be possible to sink them into their successor, creating one common
1381// instruction instead. For every value that would be required to be provided by
1382// PHI node (because an operand varies in each input block), add to PHIOperands.
1383static bool canSinkInstructions(
1384 ArrayRef<Instruction *> Insts,
1385 DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
1386 // Prune out obviously bad instructions to move. Any non-store instruction
1387 // must have exactly one use, and we check later that use is by a single,
1388 // common PHI instruction in the successor.
1389 for (auto *I : Insts) {
1390 // These instructions may change or break semantics if moved.
1391 if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
1392 I->getType()->isTokenTy())
1393 return false;
1394
1395 // Conservatively return false if I is an inline-asm instruction. Sinking
1396 // and merging inline-asm instructions can potentially create arguments
1397 // that cannot satisfy the inline-asm constraints.
1398 if (const auto *C = dyn_cast<CallInst>(I))
1399 if (C->isInlineAsm())
1400 return false;
1401
1402 // Everything must have only one use too, apart from stores which
1403 // have no uses.
1404 if (!isa<StoreInst>(I) && !I->hasOneUse())
1405 return false;
1406 }
1407
1408 const Instruction *I0 = Insts.front();
1409 for (auto *I : Insts)
1410 if (!I->isSameOperationAs(I0))
1411 return false;
1412
1413 // All instructions in Insts are known to be the same opcode. If they aren't
1414 // stores, check the only user of each is a PHI or in the same block as the
1415 // instruction, because if a user is in the same block as an instruction
1416 // we're contemplating sinking, it must already be determined to be sinkable.
1417 if (!isa<StoreInst>(I0)) {
1418 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1419 auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
1420 if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
1421 auto *U = cast<Instruction>(*I->user_begin());
1422 return (PNUse &&
1423 PNUse->getParent() == Succ &&
1424 PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
1425 U->getParent() == I->getParent();
1426 }))
1427 return false;
1428 }
1429
1430 // Because SROA can't handle speculating stores of selects, try not
1431 // to sink loads or stores of allocas when we'd have to create a PHI for
1432 // the address operand. Also, because it is likely that loads or stores
1433 // of allocas will disappear when Mem2Reg/SROA is run, don't sink them.
1434 // This can cause code churn which can have unintended consequences down
1435 // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244.
1436 // FIXME: This is a workaround for a deficiency in SROA - see
1437 // https://llvm.org/bugs/show_bug.cgi?id=30188
1438 if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) {
1439 return isa<AllocaInst>(I->getOperand(1));
1440 }))
1441 return false;
1442 if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) {
1443 return isa<AllocaInst>(I->getOperand(0));
1444 }))
1445 return false;
1446
1447 for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
1448 if (I0->getOperand(OI)->getType()->isTokenTy())
1449 // Don't touch any operand of token type.
1450 return false;
1451
1452 auto SameAsI0 = [&I0, OI](const Instruction *I) {
1453 assert(I->getNumOperands() == I0->getNumOperands())((I->getNumOperands() == I0->getNumOperands()) ? static_cast
<void> (0) : __assert_fail ("I->getNumOperands() == I0->getNumOperands()"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1453, __PRETTY_FUNCTION__))
;
1454 return I->getOperand(OI) == I0->getOperand(OI);
1455 };
1456 if (!all_of(Insts, SameAsI0)) {
1457 if (!canReplaceOperandWithVariable(I0, OI))
1458 // We can't create a PHI from this GEP.
1459 return false;
1460 // Don't create indirect calls! The called value is the final operand.
1461 if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI == OE - 1) {
1462 // FIXME: if the call was *already* indirect, we should do this.
1463 return false;
1464 }
1465 for (auto *I : Insts)
1466 PHIOperands[I].push_back(I->getOperand(OI));
1467 }
1468 }
1469 return true;
1470}
1471
1472// Assuming canSinkLastInstruction(Blocks) has returned true, sink the last
1473// instruction of every block in Blocks to their common successor, commoning
1474// into one instruction.
1475static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
1476 auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
1477
1478 // canSinkLastInstruction returning true guarantees that every block has at
1479 // least one non-terminator instruction.
1480 SmallVector<Instruction*,4> Insts;
1481 for (auto *BB : Blocks) {
1482 Instruction *I = BB->getTerminator();
1483 do {
1484 I = I->getPrevNode();
1485 } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
1486 if (!isa<DbgInfoIntrinsic>(I))
1487 Insts.push_back(I);
1488 }
1489
1490 // The only checking we need to do now is that all users of all instructions
1491 // are the same PHI node. canSinkLastInstruction should have checked this but
1492 // it is slightly over-aggressive - it gets confused by commutative instructions
1493 // so double-check it here.
1494 Instruction *I0 = Insts.front();
1495 if (!isa<StoreInst>(I0)) {
1496 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1497 if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
1498 auto *U = cast<Instruction>(*I->user_begin());
1499 return U == PNUse;
1500 }))
1501 return false;
1502 }
1503
1504 // We don't need to do any more checking here; canSinkLastInstruction should
1505 // have done it all for us.
1506 SmallVector<Value*, 4> NewOperands;
1507 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
1508 // This check is different to that in canSinkLastInstruction. There, we
1509 // cared about the global view once simplifycfg (and instcombine) have
1510 // completed - it takes into account PHIs that become trivially
1511 // simplifiable. However here we need a more local view; if an operand
1512 // differs we create a PHI and rely on instcombine to clean up the very
1513 // small mess we may make.
1514 bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
1515 return I->getOperand(O) != I0->getOperand(O);
1516 });
1517 if (!NeedPHI) {
1518 NewOperands.push_back(I0->getOperand(O));
1519 continue;
1520 }
1521
1522 // Create a new PHI in the successor block and populate it.
1523 auto *Op = I0->getOperand(O);
1524 assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!")((!Op->getType()->isTokenTy() && "Can't PHI tokens!"
) ? static_cast<void> (0) : __assert_fail ("!Op->getType()->isTokenTy() && \"Can't PHI tokens!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1524, __PRETTY_FUNCTION__))
;
1525 auto *PN = PHINode::Create(Op->getType(), Insts.size(),
1526 Op->getName() + ".sink", &BBEnd->front());
1527 for (auto *I : Insts)
1528 PN->addIncoming(I->getOperand(O), I->getParent());
1529 NewOperands.push_back(PN);
1530 }
1531
1532 // Arbitrarily use I0 as the new "common" instruction; remap its operands
1533 // and move it to the start of the successor block.
1534 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
1535 I0->getOperandUse(O).set(NewOperands[O]);
1536 I0->moveBefore(&*BBEnd->getFirstInsertionPt());
1537
1538 // The debug location for the "common" instruction is the merged locations of
1539 // all the commoned instructions. We start with the original location of the
1540 // "common" instruction and iteratively merge each location in the loop below.
1541 const DILocation *Loc = I0->getDebugLoc();
1542
1543 // Update metadata and IR flags, and merge debug locations.
1544 for (auto *I : Insts)
1545 if (I != I0) {
1546 Loc = DILocation::getMergedLocation(Loc, I->getDebugLoc());
1547 combineMetadataForCSE(I0, I);
1548 I0->andIRFlags(I);
1549 }
1550 if (!isa<CallInst>(I0))
1551 I0->setDebugLoc(Loc);
1552
1553 if (!isa<StoreInst>(I0)) {
1554 // canSinkLastInstruction checked that all instructions were used by
1555 // one and only one PHI node. Find that now, RAUW it to our common
1556 // instruction and nuke it.
1557 assert(I0->hasOneUse())((I0->hasOneUse()) ? static_cast<void> (0) : __assert_fail
("I0->hasOneUse()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1557, __PRETTY_FUNCTION__))
;
1558 auto *PN = cast<PHINode>(*I0->user_begin());
1559 PN->replaceAllUsesWith(I0);
1560 PN->eraseFromParent();
1561 }
1562
1563 // Finally nuke all instructions apart from the common instruction.
1564 for (auto *I : Insts)
1565 if (I != I0)
1566 I->eraseFromParent();
1567
1568 return true;
1569}
1570
1571namespace {
1572
1573 // LockstepReverseIterator - Iterates through instructions
1574 // in a set of blocks in reverse order from the first non-terminator.
1575 // For example (assume all blocks have size n):
1576 // LockstepReverseIterator I([B1, B2, B3]);
1577 // *I-- = [B1[n], B2[n], B3[n]];
1578 // *I-- = [B1[n-1], B2[n-1], B3[n-1]];
1579 // *I-- = [B1[n-2], B2[n-2], B3[n-2]];
1580 // ...
1581 class LockstepReverseIterator {
1582 ArrayRef<BasicBlock*> Blocks;
1583 SmallVector<Instruction*,4> Insts;
1584 bool Fail;
1585 public:
1586 LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) :
1587 Blocks(Blocks) {
1588 reset();
1589 }
1590
1591 void reset() {
1592 Fail = false;
1593 Insts.clear();
1594 for (auto *BB : Blocks) {
1595 Instruction *Inst = BB->getTerminator();
1596 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1597 Inst = Inst->getPrevNode();
1598 if (!Inst) {
1599 // Block wasn't big enough.
1600 Fail = true;
1601 return;
1602 }
1603 Insts.push_back(Inst);
1604 }
1605 }
1606
1607 bool isValid() const {
1608 return !Fail;
1609 }
1610
1611 void operator -- () {
1612 if (Fail)
1613 return;
1614 for (auto *&Inst : Insts) {
1615 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1616 Inst = Inst->getPrevNode();
1617 // Already at beginning of block.
1618 if (!Inst) {
1619 Fail = true;
1620 return;
1621 }
1622 }
1623 }
1624
1625 ArrayRef<Instruction*> operator * () const {
1626 return Insts;
1627 }
1628 };
1629
1630} // end anonymous namespace
1631
1632/// Given an unconditional branch that goes to BBEnd,
1633/// check whether BBEnd has only two predecessors and the other predecessor
1634/// ends with an unconditional branch. If it is true, sink any common code
1635/// in the two predecessors to BBEnd.
1636static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1637 assert(BI1->isUnconditional())((BI1->isUnconditional()) ? static_cast<void> (0) : __assert_fail
("BI1->isUnconditional()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1637, __PRETTY_FUNCTION__))
;
1638 BasicBlock *BBEnd = BI1->getSuccessor(0);
1639
1640 // We support two situations:
1641 // (1) all incoming arcs are unconditional
1642 // (2) one incoming arc is conditional
1643 //
1644 // (2) is very common in switch defaults and
1645 // else-if patterns;
1646 //
1647 // if (a) f(1);
1648 // else if (b) f(2);
1649 //
1650 // produces:
1651 //
1652 // [if]
1653 // / \
1654 // [f(1)] [if]
1655 // | | \
1656 // | | |
1657 // | [f(2)]|
1658 // \ | /
1659 // [ end ]
1660 //
1661 // [end] has two unconditional predecessor arcs and one conditional. The
1662 // conditional refers to the implicit empty 'else' arc. This conditional
1663 // arc can also be caused by an empty default block in a switch.
1664 //
1665 // In this case, we attempt to sink code from all *unconditional* arcs.
1666 // If we can sink instructions from these arcs (determined during the scan
1667 // phase below) we insert a common successor for all unconditional arcs and
1668 // connect that to [end], to enable sinking:
1669 //
1670 // [if]
1671 // / \
1672 // [x(1)] [if]
1673 // | | \
1674 // | | \
1675 // | [x(2)] |
1676 // \ / |
1677 // [sink.split] |
1678 // \ /
1679 // [ end ]
1680 //
1681 SmallVector<BasicBlock*,4> UnconditionalPreds;
1682 Instruction *Cond = nullptr;
1683 for (auto *B : predecessors(BBEnd)) {
1684 auto *T = B->getTerminator();
1685 if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional())
1686 UnconditionalPreds.push_back(B);
1687 else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond)
1688 Cond = T;
1689 else
1690 return false;
1691 }
1692 if (UnconditionalPreds.size() < 2)
1693 return false;
1694
1695 bool Changed = false;
1696 // We take a two-step approach to tail sinking. First we scan from the end of
1697 // each block upwards in lockstep. If the n'th instruction from the end of each
1698 // block can be sunk, those instructions are added to ValuesToSink and we
1699 // carry on. If we can sink an instruction but need to PHI-merge some operands
1700 // (because they're not identical in each instruction) we add these to
1701 // PHIOperands.
1702 unsigned ScanIdx = 0;
1703 SmallPtrSet<Value*,4> InstructionsToSink;
1704 DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands;
1705 LockstepReverseIterator LRI(UnconditionalPreds);
1706 while (LRI.isValid() &&
1707 canSinkInstructions(*LRI, PHIOperands)) {
1708 DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0] << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: instruction can be sunk: "
<< *(*LRI)[0] << "\n"; } } while (false)
;
1709 InstructionsToSink.insert((*LRI).begin(), (*LRI).end());
1710 ++ScanIdx;
1711 --LRI;
1712 }
1713
1714 auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
1715 unsigned NumPHIdValues = 0;
1716 for (auto *I : *LRI)
1717 for (auto *V : PHIOperands[I])
1718 if (InstructionsToSink.count(V) == 0)
1719 ++NumPHIdValues;
1720 DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: #phid values: " <<
NumPHIdValues << "\n"; } } while (false)
;
1721 unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size();
1722 if ((NumPHIdValues % UnconditionalPreds.size()) != 0)
1723 NumPHIInsts++;
1724
1725 return NumPHIInsts <= 1;
1726 };
1727
1728 if (ScanIdx > 0 && Cond) {
1729 // Check if we would actually sink anything first! This mutates the CFG and
1730 // adds an extra block. The goal in doing this is to allow instructions that
1731 // couldn't be sunk before to be sunk - obviously, speculatable instructions
1732 // (such as trunc, add) can be sunk and predicated already. So we check that
1733 // we're going to sink at least one non-speculatable instruction.
1734 LRI.reset();
1735 unsigned Idx = 0;
1736 bool Profitable = false;
1737 while (ProfitableToSinkInstruction(LRI) && Idx < ScanIdx) {
1738 if (!isSafeToSpeculativelyExecute((*LRI)[0])) {
1739 Profitable = true;
1740 break;
1741 }
1742 --LRI;
1743 ++Idx;
1744 }
1745 if (!Profitable)
1746 return false;
1747
1748 DEBUG(dbgs() << "SINK: Splitting edge\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Splitting edge\n"; }
} while (false)
;
1749 // We have a conditional edge and we're going to sink some instructions.
1750 // Insert a new block postdominating all blocks we're going to sink from.
1751 if (!SplitBlockPredecessors(BI1->getSuccessor(0), UnconditionalPreds,
1752 ".sink.split"))
1753 // Edges couldn't be split.
1754 return false;
1755 Changed = true;
1756 }
1757
1758 // Now that we've analyzed all potential sinking candidates, perform the
1759 // actual sink. We iteratively sink the last non-terminator of the source
1760 // blocks into their common successor unless doing so would require too
1761 // many PHI instructions to be generated (currently only one PHI is allowed
1762 // per sunk instruction).
1763 //
1764 // We can use InstructionsToSink to discount values needing PHI-merging that will
1765 // actually be sunk in a later iteration. This allows us to be more
1766 // aggressive in what we sink. This does allow a false positive where we
1767 // sink presuming a later value will also be sunk, but stop half way through
1768 // and never actually sink it which means we produce more PHIs than intended.
1769 // This is unlikely in practice though.
1770 for (unsigned SinkIdx = 0; SinkIdx != ScanIdx; ++SinkIdx) {
1771 DEBUG(dbgs() << "SINK: Sink: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1772 << *UnconditionalPreds[0]->getTerminator()->getPrevNode()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1773 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
;
1774
1775 // Because we've sunk every instruction in turn, the current instruction to
1776 // sink is always at index 0.
1777 LRI.reset();
1778 if (!ProfitableToSinkInstruction(LRI)) {
1779 // Too many PHIs would be created.
1780 DEBUG(dbgs() << "SINK: stopping here, too many PHIs would be created!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: stopping here, too many PHIs would be created!\n"
; } } while (false)
;
1781 break;
1782 }
1783
1784 if (!sinkLastInstruction(UnconditionalPreds))
1785 return Changed;
1786 NumSinkCommons++;
1787 Changed = true;
1788 }
1789 return Changed;
1790}
1791
1792/// \brief Determine if we can hoist sink a sole store instruction out of a
1793/// conditional block.
1794///
1795/// We are looking for code like the following:
1796/// BrBB:
1797/// store i32 %add, i32* %arrayidx2
1798/// ... // No other stores or function calls (we could be calling a memory
1799/// ... // function).
1800/// %cmp = icmp ult %x, %y
1801/// br i1 %cmp, label %EndBB, label %ThenBB
1802/// ThenBB:
1803/// store i32 %add5, i32* %arrayidx2
1804/// br label EndBB
1805/// EndBB:
1806/// ...
1807/// We are going to transform this into:
1808/// BrBB:
1809/// store i32 %add, i32* %arrayidx2
1810/// ... //
1811/// %cmp = icmp ult %x, %y
1812/// %add.add5 = select i1 %cmp, i32 %add, %add5
1813/// store i32 %add.add5, i32* %arrayidx2
1814/// ...
1815///
1816/// \return The pointer to the value of the previous store if the store can be
1817/// hoisted into the predecessor block. 0 otherwise.
1818static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1819 BasicBlock *StoreBB, BasicBlock *EndBB) {
1820 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1821 if (!StoreToHoist)
1822 return nullptr;
1823
1824 // Volatile or atomic.
1825 if (!StoreToHoist->isSimple())
1826 return nullptr;
1827
1828 Value *StorePtr = StoreToHoist->getPointerOperand();
1829
1830 // Look for a store to the same pointer in BrBB.
1831 unsigned MaxNumInstToLookAt = 9;
1832 for (Instruction &CurI : reverse(*BrBB)) {
1833 if (!MaxNumInstToLookAt)
1834 break;
1835 // Skip debug info.
1836 if (isa<DbgInfoIntrinsic>(CurI))
1837 continue;
1838 --MaxNumInstToLookAt;
1839
1840 // Could be calling an instruction that affects memory like free().
1841 if (CurI.mayHaveSideEffects() && !isa<StoreInst>(CurI))
1842 return nullptr;
1843
1844 if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
1845 // Found the previous store make sure it stores to the same location.
1846 if (SI->getPointerOperand() == StorePtr)
1847 // Found the previous store, return its value operand.
1848 return SI->getValueOperand();
1849 return nullptr; // Unknown store.
1850 }
1851 }
1852
1853 return nullptr;
1854}
1855
1856/// \brief Speculate a conditional basic block flattening the CFG.
1857///
1858/// Note that this is a very risky transform currently. Speculating
1859/// instructions like this is most often not desirable. Instead, there is an MI
1860/// pass which can do it with full awareness of the resource constraints.
1861/// However, some cases are "obvious" and we should do directly. An example of
1862/// this is speculating a single, reasonably cheap instruction.
1863///
1864/// There is only one distinct advantage to flattening the CFG at the IR level:
1865/// it makes very common but simplistic optimizations such as are common in
1866/// instcombine and the DAG combiner more powerful by removing CFG edges and
1867/// modeling their effects with easier to reason about SSA value graphs.
1868///
1869///
1870/// An illustration of this transform is turning this IR:
1871/// \code
1872/// BB:
1873/// %cmp = icmp ult %x, %y
1874/// br i1 %cmp, label %EndBB, label %ThenBB
1875/// ThenBB:
1876/// %sub = sub %x, %y
1877/// br label BB2
1878/// EndBB:
1879/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1880/// ...
1881/// \endcode
1882///
1883/// Into this IR:
1884/// \code
1885/// BB:
1886/// %cmp = icmp ult %x, %y
1887/// %sub = sub %x, %y
1888/// %cond = select i1 %cmp, 0, %sub
1889/// ...
1890/// \endcode
1891///
1892/// \returns true if the conditional block is removed.
1893static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
1894 const TargetTransformInfo &TTI) {
1895 // Be conservative for now. FP select instruction can often be expensive.
1896 Value *BrCond = BI->getCondition();
1897 if (isa<FCmpInst>(BrCond))
1898 return false;
1899
1900 BasicBlock *BB = BI->getParent();
1901 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1902
1903 // If ThenBB is actually on the false edge of the conditional branch, remember
1904 // to swap the select operands later.
1905 bool Invert = false;
1906 if (ThenBB != BI->getSuccessor(0)) {
1907 assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?")((ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?"
) ? static_cast<void> (0) : __assert_fail ("ThenBB == BI->getSuccessor(1) && \"No edge from 'if' block?\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1907, __PRETTY_FUNCTION__))
;
1908 Invert = true;
1909 }
1910 assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block")((EndBB == BI->getSuccessor(!Invert) && "No edge from to end block"
) ? static_cast<void> (0) : __assert_fail ("EndBB == BI->getSuccessor(!Invert) && \"No edge from to end block\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1910, __PRETTY_FUNCTION__))
;
1911
1912 // Keep a count of how many times instructions are used within CondBB when
1913 // they are candidates for sinking into CondBB. Specifically:
1914 // - They are defined in BB, and
1915 // - They have no side effects, and
1916 // - All of their uses are in CondBB.
1917 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1918
1919 unsigned SpeculationCost = 0;
1920 Value *SpeculatedStoreValue = nullptr;
1921 StoreInst *SpeculatedStore = nullptr;
1922 for (BasicBlock::iterator BBI = ThenBB->begin(),
1923 BBE = std::prev(ThenBB->end());
1924 BBI != BBE; ++BBI) {
1925 Instruction *I = &*BBI;
1926 // Skip debug info.
1927 if (isa<DbgInfoIntrinsic>(I))
1928 continue;
1929
1930 // Only speculatively execute a single instruction (not counting the
1931 // terminator) for now.
1932 ++SpeculationCost;
1933 if (SpeculationCost > 1)
1934 return false;
1935
1936 // Don't hoist the instruction if it's unsafe or expensive.
1937 if (!isSafeToSpeculativelyExecute(I) &&
1938 !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
1939 I, BB, ThenBB, EndBB))))
1940 return false;
1941 if (!SpeculatedStoreValue &&
1942 ComputeSpeculationCost(I, TTI) >
1943 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
1944 return false;
1945
1946 // Store the store speculation candidate.
1947 if (SpeculatedStoreValue)
1948 SpeculatedStore = cast<StoreInst>(I);
1949
1950 // Do not hoist the instruction if any of its operands are defined but not
1951 // used in BB. The transformation will prevent the operand from
1952 // being sunk into the use block.
1953 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1954 Instruction *OpI = dyn_cast<Instruction>(*i);
1955 if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects())
1956 continue; // Not a candidate for sinking.
1957
1958 ++SinkCandidateUseCounts[OpI];
1959 }
1960 }
1961
1962 // Consider any sink candidates which are only used in CondBB as costs for
1963 // speculation. Note, while we iterate over a DenseMap here, we are summing
1964 // and so iteration order isn't significant.
1965 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator
1966 I = SinkCandidateUseCounts.begin(),
1967 E = SinkCandidateUseCounts.end();
1968 I != E; ++I)
1969 if (I->first->getNumUses() == I->second) {
1970 ++SpeculationCost;
1971 if (SpeculationCost > 1)
1972 return false;
1973 }
1974
1975 // Check that the PHI nodes can be converted to selects.
1976 bool HaveRewritablePHIs = false;
1977 for (BasicBlock::iterator I = EndBB->begin();
1978 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1979 Value *OrigV = PN->getIncomingValueForBlock(BB);
1980 Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
1981
1982 // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
1983 // Skip PHIs which are trivial.
1984 if (ThenV == OrigV)
1985 continue;
1986
1987 // Don't convert to selects if we could remove undefined behavior instead.
1988 if (passingValueIsAlwaysUndefined(OrigV, PN) ||
1989 passingValueIsAlwaysUndefined(ThenV, PN))
1990 return false;
1991
1992 HaveRewritablePHIs = true;
1993 ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
1994 ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
1995 if (!OrigCE && !ThenCE)
1996 continue; // Known safe and cheap.
1997
1998 if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
1999 (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
2000 return false;
2001 unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0;
2002 unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0;
2003 unsigned MaxCost =
2004 2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2005 if (OrigCost + ThenCost > MaxCost)
2006 return false;
2007
2008 // Account for the cost of an unfolded ConstantExpr which could end up
2009 // getting expanded into Instructions.
2010 // FIXME: This doesn't account for how many operations are combined in the
2011 // constant expression.
2012 ++SpeculationCost;
2013 if (SpeculationCost > 1)
2014 return false;
2015 }
2016
2017 // If there are no PHIs to process, bail early. This helps ensure idempotence
2018 // as well.
2019 if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
2020 return false;
2021
2022 // If we get here, we can hoist the instruction and if-convert.
2023 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SPECULATIVELY EXECUTING BB"
<< *ThenBB << "\n";; } } while (false)
;
2024
2025 // Insert a select of the value of the speculated store.
2026 if (SpeculatedStoreValue) {
2027 IRBuilder<NoFolder> Builder(BI);
2028 Value *TrueV = SpeculatedStore->getValueOperand();
2029 Value *FalseV = SpeculatedStoreValue;
2030 if (Invert)
2031 std::swap(TrueV, FalseV);
2032 Value *S = Builder.CreateSelect(
2033 BrCond, TrueV, FalseV, TrueV->getName() + "." + FalseV->getName(), BI);
2034 SpeculatedStore->setOperand(0, S);
2035 SpeculatedStore->setDebugLoc(
2036 DILocation::getMergedLocation(
2037 BI->getDebugLoc(), SpeculatedStore->getDebugLoc()));
2038 }
2039
2040 // Metadata can be dependent on the condition we are hoisting above.
2041 // Conservatively strip all metadata on the instruction.
2042 for (auto &I : *ThenBB)
2043 I.dropUnknownNonDebugMetadata();
2044
2045 // Hoist the instructions.
2046 BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
2047 ThenBB->begin(), std::prev(ThenBB->end()));
2048
2049 // Insert selects and rewrite the PHI operands.
2050 IRBuilder<NoFolder> Builder(BI);
2051 for (BasicBlock::iterator I = EndBB->begin();
2052 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
2053 unsigned OrigI = PN->getBasicBlockIndex(BB);
2054 unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
2055 Value *OrigV = PN->getIncomingValue(OrigI);
2056 Value *ThenV = PN->getIncomingValue(ThenI);
2057
2058 // Skip PHIs which are trivial.
2059 if (OrigV == ThenV)
2060 continue;
2061
2062 // Create a select whose true value is the speculatively executed value and
2063 // false value is the preexisting value. Swap them if the branch
2064 // destinations were inverted.
2065 Value *TrueV = ThenV, *FalseV = OrigV;
2066 if (Invert)
2067 std::swap(TrueV, FalseV);
2068 Value *V = Builder.CreateSelect(
2069 BrCond, TrueV, FalseV, TrueV->getName() + "." + FalseV->getName(), BI);
2070 PN->setIncomingValue(OrigI, V);
2071 PN->setIncomingValue(ThenI, V);
2072 }
2073
2074 ++NumSpeculations;
2075 return true;
2076}
2077
2078/// Return true if we can thread a branch across this block.
2079static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
2080 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
2081 unsigned Size = 0;
2082
2083 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2084 if (isa<DbgInfoIntrinsic>(BBI))
2085 continue;
2086 if (Size > 10)
2087 return false; // Don't clone large BB's.
2088 ++Size;
2089
2090 // We can only support instructions that do not define values that are
2091 // live outside of the current basic block.
2092 for (User *U : BBI->users()) {
2093 Instruction *UI = cast<Instruction>(U);
2094 if (UI->getParent() != BB || isa<PHINode>(UI))
2095 return false;
2096 }
2097
2098 // Looks ok, continue checking.
2099 }
2100
2101 return true;
2102}
2103
2104/// If we have a conditional branch on a PHI node value that is defined in the
2105/// same block as the branch and if any PHI entries are constants, thread edges
2106/// corresponding to that entry to be branches to their ultimate destination.
2107static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL,
2108 AssumptionCache *AC) {
2109 BasicBlock *BB = BI->getParent();
2110 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
2111 // NOTE: we currently cannot transform this case if the PHI node is used
2112 // outside of the block.
2113 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
2114 return false;
2115
2116 // Degenerate case of a single entry PHI.
2117 if (PN->getNumIncomingValues() == 1) {
2118 FoldSingleEntryPHINodes(PN->getParent());
2119 return true;
2120 }
2121
2122 // Now we know that this block has multiple preds and two succs.
2123 if (!BlockIsSimpleEnoughToThreadThrough(BB))
2124 return false;
2125
2126 // Can't fold blocks that contain noduplicate or convergent calls.
2127 if (any_of(*BB, [](const Instruction &I) {
2128 const CallInst *CI = dyn_cast<CallInst>(&I);
2129 return CI && (CI->cannotDuplicate() || CI->isConvergent());
2130 }))
2131 return false;
2132
2133 // Okay, this is a simple enough basic block. See if any phi values are
2134 // constants.
2135 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2136 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
2137 if (!CB || !CB->getType()->isIntegerTy(1))
2138 continue;
2139
2140 // Okay, we now know that all edges from PredBB should be revectored to
2141 // branch to RealDest.
2142 BasicBlock *PredBB = PN->getIncomingBlock(i);
2143 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
2144
2145 if (RealDest == BB)
2146 continue; // Skip self loops.
2147 // Skip if the predecessor's terminator is an indirect branch.
2148 if (isa<IndirectBrInst>(PredBB->getTerminator()))
2149 continue;
2150
2151 // The dest block might have PHI nodes, other predecessors and other
2152 // difficult cases. Instead of being smart about this, just insert a new
2153 // block that jumps to the destination block, effectively splitting
2154 // the edge we are about to create.
2155 BasicBlock *EdgeBB =
2156 BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge",
2157 RealDest->getParent(), RealDest);
2158 BranchInst::Create(RealDest, EdgeBB);
2159
2160 // Update PHI nodes.
2161 AddPredecessorToBlock(RealDest, EdgeBB, BB);
2162
2163 // BB may have instructions that are being threaded over. Clone these
2164 // instructions into EdgeBB. We know that there will be no uses of the
2165 // cloned instructions outside of EdgeBB.
2166 BasicBlock::iterator InsertPt = EdgeBB->begin();
2167 DenseMap<Value *, Value *> TranslateMap; // Track translated values.
2168 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2169 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
2170 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
2171 continue;
2172 }
2173 // Clone the instruction.
2174 Instruction *N = BBI->clone();
2175 if (BBI->hasName())
2176 N->setName(BBI->getName() + ".c");
2177
2178 // Update operands due to translation.
2179 for (User::op_iterator i = N->op_begin(), e = N->op_end(); i != e; ++i) {
2180 DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(*i);
2181 if (PI != TranslateMap.end())
2182 *i = PI->second;
2183 }
2184
2185 // Check for trivial simplification.
2186 if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) {
2187 if (!BBI->use_empty())
2188 TranslateMap[&*BBI] = V;
2189 if (!N->mayHaveSideEffects()) {
2190 N->deleteValue(); // Instruction folded away, don't need actual inst
2191 N = nullptr;
2192 }
2193 } else {
2194 if (!BBI->use_empty())
2195 TranslateMap[&*BBI] = N;
2196 }
2197 // Insert the new instruction into its new home.
2198 if (N)
2199 EdgeBB->getInstList().insert(InsertPt, N);
2200
2201 // Register the new instruction with the assumption cache if necessary.
2202 if (auto *II = dyn_cast_or_null<IntrinsicInst>(N))
2203 if (II->getIntrinsicID() == Intrinsic::assume)
2204 AC->registerAssumption(II);
2205 }
2206
2207 // Loop over all of the edges from PredBB to BB, changing them to branch
2208 // to EdgeBB instead.
2209 TerminatorInst *PredBBTI = PredBB->getTerminator();
2210 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
2211 if (PredBBTI->getSuccessor(i) == BB) {
2212 BB->removePredecessor(PredBB);
2213 PredBBTI->setSuccessor(i, EdgeBB);
2214 }
2215
2216 // Recurse, simplifying any other constants.
2217 return FoldCondBranchOnPHI(BI, DL, AC) | true;
2218 }
2219
2220 return false;
2221}
2222
2223/// Given a BB that starts with the specified two-entry PHI node,
2224/// see if we can eliminate it.
2225static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
2226 const DataLayout &DL) {
2227 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
2228 // statement", which has a very simple dominance structure. Basically, we
2229 // are trying to find the condition that is being branched on, which
2230 // subsequently causes this merge to happen. We really want control
2231 // dependence information for this check, but simplifycfg can't keep it up
2232 // to date, and this catches most of the cases we care about anyway.
2233 BasicBlock *BB = PN->getParent();
2234 BasicBlock *IfTrue, *IfFalse;
2235 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
2236 if (!IfCond ||
32
Assuming 'IfCond' is non-null
34
Taking false branch
2237 // Don't bother if the branch will be constant folded trivially.
2238 isa<ConstantInt>(IfCond))
33
Assuming the condition is false
2239 return false;
2240
2241 // Okay, we found that we can merge this two-entry phi node into a select.
2242 // Doing so would require us to fold *all* two entry phi nodes in this block.
2243 // At some point this becomes non-profitable (particularly if the target
2244 // doesn't support cmov's). Only do this transformation if there are two or
2245 // fewer PHI nodes in this block.
2246 unsigned NumPhis = 0;
2247 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
35
Loop condition is false. Execution continues on line 2254
2248 if (NumPhis > 2)
2249 return false;
2250
2251 // Loop over the PHI's seeing if we can promote them all to select
2252 // instructions. While we are at it, keep track of the instructions
2253 // that need to be moved to the dominating block.
2254 SmallPtrSet<Instruction *, 4> AggressiveInsts;
2255 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
2256 MaxCostVal1 = PHINodeFoldingThreshold;
2257 MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
2258 MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
2259
2260 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
36
Loop condition is false. Execution continues on line 2277
2261 PHINode *PN = cast<PHINode>(II++);
2262 if (Value *V = SimplifyInstruction(PN, {DL, PN})) {
2263 PN->replaceAllUsesWith(V);
2264 PN->eraseFromParent();
2265 continue;
2266 }
2267
2268 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
2269 MaxCostVal0, TTI) ||
2270 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
2271 MaxCostVal1, TTI))
2272 return false;
2273 }
2274
2275 // If we folded the first phi, PN dangles at this point. Refresh it. If
2276 // we ran out of PHIs then we simplified them all.
2277 PN = dyn_cast<PHINode>(BB->begin());
2278 if (!PN)
37
Assuming 'PN' is non-null
38
Taking false branch
2279 return true;
2280
2281 // Don't fold i1 branches on PHIs which contain binary operators. These can
2282 // often be turned into switches and other things.
2283 if (PN->getType()->isIntegerTy(1) &&
39
Assuming the condition is false
40
Taking false branch
2284 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
2285 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
2286 isa<BinaryOperator>(IfCond)))
2287 return false;
2288
2289 // If all PHI nodes are promotable, check to make sure that all instructions
2290 // in the predecessor blocks can be promoted as well. If not, we won't be able
2291 // to get rid of the control flow, so it's not worth promoting to select
2292 // instructions.
2293 BasicBlock *DomBlock = nullptr;
41
'DomBlock' initialized to a null pointer value
2294 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
2295 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
2296 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
42
Taking true branch
2297 IfBlock1 = nullptr;
2298 } else {
2299 DomBlock = *pred_begin(IfBlock1);
2300 for (BasicBlock::iterator I = IfBlock1->begin(); !isa<TerminatorInst>(I);
2301 ++I)
2302 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2303 // This is not an aggressive instruction that we can promote.
2304 // Because of this, we won't be able to get rid of the control flow, so
2305 // the xform is not worth it.
2306 return false;
2307 }
2308 }
2309
2310 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
43
Taking true branch
2311 IfBlock2 = nullptr;
2312 } else {
2313 DomBlock = *pred_begin(IfBlock2);
2314 for (BasicBlock::iterator I = IfBlock2->begin(); !isa<TerminatorInst>(I);
2315 ++I)
2316 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2317 // This is not an aggressive instruction that we can promote.
2318 // Because of this, we won't be able to get rid of the control flow, so
2319 // the xform is not worth it.
2320 return false;
2321 }
2322 }
2323
2324 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
2325 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
;
2326
2327 // If we can still promote the PHI nodes after this gauntlet of tests,
2328 // do all of the PHI's now.
2329 Instruction *InsertPt = DomBlock->getTerminator();
44
Called C++ object pointer is null
2330 IRBuilder<NoFolder> Builder(InsertPt);
2331
2332 // Move all 'aggressive' instructions, which are defined in the
2333 // conditional parts of the if's up to the dominating block.
2334 if (IfBlock1) {
2335 for (auto &I : *IfBlock1)
2336 I.dropUnknownNonDebugMetadata();
2337 DomBlock->getInstList().splice(InsertPt->getIterator(),
2338 IfBlock1->getInstList(), IfBlock1->begin(),
2339 IfBlock1->getTerminator()->getIterator());
2340 }
2341 if (IfBlock2) {
2342 for (auto &I : *IfBlock2)
2343 I.dropUnknownNonDebugMetadata();
2344 DomBlock->getInstList().splice(InsertPt->getIterator(),
2345 IfBlock2->getInstList(), IfBlock2->begin(),
2346 IfBlock2->getTerminator()->getIterator());
2347 }
2348
2349 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
2350 // Change the PHI node into a select instruction.
2351 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
2352 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
2353
2354 Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", InsertPt);
2355 PN->replaceAllUsesWith(Sel);
2356 Sel->takeName(PN);
2357 PN->eraseFromParent();
2358 }
2359
2360 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
2361 // has been flattened. Change DomBlock to jump directly to our new block to
2362 // avoid other simplifycfg's kicking in on the diamond.
2363 TerminatorInst *OldTI = DomBlock->getTerminator();
2364 Builder.SetInsertPoint(OldTI);
2365 Builder.CreateBr(BB);
2366 OldTI->eraseFromParent();
2367 return true;
2368}
2369
2370/// If we found a conditional branch that goes to two returning blocks,
2371/// try to merge them together into one return,
2372/// introducing a select if the return values disagree.
2373static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
2374 IRBuilder<> &Builder) {
2375 assert(BI->isConditional() && "Must be a conditional branch")((BI->isConditional() && "Must be a conditional branch"
) ? static_cast<void> (0) : __assert_fail ("BI->isConditional() && \"Must be a conditional branch\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2375, __PRETTY_FUNCTION__))
;
2376 BasicBlock *TrueSucc = BI->getSuccessor(0);
2377 BasicBlock *FalseSucc = BI->getSuccessor(1);
2378 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
2379 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
2380
2381 // Check to ensure both blocks are empty (just a return) or optionally empty
2382 // with PHI nodes. If there are other instructions, merging would cause extra
2383 // computation on one path or the other.
2384 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
2385 return false;
2386 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
2387 return false;
2388
2389 Builder.SetInsertPoint(BI);
2390 // Okay, we found a branch that is going to two return nodes. If
2391 // there is no return value for this function, just change the
2392 // branch into a return.
2393 if (FalseRet->getNumOperands() == 0) {
2394 TrueSucc->removePredecessor(BI->getParent());
2395 FalseSucc->removePredecessor(BI->getParent());
2396 Builder.CreateRetVoid();
2397 EraseTerminatorInstAndDCECond(BI);
2398 return true;
2399 }
2400
2401 // Otherwise, figure out what the true and false return values are
2402 // so we can insert a new select instruction.
2403 Value *TrueValue = TrueRet->getReturnValue();
2404 Value *FalseValue = FalseRet->getReturnValue();
2405
2406 // Unwrap any PHI nodes in the return blocks.
2407 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
2408 if (TVPN->getParent() == TrueSucc)
2409 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
2410 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
2411 if (FVPN->getParent() == FalseSucc)
2412 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
2413
2414 // In order for this transformation to be safe, we must be able to
2415 // unconditionally execute both operands to the return. This is
2416 // normally the case, but we could have a potentially-trapping
2417 // constant expression that prevents this transformation from being
2418 // safe.
2419 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
2420 if (TCV->canTrap())
2421 return false;
2422 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
2423 if (FCV->canTrap())
2424 return false;
2425
2426 // Okay, we collected all the mapped values and checked them for sanity, and
2427 // defined to really do this transformation. First, update the CFG.
2428 TrueSucc->removePredecessor(BI->getParent());
2429 FalseSucc->removePredecessor(BI->getParent());
2430
2431 // Insert select instructions where needed.
2432 Value *BrCond = BI->getCondition();
2433 if (TrueValue) {
2434 // Insert a select if the results differ.
2435 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
2436 } else if (isa<UndefValue>(TrueValue)) {
2437 TrueValue = FalseValue;
2438 } else {
2439 TrueValue =
2440 Builder.CreateSelect(BrCond, TrueValue, FalseValue, "retval", BI);
2441 }
2442 }
2443
2444 Value *RI =
2445 !TrueValue ? Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
2446
2447 (void)RI;
2448
2449 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "NewRet = " << *
RI << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "
<< *FalseSucc; } } while (false)
2450 << "\n " << *BI << "NewRet = " << *RIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "NewRet = " << *
RI << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "
<< *FalseSucc; } } while (false)
2451 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: " << *FalseSucc)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "NewRet = " << *
RI << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "
<< *FalseSucc; } } while (false)
;
2452
2453 EraseTerminatorInstAndDCECond(BI);
2454
2455 return true;
2456}
2457
2458/// Return true if the given instruction is available
2459/// in its predecessor block. If yes, the instruction will be removed.
2460static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
2461 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
2462 return false;
2463 for (Instruction &I : *PB) {
2464 Instruction *PBI = &I;
2465 // Check whether Inst and PBI generate the same value.
2466 if (Inst->isIdenticalTo(PBI)) {
2467 Inst->replaceAllUsesWith(PBI);
2468 Inst->eraseFromParent();
2469 return true;
2470 }
2471 }
2472 return false;
2473}
2474
2475/// Return true if either PBI or BI has branch weight available, and store
2476/// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does
2477/// not have branch weight, use 1:1 as its weight.
2478static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI,
2479 uint64_t &PredTrueWeight,
2480 uint64_t &PredFalseWeight,
2481 uint64_t &SuccTrueWeight,
2482 uint64_t &SuccFalseWeight) {
2483 bool PredHasWeights =
2484 PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
2485 bool SuccHasWeights =
2486 BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
2487 if (PredHasWeights || SuccHasWeights) {
2488 if (!PredHasWeights)
2489 PredTrueWeight = PredFalseWeight = 1;
2490 if (!SuccHasWeights)
2491 SuccTrueWeight = SuccFalseWeight = 1;
2492 return true;
2493 } else {
2494 return false;
2495 }
2496}
2497
2498/// If this basic block is simple enough, and if a predecessor branches to us
2499/// and one of our successors, fold the block into the predecessor and use
2500/// logical operations to pick the right destination.
2501bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
2502 BasicBlock *BB = BI->getParent();
2503
2504 Instruction *Cond = nullptr;
2505 if (BI->isConditional())
2506 Cond = dyn_cast<Instruction>(BI->getCondition());
2507 else {
2508 // For unconditional branch, check for a simple CFG pattern, where
2509 // BB has a single predecessor and BB's successor is also its predecessor's
2510 // successor. If such pattern exisits, check for CSE between BB and its
2511 // predecessor.
2512 if (BasicBlock *PB = BB->getSinglePredecessor())
2513 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2514 if (PBI->isConditional() &&
2515 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2516 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2517 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
2518 Instruction *Curr = &*I++;
2519 if (isa<CmpInst>(Curr)) {
2520 Cond = Curr;
2521 break;
2522 }
2523 // Quit if we can't remove this instruction.
2524 if (!checkCSEInPredecessor(Curr, PB))
2525 return false;
2526 }
2527 }
2528
2529 if (!Cond)
2530 return false;
2531 }
2532
2533 if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2534 Cond->getParent() != BB || !Cond->hasOneUse())
2535 return false;
2536
2537 // Make sure the instruction after the condition is the cond branch.
2538 BasicBlock::iterator CondIt = ++Cond->getIterator();
2539
2540 // Ignore dbg intrinsics.
2541 while (isa<DbgInfoIntrinsic>(CondIt))
2542 ++CondIt;
2543
2544 if (&*CondIt != BI)
2545 return false;
2546
2547 // Only allow this transformation if computing the condition doesn't involve
2548 // too many instructions and these involved instructions can be executed
2549 // unconditionally. We denote all involved instructions except the condition
2550 // as "bonus instructions", and only allow this transformation when the
2551 // number of the bonus instructions does not exceed a certain threshold.
2552 unsigned NumBonusInsts = 0;
2553 for (auto I = BB->begin(); Cond != &*I; ++I) {
2554 // Ignore dbg intrinsics.
2555 if (isa<DbgInfoIntrinsic>(I))
2556 continue;
2557 if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I))
2558 return false;
2559 // I has only one use and can be executed unconditionally.
2560 Instruction *User = dyn_cast<Instruction>(I->user_back());
2561 if (User == nullptr || User->getParent() != BB)
2562 return false;
2563 // I is used in the same BB. Since BI uses Cond and doesn't have more slots
2564 // to use any other instruction, User must be an instruction between next(I)
2565 // and Cond.
2566 ++NumBonusInsts;
2567 // Early exits once we reach the limit.
2568 if (NumBonusInsts > BonusInstThreshold)
2569 return false;
2570 }
2571
2572 // Cond is known to be a compare or binary operator. Check to make sure that
2573 // neither operand is a potentially-trapping constant expression.
2574 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2575 if (CE->canTrap())
2576 return false;
2577 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2578 if (CE->canTrap())
2579 return false;
2580
2581 // Finally, don't infinitely unroll conditional loops.
2582 BasicBlock *TrueDest = BI->getSuccessor(0);
2583 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
2584 if (TrueDest == BB || FalseDest == BB)
2585 return false;
2586
2587 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2588 BasicBlock *PredBlock = *PI;
2589 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2590
2591 // Check that we have two conditional branches. If there is a PHI node in
2592 // the common successor, verify that the same value flows in from both
2593 // blocks.
2594 SmallVector<PHINode *, 4> PHIs;
2595 if (!PBI || PBI->isUnconditional() ||
2596 (BI->isConditional() && !SafeToMergeTerminators(BI, PBI)) ||
2597 (!BI->isConditional() &&
2598 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2599 continue;
2600
2601 // Determine if the two branches share a common destination.
2602 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2603 bool InvertPredCond = false;
2604
2605 if (BI->isConditional()) {
2606 if (PBI->getSuccessor(0) == TrueDest) {
2607 Opc = Instruction::Or;
2608 } else if (PBI->getSuccessor(1) == FalseDest) {
2609 Opc = Instruction::And;
2610 } else if (PBI->getSuccessor(0) == FalseDest) {
2611 Opc = Instruction::And;
2612 InvertPredCond = true;
2613 } else if (PBI->getSuccessor(1) == TrueDest) {
2614 Opc = Instruction::Or;
2615 InvertPredCond = true;
2616 } else {
2617 continue;
2618 }
2619 } else {
2620 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2621 continue;
2622 }
2623
2624 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRANCH TO COMMON DEST:\n"
<< *PBI << *BB; } } while (false)
;
2625 IRBuilder<> Builder(PBI);
2626
2627 // If we need to invert the condition in the pred block to match, do so now.
2628 if (InvertPredCond) {
2629 Value *NewCond = PBI->getCondition();
2630
2631 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2632 CmpInst *CI = cast<CmpInst>(NewCond);
2633 CI->setPredicate(CI->getInversePredicate());
2634 } else {
2635 NewCond =
2636 Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not");
2637 }
2638
2639 PBI->setCondition(NewCond);
2640 PBI->swapSuccessors();
2641 }
2642
2643 // If we have bonus instructions, clone them into the predecessor block.
2644 // Note that there may be multiple predecessor blocks, so we cannot move
2645 // bonus instructions to a predecessor block.
2646 ValueToValueMapTy VMap; // maps original values to cloned values
2647 // We already make sure Cond is the last instruction before BI. Therefore,
2648 // all instructions before Cond other than DbgInfoIntrinsic are bonus
2649 // instructions.
2650 for (auto BonusInst = BB->begin(); Cond != &*BonusInst; ++BonusInst) {
2651 if (isa<DbgInfoIntrinsic>(BonusInst))
2652 continue;
2653 Instruction *NewBonusInst = BonusInst->clone();
2654 RemapInstruction(NewBonusInst, VMap,
2655 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2656 VMap[&*BonusInst] = NewBonusInst;
2657
2658 // If we moved a load, we cannot any longer claim any knowledge about
2659 // its potential value. The previous information might have been valid
2660 // only given the branch precondition.
2661 // For an analogous reason, we must also drop all the metadata whose
2662 // semantics we don't understand.
2663 NewBonusInst->dropUnknownNonDebugMetadata();
2664
2665 PredBlock->getInstList().insert(PBI->getIterator(), NewBonusInst);
2666 NewBonusInst->takeName(&*BonusInst);
2667 BonusInst->setName(BonusInst->getName() + ".old");
2668 }
2669
2670 // Clone Cond into the predecessor basic block, and or/and the
2671 // two conditions together.
2672 Instruction *New = Cond->clone();
2673 RemapInstruction(New, VMap,
2674 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2675 PredBlock->getInstList().insert(PBI->getIterator(), New);
2676 New->takeName(Cond);
2677 Cond->setName(New->getName() + ".old");
2678
2679 if (BI->isConditional()) {
2680 Instruction *NewCond = cast<Instruction>(
2681 Builder.CreateBinOp(Opc, PBI->getCondition(), New, "or.cond"));
2682 PBI->setCondition(NewCond);
2683
2684 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2685 bool HasWeights =
2686 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
2687 SuccTrueWeight, SuccFalseWeight);
2688 SmallVector<uint64_t, 8> NewWeights;
2689
2690 if (PBI->getSuccessor(0) == BB) {
2691 if (HasWeights) {
2692 // PBI: br i1 %x, BB, FalseDest
2693 // BI: br i1 %y, TrueDest, FalseDest
2694 // TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2695 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2696 // FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2697 // TrueWeight for PBI * FalseWeight for BI.
2698 // We assume that total weights of a BranchInst can fit into 32 bits.
2699 // Therefore, we will not have overflow using 64-bit arithmetic.
2700 NewWeights.push_back(PredFalseWeight *
2701 (SuccFalseWeight + SuccTrueWeight) +
2702 PredTrueWeight * SuccFalseWeight);
2703 }
2704 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2705 PBI->setSuccessor(0, TrueDest);
2706 }
2707 if (PBI->getSuccessor(1) == BB) {
2708 if (HasWeights) {
2709 // PBI: br i1 %x, TrueDest, BB
2710 // BI: br i1 %y, TrueDest, FalseDest
2711 // TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2712 // FalseWeight for PBI * TrueWeight for BI.
2713 NewWeights.push_back(PredTrueWeight *
2714 (SuccFalseWeight + SuccTrueWeight) +
2715 PredFalseWeight * SuccTrueWeight);
2716 // FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2717 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2718 }
2719 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2720 PBI->setSuccessor(1, FalseDest);
2721 }
2722 if (NewWeights.size() == 2) {
2723 // Halve the weights if any of them cannot fit in an uint32_t
2724 FitWeights(NewWeights);
2725
2726 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),
2727 NewWeights.end());
2728 PBI->setMetadata(
2729 LLVMContext::MD_prof,
2730 MDBuilder(BI->getContext()).createBranchWeights(MDWeights));
2731 } else
2732 PBI->setMetadata(LLVMContext::MD_prof, nullptr);
2733 } else {
2734 // Update PHI nodes in the common successors.
2735 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2736 ConstantInt *PBI_C = cast<ConstantInt>(
2737 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2738 assert(PBI_C->getType()->isIntegerTy(1))((PBI_C->getType()->isIntegerTy(1)) ? static_cast<void
> (0) : __assert_fail ("PBI_C->getType()->isIntegerTy(1)"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2738, __PRETTY_FUNCTION__))
;
2739 Instruction *MergedCond = nullptr;
2740 if (PBI->getSuccessor(0) == TrueDest) {
2741 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2742 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2743 // is false: !PBI_Cond and BI_Value
2744 Instruction *NotCond = cast<Instruction>(
2745 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2746 MergedCond = cast<Instruction>(
2747 Builder.CreateBinOp(Instruction::And, NotCond, New, "and.cond"));
2748 if (PBI_C->isOne())
2749 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2750 Instruction::Or, PBI->getCondition(), MergedCond, "or.cond"));
2751 } else {
2752 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2753 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2754 // is false: PBI_Cond and BI_Value
2755 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2756 Instruction::And, PBI->getCondition(), New, "and.cond"));
2757 if (PBI_C->isOne()) {
2758 Instruction *NotCond = cast<Instruction>(
2759 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2760 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2761 Instruction::Or, NotCond, MergedCond, "or.cond"));
2762 }
2763 }
2764 // Update PHI Node.
2765 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2766 MergedCond);
2767 }
2768 // Change PBI from Conditional to Unconditional.
2769 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2770 EraseTerminatorInstAndDCECond(PBI);
2771 PBI = New_PBI;
2772 }
2773
2774 // If BI was a loop latch, it may have had associated loop metadata.
2775 // We need to copy it to the new latch, that is, PBI.
2776 if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
2777 PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
2778
2779 // TODO: If BB is reachable from all paths through PredBlock, then we
2780 // could replace PBI's branch probabilities with BI's.
2781
2782 // Copy any debug value intrinsics into the end of PredBlock.
2783 for (Instruction &I : *BB)
2784 if (isa<DbgInfoIntrinsic>(I))
2785 I.clone()->insertBefore(PBI);
2786
2787 return true;
2788 }
2789 return false;
2790}
2791
2792// If there is only one store in BB1 and BB2, return it, otherwise return
2793// nullptr.
2794static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
2795 StoreInst *S = nullptr;
2796 for (auto *BB : {BB1, BB2}) {
2797 if (!BB)
2798 continue;
2799 for (auto &I : *BB)
2800 if (auto *SI = dyn_cast<StoreInst>(&I)) {
2801 if (S)
2802 // Multiple stores seen.
2803 return nullptr;
2804 else
2805 S = SI;
2806 }
2807 }
2808 return S;
2809}
2810
2811static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
2812 Value *AlternativeV = nullptr) {
2813 // PHI is going to be a PHI node that allows the value V that is defined in
2814 // BB to be referenced in BB's only successor.
2815 //
2816 // If AlternativeV is nullptr, the only value we care about in PHI is V. It
2817 // doesn't matter to us what the other operand is (it'll never get used). We
2818 // could just create a new PHI with an undef incoming value, but that could
2819 // increase register pressure if EarlyCSE/InstCombine can't fold it with some
2820 // other PHI. So here we directly look for some PHI in BB's successor with V
2821 // as an incoming operand. If we find one, we use it, else we create a new
2822 // one.
2823 //
2824 // If AlternativeV is not nullptr, we care about both incoming values in PHI.
2825 // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
2826 // where OtherBB is the single other predecessor of BB's only successor.
2827 PHINode *PHI = nullptr;
2828 BasicBlock *Succ = BB->getSingleSuccessor();
2829
2830 for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
2831 if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
2832 PHI = cast<PHINode>(I);
2833 if (!AlternativeV)
2834 break;
2835
2836 assert(std::distance(pred_begin(Succ), pred_end(Succ)) == 2)((std::distance(pred_begin(Succ), pred_end(Succ)) == 2) ? static_cast
<void> (0) : __assert_fail ("std::distance(pred_begin(Succ), pred_end(Succ)) == 2"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2836, __PRETTY_FUNCTION__))
;
2837 auto PredI = pred_begin(Succ);
2838 BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
2839 if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
2840 break;
2841 PHI = nullptr;
2842 }
2843 if (PHI)
2844 return PHI;
2845
2846 // If V is not an instruction defined in BB, just return it.
2847 if (!AlternativeV &&
2848 (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
2849 return V;
2850
2851 PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
2852 PHI->addIncoming(V, BB);
2853 for (BasicBlock *PredBB : predecessors(Succ))
2854 if (PredBB != BB)
2855 PHI->addIncoming(
2856 AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB);
2857 return PHI;
2858}
2859
2860static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
2861 BasicBlock *QTB, BasicBlock *QFB,
2862 BasicBlock *PostBB, Value *Address,
2863 bool InvertPCond, bool InvertQCond) {
2864 auto IsaBitcastOfPointerType = [](const Instruction &I) {
2865 return Operator::getOpcode(&I) == Instruction::BitCast &&
2866 I.getType()->isPointerTy();
2867 };
2868
2869 // If we're not in aggressive mode, we only optimize if we have some
2870 // confidence that by optimizing we'll allow P and/or Q to be if-converted.
2871 auto IsWorthwhile = [&](BasicBlock *BB) {
2872 if (!BB)
2873 return true;
2874 // Heuristic: if the block can be if-converted/phi-folded and the
2875 // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
2876 // thread this store.
2877 unsigned N = 0;
2878 for (auto &I : *BB) {
2879 // Cheap instructions viable for folding.
2880 if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
2881 isa<StoreInst>(I))
2882 ++N;
2883 // Free instructions.
2884 else if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
2885 IsaBitcastOfPointerType(I))
2886 continue;
2887 else
2888 return false;
2889 }
2890 return N <= PHINodeFoldingThreshold;
2891 };
2892
2893 if (!MergeCondStoresAggressively &&
2894 (!IsWorthwhile(PTB) || !IsWorthwhile(PFB) || !IsWorthwhile(QTB) ||
2895 !IsWorthwhile(QFB)))
2896 return false;
2897
2898 // For every pointer, there must be exactly two stores, one coming from
2899 // PTB or PFB, and the other from QTB or QFB. We don't support more than one
2900 // store (to any address) in PTB,PFB or QTB,QFB.
2901 // FIXME: We could relax this restriction with a bit more work and performance
2902 // testing.
2903 StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
2904 StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
2905 if (!PStore || !QStore)
2906 return false;
2907
2908 // Now check the stores are compatible.
2909 if (!QStore->isUnordered() || !PStore->isUnordered())
2910 return false;
2911
2912 // Check that sinking the store won't cause program behavior changes. Sinking
2913 // the store out of the Q blocks won't change any behavior as we're sinking
2914 // from a block to its unconditional successor. But we're moving a store from
2915 // the P blocks down through the middle block (QBI) and past both QFB and QTB.
2916 // So we need to check that there are no aliasing loads or stores in
2917 // QBI, QTB and QFB. We also need to check there are no conflicting memory
2918 // operations between PStore and the end of its parent block.
2919 //
2920 // The ideal way to do this is to query AliasAnalysis, but we don't
2921 // preserve AA currently so that is dangerous. Be super safe and just
2922 // check there are no other memory operations at all.
2923 for (auto &I : *QFB->getSinglePredecessor())
2924 if (I.mayReadOrWriteMemory())
2925 return false;
2926 for (auto &I : *QFB)
2927 if (&I != QStore && I.mayReadOrWriteMemory())
2928 return false;
2929 if (QTB)
2930 for (auto &I : *QTB)
2931 if (&I != QStore && I.mayReadOrWriteMemory())
2932 return false;
2933 for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
2934 I != E; ++I)
2935 if (&*I != PStore && I->mayReadOrWriteMemory())
2936 return false;
2937
2938 // OK, we're going to sink the stores to PostBB. The store has to be
2939 // conditional though, so first create the predicate.
2940 Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
2941 ->getCondition();
2942 Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
2943 ->getCondition();
2944
2945 Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
2946 PStore->getParent());
2947 Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
2948 QStore->getParent(), PPHI);
2949
2950 IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
2951
2952 Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
2953 Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
2954
2955 if (InvertPCond)
2956 PPred = QB.CreateNot(PPred);
2957 if (InvertQCond)
2958 QPred = QB.CreateNot(QPred);
2959 Value *CombinedPred = QB.CreateOr(PPred, QPred);
2960
2961 auto *T =
2962 SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(), false);
2963 QB.SetInsertPoint(T);
2964 StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
2965 AAMDNodes AAMD;
2966 PStore->getAAMetadata(AAMD, /*Merge=*/false);
2967 PStore->getAAMetadata(AAMD, /*Merge=*/true);
2968 SI->setAAMetadata(AAMD);
2969
2970 QStore->eraseFromParent();
2971 PStore->eraseFromParent();
2972
2973 return true;
2974}
2975
2976static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI) {
2977 // The intention here is to find diamonds or triangles (see below) where each
2978 // conditional block contains a store to the same address. Both of these
2979 // stores are conditional, so they can't be unconditionally sunk. But it may
2980 // be profitable to speculatively sink the stores into one merged store at the
2981 // end, and predicate the merged store on the union of the two conditions of
2982 // PBI and QBI.
2983 //
2984 // This can reduce the number of stores executed if both of the conditions are
2985 // true, and can allow the blocks to become small enough to be if-converted.
2986 // This optimization will also chain, so that ladders of test-and-set
2987 // sequences can be if-converted away.
2988 //
2989 // We only deal with simple diamonds or triangles:
2990 //
2991 // PBI or PBI or a combination of the two
2992 // / \ | \
2993 // PTB PFB | PFB
2994 // \ / | /
2995 // QBI QBI
2996 // / \ | \
2997 // QTB QFB | QFB
2998 // \ / | /
2999 // PostBB PostBB
3000 //
3001 // We model triangles as a type of diamond with a nullptr "true" block.
3002 // Triangles are canonicalized so that the fallthrough edge is represented by
3003 // a true condition, as in the diagram above.
3004 //
3005 BasicBlock *PTB = PBI->getSuccessor(0);
3006 BasicBlock *PFB = PBI->getSuccessor(1);
3007 BasicBlock *QTB = QBI->getSuccessor(0);
3008 BasicBlock *QFB = QBI->getSuccessor(1);
3009 BasicBlock *PostBB = QFB->getSingleSuccessor();
3010
3011 // Make sure we have a good guess for PostBB. If QTB's only successor is
3012 // QFB, then QFB is a better PostBB.
3013 if (QTB->getSingleSuccessor() == QFB)
3014 PostBB = QFB;
3015
3016 // If we couldn't find a good PostBB, stop.
3017 if (!PostBB)
3018 return false;
3019
3020 bool InvertPCond = false, InvertQCond = false;
3021 // Canonicalize fallthroughs to the true branches.
3022 if (PFB == QBI->getParent()) {
3023 std::swap(PFB, PTB);
3024 InvertPCond = true;
3025 }
3026 if (QFB == PostBB) {
3027 std::swap(QFB, QTB);
3028 InvertQCond = true;
3029 }
3030
3031 // From this point on we can assume PTB or QTB may be fallthroughs but PFB
3032 // and QFB may not. Model fallthroughs as a nullptr block.
3033 if (PTB == QBI->getParent())
3034 PTB = nullptr;
3035 if (QTB == PostBB)
3036 QTB = nullptr;
3037
3038 // Legality bailouts. We must have at least the non-fallthrough blocks and
3039 // the post-dominating block, and the non-fallthroughs must only have one
3040 // predecessor.
3041 auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
3042 return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
3043 };
3044 if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
3045 !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
3046 return false;
3047 if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
3048 (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
3049 return false;
3050 if (!PostBB->hasNUses(2) || !QBI->getParent()->hasNUses(2))
3051 return false;
3052
3053 // OK, this is a sequence of two diamonds or triangles.
3054 // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
3055 SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses;
3056 for (auto *BB : {PTB, PFB}) {
3057 if (!BB)
3058 continue;
3059 for (auto &I : *BB)
3060 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3061 PStoreAddresses.insert(SI->getPointerOperand());
3062 }
3063 for (auto *BB : {QTB, QFB}) {
3064 if (!BB)
3065 continue;
3066 for (auto &I : *BB)
3067 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3068 QStoreAddresses.insert(SI->getPointerOperand());
3069 }
3070
3071 set_intersect(PStoreAddresses, QStoreAddresses);
3072 // set_intersect mutates PStoreAddresses in place. Rename it here to make it
3073 // clear what it contains.
3074 auto &CommonAddresses = PStoreAddresses;
3075
3076 bool Changed = false;
3077 for (auto *Address : CommonAddresses)
3078 Changed |= mergeConditionalStoreToAddress(
3079 PTB, PFB, QTB, QFB, PostBB, Address, InvertPCond, InvertQCond);
3080 return Changed;
3081}
3082
3083/// If we have a conditional branch as a predecessor of another block,
3084/// this function tries to simplify it. We know
3085/// that PBI and BI are both conditional branches, and BI is in one of the
3086/// successor blocks of PBI - PBI branches to BI.
3087static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
3088 const DataLayout &DL) {
3089 assert(PBI->isConditional() && BI->isConditional())((PBI->isConditional() && BI->isConditional()) ?
static_cast<void> (0) : __assert_fail ("PBI->isConditional() && BI->isConditional()"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3089, __PRETTY_FUNCTION__))
;
3090 BasicBlock *BB = BI->getParent();
3091
3092 // If this block ends with a branch instruction, and if there is a
3093 // predecessor that ends on a branch of the same condition, make
3094 // this conditional branch redundant.
3095 if (PBI->getCondition() == BI->getCondition() &&
3096 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3097 // Okay, the outcome of this conditional branch is statically
3098 // knowable. If this block had a single pred, handle specially.
3099 if (BB->getSinglePredecessor()) {
3100 // Turn this into a branch on constant.
3101 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3102 BI->setCondition(
3103 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue));
3104 return true; // Nuke the branch on constant.
3105 }
3106
3107 // Otherwise, if there are multiple predecessors, insert a PHI that merges
3108 // in the constant and simplify the block result. Subsequent passes of
3109 // simplifycfg will thread the block.
3110 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
3111 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
3112 PHINode *NewPN = PHINode::Create(
3113 Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
3114 BI->getCondition()->getName() + ".pr", &BB->front());
3115 // Okay, we're going to insert the PHI node. Since PBI is not the only
3116 // predecessor, compute the PHI'd conditional value for all of the preds.
3117 // Any predecessor where the condition is not computable we keep symbolic.
3118 for (pred_iterator PI = PB; PI != PE; ++PI) {
3119 BasicBlock *P = *PI;
3120 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI &&
3121 PBI->isConditional() && PBI->getCondition() == BI->getCondition() &&
3122 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3123 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3124 NewPN->addIncoming(
3125 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue),
3126 P);
3127 } else {
3128 NewPN->addIncoming(BI->getCondition(), P);
3129 }
3130 }
3131
3132 BI->setCondition(NewPN);
3133 return true;
3134 }
3135 }
3136
3137 if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
3138 if (CE->canTrap())
3139 return false;
3140
3141 // If both branches are conditional and both contain stores to the same
3142 // address, remove the stores from the conditionals and create a conditional
3143 // merged store at the end.
3144 if (MergeCondStores && mergeConditionalStores(PBI, BI))
3145 return true;
3146
3147 // If this is a conditional branch in an empty block, and if any
3148 // predecessors are a conditional branch to one of our destinations,
3149 // fold the conditions into logical ops and one cond br.
3150 BasicBlock::iterator BBI = BB->begin();
3151 // Ignore dbg intrinsics.
3152 while (isa<DbgInfoIntrinsic>(BBI))
3153 ++BBI;
3154 if (&*BBI != BI)
3155 return false;
3156
3157 int PBIOp, BIOp;
3158 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
3159 PBIOp = 0;
3160 BIOp = 0;
3161 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
3162 PBIOp = 0;
3163 BIOp = 1;
3164 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
3165 PBIOp = 1;
3166 BIOp = 0;
3167 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
3168 PBIOp = 1;
3169 BIOp = 1;
3170 } else {
3171 return false;
3172 }
3173
3174 // Check to make sure that the other destination of this branch
3175 // isn't BB itself. If so, this is an infinite loop that will
3176 // keep getting unwound.
3177 if (PBI->getSuccessor(PBIOp) == BB)
3178 return false;
3179
3180 // Do not perform this transformation if it would require
3181 // insertion of a large number of select instructions. For targets
3182 // without predication/cmovs, this is a big pessimization.
3183
3184 // Also do not perform this transformation if any phi node in the common
3185 // destination block can trap when reached by BB or PBB (PR17073). In that
3186 // case, it would be unsafe to hoist the operation into a select instruction.
3187
3188 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
3189 unsigned NumPhis = 0;
3190 for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II);
3191 ++II, ++NumPhis) {
3192 if (NumPhis > 2) // Disable this xform.
3193 return false;
3194
3195 PHINode *PN = cast<PHINode>(II);
3196 Value *BIV = PN->getIncomingValueForBlock(BB);
3197 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
3198 if (CE->canTrap())
3199 return false;
3200
3201 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
3202 Value *PBIV = PN->getIncomingValue(PBBIdx);
3203 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
3204 if (CE->canTrap())
3205 return false;
3206 }
3207
3208 // Finally, if everything is ok, fold the branches to logical ops.
3209 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
3210
3211 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
3212 << "AND: " << *BI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
;
3213
3214 // If OtherDest *is* BB, then BB is a basic block with a single conditional
3215 // branch in it, where one edge (OtherDest) goes back to itself but the other
3216 // exits. We don't *know* that the program avoids the infinite loop
3217 // (even though that seems likely). If we do this xform naively, we'll end up
3218 // recursively unpeeling the loop. Since we know that (after the xform is
3219 // done) that the block *is* infinite if reached, we just make it an obviously
3220 // infinite loop with no cond branch.
3221 if (OtherDest == BB) {
3222 // Insert it at the end of the function, because it's either code,
3223 // or it won't matter if it's hot. :)
3224 BasicBlock *InfLoopBlock =
3225 BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
3226 BranchInst::Create(InfLoopBlock, InfLoopBlock);
3227 OtherDest = InfLoopBlock;
3228 }
3229
3230 DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3231
3232 // BI may have other predecessors. Because of this, we leave
3233 // it alone, but modify PBI.
3234
3235 // Make sure we get to CommonDest on True&True directions.
3236 Value *PBICond = PBI->getCondition();
3237 IRBuilder<NoFolder> Builder(PBI);
3238 if (PBIOp)
3239 PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not");
3240
3241 Value *BICond = BI->getCondition();
3242 if (BIOp)
3243 BICond = Builder.CreateNot(BICond, BICond->getName() + ".not");
3244
3245 // Merge the conditions.
3246 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
3247
3248 // Modify PBI to branch on the new condition to the new dests.
3249 PBI->setCondition(Cond);
3250 PBI->setSuccessor(0, CommonDest);
3251 PBI->setSuccessor(1, OtherDest);
3252
3253 // Update branch weight for PBI.
3254 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
3255 uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
3256 bool HasWeights =
3257 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
3258 SuccTrueWeight, SuccFalseWeight);
3259 if (HasWeights) {
3260 PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3261 PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3262 SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3263 SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3264 // The weight to CommonDest should be PredCommon * SuccTotal +
3265 // PredOther * SuccCommon.
3266 // The weight to OtherDest should be PredOther * SuccOther.
3267 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
3268 PredOther * SuccCommon,
3269 PredOther * SuccOther};
3270 // Halve the weights if any of them cannot fit in an uint32_t
3271 FitWeights(NewWeights);
3272
3273 PBI->setMetadata(LLVMContext::MD_prof,
3274 MDBuilder(BI->getContext())
3275 .createBranchWeights(NewWeights[0], NewWeights[1]));
3276 }
3277
3278 // OtherDest may have phi nodes. If so, add an entry from PBI's
3279 // block that are identical to the entries for BI's block.
3280 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
3281
3282 // We know that the CommonDest already had an edge from PBI to
3283 // it. If it has PHIs though, the PHIs may have different
3284 // entries for BB and PBI's BB. If so, insert a select to make
3285 // them agree.
3286 PHINode *PN;
3287 for (BasicBlock::iterator II = CommonDest->begin();
3288 (PN = dyn_cast<PHINode>(II)); ++II) {
3289 Value *BIV = PN->getIncomingValueForBlock(BB);
3290 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
3291 Value *PBIV = PN->getIncomingValue(PBBIdx);
3292 if (BIV != PBIV) {
3293 // Insert a select in PBI to pick the right value.
3294 SelectInst *NV = cast<SelectInst>(
3295 Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
3296 PN->setIncomingValue(PBBIdx, NV);
3297 // Although the select has the same condition as PBI, the original branch
3298 // weights for PBI do not apply to the new select because the select's
3299 // 'logical' edges are incoming edges of the phi that is eliminated, not
3300 // the outgoing edges of PBI.
3301 if (HasWeights) {
3302 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3303 uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3304 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3305 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3306 // The weight to PredCommonDest should be PredCommon * SuccTotal.
3307 // The weight to PredOtherDest should be PredOther * SuccCommon.
3308 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
3309 PredOther * SuccCommon};
3310
3311 FitWeights(NewWeights);
3312
3313 NV->setMetadata(LLVMContext::MD_prof,
3314 MDBuilder(BI->getContext())
3315 .createBranchWeights(NewWeights[0], NewWeights[1]));
3316 }
3317 }
3318 }
3319
3320 DEBUG(dbgs() << "INTO: " << *PBI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "INTO: " << *PBI->
getParent(); } } while (false)
;
3321 DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3322
3323 // This basic block is probably dead. We know it has at least
3324 // one fewer predecessor.
3325 return true;
3326}
3327
3328// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
3329// true or to FalseBB if Cond is false.
3330// Takes care of updating the successors and removing the old terminator.
3331// Also makes sure not to introduce new successors by assuming that edges to
3332// non-successor TrueBBs and FalseBBs aren't reachable.
3333static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
3334 BasicBlock *TrueBB, BasicBlock *FalseBB,
3335 uint32_t TrueWeight,
3336 uint32_t FalseWeight) {
3337 // Remove any superfluous successor edges from the CFG.
3338 // First, figure out which successors to preserve.
3339 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
3340 // successor.
3341 BasicBlock *KeepEdge1 = TrueBB;
3342 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
3343
3344 // Then remove the rest.
3345 for (BasicBlock *Succ : OldTerm->successors()) {
3346 // Make sure only to keep exactly one copy of each edge.
3347 if (Succ == KeepEdge1)
3348 KeepEdge1 = nullptr;
3349 else if (Succ == KeepEdge2)
3350 KeepEdge2 = nullptr;
3351 else
3352 Succ->removePredecessor(OldTerm->getParent(),
3353 /*DontDeleteUselessPHIs=*/true);
3354 }
3355
3356 IRBuilder<> Builder(OldTerm);
3357 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
3358
3359 // Insert an appropriate new terminator.
3360 if (!KeepEdge1 && !KeepEdge2) {
3361 if (TrueBB == FalseBB)
3362 // We were only looking for one successor, and it was present.
3363 // Create an unconditional branch to it.
3364 Builder.CreateBr(TrueBB);
3365 else {
3366 // We found both of the successors we were looking for.
3367 // Create a conditional branch sharing the condition of the select.
3368 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
3369 if (TrueWeight != FalseWeight)
3370 NewBI->setMetadata(LLVMContext::MD_prof,
3371 MDBuilder(OldTerm->getContext())
3372 .createBranchWeights(TrueWeight, FalseWeight));
3373 }
3374 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
3375 // Neither of the selected blocks were successors, so this
3376 // terminator must be unreachable.
3377 new UnreachableInst(OldTerm->getContext(), OldTerm);
3378 } else {
3379 // One of the selected values was a successor, but the other wasn't.
3380 // Insert an unconditional branch to the one that was found;
3381 // the edge to the one that wasn't must be unreachable.
3382 if (!KeepEdge1)
3383 // Only TrueBB was found.
3384 Builder.CreateBr(TrueBB);
3385 else
3386 // Only FalseBB was found.
3387 Builder.CreateBr(FalseBB);
3388 }
3389
3390 EraseTerminatorInstAndDCECond(OldTerm);
3391 return true;
3392}
3393
3394// Replaces
3395// (switch (select cond, X, Y)) on constant X, Y
3396// with a branch - conditional if X and Y lead to distinct BBs,
3397// unconditional otherwise.
3398static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
3399 // Check for constant integer values in the select.
3400 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
3401 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
3402 if (!TrueVal || !FalseVal)
3403 return false;
3404
3405 // Find the relevant condition and destinations.
3406 Value *Condition = Select->getCondition();
3407 BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor();
3408 BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor();
3409
3410 // Get weight for TrueBB and FalseBB.
3411 uint32_t TrueWeight = 0, FalseWeight = 0;
3412 SmallVector<uint64_t, 8> Weights;
3413 bool HasWeights = HasBranchWeights(SI);
3414 if (HasWeights) {
3415 GetBranchWeights(SI, Weights);
3416 if (Weights.size() == 1 + SI->getNumCases()) {
3417 TrueWeight =
3418 (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()];
3419 FalseWeight =
3420 (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()];
3421 }
3422 }
3423
3424 // Perform the actual simplification.
3425 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
3426 FalseWeight);
3427}
3428
3429// Replaces
3430// (indirectbr (select cond, blockaddress(@fn, BlockA),
3431// blockaddress(@fn, BlockB)))
3432// with
3433// (br cond, BlockA, BlockB).
3434static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
3435 // Check that both operands of the select are block addresses.
3436 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
3437 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
3438 if (!TBA || !FBA)
3439 return false;
3440
3441 // Extract the actual blocks.
3442 BasicBlock *TrueBB = TBA->getBasicBlock();
3443 BasicBlock *FalseBB = FBA->getBasicBlock();
3444
3445 // Perform the actual simplification.
3446 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0,
3447 0);
3448}
3449
3450/// This is called when we find an icmp instruction
3451/// (a seteq/setne with a constant) as the only instruction in a
3452/// block that ends with an uncond branch. We are looking for a very specific
3453/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
3454/// this case, we merge the first two "or's of icmp" into a switch, but then the
3455/// default value goes to an uncond block with a seteq in it, we get something
3456/// like:
3457///
3458/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
3459/// DEFAULT:
3460/// %tmp = icmp eq i8 %A, 92
3461/// br label %end
3462/// end:
3463/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
3464///
3465/// We prefer to split the edge to 'end' so that there is a true/false entry to
3466/// the PHI, merging the third icmp into the switch.
3467static bool TryToSimplifyUncondBranchWithICmpInIt(
3468 ICmpInst *ICI, IRBuilder<> &Builder, const DataLayout &DL,
3469 const TargetTransformInfo &TTI, unsigned BonusInstThreshold,
3470 AssumptionCache *AC) {
3471 BasicBlock *BB = ICI->getParent();
3472
3473 // If the block has any PHIs in it or the icmp has multiple uses, it is too
3474 // complex.
3475 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse())
3476 return false;
3477
3478 Value *V = ICI->getOperand(0);
3479 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
3480
3481 // The pattern we're looking for is where our only predecessor is a switch on
3482 // 'V' and this block is the default case for the switch. In this case we can
3483 // fold the compared value into the switch to simplify things.
3484 BasicBlock *Pred = BB->getSinglePredecessor();
3485 if (!Pred || !isa<SwitchInst>(Pred->getTerminator()))
3486 return false;
3487
3488 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
3489 if (SI->getCondition() != V)
3490 return false;
3491
3492 // If BB is reachable on a non-default case, then we simply know the value of
3493 // V in this block. Substitute it and constant fold the icmp instruction
3494 // away.
3495 if (SI->getDefaultDest() != BB) {
3496 ConstantInt *VVal = SI->findCaseDest(BB);
3497 assert(VVal && "Should have a unique destination value")((VVal && "Should have a unique destination value") ?
static_cast<void> (0) : __assert_fail ("VVal && \"Should have a unique destination value\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3497, __PRETTY_FUNCTION__))
;
3498 ICI->setOperand(0, VVal);
3499
3500 if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) {
3501 ICI->replaceAllUsesWith(V);
3502 ICI->eraseFromParent();
3503 }
3504 // BB is now empty, so it is likely to simplify away.
3505 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
3506 }
3507
3508 // Ok, the block is reachable from the default dest. If the constant we're
3509 // comparing exists in one of the other edges, then we can constant fold ICI
3510 // and zap it.
3511 if (SI->findCaseValue(Cst) != SI->case_default()) {
3512 Value *V;
3513 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3514 V = ConstantInt::getFalse(BB->getContext());
3515 else
3516 V = ConstantInt::getTrue(BB->getContext());
3517
3518 ICI->replaceAllUsesWith(V);
3519 ICI->eraseFromParent();
3520 // BB is now empty, so it is likely to simplify away.
3521 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
3522 }
3523
3524 // The use of the icmp has to be in the 'end' block, by the only PHI node in
3525 // the block.
3526 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
3527 PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
3528 if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
3529 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
3530 return false;
3531
3532 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
3533 // true in the PHI.
3534 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
3535 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
3536
3537 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3538 std::swap(DefaultCst, NewCst);
3539
3540 // Replace ICI (which is used by the PHI for the default value) with true or
3541 // false depending on if it is EQ or NE.
3542 ICI->replaceAllUsesWith(DefaultCst);
3543 ICI->eraseFromParent();
3544
3545 // Okay, the switch goes to this block on a default value. Add an edge from
3546 // the switch to the merge point on the compared value.
3547 BasicBlock *NewBB =
3548 BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB);
3549 SmallVector<uint64_t, 8> Weights;
3550 bool HasWeights = HasBranchWeights(SI);
3551 if (HasWeights) {
3552 GetBranchWeights(SI, Weights);
3553 if (Weights.size() == 1 + SI->getNumCases()) {
3554 // Split weight for default case to case for "Cst".
3555 Weights[0] = (Weights[0] + 1) >> 1;
3556 Weights.push_back(Weights[0]);
3557
3558 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3559 SI->setMetadata(
3560 LLVMContext::MD_prof,
3561 MDBuilder(SI->getContext()).createBranchWeights(MDWeights));
3562 }
3563 }
3564 SI->addCase(Cst, NewBB);
3565
3566 // NewBB branches to the phi block, add the uncond branch and the phi entry.
3567 Builder.SetInsertPoint(NewBB);
3568 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
3569 Builder.CreateBr(SuccBlock);
3570 PHIUse->addIncoming(NewCst, NewBB);
3571 return true;
3572}
3573
3574/// The specified branch is a conditional branch.
3575/// Check to see if it is branching on an or/and chain of icmp instructions, and
3576/// fold it into a switch instruction if so.
3577static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
3578 const DataLayout &DL) {
3579 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
3580 if (!Cond)
3581 return false;
3582
3583 // Change br (X == 0 | X == 1), T, F into a switch instruction.
3584 // If this is a bunch of seteq's or'd together, or if it's a bunch of
3585 // 'setne's and'ed together, collect them.
3586
3587 // Try to gather values from a chain of and/or to be turned into a switch
3588 ConstantComparesGatherer ConstantCompare(Cond, DL);
3589 // Unpack the result
3590 SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals;
3591 Value *CompVal = ConstantCompare.CompValue;
3592 unsigned UsedICmps = ConstantCompare.UsedICmps;
3593 Value *ExtraCase = ConstantCompare.Extra;
3594
3595 // If we didn't have a multiply compared value, fail.
3596 if (!CompVal)
3597 return false;
3598
3599 // Avoid turning single icmps into a switch.
3600 if (UsedICmps <= 1)
3601 return false;
3602
3603 bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
3604
3605 // There might be duplicate constants in the list, which the switch
3606 // instruction can't handle, remove them now.
3607 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
3608 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
3609
3610 // If Extra was used, we require at least two switch values to do the
3611 // transformation. A switch with one value is just a conditional branch.
3612 if (ExtraCase && Values.size() < 2)
3613 return false;
3614
3615 // TODO: Preserve branch weight metadata, similarly to how
3616 // FoldValueComparisonIntoPredecessors preserves it.
3617
3618 // Figure out which block is which destination.
3619 BasicBlock *DefaultBB = BI->getSuccessor(1);
3620 BasicBlock *EdgeBB = BI->getSuccessor(0);
3621 if (!TrueWhenEqual)
3622 std::swap(DefaultBB, EdgeBB);
3623
3624 BasicBlock *BB = BI->getParent();
3625
3626 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Converting 'icmp' chain with "
<< Values.size() << " cases into SWITCH. BB is:\n"
<< *BB; } } while (false)
3627 << " cases into SWITCH. BB is:\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Converting 'icmp' chain with "
<< Values.size() << " cases into SWITCH. BB is:\n"
<< *BB; } } while (false)
3628 << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Converting 'icmp' chain with "
<< Values.size() << " cases into SWITCH. BB is:\n"
<< *BB; } } while (false)
;
3629
3630 // If there are any extra values that couldn't be folded into the switch
3631 // then we evaluate them with an explicit branch first. Split the block
3632 // right before the condbr to handle it.
3633 if (ExtraCase) {
3634 BasicBlock *NewBB =
3635 BB->splitBasicBlock(BI->getIterator(), "switch.early.test");
3636 // Remove the uncond branch added to the old block.
3637 TerminatorInst *OldTI = BB->getTerminator();
3638 Builder.SetInsertPoint(OldTI);
3639
3640 if (TrueWhenEqual)
3641 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
3642 else
3643 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
3644
3645 OldTI->eraseFromParent();
3646
3647 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
3648 // for the edge we just added.
3649 AddPredecessorToBlock(EdgeBB, BB, NewBB);
3650
3651 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCasedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
3652 << "\nEXTRABB = " << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
;
3653 BB = NewBB;
3654 }
3655
3656 Builder.SetInsertPoint(BI);
3657 // Convert pointer to int before we switch.
3658 if (CompVal->getType()->isPointerTy()) {
3659 CompVal = Builder.CreatePtrToInt(
3660 CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
3661 }
3662
3663 // Create the new switch instruction now.
3664 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
3665
3666 // Add all of the 'cases' to the switch instruction.
3667 for (unsigned i = 0, e = Values.size(); i != e; ++i)
3668 New->addCase(Values[i], EdgeBB);
3669
3670 // We added edges from PI to the EdgeBB. As such, if there were any
3671 // PHI nodes in EdgeBB, they need entries to be added corresponding to
3672 // the number of edges added.
3673 for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
3674 PHINode *PN = cast<PHINode>(BBI);
3675 Value *InVal = PN->getIncomingValueForBlock(BB);
3676 for (unsigned i = 0, e = Values.size() - 1; i != e; ++i)
3677 PN->addIncoming(InVal, BB);
3678 }
3679
3680 // Erase the old branch instruction.
3681 EraseTerminatorInstAndDCECond(BI);
3682
3683 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain result is:\n"
<< *BB << '\n'; } } while (false)
;
3684 return true;
3685}
3686
3687bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
3688 if (isa<PHINode>(RI->getValue()))
3689 return SimplifyCommonResume(RI);
3690 else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) &&
3691 RI->getValue() == RI->getParent()->getFirstNonPHI())
3692 // The resume must unwind the exception that caused control to branch here.
3693 return SimplifySingleResume(RI);
3694
3695 return false;
3696}
3697
3698// Simplify resume that is shared by several landing pads (phi of landing pad).
3699bool SimplifyCFGOpt::SimplifyCommonResume(ResumeInst *RI) {
3700 BasicBlock *BB = RI->getParent();
3701
3702 // Check that there are no other instructions except for debug intrinsics
3703 // between the phi of landing pads (RI->getValue()) and resume instruction.
3704 BasicBlock::iterator I = cast<Instruction>(RI->getValue())->getIterator(),
3705 E = RI->getIterator();
3706 while (++I != E)
3707 if (!isa<DbgInfoIntrinsic>(I))
3708 return false;
3709
3710 SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
3711 auto *PhiLPInst = cast<PHINode>(RI->getValue());
3712
3713 // Check incoming blocks to see if any of them are trivial.
3714 for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
3715 Idx++) {
3716 auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
3717 auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);
3718
3719 // If the block has other successors, we can not delete it because
3720 // it has other dependents.
3721 if (IncomingBB->getUniqueSuccessor() != BB)
3722 continue;
3723
3724 auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
3725 // Not the landing pad that caused the control to branch here.
3726 if (IncomingValue != LandingPad)
3727 continue;
3728
3729 bool isTrivial = true;
3730
3731 I = IncomingBB->getFirstNonPHI()->getIterator();
3732 E = IncomingBB->getTerminator()->getIterator();
3733 while (++I != E)
3734 if (!isa<DbgInfoIntrinsic>(I)) {
3735 isTrivial = false;
3736 break;
3737 }
3738
3739 if (isTrivial)
3740 TrivialUnwindBlocks.insert(IncomingBB);
3741 }
3742
3743 // If no trivial unwind blocks, don't do any simplifications.
3744 if (TrivialUnwindBlocks.empty())
3745 return false;
3746
3747 // Turn all invokes that unwind here into calls.
3748 for (auto *TrivialBB : TrivialUnwindBlocks) {
3749 // Blocks that will be simplified should be removed from the phi node.
3750 // Note there could be multiple edges to the resume block, and we need
3751 // to remove them all.
3752 while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1)
3753 BB->removePredecessor(TrivialBB, true);
3754
3755 for (pred_iterator PI = pred_begin(TrivialBB), PE = pred_end(TrivialBB);
3756 PI != PE;) {
3757 BasicBlock *Pred = *PI++;
3758 removeUnwindEdge(Pred);
3759 }
3760
3761 // In each SimplifyCFG run, only the current processed block can be erased.
3762 // Otherwise, it will break the iteration of SimplifyCFG pass. So instead
3763 // of erasing TrivialBB, we only remove the branch to the common resume
3764 // block so that we can later erase the resume block since it has no
3765 // predecessors.
3766 TrivialBB->getTerminator()->eraseFromParent();
3767 new UnreachableInst(RI->getContext(), TrivialBB);
3768 }
3769
3770 // Delete the resume block if all its predecessors have been removed.
3771 if (pred_empty(BB))
3772 BB->eraseFromParent();
3773
3774 return !TrivialUnwindBlocks.empty();
3775}
3776
3777// Simplify resume that is only used by a single (non-phi) landing pad.
3778bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) {
3779 BasicBlock *BB = RI->getParent();
3780 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
3781 assert(RI->getValue() == LPInst &&((RI->getValue() == LPInst && "Resume must unwind the exception that caused control to here"
) ? static_cast<void> (0) : __assert_fail ("RI->getValue() == LPInst && \"Resume must unwind the exception that caused control to here\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3782, __PRETTY_FUNCTION__))
3782 "Resume must unwind the exception that caused control to here")((RI->getValue() == LPInst && "Resume must unwind the exception that caused control to here"
) ? static_cast<void> (0) : __assert_fail ("RI->getValue() == LPInst && \"Resume must unwind the exception that caused control to here\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3782, __PRETTY_FUNCTION__))
;
3783
3784 // Check that there are no other instructions except for debug intrinsics.
3785 BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator();
3786 while (++I != E)
3787 if (!isa<DbgInfoIntrinsic>(I))
3788 return false;
3789
3790 // Turn all invokes that unwind here into calls and delete the basic block.
3791 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3792 BasicBlock *Pred = *PI++;
3793 removeUnwindEdge(Pred);
3794 }
3795
3796 // The landingpad is now unreachable. Zap it.
3797 BB->eraseFromParent();
3798 if (LoopHeaders)
3799 LoopHeaders->erase(BB);
3800 return true;
3801}
3802
3803static bool removeEmptyCleanup(CleanupReturnInst *RI) {
3804 // If this is a trivial cleanup pad that executes no instructions, it can be
3805 // eliminated. If the cleanup pad continues to the caller, any predecessor
3806 // that is an EH pad will be updated to continue to the caller and any
3807 // predecessor that terminates with an invoke instruction will have its invoke
3808 // instruction converted to a call instruction. If the cleanup pad being
3809 // simplified does not continue to the caller, each predecessor will be
3810 // updated to continue to the unwind destination of the cleanup pad being
3811 // simplified.
3812 BasicBlock *BB = RI->getParent();
3813 CleanupPadInst *CPInst = RI->getCleanupPad();
3814 if (CPInst->getParent() != BB)
3815 // This isn't an empty cleanup.
3816 return false;
3817
3818 // We cannot kill the pad if it has multiple uses. This typically arises
3819 // from unreachable basic blocks.
3820 if (!CPInst->hasOneUse())
3821 return false;
3822
3823 // Check that there are no other instructions except for benign intrinsics.
3824 BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
3825 while (++I != E) {
3826 auto *II = dyn_cast<IntrinsicInst>(I);
3827 if (!II)
3828 return false;
3829
3830 Intrinsic::ID IntrinsicID = II->getIntrinsicID();
3831 switch (IntrinsicID) {
3832 case Intrinsic::dbg_declare:
3833 case Intrinsic::dbg_value:
3834 case Intrinsic::lifetime_end:
3835 break;
3836 default:
3837 return false;
3838 }
3839 }
3840
3841 // If the cleanup return we are simplifying unwinds to the caller, this will
3842 // set UnwindDest to nullptr.
3843 BasicBlock *UnwindDest = RI->getUnwindDest();
3844 Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
3845
3846 // We're about to remove BB from the control flow. Before we do, sink any
3847 // PHINodes into the unwind destination. Doing this before changing the
3848 // control flow avoids some potentially slow checks, since we can currently
3849 // be certain that UnwindDest and BB have no common predecessors (since they
3850 // are both EH pads).
3851 if (UnwindDest) {
3852 // First, go through the PHI nodes in UnwindDest and update any nodes that
3853 // reference the block we are removing
3854 for (BasicBlock::iterator I = UnwindDest->begin(),
3855 IE = DestEHPad->getIterator();
3856 I != IE; ++I) {
3857 PHINode *DestPN = cast<PHINode>(I);
3858
3859 int Idx = DestPN->getBasicBlockIndex(BB);
3860 // Since BB unwinds to UnwindDest, it has to be in the PHI node.
3861 assert(Idx != -1)((Idx != -1) ? static_cast<void> (0) : __assert_fail ("Idx != -1"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3861, __PRETTY_FUNCTION__))
;
3862 // This PHI node has an incoming value that corresponds to a control
3863 // path through the cleanup pad we are removing. If the incoming
3864 // value is in the cleanup pad, it must be a PHINode (because we
3865 // verified above that the block is otherwise empty). Otherwise, the
3866 // value is either a constant or a value that dominates the cleanup
3867 // pad being removed.
3868 //
3869 // Because BB and UnwindDest are both EH pads, all of their
3870 // predecessors must unwind to these blocks, and since no instruction
3871 // can have multiple unwind destinations, there will be no overlap in
3872 // incoming blocks between SrcPN and DestPN.
3873 Value *SrcVal = DestPN->getIncomingValue(Idx);
3874 PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
3875
3876 // Remove the entry for the block we are deleting.
3877 DestPN->removeIncomingValue(Idx, false);
3878
3879 if (SrcPN && SrcPN->getParent() == BB) {
3880 // If the incoming value was a PHI node in the cleanup pad we are
3881 // removing, we need to merge that PHI node's incoming values into
3882 // DestPN.
3883 for (unsigned SrcIdx = 0, SrcE = SrcPN->getNumIncomingValues();
3884 SrcIdx != SrcE; ++SrcIdx) {
3885 DestPN->addIncoming(SrcPN->getIncomingValue(SrcIdx),
3886 SrcPN->getIncomingBlock(SrcIdx));
3887 }
3888 } else {
3889 // Otherwise, the incoming value came from above BB and
3890 // so we can just reuse it. We must associate all of BB's
3891 // predecessors with this value.
3892 for (auto *pred : predecessors(BB)) {
3893 DestPN->addIncoming(SrcVal, pred);
3894 }
3895 }
3896 }
3897
3898 // Sink any remaining PHI nodes directly into UnwindDest.
3899 Instruction *InsertPt = DestEHPad;
3900 for (BasicBlock::iterator I = BB->begin(),
3901 IE = BB->getFirstNonPHI()->getIterator();
3902 I != IE;) {
3903 // The iterator must be incremented here because the instructions are
3904 // being moved to another block.
3905 PHINode *PN = cast<PHINode>(I++);
3906 if (PN->use_empty())
3907 // If the PHI node has no uses, just leave it. It will be erased
3908 // when we erase BB below.
3909 continue;
3910
3911 // Otherwise, sink this PHI node into UnwindDest.
3912 // Any predecessors to UnwindDest which are not already represented
3913 // must be back edges which inherit the value from the path through
3914 // BB. In this case, the PHI value must reference itself.
3915 for (auto *pred : predecessors(UnwindDest))
3916 if (pred != BB)
3917 PN->addIncoming(PN, pred);
3918 PN->moveBefore(InsertPt);
3919 }
3920 }
3921
3922 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3923 // The iterator must be updated here because we are removing this pred.
3924 BasicBlock *PredBB = *PI++;
3925 if (UnwindDest == nullptr) {
3926 removeUnwindEdge(PredBB);
3927 } else {
3928 TerminatorInst *TI = PredBB->getTerminator();
3929 TI->replaceUsesOfWith(BB, UnwindDest);
3930 }
3931 }
3932
3933 // The cleanup pad is now unreachable. Zap it.
3934 BB->eraseFromParent();
3935 return true;
3936}
3937
3938// Try to merge two cleanuppads together.
3939static bool mergeCleanupPad(CleanupReturnInst *RI) {
3940 // Skip any cleanuprets which unwind to caller, there is nothing to merge
3941 // with.
3942 BasicBlock *UnwindDest = RI->getUnwindDest();
3943 if (!UnwindDest)
3944 return false;
3945
3946 // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
3947 // be safe to merge without code duplication.
3948 if (UnwindDest->getSinglePredecessor() != RI->getParent())
3949 return false;
3950
3951 // Verify that our cleanuppad's unwind destination is another cleanuppad.
3952 auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
3953 if (!SuccessorCleanupPad)
3954 return false;
3955
3956 CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
3957 // Replace any uses of the successor cleanupad with the predecessor pad
3958 // The only cleanuppad uses should be this cleanupret, it's cleanupret and
3959 // funclet bundle operands.
3960 SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
3961 // Remove the old cleanuppad.
3962 SuccessorCleanupPad->eraseFromParent();
3963 // Now, we simply replace the cleanupret with a branch to the unwind
3964 // destination.
3965 BranchInst::Create(UnwindDest, RI->getParent());
3966 RI->eraseFromParent();
3967
3968 return true;
3969}
3970
3971bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
3972 // It is possible to transiantly have an undef cleanuppad operand because we
3973 // have deleted some, but not all, dead blocks.
3974 // Eventually, this block will be deleted.
3975 if (isa<UndefValue>(RI->getOperand(0)))
3976 return false;
3977
3978 if (mergeCleanupPad(RI))
3979 return true;
3980
3981 if (removeEmptyCleanup(RI))
3982 return true;
3983
3984 return false;
3985}
3986
3987bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
3988 BasicBlock *BB = RI->getParent();
3989 if (!BB->getFirstNonPHIOrDbg()->isTerminator())
3990 return false;
3991
3992 // Find predecessors that end with branches.
3993 SmallVector<BasicBlock *, 8> UncondBranchPreds;
3994 SmallVector<BranchInst *, 8> CondBranchPreds;
3995 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
3996 BasicBlock *P = *PI;
3997 TerminatorInst *PTI = P->getTerminator();
3998 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
3999 if (BI->isUnconditional())
4000 UncondBranchPreds.push_back(P);
4001 else
4002 CondBranchPreds.push_back(BI);
4003 }
4004 }
4005
4006 // If we found some, do the transformation!
4007 if (!UncondBranchPreds.empty() && DupRet) {
4008 while (!UncondBranchPreds.empty()) {
4009 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
4010 DEBUG(dbgs() << "FOLDING: " << *BBdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
4011 << "INTO UNCOND BRANCH PRED: " << *Pred)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
;
4012 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
4013 }
4014
4015 // If we eliminated all predecessors of the block, delete the block now.
4016 if (pred_empty(BB)) {
4017 // We know there are no successors, so just nuke the block.
4018 BB->eraseFromParent();
4019 if (LoopHeaders)
4020 LoopHeaders->erase(BB);
4021 }
4022
4023 return true;
4024 }
4025
4026 // Check out all of the conditional branches going to this return
4027 // instruction. If any of them just select between returns, change the
4028 // branch itself into a select/return pair.
4029 while (!CondBranchPreds.empty()) {
4030 BranchInst *BI = CondBranchPreds.pop_back_val();
4031
4032 // Check to see if the non-BB successor is also a return block.
4033 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
4034 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
4035 SimplifyCondBranchToTwoReturns(BI, Builder))
4036 return true;
4037 }
4038 return false;
4039}
4040
4041bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
4042 BasicBlock *BB = UI->getParent();
4043
4044 bool Changed = false;
4045
4046 // If there are any instructions immediately before the unreachable that can
4047 // be removed, do so.
4048 while (UI->getIterator() != BB->begin()) {
4049 BasicBlock::iterator BBI = UI->getIterator();
4050 --BBI;
4051 // Do not delete instructions that can have side effects which might cause
4052 // the unreachable to not be reachable; specifically, calls and volatile
4053 // operations may have this effect.
4054 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI))
4055 break;
4056
4057 if (BBI->mayHaveSideEffects()) {
4058 if (auto *SI = dyn_cast<StoreInst>(BBI)) {
4059 if (SI->isVolatile())
4060 break;
4061 } else if (auto *LI = dyn_cast<LoadInst>(BBI)) {
4062 if (LI->isVolatile())
4063 break;
4064 } else if (auto *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
4065 if (RMWI->isVolatile())
4066 break;
4067 } else if (auto *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
4068 if (CXI->isVolatile())
4069 break;
4070 } else if (isa<CatchPadInst>(BBI)) {
4071 // A catchpad may invoke exception object constructors and such, which
4072 // in some languages can be arbitrary code, so be conservative by
4073 // default.
4074 // For CoreCLR, it just involves a type test, so can be removed.
4075 if (classifyEHPersonality(BB->getParent()->getPersonalityFn()) !=
4076 EHPersonality::CoreCLR)
4077 break;
4078 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
4079 !isa<LandingPadInst>(BBI)) {
4080 break;
4081 }
4082 // Note that deleting LandingPad's here is in fact okay, although it
4083 // involves a bit of subtle reasoning. If this inst is a LandingPad,
4084 // all the predecessors of this block will be the unwind edges of Invokes,
4085 // and we can therefore guarantee this block will be erased.
4086 }
4087
4088 // Delete this instruction (any uses are guaranteed to be dead)
4089 if (!BBI->use_empty())
4090 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
4091 BBI->eraseFromParent();
4092 Changed = true;
4093 }
4094
4095 // If the unreachable instruction is the first in the block, take a gander
4096 // at all of the predecessors of this instruction, and simplify them.
4097 if (&BB->front() != UI)
4098 return Changed;
4099
4100 SmallVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
4101 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
4102 TerminatorInst *TI = Preds[i]->getTerminator();
4103 IRBuilder<> Builder(TI);
4104 if (auto *BI = dyn_cast<BranchInst>(TI)) {
4105 if (BI->isUnconditional()) {
4106 if (BI->getSuccessor(0) == BB) {
4107 new UnreachableInst(TI->getContext(), TI);
4108 TI->eraseFromParent();
4109 Changed = true;
4110 }
4111 } else {
4112 if (BI->getSuccessor(0) == BB) {
4113 Builder.CreateBr(BI->getSuccessor(1));
4114 EraseTerminatorInstAndDCECond(BI);
4115 } else if (BI->getSuccessor(1) == BB) {
4116 Builder.CreateBr(BI->getSuccessor(0));
4117 EraseTerminatorInstAndDCECond(BI);
4118 Changed = true;
4119 }
4120 }
4121 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
4122 for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
4123 if (i->getCaseSuccessor() != BB) {
4124 ++i;
4125 continue;
4126 }
4127 BB->removePredecessor(SI->getParent());
4128 i = SI->removeCase(i);
4129 e = SI->case_end();
4130 Changed = true;
4131 }
4132 } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
4133 if (II->getUnwindDest() == BB) {
4134 removeUnwindEdge(TI->getParent());
4135 Changed = true;
4136 }
4137 } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) {
4138 if (CSI->getUnwindDest() == BB) {
4139 removeUnwindEdge(TI->getParent());
4140 Changed = true;
4141 continue;
4142 }
4143
4144 for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(),
4145 E = CSI->handler_end();
4146 I != E; ++I) {
4147 if (*I == BB) {
4148 CSI->removeHandler(I);
4149 --I;
4150 --E;
4151 Changed = true;
4152 }
4153 }
4154 if (CSI->getNumHandlers() == 0) {
4155 BasicBlock *CatchSwitchBB = CSI->getParent();
4156 if (CSI->hasUnwindDest()) {
4157 // Redirect preds to the unwind dest
4158 CatchSwitchBB->replaceAllUsesWith(CSI->getUnwindDest());
4159 } else {
4160 // Rewrite all preds to unwind to caller (or from invoke to call).
4161 SmallVector<BasicBlock *, 8> EHPreds(predecessors(CatchSwitchBB));
4162 for (BasicBlock *EHPred : EHPreds)
4163 removeUnwindEdge(EHPred);
4164 }
4165 // The catchswitch is no longer reachable.
4166 new UnreachableInst(CSI->getContext(), CSI);
4167 CSI->eraseFromParent();
4168 Changed = true;
4169 }
4170 } else if (isa<CleanupReturnInst>(TI)) {
4171 new UnreachableInst(TI->getContext(), TI);
4172 TI->eraseFromParent();
4173 Changed = true;
4174 }
4175 }
4176
4177 // If this block is now dead, remove it.
4178 if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {
4179 // We know there are no successors, so just nuke the block.
4180 BB->eraseFromParent();
4181 if (LoopHeaders)
4182 LoopHeaders->erase(BB);
4183 return true;
4184 }
4185
4186 return Changed;
4187}
4188
4189static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
4190 assert(Cases.size() >= 1)((Cases.size() >= 1) ? static_cast<void> (0) : __assert_fail
("Cases.size() >= 1", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4190, __PRETTY_FUNCTION__))
;
4191
4192 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
4193 for (size_t I = 1, E = Cases.size(); I != E; ++I) {
4194 if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
4195 return false;
4196 }
4197 return true;
4198}
4199
4200/// Turn a switch with two reachable destinations into an integer range
4201/// comparison and branch.
4202static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
4203 assert(SI->getNumCases() > 1 && "Degenerate switch?")((SI->getNumCases() > 1 && "Degenerate switch?"
) ? static_cast<void> (0) : __assert_fail ("SI->getNumCases() > 1 && \"Degenerate switch?\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4203, __PRETTY_FUNCTION__))
;
4204
4205 bool HasDefault =
4206 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4207
4208 // Partition the cases into two sets with different destinations.
4209 BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
4210 BasicBlock *DestB = nullptr;
4211 SmallVector<ConstantInt *, 16> CasesA;
4212 SmallVector<ConstantInt *, 16> CasesB;
4213
4214 for (auto Case : SI->cases()) {
4215 BasicBlock *Dest = Case.getCaseSuccessor();
4216 if (!DestA)
4217 DestA = Dest;
4218 if (Dest == DestA) {
4219 CasesA.push_back(Case.getCaseValue());
4220 continue;
4221 }
4222 if (!DestB)
4223 DestB = Dest;
4224 if (Dest == DestB) {
4225 CasesB.push_back(Case.getCaseValue());
4226 continue;
4227 }
4228 return false; // More than two destinations.
4229 }
4230
4231 assert(DestA && DestB &&((DestA && DestB && "Single-destination switch should have been folded."
) ? static_cast<void> (0) : __assert_fail ("DestA && DestB && \"Single-destination switch should have been folded.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4232, __PRETTY_FUNCTION__))
4232 "Single-destination switch should have been folded.")((DestA && DestB && "Single-destination switch should have been folded."
) ? static_cast<void> (0) : __assert_fail ("DestA && DestB && \"Single-destination switch should have been folded.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4232, __PRETTY_FUNCTION__))
;
4233 assert(DestA != DestB)((DestA != DestB) ? static_cast<void> (0) : __assert_fail
("DestA != DestB", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4233, __PRETTY_FUNCTION__))
;
4234 assert(DestB != SI->getDefaultDest())((DestB != SI->getDefaultDest()) ? static_cast<void>
(0) : __assert_fail ("DestB != SI->getDefaultDest()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4234, __PRETTY_FUNCTION__))
;
4235 assert(!CasesB.empty() && "There must be non-default cases.")((!CasesB.empty() && "There must be non-default cases."
) ? static_cast<void> (0) : __assert_fail ("!CasesB.empty() && \"There must be non-default cases.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4235, __PRETTY_FUNCTION__))
;
4236 assert(!CasesA.empty() || HasDefault)((!CasesA.empty() || HasDefault) ? static_cast<void> (0
) : __assert_fail ("!CasesA.empty() || HasDefault", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4236, __PRETTY_FUNCTION__))
;
4237
4238 // Figure out if one of the sets of cases form a contiguous range.
4239 SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
4240 BasicBlock *ContiguousDest = nullptr;
4241 BasicBlock *OtherDest = nullptr;
4242 if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
4243 ContiguousCases = &CasesA;
4244 ContiguousDest = DestA;
4245 OtherDest = DestB;
4246 } else if (CasesAreContiguous(CasesB)) {
4247 ContiguousCases = &CasesB;
4248 ContiguousDest = DestB;
4249 OtherDest = DestA;
4250 } else
4251 return false;
4252
4253 // Start building the compare and branch.
4254
4255 Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
4256 Constant *NumCases =
4257 ConstantInt::get(Offset->getType(), ContiguousCases->size());
4258
4259 Value *Sub = SI->getCondition();
4260 if (!Offset->isNullValue())
4261 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
4262
4263 Value *Cmp;
4264 // If NumCases overflowed, then all possible values jump to the successor.
4265 if (NumCases->isNullValue() && !ContiguousCases->empty())
4266 Cmp = ConstantInt::getTrue(SI->getContext());
4267 else
4268 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
4269 BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
4270
4271 // Update weight for the newly-created conditional branch.
4272 if (HasBranchWeights(SI)) {
4273 SmallVector<uint64_t, 8> Weights;
4274 GetBranchWeights(SI, Weights);
4275 if (Weights.size() == 1 + SI->getNumCases()) {
4276 uint64_t TrueWeight = 0;
4277 uint64_t FalseWeight = 0;
4278 for (size_t I = 0, E = Weights.size(); I != E; ++I) {
4279 if (SI->getSuccessor(I) == ContiguousDest)
4280 TrueWeight += Weights[I];
4281 else
4282 FalseWeight += Weights[I];
4283 }
4284 while (TrueWeight > UINT32_MAX(4294967295U) || FalseWeight > UINT32_MAX(4294967295U)) {
4285 TrueWeight /= 2;
4286 FalseWeight /= 2;
4287 }
4288 NewBI->setMetadata(LLVMContext::MD_prof,
4289 MDBuilder(SI->getContext())
4290 .createBranchWeights((uint32_t)TrueWeight,
4291 (uint32_t)FalseWeight));
4292 }
4293 }
4294
4295 // Prune obsolete incoming values off the successors' PHI nodes.
4296 for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
4297 unsigned PreviousEdges = ContiguousCases->size();
4298 if (ContiguousDest == SI->getDefaultDest())
4299 ++PreviousEdges;
4300 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4301 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4302 }
4303 for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
4304 unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
4305 if (OtherDest == SI->getDefaultDest())
4306 ++PreviousEdges;
4307 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4308 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4309 }
4310
4311 // Drop the switch.
4312 SI->eraseFromParent();
4313
4314 return true;
4315}
4316
4317/// Compute masked bits for the condition of a switch
4318/// and use it to remove dead cases.
4319static bool EliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC,
4320 const DataLayout &DL) {
4321 Value *Cond = SI->getCondition();
4322 unsigned Bits = Cond->getType()->getIntegerBitWidth();
4323 KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI);
4324
4325 // We can also eliminate cases by determining that their values are outside of
4326 // the limited range of the condition based on how many significant (non-sign)
4327 // bits are in the condition value.
4328 unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1;
4329 unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits;
4330
4331 // Gather dead cases.
4332 SmallVector<ConstantInt *, 8> DeadCases;
4333 for (auto &Case : SI->cases()) {
4334 const APInt &CaseVal = Case.getCaseValue()->getValue();
4335 if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) ||
4336 (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
4337 DeadCases.push_back(Case.getCaseValue());
4338 DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseVal << " is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch case "
<< CaseVal << " is dead.\n"; } } while (false)
;
4339 }
4340 }
4341
4342 // If we can prove that the cases must cover all possible values, the
4343 // default destination becomes dead and we can remove it. If we know some
4344 // of the bits in the value, we can use that to more precisely compute the
4345 // number of possible unique case values.
4346 bool HasDefault =
4347 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4348 const unsigned NumUnknownBits =
4349 Bits - (Known.Zero | Known.One).countPopulation();
4350 assert(NumUnknownBits <= Bits)((NumUnknownBits <= Bits) ? static_cast<void> (0) : __assert_fail
("NumUnknownBits <= Bits", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4350, __PRETTY_FUNCTION__))
;
4351 if (HasDefault && DeadCases.empty() &&
4352 NumUnknownBits < 64 /* avoid overflow */ &&
4353 SI->getNumCases() == (1ULL << NumUnknownBits)) {
4354 DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch default is dead.\n"
; } } while (false)
;
4355 BasicBlock *NewDefault =
4356 SplitBlockPredecessors(SI->getDefaultDest(), SI->getParent(), "");
4357 SI->setDefaultDest(&*NewDefault);
4358 SplitBlock(&*NewDefault, &NewDefault->front());
4359 auto *OldTI = NewDefault->getTerminator();
4360 new UnreachableInst(SI->getContext(), OldTI);
4361 EraseTerminatorInstAndDCECond(OldTI);
4362 return true;
4363 }
4364
4365 SmallVector<uint64_t, 8> Weights;
4366 bool HasWeight = HasBranchWeights(SI);
4367 if (HasWeight) {
4368 GetBranchWeights(SI, Weights);
4369 HasWeight = (Weights.size() == 1 + SI->getNumCases());
4370 }
4371
4372 // Remove dead cases from the switch.
4373 for (ConstantInt *DeadCase : DeadCases) {
4374 SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase);
4375 assert(CaseI != SI->case_default() &&((CaseI != SI->case_default() && "Case was not found. Probably mistake in DeadCases forming."
) ? static_cast<void> (0) : __assert_fail ("CaseI != SI->case_default() && \"Case was not found. Probably mistake in DeadCases forming.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4376, __PRETTY_FUNCTION__))
4376 "Case was not found. Probably mistake in DeadCases forming.")((CaseI != SI->case_default() && "Case was not found. Probably mistake in DeadCases forming."
) ? static_cast<void> (0) : __assert_fail ("CaseI != SI->case_default() && \"Case was not found. Probably mistake in DeadCases forming.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4376, __PRETTY_FUNCTION__))
;
4377 if (HasWeight) {
4378 std::swap(Weights[CaseI->getCaseIndex() + 1], Weights.back());
4379 Weights.pop_back();
4380 }
4381
4382 // Prune unused values from PHI nodes.
4383 CaseI->getCaseSuccessor()->removePredecessor(SI->getParent());
4384 SI->removeCase(CaseI);
4385 }
4386 if (HasWeight && Weights.size() >= 2) {
4387 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
4388 SI->setMetadata(LLVMContext::MD_prof,
4389 MDBuilder(SI->getParent()->getContext())
4390 .createBranchWeights(MDWeights));
4391 }
4392
4393 return !DeadCases.empty();
4394}
4395
4396/// If BB would be eligible for simplification by
4397/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
4398/// by an unconditional branch), look at the phi node for BB in the successor
4399/// block and see if the incoming value is equal to CaseValue. If so, return
4400/// the phi node, and set PhiIndex to BB's index in the phi node.
4401static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
4402 BasicBlock *BB, int *PhiIndex) {
4403 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
4404 return nullptr; // BB must be empty to be a candidate for simplification.
4405 if (!BB->getSinglePredecessor())
4406 return nullptr; // BB must be dominated by the switch.
4407
4408 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
4409 if (!Branch || !Branch->isUnconditional())
4410 return nullptr; // Terminator must be unconditional branch.
4411
4412 BasicBlock *Succ = Branch->getSuccessor(0);
4413
4414 BasicBlock::iterator I = Succ->begin();
4415 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
4416 int Idx = PHI->getBasicBlockIndex(BB);
4417 assert(Idx >= 0 && "PHI has no entry for predecessor?")((Idx >= 0 && "PHI has no entry for predecessor?")
? static_cast<void> (0) : __assert_fail ("Idx >= 0 && \"PHI has no entry for predecessor?\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4417, __PRETTY_FUNCTION__))
;
4418
4419 Value *InValue = PHI->getIncomingValue(Idx);
4420 if (InValue != CaseValue)
4421 continue;
4422
4423 *PhiIndex = Idx;
4424 return PHI;
4425 }
4426
4427 return nullptr;
4428}
4429
4430/// Try to forward the condition of a switch instruction to a phi node
4431/// dominated by the switch, if that would mean that some of the destination
4432/// blocks of the switch can be folded away.
4433/// Returns true if a change is made.
4434static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
4435 typedef DenseMap<PHINode *, SmallVector<int, 4>> ForwardingNodesMap;
4436 ForwardingNodesMap ForwardingNodes;
4437
4438 for (auto Case : SI->cases()) {
4439 ConstantInt *CaseValue = Case.getCaseValue();
4440 BasicBlock *CaseDest = Case.getCaseSuccessor();
4441
4442 int PhiIndex;
4443 PHINode *PHI =
4444 FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIndex);
4445 if (!PHI)
4446 continue;
4447
4448 ForwardingNodes[PHI].push_back(PhiIndex);
4449 }
4450
4451 bool Changed = false;
4452
4453 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
4454 E = ForwardingNodes.end();
4455 I != E; ++I) {
4456 PHINode *Phi = I->first;
4457 SmallVectorImpl<int> &Indexes = I->second;
4458
4459 if (Indexes.size() < 2)
4460 continue;
4461
4462 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
4463 Phi->setIncomingValue(Indexes[I], SI->getCondition());
4464 Changed = true;
4465 }
4466
4467 return Changed;
4468}
4469
4470/// Return true if the backend will be able to handle
4471/// initializing an array of constants like C.
4472static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
4473 if (C->isThreadDependent())
4474 return false;
4475 if (C->isDLLImportDependent())
4476 return false;
4477
4478 if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
4479 !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
4480 !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
4481 return false;
4482
4483 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
4484 if (!CE->isGEPWithNoNotionalOverIndexing())
4485 return false;
4486 if (!ValidLookupTableConstant(CE->getOperand(0), TTI))
4487 return false;
4488 }
4489
4490 if (!TTI.shouldBuildLookupTablesForConstant(C))
4491 return false;
4492
4493 return true;
4494}
4495
4496/// If V is a Constant, return it. Otherwise, try to look up
4497/// its constant value in ConstantPool, returning 0 if it's not there.
4498static Constant *
4499LookupConstant(Value *V,
4500 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4501 if (Constant *C = dyn_cast<Constant>(V))
4502 return C;
4503 return ConstantPool.lookup(V);
4504}
4505
4506/// Try to fold instruction I into a constant. This works for
4507/// simple instructions such as binary operations where both operands are
4508/// constant or can be replaced by constants from the ConstantPool. Returns the
4509/// resulting constant on success, 0 otherwise.
4510static Constant *
4511ConstantFold(Instruction *I, const DataLayout &DL,
4512 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4513 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
4514 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
4515 if (!A)
4516 return nullptr;
4517 if (A->isAllOnesValue())
4518 return LookupConstant(Select->getTrueValue(), ConstantPool);
4519 if (A->isNullValue())
4520 return LookupConstant(Select->getFalseValue(), ConstantPool);
4521 return nullptr;
4522 }
4523
4524 SmallVector<Constant *, 4> COps;
4525 for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
4526 if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
4527 COps.push_back(A);
4528 else
4529 return nullptr;
4530 }
4531
4532 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
4533 return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
4534 COps[1], DL);
4535 }
4536
4537 return ConstantFoldInstOperands(I, COps, DL);
4538}
4539
4540/// Try to determine the resulting constant values in phi nodes
4541/// at the common destination basic block, *CommonDest, for one of the case
4542/// destionations CaseDest corresponding to value CaseVal (0 for the default
4543/// case), of a switch instruction SI.
4544static bool
4545GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
4546 BasicBlock **CommonDest,
4547 SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
4548 const DataLayout &DL, const TargetTransformInfo &TTI) {
4549 // The block from which we enter the common destination.
4550 BasicBlock *Pred = SI->getParent();
4551
4552 // If CaseDest is empty except for some side-effect free instructions through
4553 // which we can constant-propagate the CaseVal, continue to its successor.
4554 SmallDenseMap<Value *, Constant *> ConstantPool;
4555 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
4556 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
4557 ++I) {
4558 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
4559 // If the terminator is a simple branch, continue to the next block.
4560 if (T->getNumSuccessors() != 1 || T->isExceptional())
4561 return false;
4562 Pred = CaseDest;
4563 CaseDest = T->getSuccessor(0);
4564 } else if (isa<DbgInfoIntrinsic>(I)) {
4565 // Skip debug intrinsic.
4566 continue;
4567 } else if (Constant *C = ConstantFold(&*I, DL, ConstantPool)) {
4568 // Instruction is side-effect free and constant.
4569
4570 // If the instruction has uses outside this block or a phi node slot for
4571 // the block, it is not safe to bypass the instruction since it would then
4572 // no longer dominate all its uses.
4573 for (auto &Use : I->uses()) {
4574 User *User = Use.getUser();
4575 if (Instruction *I = dyn_cast<Instruction>(User))
4576 if (I->getParent() == CaseDest)
4577 continue;
4578 if (PHINode *Phi = dyn_cast<PHINode>(User))
4579 if (Phi->getIncomingBlock(Use) == CaseDest)
4580 continue;
4581 return false;
4582 }
4583
4584 ConstantPool.insert(std::make_pair(&*I, C));
4585 } else {
4586 break;
4587 }
4588 }
4589
4590 // If we did not have a CommonDest before, use the current one.
4591 if (!*CommonDest)
4592 *CommonDest = CaseDest;
4593 // If the destination isn't the common one, abort.
4594 if (CaseDest != *CommonDest)
4595 return false;
4596
4597 // Get the values for this case from phi nodes in the destination block.
4598 BasicBlock::iterator I = (*CommonDest)->begin();
4599 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
4600 int Idx = PHI->getBasicBlockIndex(Pred);
4601 if (Idx == -1)
4602 continue;
4603
4604 Constant *ConstVal =
4605 LookupConstant(PHI->getIncomingValue(Idx), ConstantPool);
4606 if (!ConstVal)
4607 return false;
4608
4609 // Be conservative about which kinds of constants we support.
4610 if (!ValidLookupTableConstant(ConstVal, TTI))
4611 return false;
4612
4613 Res.push_back(std::make_pair(PHI, ConstVal));
4614 }
4615
4616 return Res.size() > 0;
4617}
4618
4619// Helper function used to add CaseVal to the list of cases that generate
4620// Result.
4621static void MapCaseToResult(ConstantInt *CaseVal,
4622 SwitchCaseResultVectorTy &UniqueResults,
4623 Constant *Result) {
4624 for (auto &I : UniqueResults) {
4625 if (I.first == Result) {
4626 I.second.push_back(CaseVal);
4627 return;
4628 }
4629 }
4630 UniqueResults.push_back(
4631 std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal)));
4632}
4633
4634// Helper function that initializes a map containing
4635// results for the PHI node of the common destination block for a switch
4636// instruction. Returns false if multiple PHI nodes have been found or if
4637// there is not a common destination block for the switch.
4638static bool InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
4639 BasicBlock *&CommonDest,
4640 SwitchCaseResultVectorTy &UniqueResults,
4641 Constant *&DefaultResult,
4642 const DataLayout &DL,
4643 const TargetTransformInfo &TTI) {
4644 for (auto &I : SI->cases()) {
4645 ConstantInt *CaseVal = I.getCaseValue();
4646
4647 // Resulting value at phi nodes for this case value.
4648 SwitchCaseResultsTy Results;
4649 if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
4650 DL, TTI))
4651 return false;
4652
4653 // Only one value per case is permitted
4654 if (Results.size() > 1)
4655 return false;
4656 MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
4657
4658 // Check the PHI consistency.
4659 if (!PHI)
4660 PHI = Results[0].first;
4661 else if (PHI != Results[0].first)
4662 return false;
4663 }
4664 // Find the default result value.
4665 SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
4666 BasicBlock *DefaultDest = SI->getDefaultDest();
4667 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
4668 DL, TTI);
4669 // If the default value is not found abort unless the default destination
4670 // is unreachable.
4671 DefaultResult =
4672 DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
4673 if ((!DefaultResult &&
4674 !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
4675 return false;
4676
4677 return true;
4678}
4679
4680// Helper function that checks if it is possible to transform a switch with only
4681// two cases (or two cases + default) that produces a result into a select.
4682// Example:
4683// switch (a) {
4684// case 10: %0 = icmp eq i32 %a, 10
4685// return 10; %1 = select i1 %0, i32 10, i32 4
4686// case 20: ----> %2 = icmp eq i32 %a, 20
4687// return 2; %3 = select i1 %2, i32 2, i32 %1
4688// default:
4689// return 4;
4690// }
4691static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
4692 Constant *DefaultResult, Value *Condition,
4693 IRBuilder<> &Builder) {
4694 assert(ResultVector.size() == 2 &&((ResultVector.size() == 2 && "We should have exactly two unique results at this point"
) ? static_cast<void> (0) : __assert_fail ("ResultVector.size() == 2 && \"We should have exactly two unique results at this point\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4695, __PRETTY_FUNCTION__))
4695 "We should have exactly two unique results at this point")((ResultVector.size() == 2 && "We should have exactly two unique results at this point"
) ? static_cast<void> (0) : __assert_fail ("ResultVector.size() == 2 && \"We should have exactly two unique results at this point\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4695, __PRETTY_FUNCTION__))
;
4696 // If we are selecting between only two cases transform into a simple
4697 // select or a two-way select if default is possible.
4698 if (ResultVector[0].second.size() == 1 &&
4699 ResultVector[1].second.size() == 1) {
4700 ConstantInt *const FirstCase = ResultVector[0].second[0];
4701 ConstantInt *const SecondCase = ResultVector[1].second[0];
4702
4703 bool DefaultCanTrigger = DefaultResult;
4704 Value *SelectValue = ResultVector[1].first;
4705 if (DefaultCanTrigger) {
4706 Value *const ValueCompare =
4707 Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
4708 SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
4709 DefaultResult, "switch.select");
4710 }
4711 Value *const ValueCompare =
4712 Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
4713 return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
4714 SelectValue, "switch.select");
4715 }
4716
4717 return nullptr;
4718}
4719
4720// Helper function to cleanup a switch instruction that has been converted into
4721// a select, fixing up PHI nodes and basic blocks.
4722static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
4723 Value *SelectValue,
4724 IRBuilder<> &Builder) {
4725 BasicBlock *SelectBB = SI->getParent();
4726 while (PHI->getBasicBlockIndex(SelectBB) >= 0)
4727 PHI->removeIncomingValue(SelectBB);
4728 PHI->addIncoming(SelectValue, SelectBB);
4729
4730 Builder.CreateBr(PHI->getParent());
4731
4732 // Remove the switch.
4733 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
4734 BasicBlock *Succ = SI->getSuccessor(i);
4735
4736 if (Succ == PHI->getParent())
4737 continue;
4738 Succ->removePredecessor(SelectBB);
4739 }
4740 SI->eraseFromParent();
4741}
4742
4743/// If the switch is only used to initialize one or more
4744/// phi nodes in a common successor block with only two different
4745/// constant values, replace the switch with select.
4746static bool SwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
4747 AssumptionCache *AC, const DataLayout &DL,
4748 const TargetTransformInfo &TTI) {
4749 Value *const Cond = SI->getCondition();
4750 PHINode *PHI = nullptr;
4751 BasicBlock *CommonDest = nullptr;
4752 Constant *DefaultResult;
4753 SwitchCaseResultVectorTy UniqueResults;
4754 // Collect all the cases that will deliver the same value from the switch.
4755 if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
4756 DL, TTI))
4757 return false;
4758 // Selects choose between maximum two values.
4759 if (UniqueResults.size() != 2)
4760 return false;
4761 assert(PHI != nullptr && "PHI for value select not found")((PHI != nullptr && "PHI for value select not found")
? static_cast<void> (0) : __assert_fail ("PHI != nullptr && \"PHI for value select not found\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4761, __PRETTY_FUNCTION__))
;
4762
4763 Builder.SetInsertPoint(SI);
4764 Value *SelectValue =
4765 ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
4766 if (SelectValue) {
4767 RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder);
4768 return true;
4769 }
4770 // The switch couldn't be converted into a select.
4771 return false;
4772}
4773
4774namespace {
4775
4776/// This class represents a lookup table that can be used to replace a switch.
4777class SwitchLookupTable {
4778public:
4779 /// Create a lookup table to use as a switch replacement with the contents
4780 /// of Values, using DefaultValue to fill any holes in the table.
4781 SwitchLookupTable(
4782 Module &M, uint64_t TableSize, ConstantInt *Offset,
4783 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4784 Constant *DefaultValue, const DataLayout &DL);
4785
4786 /// Build instructions with Builder to retrieve the value at
4787 /// the position given by Index in the lookup table.
4788 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
4789
4790 /// Return true if a table with TableSize elements of
4791 /// type ElementType would fit in a target-legal register.
4792 static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
4793 Type *ElementType);
4794
4795private:
4796 // Depending on the contents of the table, it can be represented in
4797 // different ways.
4798 enum {
4799 // For tables where each element contains the same value, we just have to
4800 // store that single value and return it for each lookup.
4801 SingleValueKind,
4802
4803 // For tables where there is a linear relationship between table index
4804 // and values. We calculate the result with a simple multiplication
4805 // and addition instead of a table lookup.
4806 LinearMapKind,
4807
4808 // For small tables with integer elements, we can pack them into a bitmap
4809 // that fits into a target-legal register. Values are retrieved by
4810 // shift and mask operations.
4811 BitMapKind,
4812
4813 // The table is stored as an array of values. Values are retrieved by load
4814 // instructions from the table.
4815 ArrayKind
4816 } Kind;
4817
4818 // For SingleValueKind, this is the single value.
4819 Constant *SingleValue;
4820
4821 // For BitMapKind, this is the bitmap.
4822 ConstantInt *BitMap;
4823 IntegerType *BitMapElementTy;
4824
4825 // For LinearMapKind, these are the constants used to derive the value.
4826 ConstantInt *LinearOffset;
4827 ConstantInt *LinearMultiplier;
4828
4829 // For ArrayKind, this is the array.
4830 GlobalVariable *Array;
4831};
4832
4833} // end anonymous namespace
4834
4835SwitchLookupTable::SwitchLookupTable(
4836 Module &M, uint64_t TableSize, ConstantInt *Offset,
4837 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4838 Constant *DefaultValue, const DataLayout &DL)
4839 : SingleValue(nullptr), BitMap(nullptr), BitMapElementTy(nullptr),
4840 LinearOffset(nullptr), LinearMultiplier(nullptr), Array(nullptr) {
4841 assert(Values.size() && "Can't build lookup table without values!")((Values.size() && "Can't build lookup table without values!"
) ? static_cast<void> (0) : __assert_fail ("Values.size() && \"Can't build lookup table without values!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4841, __PRETTY_FUNCTION__))
;
4842 assert(TableSize >= Values.size() && "Can't fit values in table!")((TableSize >= Values.size() && "Can't fit values in table!"
) ? static_cast<void> (0) : __assert_fail ("TableSize >= Values.size() && \"Can't fit values in table!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4842, __PRETTY_FUNCTION__))
;
4843
4844 // If all values in the table are equal, this is that value.
4845 SingleValue = Values.begin()->second;
4846
4847 Type *ValueType = Values.begin()->second->getType();
4848
4849 // Build up the table contents.
4850 SmallVector<Constant *, 64> TableContents(TableSize);
4851 for (size_t I = 0, E = Values.size(); I != E; ++I) {
4852 ConstantInt *CaseVal = Values[I].first;
4853 Constant *CaseRes = Values[I].second;
4854 assert(CaseRes->getType() == ValueType)((CaseRes->getType() == ValueType) ? static_cast<void>
(0) : __assert_fail ("CaseRes->getType() == ValueType", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4854, __PRETTY_FUNCTION__))
;
4855
4856 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
4857 TableContents[Idx] = CaseRes;
4858
4859 if (CaseRes != SingleValue)
4860 SingleValue = nullptr;
4861 }
4862
4863 // Fill in any holes in the table with the default result.
4864 if (Values.size() < TableSize) {
4865 assert(DefaultValue &&((DefaultValue && "Need a default value to fill the lookup table holes."
) ? static_cast<void> (0) : __assert_fail ("DefaultValue && \"Need a default value to fill the lookup table holes.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4866, __PRETTY_FUNCTION__))
4866 "Need a default value to fill the lookup table holes.")((DefaultValue && "Need a default value to fill the lookup table holes."
) ? static_cast<void> (0) : __assert_fail ("DefaultValue && \"Need a default value to fill the lookup table holes.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4866, __PRETTY_FUNCTION__))
;
4867 assert(DefaultValue->getType() == ValueType)((DefaultValue->getType() == ValueType) ? static_cast<void
> (0) : __assert_fail ("DefaultValue->getType() == ValueType"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4867, __PRETTY_FUNCTION__))
;
4868 for (uint64_t I = 0; I < TableSize; ++I) {
4869 if (!TableContents[I])
4870 TableContents[I] = DefaultValue;
4871 }
4872
4873 if (DefaultValue != SingleValue)
4874 SingleValue = nullptr;
4875 }
4876
4877 // If each element in the table contains the same value, we only need to store
4878 // that single value.
4879 if (SingleValue) {
4880 Kind = SingleValueKind;
4881 return;
4882 }
4883
4884 // Check if we can derive the value with a linear transformation from the
4885 // table index.
4886 if (isa<IntegerType>(ValueType)) {
4887 bool LinearMappingPossible = true;
4888 APInt PrevVal;
4889 APInt DistToPrev;
4890 assert(TableSize >= 2 && "Should be a SingleValue table.")((TableSize >= 2 && "Should be a SingleValue table."
) ? static_cast<void> (0) : __assert_fail ("TableSize >= 2 && \"Should be a SingleValue table.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4890, __PRETTY_FUNCTION__))
;
4891 // Check if there is the same distance between two consecutive values.
4892 for (uint64_t I = 0; I < TableSize; ++I) {
4893 ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
4894 if (!ConstVal) {
4895 // This is an undef. We could deal with it, but undefs in lookup tables
4896 // are very seldom. It's probably not worth the additional complexity.
4897 LinearMappingPossible = false;
4898 break;
4899 }
4900 const APInt &Val = ConstVal->getValue();
4901 if (I != 0) {
4902 APInt Dist = Val - PrevVal;
4903 if (I == 1) {
4904 DistToPrev = Dist;
4905 } else if (Dist != DistToPrev) {
4906 LinearMappingPossible = false;
4907 break;
4908 }
4909 }
4910 PrevVal = Val;
4911 }
4912 if (LinearMappingPossible) {
4913 LinearOffset = cast<ConstantInt>(TableContents[0]);
4914 LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
4915 Kind = LinearMapKind;
4916 ++NumLinearMaps;
4917 return;
4918 }
4919 }
4920
4921 // If the type is integer and the table fits in a register, build a bitmap.
4922 if (WouldFitInRegister(DL, TableSize, ValueType)) {
4923 IntegerType *IT = cast<IntegerType>(ValueType);
4924 APInt TableInt(TableSize * IT->getBitWidth(), 0);
4925 for (uint64_t I = TableSize; I > 0; --I) {
4926 TableInt <<= IT->getBitWidth();
4927 // Insert values into the bitmap. Undef values are set to zero.
4928 if (!isa<UndefValue>(TableContents[I - 1])) {
4929 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
4930 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
4931 }
4932 }
4933 BitMap = ConstantInt::get(M.getContext(), TableInt);
4934 BitMapElementTy = IT;
4935 Kind = BitMapKind;
4936 ++NumBitMaps;
4937 return;
4938 }
4939
4940 // Store the table in an array.
4941 ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
4942 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
4943
4944 Array = new GlobalVariable(M, ArrayTy, /*constant=*/true,
4945 GlobalVariable::PrivateLinkage, Initializer,
4946 "switch.table");
4947 Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
4948 Kind = ArrayKind;
4949}
4950
4951Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
4952 switch (Kind) {
4953 case SingleValueKind:
4954 return SingleValue;
4955 case LinearMapKind: {
4956 // Derive the result value from the input value.
4957 Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
4958 false, "switch.idx.cast");
4959 if (!LinearMultiplier->isOne())
4960 Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
4961 if (!LinearOffset->isZero())
4962 Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
4963 return Result;
4964 }
4965 case BitMapKind: {
4966 // Type of the bitmap (e.g. i59).
4967 IntegerType *MapTy = BitMap->getType();
4968
4969 // Cast Index to the same type as the bitmap.
4970 // Note: The Index is <= the number of elements in the table, so
4971 // truncating it to the width of the bitmask is safe.
4972 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
4973
4974 // Multiply the shift amount by the element width.
4975 ShiftAmt = Builder.CreateMul(
4976 ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
4977 "switch.shiftamt");
4978
4979 // Shift down.
4980 Value *DownShifted =
4981 Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift");
4982 // Mask off.
4983 return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked");
4984 }
4985 case ArrayKind: {
4986 // Make sure the table index will not overflow when treated as signed.
4987 IntegerType *IT = cast<IntegerType>(Index->getType());
4988 uint64_t TableSize =
4989 Array->getInitializer()->getType()->getArrayNumElements();
4990 if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
4991 Index = Builder.CreateZExt(
4992 Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1),
4993 "switch.tableidx.zext");
4994
4995 Value *GEPIndices[] = {Builder.getInt32(0), Index};
4996 Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
4997 GEPIndices, "switch.gep");
4998 return Builder.CreateLoad(GEP, "switch.load");
4999 }
5000 }
5001 llvm_unreachable("Unknown lookup table kind!")::llvm::llvm_unreachable_internal("Unknown lookup table kind!"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5001)
;
5002}
5003
5004bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
5005 uint64_t TableSize,
5006 Type *ElementType) {
5007 auto *IT = dyn_cast<IntegerType>(ElementType);
5008 if (!IT)
5009 return false;
5010 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
5011 // are <= 15, we could try to narrow the type.
5012
5013 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
5014 if (TableSize >= UINT_MAX(2147483647 *2U +1U) / IT->getBitWidth())
5015 return false;
5016 return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
5017}
5018
5019/// Determine whether a lookup table should be built for this switch, based on
5020/// the number of cases, size of the table, and the types of the results.
5021static bool
5022ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
5023 const TargetTransformInfo &TTI, const DataLayout &DL,
5024 const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
5025 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX(18446744073709551615UL) / 10)
5026 return false; // TableSize overflowed, or mul below might overflow.
5027
5028 bool AllTablesFitInRegister = true;
5029 bool HasIllegalType = false;
5030 for (const auto &I : ResultTypes) {
5031 Type *Ty = I.second;
5032
5033 // Saturate this flag to true.
5034 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
5035
5036 // Saturate this flag to false.
5037 AllTablesFitInRegister =
5038 AllTablesFitInRegister &&
5039 SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
5040
5041 // If both flags saturate, we're done. NOTE: This *only* works with
5042 // saturating flags, and all flags have to saturate first due to the
5043 // non-deterministic behavior of iterating over a dense map.
5044 if (HasIllegalType && !AllTablesFitInRegister)
5045 break;
5046 }
5047
5048 // If each table would fit in a register, we should build it anyway.
5049 if (AllTablesFitInRegister)
5050 return true;
5051
5052 // Don't build a table that doesn't fit in-register if it has illegal types.
5053 if (HasIllegalType)
5054 return false;
5055
5056 // The table density should be at least 40%. This is the same criterion as for
5057 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
5058 // FIXME: Find the best cut-off.
5059 return SI->getNumCases() * 10 >= TableSize * 4;
5060}
5061
5062/// Try to reuse the switch table index compare. Following pattern:
5063/// \code
5064/// if (idx < tablesize)
5065/// r = table[idx]; // table does not contain default_value
5066/// else
5067/// r = default_value;
5068/// if (r != default_value)
5069/// ...
5070/// \endcode
5071/// Is optimized to:
5072/// \code
5073/// cond = idx < tablesize;
5074/// if (cond)
5075/// r = table[idx];
5076/// else
5077/// r = default_value;
5078/// if (cond)
5079/// ...
5080/// \endcode
5081/// Jump threading will then eliminate the second if(cond).
5082static void reuseTableCompare(
5083 User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch,
5084 Constant *DefaultValue,
5085 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) {
5086
5087 ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
5088 if (!CmpInst)
5089 return;
5090
5091 // We require that the compare is in the same block as the phi so that jump
5092 // threading can do its work afterwards.
5093 if (CmpInst->getParent() != PhiBlock)
5094 return;
5095
5096 Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
5097 if (!CmpOp1)
5098 return;
5099
5100 Value *RangeCmp = RangeCheckBranch->getCondition();
5101 Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
5102 Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
5103
5104 // Check if the compare with the default value is constant true or false.
5105 Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5106 DefaultValue, CmpOp1, true);
5107 if (DefaultConst != TrueConst && DefaultConst != FalseConst)
5108 return;
5109
5110 // Check if the compare with the case values is distinct from the default
5111 // compare result.
5112 for (auto ValuePair : Values) {
5113 Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5114 ValuePair.second, CmpOp1, true);
5115 if (!CaseConst || CaseConst == DefaultConst)
5116 return;
5117 assert((CaseConst == TrueConst || CaseConst == FalseConst) &&(((CaseConst == TrueConst || CaseConst == FalseConst) &&
"Expect true or false as compare result.") ? static_cast<
void> (0) : __assert_fail ("(CaseConst == TrueConst || CaseConst == FalseConst) && \"Expect true or false as compare result.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5118, __PRETTY_FUNCTION__))
5118 "Expect true or false as compare result.")(((CaseConst == TrueConst || CaseConst == FalseConst) &&
"Expect true or false as compare result.") ? static_cast<
void> (0) : __assert_fail ("(CaseConst == TrueConst || CaseConst == FalseConst) && \"Expect true or false as compare result.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5118, __PRETTY_FUNCTION__))
;
5119 }
5120
5121 // Check if the branch instruction dominates the phi node. It's a simple
5122 // dominance check, but sufficient for our needs.
5123 // Although this check is invariant in the calling loops, it's better to do it
5124 // at this late stage. Practically we do it at most once for a switch.
5125 BasicBlock *BranchBlock = RangeCheckBranch->getParent();
5126 for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) {
5127 BasicBlock *Pred = *PI;
5128 if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
5129 return;
5130 }
5131
5132 if (DefaultConst == FalseConst) {
5133 // The compare yields the same result. We can replace it.
5134 CmpInst->replaceAllUsesWith(RangeCmp);
5135 ++NumTableCmpReuses;
5136 } else {
5137 // The compare yields the same result, just inverted. We can replace it.
5138 Value *InvertedTableCmp = BinaryOperator::CreateXor(
5139 RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
5140 RangeCheckBranch);
5141 CmpInst->replaceAllUsesWith(InvertedTableCmp);
5142 ++NumTableCmpReuses;
5143 }
5144}
5145
5146/// If the switch is only used to initialize one or more phi nodes in a common
5147/// successor block with different constant values, replace the switch with
5148/// lookup tables.
5149static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
5150 const DataLayout &DL,
5151 const TargetTransformInfo &TTI) {
5152 assert(SI->getNumCases() > 1 && "Degenerate switch?")((SI->getNumCases() > 1 && "Degenerate switch?"
) ? static_cast<void> (0) : __assert_fail ("SI->getNumCases() > 1 && \"Degenerate switch?\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5152, __PRETTY_FUNCTION__))
;
5153
5154 // Only build lookup table when we have a target that supports it.
5155 if (!TTI.shouldBuildLookupTables())
5156 return false;
5157
5158 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
5159 // split off a dense part and build a lookup table for that.
5160
5161 // FIXME: This creates arrays of GEPs to constant strings, which means each
5162 // GEP needs a runtime relocation in PIC code. We should just build one big
5163 // string and lookup indices into that.
5164
5165 // Ignore switches with less than three cases. Lookup tables will not make
5166 // them
5167 // faster, so we don't analyze them.
5168 if (SI->getNumCases() < 3)
5169 return false;
5170
5171 // Figure out the corresponding result for each case value and phi node in the
5172 // common destination, as well as the min and max case values.
5173 assert(SI->case_begin() != SI->case_end())((SI->case_begin() != SI->case_end()) ? static_cast<
void> (0) : __assert_fail ("SI->case_begin() != SI->case_end()"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5173, __PRETTY_FUNCTION__))
;
5174 SwitchInst::CaseIt CI = SI->case_begin();
5175 ConstantInt *MinCaseVal = CI->getCaseValue();
5176 ConstantInt *MaxCaseVal = CI->getCaseValue();
5177
5178 BasicBlock *CommonDest = nullptr;
5179 typedef SmallVector<std::pair<ConstantInt *, Constant *>, 4> ResultListTy;
5180 SmallDenseMap<PHINode *, ResultListTy> ResultLists;
5181 SmallDenseMap<PHINode *, Constant *> DefaultResults;
5182 SmallDenseMap<PHINode *, Type *> ResultTypes;
5183 SmallVector<PHINode *, 4> PHIs;
5184
5185 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
5186 ConstantInt *CaseVal = CI->getCaseValue();
5187 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
5188 MinCaseVal = CaseVal;
5189 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
5190 MaxCaseVal = CaseVal;
5191
5192 // Resulting value at phi nodes for this case value.
5193 typedef SmallVector<std::pair<PHINode *, Constant *>, 4> ResultsTy;
5194 ResultsTy Results;
5195 if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
5196 Results, DL, TTI))
5197 return false;
5198
5199 // Append the result from this case to the list for each phi.
5200 for (const auto &I : Results) {
5201 PHINode *PHI = I.first;
5202 Constant *Value = I.second;
5203 if (!ResultLists.count(PHI))
5204 PHIs.push_back(PHI);
5205 ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
5206 }
5207 }
5208
5209 // Keep track of the result types.
5210 for (PHINode *PHI : PHIs) {
5211 ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
5212 }
5213
5214 uint64_t NumResults = ResultLists[PHIs[0]].size();
5215 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
5216 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
5217 bool TableHasHoles = (NumResults < TableSize);
5218
5219 // If the table has holes, we need a constant result for the default case
5220 // or a bitmask that fits in a register.
5221 SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
5222 bool HasDefaultResults =
5223 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
5224 DefaultResultsList, DL, TTI);
5225
5226 bool NeedMask = (TableHasHoles && !HasDefaultResults);
5227 if (NeedMask) {
5228 // As an extra penalty for the validity test we require more cases.
5229 if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
5230 return false;
5231 if (!DL.fitsInLegalInteger(TableSize))
5232 return false;
5233 }
5234
5235 for (const auto &I : DefaultResultsList) {
5236 PHINode *PHI = I.first;
5237 Constant *Result = I.second;
5238 DefaultResults[PHI] = Result;
5239 }
5240
5241 if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
5242 return false;
5243
5244 // Create the BB that does the lookups.
5245 Module &Mod = *CommonDest->getParent()->getParent();
5246 BasicBlock *LookupBB = BasicBlock::Create(
5247 Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest);
5248
5249 // Compute the table index value.
5250 Builder.SetInsertPoint(SI);
5251 Value *TableIndex =
5252 Builder.CreateSub(SI->getCondition(), MinCaseVal, "switch.tableidx");
5253
5254 // Compute the maximum table size representable by the integer type we are
5255 // switching upon.
5256 unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
5257 uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX(18446744073709551615UL) : 1ULL << CaseSize;
5258 assert(MaxTableSize >= TableSize &&((MaxTableSize >= TableSize && "It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? static_cast
<void> (0) : __assert_fail ("MaxTableSize >= TableSize && \"It is impossible for a switch to have more entries than the max \" \"representable value of its input integer type's size.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5260, __PRETTY_FUNCTION__))
5259 "It is impossible for a switch to have more entries than the max "((MaxTableSize >= TableSize && "It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? static_cast
<void> (0) : __assert_fail ("MaxTableSize >= TableSize && \"It is impossible for a switch to have more entries than the max \" \"representable value of its input integer type's size.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5260, __PRETTY_FUNCTION__))
5260 "representable value of its input integer type's size.")((MaxTableSize >= TableSize && "It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? static_cast
<void> (0) : __assert_fail ("MaxTableSize >= TableSize && \"It is impossible for a switch to have more entries than the max \" \"representable value of its input integer type's size.\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5260, __PRETTY_FUNCTION__))
;
5261
5262 // If the default destination is unreachable, or if the lookup table covers
5263 // all values of the conditional variable, branch directly to the lookup table
5264 // BB. Otherwise, check that the condition is within the case range.
5265 const bool DefaultIsReachable =
5266 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
5267 const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
5268 BranchInst *RangeCheckBranch = nullptr;
5269
5270 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5271 Builder.CreateBr(LookupBB);
5272 // Note: We call removeProdecessor later since we need to be able to get the
5273 // PHI value for the default case in case we're using a bit mask.
5274 } else {
5275 Value *Cmp = Builder.CreateICmpULT(
5276 TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
5277 RangeCheckBranch =
5278 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
5279 }
5280
5281 // Populate the BB that does the lookups.
5282 Builder.SetInsertPoint(LookupBB);
5283
5284 if (NeedMask) {
5285 // Before doing the lookup we do the hole check.
5286 // The LookupBB is therefore re-purposed to do the hole check
5287 // and we create a new LookupBB.
5288 BasicBlock *MaskBB = LookupBB;
5289 MaskBB->setName("switch.hole_check");
5290 LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup",
5291 CommonDest->getParent(), CommonDest);
5292
5293 // Make the mask's bitwidth at least 8bit and a power-of-2 to avoid
5294 // unnecessary illegal types.
5295 uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
5296 APInt MaskInt(TableSizePowOf2, 0);
5297 APInt One(TableSizePowOf2, 1);
5298 // Build bitmask; fill in a 1 bit for every case.
5299 const ResultListTy &ResultList = ResultLists[PHIs[0]];
5300 for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
5301 uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue())
5302 .getLimitedValue();
5303 MaskInt |= One << Idx;
5304 }
5305 ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
5306
5307 // Get the TableIndex'th bit of the bitmask.
5308 // If this bit is 0 (meaning hole) jump to the default destination,
5309 // else continue with table lookup.
5310 IntegerType *MapTy = TableMask->getType();
5311 Value *MaskIndex =
5312 Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex");
5313 Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted");
5314 Value *LoBit = Builder.CreateTrunc(
5315 Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit");
5316 Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
5317
5318 Builder.SetInsertPoint(LookupBB);
5319 AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
5320 }
5321
5322 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5323 // We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
5324 // do not delete PHINodes here.
5325 SI->getDefaultDest()->removePredecessor(SI->getParent(),
5326 /*DontDeleteUselessPHIs=*/true);
5327 }
5328
5329 bool ReturnedEarly = false;
5330 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
5331 PHINode *PHI = PHIs[I];
5332 const ResultListTy &ResultList = ResultLists[PHI];
5333
5334 // If using a bitmask, use any value to fill the lookup table holes.
5335 Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
5336 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL);
5337
5338 Value *Result = Table.BuildLookup(TableIndex, Builder);
5339
5340 // If the result is used to return immediately from the function, we want to
5341 // do that right here.
5342 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) &&
5343 PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) {
5344 Builder.CreateRet(Result);
5345 ReturnedEarly = true;
5346 break;
5347 }
5348
5349 // Do a small peephole optimization: re-use the switch table compare if
5350 // possible.
5351 if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
5352 BasicBlock *PhiBlock = PHI->getParent();
5353 // Search for compare instructions which use the phi.
5354 for (auto *User : PHI->users()) {
5355 reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
5356 }
5357 }
5358
5359 PHI->addIncoming(Result, LookupBB);
5360 }
5361
5362 if (!ReturnedEarly)
5363 Builder.CreateBr(CommonDest);
5364
5365 // Remove the switch.
5366 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
5367 BasicBlock *Succ = SI->getSuccessor(i);
5368
5369 if (Succ == SI->getDefaultDest())
5370 continue;
5371 Succ->removePredecessor(SI->getParent());
5372 }
5373 SI->eraseFromParent();
5374
5375 ++NumLookupTables;
5376 if (NeedMask)
5377 ++NumLookupTablesHoles;
5378 return true;
5379}
5380
5381static bool isSwitchDense(ArrayRef<int64_t> Values) {
5382 // See also SelectionDAGBuilder::isDense(), which this function was based on.
5383 uint64_t Diff = (uint64_t)Values.back() - (uint64_t)Values.front();
5384 uint64_t Range = Diff + 1;
5385 uint64_t NumCases = Values.size();
5386 // 40% is the default density for building a jump table in optsize/minsize mode.
5387 uint64_t MinDensity = 40;
5388
5389 return NumCases * 100 >= Range * MinDensity;
5390}
5391
5392// Try and transform a switch that has "holes" in it to a contiguous sequence
5393// of cases.
5394//
5395// A switch such as: switch(i) {case 5: case 9: case 13: case 17:} can be
5396// range-reduced to: switch ((i-5) / 4) {case 0: case 1: case 2: case 3:}.
5397//
5398// This converts a sparse switch into a dense switch which allows better
5399// lowering and could also allow transforming into a lookup table.
5400static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
5401 const DataLayout &DL,
5402 const TargetTransformInfo &TTI) {
5403 auto *CondTy = cast<IntegerType>(SI->getCondition()->getType());
5404 if (CondTy->getIntegerBitWidth() > 64 ||
5405 !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
5406 return false;
5407 // Only bother with this optimization if there are more than 3 switch cases;
5408 // SDAG will only bother creating jump tables for 4 or more cases.
5409 if (SI->getNumCases() < 4)
5410 return false;
5411
5412 // This transform is agnostic to the signedness of the input or case values. We
5413 // can treat the case values as signed or unsigned. We can optimize more common
5414 // cases such as a sequence crossing zero {-4,0,4,8} if we interpret case values
5415 // as signed.
5416 SmallVector<int64_t,4> Values;
5417 for (auto &C : SI->cases())
5418 Values.push_back(C.getCaseValue()->getValue().getSExtValue());
5419 std::sort(Values.begin(), Values.end());
5420
5421 // If the switch is already dense, there's nothing useful to do here.
5422 if (isSwitchDense(Values))
5423 return false;
5424
5425 // First, transform the values such that they start at zero and ascend.
5426 int64_t Base = Values[0];
5427 for (auto &V : Values)
5428 V -= Base;
5429
5430 // Now we have signed numbers that have been shifted so that, given enough
5431 // precision, there are no negative values. Since the rest of the transform
5432 // is bitwise only, we switch now to an unsigned representation.
5433 uint64_t GCD = 0;
5434 for (auto &V : Values)
5435 GCD = GreatestCommonDivisor64(GCD, (uint64_t)V);
5436
5437 // This transform can be done speculatively because it is so cheap - it results
5438 // in a single rotate operation being inserted. This can only happen if the
5439 // factor extracted is a power of 2.
5440 // FIXME: If the GCD is an odd number we can multiply by the multiplicative
5441 // inverse of GCD and then perform this transform.
5442 // FIXME: It's possible that optimizing a switch on powers of two might also
5443 // be beneficial - flag values are often powers of two and we could use a CLZ
5444 // as the key function.
5445 if (GCD <= 1 || !isPowerOf2_64(GCD))
5446 // No common divisor found or too expensive to compute key function.
5447 return false;
5448
5449 unsigned Shift = Log2_64(GCD);
5450 for (auto &V : Values)
5451 V = (int64_t)((uint64_t)V >> Shift);
5452
5453 if (!isSwitchDense(Values))
5454 // Transform didn't create a dense switch.
5455 return false;
5456
5457 // The obvious transform is to shift the switch condition right and emit a
5458 // check that the condition actually cleanly divided by GCD, i.e.
5459 // C & (1 << Shift - 1) == 0
5460 // inserting a new CFG edge to handle the case where it didn't divide cleanly.
5461 //
5462 // A cheaper way of doing this is a simple ROTR(C, Shift). This performs the
5463 // shift and puts the shifted-off bits in the uppermost bits. If any of these
5464 // are nonzero then the switch condition will be very large and will hit the
5465 // default case.
5466
5467 auto *Ty = cast<IntegerType>(SI->getCondition()->getType());
5468 Builder.SetInsertPoint(SI);
5469 auto *ShiftC = ConstantInt::get(Ty, Shift);
5470 auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base));
5471 auto *LShr = Builder.CreateLShr(Sub, ShiftC);
5472 auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift);
5473 auto *Rot = Builder.CreateOr(LShr, Shl);
5474 SI->replaceUsesOfWith(SI->getCondition(), Rot);
5475
5476 for (auto Case : SI->cases()) {
5477 auto *Orig = Case.getCaseValue();
5478 auto Sub = Orig->getValue() - APInt(Ty->getBitWidth(), Base);
5479 Case.setValue(
5480 cast<ConstantInt>(ConstantInt::get(Ty, Sub.lshr(ShiftC->getValue()))));
5481 }
5482 return true;
5483}
5484
5485bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
5486 BasicBlock *BB = SI->getParent();
5487
5488 if (isValueEqualityComparison(SI)) {
1
Taking false branch
18
Taking false branch
5489 // If we only have one predecessor, and if it is a branch on this value,
5490 // see if that predecessor totally determines the outcome of this switch.
5491 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5492 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
5493 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5494
5495 Value *Cond = SI->getCondition();
5496 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
5497 if (SimplifySwitchOnSelect(SI, Select))
5498 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5499
5500 // If the block only contains the switch, see if we can fold the block
5501 // away into any preds.
5502 BasicBlock::iterator BBI = BB->begin();
5503 // Ignore dbg intrinsics.
5504 while (isa<DbgInfoIntrinsic>(BBI))
5505 ++BBI;
5506 if (SI == &*BBI)
5507 if (FoldValueComparisonIntoPredecessors(SI, Builder))
5508 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5509 }
5510
5511 // Try to transform the switch into an icmp and a branch.
5512 if (TurnSwitchRangeIntoICmp(SI, Builder))
2
Taking true branch
19
Taking true branch
5513 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
3
Calling 'SimplifyCFG'
20
Calling 'SimplifyCFG'
5514
5515 // Remove unreachable cases.
5516 if (EliminateDeadSwitchCases(SI, AC, DL))
5517 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5518
5519 if (SwitchToSelect(SI, Builder, AC, DL, TTI))
5520 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5521
5522 if (ForwardSwitchConditionToPHI(SI))
5523 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5524
5525 // The conversion from switch to lookup tables results in difficult
5526 // to analyze code and makes pruning branches much harder.
5527 // This is a problem of the switch expression itself can still be
5528 // restricted as a result of inlining or CVP. There only apply this
5529 // transformation during late steps of the optimisation chain.
5530 if (LateSimplifyCFG && SwitchToLookupTable(SI, Builder, DL, TTI))
5531 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5532
5533 if (ReduceSwitchRange(SI, Builder, DL, TTI))
5534 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5535
5536 return false;
5537}
5538
5539bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
5540 BasicBlock *BB = IBI->getParent();
5541 bool Changed = false;
5542
5543 // Eliminate redundant destinations.
5544 SmallPtrSet<Value *, 8> Succs;
5545 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
5546 BasicBlock *Dest = IBI->getDestination(i);
5547 if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
5548 Dest->removePredecessor(BB);
5549 IBI->removeDestination(i);
5550 --i;
5551 --e;
5552 Changed = true;
5553 }
5554 }
5555
5556 if (IBI->getNumDestinations() == 0) {
5557 // If the indirectbr has no successors, change it to unreachable.
5558 new UnreachableInst(IBI->getContext(), IBI);
5559 EraseTerminatorInstAndDCECond(IBI);
5560 return true;
5561 }
5562
5563 if (IBI->getNumDestinations() == 1) {
5564 // If the indirectbr has one successor, change it to a direct branch.
5565 BranchInst::Create(IBI->getDestination(0), IBI);
5566 EraseTerminatorInstAndDCECond(IBI);
5567 return true;
5568 }
5569
5570 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
5571 if (SimplifyIndirectBrOnSelect(IBI, SI))
5572 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5573 }
5574 return Changed;
5575}
5576
5577/// Given an block with only a single landing pad and a unconditional branch
5578/// try to find another basic block which this one can be merged with. This
5579/// handles cases where we have multiple invokes with unique landing pads, but
5580/// a shared handler.
5581///
5582/// We specifically choose to not worry about merging non-empty blocks
5583/// here. That is a PRE/scheduling problem and is best solved elsewhere. In
5584/// practice, the optimizer produces empty landing pad blocks quite frequently
5585/// when dealing with exception dense code. (see: instcombine, gvn, if-else
5586/// sinking in this file)
5587///
5588/// This is primarily a code size optimization. We need to avoid performing
5589/// any transform which might inhibit optimization (such as our ability to
5590/// specialize a particular handler via tail commoning). We do this by not
5591/// merging any blocks which require us to introduce a phi. Since the same
5592/// values are flowing through both blocks, we don't loose any ability to
5593/// specialize. If anything, we make such specialization more likely.
5594///
5595/// TODO - This transformation could remove entries from a phi in the target
5596/// block when the inputs in the phi are the same for the two blocks being
5597/// merged. In some cases, this could result in removal of the PHI entirely.
5598static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
5599 BasicBlock *BB) {
5600 auto Succ = BB->getUniqueSuccessor();
5601 assert(Succ)((Succ) ? static_cast<void> (0) : __assert_fail ("Succ"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5601, __PRETTY_FUNCTION__))
;
5602 // If there's a phi in the successor block, we'd likely have to introduce
5603 // a phi into the merged landing pad block.
5604 if (isa<PHINode>(*Succ->begin()))
5605 return false;
5606
5607 for (BasicBlock *OtherPred : predecessors(Succ)) {
5608 if (BB == OtherPred)
5609 continue;
5610 BasicBlock::iterator I = OtherPred->begin();
5611 LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
5612 if (!LPad2 || !LPad2->isIdenticalTo(LPad))
5613 continue;
5614 for (++I; isa<DbgInfoIntrinsic>(I); ++I) {
5615 }
5616 BranchInst *BI2 = dyn_cast<BranchInst>(I);
5617 if (!BI2 || !BI2->isIdenticalTo(BI))
5618 continue;
5619
5620 // We've found an identical block. Update our predecessors to take that
5621 // path instead and make ourselves dead.
5622 SmallSet<BasicBlock *, 16> Preds;
5623 Preds.insert(pred_begin(BB), pred_end(BB));
5624 for (BasicBlock *Pred : Preds) {
5625 InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
5626 assert(II->getNormalDest() != BB && II->getUnwindDest() == BB &&((II->getNormalDest() != BB && II->getUnwindDest
() == BB && "unexpected successor") ? static_cast<
void> (0) : __assert_fail ("II->getNormalDest() != BB && II->getUnwindDest() == BB && \"unexpected successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5627, __PRETTY_FUNCTION__))
5627 "unexpected successor")((II->getNormalDest() != BB && II->getUnwindDest
() == BB && "unexpected successor") ? static_cast<
void> (0) : __assert_fail ("II->getNormalDest() != BB && II->getUnwindDest() == BB && \"unexpected successor\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5627, __PRETTY_FUNCTION__))
;
5628 II->setUnwindDest(OtherPred);
5629 }
5630
5631 // The debug info in OtherPred doesn't cover the merged control flow that
5632 // used to go through BB. We need to delete it or update it.
5633 for (auto I = OtherPred->begin(), E = OtherPred->end(); I != E;) {
5634 Instruction &Inst = *I;
5635 I++;
5636 if (isa<DbgInfoIntrinsic>(Inst))
5637 Inst.eraseFromParent();
5638 }
5639
5640 SmallSet<BasicBlock *, 16> Succs;
5641 Succs.insert(succ_begin(BB), succ_end(BB));
5642 for (BasicBlock *Succ : Succs) {
5643 Succ->removePredecessor(BB);
5644 }
5645
5646 IRBuilder<> Builder(BI);
5647 Builder.CreateUnreachable();
5648 BI->eraseFromParent();
5649 return true;
5650 }
5651 return false;
5652}
5653
5654bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI,
5655 IRBuilder<> &Builder) {
5656 BasicBlock *BB = BI->getParent();
5657
5658 if (SinkCommon && SinkThenElseCodeToEnd(BI))
5659 return true;
5660
5661 // If the Terminator is the only non-phi instruction, simplify the block.
5662 // if LoopHeader is provided, check if the block is a loop header
5663 // (This is for early invocations before loop simplify and vectorization
5664 // to keep canonical loop forms for nested loops.
5665 // These blocks can be eliminated when the pass is invoked later
5666 // in the back-end.)
5667 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
5668 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
5669 (!LoopHeaders || !LoopHeaders->count(BB)) &&
5670 TryToSimplifyUncondBranchFromEmptyBlock(BB))
5671 return true;
5672
5673 // If the only instruction in the block is a seteq/setne comparison
5674 // against a constant, try to simplify the block.
5675 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
5676 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
5677 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5678 ;
5679 if (I->isTerminator() &&
5680 TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, DL, TTI,
5681 BonusInstThreshold, AC))
5682 return true;
5683 }
5684
5685 // See if we can merge an empty landing pad block with another which is
5686 // equivalent.
5687 if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
5688 for (++I; isa<DbgInfoIntrinsic>(I); ++I) {
5689 }
5690 if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB))
5691 return true;
5692 }
5693
5694 // If this basic block is ONLY a compare and a branch, and if a predecessor
5695 // branches to us and our successor, fold the comparison into the
5696 // predecessor and use logical operations to update the incoming value
5697 // for PHI nodes in common successor.
5698 if (FoldBranchToCommonDest(BI, BonusInstThreshold))
5699 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5700 return false;
5701}
5702
5703static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
5704 BasicBlock *PredPred = nullptr;
5705 for (auto *P : predecessors(BB)) {
5706 BasicBlock *PPred = P->getSinglePredecessor();
5707 if (!PPred || (PredPred && PredPred != PPred))
5708 return nullptr;
5709 PredPred = PPred;
5710 }
5711 return PredPred;
5712}
5713
5714bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
5715 BasicBlock *BB = BI->getParent();
5716
5717 // Conditional branch
5718 if (isValueEqualityComparison(BI)) {
5719 // If we only have one predecessor, and if it is a branch on this value,
5720 // see if that predecessor totally determines the outcome of this
5721 // switch.
5722 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5723 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
5724 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5725
5726 // This block must be empty, except for the setcond inst, if it exists.
5727 // Ignore dbg intrinsics.
5728 BasicBlock::iterator I = BB->begin();
5729 // Ignore dbg intrinsics.
5730 while (isa<DbgInfoIntrinsic>(I))
5731 ++I;
5732 if (&*I == BI) {
5733 if (FoldValueComparisonIntoPredecessors(BI, Builder))
5734 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5735 } else if (&*I == cast<Instruction>(BI->getCondition())) {
5736 ++I;
5737 // Ignore dbg intrinsics.
5738 while (isa<DbgInfoIntrinsic>(I))
5739 ++I;
5740 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
5741 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5742 }
5743 }
5744
5745 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
5746 if (SimplifyBranchOnICmpChain(BI, Builder, DL))
5747 return true;
5748
5749 // If this basic block has a single dominating predecessor block and the
5750 // dominating block's condition implies BI's condition, we know the direction
5751 // of the BI branch.
5752 if (BasicBlock *Dom = BB->getSinglePredecessor()) {
5753 auto *PBI = dyn_cast_or_null<BranchInst>(Dom->getTerminator());
5754 if (PBI && PBI->isConditional() &&
5755 PBI->getSuccessor(0) != PBI->getSuccessor(1) &&
5756 (PBI->getSuccessor(0) == BB || PBI->getSuccessor(1) == BB)) {
5757 bool CondIsFalse = PBI->getSuccessor(1) == BB;
5758 Optional<bool> Implication = isImpliedCondition(
5759 PBI->getCondition(), BI->getCondition(), DL, CondIsFalse);
5760 if (Implication) {
5761 // Turn this into a branch on constant.
5762 auto *OldCond = BI->getCondition();
5763 ConstantInt *CI = *Implication
5764 ? ConstantInt::getTrue(BB->getContext())
5765 : ConstantInt::getFalse(BB->getContext());
5766 BI->setCondition(CI);
5767 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
5768 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5769 }
5770 }
5771 }
5772
5773 // If this basic block is ONLY a compare and a branch, and if a predecessor
5774 // branches to us and one of our successors, fold the comparison into the
5775 // predecessor and use logical operations to pick the right destination.
5776 if (FoldBranchToCommonDest(BI, BonusInstThreshold))
5777 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5778
5779 // We have a conditional branch to two blocks that are only reachable
5780 // from BI. We know that the condbr dominates the two blocks, so see if
5781 // there is any identical code in the "then" and "else" blocks. If so, we
5782 // can hoist it up to the branching block.
5783 if (BI->getSuccessor(0)->getSinglePredecessor()) {
5784 if (BI->getSuccessor(1)->getSinglePredecessor()) {
5785 if (HoistThenElseCodeToIf(BI, TTI))
5786 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5787 } else {
5788 // If Successor #1 has multiple preds, we may be able to conditionally
5789 // execute Successor #0 if it branches to Successor #1.
5790 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
5791 if (Succ0TI->getNumSuccessors() == 1 &&
5792 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
5793 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
5794 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5795 }
5796 } else if (BI->getSuccessor(1)->getSinglePredecessor()) {
5797 // If Successor #0 has multiple preds, we may be able to conditionally
5798 // execute Successor #1 if it branches to Successor #0.
5799 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
5800 if (Succ1TI->getNumSuccessors() == 1 &&
5801 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
5802 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
5803 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5804 }
5805
5806 // If this is a branch on a phi node in the current block, thread control
5807 // through this block if any PHI node entries are constants.
5808 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
5809 if (PN->getParent() == BI->getParent())
5810 if (FoldCondBranchOnPHI(BI, DL, AC))
5811 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5812
5813 // Scan predecessor blocks for conditional branches.
5814 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
5815 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
5816 if (PBI != BI && PBI->isConditional())
5817 if (SimplifyCondBranchToCondBranch(PBI, BI, DL))
5818 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5819
5820 // Look for diamond patterns.
5821 if (MergeCondStores)
5822 if (BasicBlock *PrevBB = allPredecessorsComeFromSameSource(BB))
5823 if (BranchInst *PBI = dyn_cast<BranchInst>(PrevBB->getTerminator()))
5824 if (PBI != BI && PBI->isConditional())
5825 if (mergeConditionalStores(PBI, BI))
5826 return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5827
5828 return false;
5829}
5830
5831/// Check if passing a value to an instruction will cause undefined behavior.
5832static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
5833 Constant *C = dyn_cast<Constant>(V);
5834 if (!C)
5835 return false;
5836
5837 if (I->use_empty())
5838 return false;
5839
5840 if (C->isNullValue() || isa<UndefValue>(C)) {
5841 // Only look at the first use, avoid hurting compile time with long uselists
5842 User *Use = *I->user_begin();
5843
5844 // Now make sure that there are no instructions in between that can alter
5845 // control flow (eg. calls)
5846 for (BasicBlock::iterator
5847 i = ++BasicBlock::iterator(I),
5848 UI = BasicBlock::iterator(dyn_cast<Instruction>(Use));
5849 i != UI; ++i)
5850 if (i == I->getParent()->end() || i->mayHaveSideEffects())
5851 return false;
5852
5853 // Look through GEPs. A load from a GEP derived from NULL is still undefined
5854 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
5855 if (GEP->getPointerOperand() == I)
5856 return passingValueIsAlwaysUndefined(V, GEP);
5857
5858 // Look through bitcasts.
5859 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
5860 return passingValueIsAlwaysUndefined(V, BC);
5861
5862 // Load from null is undefined.
5863 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
5864 if (!LI->isVolatile())
5865 return LI->getPointerAddressSpace() == 0;
5866
5867 // Store to null is undefined.
5868 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
5869 if (!SI->isVolatile())
5870 return SI->getPointerAddressSpace() == 0 &&
5871 SI->getPointerOperand() == I;
5872
5873 // A call to null is undefined.
5874 if (auto CS = CallSite(Use))
5875 return CS.getCalledValue() == I;
5876 }
5877 return false;
5878}
5879
5880/// If BB has an incoming value that will always trigger undefined behavior
5881/// (eg. null pointer dereference), remove the branch leading here.
5882static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
5883 for (BasicBlock::iterator i = BB->begin();
5884 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
5885 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
5886 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
5887 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
5888 IRBuilder<> Builder(T);
5889 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
5890 BB->removePredecessor(PHI->getIncomingBlock(i));
5891 // Turn uncoditional branches into unreachables and remove the dead
5892 // destination from conditional branches.
5893 if (BI->isUnconditional())
5894 Builder.CreateUnreachable();
5895 else
5896 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1)
5897 : BI->getSuccessor(0));
5898 BI->eraseFromParent();
5899 return true;
5900 }
5901 // TODO: SwitchInst.
5902 }
5903
5904 return false;
5905}
5906
5907bool SimplifyCFGOpt::run(BasicBlock *BB) {
5908 bool Changed = false;
5909
5910 assert(BB && BB->getParent() && "Block not embedded in function!")((BB && BB->getParent() && "Block not embedded in function!"
) ? static_cast<void> (0) : __assert_fail ("BB && BB->getParent() && \"Block not embedded in function!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5910, __PRETTY_FUNCTION__))
;
5911 assert(BB->getTerminator() && "Degenerate basic block encountered!")((BB->getTerminator() && "Degenerate basic block encountered!"
) ? static_cast<void> (0) : __assert_fail ("BB->getTerminator() && \"Degenerate basic block encountered!\""
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn306458/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5911, __PRETTY_FUNCTION__))
;
5912
5913 // Remove basic blocks that have no predecessors (except the entry block)...
5914 // or that just have themself as a predecessor. These are unreachable.
5915 if ((pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) ||
5
Assuming the condition is false
7
Taking false branch
22
Assuming the condition is false
24
Taking false branch
5916 BB->getSinglePredecessor() == BB) {
6
Assuming the condition is false
23
Assuming the condition is false
5917 DEBUG(dbgs() << "Removing BB: \n" << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Removing BB: \n" <<
*BB; } } while (false)
;
5918 DeleteDeadBlock(BB);
5919 return true;
5920 }
5921
5922 // Check to see if we can constant propagate this terminator instruction
5923 // away...
5924 Changed |= ConstantFoldTerminator(BB, true);
5925
5926 // Check for and eliminate duplicate PHI nodes in this block.
5927 Changed |= EliminateDuplicatePHINodes(BB);
5928
5929 // Check for and remove branches that will always cause undefined behavior.
5930 Changed |= removeUndefIntroducingPredecessor(BB);
5931
5932 // Merge basic blocks into their predecessor if there is only one distinct
5933 // pred, and if there is only one distinct successor of the predecessor, and
5934 // if there are no PHI nodes.
5935 //
5936 if (MergeBlockIntoPredecessor(BB))
8
Assuming the condition is false
9
Taking false branch
25
Assuming the condition is false
26
Taking false branch
5937 return true;
5938
5939 IRBuilder<> Builder(BB);
5940
5941 // If there is a trivial two-entry PHI node in this basic block, and we can
5942 // eliminate it, do so now.
5943 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
10
Taking false branch
27
Assuming 'PN' is non-null
28
Taking true branch
5944 if (PN->getNumIncomingValues() == 2)
29
Assuming the condition is true
30
Taking true branch
5945 Changed |= FoldTwoEntryPHINode(PN, TTI, DL);
31
Calling 'FoldTwoEntryPHINode'
5946
5947 Builder.SetInsertPoint(BB->getTerminator());
5948 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
11
Taking false branch
5949 if (BI->isUnconditional()) {
5950 if (SimplifyUncondBranch(BI, Builder))
5951 return true;
5952 } else {
5953 if (SimplifyCondBranch(BI, Builder))
5954 return true;
5955 }
5956 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
12
Taking false branch
5957 if (SimplifyReturn(RI, Builder))
5958 return true;
5959 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
13
Taking false branch
5960 if (SimplifyResume(RI, Builder))
5961 return true;
5962 } else if (CleanupReturnInst *RI =
14
Taking false branch
5963 dyn_cast<CleanupReturnInst>(BB->getTerminator())) {
5964 if (SimplifyCleanupReturn(RI))
5965 return true;
5966 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
15
Assuming 'SI' is non-null
16
Taking true branch
5967 if (SimplifySwitch(SI, Builder))
17
Calling 'SimplifyCFGOpt::SimplifySwitch'
5968 return true;
5969 } else if (UnreachableInst *UI =
5970 dyn_cast<UnreachableInst>(BB->getTerminator())) {
5971 if (SimplifyUnreachable(UI))
5972 return true;
5973 } else if (IndirectBrInst *IBI =
5974 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
5975 if (SimplifyIndirectBr(IBI))
5976 return true;
5977 }
5978
5979 return Changed;
5980}
5981
5982/// This function is used to do simplification of a CFG.
5983/// For example, it adjusts branches to branches to eliminate the extra hop,
5984/// eliminates unreachable basic blocks, and does other "peephole" optimization
5985/// of the CFG. It returns true if a modification was made.
5986///
5987bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
5988 unsigned BonusInstThreshold, AssumptionCache *AC,
5989 SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
5990 bool LateSimplifyCFG) {
5991 return SimplifyCFGOpt(TTI, BB->getModule()->getDataLayout(),
4
Calling 'SimplifyCFGOpt::run'
21
Calling 'SimplifyCFGOpt::run'
5992 BonusInstThreshold, AC, LoopHeaders, LateSimplifyCFG)
5993 .run(BB);
5994}