Bug Summary

File:lib/Transforms/Utils/SimplifyCFG.cpp
Warning:line 5334, column 18
Called C++ object pointer is null

Annotated Source Code

Press '?' to see keyboard shortcuts

clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name SimplifyCFG.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-eagerly-assume -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn337490/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/lib/Transforms/Utils -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-07-20-043646-20380-1 -x c++ /build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp -faddrsig
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/SmallVector.h"
23#include "llvm/ADT/Statistic.h"
24#include "llvm/ADT/StringRef.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/Transforms/Utils/Local.h"
31#include "llvm/Analysis/ValueTracking.h"
32#include "llvm/IR/Attributes.h"
33#include "llvm/IR/BasicBlock.h"
34#include "llvm/IR/CFG.h"
35#include "llvm/IR/CallSite.h"
36#include "llvm/IR/Constant.h"
37#include "llvm/IR/ConstantRange.h"
38#include "llvm/IR/Constants.h"
39#include "llvm/IR/DataLayout.h"
40#include "llvm/IR/DerivedTypes.h"
41#include "llvm/IR/Function.h"
42#include "llvm/IR/GlobalValue.h"
43#include "llvm/IR/GlobalVariable.h"
44#include "llvm/IR/IRBuilder.h"
45#include "llvm/IR/InstrTypes.h"
46#include "llvm/IR/Instruction.h"
47#include "llvm/IR/Instructions.h"
48#include "llvm/IR/IntrinsicInst.h"
49#include "llvm/IR/Intrinsics.h"
50#include "llvm/IR/LLVMContext.h"
51#include "llvm/IR/MDBuilder.h"
52#include "llvm/IR/Metadata.h"
53#include "llvm/IR/Module.h"
54#include "llvm/IR/NoFolder.h"
55#include "llvm/IR/Operator.h"
56#include "llvm/IR/PatternMatch.h"
57#include "llvm/IR/Type.h"
58#include "llvm/IR/Use.h"
59#include "llvm/IR/User.h"
60#include "llvm/IR/Value.h"
61#include "llvm/Support/Casting.h"
62#include "llvm/Support/CommandLine.h"
63#include "llvm/Support/Debug.h"
64#include "llvm/Support/ErrorHandling.h"
65#include "llvm/Support/KnownBits.h"
66#include "llvm/Support/MathExtras.h"
67#include "llvm/Support/raw_ostream.h"
68#include "llvm/Transforms/Utils/BasicBlockUtils.h"
69#include "llvm/Transforms/Utils/ValueMapper.h"
70#include <algorithm>
71#include <cassert>
72#include <climits>
73#include <cstddef>
74#include <cstdint>
75#include <iterator>
76#include <map>
77#include <set>
78#include <tuple>
79#include <utility>
80#include <vector>
81
82using namespace llvm;
83using namespace PatternMatch;
84
85#define DEBUG_TYPE"simplifycfg" "simplifycfg"
86
87// Chosen as 2 so as to be cheap, but still to have enough power to fold
88// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
89// To catch this, we need to fold a compare and a select, hence '2' being the
90// minimum reasonable default.
91static cl::opt<unsigned> PHINodeFoldingThreshold(
92 "phi-node-folding-threshold", cl::Hidden, cl::init(2),
93 cl::desc(
94 "Control the amount of phi node folding to perform (default = 2)"));
95
96static cl::opt<bool> DupRet(
97 "simplifycfg-dup-ret", cl::Hidden, cl::init(false),
98 cl::desc("Duplicate return instructions into unconditional branches"));
99
100static cl::opt<bool>
101 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
102 cl::desc("Sink common instructions down to the end block"));
103
104static cl::opt<bool> HoistCondStores(
105 "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
106 cl::desc("Hoist conditional stores if an unconditional store precedes"));
107
108static cl::opt<bool> MergeCondStores(
109 "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
110 cl::desc("Hoist conditional stores even if an unconditional store does not "
111 "precede - hoist multiple conditional stores into a single "
112 "predicated store"));
113
114static cl::opt<bool> MergeCondStoresAggressively(
115 "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
116 cl::desc("When merging conditional stores, do so even if the resultant "
117 "basic blocks are unlikely to be if-converted as a result"));
118
119static cl::opt<bool> SpeculateOneExpensiveInst(
120 "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
121 cl::desc("Allow exactly one expensive instruction to be speculatively "
122 "executed"));
123
124static cl::opt<unsigned> MaxSpeculationDepth(
125 "max-speculation-depth", cl::Hidden, cl::init(10),
126 cl::desc("Limit maximum recursion depth when calculating costs of "
127 "speculatively executed instructions"));
128
129STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps")static llvm::Statistic NumBitMaps = {"simplifycfg", "NumBitMaps"
, "Number of switch instructions turned into bitmaps", {0}, {
false}}
;
130STATISTIC(NumLinearMaps,static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, {false}}
131 "Number of switch instructions turned into linear mapping")static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, {false}}
;
132STATISTIC(NumLookupTables,static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, {false}}
133 "Number of switch instructions turned into lookup tables")static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, {false}}
;
134STATISTIC(static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, {false}}
135 NumLookupTablesHoles,static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, {false}}
136 "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}}
;
137STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares")static llvm::Statistic NumTableCmpReuses = {"simplifycfg", "NumTableCmpReuses"
, "Number of reused switch table lookup compares", {0}, {false
}}
;
138STATISTIC(NumSinkCommons,static llvm::Statistic NumSinkCommons = {"simplifycfg", "NumSinkCommons"
, "Number of common instructions sunk down to the end block",
{0}, {false}}
139 "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}}
;
140STATISTIC(NumSpeculations, "Number of speculative executed instructions")static llvm::Statistic NumSpeculations = {"simplifycfg", "NumSpeculations"
, "Number of speculative executed instructions", {0}, {false}
}
;
141
142namespace {
143
144// The first field contains the value that the switch produces when a certain
145// case group is selected, and the second field is a vector containing the
146// cases composing the case group.
147using SwitchCaseResultVectorTy =
148 SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>;
149
150// The first field contains the phi node that generates a result of the switch
151// and the second field contains the value generated for a certain case in the
152// switch for that PHI.
153using SwitchCaseResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
154
155/// ValueEqualityComparisonCase - Represents a case of a switch.
156struct ValueEqualityComparisonCase {
157 ConstantInt *Value;
158 BasicBlock *Dest;
159
160 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
161 : Value(Value), Dest(Dest) {}
162
163 bool operator<(ValueEqualityComparisonCase RHS) const {
164 // Comparing pointers is ok as we only rely on the order for uniquing.
165 return Value < RHS.Value;
166 }
167
168 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
169};
170
171class SimplifyCFGOpt {
172 const TargetTransformInfo &TTI;
173 const DataLayout &DL;
174 SmallPtrSetImpl<BasicBlock *> *LoopHeaders;
175 const SimplifyCFGOptions &Options;
176
177 Value *isValueEqualityComparison(TerminatorInst *TI);
178 BasicBlock *GetValueEqualityComparisonCases(
179 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases);
180 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
181 BasicBlock *Pred,
182 IRBuilder<> &Builder);
183 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
184 IRBuilder<> &Builder);
185
186 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
187 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
188 bool SimplifySingleResume(ResumeInst *RI);
189 bool SimplifyCommonResume(ResumeInst *RI);
190 bool SimplifyCleanupReturn(CleanupReturnInst *RI);
191 bool SimplifyUnreachable(UnreachableInst *UI);
192 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
193 bool SimplifyIndirectBr(IndirectBrInst *IBI);
194 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
195 bool SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
196
197public:
198 SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
199 SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
200 const SimplifyCFGOptions &Opts)
201 : TTI(TTI), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {}
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())(static_cast <bool> (SI1->isUnconditional() &&
SI2->isConditional()) ? void (0) : __assert_fail ("SI1->isUnconditional() && SI2->isConditional()"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 248, __extension__ __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 for (PHINode &PN : Succ->phis())
286 PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred);
287}
288
289/// Compute an abstract "cost" of speculating the given instruction,
290/// which is assumed to be safe to speculate. TCC_Free means cheap,
291/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
292/// expensive.
293static unsigned ComputeSpeculationCost(const User *I,
294 const TargetTransformInfo &TTI) {
295 assert(isSafeToSpeculativelyExecute(I) &&(static_cast <bool> (isSafeToSpeculativelyExecute(I) &&
"Instruction is not safe to speculatively execute!") ? void (
0) : __assert_fail ("isSafeToSpeculativelyExecute(I) && \"Instruction is not safe to speculatively execute!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 296, __extension__ __PRETTY_FUNCTION__))
296 "Instruction is not safe to speculatively execute!")(static_cast <bool> (isSafeToSpeculativelyExecute(I) &&
"Instruction is not safe to speculatively execute!") ? void (
0) : __assert_fail ("isSafeToSpeculativelyExecute(I) && \"Instruction is not safe to speculatively execute!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 296, __extension__ __PRETTY_FUNCTION__))
;
297 return TTI.getUserCost(I);
298}
299
300/// If we have a merge point of an "if condition" as accepted above,
301/// return true if the specified value dominates the block. We
302/// don't handle the true generality of domination here, just a special case
303/// which works well enough for us.
304///
305/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
306/// see if V (which must be an instruction) and its recursive operands
307/// that do not dominate BB have a combined cost lower than CostRemaining and
308/// are non-trapping. If both are true, the instruction is inserted into the
309/// set and true is returned.
310///
311/// The cost for most non-trapping instructions is defined as 1 except for
312/// Select whose cost is 2.
313///
314/// After this function returns, CostRemaining is decreased by the cost of
315/// V plus its non-dominating operands. If that cost is greater than
316/// CostRemaining, false is returned and CostRemaining is undefined.
317static bool DominatesMergePoint(Value *V, BasicBlock *BB,
318 SmallPtrSetImpl<Instruction *> *AggressiveInsts,
319 unsigned &CostRemaining,
320 const TargetTransformInfo &TTI,
321 unsigned Depth = 0) {
322 // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
323 // so limit the recursion depth.
324 // TODO: While this recursion limit does prevent pathological behavior, it
325 // would be better to track visited instructions to avoid cycles.
326 if (Depth == MaxSpeculationDepth)
327 return false;
328
329 Instruction *I = dyn_cast<Instruction>(V);
330 if (!I) {
331 // Non-instructions all dominate instructions, but not all constantexprs
332 // can be executed unconditionally.
333 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
334 if (C->canTrap())
335 return false;
336 return true;
337 }
338 BasicBlock *PBB = I->getParent();
339
340 // We don't want to allow weird loops that might have the "if condition" in
341 // the bottom of this block.
342 if (PBB == BB)
343 return false;
344
345 // If this instruction is defined in a block that contains an unconditional
346 // branch to BB, then it must be in the 'conditional' part of the "if
347 // statement". If not, it definitely dominates the region.
348 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
349 if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
350 return true;
351
352 // If we aren't allowing aggressive promotion anymore, then don't consider
353 // instructions in the 'if region'.
354 if (!AggressiveInsts)
355 return false;
356
357 // If we have seen this instruction before, don't count it again.
358 if (AggressiveInsts->count(I))
359 return true;
360
361 // Okay, it looks like the instruction IS in the "condition". Check to
362 // see if it's a cheap instruction to unconditionally compute, and if it
363 // only uses stuff defined outside of the condition. If so, hoist it out.
364 if (!isSafeToSpeculativelyExecute(I))
365 return false;
366
367 unsigned Cost = ComputeSpeculationCost(I, TTI);
368
369 // Allow exactly one instruction to be speculated regardless of its cost
370 // (as long as it is safe to do so).
371 // This is intended to flatten the CFG even if the instruction is a division
372 // or other expensive operation. The speculation of an expensive instruction
373 // is expected to be undone in CodeGenPrepare if the speculation has not
374 // enabled further IR optimizations.
375 if (Cost > CostRemaining &&
376 (!SpeculateOneExpensiveInst || !AggressiveInsts->empty() || Depth > 0))
377 return false;
378
379 // Avoid unsigned wrap.
380 CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
381
382 // Okay, we can only really hoist these out if their operands do
383 // not take us over the cost threshold.
384 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
385 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
386 Depth + 1))
387 return false;
388 // Okay, it's safe to do this! Remember this instruction.
389 AggressiveInsts->insert(I);
390 return true;
391}
392
393/// Extract ConstantInt from value, looking through IntToPtr
394/// and PointerNullValue. Return NULL if value is not a constant int.
395static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
396 // Normal constant int.
397 ConstantInt *CI = dyn_cast<ConstantInt>(V);
398 if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
399 return CI;
400
401 // This is some kind of pointer constant. Turn it into a pointer-sized
402 // ConstantInt if possible.
403 IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
404
405 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
406 if (isa<ConstantPointerNull>(V))
407 return ConstantInt::get(PtrTy, 0);
408
409 // IntToPtr const int.
410 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
411 if (CE->getOpcode() == Instruction::IntToPtr)
412 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
413 // The constant is very likely to have the right type already.
414 if (CI->getType() == PtrTy)
415 return CI;
416 else
417 return cast<ConstantInt>(
418 ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
419 }
420 return nullptr;
421}
422
423namespace {
424
425/// Given a chain of or (||) or and (&&) comparison of a value against a
426/// constant, this will try to recover the information required for a switch
427/// structure.
428/// It will depth-first traverse the chain of comparison, seeking for patterns
429/// like %a == 12 or %a < 4 and combine them to produce a set of integer
430/// representing the different cases for the switch.
431/// Note that if the chain is composed of '||' it will build the set of elements
432/// that matches the comparisons (i.e. any of this value validate the chain)
433/// while for a chain of '&&' it will build the set elements that make the test
434/// fail.
435struct ConstantComparesGatherer {
436 const DataLayout &DL;
437
438 /// Value found for the switch comparison
439 Value *CompValue = nullptr;
440
441 /// Extra clause to be checked before the switch
442 Value *Extra = nullptr;
443
444 /// Set of integers to match in switch
445 SmallVector<ConstantInt *, 8> Vals;
446
447 /// Number of comparisons matched in the and/or chain
448 unsigned UsedICmps = 0;
449
450 /// Construct and compute the result for the comparison instruction Cond
451 ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) {
452 gather(Cond);
453 }
454
455 ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
456 ConstantComparesGatherer &
457 operator=(const ConstantComparesGatherer &) = delete;
458
459private:
460 /// Try to set the current value used for the comparison, it succeeds only if
461 /// it wasn't set before or if the new value is the same as the old one
462 bool setValueOnce(Value *NewVal) {
463 if (CompValue && CompValue != NewVal)
464 return false;
465 CompValue = NewVal;
466 return (CompValue != nullptr);
467 }
468
469 /// Try to match Instruction "I" as a comparison against a constant and
470 /// populates the array Vals with the set of values that match (or do not
471 /// match depending on isEQ).
472 /// Return false on failure. On success, the Value the comparison matched
473 /// against is placed in CompValue.
474 /// If CompValue is already set, the function is expected to fail if a match
475 /// is found but the value compared to is different.
476 bool matchInstruction(Instruction *I, bool isEQ) {
477 // If this is an icmp against a constant, handle this as one of the cases.
478 ICmpInst *ICI;
479 ConstantInt *C;
480 if (!((ICI = dyn_cast<ICmpInst>(I)) &&
481 (C = GetConstantInt(I->getOperand(1), DL)))) {
482 return false;
483 }
484
485 Value *RHSVal;
486 const APInt *RHSC;
487
488 // Pattern match a special case
489 // (x & ~2^z) == y --> x == y || x == y|2^z
490 // This undoes a transformation done by instcombine to fuse 2 compares.
491 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) {
492 // It's a little bit hard to see why the following transformations are
493 // correct. Here is a CVC3 program to verify them for 64-bit values:
494
495 /*
496 ONE : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
497 x : BITVECTOR(64);
498 y : BITVECTOR(64);
499 z : BITVECTOR(64);
500 mask : BITVECTOR(64) = BVSHL(ONE, z);
501 QUERY( (y & ~mask = y) =>
502 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
503 );
504 QUERY( (y | mask = y) =>
505 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
506 );
507 */
508
509 // Please note that each pattern must be a dual implication (<--> or
510 // iff). One directional implication can create spurious matches. If the
511 // implication is only one-way, an unsatisfiable condition on the left
512 // side can imply a satisfiable condition on the right side. Dual
513 // implication ensures that satisfiable conditions are transformed to
514 // other satisfiable conditions and unsatisfiable conditions are
515 // transformed to other unsatisfiable conditions.
516
517 // Here is a concrete example of a unsatisfiable condition on the left
518 // implying a satisfiable condition on the right:
519 //
520 // mask = (1 << z)
521 // (x & ~mask) == y --> (x == y || x == (y | mask))
522 //
523 // Substituting y = 3, z = 0 yields:
524 // (x & -2) == 3 --> (x == 3 || x == 2)
525
526 // Pattern match a special case:
527 /*
528 QUERY( (y & ~mask = y) =>
529 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
530 );
531 */
532 if (match(ICI->getOperand(0),
533 m_And(m_Value(RHSVal), m_APInt(RHSC)))) {
534 APInt Mask = ~*RHSC;
535 if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) {
536 // If we already have a value for the switch, it has to match!
537 if (!setValueOnce(RHSVal))
538 return false;
539
540 Vals.push_back(C);
541 Vals.push_back(
542 ConstantInt::get(C->getContext(),
543 C->getValue() | Mask));
544 UsedICmps++;
545 return true;
546 }
547 }
548
549 // Pattern match a special case:
550 /*
551 QUERY( (y | mask = y) =>
552 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
553 );
554 */
555 if (match(ICI->getOperand(0),
556 m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
557 APInt Mask = *RHSC;
558 if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
559 // If we already have a value for the switch, it has to match!
560 if (!setValueOnce(RHSVal))
561 return false;
562
563 Vals.push_back(C);
564 Vals.push_back(ConstantInt::get(C->getContext(),
565 C->getValue() & ~Mask));
566 UsedICmps++;
567 return true;
568 }
569 }
570
571 // If we already have a value for the switch, it has to match!
572 if (!setValueOnce(ICI->getOperand(0)))
573 return false;
574
575 UsedICmps++;
576 Vals.push_back(C);
577 return ICI->getOperand(0);
578 }
579
580 // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
581 ConstantRange Span = ConstantRange::makeAllowedICmpRegion(
582 ICI->getPredicate(), C->getValue());
583
584 // Shift the range if the compare is fed by an add. This is the range
585 // compare idiom as emitted by instcombine.
586 Value *CandidateVal = I->getOperand(0);
587 if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) {
588 Span = Span.subtract(*RHSC);
589 CandidateVal = RHSVal;
590 }
591
592 // If this is an and/!= check, then we are looking to build the set of
593 // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
594 // x != 0 && x != 1.
595 if (!isEQ)
596 Span = Span.inverse();
597
598 // If there are a ton of values, we don't want to make a ginormous switch.
599 if (Span.isSizeLargerThan(8) || Span.isEmptySet()) {
600 return false;
601 }
602
603 // If we already have a value for the switch, it has to match!
604 if (!setValueOnce(CandidateVal))
605 return false;
606
607 // Add all values from the range to the set
608 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
609 Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
610
611 UsedICmps++;
612 return true;
613 }
614
615 /// Given a potentially 'or'd or 'and'd together collection of icmp
616 /// eq/ne/lt/gt instructions that compare a value against a constant, extract
617 /// the value being compared, and stick the list constants into the Vals
618 /// vector.
619 /// One "Extra" case is allowed to differ from the other.
620 void gather(Value *V) {
621 Instruction *I = dyn_cast<Instruction>(V);
622 bool isEQ = (I->getOpcode() == Instruction::Or);
623
624 // Keep a stack (SmallVector for efficiency) for depth-first traversal
625 SmallVector<Value *, 8> DFT;
626 SmallPtrSet<Value *, 8> Visited;
627
628 // Initialize
629 Visited.insert(V);
630 DFT.push_back(V);
631
632 while (!DFT.empty()) {
633 V = DFT.pop_back_val();
634
635 if (Instruction *I = dyn_cast<Instruction>(V)) {
636 // If it is a || (or && depending on isEQ), process the operands.
637 if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
638 if (Visited.insert(I->getOperand(1)).second)
639 DFT.push_back(I->getOperand(1));
640 if (Visited.insert(I->getOperand(0)).second)
641 DFT.push_back(I->getOperand(0));
642 continue;
643 }
644
645 // Try to match the current instruction
646 if (matchInstruction(I, isEQ))
647 // Match succeed, continue the loop
648 continue;
649 }
650
651 // One element of the sequence of || (or &&) could not be match as a
652 // comparison against the same value as the others.
653 // We allow only one "Extra" case to be checked before the switch
654 if (!Extra) {
655 Extra = V;
656 continue;
657 }
658 // Failed to parse a proper sequence, abort now
659 CompValue = nullptr;
660 break;
661 }
662 }
663};
664
665} // end anonymous namespace
666
667static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
668 Instruction *Cond = nullptr;
669 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
670 Cond = dyn_cast<Instruction>(SI->getCondition());
671 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
672 if (BI->isConditional())
673 Cond = dyn_cast<Instruction>(BI->getCondition());
674 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
675 Cond = dyn_cast<Instruction>(IBI->getAddress());
676 }
677
678 TI->eraseFromParent();
679 if (Cond)
680 RecursivelyDeleteTriviallyDeadInstructions(Cond);
681}
682
683/// Return true if the specified terminator checks
684/// to see if a value is equal to constant integer value.
685Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
686 Value *CV = nullptr;
687 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
688 // Do not permit merging of large switch instructions into their
689 // predecessors unless there is only one predecessor.
690 if (SI->getNumSuccessors() * pred_size(SI->getParent()) <= 128)
691 CV = SI->getCondition();
692 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
693 if (BI->isConditional() && BI->getCondition()->hasOneUse())
694 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
695 if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
696 CV = ICI->getOperand(0);
697 }
698
699 // Unwrap any lossless ptrtoint cast.
700 if (CV) {
701 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
702 Value *Ptr = PTII->getPointerOperand();
703 if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
704 CV = Ptr;
705 }
706 }
707 return CV;
708}
709
710/// Given a value comparison instruction,
711/// decode all of the 'cases' that it represents and return the 'default' block.
712BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases(
713 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases) {
714 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
715 Cases.reserve(SI->getNumCases());
716 for (auto Case : SI->cases())
717 Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(),
718 Case.getCaseSuccessor()));
719 return SI->getDefaultDest();
720 }
721
722 BranchInst *BI = cast<BranchInst>(TI);
723 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
724 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
725 Cases.push_back(ValueEqualityComparisonCase(
726 GetConstantInt(ICI->getOperand(1), DL), Succ));
727 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
728}
729
730/// Given a vector of bb/value pairs, remove any entries
731/// in the list that match the specified block.
732static void
733EliminateBlockCases(BasicBlock *BB,
734 std::vector<ValueEqualityComparisonCase> &Cases) {
735 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
736}
737
738/// Return true if there are any keys in C1 that exist in C2 as well.
739static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
740 std::vector<ValueEqualityComparisonCase> &C2) {
741 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
742
743 // Make V1 be smaller than V2.
744 if (V1->size() > V2->size())
745 std::swap(V1, V2);
746
747 if (V1->empty())
748 return false;
749 if (V1->size() == 1) {
750 // Just scan V2.
751 ConstantInt *TheVal = (*V1)[0].Value;
752 for (unsigned i = 0, e = V2->size(); i != e; ++i)
753 if (TheVal == (*V2)[i].Value)
754 return true;
755 }
756
757 // Otherwise, just sort both lists and compare element by element.
758 array_pod_sort(V1->begin(), V1->end());
759 array_pod_sort(V2->begin(), V2->end());
760 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
761 while (i1 != e1 && i2 != e2) {
762 if ((*V1)[i1].Value == (*V2)[i2].Value)
763 return true;
764 if ((*V1)[i1].Value < (*V2)[i2].Value)
765 ++i1;
766 else
767 ++i2;
768 }
769 return false;
770}
771
772// Set branch weights on SwitchInst. This sets the metadata if there is at
773// least one non-zero weight.
774static void setBranchWeights(SwitchInst *SI, ArrayRef<uint32_t> Weights) {
775 // Check that there is at least one non-zero weight. Otherwise, pass
776 // nullptr to setMetadata which will erase the existing metadata.
777 MDNode *N = nullptr;
778 if (llvm::any_of(Weights, [](uint32_t W) { return W != 0; }))
779 N = MDBuilder(SI->getParent()->getContext()).createBranchWeights(Weights);
780 SI->setMetadata(LLVMContext::MD_prof, N);
781}
782
783// Similar to the above, but for branch and select instructions that take
784// exactly 2 weights.
785static void setBranchWeights(Instruction *I, uint32_t TrueWeight,
786 uint32_t FalseWeight) {
787 assert(isa<BranchInst>(I) || isa<SelectInst>(I))(static_cast <bool> (isa<BranchInst>(I) || isa<
SelectInst>(I)) ? void (0) : __assert_fail ("isa<BranchInst>(I) || isa<SelectInst>(I)"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 787, __extension__ __PRETTY_FUNCTION__))
;
788 // Check that there is at least one non-zero weight. Otherwise, pass
789 // nullptr to setMetadata which will erase the existing metadata.
790 MDNode *N = nullptr;
791 if (TrueWeight || FalseWeight)
792 N = MDBuilder(I->getParent()->getContext())
793 .createBranchWeights(TrueWeight, FalseWeight);
794 I->setMetadata(LLVMContext::MD_prof, N);
795}
796
797/// If TI is known to be a terminator instruction and its block is known to
798/// only have a single predecessor block, check to see if that predecessor is
799/// also a value comparison with the same value, and if that comparison
800/// determines the outcome of this comparison. If so, simplify TI. This does a
801/// very limited form of jump threading.
802bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
803 TerminatorInst *TI, BasicBlock *Pred, IRBuilder<> &Builder) {
804 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
805 if (!PredVal)
806 return false; // Not a value comparison in predecessor.
807
808 Value *ThisVal = isValueEqualityComparison(TI);
809 assert(ThisVal && "This isn't a value comparison!!")(static_cast <bool> (ThisVal && "This isn't a value comparison!!"
) ? void (0) : __assert_fail ("ThisVal && \"This isn't a value comparison!!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 809, __extension__ __PRETTY_FUNCTION__))
;
810 if (ThisVal != PredVal)
811 return false; // Different predicates.
812
813 // TODO: Preserve branch weight metadata, similarly to how
814 // FoldValueComparisonIntoPredecessors preserves it.
815
816 // Find out information about when control will move from Pred to TI's block.
817 std::vector<ValueEqualityComparisonCase> PredCases;
818 BasicBlock *PredDef =
819 GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases);
820 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
821
822 // Find information about how control leaves this block.
823 std::vector<ValueEqualityComparisonCase> ThisCases;
824 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
825 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
826
827 // If TI's block is the default block from Pred's comparison, potentially
828 // simplify TI based on this knowledge.
829 if (PredDef == TI->getParent()) {
830 // If we are here, we know that the value is none of those cases listed in
831 // PredCases. If there are any cases in ThisCases that are in PredCases, we
832 // can simplify TI.
833 if (!ValuesOverlap(PredCases, ThisCases))
834 return false;
835
836 if (isa<BranchInst>(TI)) {
837 // Okay, one of the successors of this condbr is dead. Convert it to a
838 // uncond br.
839 assert(ThisCases.size() == 1 && "Branch can only have one case!")(static_cast <bool> (ThisCases.size() == 1 && "Branch can only have one case!"
) ? void (0) : __assert_fail ("ThisCases.size() == 1 && \"Branch can only have one case!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 839, __extension__ __PRETTY_FUNCTION__))
;
840 // Insert the new branch.
841 Instruction *NI = Builder.CreateBr(ThisDef);
842 (void)NI;
843
844 // Remove PHI node entries for the dead edge.
845 ThisCases[0].Dest->removePredecessor(TI->getParent());
846
847 LLVM_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)
848 << "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)
849 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
850
851 EraseTerminatorInstAndDCECond(TI);
852 return true;
853 }
854
855 SwitchInst *SI = cast<SwitchInst>(TI);
856 // Okay, TI has cases that are statically dead, prune them away.
857 SmallPtrSet<Constant *, 16> DeadCases;
858 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
859 DeadCases.insert(PredCases[i].Value);
860
861 LLVM_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)
862 << "Through successor TI: " << *TI)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI; } } while (false)
;
863
864 // Collect branch weights into a vector.
865 SmallVector<uint32_t, 8> Weights;
866 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
867 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
868 if (HasWeight)
869 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
870 ++MD_i) {
871 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
872 Weights.push_back(CI->getValue().getZExtValue());
873 }
874 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
875 --i;
876 if (DeadCases.count(i->getCaseValue())) {
877 if (HasWeight) {
878 std::swap(Weights[i->getCaseIndex() + 1], Weights.back());
879 Weights.pop_back();
880 }
881 i->getCaseSuccessor()->removePredecessor(TI->getParent());
882 SI->removeCase(i);
883 }
884 }
885 if (HasWeight && Weights.size() >= 2)
886 setBranchWeights(SI, Weights);
887
888 LLVM_DEBUG(dbgs() << "Leaving: " << *TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Leaving: " << *TI <<
"\n"; } } while (false)
;
889 return true;
890 }
891
892 // Otherwise, TI's block must correspond to some matched value. Find out
893 // which value (or set of values) this is.
894 ConstantInt *TIV = nullptr;
895 BasicBlock *TIBB = TI->getParent();
896 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
897 if (PredCases[i].Dest == TIBB) {
898 if (TIV)
899 return false; // Cannot handle multiple values coming to this block.
900 TIV = PredCases[i].Value;
901 }
902 assert(TIV && "No edge from pred to succ?")(static_cast <bool> (TIV && "No edge from pred to succ?"
) ? void (0) : __assert_fail ("TIV && \"No edge from pred to succ?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 902, __extension__ __PRETTY_FUNCTION__))
;
903
904 // Okay, we found the one constant that our value can be if we get into TI's
905 // BB. Find out which successor will unconditionally be branched to.
906 BasicBlock *TheRealDest = nullptr;
907 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
908 if (ThisCases[i].Value == TIV) {
909 TheRealDest = ThisCases[i].Dest;
910 break;
911 }
912
913 // If not handled by any explicit cases, it is handled by the default case.
914 if (!TheRealDest)
915 TheRealDest = ThisDef;
916
917 // Remove PHI node entries for dead edges.
918 BasicBlock *CheckEdge = TheRealDest;
919 for (BasicBlock *Succ : successors(TIBB))
920 if (Succ != CheckEdge)
921 Succ->removePredecessor(TIBB);
922 else
923 CheckEdge = nullptr;
924
925 // Insert the new branch.
926 Instruction *NI = Builder.CreateBr(TheRealDest);
927 (void)NI;
928
929 LLVM_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)
930 << "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)
931 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
932
933 EraseTerminatorInstAndDCECond(TI);
934 return true;
935}
936
937namespace {
938
939/// This class implements a stable ordering of constant
940/// integers that does not depend on their address. This is important for
941/// applications that sort ConstantInt's to ensure uniqueness.
942struct ConstantIntOrdering {
943 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
944 return LHS->getValue().ult(RHS->getValue());
945 }
946};
947
948} // end anonymous namespace
949
950static int ConstantIntSortPredicate(ConstantInt *const *P1,
951 ConstantInt *const *P2) {
952 const ConstantInt *LHS = *P1;
953 const ConstantInt *RHS = *P2;
954 if (LHS == RHS)
955 return 0;
956 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
957}
958
959static inline bool HasBranchWeights(const Instruction *I) {
960 MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
961 if (ProfMD && ProfMD->getOperand(0))
962 if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
963 return MDS->getString().equals("branch_weights");
964
965 return false;
966}
967
968/// Get Weights of a given TerminatorInst, the default weight is at the front
969/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
970/// metadata.
971static void GetBranchWeights(TerminatorInst *TI,
972 SmallVectorImpl<uint64_t> &Weights) {
973 MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
974 assert(MD)(static_cast <bool> (MD) ? void (0) : __assert_fail ("MD"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 974, __extension__ __PRETTY_FUNCTION__))
;
975 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
976 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
977 Weights.push_back(CI->getValue().getZExtValue());
978 }
979
980 // If TI is a conditional eq, the default case is the false case,
981 // and the corresponding branch-weight data is at index 2. We swap the
982 // default weight to be the first entry.
983 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
984 assert(Weights.size() == 2)(static_cast <bool> (Weights.size() == 2) ? void (0) : __assert_fail
("Weights.size() == 2", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 984, __extension__ __PRETTY_FUNCTION__))
;
985 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
986 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
987 std::swap(Weights.front(), Weights.back());
988 }
989}
990
991/// Keep halving the weights until all can fit in uint32_t.
992static void FitWeights(MutableArrayRef<uint64_t> Weights) {
993 uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
994 if (Max > UINT_MAX(2147483647 *2U +1U)) {
995 unsigned Offset = 32 - countLeadingZeros(Max);
996 for (uint64_t &I : Weights)
997 I >>= Offset;
998 }
999}
1000
1001/// The specified terminator is a value equality comparison instruction
1002/// (either a switch or a branch on "X == c").
1003/// See if any of the predecessors of the terminator block are value comparisons
1004/// on the same value. If so, and if safe to do so, fold them together.
1005bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
1006 IRBuilder<> &Builder) {
1007 BasicBlock *BB = TI->getParent();
1008 Value *CV = isValueEqualityComparison(TI); // CondVal
1009 assert(CV && "Not a comparison?")(static_cast <bool> (CV && "Not a comparison?")
? void (0) : __assert_fail ("CV && \"Not a comparison?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1009, __extension__ __PRETTY_FUNCTION__))
;
1010 bool Changed = false;
1011
1012 SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
1013 while (!Preds.empty()) {
1014 BasicBlock *Pred = Preds.pop_back_val();
1015
1016 // See if the predecessor is a comparison with the same value.
1017 TerminatorInst *PTI = Pred->getTerminator();
1018 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
1019
1020 if (PCV == CV && TI != PTI) {
1021 SmallSetVector<BasicBlock*, 4> FailBlocks;
1022 if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) {
1023 for (auto *Succ : FailBlocks) {
1024 if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split"))
1025 return false;
1026 }
1027 }
1028
1029 // Figure out which 'cases' to copy from SI to PSI.
1030 std::vector<ValueEqualityComparisonCase> BBCases;
1031 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
1032
1033 std::vector<ValueEqualityComparisonCase> PredCases;
1034 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
1035
1036 // Based on whether the default edge from PTI goes to BB or not, fill in
1037 // PredCases and PredDefault with the new switch cases we would like to
1038 // build.
1039 SmallVector<BasicBlock *, 8> NewSuccessors;
1040
1041 // Update the branch weight metadata along the way
1042 SmallVector<uint64_t, 8> Weights;
1043 bool PredHasWeights = HasBranchWeights(PTI);
1044 bool SuccHasWeights = HasBranchWeights(TI);
1045
1046 if (PredHasWeights) {
1047 GetBranchWeights(PTI, Weights);
1048 // branch-weight metadata is inconsistent here.
1049 if (Weights.size() != 1 + PredCases.size())
1050 PredHasWeights = SuccHasWeights = false;
1051 } else if (SuccHasWeights)
1052 // If there are no predecessor weights but there are successor weights,
1053 // populate Weights with 1, which will later be scaled to the sum of
1054 // successor's weights
1055 Weights.assign(1 + PredCases.size(), 1);
1056
1057 SmallVector<uint64_t, 8> SuccWeights;
1058 if (SuccHasWeights) {
1059 GetBranchWeights(TI, SuccWeights);
1060 // branch-weight metadata is inconsistent here.
1061 if (SuccWeights.size() != 1 + BBCases.size())
1062 PredHasWeights = SuccHasWeights = false;
1063 } else if (PredHasWeights)
1064 SuccWeights.assign(1 + BBCases.size(), 1);
1065
1066 if (PredDefault == BB) {
1067 // If this is the default destination from PTI, only the edges in TI
1068 // that don't occur in PTI, or that branch to BB will be activated.
1069 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1070 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1071 if (PredCases[i].Dest != BB)
1072 PTIHandled.insert(PredCases[i].Value);
1073 else {
1074 // The default destination is BB, we don't need explicit targets.
1075 std::swap(PredCases[i], PredCases.back());
1076
1077 if (PredHasWeights || SuccHasWeights) {
1078 // Increase weight for the default case.
1079 Weights[0] += Weights[i + 1];
1080 std::swap(Weights[i + 1], Weights.back());
1081 Weights.pop_back();
1082 }
1083
1084 PredCases.pop_back();
1085 --i;
1086 --e;
1087 }
1088
1089 // Reconstruct the new switch statement we will be building.
1090 if (PredDefault != BBDefault) {
1091 PredDefault->removePredecessor(Pred);
1092 PredDefault = BBDefault;
1093 NewSuccessors.push_back(BBDefault);
1094 }
1095
1096 unsigned CasesFromPred = Weights.size();
1097 uint64_t ValidTotalSuccWeight = 0;
1098 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1099 if (!PTIHandled.count(BBCases[i].Value) &&
1100 BBCases[i].Dest != BBDefault) {
1101 PredCases.push_back(BBCases[i]);
1102 NewSuccessors.push_back(BBCases[i].Dest);
1103 if (SuccHasWeights || PredHasWeights) {
1104 // The default weight is at index 0, so weight for the ith case
1105 // should be at index i+1. Scale the cases from successor by
1106 // PredDefaultWeight (Weights[0]).
1107 Weights.push_back(Weights[0] * SuccWeights[i + 1]);
1108 ValidTotalSuccWeight += SuccWeights[i + 1];
1109 }
1110 }
1111
1112 if (SuccHasWeights || PredHasWeights) {
1113 ValidTotalSuccWeight += SuccWeights[0];
1114 // Scale the cases from predecessor by ValidTotalSuccWeight.
1115 for (unsigned i = 1; i < CasesFromPred; ++i)
1116 Weights[i] *= ValidTotalSuccWeight;
1117 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
1118 Weights[0] *= SuccWeights[0];
1119 }
1120 } else {
1121 // If this is not the default destination from PSI, only the edges
1122 // in SI that occur in PSI with a destination of BB will be
1123 // activated.
1124 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1125 std::map<ConstantInt *, uint64_t> WeightsForHandled;
1126 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1127 if (PredCases[i].Dest == BB) {
1128 PTIHandled.insert(PredCases[i].Value);
1129
1130 if (PredHasWeights || SuccHasWeights) {
1131 WeightsForHandled[PredCases[i].Value] = Weights[i + 1];
1132 std::swap(Weights[i + 1], Weights.back());
1133 Weights.pop_back();
1134 }
1135
1136 std::swap(PredCases[i], PredCases.back());
1137 PredCases.pop_back();
1138 --i;
1139 --e;
1140 }
1141
1142 // Okay, now we know which constants were sent to BB from the
1143 // predecessor. Figure out where they will all go now.
1144 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1145 if (PTIHandled.count(BBCases[i].Value)) {
1146 // If this is one we are capable of getting...
1147 if (PredHasWeights || SuccHasWeights)
1148 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
1149 PredCases.push_back(BBCases[i]);
1150 NewSuccessors.push_back(BBCases[i].Dest);
1151 PTIHandled.erase(
1152 BBCases[i].Value); // This constant is taken care of
1153 }
1154
1155 // If there are any constants vectored to BB that TI doesn't handle,
1156 // they must go to the default destination of TI.
1157 for (ConstantInt *I : PTIHandled) {
1158 if (PredHasWeights || SuccHasWeights)
1159 Weights.push_back(WeightsForHandled[I]);
1160 PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault));
1161 NewSuccessors.push_back(BBDefault);
1162 }
1163 }
1164
1165 // Okay, at this point, we know which new successor Pred will get. Make
1166 // sure we update the number of entries in the PHI nodes for these
1167 // successors.
1168 for (BasicBlock *NewSuccessor : NewSuccessors)
1169 AddPredecessorToBlock(NewSuccessor, Pred, BB);
1170
1171 Builder.SetInsertPoint(PTI);
1172 // Convert pointer to int before we switch.
1173 if (CV->getType()->isPointerTy()) {
1174 CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()),
1175 "magicptr");
1176 }
1177
1178 // Now that the successors are updated, create the new Switch instruction.
1179 SwitchInst *NewSI =
1180 Builder.CreateSwitch(CV, PredDefault, PredCases.size());
1181 NewSI->setDebugLoc(PTI->getDebugLoc());
1182 for (ValueEqualityComparisonCase &V : PredCases)
1183 NewSI->addCase(V.Value, V.Dest);
1184
1185 if (PredHasWeights || SuccHasWeights) {
1186 // Halve the weights if any of them cannot fit in an uint32_t
1187 FitWeights(Weights);
1188
1189 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1190
1191 setBranchWeights(NewSI, MDWeights);
1192 }
1193
1194 EraseTerminatorInstAndDCECond(PTI);
1195
1196 // Okay, last check. If BB is still a successor of PSI, then we must
1197 // have an infinite loop case. If so, add an infinitely looping block
1198 // to handle the case to preserve the behavior of the code.
1199 BasicBlock *InfLoopBlock = nullptr;
1200 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1201 if (NewSI->getSuccessor(i) == BB) {
1202 if (!InfLoopBlock) {
1203 // Insert it at the end of the function, because it's either code,
1204 // or it won't matter if it's hot. :)
1205 InfLoopBlock = BasicBlock::Create(BB->getContext(), "infloop",
1206 BB->getParent());
1207 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1208 }
1209 NewSI->setSuccessor(i, InfLoopBlock);
1210 }
1211
1212 Changed = true;
1213 }
1214 }
1215 return Changed;
1216}
1217
1218// If we would need to insert a select that uses the value of this invoke
1219// (comments in HoistThenElseCodeToIf explain why we would need to do this), we
1220// can't hoist the invoke, as there is nowhere to put the select in this case.
1221static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1222 Instruction *I1, Instruction *I2) {
1223 for (BasicBlock *Succ : successors(BB1)) {
1224 for (const PHINode &PN : Succ->phis()) {
1225 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1226 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1227 if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
1228 return false;
1229 }
1230 }
1231 }
1232 return true;
1233}
1234
1235static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
1236
1237/// Given a conditional branch that goes to BB1 and BB2, hoist any common code
1238/// in the two blocks up into the branch block. The caller of this function
1239/// guarantees that BI's block dominates BB1 and BB2.
1240static bool HoistThenElseCodeToIf(BranchInst *BI,
1241 const TargetTransformInfo &TTI) {
1242 // This does very trivial matching, with limited scanning, to find identical
1243 // instructions in the two blocks. In particular, we don't want to get into
1244 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1245 // such, we currently just scan for obviously identical instructions in an
1246 // identical order.
1247 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1248 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1249
1250 BasicBlock::iterator BB1_Itr = BB1->begin();
1251 BasicBlock::iterator BB2_Itr = BB2->begin();
1252
1253 Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
1254 // Skip debug info if it is not identical.
1255 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1256 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1257 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1258 while (isa<DbgInfoIntrinsic>(I1))
1259 I1 = &*BB1_Itr++;
1260 while (isa<DbgInfoIntrinsic>(I2))
1261 I2 = &*BB2_Itr++;
1262 }
1263 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1264 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1265 return false;
1266
1267 BasicBlock *BIParent = BI->getParent();
1268
1269 bool Changed = false;
1270 do {
1271 // If we are hoisting the terminator instruction, don't move one (making a
1272 // broken BB), instead clone it, and remove BI.
1273 if (isa<TerminatorInst>(I1))
1274 goto HoistTerminator;
1275
1276 // If we're going to hoist a call, make sure that the two instructions we're
1277 // commoning/hoisting are both marked with musttail, or neither of them is
1278 // marked as such. Otherwise, we might end up in a situation where we hoist
1279 // from a block where the terminator is a `ret` to a block where the terminator
1280 // is a `br`, and `musttail` calls expect to be followed by a return.
1281 auto *C1 = dyn_cast<CallInst>(I1);
1282 auto *C2 = dyn_cast<CallInst>(I2);
1283 if (C1 && C2)
1284 if (C1->isMustTailCall() != C2->isMustTailCall())
1285 return Changed;
1286
1287 if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
1288 return Changed;
1289
1290 if (isa<DbgInfoIntrinsic>(I1) || isa<DbgInfoIntrinsic>(I2)) {
1291 assert (isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2))(static_cast <bool> (isa<DbgInfoIntrinsic>(I1) &&
isa<DbgInfoIntrinsic>(I2)) ? void (0) : __assert_fail (
"isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2)"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1291, __extension__ __PRETTY_FUNCTION__))
;
1292 // The debug location is an integral part of a debug info intrinsic
1293 // and can't be separated from it or replaced. Instead of attempting
1294 // to merge locations, simply hoist both copies of the intrinsic.
1295 BIParent->getInstList().splice(BI->getIterator(),
1296 BB1->getInstList(), I1);
1297 BIParent->getInstList().splice(BI->getIterator(),
1298 BB2->getInstList(), I2);
1299 Changed = true;
1300 } else {
1301 // For a normal instruction, we just move one to right before the branch,
1302 // then replace all uses of the other with the first. Finally, we remove
1303 // the now redundant second instruction.
1304 BIParent->getInstList().splice(BI->getIterator(),
1305 BB1->getInstList(), I1);
1306 if (!I2->use_empty())
1307 I2->replaceAllUsesWith(I1);
1308 I1->andIRFlags(I2);
1309 unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
1310 LLVMContext::MD_range,
1311 LLVMContext::MD_fpmath,
1312 LLVMContext::MD_invariant_load,
1313 LLVMContext::MD_nonnull,
1314 LLVMContext::MD_invariant_group,
1315 LLVMContext::MD_align,
1316 LLVMContext::MD_dereferenceable,
1317 LLVMContext::MD_dereferenceable_or_null,
1318 LLVMContext::MD_mem_parallel_loop_access};
1319 combineMetadata(I1, I2, KnownIDs);
1320
1321 // I1 and I2 are being combined into a single instruction. Its debug
1322 // location is the merged locations of the original instructions.
1323 I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
1324
1325 I2->eraseFromParent();
1326 Changed = true;
1327 }
1328
1329 I1 = &*BB1_Itr++;
1330 I2 = &*BB2_Itr++;
1331 // Skip debug info if it is not identical.
1332 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1333 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1334 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1335 while (isa<DbgInfoIntrinsic>(I1))
1336 I1 = &*BB1_Itr++;
1337 while (isa<DbgInfoIntrinsic>(I2))
1338 I2 = &*BB2_Itr++;
1339 }
1340 } while (I1->isIdenticalToWhenDefined(I2));
1341
1342 return true;
1343
1344HoistTerminator:
1345 // It may not be possible to hoist an invoke.
1346 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1347 return Changed;
1348
1349 for (BasicBlock *Succ : successors(BB1)) {
1350 for (PHINode &PN : Succ->phis()) {
1351 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1352 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1353 if (BB1V == BB2V)
1354 continue;
1355
1356 // Check for passingValueIsAlwaysUndefined here because we would rather
1357 // eliminate undefined control flow then converting it to a select.
1358 if (passingValueIsAlwaysUndefined(BB1V, &PN) ||
1359 passingValueIsAlwaysUndefined(BB2V, &PN))
1360 return Changed;
1361
1362 if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1363 return Changed;
1364 if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1365 return Changed;
1366 }
1367 }
1368
1369 // Okay, it is safe to hoist the terminator.
1370 Instruction *NT = I1->clone();
1371 BIParent->getInstList().insert(BI->getIterator(), NT);
1372 if (!NT->getType()->isVoidTy()) {
1373 I1->replaceAllUsesWith(NT);
1374 I2->replaceAllUsesWith(NT);
1375 NT->takeName(I1);
1376 }
1377
1378 IRBuilder<NoFolder> Builder(NT);
1379 // Hoisting one of the terminators from our successor is a great thing.
1380 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1381 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1382 // nodes, so we insert select instruction to compute the final result.
1383 std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
1384 for (BasicBlock *Succ : successors(BB1)) {
1385 for (PHINode &PN : Succ->phis()) {
1386 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1387 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1388 if (BB1V == BB2V)
1389 continue;
1390
1391 // These values do not agree. Insert a select instruction before NT
1392 // that determines the right value.
1393 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1394 if (!SI)
1395 SI = cast<SelectInst>(
1396 Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1397 BB1V->getName() + "." + BB2V->getName(), BI));
1398
1399 // Make the PHI node use the select for all incoming values for BB1/BB2
1400 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
1401 if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2)
1402 PN.setIncomingValue(i, SI);
1403 }
1404 }
1405
1406 // Update any PHI nodes in our new successors.
1407 for (BasicBlock *Succ : successors(BB1))
1408 AddPredecessorToBlock(Succ, BIParent, BB1);
1409
1410 EraseTerminatorInstAndDCECond(BI);
1411 return true;
1412}
1413
1414// All instructions in Insts belong to different blocks that all unconditionally
1415// branch to a common successor. Analyze each instruction and return true if it
1416// would be possible to sink them into their successor, creating one common
1417// instruction instead. For every value that would be required to be provided by
1418// PHI node (because an operand varies in each input block), add to PHIOperands.
1419static bool canSinkInstructions(
1420 ArrayRef<Instruction *> Insts,
1421 DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
1422 // Prune out obviously bad instructions to move. Any non-store instruction
1423 // must have exactly one use, and we check later that use is by a single,
1424 // common PHI instruction in the successor.
1425 for (auto *I : Insts) {
1426 // These instructions may change or break semantics if moved.
1427 if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
1428 I->getType()->isTokenTy())
1429 return false;
1430
1431 // Conservatively return false if I is an inline-asm instruction. Sinking
1432 // and merging inline-asm instructions can potentially create arguments
1433 // that cannot satisfy the inline-asm constraints.
1434 if (const auto *C = dyn_cast<CallInst>(I))
1435 if (C->isInlineAsm())
1436 return false;
1437
1438 // Everything must have only one use too, apart from stores which
1439 // have no uses.
1440 if (!isa<StoreInst>(I) && !I->hasOneUse())
1441 return false;
1442 }
1443
1444 const Instruction *I0 = Insts.front();
1445 for (auto *I : Insts)
1446 if (!I->isSameOperationAs(I0))
1447 return false;
1448
1449 // All instructions in Insts are known to be the same opcode. If they aren't
1450 // stores, check the only user of each is a PHI or in the same block as the
1451 // instruction, because if a user is in the same block as an instruction
1452 // we're contemplating sinking, it must already be determined to be sinkable.
1453 if (!isa<StoreInst>(I0)) {
1454 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1455 auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
1456 if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
1457 auto *U = cast<Instruction>(*I->user_begin());
1458 return (PNUse &&
1459 PNUse->getParent() == Succ &&
1460 PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
1461 U->getParent() == I->getParent();
1462 }))
1463 return false;
1464 }
1465
1466 // Because SROA can't handle speculating stores of selects, try not
1467 // to sink loads or stores of allocas when we'd have to create a PHI for
1468 // the address operand. Also, because it is likely that loads or stores
1469 // of allocas will disappear when Mem2Reg/SROA is run, don't sink them.
1470 // This can cause code churn which can have unintended consequences down
1471 // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244.
1472 // FIXME: This is a workaround for a deficiency in SROA - see
1473 // https://llvm.org/bugs/show_bug.cgi?id=30188
1474 if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) {
1475 return isa<AllocaInst>(I->getOperand(1));
1476 }))
1477 return false;
1478 if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) {
1479 return isa<AllocaInst>(I->getOperand(0));
1480 }))
1481 return false;
1482
1483 for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
1484 if (I0->getOperand(OI)->getType()->isTokenTy())
1485 // Don't touch any operand of token type.
1486 return false;
1487
1488 auto SameAsI0 = [&I0, OI](const Instruction *I) {
1489 assert(I->getNumOperands() == I0->getNumOperands())(static_cast <bool> (I->getNumOperands() == I0->getNumOperands
()) ? void (0) : __assert_fail ("I->getNumOperands() == I0->getNumOperands()"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1489, __extension__ __PRETTY_FUNCTION__))
;
1490 return I->getOperand(OI) == I0->getOperand(OI);
1491 };
1492 if (!all_of(Insts, SameAsI0)) {
1493 if (!canReplaceOperandWithVariable(I0, OI))
1494 // We can't create a PHI from this GEP.
1495 return false;
1496 // Don't create indirect calls! The called value is the final operand.
1497 if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI == OE - 1) {
1498 // FIXME: if the call was *already* indirect, we should do this.
1499 return false;
1500 }
1501 for (auto *I : Insts)
1502 PHIOperands[I].push_back(I->getOperand(OI));
1503 }
1504 }
1505 return true;
1506}
1507
1508// Assuming canSinkLastInstruction(Blocks) has returned true, sink the last
1509// instruction of every block in Blocks to their common successor, commoning
1510// into one instruction.
1511static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
1512 auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
1513
1514 // canSinkLastInstruction returning true guarantees that every block has at
1515 // least one non-terminator instruction.
1516 SmallVector<Instruction*,4> Insts;
1517 for (auto *BB : Blocks) {
1518 Instruction *I = BB->getTerminator();
1519 do {
1520 I = I->getPrevNode();
1521 } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
1522 if (!isa<DbgInfoIntrinsic>(I))
1523 Insts.push_back(I);
1524 }
1525
1526 // The only checking we need to do now is that all users of all instructions
1527 // are the same PHI node. canSinkLastInstruction should have checked this but
1528 // it is slightly over-aggressive - it gets confused by commutative instructions
1529 // so double-check it here.
1530 Instruction *I0 = Insts.front();
1531 if (!isa<StoreInst>(I0)) {
1532 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1533 if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
1534 auto *U = cast<Instruction>(*I->user_begin());
1535 return U == PNUse;
1536 }))
1537 return false;
1538 }
1539
1540 // We don't need to do any more checking here; canSinkLastInstruction should
1541 // have done it all for us.
1542 SmallVector<Value*, 4> NewOperands;
1543 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
1544 // This check is different to that in canSinkLastInstruction. There, we
1545 // cared about the global view once simplifycfg (and instcombine) have
1546 // completed - it takes into account PHIs that become trivially
1547 // simplifiable. However here we need a more local view; if an operand
1548 // differs we create a PHI and rely on instcombine to clean up the very
1549 // small mess we may make.
1550 bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
1551 return I->getOperand(O) != I0->getOperand(O);
1552 });
1553 if (!NeedPHI) {
1554 NewOperands.push_back(I0->getOperand(O));
1555 continue;
1556 }
1557
1558 // Create a new PHI in the successor block and populate it.
1559 auto *Op = I0->getOperand(O);
1560 assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!")(static_cast <bool> (!Op->getType()->isTokenTy() &&
"Can't PHI tokens!") ? void (0) : __assert_fail ("!Op->getType()->isTokenTy() && \"Can't PHI tokens!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1560, __extension__ __PRETTY_FUNCTION__))
;
1561 auto *PN = PHINode::Create(Op->getType(), Insts.size(),
1562 Op->getName() + ".sink", &BBEnd->front());
1563 for (auto *I : Insts)
1564 PN->addIncoming(I->getOperand(O), I->getParent());
1565 NewOperands.push_back(PN);
1566 }
1567
1568 // Arbitrarily use I0 as the new "common" instruction; remap its operands
1569 // and move it to the start of the successor block.
1570 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
1571 I0->getOperandUse(O).set(NewOperands[O]);
1572 I0->moveBefore(&*BBEnd->getFirstInsertionPt());
1573
1574 // Update metadata and IR flags, and merge debug locations.
1575 for (auto *I : Insts)
1576 if (I != I0) {
1577 // The debug location for the "common" instruction is the merged locations
1578 // of all the commoned instructions. We start with the original location
1579 // of the "common" instruction and iteratively merge each location in the
1580 // loop below.
1581 // This is an N-way merge, which will be inefficient if I0 is a CallInst.
1582 // However, as N-way merge for CallInst is rare, so we use simplified API
1583 // instead of using complex API for N-way merge.
1584 I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc());
1585 combineMetadataForCSE(I0, I);
1586 I0->andIRFlags(I);
1587 }
1588
1589 if (!isa<StoreInst>(I0)) {
1590 // canSinkLastInstruction checked that all instructions were used by
1591 // one and only one PHI node. Find that now, RAUW it to our common
1592 // instruction and nuke it.
1593 assert(I0->hasOneUse())(static_cast <bool> (I0->hasOneUse()) ? void (0) : __assert_fail
("I0->hasOneUse()", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1593, __extension__ __PRETTY_FUNCTION__))
;
1594 auto *PN = cast<PHINode>(*I0->user_begin());
1595 PN->replaceAllUsesWith(I0);
1596 PN->eraseFromParent();
1597 }
1598
1599 // Finally nuke all instructions apart from the common instruction.
1600 for (auto *I : Insts)
1601 if (I != I0)
1602 I->eraseFromParent();
1603
1604 return true;
1605}
1606
1607namespace {
1608
1609 // LockstepReverseIterator - Iterates through instructions
1610 // in a set of blocks in reverse order from the first non-terminator.
1611 // For example (assume all blocks have size n):
1612 // LockstepReverseIterator I([B1, B2, B3]);
1613 // *I-- = [B1[n], B2[n], B3[n]];
1614 // *I-- = [B1[n-1], B2[n-1], B3[n-1]];
1615 // *I-- = [B1[n-2], B2[n-2], B3[n-2]];
1616 // ...
1617 class LockstepReverseIterator {
1618 ArrayRef<BasicBlock*> Blocks;
1619 SmallVector<Instruction*,4> Insts;
1620 bool Fail;
1621
1622 public:
1623 LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) : Blocks(Blocks) {
1624 reset();
1625 }
1626
1627 void reset() {
1628 Fail = false;
1629 Insts.clear();
1630 for (auto *BB : Blocks) {
1631 Instruction *Inst = BB->getTerminator();
1632 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1633 Inst = Inst->getPrevNode();
1634 if (!Inst) {
1635 // Block wasn't big enough.
1636 Fail = true;
1637 return;
1638 }
1639 Insts.push_back(Inst);
1640 }
1641 }
1642
1643 bool isValid() const {
1644 return !Fail;
1645 }
1646
1647 void operator--() {
1648 if (Fail)
1649 return;
1650 for (auto *&Inst : Insts) {
1651 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1652 Inst = Inst->getPrevNode();
1653 // Already at beginning of block.
1654 if (!Inst) {
1655 Fail = true;
1656 return;
1657 }
1658 }
1659 }
1660
1661 ArrayRef<Instruction*> operator * () const {
1662 return Insts;
1663 }
1664 };
1665
1666} // end anonymous namespace
1667
1668/// Check whether BB's predecessors end with unconditional branches. If it is
1669/// true, sink any common code from the predecessors to BB.
1670/// We also allow one predecessor to end with conditional branch (but no more
1671/// than one).
1672static bool SinkCommonCodeFromPredecessors(BasicBlock *BB) {
1673 // We support two situations:
1674 // (1) all incoming arcs are unconditional
1675 // (2) one incoming arc is conditional
1676 //
1677 // (2) is very common in switch defaults and
1678 // else-if patterns;
1679 //
1680 // if (a) f(1);
1681 // else if (b) f(2);
1682 //
1683 // produces:
1684 //
1685 // [if]
1686 // / \
1687 // [f(1)] [if]
1688 // | | \
1689 // | | |
1690 // | [f(2)]|
1691 // \ | /
1692 // [ end ]
1693 //
1694 // [end] has two unconditional predecessor arcs and one conditional. The
1695 // conditional refers to the implicit empty 'else' arc. This conditional
1696 // arc can also be caused by an empty default block in a switch.
1697 //
1698 // In this case, we attempt to sink code from all *unconditional* arcs.
1699 // If we can sink instructions from these arcs (determined during the scan
1700 // phase below) we insert a common successor for all unconditional arcs and
1701 // connect that to [end], to enable sinking:
1702 //
1703 // [if]
1704 // / \
1705 // [x(1)] [if]
1706 // | | \
1707 // | | \
1708 // | [x(2)] |
1709 // \ / |
1710 // [sink.split] |
1711 // \ /
1712 // [ end ]
1713 //
1714 SmallVector<BasicBlock*,4> UnconditionalPreds;
1715 Instruction *Cond = nullptr;
1716 for (auto *B : predecessors(BB)) {
1717 auto *T = B->getTerminator();
1718 if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional())
1719 UnconditionalPreds.push_back(B);
1720 else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond)
1721 Cond = T;
1722 else
1723 return false;
1724 }
1725 if (UnconditionalPreds.size() < 2)
1726 return false;
1727
1728 bool Changed = false;
1729 // We take a two-step approach to tail sinking. First we scan from the end of
1730 // each block upwards in lockstep. If the n'th instruction from the end of each
1731 // block can be sunk, those instructions are added to ValuesToSink and we
1732 // carry on. If we can sink an instruction but need to PHI-merge some operands
1733 // (because they're not identical in each instruction) we add these to
1734 // PHIOperands.
1735 unsigned ScanIdx = 0;
1736 SmallPtrSet<Value*,4> InstructionsToSink;
1737 DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands;
1738 LockstepReverseIterator LRI(UnconditionalPreds);
1739 while (LRI.isValid() &&
1740 canSinkInstructions(*LRI, PHIOperands)) {
1741 LLVM_DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0]do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: instruction can be sunk: "
<< *(*LRI)[0] << "\n"; } } while (false)
1742 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: instruction can be sunk: "
<< *(*LRI)[0] << "\n"; } } while (false)
;
1743 InstructionsToSink.insert((*LRI).begin(), (*LRI).end());
1744 ++ScanIdx;
1745 --LRI;
1746 }
1747
1748 auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
1749 unsigned NumPHIdValues = 0;
1750 for (auto *I : *LRI)
1751 for (auto *V : PHIOperands[I])
1752 if (InstructionsToSink.count(V) == 0)
1753 ++NumPHIdValues;
1754 LLVM_DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: #phid values: " <<
NumPHIdValues << "\n"; } } while (false)
;
1755 unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size();
1756 if ((NumPHIdValues % UnconditionalPreds.size()) != 0)
1757 NumPHIInsts++;
1758
1759 return NumPHIInsts <= 1;
1760 };
1761
1762 if (ScanIdx > 0 && Cond) {
1763 // Check if we would actually sink anything first! This mutates the CFG and
1764 // adds an extra block. The goal in doing this is to allow instructions that
1765 // couldn't be sunk before to be sunk - obviously, speculatable instructions
1766 // (such as trunc, add) can be sunk and predicated already. So we check that
1767 // we're going to sink at least one non-speculatable instruction.
1768 LRI.reset();
1769 unsigned Idx = 0;
1770 bool Profitable = false;
1771 while (ProfitableToSinkInstruction(LRI) && Idx < ScanIdx) {
1772 if (!isSafeToSpeculativelyExecute((*LRI)[0])) {
1773 Profitable = true;
1774 break;
1775 }
1776 --LRI;
1777 ++Idx;
1778 }
1779 if (!Profitable)
1780 return false;
1781
1782 LLVM_DEBUG(dbgs() << "SINK: Splitting edge\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Splitting edge\n"; }
} while (false)
;
1783 // We have a conditional edge and we're going to sink some instructions.
1784 // Insert a new block postdominating all blocks we're going to sink from.
1785 if (!SplitBlockPredecessors(BB, UnconditionalPreds, ".sink.split"))
1786 // Edges couldn't be split.
1787 return false;
1788 Changed = true;
1789 }
1790
1791 // Now that we've analyzed all potential sinking candidates, perform the
1792 // actual sink. We iteratively sink the last non-terminator of the source
1793 // blocks into their common successor unless doing so would require too
1794 // many PHI instructions to be generated (currently only one PHI is allowed
1795 // per sunk instruction).
1796 //
1797 // We can use InstructionsToSink to discount values needing PHI-merging that will
1798 // actually be sunk in a later iteration. This allows us to be more
1799 // aggressive in what we sink. This does allow a false positive where we
1800 // sink presuming a later value will also be sunk, but stop half way through
1801 // and never actually sink it which means we produce more PHIs than intended.
1802 // This is unlikely in practice though.
1803 for (unsigned SinkIdx = 0; SinkIdx != ScanIdx; ++SinkIdx) {
1804 LLVM_DEBUG(dbgs() << "SINK: Sink: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1805 << *UnconditionalPreds[0]->getTerminator()->getPrevNode()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1806 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
;
1807
1808 // Because we've sunk every instruction in turn, the current instruction to
1809 // sink is always at index 0.
1810 LRI.reset();
1811 if (!ProfitableToSinkInstruction(LRI)) {
1812 // Too many PHIs would be created.
1813 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: stopping here, too many PHIs would be created!\n"
; } } while (false)
1814 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)
;
1815 break;
1816 }
1817
1818 if (!sinkLastInstruction(UnconditionalPreds))
1819 return Changed;
1820 NumSinkCommons++;
1821 Changed = true;
1822 }
1823 return Changed;
1824}
1825
1826/// Determine if we can hoist sink a sole store instruction out of a
1827/// conditional block.
1828///
1829/// We are looking for code like the following:
1830/// BrBB:
1831/// store i32 %add, i32* %arrayidx2
1832/// ... // No other stores or function calls (we could be calling a memory
1833/// ... // function).
1834/// %cmp = icmp ult %x, %y
1835/// br i1 %cmp, label %EndBB, label %ThenBB
1836/// ThenBB:
1837/// store i32 %add5, i32* %arrayidx2
1838/// br label EndBB
1839/// EndBB:
1840/// ...
1841/// We are going to transform this into:
1842/// BrBB:
1843/// store i32 %add, i32* %arrayidx2
1844/// ... //
1845/// %cmp = icmp ult %x, %y
1846/// %add.add5 = select i1 %cmp, i32 %add, %add5
1847/// store i32 %add.add5, i32* %arrayidx2
1848/// ...
1849///
1850/// \return The pointer to the value of the previous store if the store can be
1851/// hoisted into the predecessor block. 0 otherwise.
1852static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1853 BasicBlock *StoreBB, BasicBlock *EndBB) {
1854 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1855 if (!StoreToHoist)
1856 return nullptr;
1857
1858 // Volatile or atomic.
1859 if (!StoreToHoist->isSimple())
1860 return nullptr;
1861
1862 Value *StorePtr = StoreToHoist->getPointerOperand();
1863
1864 // Look for a store to the same pointer in BrBB.
1865 unsigned MaxNumInstToLookAt = 9;
1866 for (Instruction &CurI : reverse(BrBB->instructionsWithoutDebug())) {
1867 if (!MaxNumInstToLookAt)
1868 break;
1869 --MaxNumInstToLookAt;
1870
1871 // Could be calling an instruction that affects memory like free().
1872 if (CurI.mayHaveSideEffects() && !isa<StoreInst>(CurI))
1873 return nullptr;
1874
1875 if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
1876 // Found the previous store make sure it stores to the same location.
1877 if (SI->getPointerOperand() == StorePtr)
1878 // Found the previous store, return its value operand.
1879 return SI->getValueOperand();
1880 return nullptr; // Unknown store.
1881 }
1882 }
1883
1884 return nullptr;
1885}
1886
1887/// Speculate a conditional basic block flattening the CFG.
1888///
1889/// Note that this is a very risky transform currently. Speculating
1890/// instructions like this is most often not desirable. Instead, there is an MI
1891/// pass which can do it with full awareness of the resource constraints.
1892/// However, some cases are "obvious" and we should do directly. An example of
1893/// this is speculating a single, reasonably cheap instruction.
1894///
1895/// There is only one distinct advantage to flattening the CFG at the IR level:
1896/// it makes very common but simplistic optimizations such as are common in
1897/// instcombine and the DAG combiner more powerful by removing CFG edges and
1898/// modeling their effects with easier to reason about SSA value graphs.
1899///
1900///
1901/// An illustration of this transform is turning this IR:
1902/// \code
1903/// BB:
1904/// %cmp = icmp ult %x, %y
1905/// br i1 %cmp, label %EndBB, label %ThenBB
1906/// ThenBB:
1907/// %sub = sub %x, %y
1908/// br label BB2
1909/// EndBB:
1910/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1911/// ...
1912/// \endcode
1913///
1914/// Into this IR:
1915/// \code
1916/// BB:
1917/// %cmp = icmp ult %x, %y
1918/// %sub = sub %x, %y
1919/// %cond = select i1 %cmp, 0, %sub
1920/// ...
1921/// \endcode
1922///
1923/// \returns true if the conditional block is removed.
1924static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
1925 const TargetTransformInfo &TTI) {
1926 // Be conservative for now. FP select instruction can often be expensive.
1927 Value *BrCond = BI->getCondition();
1928 if (isa<FCmpInst>(BrCond))
1929 return false;
1930
1931 BasicBlock *BB = BI->getParent();
1932 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1933
1934 // If ThenBB is actually on the false edge of the conditional branch, remember
1935 // to swap the select operands later.
1936 bool Invert = false;
1937 if (ThenBB != BI->getSuccessor(0)) {
1938 assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?")(static_cast <bool> (ThenBB == BI->getSuccessor(1) &&
"No edge from 'if' block?") ? void (0) : __assert_fail ("ThenBB == BI->getSuccessor(1) && \"No edge from 'if' block?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1938, __extension__ __PRETTY_FUNCTION__))
;
1939 Invert = true;
1940 }
1941 assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block")(static_cast <bool> (EndBB == BI->getSuccessor(!Invert
) && "No edge from to end block") ? void (0) : __assert_fail
("EndBB == BI->getSuccessor(!Invert) && \"No edge from to end block\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1941, __extension__ __PRETTY_FUNCTION__))
;
1942
1943 // Keep a count of how many times instructions are used within CondBB when
1944 // they are candidates for sinking into CondBB. Specifically:
1945 // - They are defined in BB, and
1946 // - They have no side effects, and
1947 // - All of their uses are in CondBB.
1948 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1949
1950 SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics;
1951
1952 unsigned SpeculationCost = 0;
1953 Value *SpeculatedStoreValue = nullptr;
1954 StoreInst *SpeculatedStore = nullptr;
1955 for (BasicBlock::iterator BBI = ThenBB->begin(),
1956 BBE = std::prev(ThenBB->end());
1957 BBI != BBE; ++BBI) {
1958 Instruction *I = &*BBI;
1959 // Skip debug info.
1960 if (isa<DbgInfoIntrinsic>(I)) {
1961 SpeculatedDbgIntrinsics.push_back(I);
1962 continue;
1963 }
1964
1965 // Only speculatively execute a single instruction (not counting the
1966 // terminator) for now.
1967 ++SpeculationCost;
1968 if (SpeculationCost > 1)
1969 return false;
1970
1971 // Don't hoist the instruction if it's unsafe or expensive.
1972 if (!isSafeToSpeculativelyExecute(I) &&
1973 !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
1974 I, BB, ThenBB, EndBB))))
1975 return false;
1976 if (!SpeculatedStoreValue &&
1977 ComputeSpeculationCost(I, TTI) >
1978 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
1979 return false;
1980
1981 // Store the store speculation candidate.
1982 if (SpeculatedStoreValue)
1983 SpeculatedStore = cast<StoreInst>(I);
1984
1985 // Do not hoist the instruction if any of its operands are defined but not
1986 // used in BB. The transformation will prevent the operand from
1987 // being sunk into the use block.
1988 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1989 Instruction *OpI = dyn_cast<Instruction>(*i);
1990 if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects())
1991 continue; // Not a candidate for sinking.
1992
1993 ++SinkCandidateUseCounts[OpI];
1994 }
1995 }
1996
1997 // Consider any sink candidates which are only used in CondBB as costs for
1998 // speculation. Note, while we iterate over a DenseMap here, we are summing
1999 // and so iteration order isn't significant.
2000 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator
2001 I = SinkCandidateUseCounts.begin(),
2002 E = SinkCandidateUseCounts.end();
2003 I != E; ++I)
2004 if (I->first->getNumUses() == I->second) {
2005 ++SpeculationCost;
2006 if (SpeculationCost > 1)
2007 return false;
2008 }
2009
2010 // Check that the PHI nodes can be converted to selects.
2011 bool HaveRewritablePHIs = false;
2012 for (PHINode &PN : EndBB->phis()) {
2013 Value *OrigV = PN.getIncomingValueForBlock(BB);
2014 Value *ThenV = PN.getIncomingValueForBlock(ThenBB);
2015
2016 // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
2017 // Skip PHIs which are trivial.
2018 if (ThenV == OrigV)
2019 continue;
2020
2021 // Don't convert to selects if we could remove undefined behavior instead.
2022 if (passingValueIsAlwaysUndefined(OrigV, &PN) ||
2023 passingValueIsAlwaysUndefined(ThenV, &PN))
2024 return false;
2025
2026 HaveRewritablePHIs = true;
2027 ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
2028 ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
2029 if (!OrigCE && !ThenCE)
2030 continue; // Known safe and cheap.
2031
2032 if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
2033 (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
2034 return false;
2035 unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0;
2036 unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0;
2037 unsigned MaxCost =
2038 2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2039 if (OrigCost + ThenCost > MaxCost)
2040 return false;
2041
2042 // Account for the cost of an unfolded ConstantExpr which could end up
2043 // getting expanded into Instructions.
2044 // FIXME: This doesn't account for how many operations are combined in the
2045 // constant expression.
2046 ++SpeculationCost;
2047 if (SpeculationCost > 1)
2048 return false;
2049 }
2050
2051 // If there are no PHIs to process, bail early. This helps ensure idempotence
2052 // as well.
2053 if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
2054 return false;
2055
2056 // If we get here, we can hoist the instruction and if-convert.
2057 LLVM_DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SPECULATIVELY EXECUTING BB"
<< *ThenBB << "\n";; } } while (false)
;
2058
2059 // Insert a select of the value of the speculated store.
2060 if (SpeculatedStoreValue) {
2061 IRBuilder<NoFolder> Builder(BI);
2062 Value *TrueV = SpeculatedStore->getValueOperand();
2063 Value *FalseV = SpeculatedStoreValue;
2064 if (Invert)
2065 std::swap(TrueV, FalseV);
2066 Value *S = Builder.CreateSelect(
2067 BrCond, TrueV, FalseV, "spec.store.select", BI);
2068 SpeculatedStore->setOperand(0, S);
2069 SpeculatedStore->applyMergedLocation(BI->getDebugLoc(),
2070 SpeculatedStore->getDebugLoc());
2071 }
2072
2073 // Metadata can be dependent on the condition we are hoisting above.
2074 // Conservatively strip all metadata on the instruction.
2075 for (auto &I : *ThenBB)
2076 I.dropUnknownNonDebugMetadata();
2077
2078 // Hoist the instructions.
2079 BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
2080 ThenBB->begin(), std::prev(ThenBB->end()));
2081
2082 // Insert selects and rewrite the PHI operands.
2083 IRBuilder<NoFolder> Builder(BI);
2084 for (PHINode &PN : EndBB->phis()) {
2085 unsigned OrigI = PN.getBasicBlockIndex(BB);
2086 unsigned ThenI = PN.getBasicBlockIndex(ThenBB);
2087 Value *OrigV = PN.getIncomingValue(OrigI);
2088 Value *ThenV = PN.getIncomingValue(ThenI);
2089
2090 // Skip PHIs which are trivial.
2091 if (OrigV == ThenV)
2092 continue;
2093
2094 // Create a select whose true value is the speculatively executed value and
2095 // false value is the preexisting value. Swap them if the branch
2096 // destinations were inverted.
2097 Value *TrueV = ThenV, *FalseV = OrigV;
2098 if (Invert)
2099 std::swap(TrueV, FalseV);
2100 Value *V = Builder.CreateSelect(
2101 BrCond, TrueV, FalseV, "spec.select", BI);
2102 PN.setIncomingValue(OrigI, V);
2103 PN.setIncomingValue(ThenI, V);
2104 }
2105
2106 // Remove speculated dbg intrinsics.
2107 // FIXME: Is it possible to do this in a more elegant way? Moving/merging the
2108 // dbg value for the different flows and inserting it after the select.
2109 for (Instruction *I : SpeculatedDbgIntrinsics)
2110 I->eraseFromParent();
2111
2112 ++NumSpeculations;
2113 return true;
2114}
2115
2116/// Return true if we can thread a branch across this block.
2117static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
2118 unsigned Size = 0;
2119
2120 for (Instruction &I : BB->instructionsWithoutDebug()) {
2121 if (Size > 10)
2122 return false; // Don't clone large BB's.
2123 ++Size;
2124
2125 // We can only support instructions that do not define values that are
2126 // live outside of the current basic block.
2127 for (User *U : I.users()) {
2128 Instruction *UI = cast<Instruction>(U);
2129 if (UI->getParent() != BB || isa<PHINode>(UI))
2130 return false;
2131 }
2132
2133 // Looks ok, continue checking.
2134 }
2135
2136 return true;
2137}
2138
2139/// If we have a conditional branch on a PHI node value that is defined in the
2140/// same block as the branch and if any PHI entries are constants, thread edges
2141/// corresponding to that entry to be branches to their ultimate destination.
2142static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL,
2143 AssumptionCache *AC) {
2144 BasicBlock *BB = BI->getParent();
2145 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
2146 // NOTE: we currently cannot transform this case if the PHI node is used
2147 // outside of the block.
2148 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
2149 return false;
2150
2151 // Degenerate case of a single entry PHI.
2152 if (PN->getNumIncomingValues() == 1) {
2153 FoldSingleEntryPHINodes(PN->getParent());
2154 return true;
2155 }
2156
2157 // Now we know that this block has multiple preds and two succs.
2158 if (!BlockIsSimpleEnoughToThreadThrough(BB))
2159 return false;
2160
2161 // Can't fold blocks that contain noduplicate or convergent calls.
2162 if (any_of(*BB, [](const Instruction &I) {
2163 const CallInst *CI = dyn_cast<CallInst>(&I);
2164 return CI && (CI->cannotDuplicate() || CI->isConvergent());
2165 }))
2166 return false;
2167
2168 // Okay, this is a simple enough basic block. See if any phi values are
2169 // constants.
2170 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2171 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
2172 if (!CB || !CB->getType()->isIntegerTy(1))
2173 continue;
2174
2175 // Okay, we now know that all edges from PredBB should be revectored to
2176 // branch to RealDest.
2177 BasicBlock *PredBB = PN->getIncomingBlock(i);
2178 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
2179
2180 if (RealDest == BB)
2181 continue; // Skip self loops.
2182 // Skip if the predecessor's terminator is an indirect branch.
2183 if (isa<IndirectBrInst>(PredBB->getTerminator()))
2184 continue;
2185
2186 // The dest block might have PHI nodes, other predecessors and other
2187 // difficult cases. Instead of being smart about this, just insert a new
2188 // block that jumps to the destination block, effectively splitting
2189 // the edge we are about to create.
2190 BasicBlock *EdgeBB =
2191 BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge",
2192 RealDest->getParent(), RealDest);
2193 BranchInst::Create(RealDest, EdgeBB);
2194
2195 // Update PHI nodes.
2196 AddPredecessorToBlock(RealDest, EdgeBB, BB);
2197
2198 // BB may have instructions that are being threaded over. Clone these
2199 // instructions into EdgeBB. We know that there will be no uses of the
2200 // cloned instructions outside of EdgeBB.
2201 BasicBlock::iterator InsertPt = EdgeBB->begin();
2202 DenseMap<Value *, Value *> TranslateMap; // Track translated values.
2203 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2204 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
2205 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
2206 continue;
2207 }
2208 // Clone the instruction.
2209 Instruction *N = BBI->clone();
2210 if (BBI->hasName())
2211 N->setName(BBI->getName() + ".c");
2212
2213 // Update operands due to translation.
2214 for (User::op_iterator i = N->op_begin(), e = N->op_end(); i != e; ++i) {
2215 DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(*i);
2216 if (PI != TranslateMap.end())
2217 *i = PI->second;
2218 }
2219
2220 // Check for trivial simplification.
2221 if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) {
2222 if (!BBI->use_empty())
2223 TranslateMap[&*BBI] = V;
2224 if (!N->mayHaveSideEffects()) {
2225 N->deleteValue(); // Instruction folded away, don't need actual inst
2226 N = nullptr;
2227 }
2228 } else {
2229 if (!BBI->use_empty())
2230 TranslateMap[&*BBI] = N;
2231 }
2232 // Insert the new instruction into its new home.
2233 if (N)
2234 EdgeBB->getInstList().insert(InsertPt, N);
2235
2236 // Register the new instruction with the assumption cache if necessary.
2237 if (auto *II = dyn_cast_or_null<IntrinsicInst>(N))
2238 if (II->getIntrinsicID() == Intrinsic::assume)
2239 AC->registerAssumption(II);
2240 }
2241
2242 // Loop over all of the edges from PredBB to BB, changing them to branch
2243 // to EdgeBB instead.
2244 TerminatorInst *PredBBTI = PredBB->getTerminator();
2245 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
2246 if (PredBBTI->getSuccessor(i) == BB) {
2247 BB->removePredecessor(PredBB);
2248 PredBBTI->setSuccessor(i, EdgeBB);
2249 }
2250
2251 // Recurse, simplifying any other constants.
2252 return FoldCondBranchOnPHI(BI, DL, AC) | true;
2253 }
2254
2255 return false;
2256}
2257
2258/// Given a BB that starts with the specified two-entry PHI node,
2259/// see if we can eliminate it.
2260static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
2261 const DataLayout &DL) {
2262 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
2263 // statement", which has a very simple dominance structure. Basically, we
2264 // are trying to find the condition that is being branched on, which
2265 // subsequently causes this merge to happen. We really want control
2266 // dependence information for this check, but simplifycfg can't keep it up
2267 // to date, and this catches most of the cases we care about anyway.
2268 BasicBlock *BB = PN->getParent();
2269 const Function *Fn = BB->getParent();
2270 if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing))
2271 return false;
2272
2273 BasicBlock *IfTrue, *IfFalse;
2274 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
2275 if (!IfCond ||
2276 // Don't bother if the branch will be constant folded trivially.
2277 isa<ConstantInt>(IfCond))
2278 return false;
2279
2280 // Okay, we found that we can merge this two-entry phi node into a select.
2281 // Doing so would require us to fold *all* two entry phi nodes in this block.
2282 // At some point this becomes non-profitable (particularly if the target
2283 // doesn't support cmov's). Only do this transformation if there are two or
2284 // fewer PHI nodes in this block.
2285 unsigned NumPhis = 0;
2286 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
2287 if (NumPhis > 2)
2288 return false;
2289
2290 // Loop over the PHI's seeing if we can promote them all to select
2291 // instructions. While we are at it, keep track of the instructions
2292 // that need to be moved to the dominating block.
2293 SmallPtrSet<Instruction *, 4> AggressiveInsts;
2294 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
2295 MaxCostVal1 = PHINodeFoldingThreshold;
2296 MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
2297 MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
2298
2299 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
2300 PHINode *PN = cast<PHINode>(II++);
2301 if (Value *V = SimplifyInstruction(PN, {DL, PN})) {
2302 PN->replaceAllUsesWith(V);
2303 PN->eraseFromParent();
2304 continue;
2305 }
2306
2307 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
2308 MaxCostVal0, TTI) ||
2309 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
2310 MaxCostVal1, TTI))
2311 return false;
2312 }
2313
2314 // If we folded the first phi, PN dangles at this point. Refresh it. If
2315 // we ran out of PHIs then we simplified them all.
2316 PN = dyn_cast<PHINode>(BB->begin());
2317 if (!PN)
2318 return true;
2319
2320 // Don't fold i1 branches on PHIs which contain binary operators. These can
2321 // often be turned into switches and other things.
2322 if (PN->getType()->isIntegerTy(1) &&
2323 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
2324 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
2325 isa<BinaryOperator>(IfCond)))
2326 return false;
2327
2328 // If all PHI nodes are promotable, check to make sure that all instructions
2329 // in the predecessor blocks can be promoted as well. If not, we won't be able
2330 // to get rid of the control flow, so it's not worth promoting to select
2331 // instructions.
2332 BasicBlock *DomBlock = nullptr;
2333 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
2334 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
2335 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
2336 IfBlock1 = nullptr;
2337 } else {
2338 DomBlock = *pred_begin(IfBlock1);
2339 for (BasicBlock::iterator I = IfBlock1->begin(); !isa<TerminatorInst>(I);
2340 ++I)
2341 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2342 // This is not an aggressive instruction that we can promote.
2343 // Because of this, we won't be able to get rid of the control flow, so
2344 // the xform is not worth it.
2345 return false;
2346 }
2347 }
2348
2349 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
2350 IfBlock2 = nullptr;
2351 } else {
2352 DomBlock = *pred_begin(IfBlock2);
2353 for (BasicBlock::iterator I = IfBlock2->begin(); !isa<TerminatorInst>(I);
2354 ++I)
2355 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2356 // This is not an aggressive instruction that we can promote.
2357 // Because of this, we won't be able to get rid of the control flow, so
2358 // the xform is not worth it.
2359 return false;
2360 }
2361 }
2362
2363 LLVM_DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfConddo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
2364 << " T: " << IfTrue->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
2365 << " 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)
;
2366
2367 // If we can still promote the PHI nodes after this gauntlet of tests,
2368 // do all of the PHI's now.
2369 Instruction *InsertPt = DomBlock->getTerminator();
2370 IRBuilder<NoFolder> Builder(InsertPt);
2371
2372 // Move all 'aggressive' instructions, which are defined in the
2373 // conditional parts of the if's up to the dominating block.
2374 if (IfBlock1) {
2375 for (auto &I : *IfBlock1)
2376 I.dropUnknownNonDebugMetadata();
2377 DomBlock->getInstList().splice(InsertPt->getIterator(),
2378 IfBlock1->getInstList(), IfBlock1->begin(),
2379 IfBlock1->getTerminator()->getIterator());
2380 }
2381 if (IfBlock2) {
2382 for (auto &I : *IfBlock2)
2383 I.dropUnknownNonDebugMetadata();
2384 DomBlock->getInstList().splice(InsertPt->getIterator(),
2385 IfBlock2->getInstList(), IfBlock2->begin(),
2386 IfBlock2->getTerminator()->getIterator());
2387 }
2388
2389 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
2390 // Change the PHI node into a select instruction.
2391 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
2392 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
2393
2394 Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", InsertPt);
2395 PN->replaceAllUsesWith(Sel);
2396 Sel->takeName(PN);
2397 PN->eraseFromParent();
2398 }
2399
2400 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
2401 // has been flattened. Change DomBlock to jump directly to our new block to
2402 // avoid other simplifycfg's kicking in on the diamond.
2403 TerminatorInst *OldTI = DomBlock->getTerminator();
2404 Builder.SetInsertPoint(OldTI);
2405 Builder.CreateBr(BB);
2406 OldTI->eraseFromParent();
2407 return true;
2408}
2409
2410/// If we found a conditional branch that goes to two returning blocks,
2411/// try to merge them together into one return,
2412/// introducing a select if the return values disagree.
2413static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
2414 IRBuilder<> &Builder) {
2415 assert(BI->isConditional() && "Must be a conditional branch")(static_cast <bool> (BI->isConditional() && "Must be a conditional branch"
) ? void (0) : __assert_fail ("BI->isConditional() && \"Must be a conditional branch\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2415, __extension__ __PRETTY_FUNCTION__))
;
2416 BasicBlock *TrueSucc = BI->getSuccessor(0);
2417 BasicBlock *FalseSucc = BI->getSuccessor(1);
2418 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
2419 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
2420
2421 // Check to ensure both blocks are empty (just a return) or optionally empty
2422 // with PHI nodes. If there are other instructions, merging would cause extra
2423 // computation on one path or the other.
2424 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
2425 return false;
2426 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
2427 return false;
2428
2429 Builder.SetInsertPoint(BI);
2430 // Okay, we found a branch that is going to two return nodes. If
2431 // there is no return value for this function, just change the
2432 // branch into a return.
2433 if (FalseRet->getNumOperands() == 0) {
2434 TrueSucc->removePredecessor(BI->getParent());
2435 FalseSucc->removePredecessor(BI->getParent());
2436 Builder.CreateRetVoid();
2437 EraseTerminatorInstAndDCECond(BI);
2438 return true;
2439 }
2440
2441 // Otherwise, figure out what the true and false return values are
2442 // so we can insert a new select instruction.
2443 Value *TrueValue = TrueRet->getReturnValue();
2444 Value *FalseValue = FalseRet->getReturnValue();
2445
2446 // Unwrap any PHI nodes in the return blocks.
2447 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
2448 if (TVPN->getParent() == TrueSucc)
2449 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
2450 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
2451 if (FVPN->getParent() == FalseSucc)
2452 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
2453
2454 // In order for this transformation to be safe, we must be able to
2455 // unconditionally execute both operands to the return. This is
2456 // normally the case, but we could have a potentially-trapping
2457 // constant expression that prevents this transformation from being
2458 // safe.
2459 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
2460 if (TCV->canTrap())
2461 return false;
2462 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
2463 if (FCV->canTrap())
2464 return false;
2465
2466 // Okay, we collected all the mapped values and checked them for sanity, and
2467 // defined to really do this transformation. First, update the CFG.
2468 TrueSucc->removePredecessor(BI->getParent());
2469 FalseSucc->removePredecessor(BI->getParent());
2470
2471 // Insert select instructions where needed.
2472 Value *BrCond = BI->getCondition();
2473 if (TrueValue) {
2474 // Insert a select if the results differ.
2475 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
2476 } else if (isa<UndefValue>(TrueValue)) {
2477 TrueValue = FalseValue;
2478 } else {
2479 TrueValue =
2480 Builder.CreateSelect(BrCond, TrueValue, FalseValue, "retval", BI);
2481 }
2482 }
2483
2484 Value *RI =
2485 !TrueValue ? Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
2486
2487 (void)RI;
2488
2489 LLVM_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)
2490 << "\n " << *BI << "NewRet = " << *RI << "TRUEBLOCK: "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)
2491 << *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)
;
2492
2493 EraseTerminatorInstAndDCECond(BI);
2494
2495 return true;
2496}
2497
2498/// Return true if the given instruction is available
2499/// in its predecessor block. If yes, the instruction will be removed.
2500static bool tryCSEWithPredecessor(Instruction *Inst, BasicBlock *PB) {
2501 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
2502 return false;
2503 for (Instruction &I : *PB) {
2504 Instruction *PBI = &I;
2505 // Check whether Inst and PBI generate the same value.
2506 if (Inst->isIdenticalTo(PBI)) {
2507 Inst->replaceAllUsesWith(PBI);
2508 Inst->eraseFromParent();
2509 return true;
2510 }
2511 }
2512 return false;
2513}
2514
2515/// Return true if either PBI or BI has branch weight available, and store
2516/// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does
2517/// not have branch weight, use 1:1 as its weight.
2518static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI,
2519 uint64_t &PredTrueWeight,
2520 uint64_t &PredFalseWeight,
2521 uint64_t &SuccTrueWeight,
2522 uint64_t &SuccFalseWeight) {
2523 bool PredHasWeights =
2524 PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
2525 bool SuccHasWeights =
2526 BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
2527 if (PredHasWeights || SuccHasWeights) {
2528 if (!PredHasWeights)
2529 PredTrueWeight = PredFalseWeight = 1;
2530 if (!SuccHasWeights)
2531 SuccTrueWeight = SuccFalseWeight = 1;
2532 return true;
2533 } else {
2534 return false;
2535 }
2536}
2537
2538/// If this basic block is simple enough, and if a predecessor branches to us
2539/// and one of our successors, fold the block into the predecessor and use
2540/// logical operations to pick the right destination.
2541bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
2542 BasicBlock *BB = BI->getParent();
2543
2544 Instruction *Cond = nullptr;
2545 if (BI->isConditional())
2546 Cond = dyn_cast<Instruction>(BI->getCondition());
2547 else {
2548 // For unconditional branch, check for a simple CFG pattern, where
2549 // BB has a single predecessor and BB's successor is also its predecessor's
2550 // successor. If such pattern exists, check for CSE between BB and its
2551 // predecessor.
2552 if (BasicBlock *PB = BB->getSinglePredecessor())
2553 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2554 if (PBI->isConditional() &&
2555 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2556 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2557 for (auto I = BB->instructionsWithoutDebug().begin(),
2558 E = BB->instructionsWithoutDebug().end();
2559 I != E;) {
2560 Instruction *Curr = &*I++;
2561 if (isa<CmpInst>(Curr)) {
2562 Cond = Curr;
2563 break;
2564 }
2565 // Quit if we can't remove this instruction.
2566 if (!tryCSEWithPredecessor(Curr, PB))
2567 return false;
2568 }
2569 }
2570
2571 if (!Cond)
2572 return false;
2573 }
2574
2575 if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2576 Cond->getParent() != BB || !Cond->hasOneUse())
2577 return false;
2578
2579 // Make sure the instruction after the condition is the cond branch.
2580 BasicBlock::iterator CondIt = ++Cond->getIterator();
2581
2582 // Ignore dbg intrinsics.
2583 while (isa<DbgInfoIntrinsic>(CondIt))
2584 ++CondIt;
2585
2586 if (&*CondIt != BI)
2587 return false;
2588
2589 // Only allow this transformation if computing the condition doesn't involve
2590 // too many instructions and these involved instructions can be executed
2591 // unconditionally. We denote all involved instructions except the condition
2592 // as "bonus instructions", and only allow this transformation when the
2593 // number of the bonus instructions does not exceed a certain threshold.
2594 unsigned NumBonusInsts = 0;
2595 for (auto I = BB->begin(); Cond != &*I; ++I) {
2596 // Ignore dbg intrinsics.
2597 if (isa<DbgInfoIntrinsic>(I))
2598 continue;
2599 if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I))
2600 return false;
2601 // I has only one use and can be executed unconditionally.
2602 Instruction *User = dyn_cast<Instruction>(I->user_back());
2603 if (User == nullptr || User->getParent() != BB)
2604 return false;
2605 // I is used in the same BB. Since BI uses Cond and doesn't have more slots
2606 // to use any other instruction, User must be an instruction between next(I)
2607 // and Cond.
2608 ++NumBonusInsts;
2609 // Early exits once we reach the limit.
2610 if (NumBonusInsts > BonusInstThreshold)
2611 return false;
2612 }
2613
2614 // Cond is known to be a compare or binary operator. Check to make sure that
2615 // neither operand is a potentially-trapping constant expression.
2616 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2617 if (CE->canTrap())
2618 return false;
2619 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2620 if (CE->canTrap())
2621 return false;
2622
2623 // Finally, don't infinitely unroll conditional loops.
2624 BasicBlock *TrueDest = BI->getSuccessor(0);
2625 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
2626 if (TrueDest == BB || FalseDest == BB)
2627 return false;
2628
2629 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2630 BasicBlock *PredBlock = *PI;
2631 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2632
2633 // Check that we have two conditional branches. If there is a PHI node in
2634 // the common successor, verify that the same value flows in from both
2635 // blocks.
2636 SmallVector<PHINode *, 4> PHIs;
2637 if (!PBI || PBI->isUnconditional() ||
2638 (BI->isConditional() && !SafeToMergeTerminators(BI, PBI)) ||
2639 (!BI->isConditional() &&
2640 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2641 continue;
2642
2643 // Determine if the two branches share a common destination.
2644 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2645 bool InvertPredCond = false;
2646
2647 if (BI->isConditional()) {
2648 if (PBI->getSuccessor(0) == TrueDest) {
2649 Opc = Instruction::Or;
2650 } else if (PBI->getSuccessor(1) == FalseDest) {
2651 Opc = Instruction::And;
2652 } else if (PBI->getSuccessor(0) == FalseDest) {
2653 Opc = Instruction::And;
2654 InvertPredCond = true;
2655 } else if (PBI->getSuccessor(1) == TrueDest) {
2656 Opc = Instruction::Or;
2657 InvertPredCond = true;
2658 } else {
2659 continue;
2660 }
2661 } else {
2662 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2663 continue;
2664 }
2665
2666 LLVM_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)
;
2667 IRBuilder<> Builder(PBI);
2668
2669 // If we need to invert the condition in the pred block to match, do so now.
2670 if (InvertPredCond) {
2671 Value *NewCond = PBI->getCondition();
2672
2673 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2674 CmpInst *CI = cast<CmpInst>(NewCond);
2675 CI->setPredicate(CI->getInversePredicate());
2676 } else {
2677 NewCond =
2678 Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not");
2679 }
2680
2681 PBI->setCondition(NewCond);
2682 PBI->swapSuccessors();
2683 }
2684
2685 // If we have bonus instructions, clone them into the predecessor block.
2686 // Note that there may be multiple predecessor blocks, so we cannot move
2687 // bonus instructions to a predecessor block.
2688 ValueToValueMapTy VMap; // maps original values to cloned values
2689 // We already make sure Cond is the last instruction before BI. Therefore,
2690 // all instructions before Cond other than DbgInfoIntrinsic are bonus
2691 // instructions.
2692 for (auto BonusInst = BB->begin(); Cond != &*BonusInst; ++BonusInst) {
2693 if (isa<DbgInfoIntrinsic>(BonusInst))
2694 continue;
2695 Instruction *NewBonusInst = BonusInst->clone();
2696 RemapInstruction(NewBonusInst, VMap,
2697 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2698 VMap[&*BonusInst] = NewBonusInst;
2699
2700 // If we moved a load, we cannot any longer claim any knowledge about
2701 // its potential value. The previous information might have been valid
2702 // only given the branch precondition.
2703 // For an analogous reason, we must also drop all the metadata whose
2704 // semantics we don't understand.
2705 NewBonusInst->dropUnknownNonDebugMetadata();
2706
2707 PredBlock->getInstList().insert(PBI->getIterator(), NewBonusInst);
2708 NewBonusInst->takeName(&*BonusInst);
2709 BonusInst->setName(BonusInst->getName() + ".old");
2710 }
2711
2712 // Clone Cond into the predecessor basic block, and or/and the
2713 // two conditions together.
2714 Instruction *New = Cond->clone();
2715 RemapInstruction(New, VMap,
2716 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2717 PredBlock->getInstList().insert(PBI->getIterator(), New);
2718 New->takeName(Cond);
2719 Cond->setName(New->getName() + ".old");
2720
2721 if (BI->isConditional()) {
2722 Instruction *NewCond = cast<Instruction>(
2723 Builder.CreateBinOp(Opc, PBI->getCondition(), New, "or.cond"));
2724 PBI->setCondition(NewCond);
2725
2726 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2727 bool HasWeights =
2728 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
2729 SuccTrueWeight, SuccFalseWeight);
2730 SmallVector<uint64_t, 8> NewWeights;
2731
2732 if (PBI->getSuccessor(0) == BB) {
2733 if (HasWeights) {
2734 // PBI: br i1 %x, BB, FalseDest
2735 // BI: br i1 %y, TrueDest, FalseDest
2736 // TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2737 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2738 // FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2739 // TrueWeight for PBI * FalseWeight for BI.
2740 // We assume that total weights of a BranchInst can fit into 32 bits.
2741 // Therefore, we will not have overflow using 64-bit arithmetic.
2742 NewWeights.push_back(PredFalseWeight *
2743 (SuccFalseWeight + SuccTrueWeight) +
2744 PredTrueWeight * SuccFalseWeight);
2745 }
2746 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2747 PBI->setSuccessor(0, TrueDest);
2748 }
2749 if (PBI->getSuccessor(1) == BB) {
2750 if (HasWeights) {
2751 // PBI: br i1 %x, TrueDest, BB
2752 // BI: br i1 %y, TrueDest, FalseDest
2753 // TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2754 // FalseWeight for PBI * TrueWeight for BI.
2755 NewWeights.push_back(PredTrueWeight *
2756 (SuccFalseWeight + SuccTrueWeight) +
2757 PredFalseWeight * SuccTrueWeight);
2758 // FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2759 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2760 }
2761 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2762 PBI->setSuccessor(1, FalseDest);
2763 }
2764 if (NewWeights.size() == 2) {
2765 // Halve the weights if any of them cannot fit in an uint32_t
2766 FitWeights(NewWeights);
2767
2768 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),
2769 NewWeights.end());
2770 setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
2771 } else
2772 PBI->setMetadata(LLVMContext::MD_prof, nullptr);
2773 } else {
2774 // Update PHI nodes in the common successors.
2775 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2776 ConstantInt *PBI_C = cast<ConstantInt>(
2777 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2778 assert(PBI_C->getType()->isIntegerTy(1))(static_cast <bool> (PBI_C->getType()->isIntegerTy
(1)) ? void (0) : __assert_fail ("PBI_C->getType()->isIntegerTy(1)"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2778, __extension__ __PRETTY_FUNCTION__))
;
2779 Instruction *MergedCond = nullptr;
2780 if (PBI->getSuccessor(0) == TrueDest) {
2781 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2782 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2783 // is false: !PBI_Cond and BI_Value
2784 Instruction *NotCond = cast<Instruction>(
2785 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2786 MergedCond = cast<Instruction>(
2787 Builder.CreateBinOp(Instruction::And, NotCond, New, "and.cond"));
2788 if (PBI_C->isOne())
2789 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2790 Instruction::Or, PBI->getCondition(), MergedCond, "or.cond"));
2791 } else {
2792 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2793 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2794 // is false: PBI_Cond and BI_Value
2795 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2796 Instruction::And, PBI->getCondition(), New, "and.cond"));
2797 if (PBI_C->isOne()) {
2798 Instruction *NotCond = cast<Instruction>(
2799 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2800 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2801 Instruction::Or, NotCond, MergedCond, "or.cond"));
2802 }
2803 }
2804 // Update PHI Node.
2805 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2806 MergedCond);
2807 }
2808 // Change PBI from Conditional to Unconditional.
2809 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2810 EraseTerminatorInstAndDCECond(PBI);
2811 PBI = New_PBI;
2812 }
2813
2814 // If BI was a loop latch, it may have had associated loop metadata.
2815 // We need to copy it to the new latch, that is, PBI.
2816 if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
2817 PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
2818
2819 // TODO: If BB is reachable from all paths through PredBlock, then we
2820 // could replace PBI's branch probabilities with BI's.
2821
2822 // Copy any debug value intrinsics into the end of PredBlock.
2823 for (Instruction &I : *BB)
2824 if (isa<DbgInfoIntrinsic>(I))
2825 I.clone()->insertBefore(PBI);
2826
2827 return true;
2828 }
2829 return false;
2830}
2831
2832// If there is only one store in BB1 and BB2, return it, otherwise return
2833// nullptr.
2834static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
2835 StoreInst *S = nullptr;
2836 for (auto *BB : {BB1, BB2}) {
2837 if (!BB)
2838 continue;
2839 for (auto &I : *BB)
2840 if (auto *SI = dyn_cast<StoreInst>(&I)) {
2841 if (S)
2842 // Multiple stores seen.
2843 return nullptr;
2844 else
2845 S = SI;
2846 }
2847 }
2848 return S;
2849}
2850
2851static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
2852 Value *AlternativeV = nullptr) {
2853 // PHI is going to be a PHI node that allows the value V that is defined in
2854 // BB to be referenced in BB's only successor.
2855 //
2856 // If AlternativeV is nullptr, the only value we care about in PHI is V. It
2857 // doesn't matter to us what the other operand is (it'll never get used). We
2858 // could just create a new PHI with an undef incoming value, but that could
2859 // increase register pressure if EarlyCSE/InstCombine can't fold it with some
2860 // other PHI. So here we directly look for some PHI in BB's successor with V
2861 // as an incoming operand. If we find one, we use it, else we create a new
2862 // one.
2863 //
2864 // If AlternativeV is not nullptr, we care about both incoming values in PHI.
2865 // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
2866 // where OtherBB is the single other predecessor of BB's only successor.
2867 PHINode *PHI = nullptr;
2868 BasicBlock *Succ = BB->getSingleSuccessor();
2869
2870 for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
2871 if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
2872 PHI = cast<PHINode>(I);
2873 if (!AlternativeV)
2874 break;
2875
2876 assert(pred_size(Succ) == 2)(static_cast <bool> (pred_size(Succ) == 2) ? void (0) :
__assert_fail ("pred_size(Succ) == 2", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2876, __extension__ __PRETTY_FUNCTION__))
;
2877 auto PredI = pred_begin(Succ);
2878 BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
2879 if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
2880 break;
2881 PHI = nullptr;
2882 }
2883 if (PHI)
2884 return PHI;
2885
2886 // If V is not an instruction defined in BB, just return it.
2887 if (!AlternativeV &&
2888 (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
2889 return V;
2890
2891 PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
2892 PHI->addIncoming(V, BB);
2893 for (BasicBlock *PredBB : predecessors(Succ))
2894 if (PredBB != BB)
2895 PHI->addIncoming(
2896 AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB);
2897 return PHI;
2898}
2899
2900static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
2901 BasicBlock *QTB, BasicBlock *QFB,
2902 BasicBlock *PostBB, Value *Address,
2903 bool InvertPCond, bool InvertQCond,
2904 const DataLayout &DL) {
2905 auto IsaBitcastOfPointerType = [](const Instruction &I) {
2906 return Operator::getOpcode(&I) == Instruction::BitCast &&
2907 I.getType()->isPointerTy();
2908 };
2909
2910 // If we're not in aggressive mode, we only optimize if we have some
2911 // confidence that by optimizing we'll allow P and/or Q to be if-converted.
2912 auto IsWorthwhile = [&](BasicBlock *BB) {
2913 if (!BB)
2914 return true;
2915 // Heuristic: if the block can be if-converted/phi-folded and the
2916 // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
2917 // thread this store.
2918 unsigned N = 0;
2919 for (auto &I : BB->instructionsWithoutDebug()) {
2920 // Cheap instructions viable for folding.
2921 if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
2922 isa<StoreInst>(I))
2923 ++N;
2924 // Free instructions.
2925 else if (isa<TerminatorInst>(I) || IsaBitcastOfPointerType(I))
2926 continue;
2927 else
2928 return false;
2929 }
2930 // The store we want to merge is counted in N, so add 1 to make sure
2931 // we're counting the instructions that would be left.
2932 return N <= (PHINodeFoldingThreshold + 1);
2933 };
2934
2935 if (!MergeCondStoresAggressively &&
2936 (!IsWorthwhile(PTB) || !IsWorthwhile(PFB) || !IsWorthwhile(QTB) ||
2937 !IsWorthwhile(QFB)))
2938 return false;
2939
2940 // For every pointer, there must be exactly two stores, one coming from
2941 // PTB or PFB, and the other from QTB or QFB. We don't support more than one
2942 // store (to any address) in PTB,PFB or QTB,QFB.
2943 // FIXME: We could relax this restriction with a bit more work and performance
2944 // testing.
2945 StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
2946 StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
2947 if (!PStore || !QStore)
2948 return false;
2949
2950 // Now check the stores are compatible.
2951 if (!QStore->isUnordered() || !PStore->isUnordered())
2952 return false;
2953
2954 // Check that sinking the store won't cause program behavior changes. Sinking
2955 // the store out of the Q blocks won't change any behavior as we're sinking
2956 // from a block to its unconditional successor. But we're moving a store from
2957 // the P blocks down through the middle block (QBI) and past both QFB and QTB.
2958 // So we need to check that there are no aliasing loads or stores in
2959 // QBI, QTB and QFB. We also need to check there are no conflicting memory
2960 // operations between PStore and the end of its parent block.
2961 //
2962 // The ideal way to do this is to query AliasAnalysis, but we don't
2963 // preserve AA currently so that is dangerous. Be super safe and just
2964 // check there are no other memory operations at all.
2965 for (auto &I : *QFB->getSinglePredecessor())
2966 if (I.mayReadOrWriteMemory())
2967 return false;
2968 for (auto &I : *QFB)
2969 if (&I != QStore && I.mayReadOrWriteMemory())
2970 return false;
2971 if (QTB)
2972 for (auto &I : *QTB)
2973 if (&I != QStore && I.mayReadOrWriteMemory())
2974 return false;
2975 for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
2976 I != E; ++I)
2977 if (&*I != PStore && I->mayReadOrWriteMemory())
2978 return false;
2979
2980 // If PostBB has more than two predecessors, we need to split it so we can
2981 // sink the store.
2982 if (std::next(pred_begin(PostBB), 2) != pred_end(PostBB)) {
2983 // We know that QFB's only successor is PostBB. And QFB has a single
2984 // predecessor. If QTB exists, then its only successor is also PostBB.
2985 // If QTB does not exist, then QFB's only predecessor has a conditional
2986 // branch to QFB and PostBB.
2987 BasicBlock *TruePred = QTB ? QTB : QFB->getSinglePredecessor();
2988 BasicBlock *NewBB = SplitBlockPredecessors(PostBB, { QFB, TruePred},
2989 "condstore.split");
2990 if (!NewBB)
2991 return false;
2992 PostBB = NewBB;
2993 }
2994
2995 // OK, we're going to sink the stores to PostBB. The store has to be
2996 // conditional though, so first create the predicate.
2997 Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
2998 ->getCondition();
2999 Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
3000 ->getCondition();
3001
3002 Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
3003 PStore->getParent());
3004 Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
3005 QStore->getParent(), PPHI);
3006
3007 IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
3008
3009 Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
3010 Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
3011
3012 if (InvertPCond)
3013 PPred = QB.CreateNot(PPred);
3014 if (InvertQCond)
3015 QPred = QB.CreateNot(QPred);
3016 Value *CombinedPred = QB.CreateOr(PPred, QPred);
3017
3018 auto *T =
3019 SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(), false);
3020 QB.SetInsertPoint(T);
3021 StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
3022 AAMDNodes AAMD;
3023 PStore->getAAMetadata(AAMD, /*Merge=*/false);
3024 PStore->getAAMetadata(AAMD, /*Merge=*/true);
3025 SI->setAAMetadata(AAMD);
3026 unsigned PAlignment = PStore->getAlignment();
3027 unsigned QAlignment = QStore->getAlignment();
3028 unsigned TypeAlignment =
3029 DL.getABITypeAlignment(SI->getValueOperand()->getType());
3030 unsigned MinAlignment;
3031 unsigned MaxAlignment;
3032 std::tie(MinAlignment, MaxAlignment) = std::minmax(PAlignment, QAlignment);
3033 // Choose the minimum alignment. If we could prove both stores execute, we
3034 // could use biggest one. In this case, though, we only know that one of the
3035 // stores executes. And we don't know it's safe to take the alignment from a
3036 // store that doesn't execute.
3037 if (MinAlignment != 0) {
3038 // Choose the minimum of all non-zero alignments.
3039 SI->setAlignment(MinAlignment);
3040 } else if (MaxAlignment != 0) {
3041 // Choose the minimal alignment between the non-zero alignment and the ABI
3042 // default alignment for the type of the stored value.
3043 SI->setAlignment(std::min(MaxAlignment, TypeAlignment));
3044 } else {
3045 // If both alignments are zero, use ABI default alignment for the type of
3046 // the stored value.
3047 SI->setAlignment(TypeAlignment);
3048 }
3049
3050 QStore->eraseFromParent();
3051 PStore->eraseFromParent();
3052
3053 return true;
3054}
3055
3056static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
3057 const DataLayout &DL) {
3058 // The intention here is to find diamonds or triangles (see below) where each
3059 // conditional block contains a store to the same address. Both of these
3060 // stores are conditional, so they can't be unconditionally sunk. But it may
3061 // be profitable to speculatively sink the stores into one merged store at the
3062 // end, and predicate the merged store on the union of the two conditions of
3063 // PBI and QBI.
3064 //
3065 // This can reduce the number of stores executed if both of the conditions are
3066 // true, and can allow the blocks to become small enough to be if-converted.
3067 // This optimization will also chain, so that ladders of test-and-set
3068 // sequences can be if-converted away.
3069 //
3070 // We only deal with simple diamonds or triangles:
3071 //
3072 // PBI or PBI or a combination of the two
3073 // / \ | \
3074 // PTB PFB | PFB
3075 // \ / | /
3076 // QBI QBI
3077 // / \ | \
3078 // QTB QFB | QFB
3079 // \ / | /
3080 // PostBB PostBB
3081 //
3082 // We model triangles as a type of diamond with a nullptr "true" block.
3083 // Triangles are canonicalized so that the fallthrough edge is represented by
3084 // a true condition, as in the diagram above.
3085 BasicBlock *PTB = PBI->getSuccessor(0);
3086 BasicBlock *PFB = PBI->getSuccessor(1);
3087 BasicBlock *QTB = QBI->getSuccessor(0);
3088 BasicBlock *QFB = QBI->getSuccessor(1);
3089 BasicBlock *PostBB = QFB->getSingleSuccessor();
3090
3091 // Make sure we have a good guess for PostBB. If QTB's only successor is
3092 // QFB, then QFB is a better PostBB.
3093 if (QTB->getSingleSuccessor() == QFB)
3094 PostBB = QFB;
3095
3096 // If we couldn't find a good PostBB, stop.
3097 if (!PostBB)
3098 return false;
3099
3100 bool InvertPCond = false, InvertQCond = false;
3101 // Canonicalize fallthroughs to the true branches.
3102 if (PFB == QBI->getParent()) {
3103 std::swap(PFB, PTB);
3104 InvertPCond = true;
3105 }
3106 if (QFB == PostBB) {
3107 std::swap(QFB, QTB);
3108 InvertQCond = true;
3109 }
3110
3111 // From this point on we can assume PTB or QTB may be fallthroughs but PFB
3112 // and QFB may not. Model fallthroughs as a nullptr block.
3113 if (PTB == QBI->getParent())
3114 PTB = nullptr;
3115 if (QTB == PostBB)
3116 QTB = nullptr;
3117
3118 // Legality bailouts. We must have at least the non-fallthrough blocks and
3119 // the post-dominating block, and the non-fallthroughs must only have one
3120 // predecessor.
3121 auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
3122 return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
3123 };
3124 if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
3125 !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
3126 return false;
3127 if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
3128 (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
3129 return false;
3130 if (!QBI->getParent()->hasNUses(2))
3131 return false;
3132
3133 // OK, this is a sequence of two diamonds or triangles.
3134 // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
3135 SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses;
3136 for (auto *BB : {PTB, PFB}) {
3137 if (!BB)
3138 continue;
3139 for (auto &I : *BB)
3140 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3141 PStoreAddresses.insert(SI->getPointerOperand());
3142 }
3143 for (auto *BB : {QTB, QFB}) {
3144 if (!BB)
3145 continue;
3146 for (auto &I : *BB)
3147 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3148 QStoreAddresses.insert(SI->getPointerOperand());
3149 }
3150
3151 set_intersect(PStoreAddresses, QStoreAddresses);
3152 // set_intersect mutates PStoreAddresses in place. Rename it here to make it
3153 // clear what it contains.
3154 auto &CommonAddresses = PStoreAddresses;
3155
3156 bool Changed = false;
3157 for (auto *Address : CommonAddresses)
3158 Changed |= mergeConditionalStoreToAddress(
3159 PTB, PFB, QTB, QFB, PostBB, Address, InvertPCond, InvertQCond, DL);
3160 return Changed;
3161}
3162
3163/// If we have a conditional branch as a predecessor of another block,
3164/// this function tries to simplify it. We know
3165/// that PBI and BI are both conditional branches, and BI is in one of the
3166/// successor blocks of PBI - PBI branches to BI.
3167static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
3168 const DataLayout &DL) {
3169 assert(PBI->isConditional() && BI->isConditional())(static_cast <bool> (PBI->isConditional() &&
BI->isConditional()) ? void (0) : __assert_fail ("PBI->isConditional() && BI->isConditional()"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3169, __extension__ __PRETTY_FUNCTION__))
;
3170 BasicBlock *BB = BI->getParent();
3171
3172 // If this block ends with a branch instruction, and if there is a
3173 // predecessor that ends on a branch of the same condition, make
3174 // this conditional branch redundant.
3175 if (PBI->getCondition() == BI->getCondition() &&
3176 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3177 // Okay, the outcome of this conditional branch is statically
3178 // knowable. If this block had a single pred, handle specially.
3179 if (BB->getSinglePredecessor()) {
3180 // Turn this into a branch on constant.
3181 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3182 BI->setCondition(
3183 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue));
3184 return true; // Nuke the branch on constant.
3185 }
3186
3187 // Otherwise, if there are multiple predecessors, insert a PHI that merges
3188 // in the constant and simplify the block result. Subsequent passes of
3189 // simplifycfg will thread the block.
3190 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
3191 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
3192 PHINode *NewPN = PHINode::Create(
3193 Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
3194 BI->getCondition()->getName() + ".pr", &BB->front());
3195 // Okay, we're going to insert the PHI node. Since PBI is not the only
3196 // predecessor, compute the PHI'd conditional value for all of the preds.
3197 // Any predecessor where the condition is not computable we keep symbolic.
3198 for (pred_iterator PI = PB; PI != PE; ++PI) {
3199 BasicBlock *P = *PI;
3200 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI &&
3201 PBI->isConditional() && PBI->getCondition() == BI->getCondition() &&
3202 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3203 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3204 NewPN->addIncoming(
3205 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue),
3206 P);
3207 } else {
3208 NewPN->addIncoming(BI->getCondition(), P);
3209 }
3210 }
3211
3212 BI->setCondition(NewPN);
3213 return true;
3214 }
3215 }
3216
3217 if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
3218 if (CE->canTrap())
3219 return false;
3220
3221 // If both branches are conditional and both contain stores to the same
3222 // address, remove the stores from the conditionals and create a conditional
3223 // merged store at the end.
3224 if (MergeCondStores && mergeConditionalStores(PBI, BI, DL))
3225 return true;
3226
3227 // If this is a conditional branch in an empty block, and if any
3228 // predecessors are a conditional branch to one of our destinations,
3229 // fold the conditions into logical ops and one cond br.
3230
3231 // Ignore dbg intrinsics.
3232 if (&*BB->instructionsWithoutDebug().begin() != BI)
3233 return false;
3234
3235 int PBIOp, BIOp;
3236 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
3237 PBIOp = 0;
3238 BIOp = 0;
3239 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
3240 PBIOp = 0;
3241 BIOp = 1;
3242 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
3243 PBIOp = 1;
3244 BIOp = 0;
3245 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
3246 PBIOp = 1;
3247 BIOp = 1;
3248 } else {
3249 return false;
3250 }
3251
3252 // Check to make sure that the other destination of this branch
3253 // isn't BB itself. If so, this is an infinite loop that will
3254 // keep getting unwound.
3255 if (PBI->getSuccessor(PBIOp) == BB)
3256 return false;
3257
3258 // Do not perform this transformation if it would require
3259 // insertion of a large number of select instructions. For targets
3260 // without predication/cmovs, this is a big pessimization.
3261
3262 // Also do not perform this transformation if any phi node in the common
3263 // destination block can trap when reached by BB or PBB (PR17073). In that
3264 // case, it would be unsafe to hoist the operation into a select instruction.
3265
3266 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
3267 unsigned NumPhis = 0;
3268 for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II);
3269 ++II, ++NumPhis) {
3270 if (NumPhis > 2) // Disable this xform.
3271 return false;
3272
3273 PHINode *PN = cast<PHINode>(II);
3274 Value *BIV = PN->getIncomingValueForBlock(BB);
3275 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
3276 if (CE->canTrap())
3277 return false;
3278
3279 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
3280 Value *PBIV = PN->getIncomingValue(PBBIdx);
3281 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
3282 if (CE->canTrap())
3283 return false;
3284 }
3285
3286 // Finally, if everything is ok, fold the branches to logical ops.
3287 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
3288
3289 LLVM_DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
3290 << "AND: " << *BI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
;
3291
3292 // If OtherDest *is* BB, then BB is a basic block with a single conditional
3293 // branch in it, where one edge (OtherDest) goes back to itself but the other
3294 // exits. We don't *know* that the program avoids the infinite loop
3295 // (even though that seems likely). If we do this xform naively, we'll end up
3296 // recursively unpeeling the loop. Since we know that (after the xform is
3297 // done) that the block *is* infinite if reached, we just make it an obviously
3298 // infinite loop with no cond branch.
3299 if (OtherDest == BB) {
3300 // Insert it at the end of the function, because it's either code,
3301 // or it won't matter if it's hot. :)
3302 BasicBlock *InfLoopBlock =
3303 BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
3304 BranchInst::Create(InfLoopBlock, InfLoopBlock);
3305 OtherDest = InfLoopBlock;
3306 }
3307
3308 LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3309
3310 // BI may have other predecessors. Because of this, we leave
3311 // it alone, but modify PBI.
3312
3313 // Make sure we get to CommonDest on True&True directions.
3314 Value *PBICond = PBI->getCondition();
3315 IRBuilder<NoFolder> Builder(PBI);
3316 if (PBIOp)
3317 PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not");
3318
3319 Value *BICond = BI->getCondition();
3320 if (BIOp)
3321 BICond = Builder.CreateNot(BICond, BICond->getName() + ".not");
3322
3323 // Merge the conditions.
3324 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
3325
3326 // Modify PBI to branch on the new condition to the new dests.
3327 PBI->setCondition(Cond);
3328 PBI->setSuccessor(0, CommonDest);
3329 PBI->setSuccessor(1, OtherDest);
3330
3331 // Update branch weight for PBI.
3332 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
3333 uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
3334 bool HasWeights =
3335 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
3336 SuccTrueWeight, SuccFalseWeight);
3337 if (HasWeights) {
3338 PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3339 PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3340 SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3341 SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3342 // The weight to CommonDest should be PredCommon * SuccTotal +
3343 // PredOther * SuccCommon.
3344 // The weight to OtherDest should be PredOther * SuccOther.
3345 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
3346 PredOther * SuccCommon,
3347 PredOther * SuccOther};
3348 // Halve the weights if any of them cannot fit in an uint32_t
3349 FitWeights(NewWeights);
3350
3351 setBranchWeights(PBI, NewWeights[0], NewWeights[1]);
3352 }
3353
3354 // OtherDest may have phi nodes. If so, add an entry from PBI's
3355 // block that are identical to the entries for BI's block.
3356 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
3357
3358 // We know that the CommonDest already had an edge from PBI to
3359 // it. If it has PHIs though, the PHIs may have different
3360 // entries for BB and PBI's BB. If so, insert a select to make
3361 // them agree.
3362 for (PHINode &PN : CommonDest->phis()) {
3363 Value *BIV = PN.getIncomingValueForBlock(BB);
3364 unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent());
3365 Value *PBIV = PN.getIncomingValue(PBBIdx);
3366 if (BIV != PBIV) {
3367 // Insert a select in PBI to pick the right value.
3368 SelectInst *NV = cast<SelectInst>(
3369 Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
3370 PN.setIncomingValue(PBBIdx, NV);
3371 // Although the select has the same condition as PBI, the original branch
3372 // weights for PBI do not apply to the new select because the select's
3373 // 'logical' edges are incoming edges of the phi that is eliminated, not
3374 // the outgoing edges of PBI.
3375 if (HasWeights) {
3376 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3377 uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3378 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3379 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3380 // The weight to PredCommonDest should be PredCommon * SuccTotal.
3381 // The weight to PredOtherDest should be PredOther * SuccCommon.
3382 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
3383 PredOther * SuccCommon};
3384
3385 FitWeights(NewWeights);
3386
3387 setBranchWeights(NV, NewWeights[0], NewWeights[1]);
3388 }
3389 }
3390 }
3391
3392 LLVM_DEBUG(dbgs() << "INTO: " << *PBI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "INTO: " << *PBI->
getParent(); } } while (false)
;
3393 LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3394
3395 // This basic block is probably dead. We know it has at least
3396 // one fewer predecessor.
3397 return true;
3398}
3399
3400// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
3401// true or to FalseBB if Cond is false.
3402// Takes care of updating the successors and removing the old terminator.
3403// Also makes sure not to introduce new successors by assuming that edges to
3404// non-successor TrueBBs and FalseBBs aren't reachable.
3405static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
3406 BasicBlock *TrueBB, BasicBlock *FalseBB,
3407 uint32_t TrueWeight,
3408 uint32_t FalseWeight) {
3409 // Remove any superfluous successor edges from the CFG.
3410 // First, figure out which successors to preserve.
3411 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
3412 // successor.
3413 BasicBlock *KeepEdge1 = TrueBB;
3414 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
3415
3416 // Then remove the rest.
3417 for (BasicBlock *Succ : OldTerm->successors()) {
3418 // Make sure only to keep exactly one copy of each edge.
3419 if (Succ == KeepEdge1)
3420 KeepEdge1 = nullptr;
3421 else if (Succ == KeepEdge2)
3422 KeepEdge2 = nullptr;
3423 else
3424 Succ->removePredecessor(OldTerm->getParent(),
3425 /*DontDeleteUselessPHIs=*/true);
3426 }
3427
3428 IRBuilder<> Builder(OldTerm);
3429 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
3430
3431 // Insert an appropriate new terminator.
3432 if (!KeepEdge1 && !KeepEdge2) {
3433 if (TrueBB == FalseBB)
3434 // We were only looking for one successor, and it was present.
3435 // Create an unconditional branch to it.
3436 Builder.CreateBr(TrueBB);
3437 else {
3438 // We found both of the successors we were looking for.
3439 // Create a conditional branch sharing the condition of the select.
3440 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
3441 if (TrueWeight != FalseWeight)
3442 setBranchWeights(NewBI, TrueWeight, FalseWeight);
3443 }
3444 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
3445 // Neither of the selected blocks were successors, so this
3446 // terminator must be unreachable.
3447 new UnreachableInst(OldTerm->getContext(), OldTerm);
3448 } else {
3449 // One of the selected values was a successor, but the other wasn't.
3450 // Insert an unconditional branch to the one that was found;
3451 // the edge to the one that wasn't must be unreachable.
3452 if (!KeepEdge1)
3453 // Only TrueBB was found.
3454 Builder.CreateBr(TrueBB);
3455 else
3456 // Only FalseBB was found.
3457 Builder.CreateBr(FalseBB);
3458 }
3459
3460 EraseTerminatorInstAndDCECond(OldTerm);
3461 return true;
3462}
3463
3464// Replaces
3465// (switch (select cond, X, Y)) on constant X, Y
3466// with a branch - conditional if X and Y lead to distinct BBs,
3467// unconditional otherwise.
3468static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
3469 // Check for constant integer values in the select.
3470 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
3471 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
3472 if (!TrueVal || !FalseVal)
3473 return false;
3474
3475 // Find the relevant condition and destinations.
3476 Value *Condition = Select->getCondition();
3477 BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor();
3478 BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor();
3479
3480 // Get weight for TrueBB and FalseBB.
3481 uint32_t TrueWeight = 0, FalseWeight = 0;
3482 SmallVector<uint64_t, 8> Weights;
3483 bool HasWeights = HasBranchWeights(SI);
3484 if (HasWeights) {
3485 GetBranchWeights(SI, Weights);
3486 if (Weights.size() == 1 + SI->getNumCases()) {
3487 TrueWeight =
3488 (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()];
3489 FalseWeight =
3490 (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()];
3491 }
3492 }
3493
3494 // Perform the actual simplification.
3495 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
3496 FalseWeight);
3497}
3498
3499// Replaces
3500// (indirectbr (select cond, blockaddress(@fn, BlockA),
3501// blockaddress(@fn, BlockB)))
3502// with
3503// (br cond, BlockA, BlockB).
3504static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
3505 // Check that both operands of the select are block addresses.
3506 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
3507 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
3508 if (!TBA || !FBA)
3509 return false;
3510
3511 // Extract the actual blocks.
3512 BasicBlock *TrueBB = TBA->getBasicBlock();
3513 BasicBlock *FalseBB = FBA->getBasicBlock();
3514
3515 // Perform the actual simplification.
3516 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0,
3517 0);
3518}
3519
3520/// This is called when we find an icmp instruction
3521/// (a seteq/setne with a constant) as the only instruction in a
3522/// block that ends with an uncond branch. We are looking for a very specific
3523/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
3524/// this case, we merge the first two "or's of icmp" into a switch, but then the
3525/// default value goes to an uncond block with a seteq in it, we get something
3526/// like:
3527///
3528/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
3529/// DEFAULT:
3530/// %tmp = icmp eq i8 %A, 92
3531/// br label %end
3532/// end:
3533/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
3534///
3535/// We prefer to split the edge to 'end' so that there is a true/false entry to
3536/// the PHI, merging the third icmp into the switch.
3537static bool tryToSimplifyUncondBranchWithICmpInIt(
3538 ICmpInst *ICI, IRBuilder<> &Builder, const DataLayout &DL,
3539 const TargetTransformInfo &TTI, const SimplifyCFGOptions &Options) {
3540 BasicBlock *BB = ICI->getParent();
3541
3542 // If the block has any PHIs in it or the icmp has multiple uses, it is too
3543 // complex.
3544 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse())
3545 return false;
3546
3547 Value *V = ICI->getOperand(0);
3548 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
3549
3550 // The pattern we're looking for is where our only predecessor is a switch on
3551 // 'V' and this block is the default case for the switch. In this case we can
3552 // fold the compared value into the switch to simplify things.
3553 BasicBlock *Pred = BB->getSinglePredecessor();
3554 if (!Pred || !isa<SwitchInst>(Pred->getTerminator()))
3555 return false;
3556
3557 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
3558 if (SI->getCondition() != V)
3559 return false;
3560
3561 // If BB is reachable on a non-default case, then we simply know the value of
3562 // V in this block. Substitute it and constant fold the icmp instruction
3563 // away.
3564 if (SI->getDefaultDest() != BB) {
3565 ConstantInt *VVal = SI->findCaseDest(BB);
3566 assert(VVal && "Should have a unique destination value")(static_cast <bool> (VVal && "Should have a unique destination value"
) ? void (0) : __assert_fail ("VVal && \"Should have a unique destination value\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3566, __extension__ __PRETTY_FUNCTION__))
;
3567 ICI->setOperand(0, VVal);
3568
3569 if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) {
3570 ICI->replaceAllUsesWith(V);
3571 ICI->eraseFromParent();
3572 }
3573 // BB is now empty, so it is likely to simplify away.
3574 return simplifyCFG(BB, TTI, Options) | true;
3575 }
3576
3577 // Ok, the block is reachable from the default dest. If the constant we're
3578 // comparing exists in one of the other edges, then we can constant fold ICI
3579 // and zap it.
3580 if (SI->findCaseValue(Cst) != SI->case_default()) {
3581 Value *V;
3582 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3583 V = ConstantInt::getFalse(BB->getContext());
3584 else
3585 V = ConstantInt::getTrue(BB->getContext());
3586
3587 ICI->replaceAllUsesWith(V);
3588 ICI->eraseFromParent();
3589 // BB is now empty, so it is likely to simplify away.
3590 return simplifyCFG(BB, TTI, Options) | true;
3591 }
3592
3593 // The use of the icmp has to be in the 'end' block, by the only PHI node in
3594 // the block.
3595 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
3596 PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
3597 if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
3598 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
3599 return false;
3600
3601 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
3602 // true in the PHI.
3603 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
3604 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
3605
3606 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3607 std::swap(DefaultCst, NewCst);
3608
3609 // Replace ICI (which is used by the PHI for the default value) with true or
3610 // false depending on if it is EQ or NE.
3611 ICI->replaceAllUsesWith(DefaultCst);
3612 ICI->eraseFromParent();
3613
3614 // Okay, the switch goes to this block on a default value. Add an edge from
3615 // the switch to the merge point on the compared value.
3616 BasicBlock *NewBB =
3617 BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB);
3618 SmallVector<uint64_t, 8> Weights;
3619 bool HasWeights = HasBranchWeights(SI);
3620 if (HasWeights) {
3621 GetBranchWeights(SI, Weights);
3622 if (Weights.size() == 1 + SI->getNumCases()) {
3623 // Split weight for default case to case for "Cst".
3624 Weights[0] = (Weights[0] + 1) >> 1;
3625 Weights.push_back(Weights[0]);
3626
3627 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3628 setBranchWeights(SI, MDWeights);
3629 }
3630 }
3631 SI->addCase(Cst, NewBB);
3632
3633 // NewBB branches to the phi block, add the uncond branch and the phi entry.
3634 Builder.SetInsertPoint(NewBB);
3635 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
3636 Builder.CreateBr(SuccBlock);
3637 PHIUse->addIncoming(NewCst, NewBB);
3638 return true;
3639}
3640
3641/// The specified branch is a conditional branch.
3642/// Check to see if it is branching on an or/and chain of icmp instructions, and
3643/// fold it into a switch instruction if so.
3644static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
3645 const DataLayout &DL) {
3646 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
3647 if (!Cond)
3648 return false;
3649
3650 // Change br (X == 0 | X == 1), T, F into a switch instruction.
3651 // If this is a bunch of seteq's or'd together, or if it's a bunch of
3652 // 'setne's and'ed together, collect them.
3653
3654 // Try to gather values from a chain of and/or to be turned into a switch
3655 ConstantComparesGatherer ConstantCompare(Cond, DL);
3656 // Unpack the result
3657 SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals;
3658 Value *CompVal = ConstantCompare.CompValue;
3659 unsigned UsedICmps = ConstantCompare.UsedICmps;
3660 Value *ExtraCase = ConstantCompare.Extra;
3661
3662 // If we didn't have a multiply compared value, fail.
3663 if (!CompVal)
3664 return false;
3665
3666 // Avoid turning single icmps into a switch.
3667 if (UsedICmps <= 1)
3668 return false;
3669
3670 bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
3671
3672 // There might be duplicate constants in the list, which the switch
3673 // instruction can't handle, remove them now.
3674 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
3675 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
3676
3677 // If Extra was used, we require at least two switch values to do the
3678 // transformation. A switch with one value is just a conditional branch.
3679 if (ExtraCase && Values.size() < 2)
3680 return false;
3681
3682 // TODO: Preserve branch weight metadata, similarly to how
3683 // FoldValueComparisonIntoPredecessors preserves it.
3684
3685 // Figure out which block is which destination.
3686 BasicBlock *DefaultBB = BI->getSuccessor(1);
3687 BasicBlock *EdgeBB = BI->getSuccessor(0);
3688 if (!TrueWhenEqual)
3689 std::swap(DefaultBB, EdgeBB);
3690
3691 BasicBlock *BB = BI->getParent();
3692
3693 LLVM_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)
3694 << " 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)
3695 << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Converting 'icmp' chain with "
<< Values.size() << " cases into SWITCH. BB is:\n"
<< *BB; } } while (false)
;
3696
3697 // If there are any extra values that couldn't be folded into the switch
3698 // then we evaluate them with an explicit branch first. Split the block
3699 // right before the condbr to handle it.
3700 if (ExtraCase) {
3701 BasicBlock *NewBB =
3702 BB->splitBasicBlock(BI->getIterator(), "switch.early.test");
3703 // Remove the uncond branch added to the old block.
3704 TerminatorInst *OldTI = BB->getTerminator();
3705 Builder.SetInsertPoint(OldTI);
3706
3707 if (TrueWhenEqual)
3708 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
3709 else
3710 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
3711
3712 OldTI->eraseFromParent();
3713
3714 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
3715 // for the edge we just added.
3716 AddPredecessorToBlock(EdgeBB, BB, NewBB);
3717
3718 LLVM_DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCasedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
3719 << "\nEXTRABB = " << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
;
3720 BB = NewBB;
3721 }
3722
3723 Builder.SetInsertPoint(BI);
3724 // Convert pointer to int before we switch.
3725 if (CompVal->getType()->isPointerTy()) {
3726 CompVal = Builder.CreatePtrToInt(
3727 CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
3728 }
3729
3730 // Create the new switch instruction now.
3731 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
3732
3733 // Add all of the 'cases' to the switch instruction.
3734 for (unsigned i = 0, e = Values.size(); i != e; ++i)
3735 New->addCase(Values[i], EdgeBB);
3736
3737 // We added edges from PI to the EdgeBB. As such, if there were any
3738 // PHI nodes in EdgeBB, they need entries to be added corresponding to
3739 // the number of edges added.
3740 for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
3741 PHINode *PN = cast<PHINode>(BBI);
3742 Value *InVal = PN->getIncomingValueForBlock(BB);
3743 for (unsigned i = 0, e = Values.size() - 1; i != e; ++i)
3744 PN->addIncoming(InVal, BB);
3745 }
3746
3747 // Erase the old branch instruction.
3748 EraseTerminatorInstAndDCECond(BI);
3749
3750 LLVM_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)
;
3751 return true;
3752}
3753
3754bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
3755 if (isa<PHINode>(RI->getValue()))
3756 return SimplifyCommonResume(RI);
3757 else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) &&
3758 RI->getValue() == RI->getParent()->getFirstNonPHI())
3759 // The resume must unwind the exception that caused control to branch here.
3760 return SimplifySingleResume(RI);
3761
3762 return false;
3763}
3764
3765// Simplify resume that is shared by several landing pads (phi of landing pad).
3766bool SimplifyCFGOpt::SimplifyCommonResume(ResumeInst *RI) {
3767 BasicBlock *BB = RI->getParent();
3768
3769 // Check that there are no other instructions except for debug intrinsics
3770 // between the phi of landing pads (RI->getValue()) and resume instruction.
3771 BasicBlock::iterator I = cast<Instruction>(RI->getValue())->getIterator(),
3772 E = RI->getIterator();
3773 while (++I != E)
3774 if (!isa<DbgInfoIntrinsic>(I))
3775 return false;
3776
3777 SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
3778 auto *PhiLPInst = cast<PHINode>(RI->getValue());
3779
3780 // Check incoming blocks to see if any of them are trivial.
3781 for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
3782 Idx++) {
3783 auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
3784 auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);
3785
3786 // If the block has other successors, we can not delete it because
3787 // it has other dependents.
3788 if (IncomingBB->getUniqueSuccessor() != BB)
3789 continue;
3790
3791 auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
3792 // Not the landing pad that caused the control to branch here.
3793 if (IncomingValue != LandingPad)
3794 continue;
3795
3796 bool isTrivial = true;
3797
3798 I = IncomingBB->getFirstNonPHI()->getIterator();
3799 E = IncomingBB->getTerminator()->getIterator();
3800 while (++I != E)
3801 if (!isa<DbgInfoIntrinsic>(I)) {
3802 isTrivial = false;
3803 break;
3804 }
3805
3806 if (isTrivial)
3807 TrivialUnwindBlocks.insert(IncomingBB);
3808 }
3809
3810 // If no trivial unwind blocks, don't do any simplifications.
3811 if (TrivialUnwindBlocks.empty())
3812 return false;
3813
3814 // Turn all invokes that unwind here into calls.
3815 for (auto *TrivialBB : TrivialUnwindBlocks) {
3816 // Blocks that will be simplified should be removed from the phi node.
3817 // Note there could be multiple edges to the resume block, and we need
3818 // to remove them all.
3819 while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1)
3820 BB->removePredecessor(TrivialBB, true);
3821
3822 for (pred_iterator PI = pred_begin(TrivialBB), PE = pred_end(TrivialBB);
3823 PI != PE;) {
3824 BasicBlock *Pred = *PI++;
3825 removeUnwindEdge(Pred);
3826 }
3827
3828 // In each SimplifyCFG run, only the current processed block can be erased.
3829 // Otherwise, it will break the iteration of SimplifyCFG pass. So instead
3830 // of erasing TrivialBB, we only remove the branch to the common resume
3831 // block so that we can later erase the resume block since it has no
3832 // predecessors.
3833 TrivialBB->getTerminator()->eraseFromParent();
3834 new UnreachableInst(RI->getContext(), TrivialBB);
3835 }
3836
3837 // Delete the resume block if all its predecessors have been removed.
3838 if (pred_empty(BB))
3839 BB->eraseFromParent();
3840
3841 return !TrivialUnwindBlocks.empty();
3842}
3843
3844// Simplify resume that is only used by a single (non-phi) landing pad.
3845bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) {
3846 BasicBlock *BB = RI->getParent();
3847 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
3848 assert(RI->getValue() == LPInst &&(static_cast <bool> (RI->getValue() == LPInst &&
"Resume must unwind the exception that caused control to here"
) ? void (0) : __assert_fail ("RI->getValue() == LPInst && \"Resume must unwind the exception that caused control to here\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3849, __extension__ __PRETTY_FUNCTION__))
3849 "Resume must unwind the exception that caused control to here")(static_cast <bool> (RI->getValue() == LPInst &&
"Resume must unwind the exception that caused control to here"
) ? void (0) : __assert_fail ("RI->getValue() == LPInst && \"Resume must unwind the exception that caused control to here\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3849, __extension__ __PRETTY_FUNCTION__))
;
3850
3851 // Check that there are no other instructions except for debug intrinsics.
3852 BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator();
3853 while (++I != E)
3854 if (!isa<DbgInfoIntrinsic>(I))
3855 return false;
3856
3857 // Turn all invokes that unwind here into calls and delete the basic block.
3858 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3859 BasicBlock *Pred = *PI++;
3860 removeUnwindEdge(Pred);
3861 }
3862
3863 // The landingpad is now unreachable. Zap it.
3864 BB->eraseFromParent();
3865 if (LoopHeaders)
3866 LoopHeaders->erase(BB);
3867 return true;
3868}
3869
3870static bool removeEmptyCleanup(CleanupReturnInst *RI) {
3871 // If this is a trivial cleanup pad that executes no instructions, it can be
3872 // eliminated. If the cleanup pad continues to the caller, any predecessor
3873 // that is an EH pad will be updated to continue to the caller and any
3874 // predecessor that terminates with an invoke instruction will have its invoke
3875 // instruction converted to a call instruction. If the cleanup pad being
3876 // simplified does not continue to the caller, each predecessor will be
3877 // updated to continue to the unwind destination of the cleanup pad being
3878 // simplified.
3879 BasicBlock *BB = RI->getParent();
3880 CleanupPadInst *CPInst = RI->getCleanupPad();
3881 if (CPInst->getParent() != BB)
3882 // This isn't an empty cleanup.
3883 return false;
3884
3885 // We cannot kill the pad if it has multiple uses. This typically arises
3886 // from unreachable basic blocks.
3887 if (!CPInst->hasOneUse())
3888 return false;
3889
3890 // Check that there are no other instructions except for benign intrinsics.
3891 BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
3892 while (++I != E) {
3893 auto *II = dyn_cast<IntrinsicInst>(I);
3894 if (!II)
3895 return false;
3896
3897 Intrinsic::ID IntrinsicID = II->getIntrinsicID();
3898 switch (IntrinsicID) {
3899 case Intrinsic::dbg_declare:
3900 case Intrinsic::dbg_value:
3901 case Intrinsic::dbg_label:
3902 case Intrinsic::lifetime_end:
3903 break;
3904 default:
3905 return false;
3906 }
3907 }
3908
3909 // If the cleanup return we are simplifying unwinds to the caller, this will
3910 // set UnwindDest to nullptr.
3911 BasicBlock *UnwindDest = RI->getUnwindDest();
3912 Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
3913
3914 // We're about to remove BB from the control flow. Before we do, sink any
3915 // PHINodes into the unwind destination. Doing this before changing the
3916 // control flow avoids some potentially slow checks, since we can currently
3917 // be certain that UnwindDest and BB have no common predecessors (since they
3918 // are both EH pads).
3919 if (UnwindDest) {
3920 // First, go through the PHI nodes in UnwindDest and update any nodes that
3921 // reference the block we are removing
3922 for (BasicBlock::iterator I = UnwindDest->begin(),
3923 IE = DestEHPad->getIterator();
3924 I != IE; ++I) {
3925 PHINode *DestPN = cast<PHINode>(I);
3926
3927 int Idx = DestPN->getBasicBlockIndex(BB);
3928 // Since BB unwinds to UnwindDest, it has to be in the PHI node.
3929 assert(Idx != -1)(static_cast <bool> (Idx != -1) ? void (0) : __assert_fail
("Idx != -1", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3929, __extension__ __PRETTY_FUNCTION__))
;
3930 // This PHI node has an incoming value that corresponds to a control
3931 // path through the cleanup pad we are removing. If the incoming
3932 // value is in the cleanup pad, it must be a PHINode (because we
3933 // verified above that the block is otherwise empty). Otherwise, the
3934 // value is either a constant or a value that dominates the cleanup
3935 // pad being removed.
3936 //
3937 // Because BB and UnwindDest are both EH pads, all of their
3938 // predecessors must unwind to these blocks, and since no instruction
3939 // can have multiple unwind destinations, there will be no overlap in
3940 // incoming blocks between SrcPN and DestPN.
3941 Value *SrcVal = DestPN->getIncomingValue(Idx);
3942 PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
3943
3944 // Remove the entry for the block we are deleting.
3945 DestPN->removeIncomingValue(Idx, false);
3946
3947 if (SrcPN && SrcPN->getParent() == BB) {
3948 // If the incoming value was a PHI node in the cleanup pad we are
3949 // removing, we need to merge that PHI node's incoming values into
3950 // DestPN.
3951 for (unsigned SrcIdx = 0, SrcE = SrcPN->getNumIncomingValues();
3952 SrcIdx != SrcE; ++SrcIdx) {
3953 DestPN->addIncoming(SrcPN->getIncomingValue(SrcIdx),
3954 SrcPN->getIncomingBlock(SrcIdx));
3955 }
3956 } else {
3957 // Otherwise, the incoming value came from above BB and
3958 // so we can just reuse it. We must associate all of BB's
3959 // predecessors with this value.
3960 for (auto *pred : predecessors(BB)) {
3961 DestPN->addIncoming(SrcVal, pred);
3962 }
3963 }
3964 }
3965
3966 // Sink any remaining PHI nodes directly into UnwindDest.
3967 Instruction *InsertPt = DestEHPad;
3968 for (BasicBlock::iterator I = BB->begin(),
3969 IE = BB->getFirstNonPHI()->getIterator();
3970 I != IE;) {
3971 // The iterator must be incremented here because the instructions are
3972 // being moved to another block.
3973 PHINode *PN = cast<PHINode>(I++);
3974 if (PN->use_empty())
3975 // If the PHI node has no uses, just leave it. It will be erased
3976 // when we erase BB below.
3977 continue;
3978
3979 // Otherwise, sink this PHI node into UnwindDest.
3980 // Any predecessors to UnwindDest which are not already represented
3981 // must be back edges which inherit the value from the path through
3982 // BB. In this case, the PHI value must reference itself.
3983 for (auto *pred : predecessors(UnwindDest))
3984 if (pred != BB)
3985 PN->addIncoming(PN, pred);
3986 PN->moveBefore(InsertPt);
3987 }
3988 }
3989
3990 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3991 // The iterator must be updated here because we are removing this pred.
3992 BasicBlock *PredBB = *PI++;
3993 if (UnwindDest == nullptr) {
3994 removeUnwindEdge(PredBB);
3995 } else {
3996 TerminatorInst *TI = PredBB->getTerminator();
3997 TI->replaceUsesOfWith(BB, UnwindDest);
3998 }
3999 }
4000
4001 // The cleanup pad is now unreachable. Zap it.
4002 BB->eraseFromParent();
4003 return true;
4004}
4005
4006// Try to merge two cleanuppads together.
4007static bool mergeCleanupPad(CleanupReturnInst *RI) {
4008 // Skip any cleanuprets which unwind to caller, there is nothing to merge
4009 // with.
4010 BasicBlock *UnwindDest = RI->getUnwindDest();
4011 if (!UnwindDest)
4012 return false;
4013
4014 // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
4015 // be safe to merge without code duplication.
4016 if (UnwindDest->getSinglePredecessor() != RI->getParent())
4017 return false;
4018
4019 // Verify that our cleanuppad's unwind destination is another cleanuppad.
4020 auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
4021 if (!SuccessorCleanupPad)
4022 return false;
4023
4024 CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
4025 // Replace any uses of the successor cleanupad with the predecessor pad
4026 // The only cleanuppad uses should be this cleanupret, it's cleanupret and
4027 // funclet bundle operands.
4028 SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
4029 // Remove the old cleanuppad.
4030 SuccessorCleanupPad->eraseFromParent();
4031 // Now, we simply replace the cleanupret with a branch to the unwind
4032 // destination.
4033 BranchInst::Create(UnwindDest, RI->getParent());
4034 RI->eraseFromParent();
4035
4036 return true;
4037}
4038
4039bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
4040 // It is possible to transiantly have an undef cleanuppad operand because we
4041 // have deleted some, but not all, dead blocks.
4042 // Eventually, this block will be deleted.
4043 if (isa<UndefValue>(RI->getOperand(0)))
4044 return false;
4045
4046 if (mergeCleanupPad(RI))
4047 return true;
4048
4049 if (removeEmptyCleanup(RI))
4050 return true;
4051
4052 return false;
4053}
4054
4055bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
4056 BasicBlock *BB = RI->getParent();
4057 if (!BB->getFirstNonPHIOrDbg()->isTerminator())
4058 return false;
4059
4060 // Find predecessors that end with branches.
4061 SmallVector<BasicBlock *, 8> UncondBranchPreds;
4062 SmallVector<BranchInst *, 8> CondBranchPreds;
4063 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
4064 BasicBlock *P = *PI;
4065 TerminatorInst *PTI = P->getTerminator();
4066 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
4067 if (BI->isUnconditional())
4068 UncondBranchPreds.push_back(P);
4069 else
4070 CondBranchPreds.push_back(BI);
4071 }
4072 }
4073
4074 // If we found some, do the transformation!
4075 if (!UncondBranchPreds.empty() && DupRet) {
4076 while (!UncondBranchPreds.empty()) {
4077 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
4078 LLVM_DEBUG(dbgs() << "FOLDING: " << *BBdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
4079 << "INTO UNCOND BRANCH PRED: " << *Pred)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
;
4080 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
4081 }
4082
4083 // If we eliminated all predecessors of the block, delete the block now.
4084 if (pred_empty(BB)) {
4085 // We know there are no successors, so just nuke the block.
4086 BB->eraseFromParent();
4087 if (LoopHeaders)
4088 LoopHeaders->erase(BB);
4089 }
4090
4091 return true;
4092 }
4093
4094 // Check out all of the conditional branches going to this return
4095 // instruction. If any of them just select between returns, change the
4096 // branch itself into a select/return pair.
4097 while (!CondBranchPreds.empty()) {
4098 BranchInst *BI = CondBranchPreds.pop_back_val();
4099
4100 // Check to see if the non-BB successor is also a return block.
4101 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
4102 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
4103 SimplifyCondBranchToTwoReturns(BI, Builder))
4104 return true;
4105 }
4106 return false;
4107}
4108
4109bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
4110 BasicBlock *BB = UI->getParent();
4111
4112 bool Changed = false;
4113
4114 // If there are any instructions immediately before the unreachable that can
4115 // be removed, do so.
4116 while (UI->getIterator() != BB->begin()) {
4117 BasicBlock::iterator BBI = UI->getIterator();
4118 --BBI;
4119 // Do not delete instructions that can have side effects which might cause
4120 // the unreachable to not be reachable; specifically, calls and volatile
4121 // operations may have this effect.
4122 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI))
4123 break;
4124
4125 if (BBI->mayHaveSideEffects()) {
4126 if (auto *SI = dyn_cast<StoreInst>(BBI)) {
4127 if (SI->isVolatile())
4128 break;
4129 } else if (auto *LI = dyn_cast<LoadInst>(BBI)) {
4130 if (LI->isVolatile())
4131 break;
4132 } else if (auto *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
4133 if (RMWI->isVolatile())
4134 break;
4135 } else if (auto *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
4136 if (CXI->isVolatile())
4137 break;
4138 } else if (isa<CatchPadInst>(BBI)) {
4139 // A catchpad may invoke exception object constructors and such, which
4140 // in some languages can be arbitrary code, so be conservative by
4141 // default.
4142 // For CoreCLR, it just involves a type test, so can be removed.
4143 if (classifyEHPersonality(BB->getParent()->getPersonalityFn()) !=
4144 EHPersonality::CoreCLR)
4145 break;
4146 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
4147 !isa<LandingPadInst>(BBI)) {
4148 break;
4149 }
4150 // Note that deleting LandingPad's here is in fact okay, although it
4151 // involves a bit of subtle reasoning. If this inst is a LandingPad,
4152 // all the predecessors of this block will be the unwind edges of Invokes,
4153 // and we can therefore guarantee this block will be erased.
4154 }
4155
4156 // Delete this instruction (any uses are guaranteed to be dead)
4157 if (!BBI->use_empty())
4158 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
4159 BBI->eraseFromParent();
4160 Changed = true;
4161 }
4162
4163 // If the unreachable instruction is the first in the block, take a gander
4164 // at all of the predecessors of this instruction, and simplify them.
4165 if (&BB->front() != UI)
4166 return Changed;
4167
4168 SmallVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
4169 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
4170 TerminatorInst *TI = Preds[i]->getTerminator();
4171 IRBuilder<> Builder(TI);
4172 if (auto *BI = dyn_cast<BranchInst>(TI)) {
4173 if (BI->isUnconditional()) {
4174 if (BI->getSuccessor(0) == BB) {
4175 new UnreachableInst(TI->getContext(), TI);
4176 TI->eraseFromParent();
4177 Changed = true;
4178 }
4179 } else {
4180 if (BI->getSuccessor(0) == BB) {
4181 Builder.CreateBr(BI->getSuccessor(1));
4182 EraseTerminatorInstAndDCECond(BI);
4183 } else if (BI->getSuccessor(1) == BB) {
4184 Builder.CreateBr(BI->getSuccessor(0));
4185 EraseTerminatorInstAndDCECond(BI);
4186 Changed = true;
4187 }
4188 }
4189 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
4190 for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
4191 if (i->getCaseSuccessor() != BB) {
4192 ++i;
4193 continue;
4194 }
4195 BB->removePredecessor(SI->getParent());
4196 i = SI->removeCase(i);
4197 e = SI->case_end();
4198 Changed = true;
4199 }
4200 } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
4201 if (II->getUnwindDest() == BB) {
4202 removeUnwindEdge(TI->getParent());
4203 Changed = true;
4204 }
4205 } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) {
4206 if (CSI->getUnwindDest() == BB) {
4207 removeUnwindEdge(TI->getParent());
4208 Changed = true;
4209 continue;
4210 }
4211
4212 for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(),
4213 E = CSI->handler_end();
4214 I != E; ++I) {
4215 if (*I == BB) {
4216 CSI->removeHandler(I);
4217 --I;
4218 --E;
4219 Changed = true;
4220 }
4221 }
4222 if (CSI->getNumHandlers() == 0) {
4223 BasicBlock *CatchSwitchBB = CSI->getParent();
4224 if (CSI->hasUnwindDest()) {
4225 // Redirect preds to the unwind dest
4226 CatchSwitchBB->replaceAllUsesWith(CSI->getUnwindDest());
4227 } else {
4228 // Rewrite all preds to unwind to caller (or from invoke to call).
4229 SmallVector<BasicBlock *, 8> EHPreds(predecessors(CatchSwitchBB));
4230 for (BasicBlock *EHPred : EHPreds)
4231 removeUnwindEdge(EHPred);
4232 }
4233 // The catchswitch is no longer reachable.
4234 new UnreachableInst(CSI->getContext(), CSI);
4235 CSI->eraseFromParent();
4236 Changed = true;
4237 }
4238 } else if (isa<CleanupReturnInst>(TI)) {
4239 new UnreachableInst(TI->getContext(), TI);
4240 TI->eraseFromParent();
4241 Changed = true;
4242 }
4243 }
4244
4245 // If this block is now dead, remove it.
4246 if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {
4247 // We know there are no successors, so just nuke the block.
4248 BB->eraseFromParent();
4249 if (LoopHeaders)
4250 LoopHeaders->erase(BB);
4251 return true;
4252 }
4253
4254 return Changed;
4255}
4256
4257static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
4258 assert(Cases.size() >= 1)(static_cast <bool> (Cases.size() >= 1) ? void (0) :
__assert_fail ("Cases.size() >= 1", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4258, __extension__ __PRETTY_FUNCTION__))
;
4259
4260 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
4261 for (size_t I = 1, E = Cases.size(); I != E; ++I) {
4262 if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
4263 return false;
4264 }
4265 return true;
4266}
4267
4268/// Turn a switch with two reachable destinations into an integer range
4269/// comparison and branch.
4270static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
4271 assert(SI->getNumCases() > 1 && "Degenerate switch?")(static_cast <bool> (SI->getNumCases() > 1 &&
"Degenerate switch?") ? void (0) : __assert_fail ("SI->getNumCases() > 1 && \"Degenerate switch?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4271, __extension__ __PRETTY_FUNCTION__))
;
4272
4273 bool HasDefault =
4274 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4275
4276 // Partition the cases into two sets with different destinations.
4277 BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
4278 BasicBlock *DestB = nullptr;
4279 SmallVector<ConstantInt *, 16> CasesA;
4280 SmallVector<ConstantInt *, 16> CasesB;
4281
4282 for (auto Case : SI->cases()) {
4283 BasicBlock *Dest = Case.getCaseSuccessor();
4284 if (!DestA)
4285 DestA = Dest;
4286 if (Dest == DestA) {
4287 CasesA.push_back(Case.getCaseValue());
4288 continue;
4289 }
4290 if (!DestB)
4291 DestB = Dest;
4292 if (Dest == DestB) {
4293 CasesB.push_back(Case.getCaseValue());
4294 continue;
4295 }
4296 return false; // More than two destinations.
4297 }
4298
4299 assert(DestA && DestB &&(static_cast <bool> (DestA && DestB && "Single-destination switch should have been folded."
) ? void (0) : __assert_fail ("DestA && DestB && \"Single-destination switch should have been folded.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4300, __extension__ __PRETTY_FUNCTION__))
4300 "Single-destination switch should have been folded.")(static_cast <bool> (DestA && DestB && "Single-destination switch should have been folded."
) ? void (0) : __assert_fail ("DestA && DestB && \"Single-destination switch should have been folded.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4300, __extension__ __PRETTY_FUNCTION__))
;
4301 assert(DestA != DestB)(static_cast <bool> (DestA != DestB) ? void (0) : __assert_fail
("DestA != DestB", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4301, __extension__ __PRETTY_FUNCTION__))
;
4302 assert(DestB != SI->getDefaultDest())(static_cast <bool> (DestB != SI->getDefaultDest()) ?
void (0) : __assert_fail ("DestB != SI->getDefaultDest()"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4302, __extension__ __PRETTY_FUNCTION__))
;
4303 assert(!CasesB.empty() && "There must be non-default cases.")(static_cast <bool> (!CasesB.empty() && "There must be non-default cases."
) ? void (0) : __assert_fail ("!CasesB.empty() && \"There must be non-default cases.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4303, __extension__ __PRETTY_FUNCTION__))
;
4304 assert(!CasesA.empty() || HasDefault)(static_cast <bool> (!CasesA.empty() || HasDefault) ? void
(0) : __assert_fail ("!CasesA.empty() || HasDefault", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4304, __extension__ __PRETTY_FUNCTION__))
;
4305
4306 // Figure out if one of the sets of cases form a contiguous range.
4307 SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
4308 BasicBlock *ContiguousDest = nullptr;
4309 BasicBlock *OtherDest = nullptr;
4310 if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
4311 ContiguousCases = &CasesA;
4312 ContiguousDest = DestA;
4313 OtherDest = DestB;
4314 } else if (CasesAreContiguous(CasesB)) {
4315 ContiguousCases = &CasesB;
4316 ContiguousDest = DestB;
4317 OtherDest = DestA;
4318 } else
4319 return false;
4320
4321 // Start building the compare and branch.
4322
4323 Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
4324 Constant *NumCases =
4325 ConstantInt::get(Offset->getType(), ContiguousCases->size());
4326
4327 Value *Sub = SI->getCondition();
4328 if (!Offset->isNullValue())
4329 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
4330
4331 Value *Cmp;
4332 // If NumCases overflowed, then all possible values jump to the successor.
4333 if (NumCases->isNullValue() && !ContiguousCases->empty())
4334 Cmp = ConstantInt::getTrue(SI->getContext());
4335 else
4336 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
4337 BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
4338
4339 // Update weight for the newly-created conditional branch.
4340 if (HasBranchWeights(SI)) {
4341 SmallVector<uint64_t, 8> Weights;
4342 GetBranchWeights(SI, Weights);
4343 if (Weights.size() == 1 + SI->getNumCases()) {
4344 uint64_t TrueWeight = 0;
4345 uint64_t FalseWeight = 0;
4346 for (size_t I = 0, E = Weights.size(); I != E; ++I) {
4347 if (SI->getSuccessor(I) == ContiguousDest)
4348 TrueWeight += Weights[I];
4349 else
4350 FalseWeight += Weights[I];
4351 }
4352 while (TrueWeight > UINT32_MAX(4294967295U) || FalseWeight > UINT32_MAX(4294967295U)) {
4353 TrueWeight /= 2;
4354 FalseWeight /= 2;
4355 }
4356 setBranchWeights(NewBI, TrueWeight, FalseWeight);
4357 }
4358 }
4359
4360 // Prune obsolete incoming values off the successors' PHI nodes.
4361 for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
4362 unsigned PreviousEdges = ContiguousCases->size();
4363 if (ContiguousDest == SI->getDefaultDest())
4364 ++PreviousEdges;
4365 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4366 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4367 }
4368 for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
4369 unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
4370 if (OtherDest == SI->getDefaultDest())
4371 ++PreviousEdges;
4372 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4373 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4374 }
4375
4376 // Drop the switch.
4377 SI->eraseFromParent();
4378
4379 return true;
4380}
4381
4382/// Compute masked bits for the condition of a switch
4383/// and use it to remove dead cases.
4384static bool eliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC,
4385 const DataLayout &DL) {
4386 Value *Cond = SI->getCondition();
4387 unsigned Bits = Cond->getType()->getIntegerBitWidth();
4388 KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI);
4389
4390 // We can also eliminate cases by determining that their values are outside of
4391 // the limited range of the condition based on how many significant (non-sign)
4392 // bits are in the condition value.
4393 unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1;
4394 unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits;
4395
4396 // Gather dead cases.
4397 SmallVector<ConstantInt *, 8> DeadCases;
4398 for (auto &Case : SI->cases()) {
4399 const APInt &CaseVal = Case.getCaseValue()->getValue();
4400 if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) ||
4401 (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
4402 DeadCases.push_back(Case.getCaseValue());
4403 LLVM_DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseValdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch case "
<< CaseVal << " is dead.\n"; } } while (false)
4404 << " is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch case "
<< CaseVal << " is dead.\n"; } } while (false)
;
4405 }
4406 }
4407
4408 // If we can prove that the cases must cover all possible values, the
4409 // default destination becomes dead and we can remove it. If we know some
4410 // of the bits in the value, we can use that to more precisely compute the
4411 // number of possible unique case values.
4412 bool HasDefault =
4413 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4414 const unsigned NumUnknownBits =
4415 Bits - (Known.Zero | Known.One).countPopulation();
4416 assert(NumUnknownBits <= Bits)(static_cast <bool> (NumUnknownBits <= Bits) ? void (
0) : __assert_fail ("NumUnknownBits <= Bits", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4416, __extension__ __PRETTY_FUNCTION__))
;
4417 if (HasDefault && DeadCases.empty() &&
4418 NumUnknownBits < 64 /* avoid overflow */ &&
4419 SI->getNumCases() == (1ULL << NumUnknownBits)) {
4420 LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch default is dead.\n"
; } } while (false)
;
4421 BasicBlock *NewDefault =
4422 SplitBlockPredecessors(SI->getDefaultDest(), SI->getParent(), "");
4423 SI->setDefaultDest(&*NewDefault);
4424 SplitBlock(&*NewDefault, &NewDefault->front());
4425 auto *OldTI = NewDefault->getTerminator();
4426 new UnreachableInst(SI->getContext(), OldTI);
4427 EraseTerminatorInstAndDCECond(OldTI);
4428 return true;
4429 }
4430
4431 SmallVector<uint64_t, 8> Weights;
4432 bool HasWeight = HasBranchWeights(SI);
4433 if (HasWeight) {
4434 GetBranchWeights(SI, Weights);
4435 HasWeight = (Weights.size() == 1 + SI->getNumCases());
4436 }
4437
4438 // Remove dead cases from the switch.
4439 for (ConstantInt *DeadCase : DeadCases) {
4440 SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase);
4441 assert(CaseI != SI->case_default() &&(static_cast <bool> (CaseI != SI->case_default() &&
"Case was not found. Probably mistake in DeadCases forming."
) ? void (0) : __assert_fail ("CaseI != SI->case_default() && \"Case was not found. Probably mistake in DeadCases forming.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4442, __extension__ __PRETTY_FUNCTION__))
4442 "Case was not found. Probably mistake in DeadCases forming.")(static_cast <bool> (CaseI != SI->case_default() &&
"Case was not found. Probably mistake in DeadCases forming."
) ? void (0) : __assert_fail ("CaseI != SI->case_default() && \"Case was not found. Probably mistake in DeadCases forming.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4442, __extension__ __PRETTY_FUNCTION__))
;
4443 if (HasWeight) {
4444 std::swap(Weights[CaseI->getCaseIndex() + 1], Weights.back());
4445 Weights.pop_back();
4446 }
4447
4448 // Prune unused values from PHI nodes.
4449 CaseI->getCaseSuccessor()->removePredecessor(SI->getParent());
4450 SI->removeCase(CaseI);
4451 }
4452 if (HasWeight && Weights.size() >= 2) {
4453 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
4454 setBranchWeights(SI, MDWeights);
4455 }
4456
4457 return !DeadCases.empty();
4458}
4459
4460/// If BB would be eligible for simplification by
4461/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
4462/// by an unconditional branch), look at the phi node for BB in the successor
4463/// block and see if the incoming value is equal to CaseValue. If so, return
4464/// the phi node, and set PhiIndex to BB's index in the phi node.
4465static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
4466 BasicBlock *BB, int *PhiIndex) {
4467 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
4468 return nullptr; // BB must be empty to be a candidate for simplification.
4469 if (!BB->getSinglePredecessor())
4470 return nullptr; // BB must be dominated by the switch.
4471
4472 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
4473 if (!Branch || !Branch->isUnconditional())
4474 return nullptr; // Terminator must be unconditional branch.
4475
4476 BasicBlock *Succ = Branch->getSuccessor(0);
4477
4478 for (PHINode &PHI : Succ->phis()) {
4479 int Idx = PHI.getBasicBlockIndex(BB);
4480 assert(Idx >= 0 && "PHI has no entry for predecessor?")(static_cast <bool> (Idx >= 0 && "PHI has no entry for predecessor?"
) ? void (0) : __assert_fail ("Idx >= 0 && \"PHI has no entry for predecessor?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4480, __extension__ __PRETTY_FUNCTION__))
;
4481
4482 Value *InValue = PHI.getIncomingValue(Idx);
4483 if (InValue != CaseValue)
4484 continue;
4485
4486 *PhiIndex = Idx;
4487 return &PHI;
4488 }
4489
4490 return nullptr;
4491}
4492
4493/// Try to forward the condition of a switch instruction to a phi node
4494/// dominated by the switch, if that would mean that some of the destination
4495/// blocks of the switch can be folded away. Return true if a change is made.
4496static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
4497 using ForwardingNodesMap = DenseMap<PHINode *, SmallVector<int, 4>>;
4498
4499 ForwardingNodesMap ForwardingNodes;
4500 BasicBlock *SwitchBlock = SI->getParent();
4501 bool Changed = false;
4502 for (auto &Case : SI->cases()) {
4503 ConstantInt *CaseValue = Case.getCaseValue();
4504 BasicBlock *CaseDest = Case.getCaseSuccessor();
4505
4506 // Replace phi operands in successor blocks that are using the constant case
4507 // value rather than the switch condition variable:
4508 // switchbb:
4509 // switch i32 %x, label %default [
4510 // i32 17, label %succ
4511 // ...
4512 // succ:
4513 // %r = phi i32 ... [ 17, %switchbb ] ...
4514 // -->
4515 // %r = phi i32 ... [ %x, %switchbb ] ...
4516
4517 for (PHINode &Phi : CaseDest->phis()) {
4518 // This only works if there is exactly 1 incoming edge from the switch to
4519 // a phi. If there is >1, that means multiple cases of the switch map to 1
4520 // value in the phi, and that phi value is not the switch condition. Thus,
4521 // this transform would not make sense (the phi would be invalid because
4522 // a phi can't have different incoming values from the same block).
4523 int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock);
4524 if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue &&
4525 count(Phi.blocks(), SwitchBlock) == 1) {
4526 Phi.setIncomingValue(SwitchBBIdx, SI->getCondition());
4527 Changed = true;
4528 }
4529 }
4530
4531 // Collect phi nodes that are indirectly using this switch's case constants.
4532 int PhiIdx;
4533 if (auto *Phi = FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIdx))
4534 ForwardingNodes[Phi].push_back(PhiIdx);
4535 }
4536
4537 for (auto &ForwardingNode : ForwardingNodes) {
4538 PHINode *Phi = ForwardingNode.first;
4539 SmallVectorImpl<int> &Indexes = ForwardingNode.second;
4540 if (Indexes.size() < 2)
4541 continue;
4542
4543 for (int Index : Indexes)
4544 Phi->setIncomingValue(Index, SI->getCondition());
4545 Changed = true;
4546 }
4547
4548 return Changed;
4549}
4550
4551/// Return true if the backend will be able to handle
4552/// initializing an array of constants like C.
4553static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
4554 if (C->isThreadDependent())
4555 return false;
4556 if (C->isDLLImportDependent())
4557 return false;
4558
4559 if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
4560 !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
4561 !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
4562 return false;
4563
4564 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
4565 if (!CE->isGEPWithNoNotionalOverIndexing())
4566 return false;
4567 if (!ValidLookupTableConstant(CE->getOperand(0), TTI))
4568 return false;
4569 }
4570
4571 if (!TTI.shouldBuildLookupTablesForConstant(C))
4572 return false;
4573
4574 return true;
4575}
4576
4577/// If V is a Constant, return it. Otherwise, try to look up
4578/// its constant value in ConstantPool, returning 0 if it's not there.
4579static Constant *
4580LookupConstant(Value *V,
4581 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4582 if (Constant *C = dyn_cast<Constant>(V))
4583 return C;
4584 return ConstantPool.lookup(V);
4585}
4586
4587/// Try to fold instruction I into a constant. This works for
4588/// simple instructions such as binary operations where both operands are
4589/// constant or can be replaced by constants from the ConstantPool. Returns the
4590/// resulting constant on success, 0 otherwise.
4591static Constant *
4592ConstantFold(Instruction *I, const DataLayout &DL,
4593 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4594 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
4595 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
4596 if (!A)
4597 return nullptr;
4598 if (A->isAllOnesValue())
4599 return LookupConstant(Select->getTrueValue(), ConstantPool);
4600 if (A->isNullValue())
4601 return LookupConstant(Select->getFalseValue(), ConstantPool);
4602 return nullptr;
4603 }
4604
4605 SmallVector<Constant *, 4> COps;
4606 for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
4607 if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
4608 COps.push_back(A);
4609 else
4610 return nullptr;
4611 }
4612
4613 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
4614 return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
4615 COps[1], DL);
4616 }
4617
4618 return ConstantFoldInstOperands(I, COps, DL);
4619}
4620
4621/// Try to determine the resulting constant values in phi nodes
4622/// at the common destination basic block, *CommonDest, for one of the case
4623/// destionations CaseDest corresponding to value CaseVal (0 for the default
4624/// case), of a switch instruction SI.
4625static bool
4626GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
4627 BasicBlock **CommonDest,
4628 SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
4629 const DataLayout &DL, const TargetTransformInfo &TTI) {
4630 // The block from which we enter the common destination.
4631 BasicBlock *Pred = SI->getParent();
4632
4633 // If CaseDest is empty except for some side-effect free instructions through
4634 // which we can constant-propagate the CaseVal, continue to its successor.
4635 SmallDenseMap<Value *, Constant *> ConstantPool;
4636 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
4637 for (Instruction &I :CaseDest->instructionsWithoutDebug()) {
4638 if (TerminatorInst *T = dyn_cast<TerminatorInst>(&I)) {
10
Assuming 'T' is non-null
11
Taking true branch
4639 // If the terminator is a simple branch, continue to the next block.
4640 if (T->getNumSuccessors() != 1 || T->isExceptional())
12
Assuming the condition is true
4641 return false;
4642 Pred = CaseDest;
4643 CaseDest = T->getSuccessor(0);
4644 } else if (Constant *C = ConstantFold(&I, DL, ConstantPool)) {
4645 // Instruction is side-effect free and constant.
4646
4647 // If the instruction has uses outside this block or a phi node slot for
4648 // the block, it is not safe to bypass the instruction since it would then
4649 // no longer dominate all its uses.
4650 for (auto &Use : I.uses()) {
4651 User *User = Use.getUser();
4652 if (Instruction *I = dyn_cast<Instruction>(User))
4653 if (I->getParent() == CaseDest)
4654 continue;
4655 if (PHINode *Phi = dyn_cast<PHINode>(User))
4656 if (Phi->getIncomingBlock(Use) == CaseDest)
4657 continue;
4658 return false;
4659 }
4660
4661 ConstantPool.insert(std::make_pair(&I, C));
4662 } else {
4663 break;
4664 }
4665 }
4666
4667 // If we did not have a CommonDest before, use the current one.
4668 if (!*CommonDest)
4669 *CommonDest = CaseDest;
4670 // If the destination isn't the common one, abort.
4671 if (CaseDest != *CommonDest)
4672 return false;
4673
4674 // Get the values for this case from phi nodes in the destination block.
4675 for (PHINode &PHI : (*CommonDest)->phis()) {
4676 int Idx = PHI.getBasicBlockIndex(Pred);
4677 if (Idx == -1)
4678 continue;
4679
4680 Constant *ConstVal =
4681 LookupConstant(PHI.getIncomingValue(Idx), ConstantPool);
4682 if (!ConstVal)
4683 return false;
4684
4685 // Be conservative about which kinds of constants we support.
4686 if (!ValidLookupTableConstant(ConstVal, TTI))
4687 return false;
4688
4689 Res.push_back(std::make_pair(&PHI, ConstVal));
4690 }
4691
4692 return Res.size() > 0;
4693}
13
Returning without writing to '*CommonDest'
4694
4695// Helper function used to add CaseVal to the list of cases that generate
4696// Result. Returns the updated number of cases that generate this result.
4697static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
4698 SwitchCaseResultVectorTy &UniqueResults,
4699 Constant *Result) {
4700 for (auto &I : UniqueResults) {
4701 if (I.first == Result) {
4702 I.second.push_back(CaseVal);
4703 return I.second.size();
4704 }
4705 }
4706 UniqueResults.push_back(
4707 std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal)));
4708 return 1;
4709}
4710
4711// Helper function that initializes a map containing
4712// results for the PHI node of the common destination block for a switch
4713// instruction. Returns false if multiple PHI nodes have been found or if
4714// there is not a common destination block for the switch.
4715static bool
4716InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
4717 SwitchCaseResultVectorTy &UniqueResults,
4718 Constant *&DefaultResult, const DataLayout &DL,
4719 const TargetTransformInfo &TTI,
4720 uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) {
4721 for (auto &I : SI->cases()) {
4722 ConstantInt *CaseVal = I.getCaseValue();
4723
4724 // Resulting value at phi nodes for this case value.
4725 SwitchCaseResultsTy Results;
4726 if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
4727 DL, TTI))
4728 return false;
4729
4730 // Only one value per case is permitted.
4731 if (Results.size() > 1)
4732 return false;
4733
4734 // Add the case->result mapping to UniqueResults.
4735 const uintptr_t NumCasesForResult =
4736 MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
4737
4738 // Early out if there are too many cases for this result.
4739 if (NumCasesForResult > MaxCasesPerResult)
4740 return false;
4741
4742 // Early out if there are too many unique results.
4743 if (UniqueResults.size() > MaxUniqueResults)
4744 return false;
4745
4746 // Check the PHI consistency.
4747 if (!PHI)
4748 PHI = Results[0].first;
4749 else if (PHI != Results[0].first)
4750 return false;
4751 }
4752 // Find the default result value.
4753 SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
4754 BasicBlock *DefaultDest = SI->getDefaultDest();
4755 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
4756 DL, TTI);
4757 // If the default value is not found abort unless the default destination
4758 // is unreachable.
4759 DefaultResult =
4760 DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
4761 if ((!DefaultResult &&
4762 !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
4763 return false;
4764
4765 return true;
4766}
4767
4768// Helper function that checks if it is possible to transform a switch with only
4769// two cases (or two cases + default) that produces a result into a select.
4770// Example:
4771// switch (a) {
4772// case 10: %0 = icmp eq i32 %a, 10
4773// return 10; %1 = select i1 %0, i32 10, i32 4
4774// case 20: ----> %2 = icmp eq i32 %a, 20
4775// return 2; %3 = select i1 %2, i32 2, i32 %1
4776// default:
4777// return 4;
4778// }
4779static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
4780 Constant *DefaultResult, Value *Condition,
4781 IRBuilder<> &Builder) {
4782 assert(ResultVector.size() == 2 &&(static_cast <bool> (ResultVector.size() == 2 &&
"We should have exactly two unique results at this point") ?
void (0) : __assert_fail ("ResultVector.size() == 2 && \"We should have exactly two unique results at this point\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4783, __extension__ __PRETTY_FUNCTION__))
4783 "We should have exactly two unique results at this point")(static_cast <bool> (ResultVector.size() == 2 &&
"We should have exactly two unique results at this point") ?
void (0) : __assert_fail ("ResultVector.size() == 2 && \"We should have exactly two unique results at this point\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4783, __extension__ __PRETTY_FUNCTION__))
;
4784 // If we are selecting between only two cases transform into a simple
4785 // select or a two-way select if default is possible.
4786 if (ResultVector[0].second.size() == 1 &&
4787 ResultVector[1].second.size() == 1) {
4788 ConstantInt *const FirstCase = ResultVector[0].second[0];
4789 ConstantInt *const SecondCase = ResultVector[1].second[0];
4790
4791 bool DefaultCanTrigger = DefaultResult;
4792 Value *SelectValue = ResultVector[1].first;
4793 if (DefaultCanTrigger) {
4794 Value *const ValueCompare =
4795 Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
4796 SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
4797 DefaultResult, "switch.select");
4798 }
4799 Value *const ValueCompare =
4800 Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
4801 return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
4802 SelectValue, "switch.select");
4803 }
4804
4805 return nullptr;
4806}
4807
4808// Helper function to cleanup a switch instruction that has been converted into
4809// a select, fixing up PHI nodes and basic blocks.
4810static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
4811 Value *SelectValue,
4812 IRBuilder<> &Builder) {
4813 BasicBlock *SelectBB = SI->getParent();
4814 while (PHI->getBasicBlockIndex(SelectBB) >= 0)
4815 PHI->removeIncomingValue(SelectBB);
4816 PHI->addIncoming(SelectValue, SelectBB);
4817
4818 Builder.CreateBr(PHI->getParent());
4819
4820 // Remove the switch.
4821 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
4822 BasicBlock *Succ = SI->getSuccessor(i);
4823
4824 if (Succ == PHI->getParent())
4825 continue;
4826 Succ->removePredecessor(SelectBB);
4827 }
4828 SI->eraseFromParent();
4829}
4830
4831/// If the switch is only used to initialize one or more
4832/// phi nodes in a common successor block with only two different
4833/// constant values, replace the switch with select.
4834static bool switchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
4835 const DataLayout &DL,
4836 const TargetTransformInfo &TTI) {
4837 Value *const Cond = SI->getCondition();
4838 PHINode *PHI = nullptr;
4839 BasicBlock *CommonDest = nullptr;
4840 Constant *DefaultResult;
4841 SwitchCaseResultVectorTy UniqueResults;
4842 // Collect all the cases that will deliver the same value from the switch.
4843 if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
4844 DL, TTI, 2, 1))
4845 return false;
4846 // Selects choose between maximum two values.
4847 if (UniqueResults.size() != 2)
4848 return false;
4849 assert(PHI != nullptr && "PHI for value select not found")(static_cast <bool> (PHI != nullptr && "PHI for value select not found"
) ? void (0) : __assert_fail ("PHI != nullptr && \"PHI for value select not found\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4849, __extension__ __PRETTY_FUNCTION__))
;
4850
4851 Builder.SetInsertPoint(SI);
4852 Value *SelectValue =
4853 ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
4854 if (SelectValue) {
4855 RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder);
4856 return true;
4857 }
4858 // The switch couldn't be converted into a select.
4859 return false;
4860}
4861
4862namespace {
4863
4864/// This class represents a lookup table that can be used to replace a switch.
4865class SwitchLookupTable {
4866public:
4867 /// Create a lookup table to use as a switch replacement with the contents
4868 /// of Values, using DefaultValue to fill any holes in the table.
4869 SwitchLookupTable(
4870 Module &M, uint64_t TableSize, ConstantInt *Offset,
4871 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4872 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName);
4873
4874 /// Build instructions with Builder to retrieve the value at
4875 /// the position given by Index in the lookup table.
4876 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
4877
4878 /// Return true if a table with TableSize elements of
4879 /// type ElementType would fit in a target-legal register.
4880 static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
4881 Type *ElementType);
4882
4883private:
4884 // Depending on the contents of the table, it can be represented in
4885 // different ways.
4886 enum {
4887 // For tables where each element contains the same value, we just have to
4888 // store that single value and return it for each lookup.
4889 SingleValueKind,
4890
4891 // For tables where there is a linear relationship between table index
4892 // and values. We calculate the result with a simple multiplication
4893 // and addition instead of a table lookup.
4894 LinearMapKind,
4895
4896 // For small tables with integer elements, we can pack them into a bitmap
4897 // that fits into a target-legal register. Values are retrieved by
4898 // shift and mask operations.
4899 BitMapKind,
4900
4901 // The table is stored as an array of values. Values are retrieved by load
4902 // instructions from the table.
4903 ArrayKind
4904 } Kind;
4905
4906 // For SingleValueKind, this is the single value.
4907 Constant *SingleValue = nullptr;
4908
4909 // For BitMapKind, this is the bitmap.
4910 ConstantInt *BitMap = nullptr;
4911 IntegerType *BitMapElementTy = nullptr;
4912
4913 // For LinearMapKind, these are the constants used to derive the value.
4914 ConstantInt *LinearOffset = nullptr;
4915 ConstantInt *LinearMultiplier = nullptr;
4916
4917 // For ArrayKind, this is the array.
4918 GlobalVariable *Array = nullptr;
4919};
4920
4921} // end anonymous namespace
4922
4923SwitchLookupTable::SwitchLookupTable(
4924 Module &M, uint64_t TableSize, ConstantInt *Offset,
4925 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4926 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName) {
4927 assert(Values.size() && "Can't build lookup table without values!")(static_cast <bool> (Values.size() && "Can't build lookup table without values!"
) ? void (0) : __assert_fail ("Values.size() && \"Can't build lookup table without values!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4927, __extension__ __PRETTY_FUNCTION__))
;
4928 assert(TableSize >= Values.size() && "Can't fit values in table!")(static_cast <bool> (TableSize >= Values.size() &&
"Can't fit values in table!") ? void (0) : __assert_fail ("TableSize >= Values.size() && \"Can't fit values in table!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4928, __extension__ __PRETTY_FUNCTION__))
;
4929
4930 // If all values in the table are equal, this is that value.
4931 SingleValue = Values.begin()->second;
4932
4933 Type *ValueType = Values.begin()->second->getType();
4934
4935 // Build up the table contents.
4936 SmallVector<Constant *, 64> TableContents(TableSize);
4937 for (size_t I = 0, E = Values.size(); I != E; ++I) {
4938 ConstantInt *CaseVal = Values[I].first;
4939 Constant *CaseRes = Values[I].second;
4940 assert(CaseRes->getType() == ValueType)(static_cast <bool> (CaseRes->getType() == ValueType
) ? void (0) : __assert_fail ("CaseRes->getType() == ValueType"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4940, __extension__ __PRETTY_FUNCTION__))
;
4941
4942 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
4943 TableContents[Idx] = CaseRes;
4944
4945 if (CaseRes != SingleValue)
4946 SingleValue = nullptr;
4947 }
4948
4949 // Fill in any holes in the table with the default result.
4950 if (Values.size() < TableSize) {
4951 assert(DefaultValue &&(static_cast <bool> (DefaultValue && "Need a default value to fill the lookup table holes."
) ? void (0) : __assert_fail ("DefaultValue && \"Need a default value to fill the lookup table holes.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4952, __extension__ __PRETTY_FUNCTION__))
4952 "Need a default value to fill the lookup table holes.")(static_cast <bool> (DefaultValue && "Need a default value to fill the lookup table holes."
) ? void (0) : __assert_fail ("DefaultValue && \"Need a default value to fill the lookup table holes.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4952, __extension__ __PRETTY_FUNCTION__))
;
4953 assert(DefaultValue->getType() == ValueType)(static_cast <bool> (DefaultValue->getType() == ValueType
) ? void (0) : __assert_fail ("DefaultValue->getType() == ValueType"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4953, __extension__ __PRETTY_FUNCTION__))
;
4954 for (uint64_t I = 0; I < TableSize; ++I) {
4955 if (!TableContents[I])
4956 TableContents[I] = DefaultValue;
4957 }
4958
4959 if (DefaultValue != SingleValue)
4960 SingleValue = nullptr;
4961 }
4962
4963 // If each element in the table contains the same value, we only need to store
4964 // that single value.
4965 if (SingleValue) {
4966 Kind = SingleValueKind;
4967 return;
4968 }
4969
4970 // Check if we can derive the value with a linear transformation from the
4971 // table index.
4972 if (isa<IntegerType>(ValueType)) {
4973 bool LinearMappingPossible = true;
4974 APInt PrevVal;
4975 APInt DistToPrev;
4976 assert(TableSize >= 2 && "Should be a SingleValue table.")(static_cast <bool> (TableSize >= 2 && "Should be a SingleValue table."
) ? void (0) : __assert_fail ("TableSize >= 2 && \"Should be a SingleValue table.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4976, __extension__ __PRETTY_FUNCTION__))
;
4977 // Check if there is the same distance between two consecutive values.
4978 for (uint64_t I = 0; I < TableSize; ++I) {
4979 ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
4980 if (!ConstVal) {
4981 // This is an undef. We could deal with it, but undefs in lookup tables
4982 // are very seldom. It's probably not worth the additional complexity.
4983 LinearMappingPossible = false;
4984 break;
4985 }
4986 const APInt &Val = ConstVal->getValue();
4987 if (I != 0) {
4988 APInt Dist = Val - PrevVal;
4989 if (I == 1) {
4990 DistToPrev = Dist;
4991 } else if (Dist != DistToPrev) {
4992 LinearMappingPossible = false;
4993 break;
4994 }
4995 }
4996 PrevVal = Val;
4997 }
4998 if (LinearMappingPossible) {
4999 LinearOffset = cast<ConstantInt>(TableContents[0]);
5000 LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
5001 Kind = LinearMapKind;
5002 ++NumLinearMaps;
5003 return;
5004 }
5005 }
5006
5007 // If the type is integer and the table fits in a register, build a bitmap.
5008 if (WouldFitInRegister(DL, TableSize, ValueType)) {
5009 IntegerType *IT = cast<IntegerType>(ValueType);
5010 APInt TableInt(TableSize * IT->getBitWidth(), 0);
5011 for (uint64_t I = TableSize; I > 0; --I) {
5012 TableInt <<= IT->getBitWidth();
5013 // Insert values into the bitmap. Undef values are set to zero.
5014 if (!isa<UndefValue>(TableContents[I - 1])) {
5015 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
5016 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
5017 }
5018 }
5019 BitMap = ConstantInt::get(M.getContext(), TableInt);
5020 BitMapElementTy = IT;
5021 Kind = BitMapKind;
5022 ++NumBitMaps;
5023 return;
5024 }
5025
5026 // Store the table in an array.
5027 ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
5028 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
5029
5030 Array = new GlobalVariable(M, ArrayTy, /*constant=*/true,
5031 GlobalVariable::PrivateLinkage, Initializer,
5032 "switch.table." + FuncName);
5033 Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
5034 Kind = ArrayKind;
5035}
5036
5037Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
5038 switch (Kind) {
5039 case SingleValueKind:
5040 return SingleValue;
5041 case LinearMapKind: {
5042 // Derive the result value from the input value.
5043 Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
5044 false, "switch.idx.cast");
5045 if (!LinearMultiplier->isOne())
5046 Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
5047 if (!LinearOffset->isZero())
5048 Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
5049 return Result;
5050 }
5051 case BitMapKind: {
5052 // Type of the bitmap (e.g. i59).
5053 IntegerType *MapTy = BitMap->getType();
5054
5055 // Cast Index to the same type as the bitmap.
5056 // Note: The Index is <= the number of elements in the table, so
5057 // truncating it to the width of the bitmask is safe.
5058 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
5059
5060 // Multiply the shift amount by the element width.
5061 ShiftAmt = Builder.CreateMul(
5062 ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
5063 "switch.shiftamt");
5064
5065 // Shift down.
5066 Value *DownShifted =
5067 Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift");
5068 // Mask off.
5069 return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked");
5070 }
5071 case ArrayKind: {
5072 // Make sure the table index will not overflow when treated as signed.
5073 IntegerType *IT = cast<IntegerType>(Index->getType());
5074 uint64_t TableSize =
5075 Array->getInitializer()->getType()->getArrayNumElements();
5076 if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
5077 Index = Builder.CreateZExt(
5078 Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1),
5079 "switch.tableidx.zext");
5080
5081 Value *GEPIndices[] = {Builder.getInt32(0), Index};
5082 Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
5083 GEPIndices, "switch.gep");
5084 return Builder.CreateLoad(GEP, "switch.load");
5085 }
5086 }
5087 llvm_unreachable("Unknown lookup table kind!")::llvm::llvm_unreachable_internal("Unknown lookup table kind!"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5087)
;
5088}
5089
5090bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
5091 uint64_t TableSize,
5092 Type *ElementType) {
5093 auto *IT = dyn_cast<IntegerType>(ElementType);
5094 if (!IT)
5095 return false;
5096 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
5097 // are <= 15, we could try to narrow the type.
5098
5099 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
5100 if (TableSize >= UINT_MAX(2147483647 *2U +1U) / IT->getBitWidth())
5101 return false;
5102 return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
5103}
5104
5105/// Determine whether a lookup table should be built for this switch, based on
5106/// the number of cases, size of the table, and the types of the results.
5107static bool
5108ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
5109 const TargetTransformInfo &TTI, const DataLayout &DL,
5110 const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
5111 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX(18446744073709551615UL) / 10)
5112 return false; // TableSize overflowed, or mul below might overflow.
5113
5114 bool AllTablesFitInRegister = true;
5115 bool HasIllegalType = false;
5116 for (const auto &I : ResultTypes) {
5117 Type *Ty = I.second;
5118
5119 // Saturate this flag to true.
5120 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
5121
5122 // Saturate this flag to false.
5123 AllTablesFitInRegister =
5124 AllTablesFitInRegister &&
5125 SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
5126
5127 // If both flags saturate, we're done. NOTE: This *only* works with
5128 // saturating flags, and all flags have to saturate first due to the
5129 // non-deterministic behavior of iterating over a dense map.
5130 if (HasIllegalType && !AllTablesFitInRegister)
5131 break;
5132 }
5133
5134 // If each table would fit in a register, we should build it anyway.
5135 if (AllTablesFitInRegister)
5136 return true;
5137
5138 // Don't build a table that doesn't fit in-register if it has illegal types.
5139 if (HasIllegalType)
5140 return false;
5141
5142 // The table density should be at least 40%. This is the same criterion as for
5143 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
5144 // FIXME: Find the best cut-off.
5145 return SI->getNumCases() * 10 >= TableSize * 4;
5146}
5147
5148/// Try to reuse the switch table index compare. Following pattern:
5149/// \code
5150/// if (idx < tablesize)
5151/// r = table[idx]; // table does not contain default_value
5152/// else
5153/// r = default_value;
5154/// if (r != default_value)
5155/// ...
5156/// \endcode
5157/// Is optimized to:
5158/// \code
5159/// cond = idx < tablesize;
5160/// if (cond)
5161/// r = table[idx];
5162/// else
5163/// r = default_value;
5164/// if (cond)
5165/// ...
5166/// \endcode
5167/// Jump threading will then eliminate the second if(cond).
5168static void reuseTableCompare(
5169 User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch,
5170 Constant *DefaultValue,
5171 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) {
5172 ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
5173 if (!CmpInst)
5174 return;
5175
5176 // We require that the compare is in the same block as the phi so that jump
5177 // threading can do its work afterwards.
5178 if (CmpInst->getParent() != PhiBlock)
5179 return;
5180
5181 Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
5182 if (!CmpOp1)
5183 return;
5184
5185 Value *RangeCmp = RangeCheckBranch->getCondition();
5186 Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
5187 Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
5188
5189 // Check if the compare with the default value is constant true or false.
5190 Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5191 DefaultValue, CmpOp1, true);
5192 if (DefaultConst != TrueConst && DefaultConst != FalseConst)
5193 return;
5194
5195 // Check if the compare with the case values is distinct from the default
5196 // compare result.
5197 for (auto ValuePair : Values) {
5198 Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5199 ValuePair.second, CmpOp1, true);
5200 if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst))
5201 return;
5202 assert((CaseConst == TrueConst || CaseConst == FalseConst) &&(static_cast <bool> ((CaseConst == TrueConst || CaseConst
== FalseConst) && "Expect true or false as compare result."
) ? void (0) : __assert_fail ("(CaseConst == TrueConst || CaseConst == FalseConst) && \"Expect true or false as compare result.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5203, __extension__ __PRETTY_FUNCTION__))
5203 "Expect true or false as compare result.")(static_cast <bool> ((CaseConst == TrueConst || CaseConst
== FalseConst) && "Expect true or false as compare result."
) ? void (0) : __assert_fail ("(CaseConst == TrueConst || CaseConst == FalseConst) && \"Expect true or false as compare result.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5203, __extension__ __PRETTY_FUNCTION__))
;
5204 }
5205
5206 // Check if the branch instruction dominates the phi node. It's a simple
5207 // dominance check, but sufficient for our needs.
5208 // Although this check is invariant in the calling loops, it's better to do it
5209 // at this late stage. Practically we do it at most once for a switch.
5210 BasicBlock *BranchBlock = RangeCheckBranch->getParent();
5211 for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) {
5212 BasicBlock *Pred = *PI;
5213 if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
5214 return;
5215 }
5216
5217 if (DefaultConst == FalseConst) {
5218 // The compare yields the same result. We can replace it.
5219 CmpInst->replaceAllUsesWith(RangeCmp);
5220 ++NumTableCmpReuses;
5221 } else {
5222 // The compare yields the same result, just inverted. We can replace it.
5223 Value *InvertedTableCmp = BinaryOperator::CreateXor(
5224 RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
5225 RangeCheckBranch);
5226 CmpInst->replaceAllUsesWith(InvertedTableCmp);
5227 ++NumTableCmpReuses;
5228 }
5229}
5230
5231/// If the switch is only used to initialize one or more phi nodes in a common
5232/// successor block with different constant values, replace the switch with
5233/// lookup tables.
5234static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
5235 const DataLayout &DL,
5236 const TargetTransformInfo &TTI) {
5237 assert(SI->getNumCases() > 1 && "Degenerate switch?")(static_cast <bool> (SI->getNumCases() > 1 &&
"Degenerate switch?") ? void (0) : __assert_fail ("SI->getNumCases() > 1 && \"Degenerate switch?\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5237, __extension__ __PRETTY_FUNCTION__))
;
5238
5239 Function *Fn = SI->getParent()->getParent();
5240 // Only build lookup table when we have a target that supports it or the
5241 // attribute is not set.
5242 if (!TTI.shouldBuildLookupTables() ||
1
Assuming the condition is false
2
Assuming the condition is false
3
Taking false branch
5243 (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true"))
5244 return false;
5245
5246 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
5247 // split off a dense part and build a lookup table for that.
5248
5249 // FIXME: This creates arrays of GEPs to constant strings, which means each
5250 // GEP needs a runtime relocation in PIC code. We should just build one big
5251 // string and lookup indices into that.
5252
5253 // Ignore switches with less than three cases. Lookup tables will not make
5254 // them faster, so we don't analyze them.
5255 if (SI->getNumCases() < 3)
4
Assuming the condition is false
5
Taking false branch
5256 return false;
5257
5258 // Figure out the corresponding result for each case value and phi node in the
5259 // common destination, as well as the min and max case values.
5260 assert(SI->case_begin() != SI->case_end())(static_cast <bool> (SI->case_begin() != SI->case_end
()) ? void (0) : __assert_fail ("SI->case_begin() != SI->case_end()"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5260, __extension__ __PRETTY_FUNCTION__))
;
5261 SwitchInst::CaseIt CI = SI->case_begin();
5262 ConstantInt *MinCaseVal = CI->getCaseValue();
5263 ConstantInt *MaxCaseVal = CI->getCaseValue();
5264
5265 BasicBlock *CommonDest = nullptr;
6
'CommonDest' initialized to a null pointer value
5266
5267 using ResultListTy = SmallVector<std::pair<ConstantInt *, Constant *>, 4>;
5268 SmallDenseMap<PHINode *, ResultListTy> ResultLists;
5269
5270 SmallDenseMap<PHINode *, Constant *> DefaultResults;
5271 SmallDenseMap<PHINode *, Type *> ResultTypes;
5272 SmallVector<PHINode *, 4> PHIs;
5273
5274 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
7
Loop condition is false. Execution continues on line 5299
5275 ConstantInt *CaseVal = CI->getCaseValue();
5276 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
5277 MinCaseVal = CaseVal;
5278 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
5279 MaxCaseVal = CaseVal;
5280
5281 // Resulting value at phi nodes for this case value.
5282 using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
5283 ResultsTy Results;
5284 if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
5285 Results, DL, TTI))
5286 return false;
5287
5288 // Append the result from this case to the list for each phi.
5289 for (const auto &I : Results) {
5290 PHINode *PHI = I.first;
5291 Constant *Value = I.second;
5292 if (!ResultLists.count(PHI))
5293 PHIs.push_back(PHI);
5294 ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
5295 }
5296 }
5297
5298 // Keep track of the result types.
5299 for (PHINode *PHI : PHIs) {
8
Assuming '__begin1' is equal to '__end1'
5300 ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
5301 }
5302
5303 uint64_t NumResults = ResultLists[PHIs[0]].size();
5304 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
5305 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
5306 bool TableHasHoles = (NumResults < TableSize);
5307
5308 // If the table has holes, we need a constant result for the default case
5309 // or a bitmask that fits in a register.
5310 SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
5311 bool HasDefaultResults =
5312 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
9
Calling 'GetCaseResults'
14
Returning from 'GetCaseResults'
5313 DefaultResultsList, DL, TTI);
5314
5315 bool NeedMask = (TableHasHoles && !HasDefaultResults);
5316 if (NeedMask) {
15
Taking false branch
5317 // As an extra penalty for the validity test we require more cases.
5318 if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
5319 return false;
5320 if (!DL.fitsInLegalInteger(TableSize))
5321 return false;
5322 }
5323
5324 for (const auto &I : DefaultResultsList) {
16
Assuming '__begin1' is equal to '__end1'
5325 PHINode *PHI = I.first;
5326 Constant *Result = I.second;
5327 DefaultResults[PHI] = Result;
5328 }
5329
5330 if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
17
Taking false branch
5331 return false;
5332
5333 // Create the BB that does the lookups.
5334 Module &Mod = *CommonDest->getParent()->getParent();
18
Called C++ object pointer is null
5335 BasicBlock *LookupBB = BasicBlock::Create(
5336 Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest);
5337
5338 // Compute the table index value.
5339 Builder.SetInsertPoint(SI);
5340 Value *TableIndex;
5341 if (MinCaseVal->isNullValue())
5342 TableIndex = SI->getCondition();
5343 else
5344 TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
5345 "switch.tableidx");
5346
5347 // Compute the maximum table size representable by the integer type we are
5348 // switching upon.
5349 unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
5350 uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX(18446744073709551615UL) : 1ULL << CaseSize;
5351 assert(MaxTableSize >= TableSize &&(static_cast <bool> (MaxTableSize >= TableSize &&
"It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? 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.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5353, __extension__ __PRETTY_FUNCTION__))
5352 "It is impossible for a switch to have more entries than the max "(static_cast <bool> (MaxTableSize >= TableSize &&
"It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? 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.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5353, __extension__ __PRETTY_FUNCTION__))
5353 "representable value of its input integer type's size.")(static_cast <bool> (MaxTableSize >= TableSize &&
"It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.") ? 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.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5353, __extension__ __PRETTY_FUNCTION__))
;
5354
5355 // If the default destination is unreachable, or if the lookup table covers
5356 // all values of the conditional variable, branch directly to the lookup table
5357 // BB. Otherwise, check that the condition is within the case range.
5358 const bool DefaultIsReachable =
5359 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
5360 const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
5361 BranchInst *RangeCheckBranch = nullptr;
5362
5363 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5364 Builder.CreateBr(LookupBB);
5365 // Note: We call removeProdecessor later since we need to be able to get the
5366 // PHI value for the default case in case we're using a bit mask.
5367 } else {
5368 Value *Cmp = Builder.CreateICmpULT(
5369 TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
5370 RangeCheckBranch =
5371 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
5372 }
5373
5374 // Populate the BB that does the lookups.
5375 Builder.SetInsertPoint(LookupBB);
5376
5377 if (NeedMask) {
5378 // Before doing the lookup, we do the hole check. The LookupBB is therefore
5379 // re-purposed to do the hole check, and we create a new LookupBB.
5380 BasicBlock *MaskBB = LookupBB;
5381 MaskBB->setName("switch.hole_check");
5382 LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup",
5383 CommonDest->getParent(), CommonDest);
5384
5385 // Make the mask's bitwidth at least 8-bit and a power-of-2 to avoid
5386 // unnecessary illegal types.
5387 uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
5388 APInt MaskInt(TableSizePowOf2, 0);
5389 APInt One(TableSizePowOf2, 1);
5390 // Build bitmask; fill in a 1 bit for every case.
5391 const ResultListTy &ResultList = ResultLists[PHIs[0]];
5392 for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
5393 uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue())
5394 .getLimitedValue();
5395 MaskInt |= One << Idx;
5396 }
5397 ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
5398
5399 // Get the TableIndex'th bit of the bitmask.
5400 // If this bit is 0 (meaning hole) jump to the default destination,
5401 // else continue with table lookup.
5402 IntegerType *MapTy = TableMask->getType();
5403 Value *MaskIndex =
5404 Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex");
5405 Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted");
5406 Value *LoBit = Builder.CreateTrunc(
5407 Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit");
5408 Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
5409
5410 Builder.SetInsertPoint(LookupBB);
5411 AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
5412 }
5413
5414 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5415 // We cached PHINodes in PHIs. To avoid accessing deleted PHINodes later,
5416 // do not delete PHINodes here.
5417 SI->getDefaultDest()->removePredecessor(SI->getParent(),
5418 /*DontDeleteUselessPHIs=*/true);
5419 }
5420
5421 bool ReturnedEarly = false;
5422 for (PHINode *PHI : PHIs) {
5423 const ResultListTy &ResultList = ResultLists[PHI];
5424
5425 // If using a bitmask, use any value to fill the lookup table holes.
5426 Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
5427 StringRef FuncName = Fn->getName();
5428 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL,
5429 FuncName);
5430
5431 Value *Result = Table.BuildLookup(TableIndex, Builder);
5432
5433 // If the result is used to return immediately from the function, we want to
5434 // do that right here.
5435 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) &&
5436 PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) {
5437 Builder.CreateRet(Result);
5438 ReturnedEarly = true;
5439 break;
5440 }
5441
5442 // Do a small peephole optimization: re-use the switch table compare if
5443 // possible.
5444 if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
5445 BasicBlock *PhiBlock = PHI->getParent();
5446 // Search for compare instructions which use the phi.
5447 for (auto *User : PHI->users()) {
5448 reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
5449 }
5450 }
5451
5452 PHI->addIncoming(Result, LookupBB);
5453 }
5454
5455 if (!ReturnedEarly)
5456 Builder.CreateBr(CommonDest);
5457
5458 // Remove the switch.
5459 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
5460 BasicBlock *Succ = SI->getSuccessor(i);
5461
5462 if (Succ == SI->getDefaultDest())
5463 continue;
5464 Succ->removePredecessor(SI->getParent());
5465 }
5466 SI->eraseFromParent();
5467
5468 ++NumLookupTables;
5469 if (NeedMask)
5470 ++NumLookupTablesHoles;
5471 return true;
5472}
5473
5474static bool isSwitchDense(ArrayRef<int64_t> Values) {
5475 // See also SelectionDAGBuilder::isDense(), which this function was based on.
5476 uint64_t Diff = (uint64_t)Values.back() - (uint64_t)Values.front();
5477 uint64_t Range = Diff + 1;
5478 uint64_t NumCases = Values.size();
5479 // 40% is the default density for building a jump table in optsize/minsize mode.
5480 uint64_t MinDensity = 40;
5481
5482 return NumCases * 100 >= Range * MinDensity;
5483}
5484
5485/// Try to transform a switch that has "holes" in it to a contiguous sequence
5486/// of cases.
5487///
5488/// A switch such as: switch(i) {case 5: case 9: case 13: case 17:} can be
5489/// range-reduced to: switch ((i-5) / 4) {case 0: case 1: case 2: case 3:}.
5490///
5491/// This converts a sparse switch into a dense switch which allows better
5492/// lowering and could also allow transforming into a lookup table.
5493static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
5494 const DataLayout &DL,
5495 const TargetTransformInfo &TTI) {
5496 auto *CondTy = cast<IntegerType>(SI->getCondition()->getType());
5497 if (CondTy->getIntegerBitWidth() > 64 ||
5498 !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
5499 return false;
5500 // Only bother with this optimization if there are more than 3 switch cases;
5501 // SDAG will only bother creating jump tables for 4 or more cases.
5502 if (SI->getNumCases() < 4)
5503 return false;
5504
5505 // This transform is agnostic to the signedness of the input or case values. We
5506 // can treat the case values as signed or unsigned. We can optimize more common
5507 // cases such as a sequence crossing zero {-4,0,4,8} if we interpret case values
5508 // as signed.
5509 SmallVector<int64_t,4> Values;
5510 for (auto &C : SI->cases())
5511 Values.push_back(C.getCaseValue()->getValue().getSExtValue());
5512 llvm::sort(Values.begin(), Values.end());
5513
5514 // If the switch is already dense, there's nothing useful to do here.
5515 if (isSwitchDense(Values))
5516 return false;
5517
5518 // First, transform the values such that they start at zero and ascend.
5519 int64_t Base = Values[0];
5520 for (auto &V : Values)
5521 V -= (uint64_t)(Base);
5522
5523 // Now we have signed numbers that have been shifted so that, given enough
5524 // precision, there are no negative values. Since the rest of the transform
5525 // is bitwise only, we switch now to an unsigned representation.
5526 uint64_t GCD = 0;
5527 for (auto &V : Values)
5528 GCD = GreatestCommonDivisor64(GCD, (uint64_t)V);
5529
5530 // This transform can be done speculatively because it is so cheap - it results
5531 // in a single rotate operation being inserted. This can only happen if the
5532 // factor extracted is a power of 2.
5533 // FIXME: If the GCD is an odd number we can multiply by the multiplicative
5534 // inverse of GCD and then perform this transform.
5535 // FIXME: It's possible that optimizing a switch on powers of two might also
5536 // be beneficial - flag values are often powers of two and we could use a CLZ
5537 // as the key function.
5538 if (GCD <= 1 || !isPowerOf2_64(GCD))
5539 // No common divisor found or too expensive to compute key function.
5540 return false;
5541
5542 unsigned Shift = Log2_64(GCD);
5543 for (auto &V : Values)
5544 V = (int64_t)((uint64_t)V >> Shift);
5545
5546 if (!isSwitchDense(Values))
5547 // Transform didn't create a dense switch.
5548 return false;
5549
5550 // The obvious transform is to shift the switch condition right and emit a
5551 // check that the condition actually cleanly divided by GCD, i.e.
5552 // C & (1 << Shift - 1) == 0
5553 // inserting a new CFG edge to handle the case where it didn't divide cleanly.
5554 //
5555 // A cheaper way of doing this is a simple ROTR(C, Shift). This performs the
5556 // shift and puts the shifted-off bits in the uppermost bits. If any of these
5557 // are nonzero then the switch condition will be very large and will hit the
5558 // default case.
5559
5560 auto *Ty = cast<IntegerType>(SI->getCondition()->getType());
5561 Builder.SetInsertPoint(SI);
5562 auto *ShiftC = ConstantInt::get(Ty, Shift);
5563 auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base));
5564 auto *LShr = Builder.CreateLShr(Sub, ShiftC);
5565 auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift);
5566 auto *Rot = Builder.CreateOr(LShr, Shl);
5567 SI->replaceUsesOfWith(SI->getCondition(), Rot);
5568
5569 for (auto Case : SI->cases()) {
5570 auto *Orig = Case.getCaseValue();
5571 auto Sub = Orig->getValue() - APInt(Ty->getBitWidth(), Base);
5572 Case.setValue(
5573 cast<ConstantInt>(ConstantInt::get(Ty, Sub.lshr(ShiftC->getValue()))));
5574 }
5575 return true;
5576}
5577
5578bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
5579 BasicBlock *BB = SI->getParent();
5580
5581 if (isValueEqualityComparison(SI)) {
5582 // If we only have one predecessor, and if it is a branch on this value,
5583 // see if that predecessor totally determines the outcome of this switch.
5584 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5585 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
5586 return simplifyCFG(BB, TTI, Options) | true;
5587
5588 Value *Cond = SI->getCondition();
5589 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
5590 if (SimplifySwitchOnSelect(SI, Select))
5591 return simplifyCFG(BB, TTI, Options) | true;
5592
5593 // If the block only contains the switch, see if we can fold the block
5594 // away into any preds.
5595 if (SI == &*BB->instructionsWithoutDebug().begin())
5596 if (FoldValueComparisonIntoPredecessors(SI, Builder))
5597 return simplifyCFG(BB, TTI, Options) | true;
5598 }
5599
5600 // Try to transform the switch into an icmp and a branch.
5601 if (TurnSwitchRangeIntoICmp(SI, Builder))
5602 return simplifyCFG(BB, TTI, Options) | true;
5603
5604 // Remove unreachable cases.
5605 if (eliminateDeadSwitchCases(SI, Options.AC, DL))
5606 return simplifyCFG(BB, TTI, Options) | true;
5607
5608 if (switchToSelect(SI, Builder, DL, TTI))
5609 return simplifyCFG(BB, TTI, Options) | true;
5610
5611 if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI))
5612 return simplifyCFG(BB, TTI, Options) | true;
5613
5614 // The conversion from switch to lookup tables results in difficult-to-analyze
5615 // code and makes pruning branches much harder. This is a problem if the
5616 // switch expression itself can still be restricted as a result of inlining or
5617 // CVP. Therefore, only apply this transformation during late stages of the
5618 // optimisation pipeline.
5619 if (Options.ConvertSwitchToLookupTable &&
5620 SwitchToLookupTable(SI, Builder, DL, TTI))
5621 return simplifyCFG(BB, TTI, Options) | true;
5622
5623 if (ReduceSwitchRange(SI, Builder, DL, TTI))
5624 return simplifyCFG(BB, TTI, Options) | true;
5625
5626 return false;
5627}
5628
5629bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
5630 BasicBlock *BB = IBI->getParent();
5631 bool Changed = false;
5632
5633 // Eliminate redundant destinations.
5634 SmallPtrSet<Value *, 8> Succs;
5635 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
5636 BasicBlock *Dest = IBI->getDestination(i);
5637 if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
5638 Dest->removePredecessor(BB);
5639 IBI->removeDestination(i);
5640 --i;
5641 --e;
5642 Changed = true;
5643 }
5644 }
5645
5646 if (IBI->getNumDestinations() == 0) {
5647 // If the indirectbr has no successors, change it to unreachable.
5648 new UnreachableInst(IBI->getContext(), IBI);
5649 EraseTerminatorInstAndDCECond(IBI);
5650 return true;
5651 }
5652
5653 if (IBI->getNumDestinations() == 1) {
5654 // If the indirectbr has one successor, change it to a direct branch.
5655 BranchInst::Create(IBI->getDestination(0), IBI);
5656 EraseTerminatorInstAndDCECond(IBI);
5657 return true;
5658 }
5659
5660 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
5661 if (SimplifyIndirectBrOnSelect(IBI, SI))
5662 return simplifyCFG(BB, TTI, Options) | true;
5663 }
5664 return Changed;
5665}
5666
5667/// Given an block with only a single landing pad and a unconditional branch
5668/// try to find another basic block which this one can be merged with. This
5669/// handles cases where we have multiple invokes with unique landing pads, but
5670/// a shared handler.
5671///
5672/// We specifically choose to not worry about merging non-empty blocks
5673/// here. That is a PRE/scheduling problem and is best solved elsewhere. In
5674/// practice, the optimizer produces empty landing pad blocks quite frequently
5675/// when dealing with exception dense code. (see: instcombine, gvn, if-else
5676/// sinking in this file)
5677///
5678/// This is primarily a code size optimization. We need to avoid performing
5679/// any transform which might inhibit optimization (such as our ability to
5680/// specialize a particular handler via tail commoning). We do this by not
5681/// merging any blocks which require us to introduce a phi. Since the same
5682/// values are flowing through both blocks, we don't lose any ability to
5683/// specialize. If anything, we make such specialization more likely.
5684///
5685/// TODO - This transformation could remove entries from a phi in the target
5686/// block when the inputs in the phi are the same for the two blocks being
5687/// merged. In some cases, this could result in removal of the PHI entirely.
5688static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
5689 BasicBlock *BB) {
5690 auto Succ = BB->getUniqueSuccessor();
5691 assert(Succ)(static_cast <bool> (Succ) ? void (0) : __assert_fail (
"Succ", "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5691, __extension__ __PRETTY_FUNCTION__))
;
5692 // If there's a phi in the successor block, we'd likely have to introduce
5693 // a phi into the merged landing pad block.
5694 if (isa<PHINode>(*Succ->begin()))
5695 return false;
5696
5697 for (BasicBlock *OtherPred : predecessors(Succ)) {
5698 if (BB == OtherPred)
5699 continue;
5700 BasicBlock::iterator I = OtherPred->begin();
5701 LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
5702 if (!LPad2 || !LPad2->isIdenticalTo(LPad))
5703 continue;
5704 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5705 ;
5706 BranchInst *BI2 = dyn_cast<BranchInst>(I);
5707 if (!BI2 || !BI2->isIdenticalTo(BI))
5708 continue;
5709
5710 // We've found an identical block. Update our predecessors to take that
5711 // path instead and make ourselves dead.
5712 SmallPtrSet<BasicBlock *, 16> Preds;
5713 Preds.insert(pred_begin(BB), pred_end(BB));
5714 for (BasicBlock *Pred : Preds) {
5715 InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
5716 assert(II->getNormalDest() != BB && II->getUnwindDest() == BB &&(static_cast <bool> (II->getNormalDest() != BB &&
II->getUnwindDest() == BB && "unexpected successor"
) ? void (0) : __assert_fail ("II->getNormalDest() != BB && II->getUnwindDest() == BB && \"unexpected successor\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5717, __extension__ __PRETTY_FUNCTION__))
5717 "unexpected successor")(static_cast <bool> (II->getNormalDest() != BB &&
II->getUnwindDest() == BB && "unexpected successor"
) ? void (0) : __assert_fail ("II->getNormalDest() != BB && II->getUnwindDest() == BB && \"unexpected successor\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5717, __extension__ __PRETTY_FUNCTION__))
;
5718 II->setUnwindDest(OtherPred);
5719 }
5720
5721 // The debug info in OtherPred doesn't cover the merged control flow that
5722 // used to go through BB. We need to delete it or update it.
5723 for (auto I = OtherPred->begin(), E = OtherPred->end(); I != E;) {
5724 Instruction &Inst = *I;
5725 I++;
5726 if (isa<DbgInfoIntrinsic>(Inst))
5727 Inst.eraseFromParent();
5728 }
5729
5730 SmallPtrSet<BasicBlock *, 16> Succs;
5731 Succs.insert(succ_begin(BB), succ_end(BB));
5732 for (BasicBlock *Succ : Succs) {
5733 Succ->removePredecessor(BB);
5734 }
5735
5736 IRBuilder<> Builder(BI);
5737 Builder.CreateUnreachable();
5738 BI->eraseFromParent();
5739 return true;
5740 }
5741 return false;
5742}
5743
5744bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI,
5745 IRBuilder<> &Builder) {
5746 BasicBlock *BB = BI->getParent();
5747 BasicBlock *Succ = BI->getSuccessor(0);
5748
5749 // If the Terminator is the only non-phi instruction, simplify the block.
5750 // If LoopHeader is provided, check if the block or its successor is a loop
5751 // header. (This is for early invocations before loop simplify and
5752 // vectorization to keep canonical loop forms for nested loops. These blocks
5753 // can be eliminated when the pass is invoked later in the back-end.)
5754 // Note that if BB has only one predecessor then we do not introduce new
5755 // backedge, so we can eliminate BB.
5756 bool NeedCanonicalLoop =
5757 Options.NeedCanonicalLoop &&
5758 (LoopHeaders && pred_size(BB) > 1 &&
5759 (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
5760 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
5761 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
5762 !NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB))
5763 return true;
5764
5765 // If the only instruction in the block is a seteq/setne comparison against a
5766 // constant, try to simplify the block.
5767 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
5768 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
5769 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5770 ;
5771 if (I->isTerminator() &&
5772 tryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, DL, TTI, Options))
5773 return true;
5774 }
5775
5776 // See if we can merge an empty landing pad block with another which is
5777 // equivalent.
5778 if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
5779 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5780 ;
5781 if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB))
5782 return true;
5783 }
5784
5785 // If this basic block is ONLY a compare and a branch, and if a predecessor
5786 // branches to us and our successor, fold the comparison into the
5787 // predecessor and use logical operations to update the incoming value
5788 // for PHI nodes in common successor.
5789 if (FoldBranchToCommonDest(BI, Options.BonusInstThreshold))
5790 return simplifyCFG(BB, TTI, Options) | true;
5791 return false;
5792}
5793
5794static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
5795 BasicBlock *PredPred = nullptr;
5796 for (auto *P : predecessors(BB)) {
5797 BasicBlock *PPred = P->getSinglePredecessor();
5798 if (!PPred || (PredPred && PredPred != PPred))
5799 return nullptr;
5800 PredPred = PPred;
5801 }
5802 return PredPred;
5803}
5804
5805bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
5806 BasicBlock *BB = BI->getParent();
5807 const Function *Fn = BB->getParent();
5808 if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing))
5809 return false;
5810
5811 // Conditional branch
5812 if (isValueEqualityComparison(BI)) {
5813 // If we only have one predecessor, and if it is a branch on this value,
5814 // see if that predecessor totally determines the outcome of this
5815 // switch.
5816 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5817 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
5818 return simplifyCFG(BB, TTI, Options) | true;
5819
5820 // This block must be empty, except for the setcond inst, if it exists.
5821 // Ignore dbg intrinsics.
5822 auto I = BB->instructionsWithoutDebug().begin();
5823 if (&*I == BI) {
5824 if (FoldValueComparisonIntoPredecessors(BI, Builder))
5825 return simplifyCFG(BB, TTI, Options) | true;
5826 } else if (&*I == cast<Instruction>(BI->getCondition())) {
5827 ++I;
5828 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
5829 return simplifyCFG(BB, TTI, Options) | true;
5830 }
5831 }
5832
5833 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
5834 if (SimplifyBranchOnICmpChain(BI, Builder, DL))
5835 return true;
5836
5837 // If this basic block has a single dominating predecessor block and the
5838 // dominating block's condition implies BI's condition, we know the direction
5839 // of the BI branch.
5840 if (BasicBlock *Dom = BB->getSinglePredecessor()) {
5841 auto *PBI = dyn_cast_or_null<BranchInst>(Dom->getTerminator());
5842 if (PBI && PBI->isConditional() &&
5843 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
5844 assert(PBI->getSuccessor(0) == BB || PBI->getSuccessor(1) == BB)(static_cast <bool> (PBI->getSuccessor(0) == BB || PBI
->getSuccessor(1) == BB) ? void (0) : __assert_fail ("PBI->getSuccessor(0) == BB || PBI->getSuccessor(1) == BB"
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5844, __extension__ __PRETTY_FUNCTION__))
;
5845 bool CondIsTrue = PBI->getSuccessor(0) == BB;
5846 Optional<bool> Implication = isImpliedCondition(
5847 PBI->getCondition(), BI->getCondition(), DL, CondIsTrue);
5848 if (Implication) {
5849 // Turn this into a branch on constant.
5850 auto *OldCond = BI->getCondition();
5851 ConstantInt *CI = *Implication
5852 ? ConstantInt::getTrue(BB->getContext())
5853 : ConstantInt::getFalse(BB->getContext());
5854 BI->setCondition(CI);
5855 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
5856 return simplifyCFG(BB, TTI, Options) | true;
5857 }
5858 }
5859 }
5860
5861 // If this basic block is ONLY a compare and a branch, and if a predecessor
5862 // branches to us and one of our successors, fold the comparison into the
5863 // predecessor and use logical operations to pick the right destination.
5864 if (FoldBranchToCommonDest(BI, Options.BonusInstThreshold))
5865 return simplifyCFG(BB, TTI, Options) | true;
5866
5867 // We have a conditional branch to two blocks that are only reachable
5868 // from BI. We know that the condbr dominates the two blocks, so see if
5869 // there is any identical code in the "then" and "else" blocks. If so, we
5870 // can hoist it up to the branching block.
5871 if (BI->getSuccessor(0)->getSinglePredecessor()) {
5872 if (BI->getSuccessor(1)->getSinglePredecessor()) {
5873 if (HoistThenElseCodeToIf(BI, TTI))
5874 return simplifyCFG(BB, TTI, Options) | true;
5875 } else {
5876 // If Successor #1 has multiple preds, we may be able to conditionally
5877 // execute Successor #0 if it branches to Successor #1.