Bug Summary

File:lib/Transforms/Utils/SimplifyCFG.cpp
Warning:line 2358, column 27
Called C++ object pointer is null

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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~svn326551/build-llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-7~svn326551/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn326551/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/x86_64-linux-gnu/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/x86_64-linux-gnu/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0/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/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~svn326551/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-checker optin.performance.Padding -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-03-02-155150-1477-1 -x c++ /build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp
1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Peephole optimize the CFG.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/ADT/APInt.h"
15#include "llvm/ADT/ArrayRef.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/Optional.h"
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/ADT/SetOperations.h"
20#include "llvm/ADT/SetVector.h"
21#include "llvm/ADT/SmallPtrSet.h"
22#include "llvm/ADT/SmallSet.h"
23#include "llvm/ADT/SmallVector.h"
24#include "llvm/ADT/Statistic.h"
25#include "llvm/ADT/StringRef.h"
26#include "llvm/Analysis/AssumptionCache.h"
27#include "llvm/Analysis/ConstantFolding.h"
28#include "llvm/Analysis/EHPersonalities.h"
29#include "llvm/Analysis/InstructionSimplify.h"
30#include "llvm/Analysis/TargetTransformInfo.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/Local.h"
70#include "llvm/Transforms/Utils/ValueMapper.h"
71#include <algorithm>
72#include <cassert>
73#include <climits>
74#include <cstddef>
75#include <cstdint>
76#include <iterator>
77#include <map>
78#include <set>
79#include <tuple>
80#include <utility>
81#include <vector>
82
83using namespace llvm;
84using namespace PatternMatch;
85
86#define DEBUG_TYPE"simplifycfg" "simplifycfg"
87
88// Chosen as 2 so as to be cheap, but still to have enough power to fold
89// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
90// To catch this, we need to fold a compare and a select, hence '2' being the
91// minimum reasonable default.
92static cl::opt<unsigned> PHINodeFoldingThreshold(
93 "phi-node-folding-threshold", cl::Hidden, cl::init(2),
94 cl::desc(
95 "Control the amount of phi node folding to perform (default = 2)"));
96
97static cl::opt<bool> DupRet(
98 "simplifycfg-dup-ret", cl::Hidden, cl::init(false),
99 cl::desc("Duplicate return instructions into unconditional branches"));
100
101static cl::opt<bool>
102 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
103 cl::desc("Sink common instructions down to the end block"));
104
105static cl::opt<bool> HoistCondStores(
106 "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
107 cl::desc("Hoist conditional stores if an unconditional store precedes"));
108
109static cl::opt<bool> MergeCondStores(
110 "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
111 cl::desc("Hoist conditional stores even if an unconditional store does not "
112 "precede - hoist multiple conditional stores into a single "
113 "predicated store"));
114
115static cl::opt<bool> MergeCondStoresAggressively(
116 "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
117 cl::desc("When merging conditional stores, do so even if the resultant "
118 "basic blocks are unlikely to be if-converted as a result"));
119
120static cl::opt<bool> SpeculateOneExpensiveInst(
121 "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
122 cl::desc("Allow exactly one expensive instruction to be speculatively "
123 "executed"));
124
125static cl::opt<unsigned> MaxSpeculationDepth(
126 "max-speculation-depth", cl::Hidden, cl::init(10),
127 cl::desc("Limit maximum recursion depth when calculating costs of "
128 "speculatively executed instructions"));
129
130STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps")static llvm::Statistic NumBitMaps = {"simplifycfg", "NumBitMaps"
, "Number of switch instructions turned into bitmaps", {0}, {
false}}
;
131STATISTIC(NumLinearMaps,static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, {false}}
132 "Number of switch instructions turned into linear mapping")static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping",
{0}, {false}}
;
133STATISTIC(NumLookupTables,static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, {false}}
134 "Number of switch instructions turned into lookup tables")static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables", {
0}, {false}}
;
135STATISTIC(static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, {false}}
136 NumLookupTablesHoles,static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
, {0}, {false}}
137 "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}}
;
138STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares")static llvm::Statistic NumTableCmpReuses = {"simplifycfg", "NumTableCmpReuses"
, "Number of reused switch table lookup compares", {0}, {false
}}
;
139STATISTIC(NumSinkCommons,static llvm::Statistic NumSinkCommons = {"simplifycfg", "NumSinkCommons"
, "Number of common instructions sunk down to the end block",
{0}, {false}}
140 "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}}
;
141STATISTIC(NumSpeculations, "Number of speculative executed instructions")static llvm::Statistic NumSpeculations = {"simplifycfg", "NumSpeculations"
, "Number of speculative executed instructions", {0}, {false}
}
;
142
143namespace {
144
145// The first field contains the value that the switch produces when a certain
146// case group is selected, and the second field is a vector containing the
147// cases composing the case group.
148using SwitchCaseResultVectorTy =
149 SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>;
150
151// The first field contains the phi node that generates a result of the switch
152// and the second field contains the value generated for a certain case in the
153// switch for that PHI.
154using SwitchCaseResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
155
156/// ValueEqualityComparisonCase - Represents a case of a switch.
157struct ValueEqualityComparisonCase {
158 ConstantInt *Value;
159 BasicBlock *Dest;
160
161 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
162 : Value(Value), Dest(Dest) {}
163
164 bool operator<(ValueEqualityComparisonCase RHS) const {
165 // Comparing pointers is ok as we only rely on the order for uniquing.
166 return Value < RHS.Value;
167 }
168
169 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
170};
171
172class SimplifyCFGOpt {
173 const TargetTransformInfo &TTI;
174 const DataLayout &DL;
175 SmallPtrSetImpl<BasicBlock *> *LoopHeaders;
176 const SimplifyCFGOptions &Options;
177
178 Value *isValueEqualityComparison(TerminatorInst *TI);
179 BasicBlock *GetValueEqualityComparisonCases(
180 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases);
181 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
182 BasicBlock *Pred,
183 IRBuilder<> &Builder);
184 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
185 IRBuilder<> &Builder);
186
187 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
188 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
189 bool SimplifySingleResume(ResumeInst *RI);
190 bool SimplifyCommonResume(ResumeInst *RI);
191 bool SimplifyCleanupReturn(CleanupReturnInst *RI);
192 bool SimplifyUnreachable(UnreachableInst *UI);
193 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
194 bool SimplifyIndirectBr(IndirectBrInst *IBI);
195 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
196 bool SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
197
198public:
199 SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
200 SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
201 const SimplifyCFGOptions &Opts)
202 : TTI(TTI), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {}
203
204 bool run(BasicBlock *BB);
205};
206
207} // end anonymous namespace
208
209/// Return true if it is safe to merge these two
210/// terminator instructions together.
211static bool
212SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2,
213 SmallSetVector<BasicBlock *, 4> *FailBlocks = nullptr) {
214 if (SI1 == SI2)
215 return false; // Can't merge with self!
216
217 // It is not safe to merge these two switch instructions if they have a common
218 // successor, and if that successor has a PHI node, and if *that* PHI node has
219 // conflicting incoming values from the two switch blocks.
220 BasicBlock *SI1BB = SI1->getParent();
221 BasicBlock *SI2BB = SI2->getParent();
222
223 SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
224 bool Fail = false;
225 for (BasicBlock *Succ : successors(SI2BB))
226 if (SI1Succs.count(Succ))
227 for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
228 PHINode *PN = cast<PHINode>(BBI);
229 if (PN->getIncomingValueForBlock(SI1BB) !=
230 PN->getIncomingValueForBlock(SI2BB)) {
231 if (FailBlocks)
232 FailBlocks->insert(Succ);
233 Fail = true;
234 }
235 }
236
237 return !Fail;
238}
239
240/// Return true if it is safe and profitable to merge these two terminator
241/// instructions together, where SI1 is an unconditional branch. PhiNodes will
242/// store all PHI nodes in common successors.
243static bool
244isProfitableToFoldUnconditional(BranchInst *SI1, BranchInst *SI2,
245 Instruction *Cond,
246 SmallVectorImpl<PHINode *> &PhiNodes) {
247 if (SI1 == SI2)
248 return false; // Can't merge with self!
249 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 249, __extension__ __PRETTY_FUNCTION__))
;
250
251 // We fold the unconditional branch if we can easily update all PHI nodes in
252 // common successors:
253 // 1> We have a constant incoming value for the conditional branch;
254 // 2> We have "Cond" as the incoming value for the unconditional branch;
255 // 3> SI2->getCondition() and Cond have same operands.
256 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
257 if (!Ci2)
258 return false;
259 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
260 Cond->getOperand(1) == Ci2->getOperand(1)) &&
261 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
262 Cond->getOperand(1) == Ci2->getOperand(0)))
263 return false;
264
265 BasicBlock *SI1BB = SI1->getParent();
266 BasicBlock *SI2BB = SI2->getParent();
267 SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
268 for (BasicBlock *Succ : successors(SI2BB))
269 if (SI1Succs.count(Succ))
270 for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
271 PHINode *PN = cast<PHINode>(BBI);
272 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
273 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
274 return false;
275 PhiNodes.push_back(PN);
276 }
277 return true;
278}
279
280/// Update PHI nodes in Succ to indicate that there will now be entries in it
281/// from the 'NewPred' block. The values that will be flowing into the PHI nodes
282/// will be the same as those coming in from ExistPred, an existing predecessor
283/// of Succ.
284static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
285 BasicBlock *ExistPred) {
286 for (PHINode &PN : Succ->phis())
287 PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred);
288}
289
290/// Compute an abstract "cost" of speculating the given instruction,
291/// which is assumed to be safe to speculate. TCC_Free means cheap,
292/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
293/// expensive.
294static unsigned ComputeSpeculationCost(const User *I,
295 const TargetTransformInfo &TTI) {
296 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 297, __extension__ __PRETTY_FUNCTION__))
297 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 297, __extension__ __PRETTY_FUNCTION__))
;
298 return TTI.getUserCost(I);
299}
300
301/// If we have a merge point of an "if condition" as accepted above,
302/// return true if the specified value dominates the block. We
303/// don't handle the true generality of domination here, just a special case
304/// which works well enough for us.
305///
306/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
307/// see if V (which must be an instruction) and its recursive operands
308/// that do not dominate BB have a combined cost lower than CostRemaining and
309/// are non-trapping. If both are true, the instruction is inserted into the
310/// set and true is returned.
311///
312/// The cost for most non-trapping instructions is defined as 1 except for
313/// Select whose cost is 2.
314///
315/// After this function returns, CostRemaining is decreased by the cost of
316/// V plus its non-dominating operands. If that cost is greater than
317/// CostRemaining, false is returned and CostRemaining is undefined.
318static bool DominatesMergePoint(Value *V, BasicBlock *BB,
319 SmallPtrSetImpl<Instruction *> *AggressiveInsts,
320 unsigned &CostRemaining,
321 const TargetTransformInfo &TTI,
322 unsigned Depth = 0) {
323 // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
324 // so limit the recursion depth.
325 // TODO: While this recursion limit does prevent pathological behavior, it
326 // would be better to track visited instructions to avoid cycles.
327 if (Depth == MaxSpeculationDepth)
328 return false;
329
330 Instruction *I = dyn_cast<Instruction>(V);
331 if (!I) {
332 // Non-instructions all dominate instructions, but not all constantexprs
333 // can be executed unconditionally.
334 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
335 if (C->canTrap())
336 return false;
337 return true;
338 }
339 BasicBlock *PBB = I->getParent();
340
341 // We don't want to allow weird loops that might have the "if condition" in
342 // the bottom of this block.
343 if (PBB == BB)
344 return false;
345
346 // If this instruction is defined in a block that contains an unconditional
347 // branch to BB, then it must be in the 'conditional' part of the "if
348 // statement". If not, it definitely dominates the region.
349 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
350 if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
351 return true;
352
353 // If we aren't allowing aggressive promotion anymore, then don't consider
354 // instructions in the 'if region'.
355 if (!AggressiveInsts)
356 return false;
357
358 // If we have seen this instruction before, don't count it again.
359 if (AggressiveInsts->count(I))
360 return true;
361
362 // Okay, it looks like the instruction IS in the "condition". Check to
363 // see if it's a cheap instruction to unconditionally compute, and if it
364 // only uses stuff defined outside of the condition. If so, hoist it out.
365 if (!isSafeToSpeculativelyExecute(I))
366 return false;
367
368 unsigned Cost = ComputeSpeculationCost(I, TTI);
369
370 // Allow exactly one instruction to be speculated regardless of its cost
371 // (as long as it is safe to do so).
372 // This is intended to flatten the CFG even if the instruction is a division
373 // or other expensive operation. The speculation of an expensive instruction
374 // is expected to be undone in CodeGenPrepare if the speculation has not
375 // enabled further IR optimizations.
376 if (Cost > CostRemaining &&
377 (!SpeculateOneExpensiveInst || !AggressiveInsts->empty() || Depth > 0))
378 return false;
379
380 // Avoid unsigned wrap.
381 CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
382
383 // Okay, we can only really hoist these out if their operands do
384 // not take us over the cost threshold.
385 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
386 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
387 Depth + 1))
388 return false;
389 // Okay, it's safe to do this! Remember this instruction.
390 AggressiveInsts->insert(I);
391 return true;
392}
393
394/// Extract ConstantInt from value, looking through IntToPtr
395/// and PointerNullValue. Return NULL if value is not a constant int.
396static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
397 // Normal constant int.
398 ConstantInt *CI = dyn_cast<ConstantInt>(V);
399 if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
400 return CI;
401
402 // This is some kind of pointer constant. Turn it into a pointer-sized
403 // ConstantInt if possible.
404 IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
405
406 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
407 if (isa<ConstantPointerNull>(V))
408 return ConstantInt::get(PtrTy, 0);
409
410 // IntToPtr const int.
411 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
412 if (CE->getOpcode() == Instruction::IntToPtr)
413 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
414 // The constant is very likely to have the right type already.
415 if (CI->getType() == PtrTy)
416 return CI;
417 else
418 return cast<ConstantInt>(
419 ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
420 }
421 return nullptr;
422}
423
424namespace {
425
426/// Given a chain of or (||) or and (&&) comparison of a value against a
427/// constant, this will try to recover the information required for a switch
428/// structure.
429/// It will depth-first traverse the chain of comparison, seeking for patterns
430/// like %a == 12 or %a < 4 and combine them to produce a set of integer
431/// representing the different cases for the switch.
432/// Note that if the chain is composed of '||' it will build the set of elements
433/// that matches the comparisons (i.e. any of this value validate the chain)
434/// while for a chain of '&&' it will build the set elements that make the test
435/// fail.
436struct ConstantComparesGatherer {
437 const DataLayout &DL;
438
439 /// Value found for the switch comparison
440 Value *CompValue = nullptr;
441
442 /// Extra clause to be checked before the switch
443 Value *Extra = nullptr;
444
445 /// Set of integers to match in switch
446 SmallVector<ConstantInt *, 8> Vals;
447
448 /// Number of comparisons matched in the and/or chain
449 unsigned UsedICmps = 0;
450
451 /// Construct and compute the result for the comparison instruction Cond
452 ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) {
453 gather(Cond);
454 }
455
456 ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
457 ConstantComparesGatherer &
458 operator=(const ConstantComparesGatherer &) = delete;
459
460private:
461 /// Try to set the current value used for the comparison, it succeeds only if
462 /// it wasn't set before or if the new value is the same as the old one
463 bool setValueOnce(Value *NewVal) {
464 if (CompValue && CompValue != NewVal)
465 return false;
466 CompValue = NewVal;
467 return (CompValue != nullptr);
468 }
469
470 /// Try to match Instruction "I" as a comparison against a constant and
471 /// populates the array Vals with the set of values that match (or do not
472 /// match depending on isEQ).
473 /// Return false on failure. On success, the Value the comparison matched
474 /// against is placed in CompValue.
475 /// If CompValue is already set, the function is expected to fail if a match
476 /// is found but the value compared to is different.
477 bool matchInstruction(Instruction *I, bool isEQ) {
478 // If this is an icmp against a constant, handle this as one of the cases.
479 ICmpInst *ICI;
480 ConstantInt *C;
481 if (!((ICI = dyn_cast<ICmpInst>(I)) &&
482 (C = GetConstantInt(I->getOperand(1), DL)))) {
483 return false;
484 }
485
486 Value *RHSVal;
487 const APInt *RHSC;
488
489 // Pattern match a special case
490 // (x & ~2^z) == y --> x == y || x == y|2^z
491 // This undoes a transformation done by instcombine to fuse 2 compares.
492 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) {
493 // It's a little bit hard to see why the following transformations are
494 // correct. Here is a CVC3 program to verify them for 64-bit values:
495
496 /*
497 ONE : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
498 x : BITVECTOR(64);
499 y : BITVECTOR(64);
500 z : BITVECTOR(64);
501 mask : BITVECTOR(64) = BVSHL(ONE, z);
502 QUERY( (y & ~mask = y) =>
503 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
504 );
505 QUERY( (y | mask = y) =>
506 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
507 );
508 */
509
510 // Please note that each pattern must be a dual implication (<--> or
511 // iff). One directional implication can create spurious matches. If the
512 // implication is only one-way, an unsatisfiable condition on the left
513 // side can imply a satisfiable condition on the right side. Dual
514 // implication ensures that satisfiable conditions are transformed to
515 // other satisfiable conditions and unsatisfiable conditions are
516 // transformed to other unsatisfiable conditions.
517
518 // Here is a concrete example of a unsatisfiable condition on the left
519 // implying a satisfiable condition on the right:
520 //
521 // mask = (1 << z)
522 // (x & ~mask) == y --> (x == y || x == (y | mask))
523 //
524 // Substituting y = 3, z = 0 yields:
525 // (x & -2) == 3 --> (x == 3 || x == 2)
526
527 // Pattern match a special case:
528 /*
529 QUERY( (y & ~mask = y) =>
530 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
531 );
532 */
533 if (match(ICI->getOperand(0),
534 m_And(m_Value(RHSVal), m_APInt(RHSC)))) {
535 APInt Mask = ~*RHSC;
536 if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) {
537 // If we already have a value for the switch, it has to match!
538 if (!setValueOnce(RHSVal))
539 return false;
540
541 Vals.push_back(C);
542 Vals.push_back(
543 ConstantInt::get(C->getContext(),
544 C->getValue() | Mask));
545 UsedICmps++;
546 return true;
547 }
548 }
549
550 // Pattern match a special case:
551 /*
552 QUERY( (y | mask = y) =>
553 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
554 );
555 */
556 if (match(ICI->getOperand(0),
557 m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
558 APInt Mask = *RHSC;
559 if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
560 // If we already have a value for the switch, it has to match!
561 if (!setValueOnce(RHSVal))
562 return false;
563
564 Vals.push_back(C);
565 Vals.push_back(ConstantInt::get(C->getContext(),
566 C->getValue() & ~Mask));
567 UsedICmps++;
568 return true;
569 }
570 }
571
572 // If we already have a value for the switch, it has to match!
573 if (!setValueOnce(ICI->getOperand(0)))
574 return false;
575
576 UsedICmps++;
577 Vals.push_back(C);
578 return ICI->getOperand(0);
579 }
580
581 // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
582 ConstantRange Span = ConstantRange::makeAllowedICmpRegion(
583 ICI->getPredicate(), C->getValue());
584
585 // Shift the range if the compare is fed by an add. This is the range
586 // compare idiom as emitted by instcombine.
587 Value *CandidateVal = I->getOperand(0);
588 if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) {
589 Span = Span.subtract(*RHSC);
590 CandidateVal = RHSVal;
591 }
592
593 // If this is an and/!= check, then we are looking to build the set of
594 // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
595 // x != 0 && x != 1.
596 if (!isEQ)
597 Span = Span.inverse();
598
599 // If there are a ton of values, we don't want to make a ginormous switch.
600 if (Span.isSizeLargerThan(8) || Span.isEmptySet()) {
601 return false;
602 }
603
604 // If we already have a value for the switch, it has to match!
605 if (!setValueOnce(CandidateVal))
606 return false;
607
608 // Add all values from the range to the set
609 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
610 Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
611
612 UsedICmps++;
613 return true;
614 }
615
616 /// Given a potentially 'or'd or 'and'd together collection of icmp
617 /// eq/ne/lt/gt instructions that compare a value against a constant, extract
618 /// the value being compared, and stick the list constants into the Vals
619 /// vector.
620 /// One "Extra" case is allowed to differ from the other.
621 void gather(Value *V) {
622 Instruction *I = dyn_cast<Instruction>(V);
623 bool isEQ = (I->getOpcode() == Instruction::Or);
624
625 // Keep a stack (SmallVector for efficiency) for depth-first traversal
626 SmallVector<Value *, 8> DFT;
627 SmallPtrSet<Value *, 8> Visited;
628
629 // Initialize
630 Visited.insert(V);
631 DFT.push_back(V);
632
633 while (!DFT.empty()) {
634 V = DFT.pop_back_val();
635
636 if (Instruction *I = dyn_cast<Instruction>(V)) {
637 // If it is a || (or && depending on isEQ), process the operands.
638 if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
639 if (Visited.insert(I->getOperand(1)).second)
640 DFT.push_back(I->getOperand(1));
641 if (Visited.insert(I->getOperand(0)).second)
642 DFT.push_back(I->getOperand(0));
643 continue;
644 }
645
646 // Try to match the current instruction
647 if (matchInstruction(I, isEQ))
648 // Match succeed, continue the loop
649 continue;
650 }
651
652 // One element of the sequence of || (or &&) could not be match as a
653 // comparison against the same value as the others.
654 // We allow only one "Extra" case to be checked before the switch
655 if (!Extra) {
656 Extra = V;
657 continue;
658 }
659 // Failed to parse a proper sequence, abort now
660 CompValue = nullptr;
661 break;
662 }
663 }
664};
665
666} // end anonymous namespace
667
668static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
669 Instruction *Cond = nullptr;
670 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
671 Cond = dyn_cast<Instruction>(SI->getCondition());
672 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
673 if (BI->isConditional())
674 Cond = dyn_cast<Instruction>(BI->getCondition());
675 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
676 Cond = dyn_cast<Instruction>(IBI->getAddress());
677 }
678
679 TI->eraseFromParent();
680 if (Cond)
681 RecursivelyDeleteTriviallyDeadInstructions(Cond);
682}
683
684/// Return true if the specified terminator checks
685/// to see if a value is equal to constant integer value.
686Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
687 Value *CV = nullptr;
688 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
689 // Do not permit merging of large switch instructions into their
690 // predecessors unless there is only one predecessor.
691 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
692 pred_end(SI->getParent())) <=
693 128)
694 CV = SI->getCondition();
695 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
696 if (BI->isConditional() && BI->getCondition()->hasOneUse())
697 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
698 if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
699 CV = ICI->getOperand(0);
700 }
701
702 // Unwrap any lossless ptrtoint cast.
703 if (CV) {
704 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
705 Value *Ptr = PTII->getPointerOperand();
706 if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
707 CV = Ptr;
708 }
709 }
710 return CV;
711}
712
713/// Given a value comparison instruction,
714/// decode all of the 'cases' that it represents and return the 'default' block.
715BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases(
716 TerminatorInst *TI, std::vector<ValueEqualityComparisonCase> &Cases) {
717 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
718 Cases.reserve(SI->getNumCases());
719 for (auto Case : SI->cases())
720 Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(),
721 Case.getCaseSuccessor()));
722 return SI->getDefaultDest();
723 }
724
725 BranchInst *BI = cast<BranchInst>(TI);
726 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
727 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
728 Cases.push_back(ValueEqualityComparisonCase(
729 GetConstantInt(ICI->getOperand(1), DL), Succ));
730 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
731}
732
733/// Given a vector of bb/value pairs, remove any entries
734/// in the list that match the specified block.
735static void
736EliminateBlockCases(BasicBlock *BB,
737 std::vector<ValueEqualityComparisonCase> &Cases) {
738 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
739}
740
741/// Return true if there are any keys in C1 that exist in C2 as well.
742static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
743 std::vector<ValueEqualityComparisonCase> &C2) {
744 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
745
746 // Make V1 be smaller than V2.
747 if (V1->size() > V2->size())
748 std::swap(V1, V2);
749
750 if (V1->empty())
751 return false;
752 if (V1->size() == 1) {
753 // Just scan V2.
754 ConstantInt *TheVal = (*V1)[0].Value;
755 for (unsigned i = 0, e = V2->size(); i != e; ++i)
756 if (TheVal == (*V2)[i].Value)
757 return true;
758 }
759
760 // Otherwise, just sort both lists and compare element by element.
761 array_pod_sort(V1->begin(), V1->end());
762 array_pod_sort(V2->begin(), V2->end());
763 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
764 while (i1 != e1 && i2 != e2) {
765 if ((*V1)[i1].Value == (*V2)[i2].Value)
766 return true;
767 if ((*V1)[i1].Value < (*V2)[i2].Value)
768 ++i1;
769 else
770 ++i2;
771 }
772 return false;
773}
774
775// Set branch weights on SwitchInst. This sets the metadata if there is at
776// least one non-zero weight.
777static void setBranchWeights(SwitchInst *SI, ArrayRef<uint32_t> Weights) {
778 // Check that there is at least one non-zero weight. Otherwise, pass
779 // nullptr to setMetadata which will erase the existing metadata.
780 MDNode *N = nullptr;
781 if (llvm::any_of(Weights, [](uint32_t W) { return W != 0; }))
782 N = MDBuilder(SI->getParent()->getContext()).createBranchWeights(Weights);
783 SI->setMetadata(LLVMContext::MD_prof, N);
784}
785
786// Similar to the above, but for branch and select instructions that take
787// exactly 2 weights.
788static void setBranchWeights(Instruction *I, uint32_t TrueWeight,
789 uint32_t FalseWeight) {
790 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 790, __extension__ __PRETTY_FUNCTION__))
;
791 // Check that there is at least one non-zero weight. Otherwise, pass
792 // nullptr to setMetadata which will erase the existing metadata.
793 MDNode *N = nullptr;
794 if (TrueWeight || FalseWeight)
795 N = MDBuilder(I->getParent()->getContext())
796 .createBranchWeights(TrueWeight, FalseWeight);
797 I->setMetadata(LLVMContext::MD_prof, N);
798}
799
800/// If TI is known to be a terminator instruction and its block is known to
801/// only have a single predecessor block, check to see if that predecessor is
802/// also a value comparison with the same value, and if that comparison
803/// determines the outcome of this comparison. If so, simplify TI. This does a
804/// very limited form of jump threading.
805bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
806 TerminatorInst *TI, BasicBlock *Pred, IRBuilder<> &Builder) {
807 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
808 if (!PredVal)
809 return false; // Not a value comparison in predecessor.
810
811 Value *ThisVal = isValueEqualityComparison(TI);
812 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 812, __extension__ __PRETTY_FUNCTION__))
;
813 if (ThisVal != PredVal)
814 return false; // Different predicates.
815
816 // TODO: Preserve branch weight metadata, similarly to how
817 // FoldValueComparisonIntoPredecessors preserves it.
818
819 // Find out information about when control will move from Pred to TI's block.
820 std::vector<ValueEqualityComparisonCase> PredCases;
821 BasicBlock *PredDef =
822 GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases);
823 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
824
825 // Find information about how control leaves this block.
826 std::vector<ValueEqualityComparisonCase> ThisCases;
827 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
828 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
829
830 // If TI's block is the default block from Pred's comparison, potentially
831 // simplify TI based on this knowledge.
832 if (PredDef == TI->getParent()) {
833 // If we are here, we know that the value is none of those cases listed in
834 // PredCases. If there are any cases in ThisCases that are in PredCases, we
835 // can simplify TI.
836 if (!ValuesOverlap(PredCases, ThisCases))
837 return false;
838
839 if (isa<BranchInst>(TI)) {
840 // Okay, one of the successors of this condbr is dead. Convert it to a
841 // uncond br.
842 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 842, __extension__ __PRETTY_FUNCTION__))
;
843 // Insert the new branch.
844 Instruction *NI = Builder.CreateBr(ThisDef);
845 (void)NI;
846
847 // Remove PHI node entries for the dead edge.
848 ThisCases[0].Dest->removePredecessor(TI->getParent());
849
850 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)
851 << "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)
852 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
853
854 EraseTerminatorInstAndDCECond(TI);
855 return true;
856 }
857
858 SwitchInst *SI = cast<SwitchInst>(TI);
859 // Okay, TI has cases that are statically dead, prune them away.
860 SmallPtrSet<Constant *, 16> DeadCases;
861 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
862 DeadCases.insert(PredCases[i].Value);
863
864 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)
865 << "Through successor TI: " << *TI)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI; } } while (false)
;
866
867 // Collect branch weights into a vector.
868 SmallVector<uint32_t, 8> Weights;
869 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
870 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
871 if (HasWeight)
872 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
873 ++MD_i) {
874 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
875 Weights.push_back(CI->getValue().getZExtValue());
876 }
877 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
878 --i;
879 if (DeadCases.count(i->getCaseValue())) {
880 if (HasWeight) {
881 std::swap(Weights[i->getCaseIndex() + 1], Weights.back());
882 Weights.pop_back();
883 }
884 i->getCaseSuccessor()->removePredecessor(TI->getParent());
885 SI->removeCase(i);
886 }
887 }
888 if (HasWeight && Weights.size() >= 2)
889 setBranchWeights(SI, Weights);
890
891 DEBUG(dbgs() << "Leaving: " << *TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Leaving: " << *TI <<
"\n"; } } while (false)
;
892 return true;
893 }
894
895 // Otherwise, TI's block must correspond to some matched value. Find out
896 // which value (or set of values) this is.
897 ConstantInt *TIV = nullptr;
898 BasicBlock *TIBB = TI->getParent();
899 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
900 if (PredCases[i].Dest == TIBB) {
901 if (TIV)
902 return false; // Cannot handle multiple values coming to this block.
903 TIV = PredCases[i].Value;
904 }
905 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 905, __extension__ __PRETTY_FUNCTION__))
;
906
907 // Okay, we found the one constant that our value can be if we get into TI's
908 // BB. Find out which successor will unconditionally be branched to.
909 BasicBlock *TheRealDest = nullptr;
910 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
911 if (ThisCases[i].Value == TIV) {
912 TheRealDest = ThisCases[i].Dest;
913 break;
914 }
915
916 // If not handled by any explicit cases, it is handled by the default case.
917 if (!TheRealDest)
918 TheRealDest = ThisDef;
919
920 // Remove PHI node entries for dead edges.
921 BasicBlock *CheckEdge = TheRealDest;
922 for (BasicBlock *Succ : successors(TIBB))
923 if (Succ != CheckEdge)
924 Succ->removePredecessor(TIBB);
925 else
926 CheckEdge = nullptr;
927
928 // Insert the new branch.
929 Instruction *NI = Builder.CreateBr(TheRealDest);
930 (void)NI;
931
932 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)
933 << "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)
934 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Threading pred instr: " <<
*Pred->getTerminator() << "Through successor TI: " <<
*TI << "Leaving: " << *NI << "\n"; } } while
(false)
;
935
936 EraseTerminatorInstAndDCECond(TI);
937 return true;
938}
939
940namespace {
941
942/// This class implements a stable ordering of constant
943/// integers that does not depend on their address. This is important for
944/// applications that sort ConstantInt's to ensure uniqueness.
945struct ConstantIntOrdering {
946 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
947 return LHS->getValue().ult(RHS->getValue());
948 }
949};
950
951} // end anonymous namespace
952
953static int ConstantIntSortPredicate(ConstantInt *const *P1,
954 ConstantInt *const *P2) {
955 const ConstantInt *LHS = *P1;
956 const ConstantInt *RHS = *P2;
957 if (LHS == RHS)
958 return 0;
959 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
960}
961
962static inline bool HasBranchWeights(const Instruction *I) {
963 MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
964 if (ProfMD && ProfMD->getOperand(0))
965 if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
966 return MDS->getString().equals("branch_weights");
967
968 return false;
969}
970
971/// Get Weights of a given TerminatorInst, the default weight is at the front
972/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
973/// metadata.
974static void GetBranchWeights(TerminatorInst *TI,
975 SmallVectorImpl<uint64_t> &Weights) {
976 MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
977 assert(MD)(static_cast <bool> (MD) ? void (0) : __assert_fail ("MD"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 977, __extension__ __PRETTY_FUNCTION__))
;
978 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
979 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
980 Weights.push_back(CI->getValue().getZExtValue());
981 }
982
983 // If TI is a conditional eq, the default case is the false case,
984 // and the corresponding branch-weight data is at index 2. We swap the
985 // default weight to be the first entry.
986 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
987 assert(Weights.size() == 2)(static_cast <bool> (Weights.size() == 2) ? void (0) : __assert_fail
("Weights.size() == 2", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 987, __extension__ __PRETTY_FUNCTION__))
;
988 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
989 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
990 std::swap(Weights.front(), Weights.back());
991 }
992}
993
994/// Keep halving the weights until all can fit in uint32_t.
995static void FitWeights(MutableArrayRef<uint64_t> Weights) {
996 uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
997 if (Max > UINT_MAX(2147483647 *2U +1U)) {
998 unsigned Offset = 32 - countLeadingZeros(Max);
999 for (uint64_t &I : Weights)
1000 I >>= Offset;
1001 }
1002}
1003
1004/// The specified terminator is a value equality comparison instruction
1005/// (either a switch or a branch on "X == c").
1006/// See if any of the predecessors of the terminator block are value comparisons
1007/// on the same value. If so, and if safe to do so, fold them together.
1008bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
1009 IRBuilder<> &Builder) {
1010 BasicBlock *BB = TI->getParent();
1011 Value *CV = isValueEqualityComparison(TI); // CondVal
1012 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1012, __extension__ __PRETTY_FUNCTION__))
;
1013 bool Changed = false;
1014
1015 SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
1016 while (!Preds.empty()) {
1017 BasicBlock *Pred = Preds.pop_back_val();
1018
1019 // See if the predecessor is a comparison with the same value.
1020 TerminatorInst *PTI = Pred->getTerminator();
1021 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
1022
1023 if (PCV == CV && TI != PTI) {
1024 SmallSetVector<BasicBlock*, 4> FailBlocks;
1025 if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) {
1026 for (auto *Succ : FailBlocks) {
1027 if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split"))
1028 return false;
1029 }
1030 }
1031
1032 // Figure out which 'cases' to copy from SI to PSI.
1033 std::vector<ValueEqualityComparisonCase> BBCases;
1034 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
1035
1036 std::vector<ValueEqualityComparisonCase> PredCases;
1037 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
1038
1039 // Based on whether the default edge from PTI goes to BB or not, fill in
1040 // PredCases and PredDefault with the new switch cases we would like to
1041 // build.
1042 SmallVector<BasicBlock *, 8> NewSuccessors;
1043
1044 // Update the branch weight metadata along the way
1045 SmallVector<uint64_t, 8> Weights;
1046 bool PredHasWeights = HasBranchWeights(PTI);
1047 bool SuccHasWeights = HasBranchWeights(TI);
1048
1049 if (PredHasWeights) {
1050 GetBranchWeights(PTI, Weights);
1051 // branch-weight metadata is inconsistent here.
1052 if (Weights.size() != 1 + PredCases.size())
1053 PredHasWeights = SuccHasWeights = false;
1054 } else if (SuccHasWeights)
1055 // If there are no predecessor weights but there are successor weights,
1056 // populate Weights with 1, which will later be scaled to the sum of
1057 // successor's weights
1058 Weights.assign(1 + PredCases.size(), 1);
1059
1060 SmallVector<uint64_t, 8> SuccWeights;
1061 if (SuccHasWeights) {
1062 GetBranchWeights(TI, SuccWeights);
1063 // branch-weight metadata is inconsistent here.
1064 if (SuccWeights.size() != 1 + BBCases.size())
1065 PredHasWeights = SuccHasWeights = false;
1066 } else if (PredHasWeights)
1067 SuccWeights.assign(1 + BBCases.size(), 1);
1068
1069 if (PredDefault == BB) {
1070 // If this is the default destination from PTI, only the edges in TI
1071 // that don't occur in PTI, or that branch to BB will be activated.
1072 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1073 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1074 if (PredCases[i].Dest != BB)
1075 PTIHandled.insert(PredCases[i].Value);
1076 else {
1077 // The default destination is BB, we don't need explicit targets.
1078 std::swap(PredCases[i], PredCases.back());
1079
1080 if (PredHasWeights || SuccHasWeights) {
1081 // Increase weight for the default case.
1082 Weights[0] += Weights[i + 1];
1083 std::swap(Weights[i + 1], Weights.back());
1084 Weights.pop_back();
1085 }
1086
1087 PredCases.pop_back();
1088 --i;
1089 --e;
1090 }
1091
1092 // Reconstruct the new switch statement we will be building.
1093 if (PredDefault != BBDefault) {
1094 PredDefault->removePredecessor(Pred);
1095 PredDefault = BBDefault;
1096 NewSuccessors.push_back(BBDefault);
1097 }
1098
1099 unsigned CasesFromPred = Weights.size();
1100 uint64_t ValidTotalSuccWeight = 0;
1101 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1102 if (!PTIHandled.count(BBCases[i].Value) &&
1103 BBCases[i].Dest != BBDefault) {
1104 PredCases.push_back(BBCases[i]);
1105 NewSuccessors.push_back(BBCases[i].Dest);
1106 if (SuccHasWeights || PredHasWeights) {
1107 // The default weight is at index 0, so weight for the ith case
1108 // should be at index i+1. Scale the cases from successor by
1109 // PredDefaultWeight (Weights[0]).
1110 Weights.push_back(Weights[0] * SuccWeights[i + 1]);
1111 ValidTotalSuccWeight += SuccWeights[i + 1];
1112 }
1113 }
1114
1115 if (SuccHasWeights || PredHasWeights) {
1116 ValidTotalSuccWeight += SuccWeights[0];
1117 // Scale the cases from predecessor by ValidTotalSuccWeight.
1118 for (unsigned i = 1; i < CasesFromPred; ++i)
1119 Weights[i] *= ValidTotalSuccWeight;
1120 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
1121 Weights[0] *= SuccWeights[0];
1122 }
1123 } else {
1124 // If this is not the default destination from PSI, only the edges
1125 // in SI that occur in PSI with a destination of BB will be
1126 // activated.
1127 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1128 std::map<ConstantInt *, uint64_t> WeightsForHandled;
1129 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1130 if (PredCases[i].Dest == BB) {
1131 PTIHandled.insert(PredCases[i].Value);
1132
1133 if (PredHasWeights || SuccHasWeights) {
1134 WeightsForHandled[PredCases[i].Value] = Weights[i + 1];
1135 std::swap(Weights[i + 1], Weights.back());
1136 Weights.pop_back();
1137 }
1138
1139 std::swap(PredCases[i], PredCases.back());
1140 PredCases.pop_back();
1141 --i;
1142 --e;
1143 }
1144
1145 // Okay, now we know which constants were sent to BB from the
1146 // predecessor. Figure out where they will all go now.
1147 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1148 if (PTIHandled.count(BBCases[i].Value)) {
1149 // If this is one we are capable of getting...
1150 if (PredHasWeights || SuccHasWeights)
1151 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
1152 PredCases.push_back(BBCases[i]);
1153 NewSuccessors.push_back(BBCases[i].Dest);
1154 PTIHandled.erase(
1155 BBCases[i].Value); // This constant is taken care of
1156 }
1157
1158 // If there are any constants vectored to BB that TI doesn't handle,
1159 // they must go to the default destination of TI.
1160 for (ConstantInt *I : PTIHandled) {
1161 if (PredHasWeights || SuccHasWeights)
1162 Weights.push_back(WeightsForHandled[I]);
1163 PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault));
1164 NewSuccessors.push_back(BBDefault);
1165 }
1166 }
1167
1168 // Okay, at this point, we know which new successor Pred will get. Make
1169 // sure we update the number of entries in the PHI nodes for these
1170 // successors.
1171 for (BasicBlock *NewSuccessor : NewSuccessors)
1172 AddPredecessorToBlock(NewSuccessor, Pred, BB);
1173
1174 Builder.SetInsertPoint(PTI);
1175 // Convert pointer to int before we switch.
1176 if (CV->getType()->isPointerTy()) {
1177 CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()),
1178 "magicptr");
1179 }
1180
1181 // Now that the successors are updated, create the new Switch instruction.
1182 SwitchInst *NewSI =
1183 Builder.CreateSwitch(CV, PredDefault, PredCases.size());
1184 NewSI->setDebugLoc(PTI->getDebugLoc());
1185 for (ValueEqualityComparisonCase &V : PredCases)
1186 NewSI->addCase(V.Value, V.Dest);
1187
1188 if (PredHasWeights || SuccHasWeights) {
1189 // Halve the weights if any of them cannot fit in an uint32_t
1190 FitWeights(Weights);
1191
1192 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1193
1194 setBranchWeights(NewSI, MDWeights);
1195 }
1196
1197 EraseTerminatorInstAndDCECond(PTI);
1198
1199 // Okay, last check. If BB is still a successor of PSI, then we must
1200 // have an infinite loop case. If so, add an infinitely looping block
1201 // to handle the case to preserve the behavior of the code.
1202 BasicBlock *InfLoopBlock = nullptr;
1203 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1204 if (NewSI->getSuccessor(i) == BB) {
1205 if (!InfLoopBlock) {
1206 // Insert it at the end of the function, because it's either code,
1207 // or it won't matter if it's hot. :)
1208 InfLoopBlock = BasicBlock::Create(BB->getContext(), "infloop",
1209 BB->getParent());
1210 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1211 }
1212 NewSI->setSuccessor(i, InfLoopBlock);
1213 }
1214
1215 Changed = true;
1216 }
1217 }
1218 return Changed;
1219}
1220
1221// If we would need to insert a select that uses the value of this invoke
1222// (comments in HoistThenElseCodeToIf explain why we would need to do this), we
1223// can't hoist the invoke, as there is nowhere to put the select in this case.
1224static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1225 Instruction *I1, Instruction *I2) {
1226 for (BasicBlock *Succ : successors(BB1)) {
1227 for (const PHINode &PN : Succ->phis()) {
1228 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1229 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1230 if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
1231 return false;
1232 }
1233 }
1234 }
1235 return true;
1236}
1237
1238static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
1239
1240/// Given a conditional branch that goes to BB1 and BB2, hoist any common code
1241/// in the two blocks up into the branch block. The caller of this function
1242/// guarantees that BI's block dominates BB1 and BB2.
1243static bool HoistThenElseCodeToIf(BranchInst *BI,
1244 const TargetTransformInfo &TTI) {
1245 // This does very trivial matching, with limited scanning, to find identical
1246 // instructions in the two blocks. In particular, we don't want to get into
1247 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1248 // such, we currently just scan for obviously identical instructions in an
1249 // identical order.
1250 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1251 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1252
1253 BasicBlock::iterator BB1_Itr = BB1->begin();
1254 BasicBlock::iterator BB2_Itr = BB2->begin();
1255
1256 Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
1257 // Skip debug info if it is not identical.
1258 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1259 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1260 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1261 while (isa<DbgInfoIntrinsic>(I1))
1262 I1 = &*BB1_Itr++;
1263 while (isa<DbgInfoIntrinsic>(I2))
1264 I2 = &*BB2_Itr++;
1265 }
1266 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1267 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1268 return false;
1269
1270 BasicBlock *BIParent = BI->getParent();
1271
1272 bool Changed = false;
1273 do {
1274 // If we are hoisting the terminator instruction, don't move one (making a
1275 // broken BB), instead clone it, and remove BI.
1276 if (isa<TerminatorInst>(I1))
1277 goto HoistTerminator;
1278
1279 // If we're going to hoist a call, make sure that the two instructions we're
1280 // commoning/hoisting are both marked with musttail, or neither of them is
1281 // marked as such. Otherwise, we might end up in a situation where we hoist
1282 // from a block where the terminator is a `ret` to a block where the terminator
1283 // is a `br`, and `musttail` calls expect to be followed by a return.
1284 auto *C1 = dyn_cast<CallInst>(I1);
1285 auto *C2 = dyn_cast<CallInst>(I2);
1286 if (C1 && C2)
1287 if (C1->isMustTailCall() != C2->isMustTailCall())
1288 return Changed;
1289
1290 if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
1291 return Changed;
1292
1293 // For a normal instruction, we just move one to right before the branch,
1294 // then replace all uses of the other with the first. Finally, we remove
1295 // the now redundant second instruction.
1296 BIParent->getInstList().splice(BI->getIterator(), BB1->getInstList(), I1);
1297 if (!I2->use_empty())
1298 I2->replaceAllUsesWith(I1);
1299 I1->andIRFlags(I2);
1300 unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
1301 LLVMContext::MD_range,
1302 LLVMContext::MD_fpmath,
1303 LLVMContext::MD_invariant_load,
1304 LLVMContext::MD_nonnull,
1305 LLVMContext::MD_invariant_group,
1306 LLVMContext::MD_align,
1307 LLVMContext::MD_dereferenceable,
1308 LLVMContext::MD_dereferenceable_or_null,
1309 LLVMContext::MD_mem_parallel_loop_access};
1310 combineMetadata(I1, I2, KnownIDs);
1311
1312 // I1 and I2 are being combined into a single instruction. Its debug
1313 // location is the merged locations of the original instructions.
1314 I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
1315
1316 I2->eraseFromParent();
1317 Changed = true;
1318
1319 I1 = &*BB1_Itr++;
1320 I2 = &*BB2_Itr++;
1321 // Skip debug info if it is not identical.
1322 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1323 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1324 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1325 while (isa<DbgInfoIntrinsic>(I1))
1326 I1 = &*BB1_Itr++;
1327 while (isa<DbgInfoIntrinsic>(I2))
1328 I2 = &*BB2_Itr++;
1329 }
1330 } while (I1->isIdenticalToWhenDefined(I2));
1331
1332 return true;
1333
1334HoistTerminator:
1335 // It may not be possible to hoist an invoke.
1336 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1337 return Changed;
1338
1339 for (BasicBlock *Succ : successors(BB1)) {
1340 for (PHINode &PN : Succ->phis()) {
1341 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1342 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1343 if (BB1V == BB2V)
1344 continue;
1345
1346 // Check for passingValueIsAlwaysUndefined here because we would rather
1347 // eliminate undefined control flow then converting it to a select.
1348 if (passingValueIsAlwaysUndefined(BB1V, &PN) ||
1349 passingValueIsAlwaysUndefined(BB2V, &PN))
1350 return Changed;
1351
1352 if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1353 return Changed;
1354 if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1355 return Changed;
1356 }
1357 }
1358
1359 // Okay, it is safe to hoist the terminator.
1360 Instruction *NT = I1->clone();
1361 BIParent->getInstList().insert(BI->getIterator(), NT);
1362 if (!NT->getType()->isVoidTy()) {
1363 I1->replaceAllUsesWith(NT);
1364 I2->replaceAllUsesWith(NT);
1365 NT->takeName(I1);
1366 }
1367
1368 IRBuilder<NoFolder> Builder(NT);
1369 // Hoisting one of the terminators from our successor is a great thing.
1370 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1371 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1372 // nodes, so we insert select instruction to compute the final result.
1373 std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
1374 for (BasicBlock *Succ : successors(BB1)) {
1375 for (PHINode &PN : Succ->phis()) {
1376 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1377 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1378 if (BB1V == BB2V)
1379 continue;
1380
1381 // These values do not agree. Insert a select instruction before NT
1382 // that determines the right value.
1383 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1384 if (!SI)
1385 SI = cast<SelectInst>(
1386 Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1387 BB1V->getName() + "." + BB2V->getName(), BI));
1388
1389 // Make the PHI node use the select for all incoming values for BB1/BB2
1390 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
1391 if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2)
1392 PN.setIncomingValue(i, SI);
1393 }
1394 }
1395
1396 // Update any PHI nodes in our new successors.
1397 for (BasicBlock *Succ : successors(BB1))
1398 AddPredecessorToBlock(Succ, BIParent, BB1);
1399
1400 EraseTerminatorInstAndDCECond(BI);
1401 return true;
1402}
1403
1404// All instructions in Insts belong to different blocks that all unconditionally
1405// branch to a common successor. Analyze each instruction and return true if it
1406// would be possible to sink them into their successor, creating one common
1407// instruction instead. For every value that would be required to be provided by
1408// PHI node (because an operand varies in each input block), add to PHIOperands.
1409static bool canSinkInstructions(
1410 ArrayRef<Instruction *> Insts,
1411 DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
1412 // Prune out obviously bad instructions to move. Any non-store instruction
1413 // must have exactly one use, and we check later that use is by a single,
1414 // common PHI instruction in the successor.
1415 for (auto *I : Insts) {
1416 // These instructions may change or break semantics if moved.
1417 if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
1418 I->getType()->isTokenTy())
1419 return false;
1420
1421 // Conservatively return false if I is an inline-asm instruction. Sinking
1422 // and merging inline-asm instructions can potentially create arguments
1423 // that cannot satisfy the inline-asm constraints.
1424 if (const auto *C = dyn_cast<CallInst>(I))
1425 if (C->isInlineAsm())
1426 return false;
1427
1428 // Everything must have only one use too, apart from stores which
1429 // have no uses.
1430 if (!isa<StoreInst>(I) && !I->hasOneUse())
1431 return false;
1432 }
1433
1434 const Instruction *I0 = Insts.front();
1435 for (auto *I : Insts)
1436 if (!I->isSameOperationAs(I0))
1437 return false;
1438
1439 // All instructions in Insts are known to be the same opcode. If they aren't
1440 // stores, check the only user of each is a PHI or in the same block as the
1441 // instruction, because if a user is in the same block as an instruction
1442 // we're contemplating sinking, it must already be determined to be sinkable.
1443 if (!isa<StoreInst>(I0)) {
1444 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1445 auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
1446 if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
1447 auto *U = cast<Instruction>(*I->user_begin());
1448 return (PNUse &&
1449 PNUse->getParent() == Succ &&
1450 PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
1451 U->getParent() == I->getParent();
1452 }))
1453 return false;
1454 }
1455
1456 // Because SROA can't handle speculating stores of selects, try not
1457 // to sink loads or stores of allocas when we'd have to create a PHI for
1458 // the address operand. Also, because it is likely that loads or stores
1459 // of allocas will disappear when Mem2Reg/SROA is run, don't sink them.
1460 // This can cause code churn which can have unintended consequences down
1461 // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244.
1462 // FIXME: This is a workaround for a deficiency in SROA - see
1463 // https://llvm.org/bugs/show_bug.cgi?id=30188
1464 if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) {
1465 return isa<AllocaInst>(I->getOperand(1));
1466 }))
1467 return false;
1468 if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) {
1469 return isa<AllocaInst>(I->getOperand(0));
1470 }))
1471 return false;
1472
1473 for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
1474 if (I0->getOperand(OI)->getType()->isTokenTy())
1475 // Don't touch any operand of token type.
1476 return false;
1477
1478 auto SameAsI0 = [&I0, OI](const Instruction *I) {
1479 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1479, __extension__ __PRETTY_FUNCTION__))
;
1480 return I->getOperand(OI) == I0->getOperand(OI);
1481 };
1482 if (!all_of(Insts, SameAsI0)) {
1483 if (!canReplaceOperandWithVariable(I0, OI))
1484 // We can't create a PHI from this GEP.
1485 return false;
1486 // Don't create indirect calls! The called value is the final operand.
1487 if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI == OE - 1) {
1488 // FIXME: if the call was *already* indirect, we should do this.
1489 return false;
1490 }
1491 for (auto *I : Insts)
1492 PHIOperands[I].push_back(I->getOperand(OI));
1493 }
1494 }
1495 return true;
1496}
1497
1498// Assuming canSinkLastInstruction(Blocks) has returned true, sink the last
1499// instruction of every block in Blocks to their common successor, commoning
1500// into one instruction.
1501static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
1502 auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
1503
1504 // canSinkLastInstruction returning true guarantees that every block has at
1505 // least one non-terminator instruction.
1506 SmallVector<Instruction*,4> Insts;
1507 for (auto *BB : Blocks) {
1508 Instruction *I = BB->getTerminator();
1509 do {
1510 I = I->getPrevNode();
1511 } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
1512 if (!isa<DbgInfoIntrinsic>(I))
1513 Insts.push_back(I);
1514 }
1515
1516 // The only checking we need to do now is that all users of all instructions
1517 // are the same PHI node. canSinkLastInstruction should have checked this but
1518 // it is slightly over-aggressive - it gets confused by commutative instructions
1519 // so double-check it here.
1520 Instruction *I0 = Insts.front();
1521 if (!isa<StoreInst>(I0)) {
1522 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1523 if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
1524 auto *U = cast<Instruction>(*I->user_begin());
1525 return U == PNUse;
1526 }))
1527 return false;
1528 }
1529
1530 // We don't need to do any more checking here; canSinkLastInstruction should
1531 // have done it all for us.
1532 SmallVector<Value*, 4> NewOperands;
1533 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
1534 // This check is different to that in canSinkLastInstruction. There, we
1535 // cared about the global view once simplifycfg (and instcombine) have
1536 // completed - it takes into account PHIs that become trivially
1537 // simplifiable. However here we need a more local view; if an operand
1538 // differs we create a PHI and rely on instcombine to clean up the very
1539 // small mess we may make.
1540 bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
1541 return I->getOperand(O) != I0->getOperand(O);
1542 });
1543 if (!NeedPHI) {
1544 NewOperands.push_back(I0->getOperand(O));
1545 continue;
1546 }
1547
1548 // Create a new PHI in the successor block and populate it.
1549 auto *Op = I0->getOperand(O);
1550 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1550, __extension__ __PRETTY_FUNCTION__))
;
1551 auto *PN = PHINode::Create(Op->getType(), Insts.size(),
1552 Op->getName() + ".sink", &BBEnd->front());
1553 for (auto *I : Insts)
1554 PN->addIncoming(I->getOperand(O), I->getParent());
1555 NewOperands.push_back(PN);
1556 }
1557
1558 // Arbitrarily use I0 as the new "common" instruction; remap its operands
1559 // and move it to the start of the successor block.
1560 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
1561 I0->getOperandUse(O).set(NewOperands[O]);
1562 I0->moveBefore(&*BBEnd->getFirstInsertionPt());
1563
1564 // Update metadata and IR flags, and merge debug locations.
1565 for (auto *I : Insts)
1566 if (I != I0) {
1567 // The debug location for the "common" instruction is the merged locations
1568 // of all the commoned instructions. We start with the original location
1569 // of the "common" instruction and iteratively merge each location in the
1570 // loop below.
1571 // This is an N-way merge, which will be inefficient if I0 is a CallInst.
1572 // However, as N-way merge for CallInst is rare, so we use simplified API
1573 // instead of using complex API for N-way merge.
1574 I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc());
1575 combineMetadataForCSE(I0, I);
1576 I0->andIRFlags(I);
1577 }
1578
1579 if (!isa<StoreInst>(I0)) {
1580 // canSinkLastInstruction checked that all instructions were used by
1581 // one and only one PHI node. Find that now, RAUW it to our common
1582 // instruction and nuke it.
1583 assert(I0->hasOneUse())(static_cast <bool> (I0->hasOneUse()) ? void (0) : __assert_fail
("I0->hasOneUse()", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1583, __extension__ __PRETTY_FUNCTION__))
;
1584 auto *PN = cast<PHINode>(*I0->user_begin());
1585 PN->replaceAllUsesWith(I0);
1586 PN->eraseFromParent();
1587 }
1588
1589 // Finally nuke all instructions apart from the common instruction.
1590 for (auto *I : Insts)
1591 if (I != I0)
1592 I->eraseFromParent();
1593
1594 return true;
1595}
1596
1597namespace {
1598
1599 // LockstepReverseIterator - Iterates through instructions
1600 // in a set of blocks in reverse order from the first non-terminator.
1601 // For example (assume all blocks have size n):
1602 // LockstepReverseIterator I([B1, B2, B3]);
1603 // *I-- = [B1[n], B2[n], B3[n]];
1604 // *I-- = [B1[n-1], B2[n-1], B3[n-1]];
1605 // *I-- = [B1[n-2], B2[n-2], B3[n-2]];
1606 // ...
1607 class LockstepReverseIterator {
1608 ArrayRef<BasicBlock*> Blocks;
1609 SmallVector<Instruction*,4> Insts;
1610 bool Fail;
1611
1612 public:
1613 LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) : Blocks(Blocks) {
1614 reset();
1615 }
1616
1617 void reset() {
1618 Fail = false;
1619 Insts.clear();
1620 for (auto *BB : Blocks) {
1621 Instruction *Inst = BB->getTerminator();
1622 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1623 Inst = Inst->getPrevNode();
1624 if (!Inst) {
1625 // Block wasn't big enough.
1626 Fail = true;
1627 return;
1628 }
1629 Insts.push_back(Inst);
1630 }
1631 }
1632
1633 bool isValid() const {
1634 return !Fail;
1635 }
1636
1637 void operator--() {
1638 if (Fail)
1639 return;
1640 for (auto *&Inst : Insts) {
1641 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1642 Inst = Inst->getPrevNode();
1643 // Already at beginning of block.
1644 if (!Inst) {
1645 Fail = true;
1646 return;
1647 }
1648 }
1649 }
1650
1651 ArrayRef<Instruction*> operator * () const {
1652 return Insts;
1653 }
1654 };
1655
1656} // end anonymous namespace
1657
1658/// Check whether BB's predecessors end with unconditional branches. If it is
1659/// true, sink any common code from the predecessors to BB.
1660/// We also allow one predecessor to end with conditional branch (but no more
1661/// than one).
1662static bool SinkCommonCodeFromPredecessors(BasicBlock *BB) {
1663 // We support two situations:
1664 // (1) all incoming arcs are unconditional
1665 // (2) one incoming arc is conditional
1666 //
1667 // (2) is very common in switch defaults and
1668 // else-if patterns;
1669 //
1670 // if (a) f(1);
1671 // else if (b) f(2);
1672 //
1673 // produces:
1674 //
1675 // [if]
1676 // / \
1677 // [f(1)] [if]
1678 // | | \
1679 // | | |
1680 // | [f(2)]|
1681 // \ | /
1682 // [ end ]
1683 //
1684 // [end] has two unconditional predecessor arcs and one conditional. The
1685 // conditional refers to the implicit empty 'else' arc. This conditional
1686 // arc can also be caused by an empty default block in a switch.
1687 //
1688 // In this case, we attempt to sink code from all *unconditional* arcs.
1689 // If we can sink instructions from these arcs (determined during the scan
1690 // phase below) we insert a common successor for all unconditional arcs and
1691 // connect that to [end], to enable sinking:
1692 //
1693 // [if]
1694 // / \
1695 // [x(1)] [if]
1696 // | | \
1697 // | | \
1698 // | [x(2)] |
1699 // \ / |
1700 // [sink.split] |
1701 // \ /
1702 // [ end ]
1703 //
1704 SmallVector<BasicBlock*,4> UnconditionalPreds;
1705 Instruction *Cond = nullptr;
1706 for (auto *B : predecessors(BB)) {
1707 auto *T = B->getTerminator();
1708 if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional())
1709 UnconditionalPreds.push_back(B);
1710 else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond)
1711 Cond = T;
1712 else
1713 return false;
1714 }
1715 if (UnconditionalPreds.size() < 2)
1716 return false;
1717
1718 bool Changed = false;
1719 // We take a two-step approach to tail sinking. First we scan from the end of
1720 // each block upwards in lockstep. If the n'th instruction from the end of each
1721 // block can be sunk, those instructions are added to ValuesToSink and we
1722 // carry on. If we can sink an instruction but need to PHI-merge some operands
1723 // (because they're not identical in each instruction) we add these to
1724 // PHIOperands.
1725 unsigned ScanIdx = 0;
1726 SmallPtrSet<Value*,4> InstructionsToSink;
1727 DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands;
1728 LockstepReverseIterator LRI(UnconditionalPreds);
1729 while (LRI.isValid() &&
1730 canSinkInstructions(*LRI, PHIOperands)) {
1731 DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0] << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: instruction can be sunk: "
<< *(*LRI)[0] << "\n"; } } while (false)
;
1732 InstructionsToSink.insert((*LRI).begin(), (*LRI).end());
1733 ++ScanIdx;
1734 --LRI;
1735 }
1736
1737 auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
1738 unsigned NumPHIdValues = 0;
1739 for (auto *I : *LRI)
1740 for (auto *V : PHIOperands[I])
1741 if (InstructionsToSink.count(V) == 0)
1742 ++NumPHIdValues;
1743 DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: #phid values: " <<
NumPHIdValues << "\n"; } } while (false)
;
1744 unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size();
1745 if ((NumPHIdValues % UnconditionalPreds.size()) != 0)
1746 NumPHIInsts++;
1747
1748 return NumPHIInsts <= 1;
1749 };
1750
1751 if (ScanIdx > 0 && Cond) {
1752 // Check if we would actually sink anything first! This mutates the CFG and
1753 // adds an extra block. The goal in doing this is to allow instructions that
1754 // couldn't be sunk before to be sunk - obviously, speculatable instructions
1755 // (such as trunc, add) can be sunk and predicated already. So we check that
1756 // we're going to sink at least one non-speculatable instruction.
1757 LRI.reset();
1758 unsigned Idx = 0;
1759 bool Profitable = false;
1760 while (ProfitableToSinkInstruction(LRI) && Idx < ScanIdx) {
1761 if (!isSafeToSpeculativelyExecute((*LRI)[0])) {
1762 Profitable = true;
1763 break;
1764 }
1765 --LRI;
1766 ++Idx;
1767 }
1768 if (!Profitable)
1769 return false;
1770
1771 DEBUG(dbgs() << "SINK: Splitting edge\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Splitting edge\n"; }
} while (false)
;
1772 // We have a conditional edge and we're going to sink some instructions.
1773 // Insert a new block postdominating all blocks we're going to sink from.
1774 if (!SplitBlockPredecessors(BB, UnconditionalPreds, ".sink.split"))
1775 // Edges couldn't be split.
1776 return false;
1777 Changed = true;
1778 }
1779
1780 // Now that we've analyzed all potential sinking candidates, perform the
1781 // actual sink. We iteratively sink the last non-terminator of the source
1782 // blocks into their common successor unless doing so would require too
1783 // many PHI instructions to be generated (currently only one PHI is allowed
1784 // per sunk instruction).
1785 //
1786 // We can use InstructionsToSink to discount values needing PHI-merging that will
1787 // actually be sunk in a later iteration. This allows us to be more
1788 // aggressive in what we sink. This does allow a false positive where we
1789 // sink presuming a later value will also be sunk, but stop half way through
1790 // and never actually sink it which means we produce more PHIs than intended.
1791 // This is unlikely in practice though.
1792 for (unsigned SinkIdx = 0; SinkIdx != ScanIdx; ++SinkIdx) {
1793 DEBUG(dbgs() << "SINK: Sink: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1794 << *UnconditionalPreds[0]->getTerminator()->getPrevNode()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
1795 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: Sink: " << *UnconditionalPreds
[0]->getTerminator()->getPrevNode() << "\n"; } } while
(false)
;
1796
1797 // Because we've sunk every instruction in turn, the current instruction to
1798 // sink is always at index 0.
1799 LRI.reset();
1800 if (!ProfitableToSinkInstruction(LRI)) {
1801 // Too many PHIs would be created.
1802 DEBUG(dbgs() << "SINK: stopping here, too many PHIs would be created!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SINK: stopping here, too many PHIs would be created!\n"
; } } while (false)
;
1803 break;
1804 }
1805
1806 if (!sinkLastInstruction(UnconditionalPreds))
1807 return Changed;
1808 NumSinkCommons++;
1809 Changed = true;
1810 }
1811 return Changed;
1812}
1813
1814/// \brief Determine if we can hoist sink a sole store instruction out of a
1815/// conditional block.
1816///
1817/// We are looking for code like the following:
1818/// BrBB:
1819/// store i32 %add, i32* %arrayidx2
1820/// ... // No other stores or function calls (we could be calling a memory
1821/// ... // function).
1822/// %cmp = icmp ult %x, %y
1823/// br i1 %cmp, label %EndBB, label %ThenBB
1824/// ThenBB:
1825/// store i32 %add5, i32* %arrayidx2
1826/// br label EndBB
1827/// EndBB:
1828/// ...
1829/// We are going to transform this into:
1830/// BrBB:
1831/// store i32 %add, i32* %arrayidx2
1832/// ... //
1833/// %cmp = icmp ult %x, %y
1834/// %add.add5 = select i1 %cmp, i32 %add, %add5
1835/// store i32 %add.add5, i32* %arrayidx2
1836/// ...
1837///
1838/// \return The pointer to the value of the previous store if the store can be
1839/// hoisted into the predecessor block. 0 otherwise.
1840static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1841 BasicBlock *StoreBB, BasicBlock *EndBB) {
1842 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1843 if (!StoreToHoist)
1844 return nullptr;
1845
1846 // Volatile or atomic.
1847 if (!StoreToHoist->isSimple())
1848 return nullptr;
1849
1850 Value *StorePtr = StoreToHoist->getPointerOperand();
1851
1852 // Look for a store to the same pointer in BrBB.
1853 unsigned MaxNumInstToLookAt = 9;
1854 for (Instruction &CurI : reverse(*BrBB)) {
1855 if (!MaxNumInstToLookAt)
1856 break;
1857 // Skip debug info.
1858 if (isa<DbgInfoIntrinsic>(CurI))
1859 continue;
1860 --MaxNumInstToLookAt;
1861
1862 // Could be calling an instruction that affects memory like free().
1863 if (CurI.mayHaveSideEffects() && !isa<StoreInst>(CurI))
1864 return nullptr;
1865
1866 if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
1867 // Found the previous store make sure it stores to the same location.
1868 if (SI->getPointerOperand() == StorePtr)
1869 // Found the previous store, return its value operand.
1870 return SI->getValueOperand();
1871 return nullptr; // Unknown store.
1872 }
1873 }
1874
1875 return nullptr;
1876}
1877
1878/// \brief Speculate a conditional basic block flattening the CFG.
1879///
1880/// Note that this is a very risky transform currently. Speculating
1881/// instructions like this is most often not desirable. Instead, there is an MI
1882/// pass which can do it with full awareness of the resource constraints.
1883/// However, some cases are "obvious" and we should do directly. An example of
1884/// this is speculating a single, reasonably cheap instruction.
1885///
1886/// There is only one distinct advantage to flattening the CFG at the IR level:
1887/// it makes very common but simplistic optimizations such as are common in
1888/// instcombine and the DAG combiner more powerful by removing CFG edges and
1889/// modeling their effects with easier to reason about SSA value graphs.
1890///
1891///
1892/// An illustration of this transform is turning this IR:
1893/// \code
1894/// BB:
1895/// %cmp = icmp ult %x, %y
1896/// br i1 %cmp, label %EndBB, label %ThenBB
1897/// ThenBB:
1898/// %sub = sub %x, %y
1899/// br label BB2
1900/// EndBB:
1901/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1902/// ...
1903/// \endcode
1904///
1905/// Into this IR:
1906/// \code
1907/// BB:
1908/// %cmp = icmp ult %x, %y
1909/// %sub = sub %x, %y
1910/// %cond = select i1 %cmp, 0, %sub
1911/// ...
1912/// \endcode
1913///
1914/// \returns true if the conditional block is removed.
1915static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
1916 const TargetTransformInfo &TTI) {
1917 // Be conservative for now. FP select instruction can often be expensive.
1918 Value *BrCond = BI->getCondition();
1919 if (isa<FCmpInst>(BrCond))
1920 return false;
1921
1922 BasicBlock *BB = BI->getParent();
1923 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1924
1925 // If ThenBB is actually on the false edge of the conditional branch, remember
1926 // to swap the select operands later.
1927 bool Invert = false;
1928 if (ThenBB != BI->getSuccessor(0)) {
1929 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1929, __extension__ __PRETTY_FUNCTION__))
;
1930 Invert = true;
1931 }
1932 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 1932, __extension__ __PRETTY_FUNCTION__))
;
1933
1934 // Keep a count of how many times instructions are used within CondBB when
1935 // they are candidates for sinking into CondBB. Specifically:
1936 // - They are defined in BB, and
1937 // - They have no side effects, and
1938 // - All of their uses are in CondBB.
1939 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1940
1941 SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics;
1942
1943 unsigned SpeculationCost = 0;
1944 Value *SpeculatedStoreValue = nullptr;
1945 StoreInst *SpeculatedStore = nullptr;
1946 for (BasicBlock::iterator BBI = ThenBB->begin(),
1947 BBE = std::prev(ThenBB->end());
1948 BBI != BBE; ++BBI) {
1949 Instruction *I = &*BBI;
1950 // Skip debug info.
1951 if (isa<DbgInfoIntrinsic>(I)) {
1952 SpeculatedDbgIntrinsics.push_back(I);
1953 continue;
1954 }
1955
1956 // Only speculatively execute a single instruction (not counting the
1957 // terminator) for now.
1958 ++SpeculationCost;
1959 if (SpeculationCost > 1)
1960 return false;
1961
1962 // Don't hoist the instruction if it's unsafe or expensive.
1963 if (!isSafeToSpeculativelyExecute(I) &&
1964 !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
1965 I, BB, ThenBB, EndBB))))
1966 return false;
1967 if (!SpeculatedStoreValue &&
1968 ComputeSpeculationCost(I, TTI) >
1969 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
1970 return false;
1971
1972 // Store the store speculation candidate.
1973 if (SpeculatedStoreValue)
1974 SpeculatedStore = cast<StoreInst>(I);
1975
1976 // Do not hoist the instruction if any of its operands are defined but not
1977 // used in BB. The transformation will prevent the operand from
1978 // being sunk into the use block.
1979 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1980 Instruction *OpI = dyn_cast<Instruction>(*i);
1981 if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects())
1982 continue; // Not a candidate for sinking.
1983
1984 ++SinkCandidateUseCounts[OpI];
1985 }
1986 }
1987
1988 // Consider any sink candidates which are only used in CondBB as costs for
1989 // speculation. Note, while we iterate over a DenseMap here, we are summing
1990 // and so iteration order isn't significant.
1991 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator
1992 I = SinkCandidateUseCounts.begin(),
1993 E = SinkCandidateUseCounts.end();
1994 I != E; ++I)
1995 if (I->first->getNumUses() == I->second) {
1996 ++SpeculationCost;
1997 if (SpeculationCost > 1)
1998 return false;
1999 }
2000
2001 // Check that the PHI nodes can be converted to selects.
2002 bool HaveRewritablePHIs = false;
2003 for (PHINode &PN : EndBB->phis()) {
2004 Value *OrigV = PN.getIncomingValueForBlock(BB);
2005 Value *ThenV = PN.getIncomingValueForBlock(ThenBB);
2006
2007 // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
2008 // Skip PHIs which are trivial.
2009 if (ThenV == OrigV)
2010 continue;
2011
2012 // Don't convert to selects if we could remove undefined behavior instead.
2013 if (passingValueIsAlwaysUndefined(OrigV, &PN) ||
2014 passingValueIsAlwaysUndefined(ThenV, &PN))
2015 return false;
2016
2017 HaveRewritablePHIs = true;
2018 ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
2019 ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
2020 if (!OrigCE && !ThenCE)
2021 continue; // Known safe and cheap.
2022
2023 if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
2024 (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
2025 return false;
2026 unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0;
2027 unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0;
2028 unsigned MaxCost =
2029 2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2030 if (OrigCost + ThenCost > MaxCost)
2031 return false;
2032
2033 // Account for the cost of an unfolded ConstantExpr which could end up
2034 // getting expanded into Instructions.
2035 // FIXME: This doesn't account for how many operations are combined in the
2036 // constant expression.
2037 ++SpeculationCost;
2038 if (SpeculationCost > 1)
2039 return false;
2040 }
2041
2042 // If there are no PHIs to process, bail early. This helps ensure idempotence
2043 // as well.
2044 if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
2045 return false;
2046
2047 // If we get here, we can hoist the instruction and if-convert.
2048 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SPECULATIVELY EXECUTING BB"
<< *ThenBB << "\n";; } } while (false)
;
2049
2050 // Insert a select of the value of the speculated store.
2051 if (SpeculatedStoreValue) {
2052 IRBuilder<NoFolder> Builder(BI);
2053 Value *TrueV = SpeculatedStore->getValueOperand();
2054 Value *FalseV = SpeculatedStoreValue;
2055 if (Invert)
2056 std::swap(TrueV, FalseV);
2057 Value *S = Builder.CreateSelect(
2058 BrCond, TrueV, FalseV, "spec.store.select", BI);
2059 SpeculatedStore->setOperand(0, S);
2060 SpeculatedStore->applyMergedLocation(BI->getDebugLoc(),
2061 SpeculatedStore->getDebugLoc());
2062 }
2063
2064 // Metadata can be dependent on the condition we are hoisting above.
2065 // Conservatively strip all metadata on the instruction.
2066 for (auto &I : *ThenBB)
2067 I.dropUnknownNonDebugMetadata();
2068
2069 // Hoist the instructions.
2070 BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
2071 ThenBB->begin(), std::prev(ThenBB->end()));
2072
2073 // Insert selects and rewrite the PHI operands.
2074 IRBuilder<NoFolder> Builder(BI);
2075 for (PHINode &PN : EndBB->phis()) {
2076 unsigned OrigI = PN.getBasicBlockIndex(BB);
2077 unsigned ThenI = PN.getBasicBlockIndex(ThenBB);
2078 Value *OrigV = PN.getIncomingValue(OrigI);
2079 Value *ThenV = PN.getIncomingValue(ThenI);
2080
2081 // Skip PHIs which are trivial.
2082 if (OrigV == ThenV)
2083 continue;
2084
2085 // Create a select whose true value is the speculatively executed value and
2086 // false value is the preexisting value. Swap them if the branch
2087 // destinations were inverted.
2088 Value *TrueV = ThenV, *FalseV = OrigV;
2089 if (Invert)
2090 std::swap(TrueV, FalseV);
2091 Value *V = Builder.CreateSelect(
2092 BrCond, TrueV, FalseV, "spec.select", BI);
2093 PN.setIncomingValue(OrigI, V);
2094 PN.setIncomingValue(ThenI, V);
2095 }
2096
2097 // Remove speculated dbg intrinsics.
2098 // FIXME: Is it possible to do this in a more elegant way? Moving/merging the
2099 // dbg value for the different flows and inserting it after the select.
2100 for (Instruction *I : SpeculatedDbgIntrinsics)
2101 I->eraseFromParent();
2102
2103 ++NumSpeculations;
2104 return true;
2105}
2106
2107/// Return true if we can thread a branch across this block.
2108static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
2109 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
2110 unsigned Size = 0;
2111
2112 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2113 if (isa<DbgInfoIntrinsic>(BBI))
2114 continue;
2115 if (Size > 10)
2116 return false; // Don't clone large BB's.
2117 ++Size;
2118
2119 // We can only support instructions that do not define values that are
2120 // live outside of the current basic block.
2121 for (User *U : BBI->users()) {
2122 Instruction *UI = cast<Instruction>(U);
2123 if (UI->getParent() != BB || isa<PHINode>(UI))
2124 return false;
2125 }
2126
2127 // Looks ok, continue checking.
2128 }
2129
2130 return true;
2131}
2132
2133/// If we have a conditional branch on a PHI node value that is defined in the
2134/// same block as the branch and if any PHI entries are constants, thread edges
2135/// corresponding to that entry to be branches to their ultimate destination.
2136static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL,
2137 AssumptionCache *AC) {
2138 BasicBlock *BB = BI->getParent();
2139 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
2140 // NOTE: we currently cannot transform this case if the PHI node is used
2141 // outside of the block.
2142 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
2143 return false;
2144
2145 // Degenerate case of a single entry PHI.
2146 if (PN->getNumIncomingValues() == 1) {
2147 FoldSingleEntryPHINodes(PN->getParent());
2148 return true;
2149 }
2150
2151 // Now we know that this block has multiple preds and two succs.
2152 if (!BlockIsSimpleEnoughToThreadThrough(BB))
2153 return false;
2154
2155 // Can't fold blocks that contain noduplicate or convergent calls.
2156 if (any_of(*BB, [](const Instruction &I) {
2157 const CallInst *CI = dyn_cast<CallInst>(&I);
2158 return CI && (CI->cannotDuplicate() || CI->isConvergent());
2159 }))
2160 return false;
2161
2162 // Okay, this is a simple enough basic block. See if any phi values are
2163 // constants.
2164 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2165 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
2166 if (!CB || !CB->getType()->isIntegerTy(1))
2167 continue;
2168
2169 // Okay, we now know that all edges from PredBB should be revectored to
2170 // branch to RealDest.
2171 BasicBlock *PredBB = PN->getIncomingBlock(i);
2172 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
2173
2174 if (RealDest == BB)
2175 continue; // Skip self loops.
2176 // Skip if the predecessor's terminator is an indirect branch.
2177 if (isa<IndirectBrInst>(PredBB->getTerminator()))
2178 continue;
2179
2180 // The dest block might have PHI nodes, other predecessors and other
2181 // difficult cases. Instead of being smart about this, just insert a new
2182 // block that jumps to the destination block, effectively splitting
2183 // the edge we are about to create.
2184 BasicBlock *EdgeBB =
2185 BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge",
2186 RealDest->getParent(), RealDest);
2187 BranchInst::Create(RealDest, EdgeBB);
2188
2189 // Update PHI nodes.
2190 AddPredecessorToBlock(RealDest, EdgeBB, BB);
2191
2192 // BB may have instructions that are being threaded over. Clone these
2193 // instructions into EdgeBB. We know that there will be no uses of the
2194 // cloned instructions outside of EdgeBB.
2195 BasicBlock::iterator InsertPt = EdgeBB->begin();
2196 DenseMap<Value *, Value *> TranslateMap; // Track translated values.
2197 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2198 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
2199 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
2200 continue;
2201 }
2202 // Clone the instruction.
2203 Instruction *N = BBI->clone();
2204 if (BBI->hasName())
2205 N->setName(BBI->getName() + ".c");
2206
2207 // Update operands due to translation.
2208 for (User::op_iterator i = N->op_begin(), e = N->op_end(); i != e; ++i) {
2209 DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(*i);
2210 if (PI != TranslateMap.end())
2211 *i = PI->second;
2212 }
2213
2214 // Check for trivial simplification.
2215 if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) {
2216 if (!BBI->use_empty())
2217 TranslateMap[&*BBI] = V;
2218 if (!N->mayHaveSideEffects()) {
2219 N->deleteValue(); // Instruction folded away, don't need actual inst
2220 N = nullptr;
2221 }
2222 } else {
2223 if (!BBI->use_empty())
2224 TranslateMap[&*BBI] = N;
2225 }
2226 // Insert the new instruction into its new home.
2227 if (N)
2228 EdgeBB->getInstList().insert(InsertPt, N);
2229
2230 // Register the new instruction with the assumption cache if necessary.
2231 if (auto *II = dyn_cast_or_null<IntrinsicInst>(N))
2232 if (II->getIntrinsicID() == Intrinsic::assume)
2233 AC->registerAssumption(II);
2234 }
2235
2236 // Loop over all of the edges from PredBB to BB, changing them to branch
2237 // to EdgeBB instead.
2238 TerminatorInst *PredBBTI = PredBB->getTerminator();
2239 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
2240 if (PredBBTI->getSuccessor(i) == BB) {
2241 BB->removePredecessor(PredBB);
2242 PredBBTI->setSuccessor(i, EdgeBB);
2243 }
2244
2245 // Recurse, simplifying any other constants.
2246 return FoldCondBranchOnPHI(BI, DL, AC) | true;
2247 }
2248
2249 return false;
2250}
2251
2252/// Given a BB that starts with the specified two-entry PHI node,
2253/// see if we can eliminate it.
2254static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
2255 const DataLayout &DL) {
2256 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
2257 // statement", which has a very simple dominance structure. Basically, we
2258 // are trying to find the condition that is being branched on, which
2259 // subsequently causes this merge to happen. We really want control
2260 // dependence information for this check, but simplifycfg can't keep it up
2261 // to date, and this catches most of the cases we care about anyway.
2262 BasicBlock *BB = PN->getParent();
2263 BasicBlock *IfTrue, *IfFalse;
2264 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
2265 if (!IfCond ||
26
Assuming 'IfCond' is non-null
27
Taking false branch
2266 // Don't bother if the branch will be constant folded trivially.
2267 isa<ConstantInt>(IfCond))
2268 return false;
2269
2270 // Okay, we found that we can merge this two-entry phi node into a select.
2271 // Doing so would require us to fold *all* two entry phi nodes in this block.
2272 // At some point this becomes non-profitable (particularly if the target
2273 // doesn't support cmov's). Only do this transformation if there are two or
2274 // fewer PHI nodes in this block.
2275 unsigned NumPhis = 0;
2276 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
28
Loop condition is false. Execution continues on line 2283
2277 if (NumPhis > 2)
2278 return false;
2279
2280 // Loop over the PHI's seeing if we can promote them all to select
2281 // instructions. While we are at it, keep track of the instructions
2282 // that need to be moved to the dominating block.
2283 SmallPtrSet<Instruction *, 4> AggressiveInsts;
2284 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
2285 MaxCostVal1 = PHINodeFoldingThreshold;
2286 MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
2287 MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
2288
2289 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
29
Loop condition is false. Execution continues on line 2306
2290 PHINode *PN = cast<PHINode>(II++);
2291 if (Value *V = SimplifyInstruction(PN, {DL, PN})) {
2292 PN->replaceAllUsesWith(V);
2293 PN->eraseFromParent();
2294 continue;
2295 }
2296
2297 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
2298 MaxCostVal0, TTI) ||
2299 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
2300 MaxCostVal1, TTI))
2301 return false;
2302 }
2303
2304 // If we folded the first phi, PN dangles at this point. Refresh it. If
2305 // we ran out of PHIs then we simplified them all.
2306 PN = dyn_cast<PHINode>(BB->begin());
2307 if (!PN)
30
Assuming 'PN' is non-null
31
Taking false branch
2308 return true;
2309
2310 // Don't fold i1 branches on PHIs which contain binary operators. These can
2311 // often be turned into switches and other things.
2312 if (PN->getType()->isIntegerTy(1) &&
32
Assuming the condition is false
33
Taking false branch
2313 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
2314 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
2315 isa<BinaryOperator>(IfCond)))
2316 return false;
2317
2318 // If all PHI nodes are promotable, check to make sure that all instructions
2319 // in the predecessor blocks can be promoted as well. If not, we won't be able
2320 // to get rid of the control flow, so it's not worth promoting to select
2321 // instructions.
2322 BasicBlock *DomBlock = nullptr;
34
'DomBlock' initialized to a null pointer value
2323 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
2324 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
2325 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
35
Taking true branch
2326 IfBlock1 = nullptr;
2327 } else {
2328 DomBlock = *pred_begin(IfBlock1);
2329 for (BasicBlock::iterator I = IfBlock1->begin(); !isa<TerminatorInst>(I);
2330 ++I)
2331 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2332 // This is not an aggressive instruction that we can promote.
2333 // Because of this, we won't be able to get rid of the control flow, so
2334 // the xform is not worth it.
2335 return false;
2336 }
2337 }
2338
2339 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
36
Taking true branch
2340 IfBlock2 = nullptr;
2341 } else {
2342 DomBlock = *pred_begin(IfBlock2);
2343 for (BasicBlock::iterator I = IfBlock2->begin(); !isa<TerminatorInst>(I);
2344 ++I)
2345 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
2346 // This is not an aggressive instruction that we can promote.
2347 // Because of this, we won't be able to get rid of the control flow, so
2348 // the xform is not worth it.
2349 return false;
2350 }
2351 }
2352
2353 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
2354 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOUND IF CONDITION! " <<
*IfCond << " T: " << IfTrue->getName() <<
" F: " << IfFalse->getName() << "\n"; } } while
(false)
;
2355
2356 // If we can still promote the PHI nodes after this gauntlet of tests,
2357 // do all of the PHI's now.
2358 Instruction *InsertPt = DomBlock->getTerminator();
37
Called C++ object pointer is null
2359 IRBuilder<NoFolder> Builder(InsertPt);
2360
2361 // Move all 'aggressive' instructions, which are defined in the
2362 // conditional parts of the if's up to the dominating block.
2363 if (IfBlock1) {
2364 for (auto &I : *IfBlock1)
2365 I.dropUnknownNonDebugMetadata();
2366 DomBlock->getInstList().splice(InsertPt->getIterator(),
2367 IfBlock1->getInstList(), IfBlock1->begin(),
2368 IfBlock1->getTerminator()->getIterator());
2369 }
2370 if (IfBlock2) {
2371 for (auto &I : *IfBlock2)
2372 I.dropUnknownNonDebugMetadata();
2373 DomBlock->getInstList().splice(InsertPt->getIterator(),
2374 IfBlock2->getInstList(), IfBlock2->begin(),
2375 IfBlock2->getTerminator()->getIterator());
2376 }
2377
2378 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
2379 // Change the PHI node into a select instruction.
2380 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
2381 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
2382
2383 Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", InsertPt);
2384 PN->replaceAllUsesWith(Sel);
2385 Sel->takeName(PN);
2386 PN->eraseFromParent();
2387 }
2388
2389 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
2390 // has been flattened. Change DomBlock to jump directly to our new block to
2391 // avoid other simplifycfg's kicking in on the diamond.
2392 TerminatorInst *OldTI = DomBlock->getTerminator();
2393 Builder.SetInsertPoint(OldTI);
2394 Builder.CreateBr(BB);
2395 OldTI->eraseFromParent();
2396 return true;
2397}
2398
2399/// If we found a conditional branch that goes to two returning blocks,
2400/// try to merge them together into one return,
2401/// introducing a select if the return values disagree.
2402static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
2403 IRBuilder<> &Builder) {
2404 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2404, __extension__ __PRETTY_FUNCTION__))
;
2405 BasicBlock *TrueSucc = BI->getSuccessor(0);
2406 BasicBlock *FalseSucc = BI->getSuccessor(1);
2407 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
2408 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
2409
2410 // Check to ensure both blocks are empty (just a return) or optionally empty
2411 // with PHI nodes. If there are other instructions, merging would cause extra
2412 // computation on one path or the other.
2413 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
2414 return false;
2415 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
2416 return false;
2417
2418 Builder.SetInsertPoint(BI);
2419 // Okay, we found a branch that is going to two return nodes. If
2420 // there is no return value for this function, just change the
2421 // branch into a return.
2422 if (FalseRet->getNumOperands() == 0) {
2423 TrueSucc->removePredecessor(BI->getParent());
2424 FalseSucc->removePredecessor(BI->getParent());
2425 Builder.CreateRetVoid();
2426 EraseTerminatorInstAndDCECond(BI);
2427 return true;
2428 }
2429
2430 // Otherwise, figure out what the true and false return values are
2431 // so we can insert a new select instruction.
2432 Value *TrueValue = TrueRet->getReturnValue();
2433 Value *FalseValue = FalseRet->getReturnValue();
2434
2435 // Unwrap any PHI nodes in the return blocks.
2436 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
2437 if (TVPN->getParent() == TrueSucc)
2438 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
2439 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
2440 if (FVPN->getParent() == FalseSucc)
2441 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
2442
2443 // In order for this transformation to be safe, we must be able to
2444 // unconditionally execute both operands to the return. This is
2445 // normally the case, but we could have a potentially-trapping
2446 // constant expression that prevents this transformation from being
2447 // safe.
2448 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
2449 if (TCV->canTrap())
2450 return false;
2451 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
2452 if (FCV->canTrap())
2453 return false;
2454
2455 // Okay, we collected all the mapped values and checked them for sanity, and
2456 // defined to really do this transformation. First, update the CFG.
2457 TrueSucc->removePredecessor(BI->getParent());
2458 FalseSucc->removePredecessor(BI->getParent());
2459
2460 // Insert select instructions where needed.
2461 Value *BrCond = BI->getCondition();
2462 if (TrueValue) {
2463 // Insert a select if the results differ.
2464 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
2465 } else if (isa<UndefValue>(TrueValue)) {
2466 TrueValue = FalseValue;
2467 } else {
2468 TrueValue =
2469 Builder.CreateSelect(BrCond, TrueValue, FalseValue, "retval", BI);
2470 }
2471 }
2472
2473 Value *RI =
2474 !TrueValue ? Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
2475
2476 (void)RI;
2477
2478 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)
2479 << "\n " << *BI << "NewRet = " << *RIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "NewRet = " << *
RI << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "
<< *FalseSucc; } } while (false)
2480 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: " << *FalseSucc)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
<< "\n " << *BI << "NewRet = " << *
RI << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "
<< *FalseSucc; } } while (false)
;
2481
2482 EraseTerminatorInstAndDCECond(BI);
2483
2484 return true;
2485}
2486
2487/// Return true if the given instruction is available
2488/// in its predecessor block. If yes, the instruction will be removed.
2489static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
2490 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
2491 return false;
2492 for (Instruction &I : *PB) {
2493 Instruction *PBI = &I;
2494 // Check whether Inst and PBI generate the same value.
2495 if (Inst->isIdenticalTo(PBI)) {
2496 Inst->replaceAllUsesWith(PBI);
2497 Inst->eraseFromParent();
2498 return true;
2499 }
2500 }
2501 return false;
2502}
2503
2504/// Return true if either PBI or BI has branch weight available, and store
2505/// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does
2506/// not have branch weight, use 1:1 as its weight.
2507static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI,
2508 uint64_t &PredTrueWeight,
2509 uint64_t &PredFalseWeight,
2510 uint64_t &SuccTrueWeight,
2511 uint64_t &SuccFalseWeight) {
2512 bool PredHasWeights =
2513 PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
2514 bool SuccHasWeights =
2515 BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
2516 if (PredHasWeights || SuccHasWeights) {
2517 if (!PredHasWeights)
2518 PredTrueWeight = PredFalseWeight = 1;
2519 if (!SuccHasWeights)
2520 SuccTrueWeight = SuccFalseWeight = 1;
2521 return true;
2522 } else {
2523 return false;
2524 }
2525}
2526
2527/// If this basic block is simple enough, and if a predecessor branches to us
2528/// and one of our successors, fold the block into the predecessor and use
2529/// logical operations to pick the right destination.
2530bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
2531 BasicBlock *BB = BI->getParent();
2532
2533 Instruction *Cond = nullptr;
2534 if (BI->isConditional())
2535 Cond = dyn_cast<Instruction>(BI->getCondition());
2536 else {
2537 // For unconditional branch, check for a simple CFG pattern, where
2538 // BB has a single predecessor and BB's successor is also its predecessor's
2539 // successor. If such pattern exists, check for CSE between BB and its
2540 // predecessor.
2541 if (BasicBlock *PB = BB->getSinglePredecessor())
2542 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2543 if (PBI->isConditional() &&
2544 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2545 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2546 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
2547 Instruction *Curr = &*I++;
2548 if (isa<CmpInst>(Curr)) {
2549 Cond = Curr;
2550 break;
2551 }
2552 // Quit if we can't remove this instruction.
2553 if (!checkCSEInPredecessor(Curr, PB))
2554 return false;
2555 }
2556 }
2557
2558 if (!Cond)
2559 return false;
2560 }
2561
2562 if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2563 Cond->getParent() != BB || !Cond->hasOneUse())
2564 return false;
2565
2566 // Make sure the instruction after the condition is the cond branch.
2567 BasicBlock::iterator CondIt = ++Cond->getIterator();
2568
2569 // Ignore dbg intrinsics.
2570 while (isa<DbgInfoIntrinsic>(CondIt))
2571 ++CondIt;
2572
2573 if (&*CondIt != BI)
2574 return false;
2575
2576 // Only allow this transformation if computing the condition doesn't involve
2577 // too many instructions and these involved instructions can be executed
2578 // unconditionally. We denote all involved instructions except the condition
2579 // as "bonus instructions", and only allow this transformation when the
2580 // number of the bonus instructions does not exceed a certain threshold.
2581 unsigned NumBonusInsts = 0;
2582 for (auto I = BB->begin(); Cond != &*I; ++I) {
2583 // Ignore dbg intrinsics.
2584 if (isa<DbgInfoIntrinsic>(I))
2585 continue;
2586 if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I))
2587 return false;
2588 // I has only one use and can be executed unconditionally.
2589 Instruction *User = dyn_cast<Instruction>(I->user_back());
2590 if (User == nullptr || User->getParent() != BB)
2591 return false;
2592 // I is used in the same BB. Since BI uses Cond and doesn't have more slots
2593 // to use any other instruction, User must be an instruction between next(I)
2594 // and Cond.
2595 ++NumBonusInsts;
2596 // Early exits once we reach the limit.
2597 if (NumBonusInsts > BonusInstThreshold)
2598 return false;
2599 }
2600
2601 // Cond is known to be a compare or binary operator. Check to make sure that
2602 // neither operand is a potentially-trapping constant expression.
2603 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2604 if (CE->canTrap())
2605 return false;
2606 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2607 if (CE->canTrap())
2608 return false;
2609
2610 // Finally, don't infinitely unroll conditional loops.
2611 BasicBlock *TrueDest = BI->getSuccessor(0);
2612 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
2613 if (TrueDest == BB || FalseDest == BB)
2614 return false;
2615
2616 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2617 BasicBlock *PredBlock = *PI;
2618 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2619
2620 // Check that we have two conditional branches. If there is a PHI node in
2621 // the common successor, verify that the same value flows in from both
2622 // blocks.
2623 SmallVector<PHINode *, 4> PHIs;
2624 if (!PBI || PBI->isUnconditional() ||
2625 (BI->isConditional() && !SafeToMergeTerminators(BI, PBI)) ||
2626 (!BI->isConditional() &&
2627 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2628 continue;
2629
2630 // Determine if the two branches share a common destination.
2631 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2632 bool InvertPredCond = false;
2633
2634 if (BI->isConditional()) {
2635 if (PBI->getSuccessor(0) == TrueDest) {
2636 Opc = Instruction::Or;
2637 } else if (PBI->getSuccessor(1) == FalseDest) {
2638 Opc = Instruction::And;
2639 } else if (PBI->getSuccessor(0) == FalseDest) {
2640 Opc = Instruction::And;
2641 InvertPredCond = true;
2642 } else if (PBI->getSuccessor(1) == TrueDest) {
2643 Opc = Instruction::Or;
2644 InvertPredCond = true;
2645 } else {
2646 continue;
2647 }
2648 } else {
2649 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2650 continue;
2651 }
2652
2653 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)
;
2654 IRBuilder<> Builder(PBI);
2655
2656 // If we need to invert the condition in the pred block to match, do so now.
2657 if (InvertPredCond) {
2658 Value *NewCond = PBI->getCondition();
2659
2660 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2661 CmpInst *CI = cast<CmpInst>(NewCond);
2662 CI->setPredicate(CI->getInversePredicate());
2663 } else {
2664 NewCond =
2665 Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not");
2666 }
2667
2668 PBI->setCondition(NewCond);
2669 PBI->swapSuccessors();
2670 }
2671
2672 // If we have bonus instructions, clone them into the predecessor block.
2673 // Note that there may be multiple predecessor blocks, so we cannot move
2674 // bonus instructions to a predecessor block.
2675 ValueToValueMapTy VMap; // maps original values to cloned values
2676 // We already make sure Cond is the last instruction before BI. Therefore,
2677 // all instructions before Cond other than DbgInfoIntrinsic are bonus
2678 // instructions.
2679 for (auto BonusInst = BB->begin(); Cond != &*BonusInst; ++BonusInst) {
2680 if (isa<DbgInfoIntrinsic>(BonusInst))
2681 continue;
2682 Instruction *NewBonusInst = BonusInst->clone();
2683 RemapInstruction(NewBonusInst, VMap,
2684 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2685 VMap[&*BonusInst] = NewBonusInst;
2686
2687 // If we moved a load, we cannot any longer claim any knowledge about
2688 // its potential value. The previous information might have been valid
2689 // only given the branch precondition.
2690 // For an analogous reason, we must also drop all the metadata whose
2691 // semantics we don't understand.
2692 NewBonusInst->dropUnknownNonDebugMetadata();
2693
2694 PredBlock->getInstList().insert(PBI->getIterator(), NewBonusInst);
2695 NewBonusInst->takeName(&*BonusInst);
2696 BonusInst->setName(BonusInst->getName() + ".old");
2697 }
2698
2699 // Clone Cond into the predecessor basic block, and or/and the
2700 // two conditions together.
2701 Instruction *New = Cond->clone();
2702 RemapInstruction(New, VMap,
2703 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
2704 PredBlock->getInstList().insert(PBI->getIterator(), New);
2705 New->takeName(Cond);
2706 Cond->setName(New->getName() + ".old");
2707
2708 if (BI->isConditional()) {
2709 Instruction *NewCond = cast<Instruction>(
2710 Builder.CreateBinOp(Opc, PBI->getCondition(), New, "or.cond"));
2711 PBI->setCondition(NewCond);
2712
2713 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2714 bool HasWeights =
2715 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
2716 SuccTrueWeight, SuccFalseWeight);
2717 SmallVector<uint64_t, 8> NewWeights;
2718
2719 if (PBI->getSuccessor(0) == BB) {
2720 if (HasWeights) {
2721 // PBI: br i1 %x, BB, FalseDest
2722 // BI: br i1 %y, TrueDest, FalseDest
2723 // TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2724 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2725 // FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2726 // TrueWeight for PBI * FalseWeight for BI.
2727 // We assume that total weights of a BranchInst can fit into 32 bits.
2728 // Therefore, we will not have overflow using 64-bit arithmetic.
2729 NewWeights.push_back(PredFalseWeight *
2730 (SuccFalseWeight + SuccTrueWeight) +
2731 PredTrueWeight * SuccFalseWeight);
2732 }
2733 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2734 PBI->setSuccessor(0, TrueDest);
2735 }
2736 if (PBI->getSuccessor(1) == BB) {
2737 if (HasWeights) {
2738 // PBI: br i1 %x, TrueDest, BB
2739 // BI: br i1 %y, TrueDest, FalseDest
2740 // TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2741 // FalseWeight for PBI * TrueWeight for BI.
2742 NewWeights.push_back(PredTrueWeight *
2743 (SuccFalseWeight + SuccTrueWeight) +
2744 PredFalseWeight * SuccTrueWeight);
2745 // FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2746 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2747 }
2748 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2749 PBI->setSuccessor(1, FalseDest);
2750 }
2751 if (NewWeights.size() == 2) {
2752 // Halve the weights if any of them cannot fit in an uint32_t
2753 FitWeights(NewWeights);
2754
2755 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),
2756 NewWeights.end());
2757 setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
2758 } else
2759 PBI->setMetadata(LLVMContext::MD_prof, nullptr);
2760 } else {
2761 // Update PHI nodes in the common successors.
2762 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2763 ConstantInt *PBI_C = cast<ConstantInt>(
2764 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2765 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2765, __extension__ __PRETTY_FUNCTION__))
;
2766 Instruction *MergedCond = nullptr;
2767 if (PBI->getSuccessor(0) == TrueDest) {
2768 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2769 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2770 // is false: !PBI_Cond and BI_Value
2771 Instruction *NotCond = cast<Instruction>(
2772 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2773 MergedCond = cast<Instruction>(
2774 Builder.CreateBinOp(Instruction::And, NotCond, New, "and.cond"));
2775 if (PBI_C->isOne())
2776 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2777 Instruction::Or, PBI->getCondition(), MergedCond, "or.cond"));
2778 } else {
2779 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2780 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2781 // is false: PBI_Cond and BI_Value
2782 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2783 Instruction::And, PBI->getCondition(), New, "and.cond"));
2784 if (PBI_C->isOne()) {
2785 Instruction *NotCond = cast<Instruction>(
2786 Builder.CreateNot(PBI->getCondition(), "not.cond"));
2787 MergedCond = cast<Instruction>(Builder.CreateBinOp(
2788 Instruction::Or, NotCond, MergedCond, "or.cond"));
2789 }
2790 }
2791 // Update PHI Node.
2792 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2793 MergedCond);
2794 }
2795 // Change PBI from Conditional to Unconditional.
2796 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2797 EraseTerminatorInstAndDCECond(PBI);
2798 PBI = New_PBI;
2799 }
2800
2801 // If BI was a loop latch, it may have had associated loop metadata.
2802 // We need to copy it to the new latch, that is, PBI.
2803 if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
2804 PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
2805
2806 // TODO: If BB is reachable from all paths through PredBlock, then we
2807 // could replace PBI's branch probabilities with BI's.
2808
2809 // Copy any debug value intrinsics into the end of PredBlock.
2810 for (Instruction &I : *BB)
2811 if (isa<DbgInfoIntrinsic>(I))
2812 I.clone()->insertBefore(PBI);
2813
2814 return true;
2815 }
2816 return false;
2817}
2818
2819// If there is only one store in BB1 and BB2, return it, otherwise return
2820// nullptr.
2821static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
2822 StoreInst *S = nullptr;
2823 for (auto *BB : {BB1, BB2}) {
2824 if (!BB)
2825 continue;
2826 for (auto &I : *BB)
2827 if (auto *SI = dyn_cast<StoreInst>(&I)) {
2828 if (S)
2829 // Multiple stores seen.
2830 return nullptr;
2831 else
2832 S = SI;
2833 }
2834 }
2835 return S;
2836}
2837
2838static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
2839 Value *AlternativeV = nullptr) {
2840 // PHI is going to be a PHI node that allows the value V that is defined in
2841 // BB to be referenced in BB's only successor.
2842 //
2843 // If AlternativeV is nullptr, the only value we care about in PHI is V. It
2844 // doesn't matter to us what the other operand is (it'll never get used). We
2845 // could just create a new PHI with an undef incoming value, but that could
2846 // increase register pressure if EarlyCSE/InstCombine can't fold it with some
2847 // other PHI. So here we directly look for some PHI in BB's successor with V
2848 // as an incoming operand. If we find one, we use it, else we create a new
2849 // one.
2850 //
2851 // If AlternativeV is not nullptr, we care about both incoming values in PHI.
2852 // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
2853 // where OtherBB is the single other predecessor of BB's only successor.
2854 PHINode *PHI = nullptr;
2855 BasicBlock *Succ = BB->getSingleSuccessor();
2856
2857 for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
2858 if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
2859 PHI = cast<PHINode>(I);
2860 if (!AlternativeV)
2861 break;
2862
2863 assert(std::distance(pred_begin(Succ), pred_end(Succ)) == 2)(static_cast <bool> (std::distance(pred_begin(Succ), pred_end
(Succ)) == 2) ? void (0) : __assert_fail ("std::distance(pred_begin(Succ), pred_end(Succ)) == 2"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 2863, __extension__ __PRETTY_FUNCTION__))
;
2864 auto PredI = pred_begin(Succ);
2865 BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
2866 if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
2867 break;
2868 PHI = nullptr;
2869 }
2870 if (PHI)
2871 return PHI;
2872
2873 // If V is not an instruction defined in BB, just return it.
2874 if (!AlternativeV &&
2875 (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
2876 return V;
2877
2878 PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
2879 PHI->addIncoming(V, BB);
2880 for (BasicBlock *PredBB : predecessors(Succ))
2881 if (PredBB != BB)
2882 PHI->addIncoming(
2883 AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB);
2884 return PHI;
2885}
2886
2887static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
2888 BasicBlock *QTB, BasicBlock *QFB,
2889 BasicBlock *PostBB, Value *Address,
2890 bool InvertPCond, bool InvertQCond,
2891 const DataLayout &DL) {
2892 auto IsaBitcastOfPointerType = [](const Instruction &I) {
2893 return Operator::getOpcode(&I) == Instruction::BitCast &&
2894 I.getType()->isPointerTy();
2895 };
2896
2897 // If we're not in aggressive mode, we only optimize if we have some
2898 // confidence that by optimizing we'll allow P and/or Q to be if-converted.
2899 auto IsWorthwhile = [&](BasicBlock *BB) {
2900 if (!BB)
2901 return true;
2902 // Heuristic: if the block can be if-converted/phi-folded and the
2903 // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
2904 // thread this store.
2905 unsigned N = 0;
2906 for (auto &I : *BB) {
2907 // Cheap instructions viable for folding.
2908 if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
2909 isa<StoreInst>(I))
2910 ++N;
2911 // Free instructions.
2912 else if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
2913 IsaBitcastOfPointerType(I))
2914 continue;
2915 else
2916 return false;
2917 }
2918 // The store we want to merge is counted in N, so add 1 to make sure
2919 // we're counting the instructions that would be left.
2920 return N <= (PHINodeFoldingThreshold + 1);
2921 };
2922
2923 if (!MergeCondStoresAggressively &&
2924 (!IsWorthwhile(PTB) || !IsWorthwhile(PFB) || !IsWorthwhile(QTB) ||
2925 !IsWorthwhile(QFB)))
2926 return false;
2927
2928 // For every pointer, there must be exactly two stores, one coming from
2929 // PTB or PFB, and the other from QTB or QFB. We don't support more than one
2930 // store (to any address) in PTB,PFB or QTB,QFB.
2931 // FIXME: We could relax this restriction with a bit more work and performance
2932 // testing.
2933 StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
2934 StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
2935 if (!PStore || !QStore)
2936 return false;
2937
2938 // Now check the stores are compatible.
2939 if (!QStore->isUnordered() || !PStore->isUnordered())
2940 return false;
2941
2942 // Check that sinking the store won't cause program behavior changes. Sinking
2943 // the store out of the Q blocks won't change any behavior as we're sinking
2944 // from a block to its unconditional successor. But we're moving a store from
2945 // the P blocks down through the middle block (QBI) and past both QFB and QTB.
2946 // So we need to check that there are no aliasing loads or stores in
2947 // QBI, QTB and QFB. We also need to check there are no conflicting memory
2948 // operations between PStore and the end of its parent block.
2949 //
2950 // The ideal way to do this is to query AliasAnalysis, but we don't
2951 // preserve AA currently so that is dangerous. Be super safe and just
2952 // check there are no other memory operations at all.
2953 for (auto &I : *QFB->getSinglePredecessor())
2954 if (I.mayReadOrWriteMemory())
2955 return false;
2956 for (auto &I : *QFB)
2957 if (&I != QStore && I.mayReadOrWriteMemory())
2958 return false;
2959 if (QTB)
2960 for (auto &I : *QTB)
2961 if (&I != QStore && I.mayReadOrWriteMemory())
2962 return false;
2963 for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
2964 I != E; ++I)
2965 if (&*I != PStore && I->mayReadOrWriteMemory())
2966 return false;
2967
2968 // OK, we're going to sink the stores to PostBB. The store has to be
2969 // conditional though, so first create the predicate.
2970 Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
2971 ->getCondition();
2972 Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
2973 ->getCondition();
2974
2975 Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
2976 PStore->getParent());
2977 Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
2978 QStore->getParent(), PPHI);
2979
2980 IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
2981
2982 Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
2983 Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
2984
2985 if (InvertPCond)
2986 PPred = QB.CreateNot(PPred);
2987 if (InvertQCond)
2988 QPred = QB.CreateNot(QPred);
2989 Value *CombinedPred = QB.CreateOr(PPred, QPred);
2990
2991 auto *T =
2992 SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(), false);
2993 QB.SetInsertPoint(T);
2994 StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
2995 AAMDNodes AAMD;
2996 PStore->getAAMetadata(AAMD, /*Merge=*/false);
2997 PStore->getAAMetadata(AAMD, /*Merge=*/true);
2998 SI->setAAMetadata(AAMD);
2999 unsigned PAlignment = PStore->getAlignment();
3000 unsigned QAlignment = QStore->getAlignment();
3001 unsigned TypeAlignment =
3002 DL.getABITypeAlignment(SI->getValueOperand()->getType());
3003 unsigned MinAlignment;
3004 unsigned MaxAlignment;
3005 std::tie(MinAlignment, MaxAlignment) = std::minmax(PAlignment, QAlignment);
3006 // Choose the minimum alignment. If we could prove both stores execute, we
3007 // could use biggest one. In this case, though, we only know that one of the
3008 // stores executes. And we don't know it's safe to take the alignment from a
3009 // store that doesn't execute.
3010 if (MinAlignment != 0) {
3011 // Choose the minimum of all non-zero alignments.
3012 SI->setAlignment(MinAlignment);
3013 } else if (MaxAlignment != 0) {
3014 // Choose the minimal alignment between the non-zero alignment and the ABI
3015 // default alignment for the type of the stored value.
3016 SI->setAlignment(std::min(MaxAlignment, TypeAlignment));
3017 } else {
3018 // If both alignments are zero, use ABI default alignment for the type of
3019 // the stored value.
3020 SI->setAlignment(TypeAlignment);
3021 }
3022
3023 QStore->eraseFromParent();
3024 PStore->eraseFromParent();
3025
3026 return true;
3027}
3028
3029static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
3030 const DataLayout &DL) {
3031 // The intention here is to find diamonds or triangles (see below) where each
3032 // conditional block contains a store to the same address. Both of these
3033 // stores are conditional, so they can't be unconditionally sunk. But it may
3034 // be profitable to speculatively sink the stores into one merged store at the
3035 // end, and predicate the merged store on the union of the two conditions of
3036 // PBI and QBI.
3037 //
3038 // This can reduce the number of stores executed if both of the conditions are
3039 // true, and can allow the blocks to become small enough to be if-converted.
3040 // This optimization will also chain, so that ladders of test-and-set
3041 // sequences can be if-converted away.
3042 //
3043 // We only deal with simple diamonds or triangles:
3044 //
3045 // PBI or PBI or a combination of the two
3046 // / \ | \
3047 // PTB PFB | PFB
3048 // \ / | /
3049 // QBI QBI
3050 // / \ | \
3051 // QTB QFB | QFB
3052 // \ / | /
3053 // PostBB PostBB
3054 //
3055 // We model triangles as a type of diamond with a nullptr "true" block.
3056 // Triangles are canonicalized so that the fallthrough edge is represented by
3057 // a true condition, as in the diagram above.
3058 BasicBlock *PTB = PBI->getSuccessor(0);
3059 BasicBlock *PFB = PBI->getSuccessor(1);
3060 BasicBlock *QTB = QBI->getSuccessor(0);
3061 BasicBlock *QFB = QBI->getSuccessor(1);
3062 BasicBlock *PostBB = QFB->getSingleSuccessor();
3063
3064 // Make sure we have a good guess for PostBB. If QTB's only successor is
3065 // QFB, then QFB is a better PostBB.
3066 if (QTB->getSingleSuccessor() == QFB)
3067 PostBB = QFB;
3068
3069 // If we couldn't find a good PostBB, stop.
3070 if (!PostBB)
3071 return false;
3072
3073 bool InvertPCond = false, InvertQCond = false;
3074 // Canonicalize fallthroughs to the true branches.
3075 if (PFB == QBI->getParent()) {
3076 std::swap(PFB, PTB);
3077 InvertPCond = true;
3078 }
3079 if (QFB == PostBB) {
3080 std::swap(QFB, QTB);
3081 InvertQCond = true;
3082 }
3083
3084 // From this point on we can assume PTB or QTB may be fallthroughs but PFB
3085 // and QFB may not. Model fallthroughs as a nullptr block.
3086 if (PTB == QBI->getParent())
3087 PTB = nullptr;
3088 if (QTB == PostBB)
3089 QTB = nullptr;
3090
3091 // Legality bailouts. We must have at least the non-fallthrough blocks and
3092 // the post-dominating block, and the non-fallthroughs must only have one
3093 // predecessor.
3094 auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
3095 return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
3096 };
3097 if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
3098 !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
3099 return false;
3100 if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
3101 (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
3102 return false;
3103 if (!PostBB->hasNUses(2) || !QBI->getParent()->hasNUses(2))
3104 return false;
3105
3106 // OK, this is a sequence of two diamonds or triangles.
3107 // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
3108 SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses;
3109 for (auto *BB : {PTB, PFB}) {
3110 if (!BB)
3111 continue;
3112 for (auto &I : *BB)
3113 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3114 PStoreAddresses.insert(SI->getPointerOperand());
3115 }
3116 for (auto *BB : {QTB, QFB}) {
3117 if (!BB)
3118 continue;
3119 for (auto &I : *BB)
3120 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3121 QStoreAddresses.insert(SI->getPointerOperand());
3122 }
3123
3124 set_intersect(PStoreAddresses, QStoreAddresses);
3125 // set_intersect mutates PStoreAddresses in place. Rename it here to make it
3126 // clear what it contains.
3127 auto &CommonAddresses = PStoreAddresses;
3128
3129 bool Changed = false;
3130 for (auto *Address : CommonAddresses)
3131 Changed |= mergeConditionalStoreToAddress(
3132 PTB, PFB, QTB, QFB, PostBB, Address, InvertPCond, InvertQCond, DL);
3133 return Changed;
3134}
3135
3136/// If we have a conditional branch as a predecessor of another block,
3137/// this function tries to simplify it. We know
3138/// that PBI and BI are both conditional branches, and BI is in one of the
3139/// successor blocks of PBI - PBI branches to BI.
3140static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
3141 const DataLayout &DL) {
3142 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3142, __extension__ __PRETTY_FUNCTION__))
;
3143 BasicBlock *BB = BI->getParent();
3144
3145 // If this block ends with a branch instruction, and if there is a
3146 // predecessor that ends on a branch of the same condition, make
3147 // this conditional branch redundant.
3148 if (PBI->getCondition() == BI->getCondition() &&
3149 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3150 // Okay, the outcome of this conditional branch is statically
3151 // knowable. If this block had a single pred, handle specially.
3152 if (BB->getSinglePredecessor()) {
3153 // Turn this into a branch on constant.
3154 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3155 BI->setCondition(
3156 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue));
3157 return true; // Nuke the branch on constant.
3158 }
3159
3160 // Otherwise, if there are multiple predecessors, insert a PHI that merges
3161 // in the constant and simplify the block result. Subsequent passes of
3162 // simplifycfg will thread the block.
3163 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
3164 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
3165 PHINode *NewPN = PHINode::Create(
3166 Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
3167 BI->getCondition()->getName() + ".pr", &BB->front());
3168 // Okay, we're going to insert the PHI node. Since PBI is not the only
3169 // predecessor, compute the PHI'd conditional value for all of the preds.
3170 // Any predecessor where the condition is not computable we keep symbolic.
3171 for (pred_iterator PI = PB; PI != PE; ++PI) {
3172 BasicBlock *P = *PI;
3173 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI &&
3174 PBI->isConditional() && PBI->getCondition() == BI->getCondition() &&
3175 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3176 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3177 NewPN->addIncoming(
3178 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue),
3179 P);
3180 } else {
3181 NewPN->addIncoming(BI->getCondition(), P);
3182 }
3183 }
3184
3185 BI->setCondition(NewPN);
3186 return true;
3187 }
3188 }
3189
3190 if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
3191 if (CE->canTrap())
3192 return false;
3193
3194 // If both branches are conditional and both contain stores to the same
3195 // address, remove the stores from the conditionals and create a conditional
3196 // merged store at the end.
3197 if (MergeCondStores && mergeConditionalStores(PBI, BI, DL))
3198 return true;
3199
3200 // If this is a conditional branch in an empty block, and if any
3201 // predecessors are a conditional branch to one of our destinations,
3202 // fold the conditions into logical ops and one cond br.
3203 BasicBlock::iterator BBI = BB->begin();
3204 // Ignore dbg intrinsics.
3205 while (isa<DbgInfoIntrinsic>(BBI))
3206 ++BBI;
3207 if (&*BBI != BI)
3208 return false;
3209
3210 int PBIOp, BIOp;
3211 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
3212 PBIOp = 0;
3213 BIOp = 0;
3214 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
3215 PBIOp = 0;
3216 BIOp = 1;
3217 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
3218 PBIOp = 1;
3219 BIOp = 0;
3220 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
3221 PBIOp = 1;
3222 BIOp = 1;
3223 } else {
3224 return false;
3225 }
3226
3227 // Check to make sure that the other destination of this branch
3228 // isn't BB itself. If so, this is an infinite loop that will
3229 // keep getting unwound.
3230 if (PBI->getSuccessor(PBIOp) == BB)
3231 return false;
3232
3233 // Do not perform this transformation if it would require
3234 // insertion of a large number of select instructions. For targets
3235 // without predication/cmovs, this is a big pessimization.
3236
3237 // Also do not perform this transformation if any phi node in the common
3238 // destination block can trap when reached by BB or PBB (PR17073). In that
3239 // case, it would be unsafe to hoist the operation into a select instruction.
3240
3241 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
3242 unsigned NumPhis = 0;
3243 for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II);
3244 ++II, ++NumPhis) {
3245 if (NumPhis > 2) // Disable this xform.
3246 return false;
3247
3248 PHINode *PN = cast<PHINode>(II);
3249 Value *BIV = PN->getIncomingValueForBlock(BB);
3250 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
3251 if (CE->canTrap())
3252 return false;
3253
3254 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
3255 Value *PBIV = PN->getIncomingValue(PBBIdx);
3256 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
3257 if (CE->canTrap())
3258 return false;
3259 }
3260
3261 // Finally, if everything is ok, fold the branches to logical ops.
3262 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
3263
3264 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
3265 << "AND: " << *BI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING BRs:" << *PBI
->getParent() << "AND: " << *BI->getParent(
); } } while (false)
;
3266
3267 // If OtherDest *is* BB, then BB is a basic block with a single conditional
3268 // branch in it, where one edge (OtherDest) goes back to itself but the other
3269 // exits. We don't *know* that the program avoids the infinite loop
3270 // (even though that seems likely). If we do this xform naively, we'll end up
3271 // recursively unpeeling the loop. Since we know that (after the xform is
3272 // done) that the block *is* infinite if reached, we just make it an obviously
3273 // infinite loop with no cond branch.
3274 if (OtherDest == BB) {
3275 // Insert it at the end of the function, because it's either code,
3276 // or it won't matter if it's hot. :)
3277 BasicBlock *InfLoopBlock =
3278 BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
3279 BranchInst::Create(InfLoopBlock, InfLoopBlock);
3280 OtherDest = InfLoopBlock;
3281 }
3282
3283 DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3284
3285 // BI may have other predecessors. Because of this, we leave
3286 // it alone, but modify PBI.
3287
3288 // Make sure we get to CommonDest on True&True directions.
3289 Value *PBICond = PBI->getCondition();
3290 IRBuilder<NoFolder> Builder(PBI);
3291 if (PBIOp)
3292 PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not");
3293
3294 Value *BICond = BI->getCondition();
3295 if (BIOp)
3296 BICond = Builder.CreateNot(BICond, BICond->getName() + ".not");
3297
3298 // Merge the conditions.
3299 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
3300
3301 // Modify PBI to branch on the new condition to the new dests.
3302 PBI->setCondition(Cond);
3303 PBI->setSuccessor(0, CommonDest);
3304 PBI->setSuccessor(1, OtherDest);
3305
3306 // Update branch weight for PBI.
3307 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
3308 uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
3309 bool HasWeights =
3310 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
3311 SuccTrueWeight, SuccFalseWeight);
3312 if (HasWeights) {
3313 PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3314 PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3315 SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3316 SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3317 // The weight to CommonDest should be PredCommon * SuccTotal +
3318 // PredOther * SuccCommon.
3319 // The weight to OtherDest should be PredOther * SuccOther.
3320 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
3321 PredOther * SuccCommon,
3322 PredOther * SuccOther};
3323 // Halve the weights if any of them cannot fit in an uint32_t
3324 FitWeights(NewWeights);
3325
3326 setBranchWeights(PBI, NewWeights[0], NewWeights[1]);
3327 }
3328
3329 // OtherDest may have phi nodes. If so, add an entry from PBI's
3330 // block that are identical to the entries for BI's block.
3331 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
3332
3333 // We know that the CommonDest already had an edge from PBI to
3334 // it. If it has PHIs though, the PHIs may have different
3335 // entries for BB and PBI's BB. If so, insert a select to make
3336 // them agree.
3337 for (PHINode &PN : CommonDest->phis()) {
3338 Value *BIV = PN.getIncomingValueForBlock(BB);
3339 unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent());
3340 Value *PBIV = PN.getIncomingValue(PBBIdx);
3341 if (BIV != PBIV) {
3342 // Insert a select in PBI to pick the right value.
3343 SelectInst *NV = cast<SelectInst>(
3344 Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
3345 PN.setIncomingValue(PBBIdx, NV);
3346 // Although the select has the same condition as PBI, the original branch
3347 // weights for PBI do not apply to the new select because the select's
3348 // 'logical' edges are incoming edges of the phi that is eliminated, not
3349 // the outgoing edges of PBI.
3350 if (HasWeights) {
3351 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3352 uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3353 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3354 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3355 // The weight to PredCommonDest should be PredCommon * SuccTotal.
3356 // The weight to PredOtherDest should be PredOther * SuccCommon.
3357 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
3358 PredOther * SuccCommon};
3359
3360 FitWeights(NewWeights);
3361
3362 setBranchWeights(NV, NewWeights[0], NewWeights[1]);
3363 }
3364 }
3365 }
3366
3367 DEBUG(dbgs() << "INTO: " << *PBI->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "INTO: " << *PBI->
getParent(); } } while (false)
;
3368 DEBUG(dbgs() << *PBI->getParent()->getParent())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << *PBI->getParent()->getParent
(); } } while (false)
;
3369
3370 // This basic block is probably dead. We know it has at least
3371 // one fewer predecessor.
3372 return true;
3373}
3374
3375// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
3376// true or to FalseBB if Cond is false.
3377// Takes care of updating the successors and removing the old terminator.
3378// Also makes sure not to introduce new successors by assuming that edges to
3379// non-successor TrueBBs and FalseBBs aren't reachable.
3380static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
3381 BasicBlock *TrueBB, BasicBlock *FalseBB,
3382 uint32_t TrueWeight,
3383 uint32_t FalseWeight) {
3384 // Remove any superfluous successor edges from the CFG.
3385 // First, figure out which successors to preserve.
3386 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
3387 // successor.
3388 BasicBlock *KeepEdge1 = TrueBB;
3389 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
3390
3391 // Then remove the rest.
3392 for (BasicBlock *Succ : OldTerm->successors()) {
3393 // Make sure only to keep exactly one copy of each edge.
3394 if (Succ == KeepEdge1)
3395 KeepEdge1 = nullptr;
3396 else if (Succ == KeepEdge2)
3397 KeepEdge2 = nullptr;
3398 else
3399 Succ->removePredecessor(OldTerm->getParent(),
3400 /*DontDeleteUselessPHIs=*/true);
3401 }
3402
3403 IRBuilder<> Builder(OldTerm);
3404 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
3405
3406 // Insert an appropriate new terminator.
3407 if (!KeepEdge1 && !KeepEdge2) {
3408 if (TrueBB == FalseBB)
3409 // We were only looking for one successor, and it was present.
3410 // Create an unconditional branch to it.
3411 Builder.CreateBr(TrueBB);
3412 else {
3413 // We found both of the successors we were looking for.
3414 // Create a conditional branch sharing the condition of the select.
3415 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
3416 if (TrueWeight != FalseWeight)
3417 setBranchWeights(NewBI, TrueWeight, FalseWeight);
3418 }
3419 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
3420 // Neither of the selected blocks were successors, so this
3421 // terminator must be unreachable.
3422 new UnreachableInst(OldTerm->getContext(), OldTerm);
3423 } else {
3424 // One of the selected values was a successor, but the other wasn't.
3425 // Insert an unconditional branch to the one that was found;
3426 // the edge to the one that wasn't must be unreachable.
3427 if (!KeepEdge1)
3428 // Only TrueBB was found.
3429 Builder.CreateBr(TrueBB);
3430 else
3431 // Only FalseBB was found.
3432 Builder.CreateBr(FalseBB);
3433 }
3434
3435 EraseTerminatorInstAndDCECond(OldTerm);
3436 return true;
3437}
3438
3439// Replaces
3440// (switch (select cond, X, Y)) on constant X, Y
3441// with a branch - conditional if X and Y lead to distinct BBs,
3442// unconditional otherwise.
3443static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
3444 // Check for constant integer values in the select.
3445 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
3446 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
3447 if (!TrueVal || !FalseVal)
3448 return false;
3449
3450 // Find the relevant condition and destinations.
3451 Value *Condition = Select->getCondition();
3452 BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor();
3453 BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor();
3454
3455 // Get weight for TrueBB and FalseBB.
3456 uint32_t TrueWeight = 0, FalseWeight = 0;
3457 SmallVector<uint64_t, 8> Weights;
3458 bool HasWeights = HasBranchWeights(SI);
3459 if (HasWeights) {
3460 GetBranchWeights(SI, Weights);
3461 if (Weights.size() == 1 + SI->getNumCases()) {
3462 TrueWeight =
3463 (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()];
3464 FalseWeight =
3465 (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()];
3466 }
3467 }
3468
3469 // Perform the actual simplification.
3470 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
3471 FalseWeight);
3472}
3473
3474// Replaces
3475// (indirectbr (select cond, blockaddress(@fn, BlockA),
3476// blockaddress(@fn, BlockB)))
3477// with
3478// (br cond, BlockA, BlockB).
3479static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
3480 // Check that both operands of the select are block addresses.
3481 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
3482 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
3483 if (!TBA || !FBA)
3484 return false;
3485
3486 // Extract the actual blocks.
3487 BasicBlock *TrueBB = TBA->getBasicBlock();
3488 BasicBlock *FalseBB = FBA->getBasicBlock();
3489
3490 // Perform the actual simplification.
3491 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0,
3492 0);
3493}
3494
3495/// This is called when we find an icmp instruction
3496/// (a seteq/setne with a constant) as the only instruction in a
3497/// block that ends with an uncond branch. We are looking for a very specific
3498/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
3499/// this case, we merge the first two "or's of icmp" into a switch, but then the
3500/// default value goes to an uncond block with a seteq in it, we get something
3501/// like:
3502///
3503/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
3504/// DEFAULT:
3505/// %tmp = icmp eq i8 %A, 92
3506/// br label %end
3507/// end:
3508/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
3509///
3510/// We prefer to split the edge to 'end' so that there is a true/false entry to
3511/// the PHI, merging the third icmp into the switch.
3512static bool tryToSimplifyUncondBranchWithICmpInIt(
3513 ICmpInst *ICI, IRBuilder<> &Builder, const DataLayout &DL,
3514 const TargetTransformInfo &TTI, const SimplifyCFGOptions &Options) {
3515 BasicBlock *BB = ICI->getParent();
3516
3517 // If the block has any PHIs in it or the icmp has multiple uses, it is too
3518 // complex.
3519 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse())
1
Assuming the condition is false
2
Taking false branch
3520 return false;
3521
3522 Value *V = ICI->getOperand(0);
3523 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
3524
3525 // The pattern we're looking for is where our only predecessor is a switch on
3526 // 'V' and this block is the default case for the switch. In this case we can
3527 // fold the compared value into the switch to simplify things.
3528 BasicBlock *Pred = BB->getSinglePredecessor();
3529 if (!Pred || !isa<SwitchInst>(Pred->getTerminator()))
3
Assuming 'Pred' is non-null
4
Taking false branch
3530 return false;
3531
3532 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
3533 if (SI->getCondition() != V)
5
Assuming the condition is false
6
Taking false branch
3534 return false;
3535
3536 // If BB is reachable on a non-default case, then we simply know the value of
3537 // V in this block. Substitute it and constant fold the icmp instruction
3538 // away.
3539 if (SI->getDefaultDest() != BB) {
7
Assuming the condition is false
8
Taking false branch
3540 ConstantInt *VVal = SI->findCaseDest(BB);
3541 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3541, __extension__ __PRETTY_FUNCTION__))
;
3542 ICI->setOperand(0, VVal);
3543
3544 if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) {
3545 ICI->replaceAllUsesWith(V);
3546 ICI->eraseFromParent();
3547 }
3548 // BB is now empty, so it is likely to simplify away.
3549 return simplifyCFG(BB, TTI, Options) | true;
3550 }
3551
3552 // Ok, the block is reachable from the default dest. If the constant we're
3553 // comparing exists in one of the other edges, then we can constant fold ICI
3554 // and zap it.
3555 if (SI->findCaseValue(Cst) != SI->case_default()) {
9
Assuming the condition is true
10
Taking true branch
3556 Value *V;
3557 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
11
Assuming the condition is false
12
Taking false branch
3558 V = ConstantInt::getFalse(BB->getContext());
3559 else
3560 V = ConstantInt::getTrue(BB->getContext());
3561
3562 ICI->replaceAllUsesWith(V);
3563 ICI->eraseFromParent();
3564 // BB is now empty, so it is likely to simplify away.
3565 return simplifyCFG(BB, TTI, Options) | true;
13
Calling 'simplifyCFG'
3566 }
3567
3568 // The use of the icmp has to be in the 'end' block, by the only PHI node in
3569 // the block.
3570 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
3571 PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
3572 if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
3573 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
3574 return false;
3575
3576 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
3577 // true in the PHI.
3578 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
3579 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
3580
3581 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3582 std::swap(DefaultCst, NewCst);
3583
3584 // Replace ICI (which is used by the PHI for the default value) with true or
3585 // false depending on if it is EQ or NE.
3586 ICI->replaceAllUsesWith(DefaultCst);
3587 ICI->eraseFromParent();
3588
3589 // Okay, the switch goes to this block on a default value. Add an edge from
3590 // the switch to the merge point on the compared value.
3591 BasicBlock *NewBB =
3592 BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB);
3593 SmallVector<uint64_t, 8> Weights;
3594 bool HasWeights = HasBranchWeights(SI);
3595 if (HasWeights) {
3596 GetBranchWeights(SI, Weights);
3597 if (Weights.size() == 1 + SI->getNumCases()) {
3598 // Split weight for default case to case for "Cst".
3599 Weights[0] = (Weights[0] + 1) >> 1;
3600 Weights.push_back(Weights[0]);
3601
3602 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3603 setBranchWeights(SI, MDWeights);
3604 }
3605 }
3606 SI->addCase(Cst, NewBB);
3607
3608 // NewBB branches to the phi block, add the uncond branch and the phi entry.
3609 Builder.SetInsertPoint(NewBB);
3610 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
3611 Builder.CreateBr(SuccBlock);
3612 PHIUse->addIncoming(NewCst, NewBB);
3613 return true;
3614}
3615
3616/// The specified branch is a conditional branch.
3617/// Check to see if it is branching on an or/and chain of icmp instructions, and
3618/// fold it into a switch instruction if so.
3619static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
3620 const DataLayout &DL) {
3621 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
3622 if (!Cond)
3623 return false;
3624
3625 // Change br (X == 0 | X == 1), T, F into a switch instruction.
3626 // If this is a bunch of seteq's or'd together, or if it's a bunch of
3627 // 'setne's and'ed together, collect them.
3628
3629 // Try to gather values from a chain of and/or to be turned into a switch
3630 ConstantComparesGatherer ConstantCompare(Cond, DL);
3631 // Unpack the result
3632 SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals;
3633 Value *CompVal = ConstantCompare.CompValue;
3634 unsigned UsedICmps = ConstantCompare.UsedICmps;
3635 Value *ExtraCase = ConstantCompare.Extra;
3636
3637 // If we didn't have a multiply compared value, fail.
3638 if (!CompVal)
3639 return false;
3640
3641 // Avoid turning single icmps into a switch.
3642 if (UsedICmps <= 1)
3643 return false;
3644
3645 bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
3646
3647 // There might be duplicate constants in the list, which the switch
3648 // instruction can't handle, remove them now.
3649 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
3650 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
3651
3652 // If Extra was used, we require at least two switch values to do the
3653 // transformation. A switch with one value is just a conditional branch.
3654 if (ExtraCase && Values.size() < 2)
3655 return false;
3656
3657 // TODO: Preserve branch weight metadata, similarly to how
3658 // FoldValueComparisonIntoPredecessors preserves it.
3659
3660 // Figure out which block is which destination.
3661 BasicBlock *DefaultBB = BI->getSuccessor(1);
3662 BasicBlock *EdgeBB = BI->getSuccessor(0);
3663 if (!TrueWhenEqual)
3664 std::swap(DefaultBB, EdgeBB);
3665
3666 BasicBlock *BB = BI->getParent();
3667
3668 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)
3669 << " 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)
3670 << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "Converting 'icmp' chain with "
<< Values.size() << " cases into SWITCH. BB is:\n"
<< *BB; } } while (false)
;
3671
3672 // If there are any extra values that couldn't be folded into the switch
3673 // then we evaluate them with an explicit branch first. Split the block
3674 // right before the condbr to handle it.
3675 if (ExtraCase) {
3676 BasicBlock *NewBB =
3677 BB->splitBasicBlock(BI->getIterator(), "switch.early.test");
3678 // Remove the uncond branch added to the old block.
3679 TerminatorInst *OldTI = BB->getTerminator();
3680 Builder.SetInsertPoint(OldTI);
3681
3682 if (TrueWhenEqual)
3683 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
3684 else
3685 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
3686
3687 OldTI->eraseFromParent();
3688
3689 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
3690 // for the edge we just added.
3691 AddPredecessorToBlock(EdgeBB, BB, NewBB);
3692
3693 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCasedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
3694 << "\nEXTRABB = " << *BB)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << " ** 'icmp' chain unhandled condition: "
<< *ExtraCase << "\nEXTRABB = " << *BB; } }
while (false)
;
3695 BB = NewBB;
3696 }
3697
3698 Builder.SetInsertPoint(BI);
3699 // Convert pointer to int before we switch.
3700 if (CompVal->getType()->isPointerTy()) {
3701 CompVal = Builder.CreatePtrToInt(
3702 CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
3703 }
3704
3705 // Create the new switch instruction now.
3706 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
3707
3708 // Add all of the 'cases' to the switch instruction.
3709 for (unsigned i = 0, e = Values.size(); i != e; ++i)
3710 New->addCase(Values[i], EdgeBB);
3711
3712 // We added edges from PI to the EdgeBB. As such, if there were any
3713 // PHI nodes in EdgeBB, they need entries to be added corresponding to
3714 // the number of edges added.
3715 for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
3716 PHINode *PN = cast<PHINode>(BBI);
3717 Value *InVal = PN->getIncomingValueForBlock(BB);
3718 for (unsigned i = 0, e = Values.size() - 1; i != e; ++i)
3719 PN->addIncoming(InVal, BB);
3720 }
3721
3722 // Erase the old branch instruction.
3723 EraseTerminatorInstAndDCECond(BI);
3724
3725 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)
;
3726 return true;
3727}
3728
3729bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
3730 if (isa<PHINode>(RI->getValue()))
3731 return SimplifyCommonResume(RI);
3732 else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) &&
3733 RI->getValue() == RI->getParent()->getFirstNonPHI())
3734 // The resume must unwind the exception that caused control to branch here.
3735 return SimplifySingleResume(RI);
3736
3737 return false;
3738}
3739
3740// Simplify resume that is shared by several landing pads (phi of landing pad).
3741bool SimplifyCFGOpt::SimplifyCommonResume(ResumeInst *RI) {
3742 BasicBlock *BB = RI->getParent();
3743
3744 // Check that there are no other instructions except for debug intrinsics
3745 // between the phi of landing pads (RI->getValue()) and resume instruction.
3746 BasicBlock::iterator I = cast<Instruction>(RI->getValue())->getIterator(),
3747 E = RI->getIterator();
3748 while (++I != E)
3749 if (!isa<DbgInfoIntrinsic>(I))
3750 return false;
3751
3752 SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
3753 auto *PhiLPInst = cast<PHINode>(RI->getValue());
3754
3755 // Check incoming blocks to see if any of them are trivial.
3756 for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
3757 Idx++) {
3758 auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
3759 auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);
3760
3761 // If the block has other successors, we can not delete it because
3762 // it has other dependents.
3763 if (IncomingBB->getUniqueSuccessor() != BB)
3764 continue;
3765
3766 auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
3767 // Not the landing pad that caused the control to branch here.
3768 if (IncomingValue != LandingPad)
3769 continue;
3770
3771 bool isTrivial = true;
3772
3773 I = IncomingBB->getFirstNonPHI()->getIterator();
3774 E = IncomingBB->getTerminator()->getIterator();
3775 while (++I != E)
3776 if (!isa<DbgInfoIntrinsic>(I)) {
3777 isTrivial = false;
3778 break;
3779 }
3780
3781 if (isTrivial)
3782 TrivialUnwindBlocks.insert(IncomingBB);
3783 }
3784
3785 // If no trivial unwind blocks, don't do any simplifications.
3786 if (TrivialUnwindBlocks.empty())
3787 return false;
3788
3789 // Turn all invokes that unwind here into calls.
3790 for (auto *TrivialBB : TrivialUnwindBlocks) {
3791 // Blocks that will be simplified should be removed from the phi node.
3792 // Note there could be multiple edges to the resume block, and we need
3793 // to remove them all.
3794 while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1)
3795 BB->removePredecessor(TrivialBB, true);
3796
3797 for (pred_iterator PI = pred_begin(TrivialBB), PE = pred_end(TrivialBB);
3798 PI != PE;) {
3799 BasicBlock *Pred = *PI++;
3800 removeUnwindEdge(Pred);
3801 }
3802
3803 // In each SimplifyCFG run, only the current processed block can be erased.
3804 // Otherwise, it will break the iteration of SimplifyCFG pass. So instead
3805 // of erasing TrivialBB, we only remove the branch to the common resume
3806 // block so that we can later erase the resume block since it has no
3807 // predecessors.
3808 TrivialBB->getTerminator()->eraseFromParent();
3809 new UnreachableInst(RI->getContext(), TrivialBB);
3810 }
3811
3812 // Delete the resume block if all its predecessors have been removed.
3813 if (pred_empty(BB))
3814 BB->eraseFromParent();
3815
3816 return !TrivialUnwindBlocks.empty();
3817}
3818
3819// Simplify resume that is only used by a single (non-phi) landing pad.
3820bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) {
3821 BasicBlock *BB = RI->getParent();
3822 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
3823 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3824, __extension__ __PRETTY_FUNCTION__))
3824 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3824, __extension__ __PRETTY_FUNCTION__))
;
3825
3826 // Check that there are no other instructions except for debug intrinsics.
3827 BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator();
3828 while (++I != E)
3829 if (!isa<DbgInfoIntrinsic>(I))
3830 return false;
3831
3832 // Turn all invokes that unwind here into calls and delete the basic block.
3833 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3834 BasicBlock *Pred = *PI++;
3835 removeUnwindEdge(Pred);
3836 }
3837
3838 // The landingpad is now unreachable. Zap it.
3839 BB->eraseFromParent();
3840 if (LoopHeaders)
3841 LoopHeaders->erase(BB);
3842 return true;
3843}
3844
3845static bool removeEmptyCleanup(CleanupReturnInst *RI) {
3846 // If this is a trivial cleanup pad that executes no instructions, it can be
3847 // eliminated. If the cleanup pad continues to the caller, any predecessor
3848 // that is an EH pad will be updated to continue to the caller and any
3849 // predecessor that terminates with an invoke instruction will have its invoke
3850 // instruction converted to a call instruction. If the cleanup pad being
3851 // simplified does not continue to the caller, each predecessor will be
3852 // updated to continue to the unwind destination of the cleanup pad being
3853 // simplified.
3854 BasicBlock *BB = RI->getParent();
3855 CleanupPadInst *CPInst = RI->getCleanupPad();
3856 if (CPInst->getParent() != BB)
3857 // This isn't an empty cleanup.
3858 return false;
3859
3860 // We cannot kill the pad if it has multiple uses. This typically arises
3861 // from unreachable basic blocks.
3862 if (!CPInst->hasOneUse())
3863 return false;
3864
3865 // Check that there are no other instructions except for benign intrinsics.
3866 BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
3867 while (++I != E) {
3868 auto *II = dyn_cast<IntrinsicInst>(I);
3869 if (!II)
3870 return false;
3871
3872 Intrinsic::ID IntrinsicID = II->getIntrinsicID();
3873 switch (IntrinsicID) {
3874 case Intrinsic::dbg_declare:
3875 case Intrinsic::dbg_value:
3876 case Intrinsic::lifetime_end:
3877 break;
3878 default:
3879 return false;
3880 }
3881 }
3882
3883 // If the cleanup return we are simplifying unwinds to the caller, this will
3884 // set UnwindDest to nullptr.
3885 BasicBlock *UnwindDest = RI->getUnwindDest();
3886 Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
3887
3888 // We're about to remove BB from the control flow. Before we do, sink any
3889 // PHINodes into the unwind destination. Doing this before changing the
3890 // control flow avoids some potentially slow checks, since we can currently
3891 // be certain that UnwindDest and BB have no common predecessors (since they
3892 // are both EH pads).
3893 if (UnwindDest) {
3894 // First, go through the PHI nodes in UnwindDest and update any nodes that
3895 // reference the block we are removing
3896 for (BasicBlock::iterator I = UnwindDest->begin(),
3897 IE = DestEHPad->getIterator();
3898 I != IE; ++I) {
3899 PHINode *DestPN = cast<PHINode>(I);
3900
3901 int Idx = DestPN->getBasicBlockIndex(BB);
3902 // Since BB unwinds to UnwindDest, it has to be in the PHI node.
3903 assert(Idx != -1)(static_cast <bool> (Idx != -1) ? void (0) : __assert_fail
("Idx != -1", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 3903, __extension__ __PRETTY_FUNCTION__))
;
3904 // This PHI node has an incoming value that corresponds to a control
3905 // path through the cleanup pad we are removing. If the incoming
3906 // value is in the cleanup pad, it must be a PHINode (because we
3907 // verified above that the block is otherwise empty). Otherwise, the
3908 // value is either a constant or a value that dominates the cleanup
3909 // pad being removed.
3910 //
3911 // Because BB and UnwindDest are both EH pads, all of their
3912 // predecessors must unwind to these blocks, and since no instruction
3913 // can have multiple unwind destinations, there will be no overlap in
3914 // incoming blocks between SrcPN and DestPN.
3915 Value *SrcVal = DestPN->getIncomingValue(Idx);
3916 PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
3917
3918 // Remove the entry for the block we are deleting.
3919 DestPN->removeIncomingValue(Idx, false);
3920
3921 if (SrcPN && SrcPN->getParent() == BB) {
3922 // If the incoming value was a PHI node in the cleanup pad we are
3923 // removing, we need to merge that PHI node's incoming values into
3924 // DestPN.
3925 for (unsigned SrcIdx = 0, SrcE = SrcPN->getNumIncomingValues();
3926 SrcIdx != SrcE; ++SrcIdx) {
3927 DestPN->addIncoming(SrcPN->getIncomingValue(SrcIdx),
3928 SrcPN->getIncomingBlock(SrcIdx));
3929 }
3930 } else {
3931 // Otherwise, the incoming value came from above BB and
3932 // so we can just reuse it. We must associate all of BB's
3933 // predecessors with this value.
3934 for (auto *pred : predecessors(BB)) {
3935 DestPN->addIncoming(SrcVal, pred);
3936 }
3937 }
3938 }
3939
3940 // Sink any remaining PHI nodes directly into UnwindDest.
3941 Instruction *InsertPt = DestEHPad;
3942 for (BasicBlock::iterator I = BB->begin(),
3943 IE = BB->getFirstNonPHI()->getIterator();
3944 I != IE;) {
3945 // The iterator must be incremented here because the instructions are
3946 // being moved to another block.
3947 PHINode *PN = cast<PHINode>(I++);
3948 if (PN->use_empty())
3949 // If the PHI node has no uses, just leave it. It will be erased
3950 // when we erase BB below.
3951 continue;
3952
3953 // Otherwise, sink this PHI node into UnwindDest.
3954 // Any predecessors to UnwindDest which are not already represented
3955 // must be back edges which inherit the value from the path through
3956 // BB. In this case, the PHI value must reference itself.
3957 for (auto *pred : predecessors(UnwindDest))
3958 if (pred != BB)
3959 PN->addIncoming(PN, pred);
3960 PN->moveBefore(InsertPt);
3961 }
3962 }
3963
3964 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3965 // The iterator must be updated here because we are removing this pred.
3966 BasicBlock *PredBB = *PI++;
3967 if (UnwindDest == nullptr) {
3968 removeUnwindEdge(PredBB);
3969 } else {
3970 TerminatorInst *TI = PredBB->getTerminator();
3971 TI->replaceUsesOfWith(BB, UnwindDest);
3972 }
3973 }
3974
3975 // The cleanup pad is now unreachable. Zap it.
3976 BB->eraseFromParent();
3977 return true;
3978}
3979
3980// Try to merge two cleanuppads together.
3981static bool mergeCleanupPad(CleanupReturnInst *RI) {
3982 // Skip any cleanuprets which unwind to caller, there is nothing to merge
3983 // with.
3984 BasicBlock *UnwindDest = RI->getUnwindDest();
3985 if (!UnwindDest)
3986 return false;
3987
3988 // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
3989 // be safe to merge without code duplication.
3990 if (UnwindDest->getSinglePredecessor() != RI->getParent())
3991 return false;
3992
3993 // Verify that our cleanuppad's unwind destination is another cleanuppad.
3994 auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
3995 if (!SuccessorCleanupPad)
3996 return false;
3997
3998 CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
3999 // Replace any uses of the successor cleanupad with the predecessor pad
4000 // The only cleanuppad uses should be this cleanupret, it's cleanupret and
4001 // funclet bundle operands.
4002 SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
4003 // Remove the old cleanuppad.
4004 SuccessorCleanupPad->eraseFromParent();
4005 // Now, we simply replace the cleanupret with a branch to the unwind
4006 // destination.
4007 BranchInst::Create(UnwindDest, RI->getParent());
4008 RI->eraseFromParent();
4009
4010 return true;
4011}
4012
4013bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
4014 // It is possible to transiantly have an undef cleanuppad operand because we
4015 // have deleted some, but not all, dead blocks.
4016 // Eventually, this block will be deleted.
4017 if (isa<UndefValue>(RI->getOperand(0)))
4018 return false;
4019
4020 if (mergeCleanupPad(RI))
4021 return true;
4022
4023 if (removeEmptyCleanup(RI))
4024 return true;
4025
4026 return false;
4027}
4028
4029bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
4030 BasicBlock *BB = RI->getParent();
4031 if (!BB->getFirstNonPHIOrDbg()->isTerminator())
4032 return false;
4033
4034 // Find predecessors that end with branches.
4035 SmallVector<BasicBlock *, 8> UncondBranchPreds;
4036 SmallVector<BranchInst *, 8> CondBranchPreds;
4037 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
4038 BasicBlock *P = *PI;
4039 TerminatorInst *PTI = P->getTerminator();
4040 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
4041 if (BI->isUnconditional())
4042 UncondBranchPreds.push_back(P);
4043 else
4044 CondBranchPreds.push_back(BI);
4045 }
4046 }
4047
4048 // If we found some, do the transformation!
4049 if (!UncondBranchPreds.empty() && DupRet) {
4050 while (!UncondBranchPreds.empty()) {
4051 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
4052 DEBUG(dbgs() << "FOLDING: " << *BBdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
4053 << "INTO UNCOND BRANCH PRED: " << *Pred)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "FOLDING: " << *BB <<
"INTO UNCOND BRANCH PRED: " << *Pred; } } while (false
)
;
4054 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
4055 }
4056
4057 // If we eliminated all predecessors of the block, delete the block now.
4058 if (pred_empty(BB)) {
4059 // We know there are no successors, so just nuke the block.
4060 BB->eraseFromParent();
4061 if (LoopHeaders)
4062 LoopHeaders->erase(BB);
4063 }
4064
4065 return true;
4066 }
4067
4068 // Check out all of the conditional branches going to this return
4069 // instruction. If any of them just select between returns, change the
4070 // branch itself into a select/return pair.
4071 while (!CondBranchPreds.empty()) {
4072 BranchInst *BI = CondBranchPreds.pop_back_val();
4073
4074 // Check to see if the non-BB successor is also a return block.
4075 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
4076 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
4077 SimplifyCondBranchToTwoReturns(BI, Builder))
4078 return true;
4079 }
4080 return false;
4081}
4082
4083bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
4084 BasicBlock *BB = UI->getParent();
4085
4086 bool Changed = false;
4087
4088 // If there are any instructions immediately before the unreachable that can
4089 // be removed, do so.
4090 while (UI->getIterator() != BB->begin()) {
4091 BasicBlock::iterator BBI = UI->getIterator();
4092 --BBI;
4093 // Do not delete instructions that can have side effects which might cause
4094 // the unreachable to not be reachable; specifically, calls and volatile
4095 // operations may have this effect.
4096 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI))
4097 break;
4098
4099 if (BBI->mayHaveSideEffects()) {
4100 if (auto *SI = dyn_cast<StoreInst>(BBI)) {
4101 if (SI->isVolatile())
4102 break;
4103 } else if (auto *LI = dyn_cast<LoadInst>(BBI)) {
4104 if (LI->isVolatile())
4105 break;
4106 } else if (auto *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
4107 if (RMWI->isVolatile())
4108 break;
4109 } else if (auto *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
4110 if (CXI->isVolatile())
4111 break;
4112 } else if (isa<CatchPadInst>(BBI)) {
4113 // A catchpad may invoke exception object constructors and such, which
4114 // in some languages can be arbitrary code, so be conservative by
4115 // default.
4116 // For CoreCLR, it just involves a type test, so can be removed.
4117 if (classifyEHPersonality(BB->getParent()->getPersonalityFn()) !=
4118 EHPersonality::CoreCLR)
4119 break;
4120 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
4121 !isa<LandingPadInst>(BBI)) {
4122 break;
4123 }
4124 // Note that deleting LandingPad's here is in fact okay, although it
4125 // involves a bit of subtle reasoning. If this inst is a LandingPad,
4126 // all the predecessors of this block will be the unwind edges of Invokes,
4127 // and we can therefore guarantee this block will be erased.
4128 }
4129
4130 // Delete this instruction (any uses are guaranteed to be dead)
4131 if (!BBI->use_empty())
4132 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
4133 BBI->eraseFromParent();
4134 Changed = true;
4135 }
4136
4137 // If the unreachable instruction is the first in the block, take a gander
4138 // at all of the predecessors of this instruction, and simplify them.
4139 if (&BB->front() != UI)
4140 return Changed;
4141
4142 SmallVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
4143 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
4144 TerminatorInst *TI = Preds[i]->getTerminator();
4145 IRBuilder<> Builder(TI);
4146 if (auto *BI = dyn_cast<BranchInst>(TI)) {
4147 if (BI->isUnconditional()) {
4148 if (BI->getSuccessor(0) == BB) {
4149 new UnreachableInst(TI->getContext(), TI);
4150 TI->eraseFromParent();
4151 Changed = true;
4152 }
4153 } else {
4154 if (BI->getSuccessor(0) == BB) {
4155 Builder.CreateBr(BI->getSuccessor(1));
4156 EraseTerminatorInstAndDCECond(BI);
4157 } else if (BI->getSuccessor(1) == BB) {
4158 Builder.CreateBr(BI->getSuccessor(0));
4159 EraseTerminatorInstAndDCECond(BI);
4160 Changed = true;
4161 }
4162 }
4163 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
4164 for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
4165 if (i->getCaseSuccessor() != BB) {
4166 ++i;
4167 continue;
4168 }
4169 BB->removePredecessor(SI->getParent());
4170 i = SI->removeCase(i);
4171 e = SI->case_end();
4172 Changed = true;
4173 }
4174 } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
4175 if (II->getUnwindDest() == BB) {
4176 removeUnwindEdge(TI->getParent());
4177 Changed = true;
4178 }
4179 } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) {
4180 if (CSI->getUnwindDest() == BB) {
4181 removeUnwindEdge(TI->getParent());
4182 Changed = true;
4183 continue;
4184 }
4185
4186 for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(),
4187 E = CSI->handler_end();
4188 I != E; ++I) {
4189 if (*I == BB) {
4190 CSI->removeHandler(I);
4191 --I;
4192 --E;
4193 Changed = true;
4194 }
4195 }
4196 if (CSI->getNumHandlers() == 0) {
4197 BasicBlock *CatchSwitchBB = CSI->getParent();
4198 if (CSI->hasUnwindDest()) {
4199 // Redirect preds to the unwind dest
4200 CatchSwitchBB->replaceAllUsesWith(CSI->getUnwindDest());
4201 } else {
4202 // Rewrite all preds to unwind to caller (or from invoke to call).
4203 SmallVector<BasicBlock *, 8> EHPreds(predecessors(CatchSwitchBB));
4204 for (BasicBlock *EHPred : EHPreds)
4205 removeUnwindEdge(EHPred);
4206 }
4207 // The catchswitch is no longer reachable.
4208 new UnreachableInst(CSI->getContext(), CSI);
4209 CSI->eraseFromParent();
4210 Changed = true;
4211 }
4212 } else if (isa<CleanupReturnInst>(TI)) {
4213 new UnreachableInst(TI->getContext(), TI);
4214 TI->eraseFromParent();
4215 Changed = true;
4216 }
4217 }
4218
4219 // If this block is now dead, remove it.
4220 if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {
4221 // We know there are no successors, so just nuke the block.
4222 BB->eraseFromParent();
4223 if (LoopHeaders)
4224 LoopHeaders->erase(BB);
4225 return true;
4226 }
4227
4228 return Changed;
4229}
4230
4231static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
4232 assert(Cases.size() >= 1)(static_cast <bool> (Cases.size() >= 1) ? void (0) :
__assert_fail ("Cases.size() >= 1", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4232, __extension__ __PRETTY_FUNCTION__))
;
4233
4234 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
4235 for (size_t I = 1, E = Cases.size(); I != E; ++I) {
4236 if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
4237 return false;
4238 }
4239 return true;
4240}
4241
4242/// Turn a switch with two reachable destinations into an integer range
4243/// comparison and branch.
4244static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
4245 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4245, __extension__ __PRETTY_FUNCTION__))
;
4246
4247 bool HasDefault =
4248 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4249
4250 // Partition the cases into two sets with different destinations.
4251 BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
4252 BasicBlock *DestB = nullptr;
4253 SmallVector<ConstantInt *, 16> CasesA;
4254 SmallVector<ConstantInt *, 16> CasesB;
4255
4256 for (auto Case : SI->cases()) {
4257 BasicBlock *Dest = Case.getCaseSuccessor();
4258 if (!DestA)
4259 DestA = Dest;
4260 if (Dest == DestA) {
4261 CasesA.push_back(Case.getCaseValue());
4262 continue;
4263 }
4264 if (!DestB)
4265 DestB = Dest;
4266 if (Dest == DestB) {
4267 CasesB.push_back(Case.getCaseValue());
4268 continue;
4269 }
4270 return false; // More than two destinations.
4271 }
4272
4273 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4274, __extension__ __PRETTY_FUNCTION__))
4274 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4274, __extension__ __PRETTY_FUNCTION__))
;
4275 assert(DestA != DestB)(static_cast <bool> (DestA != DestB) ? void (0) : __assert_fail
("DestA != DestB", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4275, __extension__ __PRETTY_FUNCTION__))
;
4276 assert(DestB != SI->getDefaultDest())(static_cast <bool> (DestB != SI->getDefaultDest()) ?
void (0) : __assert_fail ("DestB != SI->getDefaultDest()"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4276, __extension__ __PRETTY_FUNCTION__))
;
4277 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4277, __extension__ __PRETTY_FUNCTION__))
;
4278 assert(!CasesA.empty() || HasDefault)(static_cast <bool> (!CasesA.empty() || HasDefault) ? void
(0) : __assert_fail ("!CasesA.empty() || HasDefault", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4278, __extension__ __PRETTY_FUNCTION__))
;
4279
4280 // Figure out if one of the sets of cases form a contiguous range.
4281 SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
4282 BasicBlock *ContiguousDest = nullptr;
4283 BasicBlock *OtherDest = nullptr;
4284 if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
4285 ContiguousCases = &CasesA;
4286 ContiguousDest = DestA;
4287 OtherDest = DestB;
4288 } else if (CasesAreContiguous(CasesB)) {
4289 ContiguousCases = &CasesB;
4290 ContiguousDest = DestB;
4291 OtherDest = DestA;
4292 } else
4293 return false;
4294
4295 // Start building the compare and branch.
4296
4297 Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
4298 Constant *NumCases =
4299 ConstantInt::get(Offset->getType(), ContiguousCases->size());
4300
4301 Value *Sub = SI->getCondition();
4302 if (!Offset->isNullValue())
4303 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
4304
4305 Value *Cmp;
4306 // If NumCases overflowed, then all possible values jump to the successor.
4307 if (NumCases->isNullValue() && !ContiguousCases->empty())
4308 Cmp = ConstantInt::getTrue(SI->getContext());
4309 else
4310 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
4311 BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
4312
4313 // Update weight for the newly-created conditional branch.
4314 if (HasBranchWeights(SI)) {
4315 SmallVector<uint64_t, 8> Weights;
4316 GetBranchWeights(SI, Weights);
4317 if (Weights.size() == 1 + SI->getNumCases()) {
4318 uint64_t TrueWeight = 0;
4319 uint64_t FalseWeight = 0;
4320 for (size_t I = 0, E = Weights.size(); I != E; ++I) {
4321 if (SI->getSuccessor(I) == ContiguousDest)
4322 TrueWeight += Weights[I];
4323 else
4324 FalseWeight += Weights[I];
4325 }
4326 while (TrueWeight > UINT32_MAX(4294967295U) || FalseWeight > UINT32_MAX(4294967295U)) {
4327 TrueWeight /= 2;
4328 FalseWeight /= 2;
4329 }
4330 setBranchWeights(NewBI, TrueWeight, FalseWeight);
4331 }
4332 }
4333
4334 // Prune obsolete incoming values off the successors' PHI nodes.
4335 for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
4336 unsigned PreviousEdges = ContiguousCases->size();
4337 if (ContiguousDest == SI->getDefaultDest())
4338 ++PreviousEdges;
4339 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4340 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4341 }
4342 for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
4343 unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
4344 if (OtherDest == SI->getDefaultDest())
4345 ++PreviousEdges;
4346 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4347 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4348 }
4349
4350 // Drop the switch.
4351 SI->eraseFromParent();
4352
4353 return true;
4354}
4355
4356/// Compute masked bits for the condition of a switch
4357/// and use it to remove dead cases.
4358static bool eliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC,
4359 const DataLayout &DL) {
4360 Value *Cond = SI->getCondition();
4361 unsigned Bits = Cond->getType()->getIntegerBitWidth();
4362 KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI);
4363
4364 // We can also eliminate cases by determining that their values are outside of
4365 // the limited range of the condition based on how many significant (non-sign)
4366 // bits are in the condition value.
4367 unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1;
4368 unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits;
4369
4370 // Gather dead cases.
4371 SmallVector<ConstantInt *, 8> DeadCases;
4372 for (auto &Case : SI->cases()) {
4373 const APInt &CaseVal = Case.getCaseValue()->getValue();
4374 if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) ||
4375 (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
4376 DeadCases.push_back(Case.getCaseValue());
4377 DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseVal << " is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch case "
<< CaseVal << " is dead.\n"; } } while (false)
;
4378 }
4379 }
4380
4381 // If we can prove that the cases must cover all possible values, the
4382 // default destination becomes dead and we can remove it. If we know some
4383 // of the bits in the value, we can use that to more precisely compute the
4384 // number of possible unique case values.
4385 bool HasDefault =
4386 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4387 const unsigned NumUnknownBits =
4388 Bits - (Known.Zero | Known.One).countPopulation();
4389 assert(NumUnknownBits <= Bits)(static_cast <bool> (NumUnknownBits <= Bits) ? void (
0) : __assert_fail ("NumUnknownBits <= Bits", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4389, __extension__ __PRETTY_FUNCTION__))
;
4390 if (HasDefault && DeadCases.empty() &&
4391 NumUnknownBits < 64 /* avoid overflow */ &&
4392 SI->getNumCases() == (1ULL << NumUnknownBits)) {
4393 DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simplifycfg")) { dbgs() << "SimplifyCFG: switch default is dead.\n"
; } } while (false)
;
4394 BasicBlock *NewDefault =
4395 SplitBlockPredecessors(SI->getDefaultDest(), SI->getParent(), "");
4396 SI->setDefaultDest(&*NewDefault);
4397 SplitBlock(&*NewDefault, &NewDefault->front());
4398 auto *OldTI = NewDefault->getTerminator();
4399 new UnreachableInst(SI->getContext(), OldTI);
4400 EraseTerminatorInstAndDCECond(OldTI);
4401 return true;
4402 }
4403
4404 SmallVector<uint64_t, 8> Weights;
4405 bool HasWeight = HasBranchWeights(SI);
4406 if (HasWeight) {
4407 GetBranchWeights(SI, Weights);
4408 HasWeight = (Weights.size() == 1 + SI->getNumCases());
4409 }
4410
4411 // Remove dead cases from the switch.
4412 for (ConstantInt *DeadCase : DeadCases) {
4413 SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase);
4414 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4415, __extension__ __PRETTY_FUNCTION__))
4415 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4415, __extension__ __PRETTY_FUNCTION__))
;
4416 if (HasWeight) {
4417 std::swap(Weights[CaseI->getCaseIndex() + 1], Weights.back());
4418 Weights.pop_back();
4419 }
4420
4421 // Prune unused values from PHI nodes.
4422 CaseI->getCaseSuccessor()->removePredecessor(SI->getParent());
4423 SI->removeCase(CaseI);
4424 }
4425 if (HasWeight && Weights.size() >= 2) {
4426 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
4427 setBranchWeights(SI, MDWeights);
4428 }
4429
4430 return !DeadCases.empty();
4431}
4432
4433/// If BB would be eligible for simplification by
4434/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
4435/// by an unconditional branch), look at the phi node for BB in the successor
4436/// block and see if the incoming value is equal to CaseValue. If so, return
4437/// the phi node, and set PhiIndex to BB's index in the phi node.
4438static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
4439 BasicBlock *BB, int *PhiIndex) {
4440 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
4441 return nullptr; // BB must be empty to be a candidate for simplification.
4442 if (!BB->getSinglePredecessor())
4443 return nullptr; // BB must be dominated by the switch.
4444
4445 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
4446 if (!Branch || !Branch->isUnconditional())
4447 return nullptr; // Terminator must be unconditional branch.
4448
4449 BasicBlock *Succ = Branch->getSuccessor(0);
4450
4451 for (PHINode &PHI : Succ->phis()) {
4452 int Idx = PHI.getBasicBlockIndex(BB);
4453 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4453, __extension__ __PRETTY_FUNCTION__))
;
4454
4455 Value *InValue = PHI.getIncomingValue(Idx);
4456 if (InValue != CaseValue)
4457 continue;
4458
4459 *PhiIndex = Idx;
4460 return &PHI;
4461 }
4462
4463 return nullptr;
4464}
4465
4466/// Try to forward the condition of a switch instruction to a phi node
4467/// dominated by the switch, if that would mean that some of the destination
4468/// blocks of the switch can be folded away. Return true if a change is made.
4469static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
4470 using ForwardingNodesMap = DenseMap<PHINode *, SmallVector<int, 4>>;
4471
4472 ForwardingNodesMap ForwardingNodes;
4473 BasicBlock *SwitchBlock = SI->getParent();
4474 bool Changed = false;
4475 for (auto &Case : SI->cases()) {
4476 ConstantInt *CaseValue = Case.getCaseValue();
4477 BasicBlock *CaseDest = Case.getCaseSuccessor();
4478
4479 // Replace phi operands in successor blocks that are using the constant case
4480 // value rather than the switch condition variable:
4481 // switchbb:
4482 // switch i32 %x, label %default [
4483 // i32 17, label %succ
4484 // ...
4485 // succ:
4486 // %r = phi i32 ... [ 17, %switchbb ] ...
4487 // -->
4488 // %r = phi i32 ... [ %x, %switchbb ] ...
4489
4490 for (PHINode &Phi : CaseDest->phis()) {
4491 // This only works if there is exactly 1 incoming edge from the switch to
4492 // a phi. If there is >1, that means multiple cases of the switch map to 1
4493 // value in the phi, and that phi value is not the switch condition. Thus,
4494 // this transform would not make sense (the phi would be invalid because
4495 // a phi can't have different incoming values from the same block).
4496 int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock);
4497 if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue &&
4498 count(Phi.blocks(), SwitchBlock) == 1) {
4499 Phi.setIncomingValue(SwitchBBIdx, SI->getCondition());
4500 Changed = true;
4501 }
4502 }
4503
4504 // Collect phi nodes that are indirectly using this switch's case constants.
4505 int PhiIdx;
4506 if (auto *Phi = FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIdx))
4507 ForwardingNodes[Phi].push_back(PhiIdx);
4508 }
4509
4510 for (auto &ForwardingNode : ForwardingNodes) {
4511 PHINode *Phi = ForwardingNode.first;
4512 SmallVectorImpl<int> &Indexes = ForwardingNode.second;
4513 if (Indexes.size() < 2)
4514 continue;
4515
4516 for (int Index : Indexes)
4517 Phi->setIncomingValue(Index, SI->getCondition());
4518 Changed = true;
4519 }
4520
4521 return Changed;
4522}
4523
4524/// Return true if the backend will be able to handle
4525/// initializing an array of constants like C.
4526static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
4527 if (C->isThreadDependent())
4528 return false;
4529 if (C->isDLLImportDependent())
4530 return false;
4531
4532 if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
4533 !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
4534 !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
4535 return false;
4536
4537 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
4538 if (!CE->isGEPWithNoNotionalOverIndexing())
4539 return false;
4540 if (!ValidLookupTableConstant(CE->getOperand(0), TTI))
4541 return false;
4542 }
4543
4544 if (!TTI.shouldBuildLookupTablesForConstant(C))
4545 return false;
4546
4547 return true;
4548}
4549
4550/// If V is a Constant, return it. Otherwise, try to look up
4551/// its constant value in ConstantPool, returning 0 if it's not there.
4552static Constant *
4553LookupConstant(Value *V,
4554 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4555 if (Constant *C = dyn_cast<Constant>(V))
4556 return C;
4557 return ConstantPool.lookup(V);
4558}
4559
4560/// Try to fold instruction I into a constant. This works for
4561/// simple instructions such as binary operations where both operands are
4562/// constant or can be replaced by constants from the ConstantPool. Returns the
4563/// resulting constant on success, 0 otherwise.
4564static Constant *
4565ConstantFold(Instruction *I, const DataLayout &DL,
4566 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
4567 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
4568 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
4569 if (!A)
4570 return nullptr;
4571 if (A->isAllOnesValue())
4572 return LookupConstant(Select->getTrueValue(), ConstantPool);
4573 if (A->isNullValue())
4574 return LookupConstant(Select->getFalseValue(), ConstantPool);
4575 return nullptr;
4576 }
4577
4578 SmallVector<Constant *, 4> COps;
4579 for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
4580 if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
4581 COps.push_back(A);
4582 else
4583 return nullptr;
4584 }
4585
4586 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
4587 return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
4588 COps[1], DL);
4589 }
4590
4591 return ConstantFoldInstOperands(I, COps, DL);
4592}
4593
4594/// Try to determine the resulting constant values in phi nodes
4595/// at the common destination basic block, *CommonDest, for one of the case
4596/// destionations CaseDest corresponding to value CaseVal (0 for the default
4597/// case), of a switch instruction SI.
4598static bool
4599GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
4600 BasicBlock **CommonDest,
4601 SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
4602 const DataLayout &DL, const TargetTransformInfo &TTI) {
4603 // The block from which we enter the common destination.
4604 BasicBlock *Pred = SI->getParent();
4605
4606 // If CaseDest is empty except for some side-effect free instructions through
4607 // which we can constant-propagate the CaseVal, continue to its successor.
4608 SmallDenseMap<Value *, Constant *> ConstantPool;
4609 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
4610 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
4611 ++I) {
4612 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
4613 // If the terminator is a simple branch, continue to the next block.
4614 if (T->getNumSuccessors() != 1 || T->isExceptional())
4615 return false;
4616 Pred = CaseDest;
4617 CaseDest = T->getSuccessor(0);
4618 } else if (isa<DbgInfoIntrinsic>(I)) {
4619 // Skip debug intrinsic.
4620 continue;
4621 } else if (Constant *C = ConstantFold(&*I, DL, ConstantPool)) {
4622 // Instruction is side-effect free and constant.
4623
4624 // If the instruction has uses outside this block or a phi node slot for
4625 // the block, it is not safe to bypass the instruction since it would then
4626 // no longer dominate all its uses.
4627 for (auto &Use : I->uses()) {
4628 User *User = Use.getUser();
4629 if (Instruction *I = dyn_cast<Instruction>(User))
4630 if (I->getParent() == CaseDest)
4631 continue;
4632 if (PHINode *Phi = dyn_cast<PHINode>(User))
4633 if (Phi->getIncomingBlock(Use) == CaseDest)
4634 continue;
4635 return false;
4636 }
4637
4638 ConstantPool.insert(std::make_pair(&*I, C));
4639 } else {
4640 break;
4641 }
4642 }
4643
4644 // If we did not have a CommonDest before, use the current one.
4645 if (!*CommonDest)
4646 *CommonDest = CaseDest;
4647 // If the destination isn't the common one, abort.
4648 if (CaseDest != *CommonDest)
4649 return false;
4650
4651 // Get the values for this case from phi nodes in the destination block.
4652 for (PHINode &PHI : (*CommonDest)->phis()) {
4653 int Idx = PHI.getBasicBlockIndex(Pred);
4654 if (Idx == -1)
4655 continue;
4656
4657 Constant *ConstVal =
4658 LookupConstant(PHI.getIncomingValue(Idx), ConstantPool);
4659 if (!ConstVal)
4660 return false;
4661
4662 // Be conservative about which kinds of constants we support.
4663 if (!ValidLookupTableConstant(ConstVal, TTI))
4664 return false;
4665
4666 Res.push_back(std::make_pair(&PHI, ConstVal));
4667 }
4668
4669 return Res.size() > 0;
4670}
4671
4672// Helper function used to add CaseVal to the list of cases that generate
4673// Result. Returns the updated number of cases that generate this result.
4674static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
4675 SwitchCaseResultVectorTy &UniqueResults,
4676 Constant *Result) {
4677 for (auto &I : UniqueResults) {
4678 if (I.first == Result) {
4679 I.second.push_back(CaseVal);
4680 return I.second.size();
4681 }
4682 }
4683 UniqueResults.push_back(
4684 std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal)));
4685 return 1;
4686}
4687
4688// Helper function that initializes a map containing
4689// results for the PHI node of the common destination block for a switch
4690// instruction. Returns false if multiple PHI nodes have been found or if
4691// there is not a common destination block for the switch.
4692static bool
4693InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
4694 SwitchCaseResultVectorTy &UniqueResults,
4695 Constant *&DefaultResult, const DataLayout &DL,
4696 const TargetTransformInfo &TTI,
4697 uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) {
4698 for (auto &I : SI->cases()) {
4699 ConstantInt *CaseVal = I.getCaseValue();
4700
4701 // Resulting value at phi nodes for this case value.
4702 SwitchCaseResultsTy Results;
4703 if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
4704 DL, TTI))
4705 return false;
4706
4707 // Only one value per case is permitted.
4708 if (Results.size() > 1)
4709 return false;
4710
4711 // Add the case->result mapping to UniqueResults.
4712 const uintptr_t NumCasesForResult =
4713 MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
4714
4715 // Early out if there are too many cases for this result.
4716 if (NumCasesForResult > MaxCasesPerResult)
4717 return false;
4718
4719 // Early out if there are too many unique results.
4720 if (UniqueResults.size() > MaxUniqueResults)
4721 return false;
4722
4723 // Check the PHI consistency.
4724 if (!PHI)
4725 PHI = Results[0].first;
4726 else if (PHI != Results[0].first)
4727 return false;
4728 }
4729 // Find the default result value.
4730 SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
4731 BasicBlock *DefaultDest = SI->getDefaultDest();
4732 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
4733 DL, TTI);
4734 // If the default value is not found abort unless the default destination
4735 // is unreachable.
4736 DefaultResult =
4737 DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
4738 if ((!DefaultResult &&
4739 !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
4740 return false;
4741
4742 return true;
4743}
4744
4745// Helper function that checks if it is possible to transform a switch with only
4746// two cases (or two cases + default) that produces a result into a select.
4747// Example:
4748// switch (a) {
4749// case 10: %0 = icmp eq i32 %a, 10
4750// return 10; %1 = select i1 %0, i32 10, i32 4
4751// case 20: ----> %2 = icmp eq i32 %a, 20
4752// return 2; %3 = select i1 %2, i32 2, i32 %1
4753// default:
4754// return 4;
4755// }
4756static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
4757 Constant *DefaultResult, Value *Condition,
4758 IRBuilder<> &Builder) {
4759 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4760, __extension__ __PRETTY_FUNCTION__))
4760 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4760, __extension__ __PRETTY_FUNCTION__))
;
4761 // If we are selecting between only two cases transform into a simple
4762 // select or a two-way select if default is possible.
4763 if (ResultVector[0].second.size() == 1 &&
4764 ResultVector[1].second.size() == 1) {
4765 ConstantInt *const FirstCase = ResultVector[0].second[0];
4766 ConstantInt *const SecondCase = ResultVector[1].second[0];
4767
4768 bool DefaultCanTrigger = DefaultResult;
4769 Value *SelectValue = ResultVector[1].first;
4770 if (DefaultCanTrigger) {
4771 Value *const ValueCompare =
4772 Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
4773 SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
4774 DefaultResult, "switch.select");
4775 }
4776 Value *const ValueCompare =
4777 Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
4778 return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
4779 SelectValue, "switch.select");
4780 }
4781
4782 return nullptr;
4783}
4784
4785// Helper function to cleanup a switch instruction that has been converted into
4786// a select, fixing up PHI nodes and basic blocks.
4787static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
4788 Value *SelectValue,
4789 IRBuilder<> &Builder) {
4790 BasicBlock *SelectBB = SI->getParent();
4791 while (PHI->getBasicBlockIndex(SelectBB) >= 0)
4792 PHI->removeIncomingValue(SelectBB);
4793 PHI->addIncoming(SelectValue, SelectBB);
4794
4795 Builder.CreateBr(PHI->getParent());
4796
4797 // Remove the switch.
4798 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
4799 BasicBlock *Succ = SI->getSuccessor(i);
4800
4801 if (Succ == PHI->getParent())
4802 continue;
4803 Succ->removePredecessor(SelectBB);
4804 }
4805 SI->eraseFromParent();
4806}
4807
4808/// If the switch is only used to initialize one or more
4809/// phi nodes in a common successor block with only two different
4810/// constant values, replace the switch with select.
4811static bool switchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
4812 const DataLayout &DL,
4813 const TargetTransformInfo &TTI) {
4814 Value *const Cond = SI->getCondition();
4815 PHINode *PHI = nullptr;
4816 BasicBlock *CommonDest = nullptr;
4817 Constant *DefaultResult;
4818 SwitchCaseResultVectorTy UniqueResults;
4819 // Collect all the cases that will deliver the same value from the switch.
4820 if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
4821 DL, TTI, 2, 1))
4822 return false;
4823 // Selects choose between maximum two values.
4824 if (UniqueResults.size() != 2)
4825 return false;
4826 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4826, __extension__ __PRETTY_FUNCTION__))
;
4827
4828 Builder.SetInsertPoint(SI);
4829 Value *SelectValue =
4830 ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
4831 if (SelectValue) {
4832 RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder);
4833 return true;
4834 }
4835 // The switch couldn't be converted into a select.
4836 return false;
4837}
4838
4839namespace {
4840
4841/// This class represents a lookup table that can be used to replace a switch.
4842class SwitchLookupTable {
4843public:
4844 /// Create a lookup table to use as a switch replacement with the contents
4845 /// of Values, using DefaultValue to fill any holes in the table.
4846 SwitchLookupTable(
4847 Module &M, uint64_t TableSize, ConstantInt *Offset,
4848 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4849 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName);
4850
4851 /// Build instructions with Builder to retrieve the value at
4852 /// the position given by Index in the lookup table.
4853 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
4854
4855 /// Return true if a table with TableSize elements of
4856 /// type ElementType would fit in a target-legal register.
4857 static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
4858 Type *ElementType);
4859
4860private:
4861 // Depending on the contents of the table, it can be represented in
4862 // different ways.
4863 enum {
4864 // For tables where each element contains the same value, we just have to
4865 // store that single value and return it for each lookup.
4866 SingleValueKind,
4867
4868 // For tables where there is a linear relationship between table index
4869 // and values. We calculate the result with a simple multiplication
4870 // and addition instead of a table lookup.
4871 LinearMapKind,
4872
4873 // For small tables with integer elements, we can pack them into a bitmap
4874 // that fits into a target-legal register. Values are retrieved by
4875 // shift and mask operations.
4876 BitMapKind,
4877
4878 // The table is stored as an array of values. Values are retrieved by load
4879 // instructions from the table.
4880 ArrayKind
4881 } Kind;
4882
4883 // For SingleValueKind, this is the single value.
4884 Constant *SingleValue = nullptr;
4885
4886 // For BitMapKind, this is the bitmap.
4887 ConstantInt *BitMap = nullptr;
4888 IntegerType *BitMapElementTy = nullptr;
4889
4890 // For LinearMapKind, these are the constants used to derive the value.
4891 ConstantInt *LinearOffset = nullptr;
4892 ConstantInt *LinearMultiplier = nullptr;
4893
4894 // For ArrayKind, this is the array.
4895 GlobalVariable *Array = nullptr;
4896};
4897
4898} // end anonymous namespace
4899
4900SwitchLookupTable::SwitchLookupTable(
4901 Module &M, uint64_t TableSize, ConstantInt *Offset,
4902 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4903 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName) {
4904 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4904, __extension__ __PRETTY_FUNCTION__))
;
4905 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4905, __extension__ __PRETTY_FUNCTION__))
;
4906
4907 // If all values in the table are equal, this is that value.
4908 SingleValue = Values.begin()->second;
4909
4910 Type *ValueType = Values.begin()->second->getType();
4911
4912 // Build up the table contents.
4913 SmallVector<Constant *, 64> TableContents(TableSize);
4914 for (size_t I = 0, E = Values.size(); I != E; ++I) {
4915 ConstantInt *CaseVal = Values[I].first;
4916 Constant *CaseRes = Values[I].second;
4917 assert(CaseRes->getType() == ValueType)(static_cast <bool> (CaseRes->getType() == ValueType
) ? void (0) : __assert_fail ("CaseRes->getType() == ValueType"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4917, __extension__ __PRETTY_FUNCTION__))
;
4918
4919 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
4920 TableContents[Idx] = CaseRes;
4921
4922 if (CaseRes != SingleValue)
4923 SingleValue = nullptr;
4924 }
4925
4926 // Fill in any holes in the table with the default result.
4927 if (Values.size() < TableSize) {
4928 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4929, __extension__ __PRETTY_FUNCTION__))
4929 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4929, __extension__ __PRETTY_FUNCTION__))
;
4930 assert(DefaultValue->getType() == ValueType)(static_cast <bool> (DefaultValue->getType() == ValueType
) ? void (0) : __assert_fail ("DefaultValue->getType() == ValueType"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4930, __extension__ __PRETTY_FUNCTION__))
;
4931 for (uint64_t I = 0; I < TableSize; ++I) {
4932 if (!TableContents[I])
4933 TableContents[I] = DefaultValue;
4934 }
4935
4936 if (DefaultValue != SingleValue)
4937 SingleValue = nullptr;
4938 }
4939
4940 // If each element in the table contains the same value, we only need to store
4941 // that single value.
4942 if (SingleValue) {
4943 Kind = SingleValueKind;
4944 return;
4945 }
4946
4947 // Check if we can derive the value with a linear transformation from the
4948 // table index.
4949 if (isa<IntegerType>(ValueType)) {
4950 bool LinearMappingPossible = true;
4951 APInt PrevVal;
4952 APInt DistToPrev;
4953 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 4953, __extension__ __PRETTY_FUNCTION__))
;
4954 // Check if there is the same distance between two consecutive values.
4955 for (uint64_t I = 0; I < TableSize; ++I) {
4956 ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
4957 if (!ConstVal) {
4958 // This is an undef. We could deal with it, but undefs in lookup tables
4959 // are very seldom. It's probably not worth the additional complexity.
4960 LinearMappingPossible = false;
4961 break;
4962 }
4963 const APInt &Val = ConstVal->getValue();
4964 if (I != 0) {
4965 APInt Dist = Val - PrevVal;
4966 if (I == 1) {
4967 DistToPrev = Dist;
4968 } else if (Dist != DistToPrev) {
4969 LinearMappingPossible = false;
4970 break;
4971 }
4972 }
4973 PrevVal = Val;
4974 }
4975 if (LinearMappingPossible) {
4976 LinearOffset = cast<ConstantInt>(TableContents[0]);
4977 LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
4978 Kind = LinearMapKind;
4979 ++NumLinearMaps;
4980 return;
4981 }
4982 }
4983
4984 // If the type is integer and the table fits in a register, build a bitmap.
4985 if (WouldFitInRegister(DL, TableSize, ValueType)) {
4986 IntegerType *IT = cast<IntegerType>(ValueType);
4987 APInt TableInt(TableSize * IT->getBitWidth(), 0);
4988 for (uint64_t I = TableSize; I > 0; --I) {
4989 TableInt <<= IT->getBitWidth();
4990 // Insert values into the bitmap. Undef values are set to zero.
4991 if (!isa<UndefValue>(TableContents[I - 1])) {
4992 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
4993 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
4994 }
4995 }
4996 BitMap = ConstantInt::get(M.getContext(), TableInt);
4997 BitMapElementTy = IT;
4998 Kind = BitMapKind;
4999 ++NumBitMaps;
5000 return;
5001 }
5002
5003 // Store the table in an array.
5004 ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
5005 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
5006
5007 Array = new GlobalVariable(M, ArrayTy, /*constant=*/true,
5008 GlobalVariable::PrivateLinkage, Initializer,
5009 "switch.table." + FuncName);
5010 Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
5011 Kind = ArrayKind;
5012}
5013
5014Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
5015 switch (Kind) {
5016 case SingleValueKind:
5017 return SingleValue;
5018 case LinearMapKind: {
5019 // Derive the result value from the input value.
5020 Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
5021 false, "switch.idx.cast");
5022 if (!LinearMultiplier->isOne())
5023 Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
5024 if (!LinearOffset->isZero())
5025 Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
5026 return Result;
5027 }
5028 case BitMapKind: {
5029 // Type of the bitmap (e.g. i59).
5030 IntegerType *MapTy = BitMap->getType();
5031
5032 // Cast Index to the same type as the bitmap.
5033 // Note: The Index is <= the number of elements in the table, so
5034 // truncating it to the width of the bitmask is safe.
5035 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
5036
5037 // Multiply the shift amount by the element width.
5038 ShiftAmt = Builder.CreateMul(
5039 ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
5040 "switch.shiftamt");
5041
5042 // Shift down.
5043 Value *DownShifted =
5044 Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift");
5045 // Mask off.
5046 return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked");
5047 }
5048 case ArrayKind: {
5049 // Make sure the table index will not overflow when treated as signed.
5050 IntegerType *IT = cast<IntegerType>(Index->getType());
5051 uint64_t TableSize =
5052 Array->getInitializer()->getType()->getArrayNumElements();
5053 if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
5054 Index = Builder.CreateZExt(
5055 Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1),
5056 "switch.tableidx.zext");
5057
5058 Value *GEPIndices[] = {Builder.getInt32(0), Index};
5059 Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
5060 GEPIndices, "switch.gep");
5061 return Builder.CreateLoad(GEP, "switch.load");
5062 }
5063 }
5064 llvm_unreachable("Unknown lookup table kind!")::llvm::llvm_unreachable_internal("Unknown lookup table kind!"
, "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5064)
;
5065}
5066
5067bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
5068 uint64_t TableSize,
5069 Type *ElementType) {
5070 auto *IT = dyn_cast<IntegerType>(ElementType);
5071 if (!IT)
5072 return false;
5073 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
5074 // are <= 15, we could try to narrow the type.
5075
5076 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
5077 if (TableSize >= UINT_MAX(2147483647 *2U +1U) / IT->getBitWidth())
5078 return false;
5079 return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
5080}
5081
5082/// Determine whether a lookup table should be built for this switch, based on
5083/// the number of cases, size of the table, and the types of the results.
5084static bool
5085ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
5086 const TargetTransformInfo &TTI, const DataLayout &DL,
5087 const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
5088 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX(18446744073709551615UL) / 10)
5089 return false; // TableSize overflowed, or mul below might overflow.
5090
5091 bool AllTablesFitInRegister = true;
5092 bool HasIllegalType = false;
5093 for (const auto &I : ResultTypes) {
5094 Type *Ty = I.second;
5095
5096 // Saturate this flag to true.
5097 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
5098
5099 // Saturate this flag to false.
5100 AllTablesFitInRegister =
5101 AllTablesFitInRegister &&
5102 SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
5103
5104 // If both flags saturate, we're done. NOTE: This *only* works with
5105 // saturating flags, and all flags have to saturate first due to the
5106 // non-deterministic behavior of iterating over a dense map.
5107 if (HasIllegalType && !AllTablesFitInRegister)
5108 break;
5109 }
5110
5111 // If each table would fit in a register, we should build it anyway.
5112 if (AllTablesFitInRegister)
5113 return true;
5114
5115 // Don't build a table that doesn't fit in-register if it has illegal types.
5116 if (HasIllegalType)
5117 return false;
5118
5119 // The table density should be at least 40%. This is the same criterion as for
5120 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
5121 // FIXME: Find the best cut-off.
5122 return SI->getNumCases() * 10 >= TableSize * 4;
5123}
5124
5125/// Try to reuse the switch table index compare. Following pattern:
5126/// \code
5127/// if (idx < tablesize)
5128/// r = table[idx]; // table does not contain default_value
5129/// else
5130/// r = default_value;
5131/// if (r != default_value)
5132/// ...
5133/// \endcode
5134/// Is optimized to:
5135/// \code
5136/// cond = idx < tablesize;
5137/// if (cond)
5138/// r = table[idx];
5139/// else
5140/// r = default_value;
5141/// if (cond)
5142/// ...
5143/// \endcode
5144/// Jump threading will then eliminate the second if(cond).
5145static void reuseTableCompare(
5146 User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch,
5147 Constant *DefaultValue,
5148 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) {
5149 ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
5150 if (!CmpInst)
5151 return;
5152
5153 // We require that the compare is in the same block as the phi so that jump
5154 // threading can do its work afterwards.
5155 if (CmpInst->getParent() != PhiBlock)
5156 return;
5157
5158 Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
5159 if (!CmpOp1)
5160 return;
5161
5162 Value *RangeCmp = RangeCheckBranch->getCondition();
5163 Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
5164 Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
5165
5166 // Check if the compare with the default value is constant true or false.
5167 Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5168 DefaultValue, CmpOp1, true);
5169 if (DefaultConst != TrueConst && DefaultConst != FalseConst)
5170 return;
5171
5172 // Check if the compare with the case values is distinct from the default
5173 // compare result.
5174 for (auto ValuePair : Values) {
5175 Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5176 ValuePair.second, CmpOp1, true);
5177 if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst))
5178 return;
5179 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5180, __extension__ __PRETTY_FUNCTION__))
5180 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5180, __extension__ __PRETTY_FUNCTION__))
;
5181 }
5182
5183 // Check if the branch instruction dominates the phi node. It's a simple
5184 // dominance check, but sufficient for our needs.
5185 // Although this check is invariant in the calling loops, it's better to do it
5186 // at this late stage. Practically we do it at most once for a switch.
5187 BasicBlock *BranchBlock = RangeCheckBranch->getParent();
5188 for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) {
5189 BasicBlock *Pred = *PI;
5190 if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
5191 return;
5192 }
5193
5194 if (DefaultConst == FalseConst) {
5195 // The compare yields the same result. We can replace it.
5196 CmpInst->replaceAllUsesWith(RangeCmp);
5197 ++NumTableCmpReuses;
5198 } else {
5199 // The compare yields the same result, just inverted. We can replace it.
5200 Value *InvertedTableCmp = BinaryOperator::CreateXor(
5201 RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
5202 RangeCheckBranch);
5203 CmpInst->replaceAllUsesWith(InvertedTableCmp);
5204 ++NumTableCmpReuses;
5205 }
5206}
5207
5208/// If the switch is only used to initialize one or more phi nodes in a common
5209/// successor block with different constant values, replace the switch with
5210/// lookup tables.
5211static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
5212 const DataLayout &DL,
5213 const TargetTransformInfo &TTI) {
5214 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5214, __extension__ __PRETTY_FUNCTION__))
;
5215
5216 Function *Fn = SI->getParent()->getParent();
5217 // Only build lookup table when we have a target that supports it or the
5218 // attribute is not set.
5219 if (!TTI.shouldBuildLookupTables() ||
5220 (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true"))
5221 return false;
5222
5223 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
5224 // split off a dense part and build a lookup table for that.
5225
5226 // FIXME: This creates arrays of GEPs to constant strings, which means each
5227 // GEP needs a runtime relocation in PIC code. We should just build one big
5228 // string and lookup indices into that.
5229
5230 // Ignore switches with less than three cases. Lookup tables will not make
5231 // them faster, so we don't analyze them.
5232 if (SI->getNumCases() < 3)
5233 return false;
5234
5235 // Figure out the corresponding result for each case value and phi node in the
5236 // common destination, as well as the min and max case values.
5237 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5237, __extension__ __PRETTY_FUNCTION__))
;
5238 SwitchInst::CaseIt CI = SI->case_begin();
5239 ConstantInt *MinCaseVal = CI->getCaseValue();
5240 ConstantInt *MaxCaseVal = CI->getCaseValue();
5241
5242 BasicBlock *CommonDest = nullptr;
5243
5244 using ResultListTy = SmallVector<std::pair<ConstantInt *, Constant *>, 4>;
5245 SmallDenseMap<PHINode *, ResultListTy> ResultLists;
5246
5247 SmallDenseMap<PHINode *, Constant *> DefaultResults;
5248 SmallDenseMap<PHINode *, Type *> ResultTypes;
5249 SmallVector<PHINode *, 4> PHIs;
5250
5251 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
5252 ConstantInt *CaseVal = CI->getCaseValue();
5253 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
5254 MinCaseVal = CaseVal;
5255 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
5256 MaxCaseVal = CaseVal;
5257
5258 // Resulting value at phi nodes for this case value.
5259 using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
5260 ResultsTy Results;
5261 if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
5262 Results, DL, TTI))
5263 return false;
5264
5265 // Append the result from this case to the list for each phi.
5266 for (const auto &I : Results) {
5267 PHINode *PHI = I.first;
5268 Constant *Value = I.second;
5269 if (!ResultLists.count(PHI))
5270 PHIs.push_back(PHI);
5271 ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
5272 }
5273 }
5274
5275 // Keep track of the result types.
5276 for (PHINode *PHI : PHIs) {
5277 ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
5278 }
5279
5280 uint64_t NumResults = ResultLists[PHIs[0]].size();
5281 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
5282 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
5283 bool TableHasHoles = (NumResults < TableSize);
5284
5285 // If the table has holes, we need a constant result for the default case
5286 // or a bitmask that fits in a register.
5287 SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
5288 bool HasDefaultResults =
5289 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
5290 DefaultResultsList, DL, TTI);
5291
5292 bool NeedMask = (TableHasHoles && !HasDefaultResults);
5293 if (NeedMask) {
5294 // As an extra penalty for the validity test we require more cases.
5295 if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
5296 return false;
5297 if (!DL.fitsInLegalInteger(TableSize))
5298 return false;
5299 }
5300
5301 for (const auto &I : DefaultResultsList) {
5302 PHINode *PHI = I.first;
5303 Constant *Result = I.second;
5304 DefaultResults[PHI] = Result;
5305 }
5306
5307 if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
5308 return false;
5309
5310 // Create the BB that does the lookups.
5311 Module &Mod = *CommonDest->getParent()->getParent();
5312 BasicBlock *LookupBB = BasicBlock::Create(
5313 Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest);
5314
5315 // Compute the table index value.
5316 Builder.SetInsertPoint(SI);
5317 Value *TableIndex;
5318 if (MinCaseVal->isNullValue())
5319 TableIndex = SI->getCondition();
5320 else
5321 TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
5322 "switch.tableidx");
5323
5324 // Compute the maximum table size representable by the integer type we are
5325 // switching upon.
5326 unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
5327 uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX(18446744073709551615UL) : 1ULL << CaseSize;
5328 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5330, __extension__ __PRETTY_FUNCTION__))
5329 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5330, __extension__ __PRETTY_FUNCTION__))
5330 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5330, __extension__ __PRETTY_FUNCTION__))
;
5331
5332 // If the default destination is unreachable, or if the lookup table covers
5333 // all values of the conditional variable, branch directly to the lookup table
5334 // BB. Otherwise, check that the condition is within the case range.
5335 const bool DefaultIsReachable =
5336 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
5337 const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
5338 BranchInst *RangeCheckBranch = nullptr;
5339
5340 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5341 Builder.CreateBr(LookupBB);
5342 // Note: We call removeProdecessor later since we need to be able to get the
5343 // PHI value for the default case in case we're using a bit mask.
5344 } else {
5345 Value *Cmp = Builder.CreateICmpULT(
5346 TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
5347 RangeCheckBranch =
5348 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
5349 }
5350
5351 // Populate the BB that does the lookups.
5352 Builder.SetInsertPoint(LookupBB);
5353
5354 if (NeedMask) {
5355 // Before doing the lookup, we do the hole check. The LookupBB is therefore
5356 // re-purposed to do the hole check, and we create a new LookupBB.
5357 BasicBlock *MaskBB = LookupBB;
5358 MaskBB->setName("switch.hole_check");
5359 LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup",
5360 CommonDest->getParent(), CommonDest);
5361
5362 // Make the mask's bitwidth at least 8-bit and a power-of-2 to avoid
5363 // unnecessary illegal types.
5364 uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
5365 APInt MaskInt(TableSizePowOf2, 0);
5366 APInt One(TableSizePowOf2, 1);
5367 // Build bitmask; fill in a 1 bit for every case.
5368 const ResultListTy &ResultList = ResultLists[PHIs[0]];
5369 for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
5370 uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue())
5371 .getLimitedValue();
5372 MaskInt |= One << Idx;
5373 }
5374 ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
5375
5376 // Get the TableIndex'th bit of the bitmask.
5377 // If this bit is 0 (meaning hole) jump to the default destination,
5378 // else continue with table lookup.
5379 IntegerType *MapTy = TableMask->getType();
5380 Value *MaskIndex =
5381 Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex");
5382 Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted");
5383 Value *LoBit = Builder.CreateTrunc(
5384 Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit");
5385 Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
5386
5387 Builder.SetInsertPoint(LookupBB);
5388 AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
5389 }
5390
5391 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5392 // We cached PHINodes in PHIs. To avoid accessing deleted PHINodes later,
5393 // do not delete PHINodes here.
5394 SI->getDefaultDest()->removePredecessor(SI->getParent(),
5395 /*DontDeleteUselessPHIs=*/true);
5396 }
5397
5398 bool ReturnedEarly = false;
5399 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
5400 PHINode *PHI = PHIs[I];
5401 const ResultListTy &ResultList = ResultLists[PHI];
5402
5403 // If using a bitmask, use any value to fill the lookup table holes.
5404 Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
5405 StringRef FuncName = Fn->getName();
5406 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL,
5407 FuncName);
5408
5409 Value *Result = Table.BuildLookup(TableIndex, Builder);
5410
5411 // If the result is used to return immediately from the function, we want to
5412 // do that right here.
5413 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) &&
5414 PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) {
5415 Builder.CreateRet(Result);
5416 ReturnedEarly = true;
5417 break;
5418 }
5419
5420 // Do a small peephole optimization: re-use the switch table compare if
5421 // possible.
5422 if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
5423 BasicBlock *PhiBlock = PHI->getParent();
5424 // Search for compare instructions which use the phi.
5425 for (auto *User : PHI->users()) {
5426 reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
5427 }
5428 }
5429
5430 PHI->addIncoming(Result, LookupBB);
5431 }
5432
5433 if (!ReturnedEarly)
5434 Builder.CreateBr(CommonDest);
5435
5436 // Remove the switch.
5437 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
5438 BasicBlock *Succ = SI->getSuccessor(i);
5439
5440 if (Succ == SI->getDefaultDest())
5441 continue;
5442 Succ->removePredecessor(SI->getParent());
5443 }
5444 SI->eraseFromParent();
5445
5446 ++NumLookupTables;
5447 if (NeedMask)
5448 ++NumLookupTablesHoles;
5449 return true;
5450}
5451
5452static bool isSwitchDense(ArrayRef<int64_t> Values) {
5453 // See also SelectionDAGBuilder::isDense(), which this function was based on.
5454 uint64_t Diff = (uint64_t)Values.back() - (uint64_t)Values.front();
5455 uint64_t Range = Diff + 1;
5456 uint64_t NumCases = Values.size();
5457 // 40% is the default density for building a jump table in optsize/minsize mode.
5458 uint64_t MinDensity = 40;
5459
5460 return NumCases * 100 >= Range * MinDensity;
5461}
5462
5463/// Try to transform a switch that has "holes" in it to a contiguous sequence
5464/// of cases.
5465///
5466/// A switch such as: switch(i) {case 5: case 9: case 13: case 17:} can be
5467/// range-reduced to: switch ((i-5) / 4) {case 0: case 1: case 2: case 3:}.
5468///
5469/// This converts a sparse switch into a dense switch which allows better
5470/// lowering and could also allow transforming into a lookup table.
5471static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
5472 const DataLayout &DL,
5473 const TargetTransformInfo &TTI) {
5474 auto *CondTy = cast<IntegerType>(SI->getCondition()->getType());
5475 if (CondTy->getIntegerBitWidth() > 64 ||
5476 !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
5477 return false;
5478 // Only bother with this optimization if there are more than 3 switch cases;
5479 // SDAG will only bother creating jump tables for 4 or more cases.
5480 if (SI->getNumCases() < 4)
5481 return false;
5482
5483 // This transform is agnostic to the signedness of the input or case values. We
5484 // can treat the case values as signed or unsigned. We can optimize more common
5485 // cases such as a sequence crossing zero {-4,0,4,8} if we interpret case values
5486 // as signed.
5487 SmallVector<int64_t,4> Values;
5488 for (auto &C : SI->cases())
5489 Values.push_back(C.getCaseValue()->getValue().getSExtValue());
5490 std::sort(Values.begin(), Values.end());
5491
5492 // If the switch is already dense, there's nothing useful to do here.
5493 if (isSwitchDense(Values))
5494 return false;
5495
5496 // First, transform the values such that they start at zero and ascend.
5497 int64_t Base = Values[0];
5498 for (auto &V : Values)
5499 V -= (uint64_t)(Base);
5500
5501 // Now we have signed numbers that have been shifted so that, given enough
5502 // precision, there are no negative values. Since the rest of the transform
5503 // is bitwise only, we switch now to an unsigned representation.
5504 uint64_t GCD = 0;
5505 for (auto &V : Values)
5506 GCD = GreatestCommonDivisor64(GCD, (uint64_t)V);
5507
5508 // This transform can be done speculatively because it is so cheap - it results
5509 // in a single rotate operation being inserted. This can only happen if the
5510 // factor extracted is a power of 2.
5511 // FIXME: If the GCD is an odd number we can multiply by the multiplicative
5512 // inverse of GCD and then perform this transform.
5513 // FIXME: It's possible that optimizing a switch on powers of two might also
5514 // be beneficial - flag values are often powers of two and we could use a CLZ
5515 // as the key function.
5516 if (GCD <= 1 || !isPowerOf2_64(GCD))
5517 // No common divisor found or too expensive to compute key function.
5518 return false;
5519
5520 unsigned Shift = Log2_64(GCD);
5521 for (auto &V : Values)
5522 V = (int64_t)((uint64_t)V >> Shift);
5523
5524 if (!isSwitchDense(Values))
5525 // Transform didn't create a dense switch.
5526 return false;
5527
5528 // The obvious transform is to shift the switch condition right and emit a
5529 // check that the condition actually cleanly divided by GCD, i.e.
5530 // C & (1 << Shift - 1) == 0
5531 // inserting a new CFG edge to handle the case where it didn't divide cleanly.
5532 //
5533 // A cheaper way of doing this is a simple ROTR(C, Shift). This performs the
5534 // shift and puts the shifted-off bits in the uppermost bits. If any of these
5535 // are nonzero then the switch condition will be very large and will hit the
5536 // default case.
5537
5538 auto *Ty = cast<IntegerType>(SI->getCondition()->getType());
5539 Builder.SetInsertPoint(SI);
5540 auto *ShiftC = ConstantInt::get(Ty, Shift);
5541 auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base));
5542 auto *LShr = Builder.CreateLShr(Sub, ShiftC);
5543 auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift);
5544 auto *Rot = Builder.CreateOr(LShr, Shl);
5545 SI->replaceUsesOfWith(SI->getCondition(), Rot);
5546
5547 for (auto Case : SI->cases()) {
5548 auto *Orig = Case.getCaseValue();
5549 auto Sub = Orig->getValue() - APInt(Ty->getBitWidth(), Base);
5550 Case.setValue(
5551 cast<ConstantInt>(ConstantInt::get(Ty, Sub.lshr(ShiftC->getValue()))));
5552 }
5553 return true;
5554}
5555
5556bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
5557 BasicBlock *BB = SI->getParent();
5558
5559 if (isValueEqualityComparison(SI)) {
5560 // If we only have one predecessor, and if it is a branch on this value,
5561 // see if that predecessor totally determines the outcome of this switch.
5562 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5563 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
5564 return simplifyCFG(BB, TTI, Options) | true;
5565
5566 Value *Cond = SI->getCondition();
5567 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
5568 if (SimplifySwitchOnSelect(SI, Select))
5569 return simplifyCFG(BB, TTI, Options) | true;
5570
5571 // If the block only contains the switch, see if we can fold the block
5572 // away into any preds.
5573 BasicBlock::iterator BBI = BB->begin();
5574 // Ignore dbg intrinsics.
5575 while (isa<DbgInfoIntrinsic>(BBI))
5576 ++BBI;
5577 if (SI == &*BBI)
5578 if (FoldValueComparisonIntoPredecessors(SI, Builder))
5579 return simplifyCFG(BB, TTI, Options) | true;
5580 }
5581
5582 // Try to transform the switch into an icmp and a branch.
5583 if (TurnSwitchRangeIntoICmp(SI, Builder))
5584 return simplifyCFG(BB, TTI, Options) | true;
5585
5586 // Remove unreachable cases.
5587 if (eliminateDeadSwitchCases(SI, Options.AC, DL))
5588 return simplifyCFG(BB, TTI, Options) | true;
5589
5590 if (switchToSelect(SI, Builder, DL, TTI))
5591 return simplifyCFG(BB, TTI, Options) | true;
5592
5593 if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI))
5594 return simplifyCFG(BB, TTI, Options) | true;
5595
5596 // The conversion from switch to lookup tables results in difficult-to-analyze
5597 // code and makes pruning branches much harder. This is a problem if the
5598 // switch expression itself can still be restricted as a result of inlining or
5599 // CVP. Therefore, only apply this transformation during late stages of the
5600 // optimisation pipeline.
5601 if (Options.ConvertSwitchToLookupTable &&
5602 SwitchToLookupTable(SI, Builder, DL, TTI))
5603 return simplifyCFG(BB, TTI, Options) | true;
5604
5605 if (ReduceSwitchRange(SI, Builder, DL, TTI))
5606 return simplifyCFG(BB, TTI, Options) | true;
5607
5608 return false;
5609}
5610
5611bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
5612 BasicBlock *BB = IBI->getParent();
5613 bool Changed = false;
5614
5615 // Eliminate redundant destinations.
5616 SmallPtrSet<Value *, 8> Succs;
5617 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
5618 BasicBlock *Dest = IBI->getDestination(i);
5619 if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
5620 Dest->removePredecessor(BB);
5621 IBI->removeDestination(i);
5622 --i;
5623 --e;
5624 Changed = true;
5625 }
5626 }
5627
5628 if (IBI->getNumDestinations() == 0) {
5629 // If the indirectbr has no successors, change it to unreachable.
5630 new UnreachableInst(IBI->getContext(), IBI);
5631 EraseTerminatorInstAndDCECond(IBI);
5632 return true;
5633 }
5634
5635 if (IBI->getNumDestinations() == 1) {
5636 // If the indirectbr has one successor, change it to a direct branch.
5637 BranchInst::Create(IBI->getDestination(0), IBI);
5638 EraseTerminatorInstAndDCECond(IBI);
5639 return true;
5640 }
5641
5642 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
5643 if (SimplifyIndirectBrOnSelect(IBI, SI))
5644 return simplifyCFG(BB, TTI, Options) | true;
5645 }
5646 return Changed;
5647}
5648
5649/// Given an block with only a single landing pad and a unconditional branch
5650/// try to find another basic block which this one can be merged with. This
5651/// handles cases where we have multiple invokes with unique landing pads, but
5652/// a shared handler.
5653///
5654/// We specifically choose to not worry about merging non-empty blocks
5655/// here. That is a PRE/scheduling problem and is best solved elsewhere. In
5656/// practice, the optimizer produces empty landing pad blocks quite frequently
5657/// when dealing with exception dense code. (see: instcombine, gvn, if-else
5658/// sinking in this file)
5659///
5660/// This is primarily a code size optimization. We need to avoid performing
5661/// any transform which might inhibit optimization (such as our ability to
5662/// specialize a particular handler via tail commoning). We do this by not
5663/// merging any blocks which require us to introduce a phi. Since the same
5664/// values are flowing through both blocks, we don't loose any ability to
5665/// specialize. If anything, we make such specialization more likely.
5666///
5667/// TODO - This transformation could remove entries from a phi in the target
5668/// block when the inputs in the phi are the same for the two blocks being
5669/// merged. In some cases, this could result in removal of the PHI entirely.
5670static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
5671 BasicBlock *BB) {
5672 auto Succ = BB->getUniqueSuccessor();
5673 assert(Succ)(static_cast <bool> (Succ) ? void (0) : __assert_fail (
"Succ", "/build/llvm-toolchain-snapshot-7~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5673, __extension__ __PRETTY_FUNCTION__))
;
5674 // If there's a phi in the successor block, we'd likely have to introduce
5675 // a phi into the merged landing pad block.
5676 if (isa<PHINode>(*Succ->begin()))
5677 return false;
5678
5679 for (BasicBlock *OtherPred : predecessors(Succ)) {
5680 if (BB == OtherPred)
5681 continue;
5682 BasicBlock::iterator I = OtherPred->begin();
5683 LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
5684 if (!LPad2 || !LPad2->isIdenticalTo(LPad))
5685 continue;
5686 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5687 ;
5688 BranchInst *BI2 = dyn_cast<BranchInst>(I);
5689 if (!BI2 || !BI2->isIdenticalTo(BI))
5690 continue;
5691
5692 // We've found an identical block. Update our predecessors to take that
5693 // path instead and make ourselves dead.
5694 SmallSet<BasicBlock *, 16> Preds;
5695 Preds.insert(pred_begin(BB), pred_end(BB));
5696 for (BasicBlock *Pred : Preds) {
5697 InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
5698 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5699, __extension__ __PRETTY_FUNCTION__))
5699 "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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5699, __extension__ __PRETTY_FUNCTION__))
;
5700 II->setUnwindDest(OtherPred);
5701 }
5702
5703 // The debug info in OtherPred doesn't cover the merged control flow that
5704 // used to go through BB. We need to delete it or update it.
5705 for (auto I = OtherPred->begin(), E = OtherPred->end(); I != E;) {
5706 Instruction &Inst = *I;
5707 I++;
5708 if (isa<DbgInfoIntrinsic>(Inst))
5709 Inst.eraseFromParent();
5710 }
5711
5712 SmallSet<BasicBlock *, 16> Succs;
5713 Succs.insert(succ_begin(BB), succ_end(BB));
5714 for (BasicBlock *Succ : Succs) {
5715 Succ->removePredecessor(BB);
5716 }
5717
5718 IRBuilder<> Builder(BI);
5719 Builder.CreateUnreachable();
5720 BI->eraseFromParent();
5721 return true;
5722 }
5723 return false;
5724}
5725
5726bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI,
5727 IRBuilder<> &Builder) {
5728 BasicBlock *BB = BI->getParent();
5729 BasicBlock *Succ = BI->getSuccessor(0);
5730
5731 // If the Terminator is the only non-phi instruction, simplify the block.
5732 // If LoopHeader is provided, check if the block or its successor is a loop
5733 // header. (This is for early invocations before loop simplify and
5734 // vectorization to keep canonical loop forms for nested loops. These blocks
5735 // can be eliminated when the pass is invoked later in the back-end.)
5736 // Note that if BB has only one predecessor then we do not introduce new
5737 // backedge, so we can eliminate BB.
5738 bool NeedCanonicalLoop =
5739 Options.NeedCanonicalLoop &&
5740 (LoopHeaders && std::distance(pred_begin(BB), pred_end(BB)) > 1 &&
5741 (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
5742 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
5743 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
5744 !NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB))
5745 return true;
5746
5747 // If the only instruction in the block is a seteq/setne comparison against a
5748 // constant, try to simplify the block.
5749 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
5750 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
5751 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5752 ;
5753 if (I->isTerminator() &&
5754 tryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, DL, TTI, Options))
5755 return true;
5756 }
5757
5758 // See if we can merge an empty landing pad block with another which is
5759 // equivalent.
5760 if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
5761 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
5762 ;
5763 if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB))
5764 return true;
5765 }
5766
5767 // If this basic block is ONLY a compare and a branch, and if a predecessor
5768 // branches to us and our successor, fold the comparison into the
5769 // predecessor and use logical operations to update the incoming value
5770 // for PHI nodes in common successor.
5771 if (FoldBranchToCommonDest(BI, Options.BonusInstThreshold))
5772 return simplifyCFG(BB, TTI, Options) | true;
5773 return false;
5774}
5775
5776static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
5777 BasicBlock *PredPred = nullptr;
5778 for (auto *P : predecessors(BB)) {
5779 BasicBlock *PPred = P->getSinglePredecessor();
5780 if (!PPred || (PredPred && PredPred != PPred))
5781 return nullptr;
5782 PredPred = PPred;
5783 }
5784 return PredPred;
5785}
5786
5787bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
5788 BasicBlock *BB = BI->getParent();
5789
5790 // Conditional branch
5791 if (isValueEqualityComparison(BI)) {
5792 // If we only have one predecessor, and if it is a branch on this value,
5793 // see if that predecessor totally determines the outcome of this
5794 // switch.
5795 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
5796 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
5797 return simplifyCFG(BB, TTI, Options) | true;
5798
5799 // This block must be empty, except for the setcond inst, if it exists.
5800 // Ignore dbg intrinsics.
5801 BasicBlock::iterator I = BB->begin();
5802 // Ignore dbg intrinsics.
5803 while (isa<DbgInfoIntrinsic>(I))
5804 ++I;
5805 if (&*I == BI) {
5806 if (FoldValueComparisonIntoPredecessors(BI, Builder))
5807 return simplifyCFG(BB, TTI, Options) | true;
5808 } else if (&*I == cast<Instruction>(BI->getCondition())) {
5809 ++I;
5810 // Ignore dbg intrinsics.
5811 while (isa<DbgInfoIntrinsic>(I))
5812 ++I;
5813 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
5814 return simplifyCFG(BB, TTI, Options) | true;
5815 }
5816 }
5817
5818 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
5819 if (SimplifyBranchOnICmpChain(BI, Builder, DL))
5820 return true;
5821
5822 // If this basic block has a single dominating predecessor block and the
5823 // dominating block's condition implies BI's condition, we know the direction
5824 // of the BI branch.
5825 if (BasicBlock *Dom = BB->getSinglePredecessor()) {
5826 auto *PBI = dyn_cast_or_null<BranchInst>(Dom->getTerminator());
5827 if (PBI && PBI->isConditional() &&
5828 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
5829 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~svn326551/lib/Transforms/Utils/SimplifyCFG.cpp"
, 5829, __extension__ __PRETTY_FUNCTION__))
;
5830 bool CondIsTrue = PBI->getSuccessor(0) == BB;
5831 Optional<bool> Implication = isImpliedCondition(
5832 PBI->getCondition(), BI->getCondition(), DL, CondIsTrue);
5833 if (Implication) {
5834 // Turn this into a branch on constant.
5835 auto *OldCond = BI->getCondition();
5836 ConstantInt *CI = *Implication
5837 ? ConstantInt::getTrue(BB->getContext())
5838 : ConstantInt::getFalse(BB->getContext());
5839 BI->setCondition(CI);
5840 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
5841 return simplifyCFG(BB, TTI, Options) | true;
5842 }
5843 }
5844 }
5845
5846 // If this basic block is ONLY a compare and a branch, and if a predecessor
5847 // branches to us and one of our successors, fold the comparison into the
5848 // predecessor and use logical operations to pick the right destination.
5849 if (FoldBranchToCommonDest(BI, Options.BonusInstThreshold))
5850 return simplifyCFG(BB, TTI, Options) | true;
5851
5852 // We have a conditional branch to two blocks that are only reachable
5853 // from BI. We know that the condbr dominates the two blocks, so see if
5854 // there is any identical code in the "then" and "else" blocks. If so, we
5855 // can hoist it up to the branching block.
5856 if (BI->getSuccessor(0)->getSinglePredecessor()) {
5857 if (BI->getSuccessor(1)->getSinglePredecessor()) {
5858 if (HoistThenElseCodeToIf(BI, TTI))
5859 return simplifyCFG(BB, TTI, Options) | true;
5860 } else {
5861 // If Successor #1 has multiple preds, we may be able to conditionally
5862 // execute Successor #0 if it branches to Successor #1.
5863 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();