1 //===- Local.cpp - Functions to perform local transformations -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This family of functions perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/Utils/Local.h"
16 #include "llvm/ADT/APInt.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/DenseMapInfo.h"
19 #include "llvm/ADT/DenseSet.h"
20 #include "llvm/ADT/Hashing.h"
21 #include "llvm/ADT/None.h"
22 #include "llvm/ADT/Optional.h"
23 #include "llvm/ADT/STLExtras.h"
24 #include "llvm/ADT/SetVector.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/Statistic.h"
28 #include "llvm/ADT/TinyPtrVector.h"
29 #include "llvm/Analysis/ConstantFolding.h"
30 #include "llvm/Analysis/EHPersonalities.h"
31 #include "llvm/Analysis/InstructionSimplify.h"
32 #include "llvm/Analysis/LazyValueInfo.h"
33 #include "llvm/Analysis/MemoryBuiltins.h"
34 #include "llvm/Analysis/TargetLibraryInfo.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/BinaryFormat/Dwarf.h"
37 #include "llvm/IR/Argument.h"
38 #include "llvm/IR/Attributes.h"
39 #include "llvm/IR/BasicBlock.h"
40 #include "llvm/IR/CFG.h"
41 #include "llvm/IR/CallSite.h"
42 #include "llvm/IR/Constant.h"
43 #include "llvm/IR/ConstantRange.h"
44 #include "llvm/IR/Constants.h"
45 #include "llvm/IR/DIBuilder.h"
46 #include "llvm/IR/DataLayout.h"
47 #include "llvm/IR/DebugInfoMetadata.h"
48 #include "llvm/IR/DebugLoc.h"
49 #include "llvm/IR/DerivedTypes.h"
50 #include "llvm/IR/Dominators.h"
51 #include "llvm/IR/Function.h"
52 #include "llvm/IR/GetElementPtrTypeIterator.h"
53 #include "llvm/IR/GlobalObject.h"
54 #include "llvm/IR/IRBuilder.h"
55 #include "llvm/IR/InstrTypes.h"
56 #include "llvm/IR/Instruction.h"
57 #include "llvm/IR/Instructions.h"
58 #include "llvm/IR/IntrinsicInst.h"
59 #include "llvm/IR/Intrinsics.h"
60 #include "llvm/IR/LLVMContext.h"
61 #include "llvm/IR/MDBuilder.h"
62 #include "llvm/IR/Metadata.h"
63 #include "llvm/IR/Module.h"
64 #include "llvm/IR/Operator.h"
65 #include "llvm/IR/PatternMatch.h"
66 #include "llvm/IR/Type.h"
67 #include "llvm/IR/Use.h"
68 #include "llvm/IR/User.h"
69 #include "llvm/IR/Value.h"
70 #include "llvm/IR/ValueHandle.h"
71 #include "llvm/Support/Casting.h"
72 #include "llvm/Support/Debug.h"
73 #include "llvm/Support/ErrorHandling.h"
74 #include "llvm/Support/KnownBits.h"
75 #include "llvm/Support/raw_ostream.h"
76 #include "llvm/Transforms/Utils/ValueMapper.h"
86 using namespace llvm::PatternMatch;
88 #define DEBUG_TYPE "local"
90 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
92 //===----------------------------------------------------------------------===//
93 // Local constant propagation.
96 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
97 /// constant value, convert it into an unconditional branch to the constant
98 /// destination. This is a nontrivial operation because the successors of this
99 /// basic block must have their PHI nodes updated.
100 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
101 /// conditions and indirectbr addresses this might make dead if
102 /// DeleteDeadConditions is true.
103 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
104 const TargetLibraryInfo *TLI,
105 DeferredDominance *DDT) {
106 TerminatorInst *T = BB->getTerminator();
107 IRBuilder<> Builder(T);
109 // Branch - See if we are conditional jumping on constant
110 if (auto *BI = dyn_cast<BranchInst>(T)) {
111 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
112 BasicBlock *Dest1 = BI->getSuccessor(0);
113 BasicBlock *Dest2 = BI->getSuccessor(1);
115 if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
116 // Are we branching on constant?
117 // YES. Change to unconditional branch...
118 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
119 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
121 // Let the basic block know that we are letting go of it. Based on this,
122 // it will adjust it's PHI nodes.
123 OldDest->removePredecessor(BB);
125 // Replace the conditional branch with an unconditional one.
126 Builder.CreateBr(Destination);
127 BI->eraseFromParent();
129 DDT->deleteEdge(BB, OldDest);
133 if (Dest2 == Dest1) { // Conditional branch to same location?
134 // This branch matches something like this:
135 // br bool %cond, label %Dest, label %Dest
136 // and changes it into: br label %Dest
138 // Let the basic block know that we are letting go of one copy of it.
139 assert(BI->getParent() && "Terminator not inserted in block!");
140 Dest1->removePredecessor(BI->getParent());
142 // Replace the conditional branch with an unconditional one.
143 Builder.CreateBr(Dest1);
144 Value *Cond = BI->getCondition();
145 BI->eraseFromParent();
146 if (DeleteDeadConditions)
147 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
153 if (auto *SI = dyn_cast<SwitchInst>(T)) {
154 // If we are switching on a constant, we can convert the switch to an
155 // unconditional branch.
156 auto *CI = dyn_cast<ConstantInt>(SI->getCondition());
157 BasicBlock *DefaultDest = SI->getDefaultDest();
158 BasicBlock *TheOnlyDest = DefaultDest;
160 // If the default is unreachable, ignore it when searching for TheOnlyDest.
161 if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
162 SI->getNumCases() > 0) {
163 TheOnlyDest = SI->case_begin()->getCaseSuccessor();
166 // Figure out which case it goes to.
167 for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
168 // Found case matching a constant operand?
169 if (i->getCaseValue() == CI) {
170 TheOnlyDest = i->getCaseSuccessor();
174 // Check to see if this branch is going to the same place as the default
175 // dest. If so, eliminate it as an explicit compare.
176 if (i->getCaseSuccessor() == DefaultDest) {
177 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
178 unsigned NCases = SI->getNumCases();
179 // Fold the case metadata into the default if there will be any branches
180 // left, unless the metadata doesn't match the switch.
181 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
182 // Collect branch weights into a vector.
183 SmallVector<uint32_t, 8> Weights;
184 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
186 auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
187 Weights.push_back(CI->getValue().getZExtValue());
189 // Merge weight of this case to the default weight.
190 unsigned idx = i->getCaseIndex();
191 Weights[0] += Weights[idx+1];
192 // Remove weight for this case.
193 std::swap(Weights[idx+1], Weights.back());
195 SI->setMetadata(LLVMContext::MD_prof,
196 MDBuilder(BB->getContext()).
197 createBranchWeights(Weights));
199 // Remove this entry.
200 BasicBlock *ParentBB = SI->getParent();
201 DefaultDest->removePredecessor(ParentBB);
202 i = SI->removeCase(i);
205 DDT->deleteEdge(ParentBB, DefaultDest);
209 // Otherwise, check to see if the switch only branches to one destination.
210 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
212 if (i->getCaseSuccessor() != TheOnlyDest)
213 TheOnlyDest = nullptr;
215 // Increment this iterator as we haven't removed the case.
219 if (CI && !TheOnlyDest) {
220 // Branching on a constant, but not any of the cases, go to the default
222 TheOnlyDest = SI->getDefaultDest();
225 // If we found a single destination that we can fold the switch into, do so
228 // Insert the new branch.
229 Builder.CreateBr(TheOnlyDest);
230 BasicBlock *BB = SI->getParent();
231 std::vector <DominatorTree::UpdateType> Updates;
233 Updates.reserve(SI->getNumSuccessors() - 1);
235 // Remove entries from PHI nodes which we no longer branch to...
236 for (BasicBlock *Succ : SI->successors()) {
237 // Found case matching a constant operand?
238 if (Succ == TheOnlyDest) {
239 TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
241 Succ->removePredecessor(BB);
243 Updates.push_back({DominatorTree::Delete, BB, Succ});
247 // Delete the old switch.
248 Value *Cond = SI->getCondition();
249 SI->eraseFromParent();
250 if (DeleteDeadConditions)
251 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
253 DDT->applyUpdates(Updates);
257 if (SI->getNumCases() == 1) {
258 // Otherwise, we can fold this switch into a conditional branch
259 // instruction if it has only one non-default destination.
260 auto FirstCase = *SI->case_begin();
261 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
262 FirstCase.getCaseValue(), "cond");
264 // Insert the new branch.
265 BranchInst *NewBr = Builder.CreateCondBr(Cond,
266 FirstCase.getCaseSuccessor(),
267 SI->getDefaultDest());
268 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
269 if (MD && MD->getNumOperands() == 3) {
270 ConstantInt *SICase =
271 mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
273 mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
274 assert(SICase && SIDef);
275 // The TrueWeight should be the weight for the single case of SI.
276 NewBr->setMetadata(LLVMContext::MD_prof,
277 MDBuilder(BB->getContext()).
278 createBranchWeights(SICase->getValue().getZExtValue(),
279 SIDef->getValue().getZExtValue()));
282 // Update make.implicit metadata to the newly-created conditional branch.
283 MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
285 NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
287 // Delete the old switch.
288 SI->eraseFromParent();
294 if (auto *IBI = dyn_cast<IndirectBrInst>(T)) {
295 // indirectbr blockaddress(@F, @BB) -> br label @BB
297 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
298 BasicBlock *TheOnlyDest = BA->getBasicBlock();
299 std::vector <DominatorTree::UpdateType> Updates;
301 Updates.reserve(IBI->getNumDestinations() - 1);
303 // Insert the new branch.
304 Builder.CreateBr(TheOnlyDest);
306 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
307 if (IBI->getDestination(i) == TheOnlyDest) {
308 TheOnlyDest = nullptr;
310 BasicBlock *ParentBB = IBI->getParent();
311 BasicBlock *DestBB = IBI->getDestination(i);
312 DestBB->removePredecessor(ParentBB);
314 Updates.push_back({DominatorTree::Delete, ParentBB, DestBB});
317 Value *Address = IBI->getAddress();
318 IBI->eraseFromParent();
319 if (DeleteDeadConditions)
320 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
322 // If we didn't find our destination in the IBI successor list, then we
323 // have undefined behavior. Replace the unconditional branch with an
324 // 'unreachable' instruction.
326 BB->getTerminator()->eraseFromParent();
327 new UnreachableInst(BB->getContext(), BB);
331 DDT->applyUpdates(Updates);
339 //===----------------------------------------------------------------------===//
340 // Local dead code elimination.
343 /// isInstructionTriviallyDead - Return true if the result produced by the
344 /// instruction is not used, and the instruction has no side effects.
346 bool llvm::isInstructionTriviallyDead(Instruction *I,
347 const TargetLibraryInfo *TLI) {
350 return wouldInstructionBeTriviallyDead(I, TLI);
353 bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
354 const TargetLibraryInfo *TLI) {
355 if (isa<TerminatorInst>(I))
358 // We don't want the landingpad-like instructions removed by anything this
363 // We don't want debug info removed by anything this general, unless
364 // debug info is empty.
365 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
366 if (DDI->getAddress())
370 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
376 if (!I->mayHaveSideEffects())
379 // Special case intrinsics that "may have side effects" but can be deleted
381 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
382 // Safe to delete llvm.stacksave if dead.
383 if (II->getIntrinsicID() == Intrinsic::stacksave)
386 // Lifetime intrinsics are dead when their right-hand is undef.
387 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
388 II->getIntrinsicID() == Intrinsic::lifetime_end)
389 return isa<UndefValue>(II->getArgOperand(1));
391 // Assumptions are dead if their condition is trivially true. Guards on
392 // true are operationally no-ops. In the future we can consider more
393 // sophisticated tradeoffs for guards considering potential for check
394 // widening, but for now we keep things simple.
395 if (II->getIntrinsicID() == Intrinsic::assume ||
396 II->getIntrinsicID() == Intrinsic::experimental_guard) {
397 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
398 return !Cond->isZero();
404 if (isAllocLikeFn(I, TLI))
407 if (CallInst *CI = isFreeCall(I, TLI))
408 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
409 return C->isNullValue() || isa<UndefValue>(C);
411 if (CallSite CS = CallSite(I))
412 if (isMathLibCallNoop(CS, TLI))
418 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
419 /// trivially dead instruction, delete it. If that makes any of its operands
420 /// trivially dead, delete them too, recursively. Return true if any
421 /// instructions were deleted.
423 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
424 const TargetLibraryInfo *TLI) {
425 Instruction *I = dyn_cast<Instruction>(V);
426 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
429 SmallVector<Instruction*, 16> DeadInsts;
430 DeadInsts.push_back(I);
433 I = DeadInsts.pop_back_val();
434 salvageDebugInfo(*I);
436 // Null out all of the instruction's operands to see if any operand becomes
438 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
439 Value *OpV = I->getOperand(i);
440 I->setOperand(i, nullptr);
442 if (!OpV->use_empty()) continue;
444 // If the operand is an instruction that became dead as we nulled out the
445 // operand, and if it is 'trivially' dead, delete it in a future loop
447 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
448 if (isInstructionTriviallyDead(OpI, TLI))
449 DeadInsts.push_back(OpI);
452 I->eraseFromParent();
453 } while (!DeadInsts.empty());
458 /// areAllUsesEqual - Check whether the uses of a value are all the same.
459 /// This is similar to Instruction::hasOneUse() except this will also return
460 /// true when there are no uses or multiple uses that all refer to the same
462 static bool areAllUsesEqual(Instruction *I) {
463 Value::user_iterator UI = I->user_begin();
464 Value::user_iterator UE = I->user_end();
469 for (++UI; UI != UE; ++UI) {
476 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
477 /// dead PHI node, due to being a def-use chain of single-use nodes that
478 /// either forms a cycle or is terminated by a trivially dead instruction,
479 /// delete it. If that makes any of its operands trivially dead, delete them
480 /// too, recursively. Return true if a change was made.
481 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
482 const TargetLibraryInfo *TLI) {
483 SmallPtrSet<Instruction*, 4> Visited;
484 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
485 I = cast<Instruction>(*I->user_begin())) {
487 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
489 // If we find an instruction more than once, we're on a cycle that
490 // won't prove fruitful.
491 if (!Visited.insert(I).second) {
492 // Break the cycle and delete the instruction and its operands.
493 I->replaceAllUsesWith(UndefValue::get(I->getType()));
494 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
502 simplifyAndDCEInstruction(Instruction *I,
503 SmallSetVector<Instruction *, 16> &WorkList,
504 const DataLayout &DL,
505 const TargetLibraryInfo *TLI) {
506 if (isInstructionTriviallyDead(I, TLI)) {
507 salvageDebugInfo(*I);
509 // Null out all of the instruction's operands to see if any operand becomes
511 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
512 Value *OpV = I->getOperand(i);
513 I->setOperand(i, nullptr);
515 if (!OpV->use_empty() || I == OpV)
518 // If the operand is an instruction that became dead as we nulled out the
519 // operand, and if it is 'trivially' dead, delete it in a future loop
521 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
522 if (isInstructionTriviallyDead(OpI, TLI))
523 WorkList.insert(OpI);
526 I->eraseFromParent();
531 if (Value *SimpleV = SimplifyInstruction(I, DL)) {
532 // Add the users to the worklist. CAREFUL: an instruction can use itself,
533 // in the case of a phi node.
534 for (User *U : I->users()) {
536 WorkList.insert(cast<Instruction>(U));
540 // Replace the instruction with its simplified value.
541 bool Changed = false;
542 if (!I->use_empty()) {
543 I->replaceAllUsesWith(SimpleV);
546 if (isInstructionTriviallyDead(I, TLI)) {
547 I->eraseFromParent();
555 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
556 /// simplify any instructions in it and recursively delete dead instructions.
558 /// This returns true if it changed the code, note that it can delete
559 /// instructions in other blocks as well in this block.
560 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
561 const TargetLibraryInfo *TLI) {
562 bool MadeChange = false;
563 const DataLayout &DL = BB->getModule()->getDataLayout();
566 // In debug builds, ensure that the terminator of the block is never replaced
567 // or deleted by these simplifications. The idea of simplification is that it
568 // cannot introduce new instructions, and there is no way to replace the
569 // terminator of a block without introducing a new instruction.
570 AssertingVH<Instruction> TerminatorVH(&BB->back());
573 SmallSetVector<Instruction *, 16> WorkList;
574 // Iterate over the original function, only adding insts to the worklist
575 // if they actually need to be revisited. This avoids having to pre-init
576 // the worklist with the entire function's worth of instructions.
577 for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end());
579 assert(!BI->isTerminator());
580 Instruction *I = &*BI;
583 // We're visiting this instruction now, so make sure it's not in the
584 // worklist from an earlier visit.
585 if (!WorkList.count(I))
586 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
589 while (!WorkList.empty()) {
590 Instruction *I = WorkList.pop_back_val();
591 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
596 //===----------------------------------------------------------------------===//
597 // Control Flow Graph Restructuring.
600 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
601 /// method is called when we're about to delete Pred as a predecessor of BB. If
602 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
604 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
605 /// nodes that collapse into identity values. For example, if we have:
606 /// x = phi(1, 0, 0, 0)
609 /// .. and delete the predecessor corresponding to the '1', this will attempt to
610 /// recursively fold the and to 0.
611 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
612 DeferredDominance *DDT) {
613 // This only adjusts blocks with PHI nodes.
614 if (!isa<PHINode>(BB->begin()))
617 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
618 // them down. This will leave us with single entry phi nodes and other phis
619 // that can be removed.
620 BB->removePredecessor(Pred, true);
622 WeakTrackingVH PhiIt = &BB->front();
623 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
624 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
625 Value *OldPhiIt = PhiIt;
627 if (!recursivelySimplifyInstruction(PN))
630 // If recursive simplification ended up deleting the next PHI node we would
631 // iterate to, then our iterator is invalid, restart scanning from the top
633 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
636 DDT->deleteEdge(Pred, BB);
639 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
640 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
641 /// between them, moving the instructions in the predecessor into DestBB and
642 /// deleting the predecessor block.
643 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT,
644 DeferredDominance *DDT) {
645 assert(!(DT && DDT) && "Cannot call with both DT and DDT.");
647 // If BB has single-entry PHI nodes, fold them.
648 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
649 Value *NewVal = PN->getIncomingValue(0);
650 // Replace self referencing PHI with undef, it must be dead.
651 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
652 PN->replaceAllUsesWith(NewVal);
653 PN->eraseFromParent();
656 BasicBlock *PredBB = DestBB->getSinglePredecessor();
657 assert(PredBB && "Block doesn't have a single predecessor!");
659 bool ReplaceEntryBB = false;
660 if (PredBB == &DestBB->getParent()->getEntryBlock())
661 ReplaceEntryBB = true;
663 // Deferred DT update: Collect all the edges that enter PredBB. These
664 // dominator edges will be redirected to DestBB.
665 std::vector <DominatorTree::UpdateType> Updates;
666 if (DDT && !ReplaceEntryBB) {
668 (2 * std::distance(pred_begin(PredBB), pred_end(PredBB))));
669 Updates.push_back({DominatorTree::Delete, PredBB, DestBB});
670 for (auto I = pred_begin(PredBB), E = pred_end(PredBB); I != E; ++I) {
671 Updates.push_back({DominatorTree::Delete, *I, PredBB});
672 // This predecessor of PredBB may already have DestBB as a successor.
673 if (llvm::find(successors(*I), DestBB) == succ_end(*I))
674 Updates.push_back({DominatorTree::Insert, *I, DestBB});
678 // Zap anything that took the address of DestBB. Not doing this will give the
679 // address an invalid value.
680 if (DestBB->hasAddressTaken()) {
681 BlockAddress *BA = BlockAddress::get(DestBB);
682 Constant *Replacement =
683 ConstantInt::get(Type::getInt32Ty(BA->getContext()), 1);
684 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
686 BA->destroyConstant();
689 // Anything that branched to PredBB now branches to DestBB.
690 PredBB->replaceAllUsesWith(DestBB);
692 // Splice all the instructions from PredBB to DestBB.
693 PredBB->getTerminator()->eraseFromParent();
694 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
696 // If the PredBB is the entry block of the function, move DestBB up to
697 // become the entry block after we erase PredBB.
699 DestBB->moveAfter(PredBB);
702 // For some irreducible CFG we end up having forward-unreachable blocks
703 // so check if getNode returns a valid node before updating the domtree.
704 if (DomTreeNode *DTN = DT->getNode(PredBB)) {
705 BasicBlock *PredBBIDom = DTN->getIDom()->getBlock();
706 DT->changeImmediateDominator(DestBB, PredBBIDom);
707 DT->eraseNode(PredBB);
712 DDT->deleteBB(PredBB); // Deferred deletion of BB.
714 // The entry block was removed and there is no external interface for the
715 // dominator tree to be notified of this change. In this corner-case we
716 // recalculate the entire tree.
717 DDT->recalculate(*(DestBB->getParent()));
719 DDT->applyUpdates(Updates);
721 PredBB->eraseFromParent(); // Nuke BB.
725 /// CanMergeValues - Return true if we can choose one of these values to use
726 /// in place of the other. Note that we will always choose the non-undef
728 static bool CanMergeValues(Value *First, Value *Second) {
729 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
732 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
733 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
735 /// Assumption: Succ is the single successor for BB.
736 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
737 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
739 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
740 << Succ->getName() << "\n");
741 // Shortcut, if there is only a single predecessor it must be BB and merging
743 if (Succ->getSinglePredecessor()) return true;
745 // Make a list of the predecessors of BB
746 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
748 // Look at all the phi nodes in Succ, to see if they present a conflict when
749 // merging these blocks
750 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
751 PHINode *PN = cast<PHINode>(I);
753 // If the incoming value from BB is again a PHINode in
754 // BB which has the same incoming value for *PI as PN does, we can
755 // merge the phi nodes and then the blocks can still be merged
756 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
757 if (BBPN && BBPN->getParent() == BB) {
758 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
759 BasicBlock *IBB = PN->getIncomingBlock(PI);
760 if (BBPreds.count(IBB) &&
761 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
762 PN->getIncomingValue(PI))) {
763 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
764 << Succ->getName() << " is conflicting with "
765 << BBPN->getName() << " with regard to common predecessor "
766 << IBB->getName() << "\n");
771 Value* Val = PN->getIncomingValueForBlock(BB);
772 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
773 // See if the incoming value for the common predecessor is equal to the
774 // one for BB, in which case this phi node will not prevent the merging
776 BasicBlock *IBB = PN->getIncomingBlock(PI);
777 if (BBPreds.count(IBB) &&
778 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
779 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
780 << Succ->getName() << " is conflicting with regard to common "
781 << "predecessor " << IBB->getName() << "\n");
791 using PredBlockVector = SmallVector<BasicBlock *, 16>;
792 using IncomingValueMap = DenseMap<BasicBlock *, Value *>;
794 /// Determines the value to use as the phi node input for a block.
796 /// Select between \p OldVal any value that we know flows from \p BB
797 /// to a particular phi on the basis of which one (if either) is not
798 /// undef. Update IncomingValues based on the selected value.
800 /// \param OldVal The value we are considering selecting.
801 /// \param BB The block that the value flows in from.
802 /// \param IncomingValues A map from block-to-value for other phi inputs
803 /// that we have examined.
805 /// \returns the selected value.
806 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
807 IncomingValueMap &IncomingValues) {
808 if (!isa<UndefValue>(OldVal)) {
809 assert((!IncomingValues.count(BB) ||
810 IncomingValues.find(BB)->second == OldVal) &&
811 "Expected OldVal to match incoming value from BB!");
813 IncomingValues.insert(std::make_pair(BB, OldVal));
817 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
818 if (It != IncomingValues.end()) return It->second;
823 /// Create a map from block to value for the operands of a
826 /// Create a map from block to value for each non-undef value flowing
829 /// \param PN The phi we are collecting the map for.
830 /// \param IncomingValues [out] The map from block to value for this phi.
831 static void gatherIncomingValuesToPhi(PHINode *PN,
832 IncomingValueMap &IncomingValues) {
833 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
834 BasicBlock *BB = PN->getIncomingBlock(i);
835 Value *V = PN->getIncomingValue(i);
837 if (!isa<UndefValue>(V))
838 IncomingValues.insert(std::make_pair(BB, V));
842 /// Replace the incoming undef values to a phi with the values
843 /// from a block-to-value map.
845 /// \param PN The phi we are replacing the undefs in.
846 /// \param IncomingValues A map from block to value.
847 static void replaceUndefValuesInPhi(PHINode *PN,
848 const IncomingValueMap &IncomingValues) {
849 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
850 Value *V = PN->getIncomingValue(i);
852 if (!isa<UndefValue>(V)) continue;
854 BasicBlock *BB = PN->getIncomingBlock(i);
855 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
856 if (It == IncomingValues.end()) continue;
858 PN->setIncomingValue(i, It->second);
862 /// Replace a value flowing from a block to a phi with
863 /// potentially multiple instances of that value flowing from the
864 /// block's predecessors to the phi.
866 /// \param BB The block with the value flowing into the phi.
867 /// \param BBPreds The predecessors of BB.
868 /// \param PN The phi that we are updating.
869 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
870 const PredBlockVector &BBPreds,
872 Value *OldVal = PN->removeIncomingValue(BB, false);
873 assert(OldVal && "No entry in PHI for Pred BB!");
875 IncomingValueMap IncomingValues;
877 // We are merging two blocks - BB, and the block containing PN - and
878 // as a result we need to redirect edges from the predecessors of BB
879 // to go to the block containing PN, and update PN
880 // accordingly. Since we allow merging blocks in the case where the
881 // predecessor and successor blocks both share some predecessors,
882 // and where some of those common predecessors might have undef
883 // values flowing into PN, we want to rewrite those values to be
884 // consistent with the non-undef values.
886 gatherIncomingValuesToPhi(PN, IncomingValues);
888 // If this incoming value is one of the PHI nodes in BB, the new entries
889 // in the PHI node are the entries from the old PHI.
890 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
891 PHINode *OldValPN = cast<PHINode>(OldVal);
892 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
893 // Note that, since we are merging phi nodes and BB and Succ might
894 // have common predecessors, we could end up with a phi node with
895 // identical incoming branches. This will be cleaned up later (and
896 // will trigger asserts if we try to clean it up now, without also
897 // simplifying the corresponding conditional branch).
898 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
899 Value *PredVal = OldValPN->getIncomingValue(i);
900 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
903 // And add a new incoming value for this predecessor for the
904 // newly retargeted branch.
905 PN->addIncoming(Selected, PredBB);
908 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
909 // Update existing incoming values in PN for this
910 // predecessor of BB.
911 BasicBlock *PredBB = BBPreds[i];
912 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
915 // And add a new incoming value for this predecessor for the
916 // newly retargeted branch.
917 PN->addIncoming(Selected, PredBB);
921 replaceUndefValuesInPhi(PN, IncomingValues);
924 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
925 /// unconditional branch, and contains no instructions other than PHI nodes,
926 /// potential side-effect free intrinsics and the branch. If possible,
927 /// eliminate BB by rewriting all the predecessors to branch to the successor
928 /// block and return true. If we can't transform, return false.
929 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
930 DeferredDominance *DDT) {
931 assert(BB != &BB->getParent()->getEntryBlock() &&
932 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
934 // We can't eliminate infinite loops.
935 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
936 if (BB == Succ) return false;
938 // Check to see if merging these blocks would cause conflicts for any of the
939 // phi nodes in BB or Succ. If not, we can safely merge.
940 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
942 // Check for cases where Succ has multiple predecessors and a PHI node in BB
943 // has uses which will not disappear when the PHI nodes are merged. It is
944 // possible to handle such cases, but difficult: it requires checking whether
945 // BB dominates Succ, which is non-trivial to calculate in the case where
946 // Succ has multiple predecessors. Also, it requires checking whether
947 // constructing the necessary self-referential PHI node doesn't introduce any
948 // conflicts; this isn't too difficult, but the previous code for doing this
951 // Note that if this check finds a live use, BB dominates Succ, so BB is
952 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
953 // folding the branch isn't profitable in that case anyway.
954 if (!Succ->getSinglePredecessor()) {
955 BasicBlock::iterator BBI = BB->begin();
956 while (isa<PHINode>(*BBI)) {
957 for (Use &U : BBI->uses()) {
958 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
959 if (PN->getIncomingBlock(U) != BB)
969 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
971 std::vector<DominatorTree::UpdateType> Updates;
973 Updates.reserve(1 + (2 * std::distance(pred_begin(BB), pred_end(BB))));
974 Updates.push_back({DominatorTree::Delete, BB, Succ});
975 // All predecessors of BB will be moved to Succ.
976 for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
977 Updates.push_back({DominatorTree::Delete, *I, BB});
978 // This predecessor of BB may already have Succ as a successor.
979 if (llvm::find(successors(*I), Succ) == succ_end(*I))
980 Updates.push_back({DominatorTree::Insert, *I, Succ});
984 if (isa<PHINode>(Succ->begin())) {
985 // If there is more than one pred of succ, and there are PHI nodes in
986 // the successor, then we need to add incoming edges for the PHI nodes
988 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
990 // Loop over all of the PHI nodes in the successor of BB.
991 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
992 PHINode *PN = cast<PHINode>(I);
994 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
998 if (Succ->getSinglePredecessor()) {
999 // BB is the only predecessor of Succ, so Succ will end up with exactly
1000 // the same predecessors BB had.
1002 // Copy over any phi, debug or lifetime instruction.
1003 BB->getTerminator()->eraseFromParent();
1004 Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
1007 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1008 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
1009 assert(PN->use_empty() && "There shouldn't be any uses here!");
1010 PN->eraseFromParent();
1014 // If the unconditional branch we replaced contains llvm.loop metadata, we
1015 // add the metadata to the branch instructions in the predecessors.
1016 unsigned LoopMDKind = BB->getContext().getMDKindID("llvm.loop");
1017 Instruction *TI = BB->getTerminator();
1019 if (MDNode *LoopMD = TI->getMetadata(LoopMDKind))
1020 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1021 BasicBlock *Pred = *PI;
1022 Pred->getTerminator()->setMetadata(LoopMDKind, LoopMD);
1025 // Everything that jumped to BB now goes to Succ.
1026 BB->replaceAllUsesWith(Succ);
1027 if (!Succ->hasName()) Succ->takeName(BB);
1030 DDT->deleteBB(BB); // Deferred deletion of the old basic block.
1031 DDT->applyUpdates(Updates);
1033 BB->eraseFromParent(); // Delete the old basic block.
1038 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
1039 /// nodes in this block. This doesn't try to be clever about PHI nodes
1040 /// which differ only in the order of the incoming values, but instcombine
1041 /// orders them so it usually won't matter.
1042 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
1043 // This implementation doesn't currently consider undef operands
1044 // specially. Theoretically, two phis which are identical except for
1045 // one having an undef where the other doesn't could be collapsed.
1047 struct PHIDenseMapInfo {
1048 static PHINode *getEmptyKey() {
1049 return DenseMapInfo<PHINode *>::getEmptyKey();
1052 static PHINode *getTombstoneKey() {
1053 return DenseMapInfo<PHINode *>::getTombstoneKey();
1056 static unsigned getHashValue(PHINode *PN) {
1057 // Compute a hash value on the operands. Instcombine will likely have
1058 // sorted them, which helps expose duplicates, but we have to check all
1059 // the operands to be safe in case instcombine hasn't run.
1060 return static_cast<unsigned>(hash_combine(
1061 hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
1062 hash_combine_range(PN->block_begin(), PN->block_end())));
1065 static bool isEqual(PHINode *LHS, PHINode *RHS) {
1066 if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
1067 RHS == getEmptyKey() || RHS == getTombstoneKey())
1069 return LHS->isIdenticalTo(RHS);
1073 // Set of unique PHINodes.
1074 DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
1076 // Examine each PHI.
1077 bool Changed = false;
1078 for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
1079 auto Inserted = PHISet.insert(PN);
1080 if (!Inserted.second) {
1081 // A duplicate. Replace this PHI with its duplicate.
1082 PN->replaceAllUsesWith(*Inserted.first);
1083 PN->eraseFromParent();
1086 // The RAUW can change PHIs that we already visited. Start over from the
1096 /// enforceKnownAlignment - If the specified pointer points to an object that
1097 /// we control, modify the object's alignment to PrefAlign. This isn't
1098 /// often possible though. If alignment is important, a more reliable approach
1099 /// is to simply align all global variables and allocation instructions to
1100 /// their preferred alignment from the beginning.
1101 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
1103 const DataLayout &DL) {
1104 assert(PrefAlign > Align);
1106 V = V->stripPointerCasts();
1108 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
1109 // TODO: ideally, computeKnownBits ought to have used
1110 // AllocaInst::getAlignment() in its computation already, making
1111 // the below max redundant. But, as it turns out,
1112 // stripPointerCasts recurses through infinite layers of bitcasts,
1113 // while computeKnownBits is not allowed to traverse more than 6
1115 Align = std::max(AI->getAlignment(), Align);
1116 if (PrefAlign <= Align)
1119 // If the preferred alignment is greater than the natural stack alignment
1120 // then don't round up. This avoids dynamic stack realignment.
1121 if (DL.exceedsNaturalStackAlignment(PrefAlign))
1123 AI->setAlignment(PrefAlign);
1127 if (auto *GO = dyn_cast<GlobalObject>(V)) {
1128 // TODO: as above, this shouldn't be necessary.
1129 Align = std::max(GO->getAlignment(), Align);
1130 if (PrefAlign <= Align)
1133 // If there is a large requested alignment and we can, bump up the alignment
1134 // of the global. If the memory we set aside for the global may not be the
1135 // memory used by the final program then it is impossible for us to reliably
1136 // enforce the preferred alignment.
1137 if (!GO->canIncreaseAlignment())
1140 GO->setAlignment(PrefAlign);
1147 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
1148 const DataLayout &DL,
1149 const Instruction *CxtI,
1150 AssumptionCache *AC,
1151 const DominatorTree *DT) {
1152 assert(V->getType()->isPointerTy() &&
1153 "getOrEnforceKnownAlignment expects a pointer!");
1155 KnownBits Known = computeKnownBits(V, DL, 0, AC, CxtI, DT);
1156 unsigned TrailZ = Known.countMinTrailingZeros();
1158 // Avoid trouble with ridiculously large TrailZ values, such as
1159 // those computed from a null pointer.
1160 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
1162 unsigned Align = 1u << std::min(Known.getBitWidth() - 1, TrailZ);
1164 // LLVM doesn't support alignments larger than this currently.
1165 Align = std::min(Align, +Value::MaximumAlignment);
1167 if (PrefAlign > Align)
1168 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
1170 // We don't need to make any adjustment.
1174 ///===---------------------------------------------------------------------===//
1175 /// Dbg Intrinsic utilities
1178 /// See if there is a dbg.value intrinsic for DIVar before I.
1179 static bool LdStHasDebugValue(DILocalVariable *DIVar, DIExpression *DIExpr,
1181 // Since we can't guarantee that the original dbg.declare instrinsic
1182 // is removed by LowerDbgDeclare(), we need to make sure that we are
1183 // not inserting the same dbg.value intrinsic over and over.
1184 BasicBlock::InstListType::iterator PrevI(I);
1185 if (PrevI != I->getParent()->getInstList().begin()) {
1187 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
1188 if (DVI->getValue() == I->getOperand(0) &&
1189 DVI->getVariable() == DIVar &&
1190 DVI->getExpression() == DIExpr)
1196 /// See if there is a dbg.value intrinsic for DIVar for the PHI node.
1197 static bool PhiHasDebugValue(DILocalVariable *DIVar,
1198 DIExpression *DIExpr,
1200 // Since we can't guarantee that the original dbg.declare instrinsic
1201 // is removed by LowerDbgDeclare(), we need to make sure that we are
1202 // not inserting the same dbg.value intrinsic over and over.
1203 SmallVector<DbgValueInst *, 1> DbgValues;
1204 findDbgValues(DbgValues, APN);
1205 for (auto *DVI : DbgValues) {
1206 assert(DVI->getValue() == APN);
1207 if ((DVI->getVariable() == DIVar) && (DVI->getExpression() == DIExpr))
1213 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
1214 /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
1215 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1216 StoreInst *SI, DIBuilder &Builder) {
1217 assert(DII->isAddressOfVariable());
1218 auto *DIVar = DII->getVariable();
1219 assert(DIVar && "Missing variable");
1220 auto *DIExpr = DII->getExpression();
1221 Value *DV = SI->getOperand(0);
1223 // If an argument is zero extended then use argument directly. The ZExt
1224 // may be zapped by an optimization pass in future.
1225 Argument *ExtendedArg = nullptr;
1226 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1227 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1228 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1229 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1231 // If this DII was already describing only a fragment of a variable, ensure
1232 // that fragment is appropriately narrowed here.
1233 // But if a fragment wasn't used, describe the value as the original
1234 // argument (rather than the zext or sext) so that it remains described even
1235 // if the sext/zext is optimized away. This widens the variable description,
1236 // leaving it up to the consumer to know how the smaller value may be
1237 // represented in a larger register.
1238 if (auto Fragment = DIExpr->getFragmentInfo()) {
1239 unsigned FragmentOffset = Fragment->OffsetInBits;
1240 SmallVector<uint64_t, 3> Ops(DIExpr->elements_begin(),
1241 DIExpr->elements_end() - 3);
1242 Ops.push_back(dwarf::DW_OP_LLVM_fragment);
1243 Ops.push_back(FragmentOffset);
1244 const DataLayout &DL = DII->getModule()->getDataLayout();
1245 Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType()));
1246 DIExpr = Builder.createExpression(Ops);
1250 if (!LdStHasDebugValue(DIVar, DIExpr, SI))
1251 Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
1255 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1256 /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
1257 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1258 LoadInst *LI, DIBuilder &Builder) {
1259 auto *DIVar = DII->getVariable();
1260 auto *DIExpr = DII->getExpression();
1261 assert(DIVar && "Missing variable");
1263 if (LdStHasDebugValue(DIVar, DIExpr, LI))
1266 // We are now tracking the loaded value instead of the address. In the
1267 // future if multi-location support is added to the IR, it might be
1268 // preferable to keep tracking both the loaded value and the original
1269 // address in case the alloca can not be elided.
1270 Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
1271 LI, DIVar, DIExpr, DII->getDebugLoc(), (Instruction *)nullptr);
1272 DbgValue->insertAfter(LI);
1275 /// Inserts a llvm.dbg.value intrinsic after a phi that has an associated
1276 /// llvm.dbg.declare or llvm.dbg.addr intrinsic.
1277 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1278 PHINode *APN, DIBuilder &Builder) {
1279 auto *DIVar = DII->getVariable();
1280 auto *DIExpr = DII->getExpression();
1281 assert(DIVar && "Missing variable");
1283 if (PhiHasDebugValue(DIVar, DIExpr, APN))
1286 BasicBlock *BB = APN->getParent();
1287 auto InsertionPt = BB->getFirstInsertionPt();
1289 // The block may be a catchswitch block, which does not have a valid
1291 // FIXME: Insert dbg.value markers in the successors when appropriate.
1292 if (InsertionPt != BB->end())
1293 Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, DII->getDebugLoc(),
1297 /// Determine whether this alloca is either a VLA or an array.
1298 static bool isArray(AllocaInst *AI) {
1299 return AI->isArrayAllocation() ||
1300 AI->getType()->getElementType()->isArrayTy();
1303 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1304 /// of llvm.dbg.value intrinsics.
1305 bool llvm::LowerDbgDeclare(Function &F) {
1306 DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1307 SmallVector<DbgDeclareInst *, 4> Dbgs;
1309 for (Instruction &BI : FI)
1310 if (auto DDI = dyn_cast<DbgDeclareInst>(&BI))
1311 Dbgs.push_back(DDI);
1316 for (auto &I : Dbgs) {
1317 DbgDeclareInst *DDI = I;
1318 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1319 // If this is an alloca for a scalar variable, insert a dbg.value
1320 // at each load and store to the alloca and erase the dbg.declare.
1321 // The dbg.values allow tracking a variable even if it is not
1322 // stored on the stack, while the dbg.declare can only describe
1323 // the stack slot (and at a lexical-scope granularity). Later
1324 // passes will attempt to elide the stack slot.
1325 if (!AI || isArray(AI))
1328 // A volatile load/store means that the alloca can't be elided anyway.
1329 if (llvm::any_of(AI->users(), [](User *U) -> bool {
1330 if (LoadInst *LI = dyn_cast<LoadInst>(U))
1331 return LI->isVolatile();
1332 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1333 return SI->isVolatile();
1338 for (auto &AIUse : AI->uses()) {
1339 User *U = AIUse.getUser();
1340 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1341 if (AIUse.getOperandNo() == 1)
1342 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1343 } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
1344 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1345 } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1346 // This is a call by-value or some other instruction that
1347 // takes a pointer to the variable. Insert a *value*
1348 // intrinsic that describes the alloca.
1349 DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
1350 DDI->getExpression(), DDI->getDebugLoc(),
1354 DDI->eraseFromParent();
1359 /// Propagate dbg.value intrinsics through the newly inserted PHIs.
1360 void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
1361 SmallVectorImpl<PHINode *> &InsertedPHIs) {
1362 assert(BB && "No BasicBlock to clone dbg.value(s) from.");
1363 if (InsertedPHIs.size() == 0)
1366 // Map existing PHI nodes to their dbg.values.
1367 ValueToValueMapTy DbgValueMap;
1368 for (auto &I : *BB) {
1369 if (auto DbgII = dyn_cast<DbgInfoIntrinsic>(&I)) {
1370 if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
1371 DbgValueMap.insert({Loc, DbgII});
1374 if (DbgValueMap.size() == 0)
1377 // Then iterate through the new PHIs and look to see if they use one of the
1378 // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
1379 // propagate the info through the new PHI.
1380 LLVMContext &C = BB->getContext();
1381 for (auto PHI : InsertedPHIs) {
1382 BasicBlock *Parent = PHI->getParent();
1383 // Avoid inserting an intrinsic into an EH block.
1384 if (Parent->getFirstNonPHI()->isEHPad())
1386 auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
1387 for (auto VI : PHI->operand_values()) {
1388 auto V = DbgValueMap.find(VI);
1389 if (V != DbgValueMap.end()) {
1390 auto *DbgII = cast<DbgInfoIntrinsic>(V->second);
1391 Instruction *NewDbgII = DbgII->clone();
1392 NewDbgII->setOperand(0, PhiMAV);
1393 auto InsertionPt = Parent->getFirstInsertionPt();
1394 assert(InsertionPt != Parent->end() && "Ill-formed basic block");
1395 NewDbgII->insertBefore(&*InsertionPt);
1401 /// Finds all intrinsics declaring local variables as living in the memory that
1402 /// 'V' points to. This may include a mix of dbg.declare and
1403 /// dbg.addr intrinsics.
1404 TinyPtrVector<DbgInfoIntrinsic *> llvm::FindDbgAddrUses(Value *V) {
1405 auto *L = LocalAsMetadata::getIfExists(V);
1408 auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L);
1412 TinyPtrVector<DbgInfoIntrinsic *> Declares;
1413 for (User *U : MDV->users()) {
1414 if (auto *DII = dyn_cast<DbgInfoIntrinsic>(U))
1415 if (DII->isAddressOfVariable())
1416 Declares.push_back(DII);
1422 void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
1423 if (auto *L = LocalAsMetadata::getIfExists(V))
1424 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1425 for (User *U : MDV->users())
1426 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
1427 DbgValues.push_back(DVI);
1430 void llvm::findDbgUsers(SmallVectorImpl<DbgInfoIntrinsic *> &DbgUsers,
1432 if (auto *L = LocalAsMetadata::getIfExists(V))
1433 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1434 for (User *U : MDV->users())
1435 if (DbgInfoIntrinsic *DII = dyn_cast<DbgInfoIntrinsic>(U))
1436 DbgUsers.push_back(DII);
1439 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
1440 Instruction *InsertBefore, DIBuilder &Builder,
1441 bool DerefBefore, int Offset, bool DerefAfter) {
1442 auto DbgAddrs = FindDbgAddrUses(Address);
1443 for (DbgInfoIntrinsic *DII : DbgAddrs) {
1444 DebugLoc Loc = DII->getDebugLoc();
1445 auto *DIVar = DII->getVariable();
1446 auto *DIExpr = DII->getExpression();
1447 assert(DIVar && "Missing variable");
1448 DIExpr = DIExpression::prepend(DIExpr, DerefBefore, Offset, DerefAfter);
1449 // Insert llvm.dbg.declare immediately after InsertBefore, and remove old
1450 // llvm.dbg.declare.
1451 Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
1452 if (DII == InsertBefore)
1453 InsertBefore = &*std::next(InsertBefore->getIterator());
1454 DII->eraseFromParent();
1456 return !DbgAddrs.empty();
1459 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1460 DIBuilder &Builder, bool DerefBefore,
1461 int Offset, bool DerefAfter) {
1462 return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder,
1463 DerefBefore, Offset, DerefAfter);
1466 static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
1467 DIBuilder &Builder, int Offset) {
1468 DebugLoc Loc = DVI->getDebugLoc();
1469 auto *DIVar = DVI->getVariable();
1470 auto *DIExpr = DVI->getExpression();
1471 assert(DIVar && "Missing variable");
1473 // This is an alloca-based llvm.dbg.value. The first thing it should do with
1474 // the alloca pointer is dereference it. Otherwise we don't know how to handle
1476 if (!DIExpr || DIExpr->getNumElements() < 1 ||
1477 DIExpr->getElement(0) != dwarf::DW_OP_deref)
1480 // Insert the offset immediately after the first deref.
1481 // We could just change the offset argument of dbg.value, but it's unsigned...
1483 SmallVector<uint64_t, 4> Ops;
1484 Ops.push_back(dwarf::DW_OP_deref);
1485 DIExpression::appendOffset(Ops, Offset);
1486 Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
1487 DIExpr = Builder.createExpression(Ops);
1490 Builder.insertDbgValueIntrinsic(NewAddress, DIVar, DIExpr, Loc, DVI);
1491 DVI->eraseFromParent();
1494 void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1495 DIBuilder &Builder, int Offset) {
1496 if (auto *L = LocalAsMetadata::getIfExists(AI))
1497 if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
1498 for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) {
1500 if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser()))
1501 replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset);
1505 void llvm::salvageDebugInfo(Instruction &I) {
1506 // This function is hot. An early check to determine whether the instruction
1507 // has any metadata to save allows it to return earlier on average.
1508 if (!I.isUsedByMetadata())
1511 SmallVector<DbgInfoIntrinsic *, 1> DbgUsers;
1512 findDbgUsers(DbgUsers, &I);
1513 if (DbgUsers.empty())
1516 auto &M = *I.getModule();
1517 auto &DL = M.getDataLayout();
1519 auto wrapMD = [&](Value *V) {
1520 return MetadataAsValue::get(I.getContext(), ValueAsMetadata::get(V));
1523 auto doSalvage = [&](DbgInfoIntrinsic *DII, SmallVectorImpl<uint64_t> &Ops) {
1524 auto *DIExpr = DII->getExpression();
1526 DIExpression::prependOpcodes(DIExpr, Ops, DIExpression::WithStackValue);
1527 DII->setOperand(0, wrapMD(I.getOperand(0)));
1528 DII->setOperand(2, MetadataAsValue::get(I.getContext(), DIExpr));
1529 DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
1532 auto applyOffset = [&](DbgInfoIntrinsic *DII, uint64_t Offset) {
1533 SmallVector<uint64_t, 8> Ops;
1534 DIExpression::appendOffset(Ops, Offset);
1535 doSalvage(DII, Ops);
1538 auto applyOps = [&](DbgInfoIntrinsic *DII,
1539 std::initializer_list<uint64_t> Opcodes) {
1540 SmallVector<uint64_t, 8> Ops(Opcodes);
1541 doSalvage(DII, Ops);
1544 if (auto *CI = dyn_cast<CastInst>(&I)) {
1545 if (!CI->isNoopCast(DL))
1548 // No-op casts are irrelevant for debug info.
1549 MetadataAsValue *CastSrc = wrapMD(I.getOperand(0));
1550 for (auto *DII : DbgUsers) {
1551 DII->setOperand(0, CastSrc);
1552 DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
1554 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
1556 M.getDataLayout().getIndexSizeInBits(GEP->getPointerAddressSpace());
1557 // Rewrite a constant GEP into a DIExpression. Since we are performing
1558 // arithmetic to compute the variable's *value* in the DIExpression, we
1559 // need to mark the expression with a DW_OP_stack_value.
1560 APInt Offset(BitWidth, 0);
1561 if (GEP->accumulateConstantOffset(M.getDataLayout(), Offset))
1562 for (auto *DII : DbgUsers)
1563 applyOffset(DII, Offset.getSExtValue());
1564 } else if (auto *BI = dyn_cast<BinaryOperator>(&I)) {
1565 // Rewrite binary operations with constant integer operands.
1566 auto *ConstInt = dyn_cast<ConstantInt>(I.getOperand(1));
1567 if (!ConstInt || ConstInt->getBitWidth() > 64)
1570 uint64_t Val = ConstInt->getSExtValue();
1571 for (auto *DII : DbgUsers) {
1572 switch (BI->getOpcode()) {
1573 case Instruction::Add:
1574 applyOffset(DII, Val);
1576 case Instruction::Sub:
1577 applyOffset(DII, -int64_t(Val));
1579 case Instruction::Mul:
1580 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_mul});
1582 case Instruction::SDiv:
1583 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_div});
1585 case Instruction::SRem:
1586 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_mod});
1588 case Instruction::Or:
1589 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_or});
1591 case Instruction::And:
1592 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_and});
1594 case Instruction::Xor:
1595 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_xor});
1597 case Instruction::Shl:
1598 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shl});
1600 case Instruction::LShr:
1601 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shr});
1603 case Instruction::AShr:
1604 applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shra});
1607 // TODO: Salvage constants from each kind of binop we know about.
1611 } else if (isa<LoadInst>(&I)) {
1612 MetadataAsValue *AddrMD = wrapMD(I.getOperand(0));
1613 for (auto *DII : DbgUsers) {
1614 // Rewrite the load into DW_OP_deref.
1615 auto *DIExpr = DII->getExpression();
1616 DIExpr = DIExpression::prepend(DIExpr, DIExpression::WithDeref);
1617 DII->setOperand(0, AddrMD);
1618 DII->setOperand(2, MetadataAsValue::get(I.getContext(), DIExpr));
1619 DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
1624 unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
1625 unsigned NumDeadInst = 0;
1626 // Delete the instructions backwards, as it has a reduced likelihood of
1627 // having to update as many def-use and use-def chains.
1628 Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
1629 while (EndInst != &BB->front()) {
1630 // Delete the next to last instruction.
1631 Instruction *Inst = &*--EndInst->getIterator();
1632 if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
1633 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
1634 if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
1638 if (!isa<DbgInfoIntrinsic>(Inst))
1640 Inst->eraseFromParent();
1645 unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap,
1646 bool PreserveLCSSA, DeferredDominance *DDT) {
1647 BasicBlock *BB = I->getParent();
1648 std::vector <DominatorTree::UpdateType> Updates;
1650 // Loop over all of the successors, removing BB's entry from any PHI
1653 Updates.reserve(BB->getTerminator()->getNumSuccessors());
1654 for (BasicBlock *Successor : successors(BB)) {
1655 Successor->removePredecessor(BB, PreserveLCSSA);
1657 Updates.push_back({DominatorTree::Delete, BB, Successor});
1659 // Insert a call to llvm.trap right before this. This turns the undefined
1660 // behavior into a hard fail instead of falling through into random code.
1663 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1664 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1665 CallTrap->setDebugLoc(I->getDebugLoc());
1667 new UnreachableInst(I->getContext(), I);
1669 // All instructions after this are dead.
1670 unsigned NumInstrsRemoved = 0;
1671 BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end();
1672 while (BBI != BBE) {
1673 if (!BBI->use_empty())
1674 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1675 BB->getInstList().erase(BBI++);
1679 DDT->applyUpdates(Updates);
1680 return NumInstrsRemoved;
1683 /// changeToCall - Convert the specified invoke into a normal call.
1684 static void changeToCall(InvokeInst *II, DeferredDominance *DDT = nullptr) {
1685 SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end());
1686 SmallVector<OperandBundleDef, 1> OpBundles;
1687 II->getOperandBundlesAsDefs(OpBundles);
1688 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, OpBundles,
1690 NewCall->takeName(II);
1691 NewCall->setCallingConv(II->getCallingConv());
1692 NewCall->setAttributes(II->getAttributes());
1693 NewCall->setDebugLoc(II->getDebugLoc());
1694 II->replaceAllUsesWith(NewCall);
1696 // Follow the call by a branch to the normal destination.
1697 BasicBlock *NormalDestBB = II->getNormalDest();
1698 BranchInst::Create(NormalDestBB, II);
1700 // Update PHI nodes in the unwind destination
1701 BasicBlock *BB = II->getParent();
1702 BasicBlock *UnwindDestBB = II->getUnwindDest();
1703 UnwindDestBB->removePredecessor(BB);
1704 II->eraseFromParent();
1706 DDT->deleteEdge(BB, UnwindDestBB);
1709 BasicBlock *llvm::changeToInvokeAndSplitBasicBlock(CallInst *CI,
1710 BasicBlock *UnwindEdge) {
1711 BasicBlock *BB = CI->getParent();
1713 // Convert this function call into an invoke instruction. First, split the
1716 BB->splitBasicBlock(CI->getIterator(), CI->getName() + ".noexc");
1718 // Delete the unconditional branch inserted by splitBasicBlock
1719 BB->getInstList().pop_back();
1721 // Create the new invoke instruction.
1722 SmallVector<Value *, 8> InvokeArgs(CI->arg_begin(), CI->arg_end());
1723 SmallVector<OperandBundleDef, 1> OpBundles;
1725 CI->getOperandBundlesAsDefs(OpBundles);
1727 // Note: we're round tripping operand bundles through memory here, and that
1728 // can potentially be avoided with a cleverer API design that we do not have
1731 InvokeInst *II = InvokeInst::Create(CI->getCalledValue(), Split, UnwindEdge,
1732 InvokeArgs, OpBundles, CI->getName(), BB);
1733 II->setDebugLoc(CI->getDebugLoc());
1734 II->setCallingConv(CI->getCallingConv());
1735 II->setAttributes(CI->getAttributes());
1737 // Make sure that anything using the call now uses the invoke! This also
1738 // updates the CallGraph if present, because it uses a WeakTrackingVH.
1739 CI->replaceAllUsesWith(II);
1741 // Delete the original call
1742 Split->getInstList().pop_front();
1746 static bool markAliveBlocks(Function &F,
1747 SmallPtrSetImpl<BasicBlock*> &Reachable,
1748 DeferredDominance *DDT = nullptr) {
1749 SmallVector<BasicBlock*, 128> Worklist;
1750 BasicBlock *BB = &F.front();
1751 Worklist.push_back(BB);
1752 Reachable.insert(BB);
1753 bool Changed = false;
1755 BB = Worklist.pop_back_val();
1757 // Do a quick scan of the basic block, turning any obviously unreachable
1758 // instructions into LLVM unreachable insts. The instruction combining pass
1759 // canonicalizes unreachable insts into stores to null or undef.
1760 for (Instruction &I : *BB) {
1761 // Assumptions that are known to be false are equivalent to unreachable.
1762 // Also, if the condition is undefined, then we make the choice most
1763 // beneficial to the optimizer, and choose that to also be unreachable.
1764 if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
1765 if (II->getIntrinsicID() == Intrinsic::assume) {
1766 if (match(II->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) {
1767 // Don't insert a call to llvm.trap right before the unreachable.
1768 changeToUnreachable(II, false, false, DDT);
1774 if (II->getIntrinsicID() == Intrinsic::experimental_guard) {
1775 // A call to the guard intrinsic bails out of the current compilation
1776 // unit if the predicate passed to it is false. If the predicate is a
1777 // constant false, then we know the guard will bail out of the current
1778 // compile unconditionally, so all code following it is dead.
1780 // Note: unlike in llvm.assume, it is not "obviously profitable" for
1781 // guards to treat `undef` as `false` since a guard on `undef` can
1782 // still be useful for widening.
1783 if (match(II->getArgOperand(0), m_Zero()))
1784 if (!isa<UnreachableInst>(II->getNextNode())) {
1785 changeToUnreachable(II->getNextNode(), /*UseLLVMTrap=*/false,
1793 if (auto *CI = dyn_cast<CallInst>(&I)) {
1794 Value *Callee = CI->getCalledValue();
1795 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1796 changeToUnreachable(CI, /*UseLLVMTrap=*/false, false, DDT);
1800 if (CI->doesNotReturn()) {
1801 // If we found a call to a no-return function, insert an unreachable
1802 // instruction after it. Make sure there isn't *already* one there
1804 if (!isa<UnreachableInst>(CI->getNextNode())) {
1805 // Don't insert a call to llvm.trap right before the unreachable.
1806 changeToUnreachable(CI->getNextNode(), false, false, DDT);
1813 // Store to undef and store to null are undefined and used to signal that
1814 // they should be changed to unreachable by passes that can't modify the
1816 if (auto *SI = dyn_cast<StoreInst>(&I)) {
1817 // Don't touch volatile stores.
1818 if (SI->isVolatile()) continue;
1820 Value *Ptr = SI->getOperand(1);
1822 if (isa<UndefValue>(Ptr) ||
1823 (isa<ConstantPointerNull>(Ptr) &&
1824 SI->getPointerAddressSpace() == 0)) {
1825 changeToUnreachable(SI, true, false, DDT);
1832 TerminatorInst *Terminator = BB->getTerminator();
1833 if (auto *II = dyn_cast<InvokeInst>(Terminator)) {
1834 // Turn invokes that call 'nounwind' functions into ordinary calls.
1835 Value *Callee = II->getCalledValue();
1836 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1837 changeToUnreachable(II, true, false, DDT);
1839 } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
1840 if (II->use_empty() && II->onlyReadsMemory()) {
1841 // jump to the normal destination branch.
1842 BasicBlock *NormalDestBB = II->getNormalDest();
1843 BasicBlock *UnwindDestBB = II->getUnwindDest();
1844 BranchInst::Create(NormalDestBB, II);
1845 UnwindDestBB->removePredecessor(II->getParent());
1846 II->eraseFromParent();
1848 DDT->deleteEdge(BB, UnwindDestBB);
1850 changeToCall(II, DDT);
1853 } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
1854 // Remove catchpads which cannot be reached.
1855 struct CatchPadDenseMapInfo {
1856 static CatchPadInst *getEmptyKey() {
1857 return DenseMapInfo<CatchPadInst *>::getEmptyKey();
1860 static CatchPadInst *getTombstoneKey() {
1861 return DenseMapInfo<CatchPadInst *>::getTombstoneKey();
1864 static unsigned getHashValue(CatchPadInst *CatchPad) {
1865 return static_cast<unsigned>(hash_combine_range(
1866 CatchPad->value_op_begin(), CatchPad->value_op_end()));
1869 static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) {
1870 if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
1871 RHS == getEmptyKey() || RHS == getTombstoneKey())
1873 return LHS->isIdenticalTo(RHS);
1877 // Set of unique CatchPads.
1878 SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
1879 CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
1881 detail::DenseSetEmpty Empty;
1882 for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(),
1883 E = CatchSwitch->handler_end();
1885 BasicBlock *HandlerBB = *I;
1886 auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
1887 if (!HandlerSet.insert({CatchPad, Empty}).second) {
1888 CatchSwitch->removeHandler(I);
1896 Changed |= ConstantFoldTerminator(BB, true, nullptr, DDT);
1897 for (BasicBlock *Successor : successors(BB))
1898 if (Reachable.insert(Successor).second)
1899 Worklist.push_back(Successor);
1900 } while (!Worklist.empty());
1904 void llvm::removeUnwindEdge(BasicBlock *BB, DeferredDominance *DDT) {
1905 TerminatorInst *TI = BB->getTerminator();
1907 if (auto *II = dyn_cast<InvokeInst>(TI)) {
1908 changeToCall(II, DDT);
1912 TerminatorInst *NewTI;
1913 BasicBlock *UnwindDest;
1915 if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
1916 NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
1917 UnwindDest = CRI->getUnwindDest();
1918 } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
1919 auto *NewCatchSwitch = CatchSwitchInst::Create(
1920 CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
1921 CatchSwitch->getName(), CatchSwitch);
1922 for (BasicBlock *PadBB : CatchSwitch->handlers())
1923 NewCatchSwitch->addHandler(PadBB);
1925 NewTI = NewCatchSwitch;
1926 UnwindDest = CatchSwitch->getUnwindDest();
1928 llvm_unreachable("Could not find unwind successor");
1931 NewTI->takeName(TI);
1932 NewTI->setDebugLoc(TI->getDebugLoc());
1933 UnwindDest->removePredecessor(BB);
1934 TI->replaceAllUsesWith(NewTI);
1935 TI->eraseFromParent();
1937 DDT->deleteEdge(BB, UnwindDest);
1940 /// removeUnreachableBlocks - Remove blocks that are not reachable, even
1941 /// if they are in a dead cycle. Return true if a change was made, false
1942 /// otherwise. If `LVI` is passed, this function preserves LazyValueInfo
1943 /// after modifying the CFG.
1944 bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI,
1945 DeferredDominance *DDT) {
1946 SmallPtrSet<BasicBlock*, 16> Reachable;
1947 bool Changed = markAliveBlocks(F, Reachable, DDT);
1949 // If there are unreachable blocks in the CFG...
1950 if (Reachable.size() == F.size())
1953 assert(Reachable.size() < F.size());
1954 NumRemoved += F.size()-Reachable.size();
1956 // Loop over all of the basic blocks that are not reachable, dropping all of
1957 // their internal references. Update DDT and LVI if available.
1958 std::vector <DominatorTree::UpdateType> Updates;
1959 for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ++I) {
1961 if (Reachable.count(BB))
1963 for (BasicBlock *Successor : successors(BB)) {
1964 if (Reachable.count(Successor))
1965 Successor->removePredecessor(BB);
1967 Updates.push_back({DominatorTree::Delete, BB, Successor});
1970 LVI->eraseBlock(BB);
1971 BB->dropAllReferences();
1974 for (Function::iterator I = ++F.begin(); I != F.end();) {
1976 if (Reachable.count(BB)) {
1981 DDT->deleteBB(BB); // deferred deletion of BB.
1984 I = F.getBasicBlockList().erase(I);
1989 DDT->applyUpdates(Updates);
1993 void llvm::combineMetadata(Instruction *K, const Instruction *J,
1994 ArrayRef<unsigned> KnownIDs) {
1995 SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
1996 K->dropUnknownNonDebugMetadata(KnownIDs);
1997 K->getAllMetadataOtherThanDebugLoc(Metadata);
1998 for (const auto &MD : Metadata) {
1999 unsigned Kind = MD.first;
2000 MDNode *JMD = J->getMetadata(Kind);
2001 MDNode *KMD = MD.second;
2005 K->setMetadata(Kind, nullptr); // Remove unknown metadata
2007 case LLVMContext::MD_dbg:
2008 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
2009 case LLVMContext::MD_tbaa:
2010 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
2012 case LLVMContext::MD_alias_scope:
2013 K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
2015 case LLVMContext::MD_noalias:
2016 case LLVMContext::MD_mem_parallel_loop_access:
2017 K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
2019 case LLVMContext::MD_range:
2020 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
2022 case LLVMContext::MD_fpmath:
2023 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
2025 case LLVMContext::MD_invariant_load:
2026 // Only set the !invariant.load if it is present in both instructions.
2027 K->setMetadata(Kind, JMD);
2029 case LLVMContext::MD_nonnull:
2030 // Only set the !nonnull if it is present in both instructions.
2031 K->setMetadata(Kind, JMD);
2033 case LLVMContext::MD_invariant_group:
2034 // Preserve !invariant.group in K.
2036 case LLVMContext::MD_align:
2037 K->setMetadata(Kind,
2038 MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
2040 case LLVMContext::MD_dereferenceable:
2041 case LLVMContext::MD_dereferenceable_or_null:
2042 K->setMetadata(Kind,
2043 MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
2047 // Set !invariant.group from J if J has it. If both instructions have it
2048 // then we will just pick it from J - even when they are different.
2049 // Also make sure that K is load or store - f.e. combining bitcast with load
2050 // could produce bitcast with invariant.group metadata, which is invalid.
2051 // FIXME: we should try to preserve both invariant.group md if they are
2052 // different, but right now instruction can only have one invariant.group.
2053 if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
2054 if (isa<LoadInst>(K) || isa<StoreInst>(K))
2055 K->setMetadata(LLVMContext::MD_invariant_group, JMD);
2058 void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J) {
2059 unsigned KnownIDs[] = {
2060 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
2061 LLVMContext::MD_noalias, LLVMContext::MD_range,
2062 LLVMContext::MD_invariant_load, LLVMContext::MD_nonnull,
2063 LLVMContext::MD_invariant_group, LLVMContext::MD_align,
2064 LLVMContext::MD_dereferenceable,
2065 LLVMContext::MD_dereferenceable_or_null};
2066 combineMetadata(K, J, KnownIDs);
2069 template <typename RootType, typename DominatesFn>
2070 static unsigned replaceDominatedUsesWith(Value *From, Value *To,
2071 const RootType &Root,
2072 const DominatesFn &Dominates) {
2073 assert(From->getType() == To->getType());
2076 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
2079 if (!Dominates(Root, U))
2082 DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
2083 << *To << " in " << *U << "\n");
2089 unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) {
2090 assert(From->getType() == To->getType());
2091 auto *BB = From->getParent();
2094 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
2097 auto *I = cast<Instruction>(U.getUser());
2098 if (I->getParent() == BB)
2106 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
2108 const BasicBlockEdge &Root) {
2109 auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) {
2110 return DT.dominates(Root, U);
2112 return ::replaceDominatedUsesWith(From, To, Root, Dominates);
2115 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
2117 const BasicBlock *BB) {
2118 auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
2119 auto *I = cast<Instruction>(U.getUser())->getParent();
2120 return DT.properlyDominates(BB, I);
2122 return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
2125 bool llvm::callsGCLeafFunction(ImmutableCallSite CS,
2126 const TargetLibraryInfo &TLI) {
2127 // Check if the function is specifically marked as a gc leaf function.
2128 if (CS.hasFnAttr("gc-leaf-function"))
2130 if (const Function *F = CS.getCalledFunction()) {
2131 if (F->hasFnAttribute("gc-leaf-function"))
2134 if (auto IID = F->getIntrinsicID())
2135 // Most LLVM intrinsics do not take safepoints.
2136 return IID != Intrinsic::experimental_gc_statepoint &&
2137 IID != Intrinsic::experimental_deoptimize;
2140 // Lib calls can be materialized by some passes, and won't be
2141 // marked as 'gc-leaf-function.' All available Libcalls are
2144 if (TLI.getLibFunc(CS, LF)) {
2151 void llvm::copyNonnullMetadata(const LoadInst &OldLI, MDNode *N,
2153 auto *NewTy = NewLI.getType();
2155 // This only directly applies if the new type is also a pointer.
2156 if (NewTy->isPointerTy()) {
2157 NewLI.setMetadata(LLVMContext::MD_nonnull, N);
2161 // The only other translation we can do is to integral loads with !range
2163 if (!NewTy->isIntegerTy())
2166 MDBuilder MDB(NewLI.getContext());
2167 const Value *Ptr = OldLI.getPointerOperand();
2168 auto *ITy = cast<IntegerType>(NewTy);
2169 auto *NullInt = ConstantExpr::getPtrToInt(
2170 ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
2171 auto *NonNullInt = ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
2172 NewLI.setMetadata(LLVMContext::MD_range,
2173 MDB.createRange(NonNullInt, NullInt));
2176 void llvm::copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI,
2177 MDNode *N, LoadInst &NewLI) {
2178 auto *NewTy = NewLI.getType();
2180 // Give up unless it is converted to a pointer where there is a single very
2181 // valuable mapping we can do reliably.
2182 // FIXME: It would be nice to propagate this in more ways, but the type
2183 // conversions make it hard.
2184 if (!NewTy->isPointerTy())
2187 unsigned BitWidth = DL.getIndexTypeSizeInBits(NewTy);
2188 if (!getConstantRangeFromMetadata(*N).contains(APInt(BitWidth, 0))) {
2189 MDNode *NN = MDNode::get(OldLI.getContext(), None);
2190 NewLI.setMetadata(LLVMContext::MD_nonnull, NN);
2196 /// A potential constituent of a bitreverse or bswap expression. See
2197 /// collectBitParts for a fuller explanation.
2199 BitPart(Value *P, unsigned BW) : Provider(P) {
2200 Provenance.resize(BW);
2203 /// The Value that this is a bitreverse/bswap of.
2206 /// The "provenance" of each bit. Provenance[A] = B means that bit A
2207 /// in Provider becomes bit B in the result of this expression.
2208 SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128.
2210 enum { Unset = -1 };
2213 } // end anonymous namespace
2215 /// Analyze the specified subexpression and see if it is capable of providing
2216 /// pieces of a bswap or bitreverse. The subexpression provides a potential
2217 /// piece of a bswap or bitreverse if it can be proven that each non-zero bit in
2218 /// the output of the expression came from a corresponding bit in some other
2219 /// value. This function is recursive, and the end result is a mapping of
2220 /// bitnumber to bitnumber. It is the caller's responsibility to validate that
2221 /// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse.
2223 /// For example, if the current subexpression if "(shl i32 %X, 24)" then we know
2224 /// that the expression deposits the low byte of %X into the high byte of the
2225 /// result and that all other bits are zero. This expression is accepted and a
2226 /// BitPart is returned with Provider set to %X and Provenance[24-31] set to
2229 /// To avoid revisiting values, the BitPart results are memoized into the
2230 /// provided map. To avoid unnecessary copying of BitParts, BitParts are
2231 /// constructed in-place in the \c BPS map. Because of this \c BPS needs to
2232 /// store BitParts objects, not pointers. As we need the concept of a nullptr
2233 /// BitParts (Value has been analyzed and the analysis failed), we an Optional
2234 /// type instead to provide the same functionality.
2236 /// Because we pass around references into \c BPS, we must use a container that
2237 /// does not invalidate internal references (std::map instead of DenseMap).
2238 static const Optional<BitPart> &
2239 collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals,
2240 std::map<Value *, Optional<BitPart>> &BPS) {
2241 auto I = BPS.find(V);
2245 auto &Result = BPS[V] = None;
2246 auto BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
2248 if (Instruction *I = dyn_cast<Instruction>(V)) {
2249 // If this is an or instruction, it may be an inner node of the bswap.
2250 if (I->getOpcode() == Instruction::Or) {
2251 auto &A = collectBitParts(I->getOperand(0), MatchBSwaps,
2252 MatchBitReversals, BPS);
2253 auto &B = collectBitParts(I->getOperand(1), MatchBSwaps,
2254 MatchBitReversals, BPS);
2258 // Try and merge the two together.
2259 if (!A->Provider || A->Provider != B->Provider)
2262 Result = BitPart(A->Provider, BitWidth);
2263 for (unsigned i = 0; i < A->Provenance.size(); ++i) {
2264 if (A->Provenance[i] != BitPart::Unset &&
2265 B->Provenance[i] != BitPart::Unset &&
2266 A->Provenance[i] != B->Provenance[i])
2267 return Result = None;
2269 if (A->Provenance[i] == BitPart::Unset)
2270 Result->Provenance[i] = B->Provenance[i];
2272 Result->Provenance[i] = A->Provenance[i];
2278 // If this is a logical shift by a constant, recurse then shift the result.
2279 if (I->isLogicalShift() && isa<ConstantInt>(I->getOperand(1))) {
2281 cast<ConstantInt>(I->getOperand(1))->getLimitedValue(~0U);
2282 // Ensure the shift amount is defined.
2283 if (BitShift > BitWidth)
2286 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2287 MatchBitReversals, BPS);
2292 // Perform the "shift" on BitProvenance.
2293 auto &P = Result->Provenance;
2294 if (I->getOpcode() == Instruction::Shl) {
2295 P.erase(std::prev(P.end(), BitShift), P.end());
2296 P.insert(P.begin(), BitShift, BitPart::Unset);
2298 P.erase(P.begin(), std::next(P.begin(), BitShift));
2299 P.insert(P.end(), BitShift, BitPart::Unset);
2305 // If this is a logical 'and' with a mask that clears bits, recurse then
2306 // unset the appropriate bits.
2307 if (I->getOpcode() == Instruction::And &&
2308 isa<ConstantInt>(I->getOperand(1))) {
2309 APInt Bit(I->getType()->getPrimitiveSizeInBits(), 1);
2310 const APInt &AndMask = cast<ConstantInt>(I->getOperand(1))->getValue();
2312 // Check that the mask allows a multiple of 8 bits for a bswap, for an
2314 unsigned NumMaskedBits = AndMask.countPopulation();
2315 if (!MatchBitReversals && NumMaskedBits % 8 != 0)
2318 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2319 MatchBitReversals, BPS);
2324 for (unsigned i = 0; i < BitWidth; ++i, Bit <<= 1)
2325 // If the AndMask is zero for this bit, clear the bit.
2326 if ((AndMask & Bit) == 0)
2327 Result->Provenance[i] = BitPart::Unset;
2331 // If this is a zext instruction zero extend the result.
2332 if (I->getOpcode() == Instruction::ZExt) {
2333 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2334 MatchBitReversals, BPS);
2338 Result = BitPart(Res->Provider, BitWidth);
2339 auto NarrowBitWidth =
2340 cast<IntegerType>(cast<ZExtInst>(I)->getSrcTy())->getBitWidth();
2341 for (unsigned i = 0; i < NarrowBitWidth; ++i)
2342 Result->Provenance[i] = Res->Provenance[i];
2343 for (unsigned i = NarrowBitWidth; i < BitWidth; ++i)
2344 Result->Provenance[i] = BitPart::Unset;
2349 // Okay, we got to something that isn't a shift, 'or' or 'and'. This must be
2350 // the input value to the bswap/bitreverse.
2351 Result = BitPart(V, BitWidth);
2352 for (unsigned i = 0; i < BitWidth; ++i)
2353 Result->Provenance[i] = i;
2357 static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To,
2358 unsigned BitWidth) {
2359 if (From % 8 != To % 8)
2361 // Convert from bit indices to byte indices and check for a byte reversal.
2365 return From == BitWidth - To - 1;
2368 static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To,
2369 unsigned BitWidth) {
2370 return From == BitWidth - To - 1;
2373 bool llvm::recognizeBSwapOrBitReverseIdiom(
2374 Instruction *I, bool MatchBSwaps, bool MatchBitReversals,
2375 SmallVectorImpl<Instruction *> &InsertedInsts) {
2376 if (Operator::getOpcode(I) != Instruction::Or)
2378 if (!MatchBSwaps && !MatchBitReversals)
2380 IntegerType *ITy = dyn_cast<IntegerType>(I->getType());
2381 if (!ITy || ITy->getBitWidth() > 128)
2382 return false; // Can't do vectors or integers > 128 bits.
2383 unsigned BW = ITy->getBitWidth();
2385 unsigned DemandedBW = BW;
2386 IntegerType *DemandedTy = ITy;
2387 if (I->hasOneUse()) {
2388 if (TruncInst *Trunc = dyn_cast<TruncInst>(I->user_back())) {
2389 DemandedTy = cast<IntegerType>(Trunc->getType());
2390 DemandedBW = DemandedTy->getBitWidth();
2394 // Try to find all the pieces corresponding to the bswap.
2395 std::map<Value *, Optional<BitPart>> BPS;
2396 auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS);
2399 auto &BitProvenance = Res->Provenance;
2401 // Now, is the bit permutation correct for a bswap or a bitreverse? We can
2402 // only byteswap values with an even number of bytes.
2403 bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true;
2404 for (unsigned i = 0; i < DemandedBW; ++i) {
2406 bitTransformIsCorrectForBSwap(BitProvenance[i], i, DemandedBW);
2408 bitTransformIsCorrectForBitReverse(BitProvenance[i], i, DemandedBW);
2411 Intrinsic::ID Intrin;
2412 if (OKForBSwap && MatchBSwaps)
2413 Intrin = Intrinsic::bswap;
2414 else if (OKForBitReverse && MatchBitReversals)
2415 Intrin = Intrinsic::bitreverse;
2419 if (ITy != DemandedTy) {
2420 Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, DemandedTy);
2421 Value *Provider = Res->Provider;
2422 IntegerType *ProviderTy = cast<IntegerType>(Provider->getType());
2423 // We may need to truncate the provider.
2424 if (DemandedTy != ProviderTy) {
2425 auto *Trunc = CastInst::Create(Instruction::Trunc, Provider, DemandedTy,
2427 InsertedInsts.push_back(Trunc);
2430 auto *CI = CallInst::Create(F, Provider, "rev", I);
2431 InsertedInsts.push_back(CI);
2432 auto *ExtInst = CastInst::Create(Instruction::ZExt, CI, ITy, "zext", I);
2433 InsertedInsts.push_back(ExtInst);
2437 Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, ITy);
2438 InsertedInsts.push_back(CallInst::Create(F, Res->Provider, "rev", I));
2442 // CodeGen has special handling for some string functions that may replace
2443 // them with target-specific intrinsics. Since that'd skip our interceptors
2444 // in ASan/MSan/TSan/DFSan, and thus make us miss some memory accesses,
2445 // we mark affected calls as NoBuiltin, which will disable optimization
2447 void llvm::maybeMarkSanitizerLibraryCallNoBuiltin(
2448 CallInst *CI, const TargetLibraryInfo *TLI) {
2449 Function *F = CI->getCalledFunction();
2451 if (F && !F->hasLocalLinkage() && F->hasName() &&
2452 TLI->getLibFunc(F->getName(), Func) && TLI->hasOptimizedCodeGen(Func) &&
2453 !F->doesNotAccessMemory())
2454 CI->addAttribute(AttributeList::FunctionIndex, Attribute::NoBuiltin);
2457 bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
2458 // We can't have a PHI with a metadata type.
2459 if (I->getOperand(OpIdx)->getType()->isMetadataTy())
2463 if (!isa<Constant>(I->getOperand(OpIdx)))
2466 switch (I->getOpcode()) {
2469 case Instruction::Call:
2470 case Instruction::Invoke:
2471 // Can't handle inline asm. Skip it.
2472 if (isa<InlineAsm>(ImmutableCallSite(I).getCalledValue()))
2474 // Many arithmetic intrinsics have no issue taking a
2475 // variable, however it's hard to distingish these from
2476 // specials such as @llvm.frameaddress that require a constant.
2477 if (isa<IntrinsicInst>(I))
2480 // Constant bundle operands may need to retain their constant-ness for
2482 if (ImmutableCallSite(I).isBundleOperand(OpIdx))
2485 case Instruction::ShuffleVector:
2486 // Shufflevector masks are constant.
2488 case Instruction::Switch:
2489 case Instruction::ExtractValue:
2490 // All operands apart from the first are constant.
2492 case Instruction::InsertValue:
2493 // All operands apart from the first and the second are constant.
2495 case Instruction::Alloca:
2496 // Static allocas (constant size in the entry block) are handled by
2497 // prologue/epilogue insertion so they're free anyway. We definitely don't
2498 // want to make them non-constant.
2499 return !dyn_cast<AllocaInst>(I)->isStaticAlloca();
2500 case Instruction::GetElementPtr:
2503 gep_type_iterator It = gep_type_begin(I);
2504 for (auto E = std::next(It, OpIdx); It != E; ++It)