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/Transforms/Utils/Local.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/Analysis/MemoryBuiltins.h"
22 #include "llvm/Analysis/ValueTracking.h"
23 #include "llvm/IR/CFG.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DIBuilder.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DebugInfo.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Dominators.h"
30 #include "llvm/IR/GetElementPtrTypeIterator.h"
31 #include "llvm/IR/GlobalAlias.h"
32 #include "llvm/IR/GlobalVariable.h"
33 #include "llvm/IR/IRBuilder.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/Intrinsics.h"
37 #include "llvm/IR/MDBuilder.h"
38 #include "llvm/IR/Metadata.h"
39 #include "llvm/IR/Operator.h"
40 #include "llvm/IR/ValueHandle.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Support/MathExtras.h"
43 #include "llvm/Support/raw_ostream.h"
46 #define DEBUG_TYPE "local"
48 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
50 //===----------------------------------------------------------------------===//
51 // Local constant propagation.
54 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
55 /// constant value, convert it into an unconditional branch to the constant
56 /// destination. This is a nontrivial operation because the successors of this
57 /// basic block must have their PHI nodes updated.
58 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
59 /// conditions and indirectbr addresses this might make dead if
60 /// DeleteDeadConditions is true.
61 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
62 const TargetLibraryInfo *TLI) {
63 TerminatorInst *T = BB->getTerminator();
64 IRBuilder<> Builder(T);
66 // Branch - See if we are conditional jumping on constant
67 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
68 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
69 BasicBlock *Dest1 = BI->getSuccessor(0);
70 BasicBlock *Dest2 = BI->getSuccessor(1);
72 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
73 // Are we branching on constant?
74 // YES. Change to unconditional branch...
75 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
76 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
78 //cerr << "Function: " << T->getParent()->getParent()
79 // << "\nRemoving branch from " << T->getParent()
80 // << "\n\nTo: " << OldDest << endl;
82 // Let the basic block know that we are letting go of it. Based on this,
83 // it will adjust it's PHI nodes.
84 OldDest->removePredecessor(BB);
86 // Replace the conditional branch with an unconditional one.
87 Builder.CreateBr(Destination);
88 BI->eraseFromParent();
92 if (Dest2 == Dest1) { // Conditional branch to same location?
93 // This branch matches something like this:
94 // br bool %cond, label %Dest, label %Dest
95 // and changes it into: br label %Dest
97 // Let the basic block know that we are letting go of one copy of it.
98 assert(BI->getParent() && "Terminator not inserted in block!");
99 Dest1->removePredecessor(BI->getParent());
101 // Replace the conditional branch with an unconditional one.
102 Builder.CreateBr(Dest1);
103 Value *Cond = BI->getCondition();
104 BI->eraseFromParent();
105 if (DeleteDeadConditions)
106 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
112 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
113 // If we are switching on a constant, we can convert the switch into a
114 // single branch instruction!
115 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
116 BasicBlock *TheOnlyDest = SI->getDefaultDest();
117 BasicBlock *DefaultDest = TheOnlyDest;
119 // Figure out which case it goes to.
120 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
122 // Found case matching a constant operand?
123 if (i.getCaseValue() == CI) {
124 TheOnlyDest = i.getCaseSuccessor();
128 // Check to see if this branch is going to the same place as the default
129 // dest. If so, eliminate it as an explicit compare.
130 if (i.getCaseSuccessor() == DefaultDest) {
131 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
132 unsigned NCases = SI->getNumCases();
133 // Fold the case metadata into the default if there will be any branches
134 // left, unless the metadata doesn't match the switch.
135 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
136 // Collect branch weights into a vector.
137 SmallVector<uint32_t, 8> Weights;
138 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
140 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
142 Weights.push_back(CI->getValue().getZExtValue());
144 // Merge weight of this case to the default weight.
145 unsigned idx = i.getCaseIndex();
146 Weights[0] += Weights[idx+1];
147 // Remove weight for this case.
148 std::swap(Weights[idx+1], Weights.back());
150 SI->setMetadata(LLVMContext::MD_prof,
151 MDBuilder(BB->getContext()).
152 createBranchWeights(Weights));
154 // Remove this entry.
155 DefaultDest->removePredecessor(SI->getParent());
161 // Otherwise, check to see if the switch only branches to one destination.
162 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
164 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
167 if (CI && !TheOnlyDest) {
168 // Branching on a constant, but not any of the cases, go to the default
170 TheOnlyDest = SI->getDefaultDest();
173 // If we found a single destination that we can fold the switch into, do so
176 // Insert the new branch.
177 Builder.CreateBr(TheOnlyDest);
178 BasicBlock *BB = SI->getParent();
180 // Remove entries from PHI nodes which we no longer branch to...
181 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
182 // Found case matching a constant operand?
183 BasicBlock *Succ = SI->getSuccessor(i);
184 if (Succ == TheOnlyDest)
185 TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
187 Succ->removePredecessor(BB);
190 // Delete the old switch.
191 Value *Cond = SI->getCondition();
192 SI->eraseFromParent();
193 if (DeleteDeadConditions)
194 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
198 if (SI->getNumCases() == 1) {
199 // Otherwise, we can fold this switch into a conditional branch
200 // instruction if it has only one non-default destination.
201 SwitchInst::CaseIt FirstCase = SI->case_begin();
202 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
203 FirstCase.getCaseValue(), "cond");
205 // Insert the new branch.
206 BranchInst *NewBr = Builder.CreateCondBr(Cond,
207 FirstCase.getCaseSuccessor(),
208 SI->getDefaultDest());
209 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
210 if (MD && MD->getNumOperands() == 3) {
211 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
212 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
213 assert(SICase && SIDef);
214 // The TrueWeight should be the weight for the single case of SI.
215 NewBr->setMetadata(LLVMContext::MD_prof,
216 MDBuilder(BB->getContext()).
217 createBranchWeights(SICase->getValue().getZExtValue(),
218 SIDef->getValue().getZExtValue()));
221 // Delete the old switch.
222 SI->eraseFromParent();
228 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
229 // indirectbr blockaddress(@F, @BB) -> br label @BB
230 if (BlockAddress *BA =
231 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
232 BasicBlock *TheOnlyDest = BA->getBasicBlock();
233 // Insert the new branch.
234 Builder.CreateBr(TheOnlyDest);
236 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
237 if (IBI->getDestination(i) == TheOnlyDest)
238 TheOnlyDest = nullptr;
240 IBI->getDestination(i)->removePredecessor(IBI->getParent());
242 Value *Address = IBI->getAddress();
243 IBI->eraseFromParent();
244 if (DeleteDeadConditions)
245 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
247 // If we didn't find our destination in the IBI successor list, then we
248 // have undefined behavior. Replace the unconditional branch with an
249 // 'unreachable' instruction.
251 BB->getTerminator()->eraseFromParent();
252 new UnreachableInst(BB->getContext(), BB);
263 //===----------------------------------------------------------------------===//
264 // Local dead code elimination.
267 /// isInstructionTriviallyDead - Return true if the result produced by the
268 /// instruction is not used, and the instruction has no side effects.
270 bool llvm::isInstructionTriviallyDead(Instruction *I,
271 const TargetLibraryInfo *TLI) {
272 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
274 // We don't want the landingpad instruction removed by anything this general.
275 if (isa<LandingPadInst>(I))
278 // We don't want debug info removed by anything this general, unless
279 // debug info is empty.
280 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
281 if (DDI->getAddress())
285 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
291 if (!I->mayHaveSideEffects()) return true;
293 // Special case intrinsics that "may have side effects" but can be deleted
295 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
296 // Safe to delete llvm.stacksave if dead.
297 if (II->getIntrinsicID() == Intrinsic::stacksave)
300 // Lifetime intrinsics are dead when their right-hand is undef.
301 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
302 II->getIntrinsicID() == Intrinsic::lifetime_end)
303 return isa<UndefValue>(II->getArgOperand(1));
305 // Assumptions are dead if their condition is trivially true.
306 if (II->getIntrinsicID() == Intrinsic::assume) {
307 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
308 return !Cond->isZero();
314 if (isAllocLikeFn(I, TLI)) return true;
316 if (CallInst *CI = isFreeCall(I, TLI))
317 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
318 return C->isNullValue() || isa<UndefValue>(C);
323 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
324 /// trivially dead instruction, delete it. If that makes any of its operands
325 /// trivially dead, delete them too, recursively. Return true if any
326 /// instructions were deleted.
328 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
329 const TargetLibraryInfo *TLI) {
330 Instruction *I = dyn_cast<Instruction>(V);
331 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
334 SmallVector<Instruction*, 16> DeadInsts;
335 DeadInsts.push_back(I);
338 I = DeadInsts.pop_back_val();
340 // Null out all of the instruction's operands to see if any operand becomes
342 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
343 Value *OpV = I->getOperand(i);
344 I->setOperand(i, nullptr);
346 if (!OpV->use_empty()) continue;
348 // If the operand is an instruction that became dead as we nulled out the
349 // operand, and if it is 'trivially' dead, delete it in a future loop
351 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
352 if (isInstructionTriviallyDead(OpI, TLI))
353 DeadInsts.push_back(OpI);
356 I->eraseFromParent();
357 } while (!DeadInsts.empty());
362 /// areAllUsesEqual - Check whether the uses of a value are all the same.
363 /// This is similar to Instruction::hasOneUse() except this will also return
364 /// true when there are no uses or multiple uses that all refer to the same
366 static bool areAllUsesEqual(Instruction *I) {
367 Value::user_iterator UI = I->user_begin();
368 Value::user_iterator UE = I->user_end();
373 for (++UI; UI != UE; ++UI) {
380 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
381 /// dead PHI node, due to being a def-use chain of single-use nodes that
382 /// either forms a cycle or is terminated by a trivially dead instruction,
383 /// delete it. If that makes any of its operands trivially dead, delete them
384 /// too, recursively. Return true if a change was made.
385 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
386 const TargetLibraryInfo *TLI) {
387 SmallPtrSet<Instruction*, 4> Visited;
388 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
389 I = cast<Instruction>(*I->user_begin())) {
391 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
393 // If we find an instruction more than once, we're on a cycle that
394 // won't prove fruitful.
395 if (!Visited.insert(I)) {
396 // Break the cycle and delete the instruction and its operands.
397 I->replaceAllUsesWith(UndefValue::get(I->getType()));
398 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
405 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
406 /// simplify any instructions in it and recursively delete dead instructions.
408 /// This returns true if it changed the code, note that it can delete
409 /// instructions in other blocks as well in this block.
410 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
411 const TargetLibraryInfo *TLI) {
412 bool MadeChange = false;
415 // In debug builds, ensure that the terminator of the block is never replaced
416 // or deleted by these simplifications. The idea of simplification is that it
417 // cannot introduce new instructions, and there is no way to replace the
418 // terminator of a block without introducing a new instruction.
419 AssertingVH<Instruction> TerminatorVH(--BB->end());
422 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
423 assert(!BI->isTerminator());
424 Instruction *Inst = BI++;
427 if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
434 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
441 //===----------------------------------------------------------------------===//
442 // Control Flow Graph Restructuring.
446 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
447 /// method is called when we're about to delete Pred as a predecessor of BB. If
448 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
450 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
451 /// nodes that collapse into identity values. For example, if we have:
452 /// x = phi(1, 0, 0, 0)
455 /// .. and delete the predecessor corresponding to the '1', this will attempt to
456 /// recursively fold the and to 0.
457 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
459 // This only adjusts blocks with PHI nodes.
460 if (!isa<PHINode>(BB->begin()))
463 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
464 // them down. This will leave us with single entry phi nodes and other phis
465 // that can be removed.
466 BB->removePredecessor(Pred, true);
468 WeakVH PhiIt = &BB->front();
469 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
470 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
471 Value *OldPhiIt = PhiIt;
473 if (!recursivelySimplifyInstruction(PN, TD))
476 // If recursive simplification ended up deleting the next PHI node we would
477 // iterate to, then our iterator is invalid, restart scanning from the top
479 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
484 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
485 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
486 /// between them, moving the instructions in the predecessor into DestBB and
487 /// deleting the predecessor block.
489 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
490 // If BB has single-entry PHI nodes, fold them.
491 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
492 Value *NewVal = PN->getIncomingValue(0);
493 // Replace self referencing PHI with undef, it must be dead.
494 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
495 PN->replaceAllUsesWith(NewVal);
496 PN->eraseFromParent();
499 BasicBlock *PredBB = DestBB->getSinglePredecessor();
500 assert(PredBB && "Block doesn't have a single predecessor!");
502 // Zap anything that took the address of DestBB. Not doing this will give the
503 // address an invalid value.
504 if (DestBB->hasAddressTaken()) {
505 BlockAddress *BA = BlockAddress::get(DestBB);
506 Constant *Replacement =
507 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
508 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
510 BA->destroyConstant();
513 // Anything that branched to PredBB now branches to DestBB.
514 PredBB->replaceAllUsesWith(DestBB);
516 // Splice all the instructions from PredBB to DestBB.
517 PredBB->getTerminator()->eraseFromParent();
518 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
520 // If the PredBB is the entry block of the function, move DestBB up to
521 // become the entry block after we erase PredBB.
522 if (PredBB == &DestBB->getParent()->getEntryBlock())
523 DestBB->moveAfter(PredBB);
526 if (DominatorTreeWrapperPass *DTWP =
527 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
528 DominatorTree &DT = DTWP->getDomTree();
529 BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock();
530 DT.changeImmediateDominator(DestBB, PredBBIDom);
531 DT.eraseNode(PredBB);
535 PredBB->eraseFromParent();
538 /// CanMergeValues - Return true if we can choose one of these values to use
539 /// in place of the other. Note that we will always choose the non-undef
541 static bool CanMergeValues(Value *First, Value *Second) {
542 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
545 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
546 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
548 /// Assumption: Succ is the single successor for BB.
550 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
551 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
553 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
554 << Succ->getName() << "\n");
555 // Shortcut, if there is only a single predecessor it must be BB and merging
557 if (Succ->getSinglePredecessor()) return true;
559 // Make a list of the predecessors of BB
560 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
562 // Look at all the phi nodes in Succ, to see if they present a conflict when
563 // merging these blocks
564 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
565 PHINode *PN = cast<PHINode>(I);
567 // If the incoming value from BB is again a PHINode in
568 // BB which has the same incoming value for *PI as PN does, we can
569 // merge the phi nodes and then the blocks can still be merged
570 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
571 if (BBPN && BBPN->getParent() == BB) {
572 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
573 BasicBlock *IBB = PN->getIncomingBlock(PI);
574 if (BBPreds.count(IBB) &&
575 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
576 PN->getIncomingValue(PI))) {
577 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
578 << Succ->getName() << " is conflicting with "
579 << BBPN->getName() << " with regard to common predecessor "
580 << IBB->getName() << "\n");
585 Value* Val = PN->getIncomingValueForBlock(BB);
586 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
587 // See if the incoming value for the common predecessor is equal to the
588 // one for BB, in which case this phi node will not prevent the merging
590 BasicBlock *IBB = PN->getIncomingBlock(PI);
591 if (BBPreds.count(IBB) &&
592 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
593 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
594 << Succ->getName() << " is conflicting with regard to common "
595 << "predecessor " << IBB->getName() << "\n");
605 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
606 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
608 /// \brief Determines the value to use as the phi node input for a block.
610 /// Select between \p OldVal any value that we know flows from \p BB
611 /// to a particular phi on the basis of which one (if either) is not
612 /// undef. Update IncomingValues based on the selected value.
614 /// \param OldVal The value we are considering selecting.
615 /// \param BB The block that the value flows in from.
616 /// \param IncomingValues A map from block-to-value for other phi inputs
617 /// that we have examined.
619 /// \returns the selected value.
620 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
621 IncomingValueMap &IncomingValues) {
622 if (!isa<UndefValue>(OldVal)) {
623 assert((!IncomingValues.count(BB) ||
624 IncomingValues.find(BB)->second == OldVal) &&
625 "Expected OldVal to match incoming value from BB!");
627 IncomingValues.insert(std::make_pair(BB, OldVal));
631 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
632 if (It != IncomingValues.end()) return It->second;
637 /// \brief Create a map from block to value for the operands of a
640 /// Create a map from block to value for each non-undef value flowing
643 /// \param PN The phi we are collecting the map for.
644 /// \param IncomingValues [out] The map from block to value for this phi.
645 static void gatherIncomingValuesToPhi(PHINode *PN,
646 IncomingValueMap &IncomingValues) {
647 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
648 BasicBlock *BB = PN->getIncomingBlock(i);
649 Value *V = PN->getIncomingValue(i);
651 if (!isa<UndefValue>(V))
652 IncomingValues.insert(std::make_pair(BB, V));
656 /// \brief Replace the incoming undef values to a phi with the values
657 /// from a block-to-value map.
659 /// \param PN The phi we are replacing the undefs in.
660 /// \param IncomingValues A map from block to value.
661 static void replaceUndefValuesInPhi(PHINode *PN,
662 const IncomingValueMap &IncomingValues) {
663 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
664 Value *V = PN->getIncomingValue(i);
666 if (!isa<UndefValue>(V)) continue;
668 BasicBlock *BB = PN->getIncomingBlock(i);
669 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
670 if (It == IncomingValues.end()) continue;
672 PN->setIncomingValue(i, It->second);
676 /// \brief Replace a value flowing from a block to a phi with
677 /// potentially multiple instances of that value flowing from the
678 /// block's predecessors to the phi.
680 /// \param BB The block with the value flowing into the phi.
681 /// \param BBPreds The predecessors of BB.
682 /// \param PN The phi that we are updating.
683 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
684 const PredBlockVector &BBPreds,
686 Value *OldVal = PN->removeIncomingValue(BB, false);
687 assert(OldVal && "No entry in PHI for Pred BB!");
689 IncomingValueMap IncomingValues;
691 // We are merging two blocks - BB, and the block containing PN - and
692 // as a result we need to redirect edges from the predecessors of BB
693 // to go to the block containing PN, and update PN
694 // accordingly. Since we allow merging blocks in the case where the
695 // predecessor and successor blocks both share some predecessors,
696 // and where some of those common predecessors might have undef
697 // values flowing into PN, we want to rewrite those values to be
698 // consistent with the non-undef values.
700 gatherIncomingValuesToPhi(PN, IncomingValues);
702 // If this incoming value is one of the PHI nodes in BB, the new entries
703 // in the PHI node are the entries from the old PHI.
704 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
705 PHINode *OldValPN = cast<PHINode>(OldVal);
706 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
707 // Note that, since we are merging phi nodes and BB and Succ might
708 // have common predecessors, we could end up with a phi node with
709 // identical incoming branches. This will be cleaned up later (and
710 // will trigger asserts if we try to clean it up now, without also
711 // simplifying the corresponding conditional branch).
712 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
713 Value *PredVal = OldValPN->getIncomingValue(i);
714 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
717 // And add a new incoming value for this predecessor for the
718 // newly retargeted branch.
719 PN->addIncoming(Selected, PredBB);
722 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
723 // Update existing incoming values in PN for this
724 // predecessor of BB.
725 BasicBlock *PredBB = BBPreds[i];
726 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
729 // And add a new incoming value for this predecessor for the
730 // newly retargeted branch.
731 PN->addIncoming(Selected, PredBB);
735 replaceUndefValuesInPhi(PN, IncomingValues);
738 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
739 /// unconditional branch, and contains no instructions other than PHI nodes,
740 /// potential side-effect free intrinsics and the branch. If possible,
741 /// eliminate BB by rewriting all the predecessors to branch to the successor
742 /// block and return true. If we can't transform, return false.
743 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
744 assert(BB != &BB->getParent()->getEntryBlock() &&
745 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
747 // We can't eliminate infinite loops.
748 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
749 if (BB == Succ) return false;
751 // Check to see if merging these blocks would cause conflicts for any of the
752 // phi nodes in BB or Succ. If not, we can safely merge.
753 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
755 // Check for cases where Succ has multiple predecessors and a PHI node in BB
756 // has uses which will not disappear when the PHI nodes are merged. It is
757 // possible to handle such cases, but difficult: it requires checking whether
758 // BB dominates Succ, which is non-trivial to calculate in the case where
759 // Succ has multiple predecessors. Also, it requires checking whether
760 // constructing the necessary self-referential PHI node doesn't introduce any
761 // conflicts; this isn't too difficult, but the previous code for doing this
764 // Note that if this check finds a live use, BB dominates Succ, so BB is
765 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
766 // folding the branch isn't profitable in that case anyway.
767 if (!Succ->getSinglePredecessor()) {
768 BasicBlock::iterator BBI = BB->begin();
769 while (isa<PHINode>(*BBI)) {
770 for (Use &U : BBI->uses()) {
771 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
772 if (PN->getIncomingBlock(U) != BB)
782 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
784 if (isa<PHINode>(Succ->begin())) {
785 // If there is more than one pred of succ, and there are PHI nodes in
786 // the successor, then we need to add incoming edges for the PHI nodes
788 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
790 // Loop over all of the PHI nodes in the successor of BB.
791 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
792 PHINode *PN = cast<PHINode>(I);
794 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
798 if (Succ->getSinglePredecessor()) {
799 // BB is the only predecessor of Succ, so Succ will end up with exactly
800 // the same predecessors BB had.
802 // Copy over any phi, debug or lifetime instruction.
803 BB->getTerminator()->eraseFromParent();
804 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
806 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
807 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
808 assert(PN->use_empty() && "There shouldn't be any uses here!");
809 PN->eraseFromParent();
813 // Everything that jumped to BB now goes to Succ.
814 BB->replaceAllUsesWith(Succ);
815 if (!Succ->hasName()) Succ->takeName(BB);
816 BB->eraseFromParent(); // Delete the old basic block.
820 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
821 /// nodes in this block. This doesn't try to be clever about PHI nodes
822 /// which differ only in the order of the incoming values, but instcombine
823 /// orders them so it usually won't matter.
825 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
826 bool Changed = false;
828 // This implementation doesn't currently consider undef operands
829 // specially. Theoretically, two phis which are identical except for
830 // one having an undef where the other doesn't could be collapsed.
832 // Map from PHI hash values to PHI nodes. If multiple PHIs have
833 // the same hash value, the element is the first PHI in the
834 // linked list in CollisionMap.
835 DenseMap<uintptr_t, PHINode *> HashMap;
837 // Maintain linked lists of PHI nodes with common hash values.
838 DenseMap<PHINode *, PHINode *> CollisionMap;
841 for (BasicBlock::iterator I = BB->begin();
842 PHINode *PN = dyn_cast<PHINode>(I++); ) {
843 // Compute a hash value on the operands. Instcombine will likely have sorted
844 // them, which helps expose duplicates, but we have to check all the
845 // operands to be safe in case instcombine hasn't run.
847 // This hash algorithm is quite weak as hash functions go, but it seems
848 // to do a good enough job for this particular purpose, and is very quick.
849 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
850 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
851 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
853 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
855 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
856 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
858 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
860 // If we've never seen this hash value before, it's a unique PHI.
861 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
862 HashMap.insert(std::make_pair(Hash, PN));
863 if (Pair.second) continue;
864 // Otherwise it's either a duplicate or a hash collision.
865 for (PHINode *OtherPN = Pair.first->second; ; ) {
866 if (OtherPN->isIdenticalTo(PN)) {
867 // A duplicate. Replace this PHI with its duplicate.
868 PN->replaceAllUsesWith(OtherPN);
869 PN->eraseFromParent();
873 // A non-duplicate hash collision.
874 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
875 if (I == CollisionMap.end()) {
876 // Set this PHI to be the head of the linked list of colliding PHIs.
877 PHINode *Old = Pair.first->second;
878 Pair.first->second = PN;
879 CollisionMap[PN] = Old;
882 // Proceed to the next PHI in the list.
890 /// enforceKnownAlignment - If the specified pointer points to an object that
891 /// we control, modify the object's alignment to PrefAlign. This isn't
892 /// often possible though. If alignment is important, a more reliable approach
893 /// is to simply align all global variables and allocation instructions to
894 /// their preferred alignment from the beginning.
896 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
897 unsigned PrefAlign, const DataLayout *TD) {
898 V = V->stripPointerCasts();
900 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
901 // If the preferred alignment is greater than the natural stack alignment
902 // then don't round up. This avoids dynamic stack realignment.
903 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
905 // If there is a requested alignment and if this is an alloca, round up.
906 if (AI->getAlignment() >= PrefAlign)
907 return AI->getAlignment();
908 AI->setAlignment(PrefAlign);
912 if (auto *GO = dyn_cast<GlobalObject>(V)) {
913 // If there is a large requested alignment and we can, bump up the alignment
915 if (GO->isDeclaration())
917 // If the memory we set aside for the global may not be the memory used by
918 // the final program then it is impossible for us to reliably enforce the
919 // preferred alignment.
920 if (GO->isWeakForLinker())
923 if (GO->getAlignment() >= PrefAlign)
924 return GO->getAlignment();
925 // We can only increase the alignment of the global if it has no alignment
926 // specified or if it is not assigned a section. If it is assigned a
927 // section, the global could be densely packed with other objects in the
928 // section, increasing the alignment could cause padding issues.
929 if (!GO->hasSection() || GO->getAlignment() == 0)
930 GO->setAlignment(PrefAlign);
931 return GO->getAlignment();
937 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
938 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
939 /// and it is more than the alignment of the ultimate object, see if we can
940 /// increase the alignment of the ultimate object, making this check succeed.
941 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
942 const DataLayout *DL,
943 AssumptionTracker *AT,
944 const Instruction *CxtI,
945 const DominatorTree *DT) {
946 assert(V->getType()->isPointerTy() &&
947 "getOrEnforceKnownAlignment expects a pointer!");
948 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
950 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
951 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AT, CxtI, DT);
952 unsigned TrailZ = KnownZero.countTrailingOnes();
954 // Avoid trouble with ridiculously large TrailZ values, such as
955 // those computed from a null pointer.
956 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
958 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
960 // LLVM doesn't support alignments larger than this currently.
961 Align = std::min(Align, +Value::MaximumAlignment);
963 if (PrefAlign > Align)
964 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
966 // We don't need to make any adjustment.
970 ///===---------------------------------------------------------------------===//
971 /// Dbg Intrinsic utilities
974 /// See if there is a dbg.value intrinsic for DIVar before I.
975 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
976 // Since we can't guarantee that the original dbg.declare instrinsic
977 // is removed by LowerDbgDeclare(), we need to make sure that we are
978 // not inserting the same dbg.value intrinsic over and over.
979 llvm::BasicBlock::InstListType::iterator PrevI(I);
980 if (PrevI != I->getParent()->getInstList().begin()) {
982 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
983 if (DVI->getValue() == I->getOperand(0) &&
984 DVI->getOffset() == 0 &&
985 DVI->getVariable() == DIVar)
991 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
992 /// that has an associated llvm.dbg.decl intrinsic.
993 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
994 StoreInst *SI, DIBuilder &Builder) {
995 DIVariable DIVar(DDI->getVariable());
996 DIExpression DIExpr(DDI->getExpression());
997 assert((!DIVar || DIVar.isVariable()) &&
998 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1002 if (LdStHasDebugValue(DIVar, SI))
1005 Instruction *DbgVal = nullptr;
1006 // If an argument is zero extended then use argument directly. The ZExt
1007 // may be zapped by an optimization pass in future.
1008 Argument *ExtendedArg = nullptr;
1009 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1010 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1011 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1012 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1014 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, DIExpr, SI);
1016 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar,
1018 DbgVal->setDebugLoc(DDI->getDebugLoc());
1022 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1023 /// that has an associated llvm.dbg.decl intrinsic.
1024 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1025 LoadInst *LI, DIBuilder &Builder) {
1026 DIVariable DIVar(DDI->getVariable());
1027 DIExpression DIExpr(DDI->getExpression());
1028 assert((!DIVar || DIVar.isVariable()) &&
1029 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1033 if (LdStHasDebugValue(DIVar, LI))
1036 Instruction *DbgVal =
1037 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, DIVar, DIExpr, LI);
1038 DbgVal->setDebugLoc(DDI->getDebugLoc());
1042 /// Determine whether this alloca is either a VLA or an array.
1043 static bool isArray(AllocaInst *AI) {
1044 return AI->isArrayAllocation() ||
1045 AI->getType()->getElementType()->isArrayTy();
1048 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1049 /// of llvm.dbg.value intrinsics.
1050 bool llvm::LowerDbgDeclare(Function &F) {
1051 DIBuilder DIB(*F.getParent());
1052 SmallVector<DbgDeclareInst *, 4> Dbgs;
1054 for (BasicBlock::iterator BI : FI)
1055 if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
1056 Dbgs.push_back(DDI);
1061 for (auto &I : Dbgs) {
1062 DbgDeclareInst *DDI = I;
1063 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1064 // If this is an alloca for a scalar variable, insert a dbg.value
1065 // at each load and store to the alloca and erase the dbg.declare.
1066 // The dbg.values allow tracking a variable even if it is not
1067 // stored on the stack, while the dbg.declare can only describe
1068 // the stack slot (and at a lexical-scope granularity). Later
1069 // passes will attempt to elide the stack slot.
1070 if (AI && !isArray(AI)) {
1071 for (User *U : AI->users())
1072 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1073 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1074 else if (LoadInst *LI = dyn_cast<LoadInst>(U))
1075 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1076 else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1077 // This is a call by-value or some other instruction that
1078 // takes a pointer to the variable. Insert a *value*
1079 // intrinsic that describes the alloca.
1080 auto DbgVal = DIB.insertDbgValueIntrinsic(
1081 AI, 0, DIVariable(DDI->getVariable()),
1082 DIExpression(DDI->getExpression()), CI);
1083 DbgVal->setDebugLoc(DDI->getDebugLoc());
1085 DDI->eraseFromParent();
1091 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1092 /// alloca 'V', if any.
1093 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1094 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
1095 for (User *U : DebugNode->users())
1096 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1102 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1103 DIBuilder &Builder) {
1104 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1107 DIVariable DIVar(DDI->getVariable());
1108 DIExpression DIExpr(DDI->getExpression());
1109 assert((!DIVar || DIVar.isVariable()) &&
1110 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1114 // Create a copy of the original DIDescriptor for user variable, appending
1115 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1116 // will take a value storing address of the memory for variable, not
1118 Type *Int64Ty = Type::getInt64Ty(AI->getContext());
1119 SmallVector<Value *, 4> NewDIExpr;
1121 for (unsigned i = 0, n = DIExpr.getNumElements(); i < n; ++i) {
1122 NewDIExpr.push_back(ConstantInt::get(Int64Ty, DIExpr.getElement(i)));
1125 NewDIExpr.push_back(ConstantInt::get(Int64Ty, dwarf::DW_OP_deref));
1127 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1128 // and remove old llvm.dbg.declare.
1129 BasicBlock *BB = AI->getParent();
1130 Builder.insertDeclare(NewAllocaAddress, DIVar,
1131 Builder.createExpression(NewDIExpr), BB);
1132 DDI->eraseFromParent();
1136 /// changeToUnreachable - Insert an unreachable instruction before the specified
1137 /// instruction, making it and the rest of the code in the block dead.
1138 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1139 BasicBlock *BB = I->getParent();
1140 // Loop over all of the successors, removing BB's entry from any PHI
1142 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1143 (*SI)->removePredecessor(BB);
1145 // Insert a call to llvm.trap right before this. This turns the undefined
1146 // behavior into a hard fail instead of falling through into random code.
1149 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1150 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1151 CallTrap->setDebugLoc(I->getDebugLoc());
1153 new UnreachableInst(I->getContext(), I);
1155 // All instructions after this are dead.
1156 BasicBlock::iterator BBI = I, BBE = BB->end();
1157 while (BBI != BBE) {
1158 if (!BBI->use_empty())
1159 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1160 BB->getInstList().erase(BBI++);
1164 /// changeToCall - Convert the specified invoke into a normal call.
1165 static void changeToCall(InvokeInst *II) {
1166 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1167 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1168 NewCall->takeName(II);
1169 NewCall->setCallingConv(II->getCallingConv());
1170 NewCall->setAttributes(II->getAttributes());
1171 NewCall->setDebugLoc(II->getDebugLoc());
1172 II->replaceAllUsesWith(NewCall);
1174 // Follow the call by a branch to the normal destination.
1175 BranchInst::Create(II->getNormalDest(), II);
1177 // Update PHI nodes in the unwind destination
1178 II->getUnwindDest()->removePredecessor(II->getParent());
1179 II->eraseFromParent();
1182 static bool markAliveBlocks(BasicBlock *BB,
1183 SmallPtrSetImpl<BasicBlock*> &Reachable) {
1185 SmallVector<BasicBlock*, 128> Worklist;
1186 Worklist.push_back(BB);
1187 Reachable.insert(BB);
1188 bool Changed = false;
1190 BB = Worklist.pop_back_val();
1192 // Do a quick scan of the basic block, turning any obviously unreachable
1193 // instructions into LLVM unreachable insts. The instruction combining pass
1194 // canonicalizes unreachable insts into stores to null or undef.
1195 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1196 // Assumptions that are known to be false are equivalent to unreachable.
1197 // Also, if the condition is undefined, then we make the choice most
1198 // beneficial to the optimizer, and choose that to also be unreachable.
1199 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
1200 if (II->getIntrinsicID() == Intrinsic::assume) {
1201 bool MakeUnreachable = false;
1202 if (isa<UndefValue>(II->getArgOperand(0)))
1203 MakeUnreachable = true;
1204 else if (ConstantInt *Cond =
1205 dyn_cast<ConstantInt>(II->getArgOperand(0)))
1206 MakeUnreachable = Cond->isZero();
1208 if (MakeUnreachable) {
1209 // Don't insert a call to llvm.trap right before the unreachable.
1210 changeToUnreachable(BBI, false);
1216 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1217 if (CI->doesNotReturn()) {
1218 // If we found a call to a no-return function, insert an unreachable
1219 // instruction after it. Make sure there isn't *already* one there
1222 if (!isa<UnreachableInst>(BBI)) {
1223 // Don't insert a call to llvm.trap right before the unreachable.
1224 changeToUnreachable(BBI, false);
1231 // Store to undef and store to null are undefined and used to signal that
1232 // they should be changed to unreachable by passes that can't modify the
1234 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1235 // Don't touch volatile stores.
1236 if (SI->isVolatile()) continue;
1238 Value *Ptr = SI->getOperand(1);
1240 if (isa<UndefValue>(Ptr) ||
1241 (isa<ConstantPointerNull>(Ptr) &&
1242 SI->getPointerAddressSpace() == 0)) {
1243 changeToUnreachable(SI, true);
1250 // Turn invokes that call 'nounwind' functions into ordinary calls.
1251 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1252 Value *Callee = II->getCalledValue();
1253 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1254 changeToUnreachable(II, true);
1256 } else if (II->doesNotThrow()) {
1257 if (II->use_empty() && II->onlyReadsMemory()) {
1258 // jump to the normal destination branch.
1259 BranchInst::Create(II->getNormalDest(), II);
1260 II->getUnwindDest()->removePredecessor(II->getParent());
1261 II->eraseFromParent();
1268 Changed |= ConstantFoldTerminator(BB, true);
1269 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1270 if (Reachable.insert(*SI))
1271 Worklist.push_back(*SI);
1272 } while (!Worklist.empty());
1276 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1277 /// if they are in a dead cycle. Return true if a change was made, false
1279 bool llvm::removeUnreachableBlocks(Function &F) {
1280 SmallPtrSet<BasicBlock*, 128> Reachable;
1281 bool Changed = markAliveBlocks(F.begin(), Reachable);
1283 // If there are unreachable blocks in the CFG...
1284 if (Reachable.size() == F.size())
1287 assert(Reachable.size() < F.size());
1288 NumRemoved += F.size()-Reachable.size();
1290 // Loop over all of the basic blocks that are not reachable, dropping all of
1291 // their internal references...
1292 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1293 if (Reachable.count(BB))
1296 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1297 if (Reachable.count(*SI))
1298 (*SI)->removePredecessor(BB);
1299 BB->dropAllReferences();
1302 for (Function::iterator I = ++F.begin(); I != F.end();)
1303 if (!Reachable.count(I))
1304 I = F.getBasicBlockList().erase(I);
1311 void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
1312 SmallVector<std::pair<unsigned, MDNode*>, 4> Metadata;
1313 K->dropUnknownMetadata(KnownIDs);
1314 K->getAllMetadataOtherThanDebugLoc(Metadata);
1315 for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
1316 unsigned Kind = Metadata[i].first;
1317 MDNode *JMD = J->getMetadata(Kind);
1318 MDNode *KMD = Metadata[i].second;
1322 K->setMetadata(Kind, nullptr); // Remove unknown metadata
1324 case LLVMContext::MD_dbg:
1325 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1326 case LLVMContext::MD_tbaa:
1327 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
1329 case LLVMContext::MD_alias_scope:
1330 case LLVMContext::MD_noalias:
1331 K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
1333 case LLVMContext::MD_range:
1334 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
1336 case LLVMContext::MD_fpmath:
1337 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
1339 case LLVMContext::MD_invariant_load:
1340 // Only set the !invariant.load if it is present in both instructions.
1341 K->setMetadata(Kind, JMD);