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;
141 mdconst::dyn_extract<ConstantInt>(MD->getOperand(MD_i));
143 Weights.push_back(CI->getValue().getZExtValue());
145 // Merge weight of this case to the default weight.
146 unsigned idx = i.getCaseIndex();
147 Weights[0] += Weights[idx+1];
148 // Remove weight for this case.
149 std::swap(Weights[idx+1], Weights.back());
151 SI->setMetadata(LLVMContext::MD_prof,
152 MDBuilder(BB->getContext()).
153 createBranchWeights(Weights));
155 // Remove this entry.
156 DefaultDest->removePredecessor(SI->getParent());
162 // Otherwise, check to see if the switch only branches to one destination.
163 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
165 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
168 if (CI && !TheOnlyDest) {
169 // Branching on a constant, but not any of the cases, go to the default
171 TheOnlyDest = SI->getDefaultDest();
174 // If we found a single destination that we can fold the switch into, do so
177 // Insert the new branch.
178 Builder.CreateBr(TheOnlyDest);
179 BasicBlock *BB = SI->getParent();
181 // Remove entries from PHI nodes which we no longer branch to...
182 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
183 // Found case matching a constant operand?
184 BasicBlock *Succ = SI->getSuccessor(i);
185 if (Succ == TheOnlyDest)
186 TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
188 Succ->removePredecessor(BB);
191 // Delete the old switch.
192 Value *Cond = SI->getCondition();
193 SI->eraseFromParent();
194 if (DeleteDeadConditions)
195 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
199 if (SI->getNumCases() == 1) {
200 // Otherwise, we can fold this switch into a conditional branch
201 // instruction if it has only one non-default destination.
202 SwitchInst::CaseIt FirstCase = SI->case_begin();
203 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
204 FirstCase.getCaseValue(), "cond");
206 // Insert the new branch.
207 BranchInst *NewBr = Builder.CreateCondBr(Cond,
208 FirstCase.getCaseSuccessor(),
209 SI->getDefaultDest());
210 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
211 if (MD && MD->getNumOperands() == 3) {
212 ConstantInt *SICase =
213 mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
215 mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
216 assert(SICase && SIDef);
217 // The TrueWeight should be the weight for the single case of SI.
218 NewBr->setMetadata(LLVMContext::MD_prof,
219 MDBuilder(BB->getContext()).
220 createBranchWeights(SICase->getValue().getZExtValue(),
221 SIDef->getValue().getZExtValue()));
224 // Delete the old switch.
225 SI->eraseFromParent();
231 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
232 // indirectbr blockaddress(@F, @BB) -> br label @BB
233 if (BlockAddress *BA =
234 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
235 BasicBlock *TheOnlyDest = BA->getBasicBlock();
236 // Insert the new branch.
237 Builder.CreateBr(TheOnlyDest);
239 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
240 if (IBI->getDestination(i) == TheOnlyDest)
241 TheOnlyDest = nullptr;
243 IBI->getDestination(i)->removePredecessor(IBI->getParent());
245 Value *Address = IBI->getAddress();
246 IBI->eraseFromParent();
247 if (DeleteDeadConditions)
248 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
250 // If we didn't find our destination in the IBI successor list, then we
251 // have undefined behavior. Replace the unconditional branch with an
252 // 'unreachable' instruction.
254 BB->getTerminator()->eraseFromParent();
255 new UnreachableInst(BB->getContext(), BB);
266 //===----------------------------------------------------------------------===//
267 // Local dead code elimination.
270 /// isInstructionTriviallyDead - Return true if the result produced by the
271 /// instruction is not used, and the instruction has no side effects.
273 bool llvm::isInstructionTriviallyDead(Instruction *I,
274 const TargetLibraryInfo *TLI) {
275 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
277 // We don't want the landingpad instruction removed by anything this general.
278 if (isa<LandingPadInst>(I))
281 // We don't want debug info removed by anything this general, unless
282 // debug info is empty.
283 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
284 if (DDI->getAddress())
288 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
294 if (!I->mayHaveSideEffects()) return true;
296 // Special case intrinsics that "may have side effects" but can be deleted
298 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
299 // Safe to delete llvm.stacksave if dead.
300 if (II->getIntrinsicID() == Intrinsic::stacksave)
303 // Lifetime intrinsics are dead when their right-hand is undef.
304 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
305 II->getIntrinsicID() == Intrinsic::lifetime_end)
306 return isa<UndefValue>(II->getArgOperand(1));
308 // Assumptions are dead if their condition is trivially true.
309 if (II->getIntrinsicID() == Intrinsic::assume) {
310 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
311 return !Cond->isZero();
317 if (isAllocLikeFn(I, TLI)) return true;
319 if (CallInst *CI = isFreeCall(I, TLI))
320 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
321 return C->isNullValue() || isa<UndefValue>(C);
326 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
327 /// trivially dead instruction, delete it. If that makes any of its operands
328 /// trivially dead, delete them too, recursively. Return true if any
329 /// instructions were deleted.
331 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
332 const TargetLibraryInfo *TLI) {
333 Instruction *I = dyn_cast<Instruction>(V);
334 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
337 SmallVector<Instruction*, 16> DeadInsts;
338 DeadInsts.push_back(I);
341 I = DeadInsts.pop_back_val();
343 // Null out all of the instruction's operands to see if any operand becomes
345 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
346 Value *OpV = I->getOperand(i);
347 I->setOperand(i, nullptr);
349 if (!OpV->use_empty()) continue;
351 // If the operand is an instruction that became dead as we nulled out the
352 // operand, and if it is 'trivially' dead, delete it in a future loop
354 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
355 if (isInstructionTriviallyDead(OpI, TLI))
356 DeadInsts.push_back(OpI);
359 I->eraseFromParent();
360 } while (!DeadInsts.empty());
365 /// areAllUsesEqual - Check whether the uses of a value are all the same.
366 /// This is similar to Instruction::hasOneUse() except this will also return
367 /// true when there are no uses or multiple uses that all refer to the same
369 static bool areAllUsesEqual(Instruction *I) {
370 Value::user_iterator UI = I->user_begin();
371 Value::user_iterator UE = I->user_end();
376 for (++UI; UI != UE; ++UI) {
383 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
384 /// dead PHI node, due to being a def-use chain of single-use nodes that
385 /// either forms a cycle or is terminated by a trivially dead instruction,
386 /// delete it. If that makes any of its operands trivially dead, delete them
387 /// too, recursively. Return true if a change was made.
388 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
389 const TargetLibraryInfo *TLI) {
390 SmallPtrSet<Instruction*, 4> Visited;
391 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
392 I = cast<Instruction>(*I->user_begin())) {
394 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
396 // If we find an instruction more than once, we're on a cycle that
397 // won't prove fruitful.
398 if (!Visited.insert(I).second) {
399 // Break the cycle and delete the instruction and its operands.
400 I->replaceAllUsesWith(UndefValue::get(I->getType()));
401 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
408 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
409 /// simplify any instructions in it and recursively delete dead instructions.
411 /// This returns true if it changed the code, note that it can delete
412 /// instructions in other blocks as well in this block.
413 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
414 const TargetLibraryInfo *TLI) {
415 bool MadeChange = false;
418 // In debug builds, ensure that the terminator of the block is never replaced
419 // or deleted by these simplifications. The idea of simplification is that it
420 // cannot introduce new instructions, and there is no way to replace the
421 // terminator of a block without introducing a new instruction.
422 AssertingVH<Instruction> TerminatorVH(--BB->end());
425 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
426 assert(!BI->isTerminator());
427 Instruction *Inst = BI++;
430 if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
437 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
444 //===----------------------------------------------------------------------===//
445 // Control Flow Graph Restructuring.
449 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
450 /// method is called when we're about to delete Pred as a predecessor of BB. If
451 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
453 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
454 /// nodes that collapse into identity values. For example, if we have:
455 /// x = phi(1, 0, 0, 0)
458 /// .. and delete the predecessor corresponding to the '1', this will attempt to
459 /// recursively fold the and to 0.
460 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
462 // This only adjusts blocks with PHI nodes.
463 if (!isa<PHINode>(BB->begin()))
466 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
467 // them down. This will leave us with single entry phi nodes and other phis
468 // that can be removed.
469 BB->removePredecessor(Pred, true);
471 WeakVH PhiIt = &BB->front();
472 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
473 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
474 Value *OldPhiIt = PhiIt;
476 if (!recursivelySimplifyInstruction(PN, TD))
479 // If recursive simplification ended up deleting the next PHI node we would
480 // iterate to, then our iterator is invalid, restart scanning from the top
482 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
487 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
488 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
489 /// between them, moving the instructions in the predecessor into DestBB and
490 /// deleting the predecessor block.
492 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
493 // If BB has single-entry PHI nodes, fold them.
494 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
495 Value *NewVal = PN->getIncomingValue(0);
496 // Replace self referencing PHI with undef, it must be dead.
497 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
498 PN->replaceAllUsesWith(NewVal);
499 PN->eraseFromParent();
502 BasicBlock *PredBB = DestBB->getSinglePredecessor();
503 assert(PredBB && "Block doesn't have a single predecessor!");
505 // Zap anything that took the address of DestBB. Not doing this will give the
506 // address an invalid value.
507 if (DestBB->hasAddressTaken()) {
508 BlockAddress *BA = BlockAddress::get(DestBB);
509 Constant *Replacement =
510 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
511 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
513 BA->destroyConstant();
516 // Anything that branched to PredBB now branches to DestBB.
517 PredBB->replaceAllUsesWith(DestBB);
519 // Splice all the instructions from PredBB to DestBB.
520 PredBB->getTerminator()->eraseFromParent();
521 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
523 // If the PredBB is the entry block of the function, move DestBB up to
524 // become the entry block after we erase PredBB.
525 if (PredBB == &DestBB->getParent()->getEntryBlock())
526 DestBB->moveAfter(PredBB);
529 if (DominatorTreeWrapperPass *DTWP =
530 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
531 DominatorTree &DT = DTWP->getDomTree();
532 BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock();
533 DT.changeImmediateDominator(DestBB, PredBBIDom);
534 DT.eraseNode(PredBB);
538 PredBB->eraseFromParent();
541 /// CanMergeValues - Return true if we can choose one of these values to use
542 /// in place of the other. Note that we will always choose the non-undef
544 static bool CanMergeValues(Value *First, Value *Second) {
545 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
548 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
549 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
551 /// Assumption: Succ is the single successor for BB.
553 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
554 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
556 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
557 << Succ->getName() << "\n");
558 // Shortcut, if there is only a single predecessor it must be BB and merging
560 if (Succ->getSinglePredecessor()) return true;
562 // Make a list of the predecessors of BB
563 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
565 // Look at all the phi nodes in Succ, to see if they present a conflict when
566 // merging these blocks
567 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
568 PHINode *PN = cast<PHINode>(I);
570 // If the incoming value from BB is again a PHINode in
571 // BB which has the same incoming value for *PI as PN does, we can
572 // merge the phi nodes and then the blocks can still be merged
573 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
574 if (BBPN && BBPN->getParent() == BB) {
575 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
576 BasicBlock *IBB = PN->getIncomingBlock(PI);
577 if (BBPreds.count(IBB) &&
578 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
579 PN->getIncomingValue(PI))) {
580 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
581 << Succ->getName() << " is conflicting with "
582 << BBPN->getName() << " with regard to common predecessor "
583 << IBB->getName() << "\n");
588 Value* Val = PN->getIncomingValueForBlock(BB);
589 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
590 // See if the incoming value for the common predecessor is equal to the
591 // one for BB, in which case this phi node will not prevent the merging
593 BasicBlock *IBB = PN->getIncomingBlock(PI);
594 if (BBPreds.count(IBB) &&
595 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
596 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
597 << Succ->getName() << " is conflicting with regard to common "
598 << "predecessor " << IBB->getName() << "\n");
608 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
609 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
611 /// \brief Determines the value to use as the phi node input for a block.
613 /// Select between \p OldVal any value that we know flows from \p BB
614 /// to a particular phi on the basis of which one (if either) is not
615 /// undef. Update IncomingValues based on the selected value.
617 /// \param OldVal The value we are considering selecting.
618 /// \param BB The block that the value flows in from.
619 /// \param IncomingValues A map from block-to-value for other phi inputs
620 /// that we have examined.
622 /// \returns the selected value.
623 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
624 IncomingValueMap &IncomingValues) {
625 if (!isa<UndefValue>(OldVal)) {
626 assert((!IncomingValues.count(BB) ||
627 IncomingValues.find(BB)->second == OldVal) &&
628 "Expected OldVal to match incoming value from BB!");
630 IncomingValues.insert(std::make_pair(BB, OldVal));
634 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
635 if (It != IncomingValues.end()) return It->second;
640 /// \brief Create a map from block to value for the operands of a
643 /// Create a map from block to value for each non-undef value flowing
646 /// \param PN The phi we are collecting the map for.
647 /// \param IncomingValues [out] The map from block to value for this phi.
648 static void gatherIncomingValuesToPhi(PHINode *PN,
649 IncomingValueMap &IncomingValues) {
650 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
651 BasicBlock *BB = PN->getIncomingBlock(i);
652 Value *V = PN->getIncomingValue(i);
654 if (!isa<UndefValue>(V))
655 IncomingValues.insert(std::make_pair(BB, V));
659 /// \brief Replace the incoming undef values to a phi with the values
660 /// from a block-to-value map.
662 /// \param PN The phi we are replacing the undefs in.
663 /// \param IncomingValues A map from block to value.
664 static void replaceUndefValuesInPhi(PHINode *PN,
665 const IncomingValueMap &IncomingValues) {
666 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
667 Value *V = PN->getIncomingValue(i);
669 if (!isa<UndefValue>(V)) continue;
671 BasicBlock *BB = PN->getIncomingBlock(i);
672 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
673 if (It == IncomingValues.end()) continue;
675 PN->setIncomingValue(i, It->second);
679 /// \brief Replace a value flowing from a block to a phi with
680 /// potentially multiple instances of that value flowing from the
681 /// block's predecessors to the phi.
683 /// \param BB The block with the value flowing into the phi.
684 /// \param BBPreds The predecessors of BB.
685 /// \param PN The phi that we are updating.
686 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
687 const PredBlockVector &BBPreds,
689 Value *OldVal = PN->removeIncomingValue(BB, false);
690 assert(OldVal && "No entry in PHI for Pred BB!");
692 IncomingValueMap IncomingValues;
694 // We are merging two blocks - BB, and the block containing PN - and
695 // as a result we need to redirect edges from the predecessors of BB
696 // to go to the block containing PN, and update PN
697 // accordingly. Since we allow merging blocks in the case where the
698 // predecessor and successor blocks both share some predecessors,
699 // and where some of those common predecessors might have undef
700 // values flowing into PN, we want to rewrite those values to be
701 // consistent with the non-undef values.
703 gatherIncomingValuesToPhi(PN, IncomingValues);
705 // If this incoming value is one of the PHI nodes in BB, the new entries
706 // in the PHI node are the entries from the old PHI.
707 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
708 PHINode *OldValPN = cast<PHINode>(OldVal);
709 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
710 // Note that, since we are merging phi nodes and BB and Succ might
711 // have common predecessors, we could end up with a phi node with
712 // identical incoming branches. This will be cleaned up later (and
713 // will trigger asserts if we try to clean it up now, without also
714 // simplifying the corresponding conditional branch).
715 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
716 Value *PredVal = OldValPN->getIncomingValue(i);
717 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
720 // And add a new incoming value for this predecessor for the
721 // newly retargeted branch.
722 PN->addIncoming(Selected, PredBB);
725 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
726 // Update existing incoming values in PN for this
727 // predecessor of BB.
728 BasicBlock *PredBB = BBPreds[i];
729 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
732 // And add a new incoming value for this predecessor for the
733 // newly retargeted branch.
734 PN->addIncoming(Selected, PredBB);
738 replaceUndefValuesInPhi(PN, IncomingValues);
741 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
742 /// unconditional branch, and contains no instructions other than PHI nodes,
743 /// potential side-effect free intrinsics and the branch. If possible,
744 /// eliminate BB by rewriting all the predecessors to branch to the successor
745 /// block and return true. If we can't transform, return false.
746 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
747 assert(BB != &BB->getParent()->getEntryBlock() &&
748 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
750 // We can't eliminate infinite loops.
751 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
752 if (BB == Succ) return false;
754 // Check to see if merging these blocks would cause conflicts for any of the
755 // phi nodes in BB or Succ. If not, we can safely merge.
756 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
758 // Check for cases where Succ has multiple predecessors and a PHI node in BB
759 // has uses which will not disappear when the PHI nodes are merged. It is
760 // possible to handle such cases, but difficult: it requires checking whether
761 // BB dominates Succ, which is non-trivial to calculate in the case where
762 // Succ has multiple predecessors. Also, it requires checking whether
763 // constructing the necessary self-referential PHI node doesn't introduce any
764 // conflicts; this isn't too difficult, but the previous code for doing this
767 // Note that if this check finds a live use, BB dominates Succ, so BB is
768 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
769 // folding the branch isn't profitable in that case anyway.
770 if (!Succ->getSinglePredecessor()) {
771 BasicBlock::iterator BBI = BB->begin();
772 while (isa<PHINode>(*BBI)) {
773 for (Use &U : BBI->uses()) {
774 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
775 if (PN->getIncomingBlock(U) != BB)
785 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
787 if (isa<PHINode>(Succ->begin())) {
788 // If there is more than one pred of succ, and there are PHI nodes in
789 // the successor, then we need to add incoming edges for the PHI nodes
791 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
793 // Loop over all of the PHI nodes in the successor of BB.
794 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
795 PHINode *PN = cast<PHINode>(I);
797 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
801 if (Succ->getSinglePredecessor()) {
802 // BB is the only predecessor of Succ, so Succ will end up with exactly
803 // the same predecessors BB had.
805 // Copy over any phi, debug or lifetime instruction.
806 BB->getTerminator()->eraseFromParent();
807 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
809 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
810 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
811 assert(PN->use_empty() && "There shouldn't be any uses here!");
812 PN->eraseFromParent();
816 // Everything that jumped to BB now goes to Succ.
817 BB->replaceAllUsesWith(Succ);
818 if (!Succ->hasName()) Succ->takeName(BB);
819 BB->eraseFromParent(); // Delete the old basic block.
823 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
824 /// nodes in this block. This doesn't try to be clever about PHI nodes
825 /// which differ only in the order of the incoming values, but instcombine
826 /// orders them so it usually won't matter.
828 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
829 bool Changed = false;
831 // This implementation doesn't currently consider undef operands
832 // specially. Theoretically, two phis which are identical except for
833 // one having an undef where the other doesn't could be collapsed.
835 // Map from PHI hash values to PHI nodes. If multiple PHIs have
836 // the same hash value, the element is the first PHI in the
837 // linked list in CollisionMap.
838 DenseMap<uintptr_t, PHINode *> HashMap;
840 // Maintain linked lists of PHI nodes with common hash values.
841 DenseMap<PHINode *, PHINode *> CollisionMap;
844 for (BasicBlock::iterator I = BB->begin();
845 PHINode *PN = dyn_cast<PHINode>(I++); ) {
846 // Compute a hash value on the operands. Instcombine will likely have sorted
847 // them, which helps expose duplicates, but we have to check all the
848 // operands to be safe in case instcombine hasn't run.
850 // This hash algorithm is quite weak as hash functions go, but it seems
851 // to do a good enough job for this particular purpose, and is very quick.
852 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
853 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
854 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
856 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
858 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
859 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
861 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
863 // If we've never seen this hash value before, it's a unique PHI.
864 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
865 HashMap.insert(std::make_pair(Hash, PN));
866 if (Pair.second) continue;
867 // Otherwise it's either a duplicate or a hash collision.
868 for (PHINode *OtherPN = Pair.first->second; ; ) {
869 if (OtherPN->isIdenticalTo(PN)) {
870 // A duplicate. Replace this PHI with its duplicate.
871 PN->replaceAllUsesWith(OtherPN);
872 PN->eraseFromParent();
876 // A non-duplicate hash collision.
877 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
878 if (I == CollisionMap.end()) {
879 // Set this PHI to be the head of the linked list of colliding PHIs.
880 PHINode *Old = Pair.first->second;
881 Pair.first->second = PN;
882 CollisionMap[PN] = Old;
885 // Proceed to the next PHI in the list.
893 /// enforceKnownAlignment - If the specified pointer points to an object that
894 /// we control, modify the object's alignment to PrefAlign. This isn't
895 /// often possible though. If alignment is important, a more reliable approach
896 /// is to simply align all global variables and allocation instructions to
897 /// their preferred alignment from the beginning.
899 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
900 unsigned PrefAlign, const DataLayout *TD) {
901 V = V->stripPointerCasts();
903 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
904 // If the preferred alignment is greater than the natural stack alignment
905 // then don't round up. This avoids dynamic stack realignment.
906 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
908 // If there is a requested alignment and if this is an alloca, round up.
909 if (AI->getAlignment() >= PrefAlign)
910 return AI->getAlignment();
911 AI->setAlignment(PrefAlign);
915 if (auto *GO = dyn_cast<GlobalObject>(V)) {
916 // If there is a large requested alignment and we can, bump up the alignment
918 if (GO->isDeclaration())
920 // If the memory we set aside for the global may not be the memory used by
921 // the final program then it is impossible for us to reliably enforce the
922 // preferred alignment.
923 if (GO->isWeakForLinker())
926 if (GO->getAlignment() >= PrefAlign)
927 return GO->getAlignment();
928 // We can only increase the alignment of the global if it has no alignment
929 // specified or if it is not assigned a section. If it is assigned a
930 // section, the global could be densely packed with other objects in the
931 // section, increasing the alignment could cause padding issues.
932 if (!GO->hasSection() || GO->getAlignment() == 0)
933 GO->setAlignment(PrefAlign);
934 return GO->getAlignment();
940 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
941 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
942 /// and it is more than the alignment of the ultimate object, see if we can
943 /// increase the alignment of the ultimate object, making this check succeed.
944 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
945 const DataLayout *DL,
947 const Instruction *CxtI,
948 const DominatorTree *DT) {
949 assert(V->getType()->isPointerTy() &&
950 "getOrEnforceKnownAlignment expects a pointer!");
951 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
953 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
954 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
955 unsigned TrailZ = KnownZero.countTrailingOnes();
957 // Avoid trouble with ridiculously large TrailZ values, such as
958 // those computed from a null pointer.
959 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
961 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
963 // LLVM doesn't support alignments larger than this currently.
964 Align = std::min(Align, +Value::MaximumAlignment);
966 if (PrefAlign > Align)
967 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
969 // We don't need to make any adjustment.
973 ///===---------------------------------------------------------------------===//
974 /// Dbg Intrinsic utilities
977 /// See if there is a dbg.value intrinsic for DIVar before I.
978 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
979 // Since we can't guarantee that the original dbg.declare instrinsic
980 // is removed by LowerDbgDeclare(), we need to make sure that we are
981 // not inserting the same dbg.value intrinsic over and over.
982 llvm::BasicBlock::InstListType::iterator PrevI(I);
983 if (PrevI != I->getParent()->getInstList().begin()) {
985 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
986 if (DVI->getValue() == I->getOperand(0) &&
987 DVI->getOffset() == 0 &&
988 DVI->getVariable() == DIVar)
994 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
995 /// that has an associated llvm.dbg.decl intrinsic.
996 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
997 StoreInst *SI, DIBuilder &Builder) {
998 DIVariable DIVar(DDI->getVariable());
999 DIExpression DIExpr(DDI->getExpression());
1000 assert((!DIVar || DIVar.isVariable()) &&
1001 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1005 if (LdStHasDebugValue(DIVar, SI))
1008 Instruction *DbgVal = nullptr;
1009 // If an argument is zero extended then use argument directly. The ZExt
1010 // may be zapped by an optimization pass in future.
1011 Argument *ExtendedArg = nullptr;
1012 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1013 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1014 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1015 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1017 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, DIExpr, SI);
1019 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar,
1021 DbgVal->setDebugLoc(DDI->getDebugLoc());
1025 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1026 /// that has an associated llvm.dbg.decl intrinsic.
1027 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1028 LoadInst *LI, DIBuilder &Builder) {
1029 DIVariable DIVar(DDI->getVariable());
1030 DIExpression DIExpr(DDI->getExpression());
1031 assert((!DIVar || DIVar.isVariable()) &&
1032 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1036 if (LdStHasDebugValue(DIVar, LI))
1039 Instruction *DbgVal =
1040 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, DIVar, DIExpr, LI);
1041 DbgVal->setDebugLoc(DDI->getDebugLoc());
1045 /// Determine whether this alloca is either a VLA or an array.
1046 static bool isArray(AllocaInst *AI) {
1047 return AI->isArrayAllocation() ||
1048 AI->getType()->getElementType()->isArrayTy();
1051 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1052 /// of llvm.dbg.value intrinsics.
1053 bool llvm::LowerDbgDeclare(Function &F) {
1054 DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1055 SmallVector<DbgDeclareInst *, 4> Dbgs;
1057 for (BasicBlock::iterator BI : FI)
1058 if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
1059 Dbgs.push_back(DDI);
1064 for (auto &I : Dbgs) {
1065 DbgDeclareInst *DDI = I;
1066 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1067 // If this is an alloca for a scalar variable, insert a dbg.value
1068 // at each load and store to the alloca and erase the dbg.declare.
1069 // The dbg.values allow tracking a variable even if it is not
1070 // stored on the stack, while the dbg.declare can only describe
1071 // the stack slot (and at a lexical-scope granularity). Later
1072 // passes will attempt to elide the stack slot.
1073 if (AI && !isArray(AI)) {
1074 for (User *U : AI->users())
1075 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1076 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1077 else if (LoadInst *LI = dyn_cast<LoadInst>(U))
1078 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1079 else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1080 // This is a call by-value or some other instruction that
1081 // takes a pointer to the variable. Insert a *value*
1082 // intrinsic that describes the alloca.
1083 auto DbgVal = DIB.insertDbgValueIntrinsic(
1084 AI, 0, DIVariable(DDI->getVariable()),
1085 DIExpression(DDI->getExpression()), CI);
1086 DbgVal->setDebugLoc(DDI->getDebugLoc());
1088 DDI->eraseFromParent();
1094 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1095 /// alloca 'V', if any.
1096 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1097 if (auto *L = LocalAsMetadata::getIfExists(V))
1098 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1099 for (User *U : MDV->users())
1100 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1106 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1107 DIBuilder &Builder) {
1108 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1111 DIVariable DIVar(DDI->getVariable());
1112 DIExpression DIExpr(DDI->getExpression());
1113 assert((!DIVar || DIVar.isVariable()) &&
1114 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1118 // Create a copy of the original DIDescriptor for user variable, prepending
1119 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1120 // will take a value storing address of the memory for variable, not
1122 SmallVector<int64_t, 4> NewDIExpr;
1123 NewDIExpr.push_back(dwarf::DW_OP_deref);
1125 for (unsigned i = 0, n = DIExpr.getNumElements(); i < n; ++i)
1126 NewDIExpr.push_back(DIExpr.getElement(i));
1128 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1129 // and remove old llvm.dbg.declare.
1130 BasicBlock *BB = AI->getParent();
1131 Builder.insertDeclare(NewAllocaAddress, DIVar,
1132 Builder.createExpression(NewDIExpr), BB);
1133 DDI->eraseFromParent();
1137 /// changeToUnreachable - Insert an unreachable instruction before the specified
1138 /// instruction, making it and the rest of the code in the block dead.
1139 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1140 BasicBlock *BB = I->getParent();
1141 // Loop over all of the successors, removing BB's entry from any PHI
1143 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1144 (*SI)->removePredecessor(BB);
1146 // Insert a call to llvm.trap right before this. This turns the undefined
1147 // behavior into a hard fail instead of falling through into random code.
1150 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1151 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1152 CallTrap->setDebugLoc(I->getDebugLoc());
1154 new UnreachableInst(I->getContext(), I);
1156 // All instructions after this are dead.
1157 BasicBlock::iterator BBI = I, BBE = BB->end();
1158 while (BBI != BBE) {
1159 if (!BBI->use_empty())
1160 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1161 BB->getInstList().erase(BBI++);
1165 /// changeToCall - Convert the specified invoke into a normal call.
1166 static void changeToCall(InvokeInst *II) {
1167 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1168 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1169 NewCall->takeName(II);
1170 NewCall->setCallingConv(II->getCallingConv());
1171 NewCall->setAttributes(II->getAttributes());
1172 NewCall->setDebugLoc(II->getDebugLoc());
1173 II->replaceAllUsesWith(NewCall);
1175 // Follow the call by a branch to the normal destination.
1176 BranchInst::Create(II->getNormalDest(), II);
1178 // Update PHI nodes in the unwind destination
1179 II->getUnwindDest()->removePredecessor(II->getParent());
1180 II->eraseFromParent();
1183 static bool markAliveBlocks(BasicBlock *BB,
1184 SmallPtrSetImpl<BasicBlock*> &Reachable) {
1186 SmallVector<BasicBlock*, 128> Worklist;
1187 Worklist.push_back(BB);
1188 Reachable.insert(BB);
1189 bool Changed = false;
1191 BB = Worklist.pop_back_val();
1193 // Do a quick scan of the basic block, turning any obviously unreachable
1194 // instructions into LLVM unreachable insts. The instruction combining pass
1195 // canonicalizes unreachable insts into stores to null or undef.
1196 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1197 // Assumptions that are known to be false are equivalent to unreachable.
1198 // Also, if the condition is undefined, then we make the choice most
1199 // beneficial to the optimizer, and choose that to also be unreachable.
1200 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
1201 if (II->getIntrinsicID() == Intrinsic::assume) {
1202 bool MakeUnreachable = false;
1203 if (isa<UndefValue>(II->getArgOperand(0)))
1204 MakeUnreachable = true;
1205 else if (ConstantInt *Cond =
1206 dyn_cast<ConstantInt>(II->getArgOperand(0)))
1207 MakeUnreachable = Cond->isZero();
1209 if (MakeUnreachable) {
1210 // Don't insert a call to llvm.trap right before the unreachable.
1211 changeToUnreachable(BBI, false);
1217 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1218 if (CI->doesNotReturn()) {
1219 // If we found a call to a no-return function, insert an unreachable
1220 // instruction after it. Make sure there isn't *already* one there
1223 if (!isa<UnreachableInst>(BBI)) {
1224 // Don't insert a call to llvm.trap right before the unreachable.
1225 changeToUnreachable(BBI, false);
1232 // Store to undef and store to null are undefined and used to signal that
1233 // they should be changed to unreachable by passes that can't modify the
1235 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1236 // Don't touch volatile stores.
1237 if (SI->isVolatile()) continue;
1239 Value *Ptr = SI->getOperand(1);
1241 if (isa<UndefValue>(Ptr) ||
1242 (isa<ConstantPointerNull>(Ptr) &&
1243 SI->getPointerAddressSpace() == 0)) {
1244 changeToUnreachable(SI, true);
1251 // Turn invokes that call 'nounwind' functions into ordinary calls.
1252 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1253 Value *Callee = II->getCalledValue();
1254 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1255 changeToUnreachable(II, true);
1257 } else if (II->doesNotThrow()) {
1258 if (II->use_empty() && II->onlyReadsMemory()) {
1259 // jump to the normal destination branch.
1260 BranchInst::Create(II->getNormalDest(), II);
1261 II->getUnwindDest()->removePredecessor(II->getParent());
1262 II->eraseFromParent();
1269 Changed |= ConstantFoldTerminator(BB, true);
1270 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1271 if (Reachable.insert(*SI).second)
1272 Worklist.push_back(*SI);
1273 } while (!Worklist.empty());
1277 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1278 /// if they are in a dead cycle. Return true if a change was made, false
1280 bool llvm::removeUnreachableBlocks(Function &F) {
1281 SmallPtrSet<BasicBlock*, 128> Reachable;
1282 bool Changed = markAliveBlocks(F.begin(), Reachable);
1284 // If there are unreachable blocks in the CFG...
1285 if (Reachable.size() == F.size())
1288 assert(Reachable.size() < F.size());
1289 NumRemoved += F.size()-Reachable.size();
1291 // Loop over all of the basic blocks that are not reachable, dropping all of
1292 // their internal references...
1293 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1294 if (Reachable.count(BB))
1297 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1298 if (Reachable.count(*SI))
1299 (*SI)->removePredecessor(BB);
1300 BB->dropAllReferences();
1303 for (Function::iterator I = ++F.begin(); I != F.end();)
1304 if (!Reachable.count(I))
1305 I = F.getBasicBlockList().erase(I);
1312 void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
1313 SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
1314 K->dropUnknownMetadata(KnownIDs);
1315 K->getAllMetadataOtherThanDebugLoc(Metadata);
1316 for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
1317 unsigned Kind = Metadata[i].first;
1318 MDNode *JMD = J->getMetadata(Kind);
1319 MDNode *KMD = Metadata[i].second;
1323 K->setMetadata(Kind, nullptr); // Remove unknown metadata
1325 case LLVMContext::MD_dbg:
1326 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1327 case LLVMContext::MD_tbaa:
1328 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
1330 case LLVMContext::MD_alias_scope:
1331 case LLVMContext::MD_noalias:
1332 K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
1334 case LLVMContext::MD_range:
1335 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
1337 case LLVMContext::MD_fpmath:
1338 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
1340 case LLVMContext::MD_invariant_load:
1341 // Only set the !invariant.load if it is present in both instructions.
1342 K->setMetadata(Kind, JMD);
1344 case LLVMContext::MD_nonnull:
1345 // Only set the !nonnull if it is present in both instructions.
1346 K->setMetadata(Kind, JMD);