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));
306 if (isAllocLikeFn(I, TLI)) return true;
308 if (CallInst *CI = isFreeCall(I, TLI))
309 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
310 return C->isNullValue() || isa<UndefValue>(C);
315 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
316 /// trivially dead instruction, delete it. If that makes any of its operands
317 /// trivially dead, delete them too, recursively. Return true if any
318 /// instructions were deleted.
320 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
321 const TargetLibraryInfo *TLI) {
322 Instruction *I = dyn_cast<Instruction>(V);
323 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
326 SmallVector<Instruction*, 16> DeadInsts;
327 DeadInsts.push_back(I);
330 I = DeadInsts.pop_back_val();
332 // Null out all of the instruction's operands to see if any operand becomes
334 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
335 Value *OpV = I->getOperand(i);
336 I->setOperand(i, nullptr);
338 if (!OpV->use_empty()) continue;
340 // If the operand is an instruction that became dead as we nulled out the
341 // operand, and if it is 'trivially' dead, delete it in a future loop
343 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
344 if (isInstructionTriviallyDead(OpI, TLI))
345 DeadInsts.push_back(OpI);
348 I->eraseFromParent();
349 } while (!DeadInsts.empty());
354 /// areAllUsesEqual - Check whether the uses of a value are all the same.
355 /// This is similar to Instruction::hasOneUse() except this will also return
356 /// true when there are no uses or multiple uses that all refer to the same
358 static bool areAllUsesEqual(Instruction *I) {
359 Value::user_iterator UI = I->user_begin();
360 Value::user_iterator UE = I->user_end();
365 for (++UI; UI != UE; ++UI) {
372 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
373 /// dead PHI node, due to being a def-use chain of single-use nodes that
374 /// either forms a cycle or is terminated by a trivially dead instruction,
375 /// delete it. If that makes any of its operands trivially dead, delete them
376 /// too, recursively. Return true if a change was made.
377 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
378 const TargetLibraryInfo *TLI) {
379 SmallPtrSet<Instruction*, 4> Visited;
380 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
381 I = cast<Instruction>(*I->user_begin())) {
383 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
385 // If we find an instruction more than once, we're on a cycle that
386 // won't prove fruitful.
387 if (!Visited.insert(I)) {
388 // Break the cycle and delete the instruction and its operands.
389 I->replaceAllUsesWith(UndefValue::get(I->getType()));
390 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
397 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
398 /// simplify any instructions in it and recursively delete dead instructions.
400 /// This returns true if it changed the code, note that it can delete
401 /// instructions in other blocks as well in this block.
402 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
403 const TargetLibraryInfo *TLI) {
404 bool MadeChange = false;
407 // In debug builds, ensure that the terminator of the block is never replaced
408 // or deleted by these simplifications. The idea of simplification is that it
409 // cannot introduce new instructions, and there is no way to replace the
410 // terminator of a block without introducing a new instruction.
411 AssertingVH<Instruction> TerminatorVH(--BB->end());
414 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
415 assert(!BI->isTerminator());
416 Instruction *Inst = BI++;
419 if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
426 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
433 //===----------------------------------------------------------------------===//
434 // Control Flow Graph Restructuring.
438 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
439 /// method is called when we're about to delete Pred as a predecessor of BB. If
440 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
442 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
443 /// nodes that collapse into identity values. For example, if we have:
444 /// x = phi(1, 0, 0, 0)
447 /// .. and delete the predecessor corresponding to the '1', this will attempt to
448 /// recursively fold the and to 0.
449 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
451 // This only adjusts blocks with PHI nodes.
452 if (!isa<PHINode>(BB->begin()))
455 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
456 // them down. This will leave us with single entry phi nodes and other phis
457 // that can be removed.
458 BB->removePredecessor(Pred, true);
460 WeakVH PhiIt = &BB->front();
461 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
462 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
463 Value *OldPhiIt = PhiIt;
465 if (!recursivelySimplifyInstruction(PN, TD))
468 // If recursive simplification ended up deleting the next PHI node we would
469 // iterate to, then our iterator is invalid, restart scanning from the top
471 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
476 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
477 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
478 /// between them, moving the instructions in the predecessor into DestBB and
479 /// deleting the predecessor block.
481 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
482 // If BB has single-entry PHI nodes, fold them.
483 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
484 Value *NewVal = PN->getIncomingValue(0);
485 // Replace self referencing PHI with undef, it must be dead.
486 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
487 PN->replaceAllUsesWith(NewVal);
488 PN->eraseFromParent();
491 BasicBlock *PredBB = DestBB->getSinglePredecessor();
492 assert(PredBB && "Block doesn't have a single predecessor!");
494 // Zap anything that took the address of DestBB. Not doing this will give the
495 // address an invalid value.
496 if (DestBB->hasAddressTaken()) {
497 BlockAddress *BA = BlockAddress::get(DestBB);
498 Constant *Replacement =
499 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
500 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
502 BA->destroyConstant();
505 // Anything that branched to PredBB now branches to DestBB.
506 PredBB->replaceAllUsesWith(DestBB);
508 // Splice all the instructions from PredBB to DestBB.
509 PredBB->getTerminator()->eraseFromParent();
510 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
512 // If the PredBB is the entry block of the function, move DestBB up to
513 // become the entry block after we erase PredBB.
514 if (PredBB == &DestBB->getParent()->getEntryBlock())
515 DestBB->moveAfter(PredBB);
518 if (DominatorTreeWrapperPass *DTWP =
519 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
520 DominatorTree &DT = DTWP->getDomTree();
521 BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock();
522 DT.changeImmediateDominator(DestBB, PredBBIDom);
523 DT.eraseNode(PredBB);
527 PredBB->eraseFromParent();
530 /// CanMergeValues - Return true if we can choose one of these values to use
531 /// in place of the other. Note that we will always choose the non-undef
533 static bool CanMergeValues(Value *First, Value *Second) {
534 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
537 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
538 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
540 /// Assumption: Succ is the single successor for BB.
542 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
543 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
545 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
546 << Succ->getName() << "\n");
547 // Shortcut, if there is only a single predecessor it must be BB and merging
549 if (Succ->getSinglePredecessor()) return true;
551 // Make a list of the predecessors of BB
552 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
554 // Look at all the phi nodes in Succ, to see if they present a conflict when
555 // merging these blocks
556 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
557 PHINode *PN = cast<PHINode>(I);
559 // If the incoming value from BB is again a PHINode in
560 // BB which has the same incoming value for *PI as PN does, we can
561 // merge the phi nodes and then the blocks can still be merged
562 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
563 if (BBPN && BBPN->getParent() == BB) {
564 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
565 BasicBlock *IBB = PN->getIncomingBlock(PI);
566 if (BBPreds.count(IBB) &&
567 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
568 PN->getIncomingValue(PI))) {
569 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
570 << Succ->getName() << " is conflicting with "
571 << BBPN->getName() << " with regard to common predecessor "
572 << IBB->getName() << "\n");
577 Value* Val = PN->getIncomingValueForBlock(BB);
578 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
579 // See if the incoming value for the common predecessor is equal to the
580 // one for BB, in which case this phi node will not prevent the merging
582 BasicBlock *IBB = PN->getIncomingBlock(PI);
583 if (BBPreds.count(IBB) &&
584 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
585 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
586 << Succ->getName() << " is conflicting with regard to common "
587 << "predecessor " << IBB->getName() << "\n");
597 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
598 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
600 /// \brief Determines the value to use as the phi node input for a block.
602 /// Select between \p OldVal any value that we know flows from \p BB
603 /// to a particular phi on the basis of which one (if either) is not
604 /// undef. Update IncomingValues based on the selected value.
606 /// \param OldVal The value we are considering selecting.
607 /// \param BB The block that the value flows in from.
608 /// \param IncomingValues A map from block-to-value for other phi inputs
609 /// that we have examined.
611 /// \returns the selected value.
612 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
613 IncomingValueMap &IncomingValues) {
614 if (!isa<UndefValue>(OldVal)) {
615 assert((!IncomingValues.count(BB) ||
616 IncomingValues.find(BB)->second == OldVal) &&
617 "Expected OldVal to match incoming value from BB!");
619 IncomingValues.insert(std::make_pair(BB, OldVal));
623 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
624 if (It != IncomingValues.end()) return It->second;
629 /// \brief Create a map from block to value for the operands of a
632 /// Create a map from block to value for each non-undef value flowing
635 /// \param PN The phi we are collecting the map for.
636 /// \param IncomingValues [out] The map from block to value for this phi.
637 static void gatherIncomingValuesToPhi(PHINode *PN,
638 IncomingValueMap &IncomingValues) {
639 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
640 BasicBlock *BB = PN->getIncomingBlock(i);
641 Value *V = PN->getIncomingValue(i);
643 if (!isa<UndefValue>(V))
644 IncomingValues.insert(std::make_pair(BB, V));
648 /// \brief Replace the incoming undef values to a phi with the values
649 /// from a block-to-value map.
651 /// \param PN The phi we are replacing the undefs in.
652 /// \param IncomingValues A map from block to value.
653 static void replaceUndefValuesInPhi(PHINode *PN,
654 const IncomingValueMap &IncomingValues) {
655 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
656 Value *V = PN->getIncomingValue(i);
658 if (!isa<UndefValue>(V)) continue;
660 BasicBlock *BB = PN->getIncomingBlock(i);
661 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
662 if (It == IncomingValues.end()) continue;
664 PN->setIncomingValue(i, It->second);
668 /// \brief Replace a value flowing from a block to a phi with
669 /// potentially multiple instances of that value flowing from the
670 /// block's predecessors to the phi.
672 /// \param BB The block with the value flowing into the phi.
673 /// \param BBPreds The predecessors of BB.
674 /// \param PN The phi that we are updating.
675 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
676 const PredBlockVector &BBPreds,
678 Value *OldVal = PN->removeIncomingValue(BB, false);
679 assert(OldVal && "No entry in PHI for Pred BB!");
681 IncomingValueMap IncomingValues;
683 // We are merging two blocks - BB, and the block containing PN - and
684 // as a result we need to redirect edges from the predecessors of BB
685 // to go to the block containing PN, and update PN
686 // accordingly. Since we allow merging blocks in the case where the
687 // predecessor and successor blocks both share some predecessors,
688 // and where some of those common predecessors might have undef
689 // values flowing into PN, we want to rewrite those values to be
690 // consistent with the non-undef values.
692 gatherIncomingValuesToPhi(PN, IncomingValues);
694 // If this incoming value is one of the PHI nodes in BB, the new entries
695 // in the PHI node are the entries from the old PHI.
696 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
697 PHINode *OldValPN = cast<PHINode>(OldVal);
698 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
699 // Note that, since we are merging phi nodes and BB and Succ might
700 // have common predecessors, we could end up with a phi node with
701 // identical incoming branches. This will be cleaned up later (and
702 // will trigger asserts if we try to clean it up now, without also
703 // simplifying the corresponding conditional branch).
704 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
705 Value *PredVal = OldValPN->getIncomingValue(i);
706 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
709 // And add a new incoming value for this predecessor for the
710 // newly retargeted branch.
711 PN->addIncoming(Selected, PredBB);
714 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
715 // Update existing incoming values in PN for this
716 // predecessor of BB.
717 BasicBlock *PredBB = BBPreds[i];
718 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
721 // And add a new incoming value for this predecessor for the
722 // newly retargeted branch.
723 PN->addIncoming(Selected, PredBB);
727 replaceUndefValuesInPhi(PN, IncomingValues);
730 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
731 /// unconditional branch, and contains no instructions other than PHI nodes,
732 /// potential side-effect free intrinsics and the branch. If possible,
733 /// eliminate BB by rewriting all the predecessors to branch to the successor
734 /// block and return true. If we can't transform, return false.
735 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
736 assert(BB != &BB->getParent()->getEntryBlock() &&
737 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
739 // We can't eliminate infinite loops.
740 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
741 if (BB == Succ) return false;
743 // Check to see if merging these blocks would cause conflicts for any of the
744 // phi nodes in BB or Succ. If not, we can safely merge.
745 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
747 // Check for cases where Succ has multiple predecessors and a PHI node in BB
748 // has uses which will not disappear when the PHI nodes are merged. It is
749 // possible to handle such cases, but difficult: it requires checking whether
750 // BB dominates Succ, which is non-trivial to calculate in the case where
751 // Succ has multiple predecessors. Also, it requires checking whether
752 // constructing the necessary self-referential PHI node doesn't introduce any
753 // conflicts; this isn't too difficult, but the previous code for doing this
756 // Note that if this check finds a live use, BB dominates Succ, so BB is
757 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
758 // folding the branch isn't profitable in that case anyway.
759 if (!Succ->getSinglePredecessor()) {
760 BasicBlock::iterator BBI = BB->begin();
761 while (isa<PHINode>(*BBI)) {
762 for (Use &U : BBI->uses()) {
763 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
764 if (PN->getIncomingBlock(U) != BB)
774 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
776 if (isa<PHINode>(Succ->begin())) {
777 // If there is more than one pred of succ, and there are PHI nodes in
778 // the successor, then we need to add incoming edges for the PHI nodes
780 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
782 // Loop over all of the PHI nodes in the successor of BB.
783 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
784 PHINode *PN = cast<PHINode>(I);
786 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
790 if (Succ->getSinglePredecessor()) {
791 // BB is the only predecessor of Succ, so Succ will end up with exactly
792 // the same predecessors BB had.
794 // Copy over any phi, debug or lifetime instruction.
795 BB->getTerminator()->eraseFromParent();
796 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
798 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
799 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
800 assert(PN->use_empty() && "There shouldn't be any uses here!");
801 PN->eraseFromParent();
805 // Everything that jumped to BB now goes to Succ.
806 BB->replaceAllUsesWith(Succ);
807 if (!Succ->hasName()) Succ->takeName(BB);
808 BB->eraseFromParent(); // Delete the old basic block.
812 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
813 /// nodes in this block. This doesn't try to be clever about PHI nodes
814 /// which differ only in the order of the incoming values, but instcombine
815 /// orders them so it usually won't matter.
817 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
818 bool Changed = false;
820 // This implementation doesn't currently consider undef operands
821 // specially. Theoretically, two phis which are identical except for
822 // one having an undef where the other doesn't could be collapsed.
824 // Map from PHI hash values to PHI nodes. If multiple PHIs have
825 // the same hash value, the element is the first PHI in the
826 // linked list in CollisionMap.
827 DenseMap<uintptr_t, PHINode *> HashMap;
829 // Maintain linked lists of PHI nodes with common hash values.
830 DenseMap<PHINode *, PHINode *> CollisionMap;
833 for (BasicBlock::iterator I = BB->begin();
834 PHINode *PN = dyn_cast<PHINode>(I++); ) {
835 // Compute a hash value on the operands. Instcombine will likely have sorted
836 // them, which helps expose duplicates, but we have to check all the
837 // operands to be safe in case instcombine hasn't run.
839 // This hash algorithm is quite weak as hash functions go, but it seems
840 // to do a good enough job for this particular purpose, and is very quick.
841 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
842 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
843 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
845 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
847 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
848 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
850 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
852 // If we've never seen this hash value before, it's a unique PHI.
853 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
854 HashMap.insert(std::make_pair(Hash, PN));
855 if (Pair.second) continue;
856 // Otherwise it's either a duplicate or a hash collision.
857 for (PHINode *OtherPN = Pair.first->second; ; ) {
858 if (OtherPN->isIdenticalTo(PN)) {
859 // A duplicate. Replace this PHI with its duplicate.
860 PN->replaceAllUsesWith(OtherPN);
861 PN->eraseFromParent();
865 // A non-duplicate hash collision.
866 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
867 if (I == CollisionMap.end()) {
868 // Set this PHI to be the head of the linked list of colliding PHIs.
869 PHINode *Old = Pair.first->second;
870 Pair.first->second = PN;
871 CollisionMap[PN] = Old;
874 // Proceed to the next PHI in the list.
882 /// enforceKnownAlignment - If the specified pointer points to an object that
883 /// we control, modify the object's alignment to PrefAlign. This isn't
884 /// often possible though. If alignment is important, a more reliable approach
885 /// is to simply align all global variables and allocation instructions to
886 /// their preferred alignment from the beginning.
888 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
889 unsigned PrefAlign, const DataLayout *TD) {
890 V = V->stripPointerCasts();
892 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
893 // If the preferred alignment is greater than the natural stack alignment
894 // then don't round up. This avoids dynamic stack realignment.
895 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
897 // If there is a requested alignment and if this is an alloca, round up.
898 if (AI->getAlignment() >= PrefAlign)
899 return AI->getAlignment();
900 AI->setAlignment(PrefAlign);
904 if (auto *GO = dyn_cast<GlobalObject>(V)) {
905 // If there is a large requested alignment and we can, bump up the alignment
907 if (GO->isDeclaration())
909 // If the memory we set aside for the global may not be the memory used by
910 // the final program then it is impossible for us to reliably enforce the
911 // preferred alignment.
912 if (GO->isWeakForLinker())
915 if (GO->getAlignment() >= PrefAlign)
916 return GO->getAlignment();
917 // We can only increase the alignment of the global if it has no alignment
918 // specified or if it is not assigned a section. If it is assigned a
919 // section, the global could be densely packed with other objects in the
920 // section, increasing the alignment could cause padding issues.
921 if (!GO->hasSection() || GO->getAlignment() == 0)
922 GO->setAlignment(PrefAlign);
923 return GO->getAlignment();
929 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
930 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
931 /// and it is more than the alignment of the ultimate object, see if we can
932 /// increase the alignment of the ultimate object, making this check succeed.
933 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
934 const DataLayout *DL) {
935 assert(V->getType()->isPointerTy() &&
936 "getOrEnforceKnownAlignment expects a pointer!");
937 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
939 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
940 computeKnownBits(V, KnownZero, KnownOne, DL);
941 unsigned TrailZ = KnownZero.countTrailingOnes();
943 // Avoid trouble with ridiculously large TrailZ values, such as
944 // those computed from a null pointer.
945 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
947 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
949 // LLVM doesn't support alignments larger than this currently.
950 Align = std::min(Align, +Value::MaximumAlignment);
952 if (PrefAlign > Align)
953 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
955 // We don't need to make any adjustment.
959 ///===---------------------------------------------------------------------===//
960 /// Dbg Intrinsic utilities
963 /// See if there is a dbg.value intrinsic for DIVar before I.
964 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
965 // Since we can't guarantee that the original dbg.declare instrinsic
966 // is removed by LowerDbgDeclare(), we need to make sure that we are
967 // not inserting the same dbg.value intrinsic over and over.
968 llvm::BasicBlock::InstListType::iterator PrevI(I);
969 if (PrevI != I->getParent()->getInstList().begin()) {
971 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
972 if (DVI->getValue() == I->getOperand(0) &&
973 DVI->getOffset() == 0 &&
974 DVI->getVariable() == DIVar)
980 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
981 /// that has an associated llvm.dbg.decl intrinsic.
982 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
983 StoreInst *SI, DIBuilder &Builder) {
984 DIVariable DIVar(DDI->getVariable());
985 assert((!DIVar || DIVar.isVariable()) &&
986 "Variable in DbgDeclareInst should be either null or a DIVariable.");
990 if (LdStHasDebugValue(DIVar, SI))
993 Instruction *DbgVal = nullptr;
994 // If an argument is zero extended then use argument directly. The ZExt
995 // may be zapped by an optimization pass in future.
996 Argument *ExtendedArg = nullptr;
997 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
998 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
999 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1000 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1002 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
1004 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
1005 DbgVal->setDebugLoc(DDI->getDebugLoc());
1009 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1010 /// that has an associated llvm.dbg.decl intrinsic.
1011 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1012 LoadInst *LI, DIBuilder &Builder) {
1013 DIVariable DIVar(DDI->getVariable());
1014 assert((!DIVar || DIVar.isVariable()) &&
1015 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1019 if (LdStHasDebugValue(DIVar, LI))
1022 Instruction *DbgVal =
1023 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
1025 DbgVal->setDebugLoc(DDI->getDebugLoc());
1029 /// Determine whether this alloca is either a VLA or an array.
1030 static bool isArray(AllocaInst *AI) {
1031 return AI->isArrayAllocation() ||
1032 AI->getType()->getElementType()->isArrayTy();
1035 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1036 /// of llvm.dbg.value intrinsics.
1037 bool llvm::LowerDbgDeclare(Function &F) {
1038 DIBuilder DIB(*F.getParent());
1039 SmallVector<DbgDeclareInst *, 4> Dbgs;
1041 for (BasicBlock::iterator BI : FI)
1042 if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
1043 Dbgs.push_back(DDI);
1048 for (auto &I : Dbgs) {
1049 DbgDeclareInst *DDI = I;
1050 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1051 // If this is an alloca for a scalar variable, insert a dbg.value
1052 // at each load and store to the alloca and erase the dbg.declare.
1053 // The dbg.values allow tracking a variable even if it is not
1054 // stored on the stack, while the dbg.declare can only describe
1055 // the stack slot (and at a lexical-scope granularity). Later
1056 // passes will attempt to elide the stack slot.
1057 if (AI && !isArray(AI)) {
1058 for (User *U : AI->users())
1059 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1060 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1061 else if (LoadInst *LI = dyn_cast<LoadInst>(U))
1062 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1063 else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1064 // This is a call by-value or some other instruction that
1065 // takes a pointer to the variable. Insert a *value*
1066 // intrinsic that describes the alloca.
1068 DIB.insertDbgValueIntrinsic(AI, 0,
1069 DIVariable(DDI->getVariable()), CI);
1070 DbgVal->setDebugLoc(DDI->getDebugLoc());
1072 DDI->eraseFromParent();
1078 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1079 /// alloca 'V', if any.
1080 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1081 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
1082 for (User *U : DebugNode->users())
1083 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1089 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1090 DIBuilder &Builder) {
1091 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1094 DIVariable DIVar(DDI->getVariable());
1095 assert((!DIVar || DIVar.isVariable()) &&
1096 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1100 // Create a copy of the original DIDescriptor for user variable, appending
1101 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1102 // will take a value storing address of the memory for variable, not
1104 Type *Int64Ty = Type::getInt64Ty(AI->getContext());
1105 SmallVector<Value*, 4> NewDIVarAddress;
1106 if (DIVar.hasComplexAddress()) {
1107 for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
1108 NewDIVarAddress.push_back(
1109 ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
1112 NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
1113 DIVariable NewDIVar = Builder.createComplexVariable(
1114 DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
1115 DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
1116 NewDIVarAddress, DIVar.getArgNumber());
1118 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1119 // and remove old llvm.dbg.declare.
1120 BasicBlock *BB = AI->getParent();
1121 Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
1122 DDI->eraseFromParent();
1126 /// changeToUnreachable - Insert an unreachable instruction before the specified
1127 /// instruction, making it and the rest of the code in the block dead.
1128 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1129 BasicBlock *BB = I->getParent();
1130 // Loop over all of the successors, removing BB's entry from any PHI
1132 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1133 (*SI)->removePredecessor(BB);
1135 // Insert a call to llvm.trap right before this. This turns the undefined
1136 // behavior into a hard fail instead of falling through into random code.
1139 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1140 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1141 CallTrap->setDebugLoc(I->getDebugLoc());
1143 new UnreachableInst(I->getContext(), I);
1145 // All instructions after this are dead.
1146 BasicBlock::iterator BBI = I, BBE = BB->end();
1147 while (BBI != BBE) {
1148 if (!BBI->use_empty())
1149 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1150 BB->getInstList().erase(BBI++);
1154 /// changeToCall - Convert the specified invoke into a normal call.
1155 static void changeToCall(InvokeInst *II) {
1156 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1157 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1158 NewCall->takeName(II);
1159 NewCall->setCallingConv(II->getCallingConv());
1160 NewCall->setAttributes(II->getAttributes());
1161 NewCall->setDebugLoc(II->getDebugLoc());
1162 II->replaceAllUsesWith(NewCall);
1164 // Follow the call by a branch to the normal destination.
1165 BranchInst::Create(II->getNormalDest(), II);
1167 // Update PHI nodes in the unwind destination
1168 II->getUnwindDest()->removePredecessor(II->getParent());
1169 II->eraseFromParent();
1172 static bool markAliveBlocks(BasicBlock *BB,
1173 SmallPtrSet<BasicBlock*, 128> &Reachable) {
1175 SmallVector<BasicBlock*, 128> Worklist;
1176 Worklist.push_back(BB);
1177 Reachable.insert(BB);
1178 bool Changed = false;
1180 BB = Worklist.pop_back_val();
1182 // Do a quick scan of the basic block, turning any obviously unreachable
1183 // instructions into LLVM unreachable insts. The instruction combining pass
1184 // canonicalizes unreachable insts into stores to null or undef.
1185 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1186 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1187 if (CI->doesNotReturn()) {
1188 // If we found a call to a no-return function, insert an unreachable
1189 // instruction after it. Make sure there isn't *already* one there
1192 if (!isa<UnreachableInst>(BBI)) {
1193 // Don't insert a call to llvm.trap right before the unreachable.
1194 changeToUnreachable(BBI, false);
1201 // Store to undef and store to null are undefined and used to signal that
1202 // they should be changed to unreachable by passes that can't modify the
1204 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1205 // Don't touch volatile stores.
1206 if (SI->isVolatile()) continue;
1208 Value *Ptr = SI->getOperand(1);
1210 if (isa<UndefValue>(Ptr) ||
1211 (isa<ConstantPointerNull>(Ptr) &&
1212 SI->getPointerAddressSpace() == 0)) {
1213 changeToUnreachable(SI, true);
1220 // Turn invokes that call 'nounwind' functions into ordinary calls.
1221 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1222 Value *Callee = II->getCalledValue();
1223 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1224 changeToUnreachable(II, true);
1226 } else if (II->doesNotThrow()) {
1227 if (II->use_empty() && II->onlyReadsMemory()) {
1228 // jump to the normal destination branch.
1229 BranchInst::Create(II->getNormalDest(), II);
1230 II->getUnwindDest()->removePredecessor(II->getParent());
1231 II->eraseFromParent();
1238 Changed |= ConstantFoldTerminator(BB, true);
1239 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1240 if (Reachable.insert(*SI))
1241 Worklist.push_back(*SI);
1242 } while (!Worklist.empty());
1246 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1247 /// if they are in a dead cycle. Return true if a change was made, false
1249 bool llvm::removeUnreachableBlocks(Function &F) {
1250 SmallPtrSet<BasicBlock*, 128> Reachable;
1251 bool Changed = markAliveBlocks(F.begin(), Reachable);
1253 // If there are unreachable blocks in the CFG...
1254 if (Reachable.size() == F.size())
1257 assert(Reachable.size() < F.size());
1258 NumRemoved += F.size()-Reachable.size();
1260 // Loop over all of the basic blocks that are not reachable, dropping all of
1261 // their internal references...
1262 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1263 if (Reachable.count(BB))
1266 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1267 if (Reachable.count(*SI))
1268 (*SI)->removePredecessor(BB);
1269 BB->dropAllReferences();
1272 for (Function::iterator I = ++F.begin(); I != F.end();)
1273 if (!Reachable.count(I))
1274 I = F.getBasicBlockList().erase(I);