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/Dominators.h"
21 #include "llvm/Analysis/InstructionSimplify.h"
22 #include "llvm/Analysis/MemoryBuiltins.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/DIBuilder.h"
25 #include "llvm/DebugInfo.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/GlobalAlias.h"
30 #include "llvm/IR/GlobalVariable.h"
31 #include "llvm/IR/IRBuilder.h"
32 #include "llvm/IR/Instructions.h"
33 #include "llvm/IR/IntrinsicInst.h"
34 #include "llvm/IR/Intrinsics.h"
35 #include "llvm/IR/MDBuilder.h"
36 #include "llvm/IR/Metadata.h"
37 #include "llvm/IR/Operator.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/GetElementPtrTypeIterator.h"
41 #include "llvm/Support/MathExtras.h"
42 #include "llvm/Support/ValueHandle.h"
43 #include "llvm/Support/raw_ostream.h"
46 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
48 //===----------------------------------------------------------------------===//
49 // Local constant propagation.
52 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
53 /// constant value, convert it into an unconditional branch to the constant
54 /// destination. This is a nontrivial operation because the successors of this
55 /// basic block must have their PHI nodes updated.
56 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
57 /// conditions and indirectbr addresses this might make dead if
58 /// DeleteDeadConditions is true.
59 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
60 const TargetLibraryInfo *TLI) {
61 TerminatorInst *T = BB->getTerminator();
62 IRBuilder<> Builder(T);
64 // Branch - See if we are conditional jumping on constant
65 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
66 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
67 BasicBlock *Dest1 = BI->getSuccessor(0);
68 BasicBlock *Dest2 = BI->getSuccessor(1);
70 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
71 // Are we branching on constant?
72 // YES. Change to unconditional branch...
73 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
74 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
76 //cerr << "Function: " << T->getParent()->getParent()
77 // << "\nRemoving branch from " << T->getParent()
78 // << "\n\nTo: " << OldDest << endl;
80 // Let the basic block know that we are letting go of it. Based on this,
81 // it will adjust it's PHI nodes.
82 OldDest->removePredecessor(BB);
84 // Replace the conditional branch with an unconditional one.
85 Builder.CreateBr(Destination);
86 BI->eraseFromParent();
90 if (Dest2 == Dest1) { // Conditional branch to same location?
91 // This branch matches something like this:
92 // br bool %cond, label %Dest, label %Dest
93 // and changes it into: br label %Dest
95 // Let the basic block know that we are letting go of one copy of it.
96 assert(BI->getParent() && "Terminator not inserted in block!");
97 Dest1->removePredecessor(BI->getParent());
99 // Replace the conditional branch with an unconditional one.
100 Builder.CreateBr(Dest1);
101 Value *Cond = BI->getCondition();
102 BI->eraseFromParent();
103 if (DeleteDeadConditions)
104 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
110 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
111 // If we are switching on a constant, we can convert the switch into a
112 // single branch instruction!
113 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
114 BasicBlock *TheOnlyDest = SI->getDefaultDest();
115 BasicBlock *DefaultDest = TheOnlyDest;
117 // Figure out which case it goes to.
118 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
120 // Found case matching a constant operand?
121 if (i.getCaseValue() == CI) {
122 TheOnlyDest = i.getCaseSuccessor();
126 // Check to see if this branch is going to the same place as the default
127 // dest. If so, eliminate it as an explicit compare.
128 if (i.getCaseSuccessor() == DefaultDest) {
129 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
130 // MD should have 2 + NumCases operands.
131 if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
132 // Collect branch weights into a vector.
133 SmallVector<uint32_t, 8> Weights;
134 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
136 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
138 Weights.push_back(CI->getValue().getZExtValue());
140 // Merge weight of this case to the default weight.
141 unsigned idx = i.getCaseIndex();
142 Weights[0] += Weights[idx+1];
143 // Remove weight for this case.
144 std::swap(Weights[idx+1], Weights.back());
146 SI->setMetadata(LLVMContext::MD_prof,
147 MDBuilder(BB->getContext()).
148 createBranchWeights(Weights));
150 // Remove this entry.
151 DefaultDest->removePredecessor(SI->getParent());
157 // Otherwise, check to see if the switch only branches to one destination.
158 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
160 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0;
163 if (CI && !TheOnlyDest) {
164 // Branching on a constant, but not any of the cases, go to the default
166 TheOnlyDest = SI->getDefaultDest();
169 // If we found a single destination that we can fold the switch into, do so
172 // Insert the new branch.
173 Builder.CreateBr(TheOnlyDest);
174 BasicBlock *BB = SI->getParent();
176 // Remove entries from PHI nodes which we no longer branch to...
177 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
178 // Found case matching a constant operand?
179 BasicBlock *Succ = SI->getSuccessor(i);
180 if (Succ == TheOnlyDest)
181 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
183 Succ->removePredecessor(BB);
186 // Delete the old switch.
187 Value *Cond = SI->getCondition();
188 SI->eraseFromParent();
189 if (DeleteDeadConditions)
190 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
194 if (SI->getNumCases() == 1) {
195 // Otherwise, we can fold this switch into a conditional branch
196 // instruction if it has only one non-default destination.
197 SwitchInst::CaseIt FirstCase = SI->case_begin();
198 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
199 FirstCase.getCaseValue(), "cond");
201 // Insert the new branch.
202 BranchInst *NewBr = Builder.CreateCondBr(Cond,
203 FirstCase.getCaseSuccessor(),
204 SI->getDefaultDest());
205 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
206 if (MD && MD->getNumOperands() == 3) {
207 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
208 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
209 assert(SICase && SIDef);
210 // The TrueWeight should be the weight for the single case of SI.
211 NewBr->setMetadata(LLVMContext::MD_prof,
212 MDBuilder(BB->getContext()).
213 createBranchWeights(SICase->getValue().getZExtValue(),
214 SIDef->getValue().getZExtValue()));
217 // Delete the old switch.
218 SI->eraseFromParent();
224 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
225 // indirectbr blockaddress(@F, @BB) -> br label @BB
226 if (BlockAddress *BA =
227 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
228 BasicBlock *TheOnlyDest = BA->getBasicBlock();
229 // Insert the new branch.
230 Builder.CreateBr(TheOnlyDest);
232 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
233 if (IBI->getDestination(i) == TheOnlyDest)
236 IBI->getDestination(i)->removePredecessor(IBI->getParent());
238 Value *Address = IBI->getAddress();
239 IBI->eraseFromParent();
240 if (DeleteDeadConditions)
241 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
243 // If we didn't find our destination in the IBI successor list, then we
244 // have undefined behavior. Replace the unconditional branch with an
245 // 'unreachable' instruction.
247 BB->getTerminator()->eraseFromParent();
248 new UnreachableInst(BB->getContext(), BB);
259 //===----------------------------------------------------------------------===//
260 // Local dead code elimination.
263 /// isInstructionTriviallyDead - Return true if the result produced by the
264 /// instruction is not used, and the instruction has no side effects.
266 bool llvm::isInstructionTriviallyDead(Instruction *I,
267 const TargetLibraryInfo *TLI) {
268 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
270 // We don't want the landingpad instruction removed by anything this general.
271 if (isa<LandingPadInst>(I))
274 // We don't want debug info removed by anything this general, unless
275 // debug info is empty.
276 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
277 if (DDI->getAddress())
281 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
287 if (!I->mayHaveSideEffects()) return true;
289 // Special case intrinsics that "may have side effects" but can be deleted
291 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
292 // Safe to delete llvm.stacksave if dead.
293 if (II->getIntrinsicID() == Intrinsic::stacksave)
296 // Lifetime intrinsics are dead when their right-hand is undef.
297 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
298 II->getIntrinsicID() == Intrinsic::lifetime_end)
299 return isa<UndefValue>(II->getArgOperand(1));
302 if (isAllocLikeFn(I, TLI)) return true;
304 if (CallInst *CI = isFreeCall(I, TLI))
305 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
306 return C->isNullValue() || isa<UndefValue>(C);
311 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
312 /// trivially dead instruction, delete it. If that makes any of its operands
313 /// trivially dead, delete them too, recursively. Return true if any
314 /// instructions were deleted.
316 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
317 const TargetLibraryInfo *TLI) {
318 Instruction *I = dyn_cast<Instruction>(V);
319 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
322 SmallVector<Instruction*, 16> DeadInsts;
323 DeadInsts.push_back(I);
326 I = DeadInsts.pop_back_val();
328 // Null out all of the instruction's operands to see if any operand becomes
330 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
331 Value *OpV = I->getOperand(i);
334 if (!OpV->use_empty()) continue;
336 // If the operand is an instruction that became dead as we nulled out the
337 // operand, and if it is 'trivially' dead, delete it in a future loop
339 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
340 if (isInstructionTriviallyDead(OpI, TLI))
341 DeadInsts.push_back(OpI);
344 I->eraseFromParent();
345 } while (!DeadInsts.empty());
350 /// areAllUsesEqual - Check whether the uses of a value are all the same.
351 /// This is similar to Instruction::hasOneUse() except this will also return
352 /// true when there are no uses or multiple uses that all refer to the same
354 static bool areAllUsesEqual(Instruction *I) {
355 Value::use_iterator UI = I->use_begin();
356 Value::use_iterator UE = I->use_end();
361 for (++UI; UI != UE; ++UI) {
368 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
369 /// dead PHI node, due to being a def-use chain of single-use nodes that
370 /// either forms a cycle or is terminated by a trivially dead instruction,
371 /// delete it. If that makes any of its operands trivially dead, delete them
372 /// too, recursively. Return true if a change was made.
373 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
374 const TargetLibraryInfo *TLI) {
375 SmallPtrSet<Instruction*, 4> Visited;
376 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
377 I = cast<Instruction>(*I->use_begin())) {
379 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
381 // If we find an instruction more than once, we're on a cycle that
382 // won't prove fruitful.
383 if (!Visited.insert(I)) {
384 // Break the cycle and delete the instruction and its operands.
385 I->replaceAllUsesWith(UndefValue::get(I->getType()));
386 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
393 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
394 /// simplify any instructions in it and recursively delete dead instructions.
396 /// This returns true if it changed the code, note that it can delete
397 /// instructions in other blocks as well in this block.
398 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
399 const TargetLibraryInfo *TLI) {
400 bool MadeChange = false;
403 // In debug builds, ensure that the terminator of the block is never replaced
404 // or deleted by these simplifications. The idea of simplification is that it
405 // cannot introduce new instructions, and there is no way to replace the
406 // terminator of a block without introducing a new instruction.
407 AssertingVH<Instruction> TerminatorVH(--BB->end());
410 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
411 assert(!BI->isTerminator());
412 Instruction *Inst = BI++;
415 if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
422 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
429 //===----------------------------------------------------------------------===//
430 // Control Flow Graph Restructuring.
434 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
435 /// method is called when we're about to delete Pred as a predecessor of BB. If
436 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
438 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
439 /// nodes that collapse into identity values. For example, if we have:
440 /// x = phi(1, 0, 0, 0)
443 /// .. and delete the predecessor corresponding to the '1', this will attempt to
444 /// recursively fold the and to 0.
445 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
447 // This only adjusts blocks with PHI nodes.
448 if (!isa<PHINode>(BB->begin()))
451 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
452 // them down. This will leave us with single entry phi nodes and other phis
453 // that can be removed.
454 BB->removePredecessor(Pred, true);
456 WeakVH PhiIt = &BB->front();
457 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
458 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
459 Value *OldPhiIt = PhiIt;
461 if (!recursivelySimplifyInstruction(PN, TD))
464 // If recursive simplification ended up deleting the next PHI node we would
465 // iterate to, then our iterator is invalid, restart scanning from the top
467 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
472 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
473 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
474 /// between them, moving the instructions in the predecessor into DestBB and
475 /// deleting the predecessor block.
477 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
478 // If BB has single-entry PHI nodes, fold them.
479 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
480 Value *NewVal = PN->getIncomingValue(0);
481 // Replace self referencing PHI with undef, it must be dead.
482 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
483 PN->replaceAllUsesWith(NewVal);
484 PN->eraseFromParent();
487 BasicBlock *PredBB = DestBB->getSinglePredecessor();
488 assert(PredBB && "Block doesn't have a single predecessor!");
490 // Zap anything that took the address of DestBB. Not doing this will give the
491 // address an invalid value.
492 if (DestBB->hasAddressTaken()) {
493 BlockAddress *BA = BlockAddress::get(DestBB);
494 Constant *Replacement =
495 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
496 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
498 BA->destroyConstant();
501 // Anything that branched to PredBB now branches to DestBB.
502 PredBB->replaceAllUsesWith(DestBB);
504 // Splice all the instructions from PredBB to DestBB.
505 PredBB->getTerminator()->eraseFromParent();
507 // First splice over the PHI nodes.
508 BasicBlock::iterator PI = PredBB->begin();
509 while (isa<PHINode>(PI))
512 if (PI != PredBB->begin())
513 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList(),
514 PredBB->begin(), PI);
516 // Now splice over the rest of the instructions.
517 DestBB->getInstList().splice(DestBB->getFirstInsertionPt(),
518 PredBB->getInstList(), PI, PredBB->end());
521 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
523 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
524 DT->changeImmediateDominator(DestBB, PredBBIDom);
525 DT->eraseNode(PredBB);
530 PredBB->eraseFromParent();
533 /// CanMergeValues - Return true if we can choose one of these values to use
534 /// in place of the other. Note that we will always choose the non-undef
536 static bool CanMergeValues(Value *First, Value *Second) {
537 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
540 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
541 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
543 /// Assumption: Succ is the single successor for BB.
545 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
546 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
548 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
549 << Succ->getName() << "\n");
550 // Shortcut, if there is only a single predecessor it must be BB and merging
552 if (Succ->getSinglePredecessor()) return true;
554 // Make a list of the predecessors of BB
555 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
557 // Look at all the phi nodes in Succ, to see if they present a conflict when
558 // merging these blocks
559 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
560 PHINode *PN = cast<PHINode>(I);
562 // If the incoming value from BB is again a PHINode in
563 // BB which has the same incoming value for *PI as PN does, we can
564 // merge the phi nodes and then the blocks can still be merged
565 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
566 if (BBPN && BBPN->getParent() == BB) {
567 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
568 BasicBlock *IBB = PN->getIncomingBlock(PI);
569 if (BBPreds.count(IBB) &&
570 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
571 PN->getIncomingValue(PI))) {
572 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
573 << Succ->getName() << " is conflicting with "
574 << BBPN->getName() << " with regard to common predecessor "
575 << IBB->getName() << "\n");
580 Value* Val = PN->getIncomingValueForBlock(BB);
581 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
582 // See if the incoming value for the common predecessor is equal to the
583 // one for BB, in which case this phi node will not prevent the merging
585 BasicBlock *IBB = PN->getIncomingBlock(PI);
586 if (BBPreds.count(IBB) &&
587 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
588 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
589 << Succ->getName() << " is conflicting with regard to common "
590 << "predecessor " << IBB->getName() << "\n");
600 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
601 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
603 /// \brief Determines the value to use as the phi node input for a block.
605 /// Select between \p OldVal any value that we know flows from \p BB
606 /// to a particular phi on the basis of which one (if either) is not
607 /// undef. Update IncomingValues based on the selected value.
609 /// \param OldVal The value we are considering selecting.
610 /// \param BB The block that the value flows in from.
611 /// \param IncomingValues A map from block-to-value for other phi inputs
612 /// that we have examined.
614 /// \returns the selected value.
615 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
616 IncomingValueMap &IncomingValues) {
617 if (!isa<UndefValue>(OldVal)) {
618 assert((!IncomingValues.count(BB) ||
619 IncomingValues.find(BB)->second == OldVal) &&
620 "Expected OldVal to match incoming value from BB!");
622 IncomingValues.insert(std::make_pair(BB, OldVal));
626 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
627 if (It != IncomingValues.end()) return It->second;
632 /// \brief Create a map from block to value for the operands of a
635 /// Create a map from block to value for each non-undef value flowing
638 /// \param PN The phi we are collecting the map for.
639 /// \param IncomingValues [out] The map from block to value for this phi.
640 static void gatherIncomingValuesToPhi(PHINode *PN,
641 IncomingValueMap &IncomingValues) {
642 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
643 BasicBlock *BB = PN->getIncomingBlock(i);
644 Value *V = PN->getIncomingValue(i);
646 if (!isa<UndefValue>(V))
647 IncomingValues.insert(std::make_pair(BB, V));
651 /// \brief Replace the incoming undef values to a phi with the values
652 /// from a block-to-value map.
654 /// \param PN The phi we are replacing the undefs in.
655 /// \param IncomingValues A map from block to value.
656 static void replaceUndefValuesInPhi(PHINode *PN,
657 const IncomingValueMap &IncomingValues) {
658 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
659 Value *V = PN->getIncomingValue(i);
661 if (!isa<UndefValue>(V)) continue;
663 BasicBlock *BB = PN->getIncomingBlock(i);
664 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
665 if (It == IncomingValues.end()) continue;
667 PN->setIncomingValue(i, It->second);
671 /// \brief Replace a value flowing from a block to a phi with
672 /// potentially multiple instances of that value flowing from the
673 /// block's predecessors to the phi.
675 /// \param BB The block with the value flowing into the phi.
676 /// \param BBPreds The predecessors of BB.
677 /// \param PN The phi that we are updating.
678 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
679 const PredBlockVector &BBPreds,
681 Value *OldVal = PN->removeIncomingValue(BB, false);
682 assert(OldVal && "No entry in PHI for Pred BB!");
684 IncomingValueMap IncomingValues;
686 // We are merging two blocks - BB, and the block containing PN - and
687 // as a result we need to redirect edges from the predecessors of BB
688 // to go to the block containing PN, and update PN
689 // accordingly. Since we allow merging blocks in the case where the
690 // predecessor and successor blocks both share some predecessors,
691 // and where some of those common predecessors might have undef
692 // values flowing into PN, we want to rewrite those values to be
693 // consistent with the non-undef values.
695 gatherIncomingValuesToPhi(PN, IncomingValues);
697 // If this incoming value is one of the PHI nodes in BB, the new entries
698 // in the PHI node are the entries from the old PHI.
699 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
700 PHINode *OldValPN = cast<PHINode>(OldVal);
701 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
702 // Note that, since we are merging phi nodes and BB and Succ might
703 // have common predecessors, we could end up with a phi node with
704 // identical incoming branches. This will be cleaned up later (and
705 // will trigger asserts if we try to clean it up now, without also
706 // simplifying the corresponding conditional branch).
707 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
708 Value *PredVal = OldValPN->getIncomingValue(i);
709 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
712 // And add a new incoming value for this predecessor for the
713 // newly retargeted branch.
714 PN->addIncoming(Selected, PredBB);
717 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
718 // Update existing incoming values in PN for this
719 // predecessor of BB.
720 BasicBlock *PredBB = BBPreds[i];
721 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
724 // And add a new incoming value for this predecessor for the
725 // newly retargeted branch.
726 PN->addIncoming(Selected, PredBB);
730 replaceUndefValuesInPhi(PN, IncomingValues);
733 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
734 /// unconditional branch, and contains no instructions other than PHI nodes,
735 /// potential side-effect free intrinsics and the branch. If possible,
736 /// eliminate BB by rewriting all the predecessors to branch to the successor
737 /// block and return true. If we can't transform, return false.
738 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
739 assert(BB != &BB->getParent()->getEntryBlock() &&
740 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
742 // We can't eliminate infinite loops.
743 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
744 if (BB == Succ) return false;
746 // Check to see if merging these blocks would cause conflicts for any of the
747 // phi nodes in BB or Succ. If not, we can safely merge.
748 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
750 // Check for cases where Succ has multiple predecessors and a PHI node in BB
751 // has uses which will not disappear when the PHI nodes are merged. It is
752 // possible to handle such cases, but difficult: it requires checking whether
753 // BB dominates Succ, which is non-trivial to calculate in the case where
754 // Succ has multiple predecessors. Also, it requires checking whether
755 // constructing the necessary self-referential PHI node doesn't introduce any
756 // conflicts; this isn't too difficult, but the previous code for doing this
759 // Note that if this check finds a live use, BB dominates Succ, so BB is
760 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
761 // folding the branch isn't profitable in that case anyway.
762 if (!Succ->getSinglePredecessor()) {
763 BasicBlock::iterator BBI = BB->begin();
764 while (isa<PHINode>(*BBI)) {
765 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
767 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
768 if (PN->getIncomingBlock(UI) != BB)
778 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
780 if (isa<PHINode>(Succ->begin())) {
781 // If there is more than one pred of succ, and there are PHI nodes in
782 // the successor, then we need to add incoming edges for the PHI nodes
784 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
786 // Loop over all of the PHI nodes in the successor of BB.
787 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
788 PHINode *PN = cast<PHINode>(I);
790 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
794 if (Succ->getSinglePredecessor()) {
795 // BB is the only predecessor of Succ, so Succ will end up with exactly
796 // the same predecessors BB had.
798 // Copy over any phi, debug or lifetime instruction.
799 BB->getTerminator()->eraseFromParent();
800 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
802 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
803 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
804 assert(PN->use_empty() && "There shouldn't be any uses here!");
805 PN->eraseFromParent();
809 // Everything that jumped to BB now goes to Succ.
810 BB->replaceAllUsesWith(Succ);
811 if (!Succ->hasName()) Succ->takeName(BB);
812 BB->eraseFromParent(); // Delete the old basic block.
816 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
817 /// nodes in this block. This doesn't try to be clever about PHI nodes
818 /// which differ only in the order of the incoming values, but instcombine
819 /// orders them so it usually won't matter.
821 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
822 bool Changed = false;
824 // This implementation doesn't currently consider undef operands
825 // specially. Theoretically, two phis which are identical except for
826 // one having an undef where the other doesn't could be collapsed.
828 // Map from PHI hash values to PHI nodes. If multiple PHIs have
829 // the same hash value, the element is the first PHI in the
830 // linked list in CollisionMap.
831 DenseMap<uintptr_t, PHINode *> HashMap;
833 // Maintain linked lists of PHI nodes with common hash values.
834 DenseMap<PHINode *, PHINode *> CollisionMap;
837 for (BasicBlock::iterator I = BB->begin();
838 PHINode *PN = dyn_cast<PHINode>(I++); ) {
839 // Compute a hash value on the operands. Instcombine will likely have sorted
840 // them, which helps expose duplicates, but we have to check all the
841 // operands to be safe in case instcombine hasn't run.
843 // This hash algorithm is quite weak as hash functions go, but it seems
844 // to do a good enough job for this particular purpose, and is very quick.
845 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
846 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
847 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
849 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
851 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
852 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
854 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
856 // If we've never seen this hash value before, it's a unique PHI.
857 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
858 HashMap.insert(std::make_pair(Hash, PN));
859 if (Pair.second) continue;
860 // Otherwise it's either a duplicate or a hash collision.
861 for (PHINode *OtherPN = Pair.first->second; ; ) {
862 if (OtherPN->isIdenticalTo(PN)) {
863 // A duplicate. Replace this PHI with its duplicate.
864 PN->replaceAllUsesWith(OtherPN);
865 PN->eraseFromParent();
869 // A non-duplicate hash collision.
870 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
871 if (I == CollisionMap.end()) {
872 // Set this PHI to be the head of the linked list of colliding PHIs.
873 PHINode *Old = Pair.first->second;
874 Pair.first->second = PN;
875 CollisionMap[PN] = Old;
878 // Proceed to the next PHI in the list.
886 /// enforceKnownAlignment - If the specified pointer points to an object that
887 /// we control, modify the object's alignment to PrefAlign. This isn't
888 /// often possible though. If alignment is important, a more reliable approach
889 /// is to simply align all global variables and allocation instructions to
890 /// their preferred alignment from the beginning.
892 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
893 unsigned PrefAlign, const DataLayout *TD) {
894 V = V->stripPointerCasts();
896 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
897 // If the preferred alignment is greater than the natural stack alignment
898 // then don't round up. This avoids dynamic stack realignment.
899 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
901 // If there is a requested alignment and if this is an alloca, round up.
902 if (AI->getAlignment() >= PrefAlign)
903 return AI->getAlignment();
904 AI->setAlignment(PrefAlign);
908 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
909 // If there is a large requested alignment and we can, bump up the alignment
911 if (GV->isDeclaration()) return Align;
912 // If the memory we set aside for the global may not be the memory used by
913 // the final program then it is impossible for us to reliably enforce the
914 // preferred alignment.
915 if (GV->isWeakForLinker()) return Align;
917 if (GV->getAlignment() >= PrefAlign)
918 return GV->getAlignment();
919 // We can only increase the alignment of the global if it has no alignment
920 // specified or if it is not assigned a section. If it is assigned a
921 // section, the global could be densely packed with other objects in the
922 // section, increasing the alignment could cause padding issues.
923 if (!GV->hasSection() || GV->getAlignment() == 0)
924 GV->setAlignment(PrefAlign);
925 return GV->getAlignment();
931 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
932 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
933 /// and it is more than the alignment of the ultimate object, see if we can
934 /// increase the alignment of the ultimate object, making this check succeed.
935 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
936 const DataLayout *DL) {
937 assert(V->getType()->isPointerTy() &&
938 "getOrEnforceKnownAlignment expects a pointer!");
939 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
941 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
942 ComputeMaskedBits(V, KnownZero, KnownOne, DL);
943 unsigned TrailZ = KnownZero.countTrailingOnes();
945 // Avoid trouble with ridiculously large TrailZ values, such as
946 // those computed from a null pointer.
947 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
949 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
951 // LLVM doesn't support alignments larger than this currently.
952 Align = std::min(Align, +Value::MaximumAlignment);
954 if (PrefAlign > Align)
955 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
957 // We don't need to make any adjustment.
961 ///===---------------------------------------------------------------------===//
962 /// Dbg Intrinsic utilities
965 /// See if there is a dbg.value intrinsic for DIVar before I.
966 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
967 // Since we can't guarantee that the original dbg.declare instrinsic
968 // is removed by LowerDbgDeclare(), we need to make sure that we are
969 // not inserting the same dbg.value intrinsic over and over.
970 llvm::BasicBlock::InstListType::iterator PrevI(I);
971 if (PrevI != I->getParent()->getInstList().begin()) {
973 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
974 if (DVI->getValue() == I->getOperand(0) &&
975 DVI->getOffset() == 0 &&
976 DVI->getVariable() == DIVar)
982 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
983 /// that has an associated llvm.dbg.decl intrinsic.
984 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
985 StoreInst *SI, DIBuilder &Builder) {
986 DIVariable DIVar(DDI->getVariable());
987 assert((!DIVar || DIVar.isVariable()) &&
988 "Variable in DbgDeclareInst should be either null or a DIVariable.");
992 if (LdStHasDebugValue(DIVar, SI))
995 Instruction *DbgVal = NULL;
996 // If an argument is zero extended then use argument directly. The ZExt
997 // may be zapped by an optimization pass in future.
998 Argument *ExtendedArg = NULL;
999 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1000 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1001 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1002 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1004 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
1006 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
1008 // Propagate any debug metadata from the store onto the dbg.value.
1009 DebugLoc SIDL = SI->getDebugLoc();
1010 if (!SIDL.isUnknown())
1011 DbgVal->setDebugLoc(SIDL);
1012 // Otherwise propagate debug metadata from dbg.declare.
1014 DbgVal->setDebugLoc(DDI->getDebugLoc());
1018 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1019 /// that has an associated llvm.dbg.decl intrinsic.
1020 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1021 LoadInst *LI, DIBuilder &Builder) {
1022 DIVariable DIVar(DDI->getVariable());
1023 assert((!DIVar || DIVar.isVariable()) &&
1024 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1028 if (LdStHasDebugValue(DIVar, LI))
1031 Instruction *DbgVal =
1032 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
1035 // Propagate any debug metadata from the store onto the dbg.value.
1036 DebugLoc LIDL = LI->getDebugLoc();
1037 if (!LIDL.isUnknown())
1038 DbgVal->setDebugLoc(LIDL);
1039 // Otherwise propagate debug metadata from dbg.declare.
1041 DbgVal->setDebugLoc(DDI->getDebugLoc());
1045 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1046 /// of llvm.dbg.value intrinsics.
1047 bool llvm::LowerDbgDeclare(Function &F) {
1048 DIBuilder DIB(*F.getParent());
1049 SmallVector<DbgDeclareInst *, 4> Dbgs;
1050 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1051 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
1052 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
1053 Dbgs.push_back(DDI);
1058 for (SmallVectorImpl<DbgDeclareInst *>::iterator I = Dbgs.begin(),
1059 E = Dbgs.end(); I != E; ++I) {
1060 DbgDeclareInst *DDI = *I;
1061 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
1062 // We only remove the dbg.declare intrinsic if all uses are
1063 // converted to dbg.value intrinsics.
1064 bool RemoveDDI = true;
1065 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
1067 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
1068 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1069 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
1070 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1074 DDI->eraseFromParent();
1080 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1081 /// alloca 'V', if any.
1082 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1083 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
1084 for (Value::use_iterator UI = DebugNode->use_begin(),
1085 E = DebugNode->use_end(); UI != E; ++UI)
1086 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))
1092 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1093 DIBuilder &Builder) {
1094 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1097 DIVariable DIVar(DDI->getVariable());
1098 assert((!DIVar || DIVar.isVariable()) &&
1099 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1103 // Create a copy of the original DIDescriptor for user variable, appending
1104 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1105 // will take a value storing address of the memory for variable, not
1107 Type *Int64Ty = Type::getInt64Ty(AI->getContext());
1108 SmallVector<Value*, 4> NewDIVarAddress;
1109 if (DIVar.hasComplexAddress()) {
1110 for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
1111 NewDIVarAddress.push_back(
1112 ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
1115 NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
1116 DIVariable NewDIVar = Builder.createComplexVariable(
1117 DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
1118 DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
1119 NewDIVarAddress, DIVar.getArgNumber());
1121 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1122 // and remove old llvm.dbg.declare.
1123 BasicBlock *BB = AI->getParent();
1124 Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
1125 DDI->eraseFromParent();
1129 /// changeToUnreachable - Insert an unreachable instruction before the specified
1130 /// instruction, making it and the rest of the code in the block dead.
1131 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1132 BasicBlock *BB = I->getParent();
1133 // Loop over all of the successors, removing BB's entry from any PHI
1135 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1136 (*SI)->removePredecessor(BB);
1138 // Insert a call to llvm.trap right before this. This turns the undefined
1139 // behavior into a hard fail instead of falling through into random code.
1142 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1143 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1144 CallTrap->setDebugLoc(I->getDebugLoc());
1146 new UnreachableInst(I->getContext(), I);
1148 // All instructions after this are dead.
1149 BasicBlock::iterator BBI = I, BBE = BB->end();
1150 while (BBI != BBE) {
1151 if (!BBI->use_empty())
1152 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1153 BB->getInstList().erase(BBI++);
1157 /// changeToCall - Convert the specified invoke into a normal call.
1158 static void changeToCall(InvokeInst *II) {
1159 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1160 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1161 NewCall->takeName(II);
1162 NewCall->setCallingConv(II->getCallingConv());
1163 NewCall->setAttributes(II->getAttributes());
1164 NewCall->setDebugLoc(II->getDebugLoc());
1165 II->replaceAllUsesWith(NewCall);
1167 // Follow the call by a branch to the normal destination.
1168 BranchInst::Create(II->getNormalDest(), II);
1170 // Update PHI nodes in the unwind destination
1171 II->getUnwindDest()->removePredecessor(II->getParent());
1172 II->eraseFromParent();
1175 static bool markAliveBlocks(BasicBlock *BB,
1176 SmallPtrSet<BasicBlock*, 128> &Reachable) {
1178 SmallVector<BasicBlock*, 128> Worklist;
1179 Worklist.push_back(BB);
1180 Reachable.insert(BB);
1181 bool Changed = false;
1183 BB = Worklist.pop_back_val();
1185 // Do a quick scan of the basic block, turning any obviously unreachable
1186 // instructions into LLVM unreachable insts. The instruction combining pass
1187 // canonicalizes unreachable insts into stores to null or undef.
1188 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1189 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1190 if (CI->doesNotReturn()) {
1191 // If we found a call to a no-return function, insert an unreachable
1192 // instruction after it. Make sure there isn't *already* one there
1195 if (!isa<UnreachableInst>(BBI)) {
1196 // Don't insert a call to llvm.trap right before the unreachable.
1197 changeToUnreachable(BBI, false);
1204 // Store to undef and store to null are undefined and used to signal that
1205 // they should be changed to unreachable by passes that can't modify the
1207 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1208 // Don't touch volatile stores.
1209 if (SI->isVolatile()) continue;
1211 Value *Ptr = SI->getOperand(1);
1213 if (isa<UndefValue>(Ptr) ||
1214 (isa<ConstantPointerNull>(Ptr) &&
1215 SI->getPointerAddressSpace() == 0)) {
1216 changeToUnreachable(SI, true);
1223 // Turn invokes that call 'nounwind' functions into ordinary calls.
1224 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1225 Value *Callee = II->getCalledValue();
1226 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1227 changeToUnreachable(II, true);
1229 } else if (II->doesNotThrow()) {
1230 if (II->use_empty() && II->onlyReadsMemory()) {
1231 // jump to the normal destination branch.
1232 BranchInst::Create(II->getNormalDest(), II);
1233 II->getUnwindDest()->removePredecessor(II->getParent());
1234 II->eraseFromParent();
1241 Changed |= ConstantFoldTerminator(BB, true);
1242 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1243 if (Reachable.insert(*SI))
1244 Worklist.push_back(*SI);
1245 } while (!Worklist.empty());
1249 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1250 /// if they are in a dead cycle. Return true if a change was made, false
1252 bool llvm::removeUnreachableBlocks(Function &F) {
1253 SmallPtrSet<BasicBlock*, 128> Reachable;
1254 bool Changed = markAliveBlocks(F.begin(), Reachable);
1256 // If there are unreachable blocks in the CFG...
1257 if (Reachable.size() == F.size())
1260 assert(Reachable.size() < F.size());
1261 NumRemoved += F.size()-Reachable.size();
1263 // Loop over all of the basic blocks that are not reachable, dropping all of
1264 // their internal references...
1265 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1266 if (Reachable.count(BB))
1269 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1270 if (Reachable.count(*SI))
1271 (*SI)->removePredecessor(BB);
1272 BB->dropAllReferences();
1275 for (Function::iterator I = ++F.begin(); I != F.end();)
1276 if (!Reachable.count(I))
1277 I = F.getBasicBlockList().erase(I);