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/DIBuilder.h"
24 #include "llvm/DebugInfo.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DerivedTypes.h"
28 #include "llvm/IR/Dominators.h"
29 #include "llvm/IR/GetElementPtrTypeIterator.h"
30 #include "llvm/IR/GlobalAlias.h"
31 #include "llvm/IR/GlobalVariable.h"
32 #include "llvm/IR/IRBuilder.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/IntrinsicInst.h"
35 #include "llvm/IR/Intrinsics.h"
36 #include "llvm/IR/MDBuilder.h"
37 #include "llvm/IR/Metadata.h"
38 #include "llvm/IR/Operator.h"
39 #include "llvm/IR/ValueHandle.h"
40 #include "llvm/Support/CFG.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Support/MathExtras.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 unsigned NCases = SI->getNumCases();
131 // Fold the case metadata into the default if there will be any branches
132 // left, unless the metadata doesn't match the switch.
133 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
134 // Collect branch weights into a vector.
135 SmallVector<uint32_t, 8> Weights;
136 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
138 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
140 Weights.push_back(CI->getValue().getZExtValue());
142 // Merge weight of this case to the default weight.
143 unsigned idx = i.getCaseIndex();
144 Weights[0] += Weights[idx+1];
145 // Remove weight for this case.
146 std::swap(Weights[idx+1], Weights.back());
148 SI->setMetadata(LLVMContext::MD_prof,
149 MDBuilder(BB->getContext()).
150 createBranchWeights(Weights));
152 // Remove this entry.
153 DefaultDest->removePredecessor(SI->getParent());
159 // Otherwise, check to see if the switch only branches to one destination.
160 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
162 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0;
165 if (CI && !TheOnlyDest) {
166 // Branching on a constant, but not any of the cases, go to the default
168 TheOnlyDest = SI->getDefaultDest();
171 // If we found a single destination that we can fold the switch into, do so
174 // Insert the new branch.
175 Builder.CreateBr(TheOnlyDest);
176 BasicBlock *BB = SI->getParent();
178 // Remove entries from PHI nodes which we no longer branch to...
179 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
180 // Found case matching a constant operand?
181 BasicBlock *Succ = SI->getSuccessor(i);
182 if (Succ == TheOnlyDest)
183 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
185 Succ->removePredecessor(BB);
188 // Delete the old switch.
189 Value *Cond = SI->getCondition();
190 SI->eraseFromParent();
191 if (DeleteDeadConditions)
192 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
196 if (SI->getNumCases() == 1) {
197 // Otherwise, we can fold this switch into a conditional branch
198 // instruction if it has only one non-default destination.
199 SwitchInst::CaseIt FirstCase = SI->case_begin();
200 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
201 FirstCase.getCaseValue(), "cond");
203 // Insert the new branch.
204 BranchInst *NewBr = Builder.CreateCondBr(Cond,
205 FirstCase.getCaseSuccessor(),
206 SI->getDefaultDest());
207 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
208 if (MD && MD->getNumOperands() == 3) {
209 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
210 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
211 assert(SICase && SIDef);
212 // The TrueWeight should be the weight for the single case of SI.
213 NewBr->setMetadata(LLVMContext::MD_prof,
214 MDBuilder(BB->getContext()).
215 createBranchWeights(SICase->getValue().getZExtValue(),
216 SIDef->getValue().getZExtValue()));
219 // Delete the old switch.
220 SI->eraseFromParent();
226 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
227 // indirectbr blockaddress(@F, @BB) -> br label @BB
228 if (BlockAddress *BA =
229 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
230 BasicBlock *TheOnlyDest = BA->getBasicBlock();
231 // Insert the new branch.
232 Builder.CreateBr(TheOnlyDest);
234 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
235 if (IBI->getDestination(i) == TheOnlyDest)
238 IBI->getDestination(i)->removePredecessor(IBI->getParent());
240 Value *Address = IBI->getAddress();
241 IBI->eraseFromParent();
242 if (DeleteDeadConditions)
243 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
245 // If we didn't find our destination in the IBI successor list, then we
246 // have undefined behavior. Replace the unconditional branch with an
247 // 'unreachable' instruction.
249 BB->getTerminator()->eraseFromParent();
250 new UnreachableInst(BB->getContext(), BB);
261 //===----------------------------------------------------------------------===//
262 // Local dead code elimination.
265 /// isInstructionTriviallyDead - Return true if the result produced by the
266 /// instruction is not used, and the instruction has no side effects.
268 bool llvm::isInstructionTriviallyDead(Instruction *I,
269 const TargetLibraryInfo *TLI) {
270 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
272 // We don't want the landingpad instruction removed by anything this general.
273 if (isa<LandingPadInst>(I))
276 // We don't want debug info removed by anything this general, unless
277 // debug info is empty.
278 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
279 if (DDI->getAddress())
283 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
289 if (!I->mayHaveSideEffects()) return true;
291 // Special case intrinsics that "may have side effects" but can be deleted
293 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
294 // Safe to delete llvm.stacksave if dead.
295 if (II->getIntrinsicID() == Intrinsic::stacksave)
298 // Lifetime intrinsics are dead when their right-hand is undef.
299 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
300 II->getIntrinsicID() == Intrinsic::lifetime_end)
301 return isa<UndefValue>(II->getArgOperand(1));
304 if (isAllocLikeFn(I, TLI)) return true;
306 if (CallInst *CI = isFreeCall(I, TLI))
307 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
308 return C->isNullValue() || isa<UndefValue>(C);
313 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
314 /// trivially dead instruction, delete it. If that makes any of its operands
315 /// trivially dead, delete them too, recursively. Return true if any
316 /// instructions were deleted.
318 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
319 const TargetLibraryInfo *TLI) {
320 Instruction *I = dyn_cast<Instruction>(V);
321 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
324 SmallVector<Instruction*, 16> DeadInsts;
325 DeadInsts.push_back(I);
328 I = DeadInsts.pop_back_val();
330 // Null out all of the instruction's operands to see if any operand becomes
332 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
333 Value *OpV = I->getOperand(i);
336 if (!OpV->use_empty()) continue;
338 // If the operand is an instruction that became dead as we nulled out the
339 // operand, and if it is 'trivially' dead, delete it in a future loop
341 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
342 if (isInstructionTriviallyDead(OpI, TLI))
343 DeadInsts.push_back(OpI);
346 I->eraseFromParent();
347 } while (!DeadInsts.empty());
352 /// areAllUsesEqual - Check whether the uses of a value are all the same.
353 /// This is similar to Instruction::hasOneUse() except this will also return
354 /// true when there are no uses or multiple uses that all refer to the same
356 static bool areAllUsesEqual(Instruction *I) {
357 Value::use_iterator UI = I->use_begin();
358 Value::use_iterator UE = I->use_end();
363 for (++UI; UI != UE; ++UI) {
370 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
371 /// dead PHI node, due to being a def-use chain of single-use nodes that
372 /// either forms a cycle or is terminated by a trivially dead instruction,
373 /// delete it. If that makes any of its operands trivially dead, delete them
374 /// too, recursively. Return true if a change was made.
375 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
376 const TargetLibraryInfo *TLI) {
377 SmallPtrSet<Instruction*, 4> Visited;
378 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
379 I = cast<Instruction>(*I->use_begin())) {
381 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
383 // If we find an instruction more than once, we're on a cycle that
384 // won't prove fruitful.
385 if (!Visited.insert(I)) {
386 // Break the cycle and delete the instruction and its operands.
387 I->replaceAllUsesWith(UndefValue::get(I->getType()));
388 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
395 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
396 /// simplify any instructions in it and recursively delete dead instructions.
398 /// This returns true if it changed the code, note that it can delete
399 /// instructions in other blocks as well in this block.
400 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
401 const TargetLibraryInfo *TLI) {
402 bool MadeChange = false;
405 // In debug builds, ensure that the terminator of the block is never replaced
406 // or deleted by these simplifications. The idea of simplification is that it
407 // cannot introduce new instructions, and there is no way to replace the
408 // terminator of a block without introducing a new instruction.
409 AssertingVH<Instruction> TerminatorVH(--BB->end());
412 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
413 assert(!BI->isTerminator());
414 Instruction *Inst = BI++;
417 if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
424 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
431 //===----------------------------------------------------------------------===//
432 // Control Flow Graph Restructuring.
436 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
437 /// method is called when we're about to delete Pred as a predecessor of BB. If
438 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
440 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
441 /// nodes that collapse into identity values. For example, if we have:
442 /// x = phi(1, 0, 0, 0)
445 /// .. and delete the predecessor corresponding to the '1', this will attempt to
446 /// recursively fold the and to 0.
447 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
449 // This only adjusts blocks with PHI nodes.
450 if (!isa<PHINode>(BB->begin()))
453 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
454 // them down. This will leave us with single entry phi nodes and other phis
455 // that can be removed.
456 BB->removePredecessor(Pred, true);
458 WeakVH PhiIt = &BB->front();
459 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
460 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
461 Value *OldPhiIt = PhiIt;
463 if (!recursivelySimplifyInstruction(PN, TD))
466 // If recursive simplification ended up deleting the next PHI node we would
467 // iterate to, then our iterator is invalid, restart scanning from the top
469 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
474 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
475 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
476 /// between them, moving the instructions in the predecessor into DestBB and
477 /// deleting the predecessor block.
479 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
480 // If BB has single-entry PHI nodes, fold them.
481 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
482 Value *NewVal = PN->getIncomingValue(0);
483 // Replace self referencing PHI with undef, it must be dead.
484 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
485 PN->replaceAllUsesWith(NewVal);
486 PN->eraseFromParent();
489 BasicBlock *PredBB = DestBB->getSinglePredecessor();
490 assert(PredBB && "Block doesn't have a single predecessor!");
492 // Zap anything that took the address of DestBB. Not doing this will give the
493 // address an invalid value.
494 if (DestBB->hasAddressTaken()) {
495 BlockAddress *BA = BlockAddress::get(DestBB);
496 Constant *Replacement =
497 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
498 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
500 BA->destroyConstant();
503 // Anything that branched to PredBB now branches to DestBB.
504 PredBB->replaceAllUsesWith(DestBB);
506 // Splice all the instructions from PredBB to DestBB.
507 PredBB->getTerminator()->eraseFromParent();
508 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
511 if (DominatorTreeWrapperPass *DTWP =
512 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
513 DominatorTree &DT = DTWP->getDomTree();
514 BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock();
515 DT.changeImmediateDominator(DestBB, PredBBIDom);
516 DT.eraseNode(PredBB);
520 PredBB->eraseFromParent();
523 /// CanMergeValues - Return true if we can choose one of these values to use
524 /// in place of the other. Note that we will always choose the non-undef
526 static bool CanMergeValues(Value *First, Value *Second) {
527 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
530 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
531 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
533 /// Assumption: Succ is the single successor for BB.
535 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
536 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
538 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
539 << Succ->getName() << "\n");
540 // Shortcut, if there is only a single predecessor it must be BB and merging
542 if (Succ->getSinglePredecessor()) return true;
544 // Make a list of the predecessors of BB
545 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
547 // Look at all the phi nodes in Succ, to see if they present a conflict when
548 // merging these blocks
549 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
550 PHINode *PN = cast<PHINode>(I);
552 // If the incoming value from BB is again a PHINode in
553 // BB which has the same incoming value for *PI as PN does, we can
554 // merge the phi nodes and then the blocks can still be merged
555 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
556 if (BBPN && BBPN->getParent() == BB) {
557 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
558 BasicBlock *IBB = PN->getIncomingBlock(PI);
559 if (BBPreds.count(IBB) &&
560 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
561 PN->getIncomingValue(PI))) {
562 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
563 << Succ->getName() << " is conflicting with "
564 << BBPN->getName() << " with regard to common predecessor "
565 << IBB->getName() << "\n");
570 Value* Val = PN->getIncomingValueForBlock(BB);
571 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
572 // See if the incoming value for the common predecessor is equal to the
573 // one for BB, in which case this phi node will not prevent the merging
575 BasicBlock *IBB = PN->getIncomingBlock(PI);
576 if (BBPreds.count(IBB) &&
577 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
578 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
579 << Succ->getName() << " is conflicting with regard to common "
580 << "predecessor " << IBB->getName() << "\n");
590 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
591 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
593 /// \brief Determines the value to use as the phi node input for a block.
595 /// Select between \p OldVal any value that we know flows from \p BB
596 /// to a particular phi on the basis of which one (if either) is not
597 /// undef. Update IncomingValues based on the selected value.
599 /// \param OldVal The value we are considering selecting.
600 /// \param BB The block that the value flows in from.
601 /// \param IncomingValues A map from block-to-value for other phi inputs
602 /// that we have examined.
604 /// \returns the selected value.
605 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
606 IncomingValueMap &IncomingValues) {
607 if (!isa<UndefValue>(OldVal)) {
608 assert((!IncomingValues.count(BB) ||
609 IncomingValues.find(BB)->second == OldVal) &&
610 "Expected OldVal to match incoming value from BB!");
612 IncomingValues.insert(std::make_pair(BB, OldVal));
616 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
617 if (It != IncomingValues.end()) return It->second;
622 /// \brief Create a map from block to value for the operands of a
625 /// Create a map from block to value for each non-undef value flowing
628 /// \param PN The phi we are collecting the map for.
629 /// \param IncomingValues [out] The map from block to value for this phi.
630 static void gatherIncomingValuesToPhi(PHINode *PN,
631 IncomingValueMap &IncomingValues) {
632 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
633 BasicBlock *BB = PN->getIncomingBlock(i);
634 Value *V = PN->getIncomingValue(i);
636 if (!isa<UndefValue>(V))
637 IncomingValues.insert(std::make_pair(BB, V));
641 /// \brief Replace the incoming undef values to a phi with the values
642 /// from a block-to-value map.
644 /// \param PN The phi we are replacing the undefs in.
645 /// \param IncomingValues A map from block to value.
646 static void replaceUndefValuesInPhi(PHINode *PN,
647 const IncomingValueMap &IncomingValues) {
648 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
649 Value *V = PN->getIncomingValue(i);
651 if (!isa<UndefValue>(V)) continue;
653 BasicBlock *BB = PN->getIncomingBlock(i);
654 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
655 if (It == IncomingValues.end()) continue;
657 PN->setIncomingValue(i, It->second);
661 /// \brief Replace a value flowing from a block to a phi with
662 /// potentially multiple instances of that value flowing from the
663 /// block's predecessors to the phi.
665 /// \param BB The block with the value flowing into the phi.
666 /// \param BBPreds The predecessors of BB.
667 /// \param PN The phi that we are updating.
668 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
669 const PredBlockVector &BBPreds,
671 Value *OldVal = PN->removeIncomingValue(BB, false);
672 assert(OldVal && "No entry in PHI for Pred BB!");
674 IncomingValueMap IncomingValues;
676 // We are merging two blocks - BB, and the block containing PN - and
677 // as a result we need to redirect edges from the predecessors of BB
678 // to go to the block containing PN, and update PN
679 // accordingly. Since we allow merging blocks in the case where the
680 // predecessor and successor blocks both share some predecessors,
681 // and where some of those common predecessors might have undef
682 // values flowing into PN, we want to rewrite those values to be
683 // consistent with the non-undef values.
685 gatherIncomingValuesToPhi(PN, IncomingValues);
687 // If this incoming value is one of the PHI nodes in BB, the new entries
688 // in the PHI node are the entries from the old PHI.
689 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
690 PHINode *OldValPN = cast<PHINode>(OldVal);
691 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
692 // Note that, since we are merging phi nodes and BB and Succ might
693 // have common predecessors, we could end up with a phi node with
694 // identical incoming branches. This will be cleaned up later (and
695 // will trigger asserts if we try to clean it up now, without also
696 // simplifying the corresponding conditional branch).
697 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
698 Value *PredVal = OldValPN->getIncomingValue(i);
699 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
702 // And add a new incoming value for this predecessor for the
703 // newly retargeted branch.
704 PN->addIncoming(Selected, PredBB);
707 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
708 // Update existing incoming values in PN for this
709 // predecessor of BB.
710 BasicBlock *PredBB = BBPreds[i];
711 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
714 // And add a new incoming value for this predecessor for the
715 // newly retargeted branch.
716 PN->addIncoming(Selected, PredBB);
720 replaceUndefValuesInPhi(PN, IncomingValues);
723 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
724 /// unconditional branch, and contains no instructions other than PHI nodes,
725 /// potential side-effect free intrinsics and the branch. If possible,
726 /// eliminate BB by rewriting all the predecessors to branch to the successor
727 /// block and return true. If we can't transform, return false.
728 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
729 assert(BB != &BB->getParent()->getEntryBlock() &&
730 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
732 // We can't eliminate infinite loops.
733 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
734 if (BB == Succ) return false;
736 // Check to see if merging these blocks would cause conflicts for any of the
737 // phi nodes in BB or Succ. If not, we can safely merge.
738 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
740 // Check for cases where Succ has multiple predecessors and a PHI node in BB
741 // has uses which will not disappear when the PHI nodes are merged. It is
742 // possible to handle such cases, but difficult: it requires checking whether
743 // BB dominates Succ, which is non-trivial to calculate in the case where
744 // Succ has multiple predecessors. Also, it requires checking whether
745 // constructing the necessary self-referential PHI node doesn't introduce any
746 // conflicts; this isn't too difficult, but the previous code for doing this
749 // Note that if this check finds a live use, BB dominates Succ, so BB is
750 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
751 // folding the branch isn't profitable in that case anyway.
752 if (!Succ->getSinglePredecessor()) {
753 BasicBlock::iterator BBI = BB->begin();
754 while (isa<PHINode>(*BBI)) {
755 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
757 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
758 if (PN->getIncomingBlock(UI) != BB)
768 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
770 if (isa<PHINode>(Succ->begin())) {
771 // If there is more than one pred of succ, and there are PHI nodes in
772 // the successor, then we need to add incoming edges for the PHI nodes
774 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
776 // Loop over all of the PHI nodes in the successor of BB.
777 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
778 PHINode *PN = cast<PHINode>(I);
780 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
784 if (Succ->getSinglePredecessor()) {
785 // BB is the only predecessor of Succ, so Succ will end up with exactly
786 // the same predecessors BB had.
788 // Copy over any phi, debug or lifetime instruction.
789 BB->getTerminator()->eraseFromParent();
790 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
792 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
793 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
794 assert(PN->use_empty() && "There shouldn't be any uses here!");
795 PN->eraseFromParent();
799 // Everything that jumped to BB now goes to Succ.
800 BB->replaceAllUsesWith(Succ);
801 if (!Succ->hasName()) Succ->takeName(BB);
802 BB->eraseFromParent(); // Delete the old basic block.
806 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
807 /// nodes in this block. This doesn't try to be clever about PHI nodes
808 /// which differ only in the order of the incoming values, but instcombine
809 /// orders them so it usually won't matter.
811 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
812 bool Changed = false;
814 // This implementation doesn't currently consider undef operands
815 // specially. Theoretically, two phis which are identical except for
816 // one having an undef where the other doesn't could be collapsed.
818 // Map from PHI hash values to PHI nodes. If multiple PHIs have
819 // the same hash value, the element is the first PHI in the
820 // linked list in CollisionMap.
821 DenseMap<uintptr_t, PHINode *> HashMap;
823 // Maintain linked lists of PHI nodes with common hash values.
824 DenseMap<PHINode *, PHINode *> CollisionMap;
827 for (BasicBlock::iterator I = BB->begin();
828 PHINode *PN = dyn_cast<PHINode>(I++); ) {
829 // Compute a hash value on the operands. Instcombine will likely have sorted
830 // them, which helps expose duplicates, but we have to check all the
831 // operands to be safe in case instcombine hasn't run.
833 // This hash algorithm is quite weak as hash functions go, but it seems
834 // to do a good enough job for this particular purpose, and is very quick.
835 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
836 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
837 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
839 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
841 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
842 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
844 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
846 // If we've never seen this hash value before, it's a unique PHI.
847 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
848 HashMap.insert(std::make_pair(Hash, PN));
849 if (Pair.second) continue;
850 // Otherwise it's either a duplicate or a hash collision.
851 for (PHINode *OtherPN = Pair.first->second; ; ) {
852 if (OtherPN->isIdenticalTo(PN)) {
853 // A duplicate. Replace this PHI with its duplicate.
854 PN->replaceAllUsesWith(OtherPN);
855 PN->eraseFromParent();
859 // A non-duplicate hash collision.
860 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
861 if (I == CollisionMap.end()) {
862 // Set this PHI to be the head of the linked list of colliding PHIs.
863 PHINode *Old = Pair.first->second;
864 Pair.first->second = PN;
865 CollisionMap[PN] = Old;
868 // Proceed to the next PHI in the list.
876 /// enforceKnownAlignment - If the specified pointer points to an object that
877 /// we control, modify the object's alignment to PrefAlign. This isn't
878 /// often possible though. If alignment is important, a more reliable approach
879 /// is to simply align all global variables and allocation instructions to
880 /// their preferred alignment from the beginning.
882 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
883 unsigned PrefAlign, const DataLayout *TD) {
884 V = V->stripPointerCasts();
886 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
887 // If the preferred alignment is greater than the natural stack alignment
888 // then don't round up. This avoids dynamic stack realignment.
889 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
891 // If there is a requested alignment and if this is an alloca, round up.
892 if (AI->getAlignment() >= PrefAlign)
893 return AI->getAlignment();
894 AI->setAlignment(PrefAlign);
898 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
899 // If there is a large requested alignment and we can, bump up the alignment
901 if (GV->isDeclaration()) return Align;
902 // If the memory we set aside for the global may not be the memory used by
903 // the final program then it is impossible for us to reliably enforce the
904 // preferred alignment.
905 if (GV->isWeakForLinker()) return Align;
907 if (GV->getAlignment() >= PrefAlign)
908 return GV->getAlignment();
909 // We can only increase the alignment of the global if it has no alignment
910 // specified or if it is not assigned a section. If it is assigned a
911 // section, the global could be densely packed with other objects in the
912 // section, increasing the alignment could cause padding issues.
913 if (!GV->hasSection() || GV->getAlignment() == 0)
914 GV->setAlignment(PrefAlign);
915 return GV->getAlignment();
921 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
922 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
923 /// and it is more than the alignment of the ultimate object, see if we can
924 /// increase the alignment of the ultimate object, making this check succeed.
925 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
926 const DataLayout *DL) {
927 assert(V->getType()->isPointerTy() &&
928 "getOrEnforceKnownAlignment expects a pointer!");
929 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
931 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
932 ComputeMaskedBits(V, KnownZero, KnownOne, DL);
933 unsigned TrailZ = KnownZero.countTrailingOnes();
935 // Avoid trouble with ridiculously large TrailZ values, such as
936 // those computed from a null pointer.
937 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
939 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
941 // LLVM doesn't support alignments larger than this currently.
942 Align = std::min(Align, +Value::MaximumAlignment);
944 if (PrefAlign > Align)
945 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
947 // We don't need to make any adjustment.
951 ///===---------------------------------------------------------------------===//
952 /// Dbg Intrinsic utilities
955 /// See if there is a dbg.value intrinsic for DIVar before I.
956 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
957 // Since we can't guarantee that the original dbg.declare instrinsic
958 // is removed by LowerDbgDeclare(), we need to make sure that we are
959 // not inserting the same dbg.value intrinsic over and over.
960 llvm::BasicBlock::InstListType::iterator PrevI(I);
961 if (PrevI != I->getParent()->getInstList().begin()) {
963 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
964 if (DVI->getValue() == I->getOperand(0) &&
965 DVI->getOffset() == 0 &&
966 DVI->getVariable() == DIVar)
972 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
973 /// that has an associated llvm.dbg.decl intrinsic.
974 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
975 StoreInst *SI, DIBuilder &Builder) {
976 DIVariable DIVar(DDI->getVariable());
977 assert((!DIVar || DIVar.isVariable()) &&
978 "Variable in DbgDeclareInst should be either null or a DIVariable.");
982 if (LdStHasDebugValue(DIVar, SI))
985 Instruction *DbgVal = NULL;
986 // If an argument is zero extended then use argument directly. The ZExt
987 // may be zapped by an optimization pass in future.
988 Argument *ExtendedArg = NULL;
989 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
990 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
991 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
992 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
994 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
996 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
998 // Propagate any debug metadata from the store onto the dbg.value.
999 DebugLoc SIDL = SI->getDebugLoc();
1000 if (!SIDL.isUnknown())
1001 DbgVal->setDebugLoc(SIDL);
1002 // Otherwise propagate debug metadata from dbg.declare.
1004 DbgVal->setDebugLoc(DDI->getDebugLoc());
1008 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1009 /// that has an associated llvm.dbg.decl intrinsic.
1010 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1011 LoadInst *LI, DIBuilder &Builder) {
1012 DIVariable DIVar(DDI->getVariable());
1013 assert((!DIVar || DIVar.isVariable()) &&
1014 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1018 if (LdStHasDebugValue(DIVar, LI))
1021 Instruction *DbgVal =
1022 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
1025 // Propagate any debug metadata from the store onto the dbg.value.
1026 DebugLoc LIDL = LI->getDebugLoc();
1027 if (!LIDL.isUnknown())
1028 DbgVal->setDebugLoc(LIDL);
1029 // Otherwise propagate debug metadata from dbg.declare.
1031 DbgVal->setDebugLoc(DDI->getDebugLoc());
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;
1040 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1041 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) {
1042 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI))
1043 Dbgs.push_back(DDI);
1048 for (SmallVectorImpl<DbgDeclareInst *>::iterator I = Dbgs.begin(),
1049 E = Dbgs.end(); I != E; ++I) {
1050 DbgDeclareInst *DDI = *I;
1051 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1052 // If this is an alloca for a scalar variable, insert a dbg.value
1053 // at each load and store to the alloca and erase the dbg.declare.
1054 if (AI && !AI->isArrayAllocation()) {
1056 // We only remove the dbg.declare intrinsic if all uses are
1057 // converted to dbg.value intrinsics.
1058 bool RemoveDDI = true;
1059 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
1061 if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
1062 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1063 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
1064 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1068 DDI->eraseFromParent();
1074 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1075 /// alloca 'V', if any.
1076 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1077 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
1078 for (Value::use_iterator UI = DebugNode->use_begin(),
1079 E = DebugNode->use_end(); UI != E; ++UI)
1080 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))
1086 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1087 DIBuilder &Builder) {
1088 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1091 DIVariable DIVar(DDI->getVariable());
1092 assert((!DIVar || DIVar.isVariable()) &&
1093 "Variable in DbgDeclareInst should be either null or a DIVariable.");
1097 // Create a copy of the original DIDescriptor for user variable, appending
1098 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1099 // will take a value storing address of the memory for variable, not
1101 Type *Int64Ty = Type::getInt64Ty(AI->getContext());
1102 SmallVector<Value*, 4> NewDIVarAddress;
1103 if (DIVar.hasComplexAddress()) {
1104 for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
1105 NewDIVarAddress.push_back(
1106 ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
1109 NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
1110 DIVariable NewDIVar = Builder.createComplexVariable(
1111 DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
1112 DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
1113 NewDIVarAddress, DIVar.getArgNumber());
1115 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1116 // and remove old llvm.dbg.declare.
1117 BasicBlock *BB = AI->getParent();
1118 Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
1119 DDI->eraseFromParent();
1123 /// changeToUnreachable - Insert an unreachable instruction before the specified
1124 /// instruction, making it and the rest of the code in the block dead.
1125 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1126 BasicBlock *BB = I->getParent();
1127 // Loop over all of the successors, removing BB's entry from any PHI
1129 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1130 (*SI)->removePredecessor(BB);
1132 // Insert a call to llvm.trap right before this. This turns the undefined
1133 // behavior into a hard fail instead of falling through into random code.
1136 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1137 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1138 CallTrap->setDebugLoc(I->getDebugLoc());
1140 new UnreachableInst(I->getContext(), I);
1142 // All instructions after this are dead.
1143 BasicBlock::iterator BBI = I, BBE = BB->end();
1144 while (BBI != BBE) {
1145 if (!BBI->use_empty())
1146 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1147 BB->getInstList().erase(BBI++);
1151 /// changeToCall - Convert the specified invoke into a normal call.
1152 static void changeToCall(InvokeInst *II) {
1153 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1154 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1155 NewCall->takeName(II);
1156 NewCall->setCallingConv(II->getCallingConv());
1157 NewCall->setAttributes(II->getAttributes());
1158 NewCall->setDebugLoc(II->getDebugLoc());
1159 II->replaceAllUsesWith(NewCall);
1161 // Follow the call by a branch to the normal destination.
1162 BranchInst::Create(II->getNormalDest(), II);
1164 // Update PHI nodes in the unwind destination
1165 II->getUnwindDest()->removePredecessor(II->getParent());
1166 II->eraseFromParent();
1169 static bool markAliveBlocks(BasicBlock *BB,
1170 SmallPtrSet<BasicBlock*, 128> &Reachable) {
1172 SmallVector<BasicBlock*, 128> Worklist;
1173 Worklist.push_back(BB);
1174 Reachable.insert(BB);
1175 bool Changed = false;
1177 BB = Worklist.pop_back_val();
1179 // Do a quick scan of the basic block, turning any obviously unreachable
1180 // instructions into LLVM unreachable insts. The instruction combining pass
1181 // canonicalizes unreachable insts into stores to null or undef.
1182 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1183 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1184 if (CI->doesNotReturn()) {
1185 // If we found a call to a no-return function, insert an unreachable
1186 // instruction after it. Make sure there isn't *already* one there
1189 if (!isa<UnreachableInst>(BBI)) {
1190 // Don't insert a call to llvm.trap right before the unreachable.
1191 changeToUnreachable(BBI, false);
1198 // Store to undef and store to null are undefined and used to signal that
1199 // they should be changed to unreachable by passes that can't modify the
1201 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1202 // Don't touch volatile stores.
1203 if (SI->isVolatile()) continue;
1205 Value *Ptr = SI->getOperand(1);
1207 if (isa<UndefValue>(Ptr) ||
1208 (isa<ConstantPointerNull>(Ptr) &&
1209 SI->getPointerAddressSpace() == 0)) {
1210 changeToUnreachable(SI, true);
1217 // Turn invokes that call 'nounwind' functions into ordinary calls.
1218 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1219 Value *Callee = II->getCalledValue();
1220 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1221 changeToUnreachable(II, true);
1223 } else if (II->doesNotThrow()) {
1224 if (II->use_empty() && II->onlyReadsMemory()) {
1225 // jump to the normal destination branch.
1226 BranchInst::Create(II->getNormalDest(), II);
1227 II->getUnwindDest()->removePredecessor(II->getParent());
1228 II->eraseFromParent();
1235 Changed |= ConstantFoldTerminator(BB, true);
1236 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1237 if (Reachable.insert(*SI))
1238 Worklist.push_back(*SI);
1239 } while (!Worklist.empty());
1243 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1244 /// if they are in a dead cycle. Return true if a change was made, false
1246 bool llvm::removeUnreachableBlocks(Function &F) {
1247 SmallPtrSet<BasicBlock*, 128> Reachable;
1248 bool Changed = markAliveBlocks(F.begin(), Reachable);
1250 // If there are unreachable blocks in the CFG...
1251 if (Reachable.size() == F.size())
1254 assert(Reachable.size() < F.size());
1255 NumRemoved += F.size()-Reachable.size();
1257 // Loop over all of the basic blocks that are not reachable, dropping all of
1258 // their internal references...
1259 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1260 if (Reachable.count(BB))
1263 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1264 if (Reachable.count(*SI))
1265 (*SI)->removePredecessor(BB);
1266 BB->dropAllReferences();
1269 for (Function::iterator I = ++F.begin(); I != F.end();)
1270 if (!Reachable.count(I))
1271 I = F.getBasicBlockList().erase(I);