1 //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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 manipulations on basic blocks, and
11 // instructions contained within basic blocks.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
16 #include "llvm/Function.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Constant.h"
20 #include "llvm/Type.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/Analysis/Dominators.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Utils/Local.h"
26 #include "llvm/Transforms/Scalar.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/ValueHandle.h"
32 /// DeleteDeadBlock - Delete the specified block, which must have no
34 void llvm::DeleteDeadBlock(BasicBlock *BB) {
35 assert((pred_begin(BB) == pred_end(BB) ||
36 // Can delete self loop.
37 BB->getSinglePredecessor() == BB) && "Block is not dead!");
38 TerminatorInst *BBTerm = BB->getTerminator();
40 // Loop through all of our successors and make sure they know that one
41 // of their predecessors is going away.
42 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
43 BBTerm->getSuccessor(i)->removePredecessor(BB);
45 // Zap all the instructions in the block.
46 while (!BB->empty()) {
47 Instruction &I = BB->back();
48 // If this instruction is used, replace uses with an arbitrary value.
49 // Because control flow can't get here, we don't care what we replace the
50 // value with. Note that since this block is unreachable, and all values
51 // contained within it must dominate their uses, that all uses will
52 // eventually be removed (they are themselves dead).
54 I.replaceAllUsesWith(UndefValue::get(I.getType()));
55 BB->getInstList().pop_back();
59 BB->eraseFromParent();
62 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
63 /// any single-entry PHI nodes in it, fold them away. This handles the case
64 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
65 /// when the block has exactly one predecessor.
66 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
67 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
68 if (PN->getIncomingValue(0) != PN)
69 PN->replaceAllUsesWith(PN->getIncomingValue(0));
71 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
72 PN->eraseFromParent();
77 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
78 /// is dead. Also recursively delete any operands that become dead as
79 /// a result. This includes tracing the def-use list from the PHI to see if
80 /// it is ultimately unused or if it reaches an unused cycle.
81 void llvm::DeleteDeadPHIs(BasicBlock *BB) {
82 // Recursively deleting a PHI may cause multiple PHIs to be deleted
83 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
84 SmallVector<WeakVH, 8> PHIs;
85 for (BasicBlock::iterator I = BB->begin();
86 PHINode *PN = dyn_cast<PHINode>(I); ++I)
89 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
90 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
91 RecursivelyDeleteDeadPHINode(PN);
94 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
95 /// if possible. The return value indicates success or failure.
96 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
97 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
98 // Can't merge the entry block. Don't merge away blocks who have their
99 // address taken: this is a bug if the predecessor block is the entry node
100 // (because we'd end up taking the address of the entry) and undesirable in
102 if (pred_begin(BB) == pred_end(BB) ||
103 BB->hasAddressTaken()) return false;
105 BasicBlock *PredBB = *PI++;
106 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
108 PredBB = 0; // There are multiple different predecessors...
112 // Can't merge if there are multiple predecessors.
113 if (!PredBB) return false;
114 // Don't break self-loops.
115 if (PredBB == BB) return false;
116 // Don't break invokes.
117 if (isa<InvokeInst>(PredBB->getTerminator())) return false;
119 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
120 BasicBlock* OnlySucc = BB;
121 for (; SI != SE; ++SI)
122 if (*SI != OnlySucc) {
123 OnlySucc = 0; // There are multiple distinct successors!
127 // Can't merge if there are multiple successors.
128 if (!OnlySucc) return false;
130 // Can't merge if there is PHI loop.
131 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
132 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
133 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
134 if (PN->getIncomingValue(i) == PN)
140 // Begin by getting rid of unneeded PHIs.
141 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
142 PN->replaceAllUsesWith(PN->getIncomingValue(0));
143 BB->getInstList().pop_front(); // Delete the phi node...
146 // Delete the unconditional branch from the predecessor...
147 PredBB->getInstList().pop_back();
149 // Move all definitions in the successor to the predecessor...
150 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
152 // Make all PHI nodes that referred to BB now refer to Pred as their
154 BB->replaceAllUsesWith(PredBB);
156 // Inherit predecessors name if it exists.
157 if (!PredBB->hasName())
158 PredBB->takeName(BB);
160 // Finally, erase the old block and update dominator info.
162 if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) {
163 DomTreeNode* DTN = DT->getNode(BB);
164 DomTreeNode* PredDTN = DT->getNode(PredBB);
167 SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
168 for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
169 DE = Children.end(); DI != DE; ++DI)
170 DT->changeImmediateDominator(*DI, PredDTN);
177 BB->eraseFromParent();
183 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
184 /// with a value, then remove and delete the original instruction.
186 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
187 BasicBlock::iterator &BI, Value *V) {
188 Instruction &I = *BI;
189 // Replaces all of the uses of the instruction with uses of the value
190 I.replaceAllUsesWith(V);
192 // Make sure to propagate a name if there is one already.
193 if (I.hasName() && !V->hasName())
196 // Delete the unnecessary instruction now...
201 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
202 /// instruction specified by I. The original instruction is deleted and BI is
203 /// updated to point to the new instruction.
205 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
206 BasicBlock::iterator &BI, Instruction *I) {
207 assert(I->getParent() == 0 &&
208 "ReplaceInstWithInst: Instruction already inserted into basic block!");
210 // Insert the new instruction into the basic block...
211 BasicBlock::iterator New = BIL.insert(BI, I);
213 // Replace all uses of the old instruction, and delete it.
214 ReplaceInstWithValue(BIL, BI, I);
216 // Move BI back to point to the newly inserted instruction
220 /// ReplaceInstWithInst - Replace the instruction specified by From with the
221 /// instruction specified by To.
223 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
224 BasicBlock::iterator BI(From);
225 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
228 /// RemoveSuccessor - Change the specified terminator instruction such that its
229 /// successor SuccNum no longer exists. Because this reduces the outgoing
230 /// degree of the current basic block, the actual terminator instruction itself
231 /// may have to be changed. In the case where the last successor of the block
232 /// is deleted, a return instruction is inserted in its place which can cause a
233 /// surprising change in program behavior if it is not expected.
235 void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
236 assert(SuccNum < TI->getNumSuccessors() &&
237 "Trying to remove a nonexistant successor!");
239 // If our old successor block contains any PHI nodes, remove the entry in the
240 // PHI nodes that comes from this branch...
242 BasicBlock *BB = TI->getParent();
243 TI->getSuccessor(SuccNum)->removePredecessor(BB);
245 TerminatorInst *NewTI = 0;
246 switch (TI->getOpcode()) {
247 case Instruction::Br:
248 // If this is a conditional branch... convert to unconditional branch.
249 if (TI->getNumSuccessors() == 2) {
250 cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
251 } else { // Otherwise convert to a return instruction...
254 // Create a value to return... if the function doesn't return null...
255 if (BB->getParent()->getReturnType() != Type::getVoidTy(TI->getContext()))
256 RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
258 // Create the return...
259 NewTI = ReturnInst::Create(TI->getContext(), RetVal);
263 case Instruction::Invoke: // Should convert to call
264 case Instruction::Switch: // Should remove entry
266 case Instruction::Ret: // Cannot happen, has no successors!
267 llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!");
270 if (NewTI) // If it's a different instruction, replace.
271 ReplaceInstWithInst(TI, NewTI);
274 /// SplitEdge - Split the edge connecting specified block. Pass P must
276 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
277 TerminatorInst *LatchTerm = BB->getTerminator();
278 unsigned SuccNum = 0;
280 unsigned e = LatchTerm->getNumSuccessors();
282 for (unsigned i = 0; ; ++i) {
283 assert(i != e && "Didn't find edge?");
284 if (LatchTerm->getSuccessor(i) == Succ) {
290 // If this is a critical edge, let SplitCriticalEdge do it.
291 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P))
292 return LatchTerm->getSuccessor(SuccNum);
294 // If the edge isn't critical, then BB has a single successor or Succ has a
295 // single pred. Split the block.
296 BasicBlock::iterator SplitPoint;
297 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
298 // If the successor only has a single pred, split the top of the successor
300 assert(SP == BB && "CFG broken");
302 return SplitBlock(Succ, Succ->begin(), P);
304 // Otherwise, if BB has a single successor, split it at the bottom of the
306 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
307 "Should have a single succ!");
308 return SplitBlock(BB, BB->getTerminator(), P);
312 /// SplitBlock - Split the specified block at the specified instruction - every
313 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
314 /// to a new block. The two blocks are joined by an unconditional branch and
315 /// the loop info is updated.
317 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
318 BasicBlock::iterator SplitIt = SplitPt;
319 while (isa<PHINode>(SplitIt))
321 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
323 // The new block lives in whichever loop the old one did. This preserves
324 // LCSSA as well, because we force the split point to be after any PHI nodes.
325 if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>())
326 if (Loop *L = LI->getLoopFor(Old))
327 L->addBasicBlockToLoop(New, LI->getBase());
329 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>())
331 // Old dominates New. New node domiantes all other nodes dominated by Old.
332 DomTreeNode *OldNode = DT->getNode(Old);
333 std::vector<DomTreeNode *> Children;
334 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
336 Children.push_back(*I);
338 DomTreeNode *NewNode = DT->addNewBlock(New,Old);
340 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
341 E = Children.end(); I != E; ++I)
342 DT->changeImmediateDominator(*I, NewNode);
345 if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>())
352 /// SplitBlockPredecessors - This method transforms BB by introducing a new
353 /// basic block into the function, and moving some of the predecessors of BB to
354 /// be predecessors of the new block. The new predecessors are indicated by the
355 /// Preds array, which has NumPreds elements in it. The new block is given a
356 /// suffix of 'Suffix'.
358 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
359 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
360 /// In particular, it does not preserve LoopSimplify (because it's
361 /// complicated to handle the case where one of the edges being split
362 /// is an exit of a loop with other exits).
364 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
365 BasicBlock *const *Preds,
366 unsigned NumPreds, const char *Suffix,
368 // Create new basic block, insert right before the original block.
369 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
370 BB->getParent(), BB);
372 // The new block unconditionally branches to the old block.
373 BranchInst *BI = BranchInst::Create(BB, NewBB);
375 LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0;
376 Loop *L = LI ? LI->getLoopFor(BB) : 0;
377 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
379 // Move the edges from Preds to point to NewBB instead of BB.
380 // While here, if we need to preserve loop analyses, collect
381 // some information about how this split will affect loops.
382 bool HasLoopExit = false;
383 bool IsLoopEntry = !!L;
384 bool SplitMakesNewLoopHeader = false;
385 for (unsigned i = 0; i != NumPreds; ++i) {
386 // This is slightly more strict than necessary; the minimum requirement
387 // is that there be no more than one indirectbr branching to BB. And
388 // all BlockAddress uses would need to be updated.
389 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
390 "Cannot split an edge from an IndirectBrInst");
392 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
395 // If we need to preserve LCSSA, determine if any of
396 // the preds is a loop exit.
398 if (Loop *PL = LI->getLoopFor(Preds[i]))
399 if (!PL->contains(BB))
401 // If we need to preserve LoopInfo, note whether any of the
402 // preds crosses an interesting loop boundary.
404 if (L->contains(Preds[i]))
407 SplitMakesNewLoopHeader = true;
412 // Update dominator tree and dominator frontier if available.
413 DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0;
415 DT->splitBlock(NewBB);
416 if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0)
417 DF->splitBlock(NewBB);
419 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
420 // node becomes an incoming value for BB's phi node. However, if the Preds
421 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
422 // account for the newly created predecessor.
424 // Insert dummy values as the incoming value.
425 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
426 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
430 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
434 // Add the new block to the nearest enclosing loop (and not an
435 // adjacent loop). To find this, examine each of the predecessors and
436 // determine which loops enclose them, and select the most-nested loop
437 // which contains the loop containing the block being split.
438 Loop *InnermostPredLoop = 0;
439 for (unsigned i = 0; i != NumPreds; ++i)
440 if (Loop *PredLoop = LI->getLoopFor(Preds[i])) {
441 // Seek a loop which actually contains the block being split (to
442 // avoid adjacent loops).
443 while (PredLoop && !PredLoop->contains(BB))
444 PredLoop = PredLoop->getParentLoop();
445 // Select the most-nested of these loops which contains the block.
447 PredLoop->contains(BB) &&
448 (!InnermostPredLoop ||
449 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
450 InnermostPredLoop = PredLoop;
452 if (InnermostPredLoop)
453 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
455 L->addBasicBlockToLoop(NewBB, LI->getBase());
456 if (SplitMakesNewLoopHeader)
457 L->moveToHeader(NewBB);
461 // Otherwise, create a new PHI node in NewBB for each PHI node in BB.
462 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
463 PHINode *PN = cast<PHINode>(I++);
465 // Check to see if all of the values coming in are the same. If so, we
466 // don't need to create a new PHI node, unless it's needed for LCSSA.
469 InVal = PN->getIncomingValueForBlock(Preds[0]);
470 for (unsigned i = 1; i != NumPreds; ++i)
471 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
478 // If all incoming values for the new PHI would be the same, just don't
479 // make a new PHI. Instead, just remove the incoming values from the old
481 for (unsigned i = 0; i != NumPreds; ++i)
482 PN->removeIncomingValue(Preds[i], false);
484 // If the values coming into the block are not the same, we need a PHI.
485 // Create the new PHI node, insert it into NewBB at the end of the block
487 PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
488 if (AA) AA->copyValue(PN, NewPHI);
490 // Move all of the PHI values for 'Preds' to the new PHI.
491 for (unsigned i = 0; i != NumPreds; ++i) {
492 Value *V = PN->removeIncomingValue(Preds[i], false);
493 NewPHI->addIncoming(V, Preds[i]);
498 // Add an incoming value to the PHI node in the loop for the preheader
500 PN->addIncoming(InVal, NewBB);
506 /// FindFunctionBackedges - Analyze the specified function to find all of the
507 /// loop backedges in the function and return them. This is a relatively cheap
508 /// (compared to computing dominators and loop info) analysis.
510 /// The output is added to Result, as pairs of <from,to> edge info.
511 void llvm::FindFunctionBackedges(const Function &F,
512 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
513 const BasicBlock *BB = &F.getEntryBlock();
514 if (succ_begin(BB) == succ_end(BB))
517 SmallPtrSet<const BasicBlock*, 8> Visited;
518 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
519 SmallPtrSet<const BasicBlock*, 8> InStack;
522 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
525 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
526 const BasicBlock *ParentBB = Top.first;
527 succ_const_iterator &I = Top.second;
529 bool FoundNew = false;
530 while (I != succ_end(ParentBB)) {
532 if (Visited.insert(BB)) {
536 // Successor is in VisitStack, it's a back edge.
537 if (InStack.count(BB))
538 Result.push_back(std::make_pair(ParentBB, BB));
542 // Go down one level if there is a unvisited successor.
544 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
547 InStack.erase(VisitStack.pop_back_val().first);
549 } while (!VisitStack.empty());
556 /// AreEquivalentAddressValues - Test if A and B will obviously have the same
557 /// value. This includes recognizing that %t0 and %t1 will have the same
558 /// value in code like this:
559 /// %t0 = getelementptr \@a, 0, 3
560 /// store i32 0, i32* %t0
561 /// %t1 = getelementptr \@a, 0, 3
562 /// %t2 = load i32* %t1
564 static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
565 // Test if the values are trivially equivalent.
566 if (A == B) return true;
568 // Test if the values come from identical arithmetic instructions.
569 // Use isIdenticalToWhenDefined instead of isIdenticalTo because
570 // this function is only used when one address use dominates the
571 // other, which means that they'll always either have the same
572 // value or one of them will have an undefined value.
573 if (isa<BinaryOperator>(A) || isa<CastInst>(A) ||
574 isa<PHINode>(A) || isa<GetElementPtrInst>(A))
575 if (const Instruction *BI = dyn_cast<Instruction>(B))
576 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
579 // Otherwise they may not be equivalent.
583 /// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
584 /// instruction before ScanFrom) checking to see if we have the value at the
585 /// memory address *Ptr locally available within a small number of instructions.
586 /// If the value is available, return it.
588 /// If not, return the iterator for the last validated instruction that the
589 /// value would be live through. If we scanned the entire block and didn't find
590 /// something that invalidates *Ptr or provides it, ScanFrom would be left at
591 /// begin() and this returns null. ScanFrom could also be left
593 /// MaxInstsToScan specifies the maximum instructions to scan in the block. If
594 /// it is set to 0, it will scan the whole block. You can also optionally
595 /// specify an alias analysis implementation, which makes this more precise.
596 Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
597 BasicBlock::iterator &ScanFrom,
598 unsigned MaxInstsToScan,
600 if (MaxInstsToScan == 0) MaxInstsToScan = ~0U;
602 // If we're using alias analysis to disambiguate get the size of *Ptr.
603 unsigned AccessSize = 0;
605 const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType();
606 AccessSize = AA->getTypeStoreSize(AccessTy);
609 while (ScanFrom != ScanBB->begin()) {
610 // We must ignore debug info directives when counting (otherwise they
611 // would affect codegen).
612 Instruction *Inst = --ScanFrom;
613 if (isa<DbgInfoIntrinsic>(Inst))
615 // We skip pointer-to-pointer bitcasts, which are NOPs.
616 // It is necessary for correctness to skip those that feed into a
617 // llvm.dbg.declare, as these are not present when debugging is off.
618 if (isa<BitCastInst>(Inst) && isa<PointerType>(Inst->getType()))
621 // Restore ScanFrom to expected value in case next test succeeds
624 // Don't scan huge blocks.
625 if (MaxInstsToScan-- == 0) return 0;
628 // If this is a load of Ptr, the loaded value is available.
629 if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
630 if (AreEquivalentAddressValues(LI->getOperand(0), Ptr))
633 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
634 // If this is a store through Ptr, the value is available!
635 if (AreEquivalentAddressValues(SI->getOperand(1), Ptr))
636 return SI->getOperand(0);
638 // If Ptr is an alloca and this is a store to a different alloca, ignore
639 // the store. This is a trivial form of alias analysis that is important
640 // for reg2mem'd code.
641 if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) &&
642 (isa<AllocaInst>(SI->getOperand(1)) ||
643 isa<GlobalVariable>(SI->getOperand(1))))
646 // If we have alias analysis and it says the store won't modify the loaded
647 // value, ignore the store.
649 (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
652 // Otherwise the store that may or may not alias the pointer, bail out.
657 // If this is some other instruction that may clobber Ptr, bail out.
658 if (Inst->mayWriteToMemory()) {
659 // If alias analysis claims that it really won't modify the load,
662 (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
665 // May modify the pointer, bail out.
671 // Got to the start of the block, we didn't find it, but are done for this