llvm-6502/lib/Transforms/Utils/BasicBlockUtils.cpp
Evan Cheng 0f1666b480 Code clean up.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100467 91177308-0d34-0410-b5e6-96231b3b80d8
2010-04-05 21:16:25 +00:00

679 lines
25 KiB
C++

//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform manipulations on basic blocks, and
// instructions contained within basic blocks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Constant.h"
#include "llvm/Type.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ValueHandle.h"
#include <algorithm>
using namespace llvm;
/// DeleteDeadBlock - Delete the specified block, which must have no
/// predecessors.
void llvm::DeleteDeadBlock(BasicBlock *BB) {
assert((pred_begin(BB) == pred_end(BB) ||
// Can delete self loop.
BB->getSinglePredecessor() == BB) && "Block is not dead!");
TerminatorInst *BBTerm = BB->getTerminator();
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
BBTerm->getSuccessor(i)->removePredecessor(BB);
// Zap all the instructions in the block.
while (!BB->empty()) {
Instruction &I = BB->back();
// If this instruction is used, replace uses with an arbitrary value.
// Because control flow can't get here, we don't care what we replace the
// value with. Note that since this block is unreachable, and all values
// contained within it must dominate their uses, that all uses will
// eventually be removed (they are themselves dead).
if (!I.use_empty())
I.replaceAllUsesWith(UndefValue::get(I.getType()));
BB->getInstList().pop_back();
}
// Zap the block!
BB->eraseFromParent();
}
/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
/// any single-entry PHI nodes in it, fold them away. This handles the case
/// when all entries to the PHI nodes in a block are guaranteed equal, such as
/// when the block has exactly one predecessor.
void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
if (PN->getIncomingValue(0) != PN)
PN->replaceAllUsesWith(PN->getIncomingValue(0));
else
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
PN->eraseFromParent();
}
}
/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
/// is dead. Also recursively delete any operands that become dead as
/// a result. This includes tracing the def-use list from the PHI to see if
/// it is ultimately unused or if it reaches an unused cycle.
bool llvm::DeleteDeadPHIs(BasicBlock *BB) {
// Recursively deleting a PHI may cause multiple PHIs to be deleted
// or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
SmallVector<WeakVH, 8> PHIs;
for (BasicBlock::iterator I = BB->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
PHIs.push_back(PN);
bool Changed = false;
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
Changed |= RecursivelyDeleteDeadPHINode(PN);
return Changed;
}
/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
/// if possible. The return value indicates success or failure.
bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
// Can't merge the entry block. Don't merge away blocks who have their
// address taken: this is a bug if the predecessor block is the entry node
// (because we'd end up taking the address of the entry) and undesirable in
// any case.
if (pred_begin(BB) == pred_end(BB) ||
BB->hasAddressTaken()) return false;
BasicBlock *PredBB = *PI++;
for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
if (*PI != PredBB) {
PredBB = 0; // There are multiple different predecessors...
break;
}
// Can't merge if there are multiple predecessors.
if (!PredBB) return false;
// Don't break self-loops.
if (PredBB == BB) return false;
// Don't break invokes.
if (isa<InvokeInst>(PredBB->getTerminator())) return false;
succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
BasicBlock* OnlySucc = BB;
for (; SI != SE; ++SI)
if (*SI != OnlySucc) {
OnlySucc = 0; // There are multiple distinct successors!
break;
}
// Can't merge if there are multiple successors.
if (!OnlySucc) return false;
// Can't merge if there is PHI loop.
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == PN)
return false;
} else
break;
}
// Begin by getting rid of unneeded PHIs.
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
PN->replaceAllUsesWith(PN->getIncomingValue(0));
BB->getInstList().pop_front(); // Delete the phi node...
}
// Delete the unconditional branch from the predecessor...
PredBB->getInstList().pop_back();
// Move all definitions in the successor to the predecessor...
PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
// Make all PHI nodes that referred to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(PredBB);
// Inherit predecessors name if it exists.
if (!PredBB->hasName())
PredBB->takeName(BB);
// Finally, erase the old block and update dominator info.
if (P) {
if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) {
DomTreeNode* DTN = DT->getNode(BB);
DomTreeNode* PredDTN = DT->getNode(PredBB);
if (DTN) {
SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
DE = Children.end(); DI != DE; ++DI)
DT->changeImmediateDominator(*DI, PredDTN);
DT->eraseNode(BB);
}
}
}
BB->eraseFromParent();
return true;
}
/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
/// with a value, then remove and delete the original instruction.
///
void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
BasicBlock::iterator &BI, Value *V) {
Instruction &I = *BI;
// Replaces all of the uses of the instruction with uses of the value
I.replaceAllUsesWith(V);
// Make sure to propagate a name if there is one already.
if (I.hasName() && !V->hasName())
V->takeName(&I);
// Delete the unnecessary instruction now...
BI = BIL.erase(BI);
}
/// ReplaceInstWithInst - Replace the instruction specified by BI with the
/// instruction specified by I. The original instruction is deleted and BI is
/// updated to point to the new instruction.
///
void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
BasicBlock::iterator &BI, Instruction *I) {
assert(I->getParent() == 0 &&
"ReplaceInstWithInst: Instruction already inserted into basic block!");
// Insert the new instruction into the basic block...
BasicBlock::iterator New = BIL.insert(BI, I);
// Replace all uses of the old instruction, and delete it.
ReplaceInstWithValue(BIL, BI, I);
// Move BI back to point to the newly inserted instruction
BI = New;
}
/// ReplaceInstWithInst - Replace the instruction specified by From with the
/// instruction specified by To.
///
void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
BasicBlock::iterator BI(From);
ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
}
/// RemoveSuccessor - Change the specified terminator instruction such that its
/// successor SuccNum no longer exists. Because this reduces the outgoing
/// degree of the current basic block, the actual terminator instruction itself
/// may have to be changed. In the case where the last successor of the block
/// is deleted, a return instruction is inserted in its place which can cause a
/// surprising change in program behavior if it is not expected.
///
void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
assert(SuccNum < TI->getNumSuccessors() &&
"Trying to remove a nonexistant successor!");
// If our old successor block contains any PHI nodes, remove the entry in the
// PHI nodes that comes from this branch...
//
BasicBlock *BB = TI->getParent();
TI->getSuccessor(SuccNum)->removePredecessor(BB);
TerminatorInst *NewTI = 0;
switch (TI->getOpcode()) {
case Instruction::Br:
// If this is a conditional branch... convert to unconditional branch.
if (TI->getNumSuccessors() == 2) {
cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
} else { // Otherwise convert to a return instruction...
Value *RetVal = 0;
// Create a value to return... if the function doesn't return null...
if (!BB->getParent()->getReturnType()->isVoidTy())
RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
// Create the return...
NewTI = ReturnInst::Create(TI->getContext(), RetVal);
}
break;
case Instruction::Invoke: // Should convert to call
case Instruction::Switch: // Should remove entry
default:
case Instruction::Ret: // Cannot happen, has no successors!
llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!");
}
if (NewTI) // If it's a different instruction, replace.
ReplaceInstWithInst(TI, NewTI);
}
/// GetSuccessorNumber - Search for the specified successor of basic block BB
/// and return its position in the terminator instruction's list of
/// successors. It is an error to call this with a block that is not a
/// successor.
unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) {
TerminatorInst *Term = BB->getTerminator();
#ifndef NDEBUG
unsigned e = Term->getNumSuccessors();
#endif
for (unsigned i = 0; ; ++i) {
assert(i != e && "Didn't find edge?");
if (Term->getSuccessor(i) == Succ)
return i;
}
return 0;
}
/// SplitEdge - Split the edge connecting specified block. Pass P must
/// not be NULL.
BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
unsigned SuccNum = GetSuccessorNumber(BB, Succ);
// If this is a critical edge, let SplitCriticalEdge do it.
TerminatorInst *LatchTerm = BB->getTerminator();
if (SplitCriticalEdge(LatchTerm, SuccNum, P))
return LatchTerm->getSuccessor(SuccNum);
// If the edge isn't critical, then BB has a single successor or Succ has a
// single pred. Split the block.
BasicBlock::iterator SplitPoint;
if (BasicBlock *SP = Succ->getSinglePredecessor()) {
// If the successor only has a single pred, split the top of the successor
// block.
assert(SP == BB && "CFG broken");
SP = NULL;
return SplitBlock(Succ, Succ->begin(), P);
} else {
// Otherwise, if BB has a single successor, split it at the bottom of the
// block.
assert(BB->getTerminator()->getNumSuccessors() == 1 &&
"Should have a single succ!");
return SplitBlock(BB, BB->getTerminator(), P);
}
}
/// SplitBlock - Split the specified block at the specified instruction - every
/// thing before SplitPt stays in Old and everything starting with SplitPt moves
/// to a new block. The two blocks are joined by an unconditional branch and
/// the loop info is updated.
///
BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
BasicBlock::iterator SplitIt = SplitPt;
while (isa<PHINode>(SplitIt))
++SplitIt;
BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
// The new block lives in whichever loop the old one did. This preserves
// LCSSA as well, because we force the split point to be after any PHI nodes.
if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>())
if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, LI->getBase());
if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) {
// Old dominates New. New node domiantes all other nodes dominated by Old.
DomTreeNode *OldNode = DT->getNode(Old);
std::vector<DomTreeNode *> Children;
for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
I != E; ++I)
Children.push_back(*I);
DomTreeNode *NewNode = DT->addNewBlock(New,Old);
for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
E = Children.end(); I != E; ++I)
DT->changeImmediateDominator(*I, NewNode);
}
if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>())
DF->splitBlock(Old);
return New;
}
/// SplitBlockPredecessors - This method transforms BB by introducing a new
/// basic block into the function, and moving some of the predecessors of BB to
/// be predecessors of the new block. The new predecessors are indicated by the
/// Preds array, which has NumPreds elements in it. The new block is given a
/// suffix of 'Suffix'.
///
/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
/// In particular, it does not preserve LoopSimplify (because it's
/// complicated to handle the case where one of the edges being split
/// is an exit of a loop with other exits).
///
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
BasicBlock *const *Preds,
unsigned NumPreds, const char *Suffix,
Pass *P) {
// Create new basic block, insert right before the original block.
BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
BB->getParent(), BB);
// The new block unconditionally branches to the old block.
BranchInst *BI = BranchInst::Create(BB, NewBB);
LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0;
Loop *L = LI ? LI->getLoopFor(BB) : 0;
bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
// Move the edges from Preds to point to NewBB instead of BB.
// While here, if we need to preserve loop analyses, collect
// some information about how this split will affect loops.
bool HasLoopExit = false;
bool IsLoopEntry = !!L;
bool SplitMakesNewLoopHeader = false;
for (unsigned i = 0; i != NumPreds; ++i) {
// This is slightly more strict than necessary; the minimum requirement
// is that there be no more than one indirectbr branching to BB. And
// all BlockAddress uses would need to be updated.
assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
if (LI) {
// If we need to preserve LCSSA, determine if any of
// the preds is a loop exit.
if (PreserveLCSSA)
if (Loop *PL = LI->getLoopFor(Preds[i]))
if (!PL->contains(BB))
HasLoopExit = true;
// If we need to preserve LoopInfo, note whether any of the
// preds crosses an interesting loop boundary.
if (L) {
if (L->contains(Preds[i]))
IsLoopEntry = false;
else
SplitMakesNewLoopHeader = true;
}
}
}
// Update dominator tree and dominator frontier if available.
DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0;
if (DT)
DT->splitBlock(NewBB);
if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0)
DF->splitBlock(NewBB);
// Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
// node becomes an incoming value for BB's phi node. However, if the Preds
// list is empty, we need to insert dummy entries into the PHI nodes in BB to
// account for the newly created predecessor.
if (NumPreds == 0) {
// Insert dummy values as the incoming value.
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
return NewBB;
}
AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
if (L) {
if (IsLoopEntry) {
// Add the new block to the nearest enclosing loop (and not an
// adjacent loop). To find this, examine each of the predecessors and
// determine which loops enclose them, and select the most-nested loop
// which contains the loop containing the block being split.
Loop *InnermostPredLoop = 0;
for (unsigned i = 0; i != NumPreds; ++i)
if (Loop *PredLoop = LI->getLoopFor(Preds[i])) {
// Seek a loop which actually contains the block being split (to
// avoid adjacent loops).
while (PredLoop && !PredLoop->contains(BB))
PredLoop = PredLoop->getParentLoop();
// Select the most-nested of these loops which contains the block.
if (PredLoop &&
PredLoop->contains(BB) &&
(!InnermostPredLoop ||
InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
InnermostPredLoop = PredLoop;
}
if (InnermostPredLoop)
InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
} else {
L->addBasicBlockToLoop(NewBB, LI->getBase());
if (SplitMakesNewLoopHeader)
L->moveToHeader(NewBB);
}
}
// Otherwise, create a new PHI node in NewBB for each PHI node in BB.
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
PHINode *PN = cast<PHINode>(I++);
// Check to see if all of the values coming in are the same. If so, we
// don't need to create a new PHI node, unless it's needed for LCSSA.
Value *InVal = 0;
if (!HasLoopExit) {
InVal = PN->getIncomingValueForBlock(Preds[0]);
for (unsigned i = 1; i != NumPreds; ++i)
if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
InVal = 0;
break;
}
}
if (InVal) {
// If all incoming values for the new PHI would be the same, just don't
// make a new PHI. Instead, just remove the incoming values from the old
// PHI.
for (unsigned i = 0; i != NumPreds; ++i)
PN->removeIncomingValue(Preds[i], false);
} else {
// If the values coming into the block are not the same, we need a PHI.
// Create the new PHI node, insert it into NewBB at the end of the block
PHINode *NewPHI =
PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
if (AA) AA->copyValue(PN, NewPHI);
// Move all of the PHI values for 'Preds' to the new PHI.
for (unsigned i = 0; i != NumPreds; ++i) {
Value *V = PN->removeIncomingValue(Preds[i], false);
NewPHI->addIncoming(V, Preds[i]);
}
InVal = NewPHI;
}
// Add an incoming value to the PHI node in the loop for the preheader
// edge.
PN->addIncoming(InVal, NewBB);
}
return NewBB;
}
/// FindFunctionBackedges - Analyze the specified function to find all of the
/// loop backedges in the function and return them. This is a relatively cheap
/// (compared to computing dominators and loop info) analysis.
///
/// The output is added to Result, as pairs of <from,to> edge info.
void llvm::FindFunctionBackedges(const Function &F,
SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
const BasicBlock *BB = &F.getEntryBlock();
if (succ_begin(BB) == succ_end(BB))
return;
SmallPtrSet<const BasicBlock*, 8> Visited;
SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
SmallPtrSet<const BasicBlock*, 8> InStack;
Visited.insert(BB);
VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
InStack.insert(BB);
do {
std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
const BasicBlock *ParentBB = Top.first;
succ_const_iterator &I = Top.second;
bool FoundNew = false;
while (I != succ_end(ParentBB)) {
BB = *I++;
if (Visited.insert(BB)) {
FoundNew = true;
break;
}
// Successor is in VisitStack, it's a back edge.
if (InStack.count(BB))
Result.push_back(std::make_pair(ParentBB, BB));
}
if (FoundNew) {
// Go down one level if there is a unvisited successor.
InStack.insert(BB);
VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
} else {
// Go up one level.
InStack.erase(VisitStack.pop_back_val().first);
}
} while (!VisitStack.empty());
}
/// AreEquivalentAddressValues - Test if A and B will obviously have the same
/// value. This includes recognizing that %t0 and %t1 will have the same
/// value in code like this:
/// %t0 = getelementptr \@a, 0, 3
/// store i32 0, i32* %t0
/// %t1 = getelementptr \@a, 0, 3
/// %t2 = load i32* %t1
///
static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
// Test if the values are trivially equivalent.
if (A == B) return true;
// Test if the values come from identical arithmetic instructions.
// Use isIdenticalToWhenDefined instead of isIdenticalTo because
// this function is only used when one address use dominates the
// other, which means that they'll always either have the same
// value or one of them will have an undefined value.
if (isa<BinaryOperator>(A) || isa<CastInst>(A) ||
isa<PHINode>(A) || isa<GetElementPtrInst>(A))
if (const Instruction *BI = dyn_cast<Instruction>(B))
if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
return true;
// Otherwise they may not be equivalent.
return false;
}
/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
/// instruction before ScanFrom) checking to see if we have the value at the
/// memory address *Ptr locally available within a small number of instructions.
/// If the value is available, return it.
///
/// If not, return the iterator for the last validated instruction that the
/// value would be live through. If we scanned the entire block and didn't find
/// something that invalidates *Ptr or provides it, ScanFrom would be left at
/// begin() and this returns null. ScanFrom could also be left
///
/// MaxInstsToScan specifies the maximum instructions to scan in the block. If
/// it is set to 0, it will scan the whole block. You can also optionally
/// specify an alias analysis implementation, which makes this more precise.
Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
BasicBlock::iterator &ScanFrom,
unsigned MaxInstsToScan,
AliasAnalysis *AA) {
if (MaxInstsToScan == 0) MaxInstsToScan = ~0U;
// If we're using alias analysis to disambiguate get the size of *Ptr.
unsigned AccessSize = 0;
if (AA) {
const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType();
AccessSize = AA->getTypeStoreSize(AccessTy);
}
while (ScanFrom != ScanBB->begin()) {
// We must ignore debug info directives when counting (otherwise they
// would affect codegen).
Instruction *Inst = --ScanFrom;
if (isa<DbgInfoIntrinsic>(Inst))
continue;
// Restore ScanFrom to expected value in case next test succeeds
ScanFrom++;
// Don't scan huge blocks.
if (MaxInstsToScan-- == 0) return 0;
--ScanFrom;
// If this is a load of Ptr, the loaded value is available.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
if (AreEquivalentAddressValues(LI->getOperand(0), Ptr))
return LI;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// If this is a store through Ptr, the value is available!
if (AreEquivalentAddressValues(SI->getOperand(1), Ptr))
return SI->getOperand(0);
// If Ptr is an alloca and this is a store to a different alloca, ignore
// the store. This is a trivial form of alias analysis that is important
// for reg2mem'd code.
if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) &&
(isa<AllocaInst>(SI->getOperand(1)) ||
isa<GlobalVariable>(SI->getOperand(1))))
continue;
// If we have alias analysis and it says the store won't modify the loaded
// value, ignore the store.
if (AA &&
(AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
continue;
// Otherwise the store that may or may not alias the pointer, bail out.
++ScanFrom;
return 0;
}
// If this is some other instruction that may clobber Ptr, bail out.
if (Inst->mayWriteToMemory()) {
// If alias analysis claims that it really won't modify the load,
// ignore it.
if (AA &&
(AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
continue;
// May modify the pointer, bail out.
++ScanFrom;
return 0;
}
}
// Got to the start of the block, we didn't find it, but are done for this
// block.
return 0;
}