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Be more precise when eliminating pointers bue to memcpy's. This allows more

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stores to be deleted in some cases.

llvm-svn: 46694
This commit is contained in:
Owen Anderson 2008-02-04 04:53:00 +00:00
parent aaba6f96da
commit af0449f9e0
1 changed files with 10 additions and 4 deletions
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14
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -52,7 +52,7 @@ namespace {
Instruction* dependency,
SetVector<Instruction*>& possiblyDead);
bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
bool RemoveUndeadPointers(Value* pointer,
bool RemoveUndeadPointers(Value* pointer, uint64_t killPointerSize,
BasicBlock::iterator& BBI,
SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead);
@ -322,6 +322,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
}
Value* killPointer = 0;
uint64_t killPointerSize = ~0UL;
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
@ -346,6 +347,11 @@ bool DSE::handleEndBlock(BasicBlock& BB,
killPointer = L->getPointerOperand();
} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
killPointer = V->getOperand(0);
} else if (isa<MemCpyInst>(BBI) &&
isa<ConstantInt>(cast<MemCpyInst>(BBI)->getLength())) {
killPointer = cast<MemCpyInst>(BBI)->getSource();
killPointerSize = cast<ConstantInt>(
cast<MemCpyInst>(BBI)->getLength())->getZExtValue();
} else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
deadPointers.erase(A);
@ -444,7 +450,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
TranslatePointerBitCasts(killPointer);
// Deal with undead pointers
MadeChange |= RemoveUndeadPointers(killPointer, BBI,
MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
deadPointers, possiblyDead);
}
@ -453,7 +459,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
/// RemoveUndeadPointers - check for uses of a pointer that make it
/// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value* killPointer,
bool DSE::RemoveUndeadPointers(Value* killPointer, uint64_t killPointerSize,
BasicBlock::iterator& BBI,
SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead) {
@ -491,7 +497,7 @@ bool DSE::RemoveUndeadPointers(Value* killPointer,
// See if this pointer could alias it
AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
killPointer, ~0U);
killPointer, killPointerSize);
// If it must-alias and a store, we can delete it
if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {