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Be more aggressive in removing dead stores, and in removing instructions trivially dead after DSE.

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This drastically improves the effect of FastDSE on kimwitu++.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39819 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2007-07-13 18:26:26 +00:00
parent 72f1596403
commit 3e8d001799
1 changed files with 24 additions and 8 deletions
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32
lib/Transforms/Scalar/FastDSE.cpp
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@ -56,6 +56,14 @@ namespace {
SetVector<Instruction*>& possiblyDead);
void DeleteDeadInstructionChains(Instruction *I,
SetVector<Instruction*> &DeadInsts);
void TranslatePointerBitCasts(Value*& v) {
assert(isa<PointerType>(v->getType()) && "Translating a non-pointer type?");
// See through pointer-to-pointer bitcasts
while (BitCastInst* C = dyn_cast<BitCastInst>(v))
if (isa<PointerType>(C->getSrcTy()))
v = C->getOperand(0);
}
// getAnalysisUsage - We require post dominance frontiers (aka Control
// Dependence Graph)
@ -93,6 +101,7 @@ bool FDSE::runOnBasicBlock(BasicBlock &BB) {
pointer = S->getPointerOperand();
else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
pointer = F->getPointerOperand();
assert(pointer && "Not a free or a store?");
StoreInst*& last = lastStore[pointer];
@ -110,6 +119,8 @@ bool FDSE::runOnBasicBlock(BasicBlock &BB) {
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
possiblyDead.insert(D);
last->eraseFromParent();
NumFastStores++;
@ -165,7 +176,7 @@ bool FDSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
Value* depPointer = dependency->getPointerOperand();
unsigned depPointerSize = TD.getTypeSize(dependency->getOperand(0)->getType());
// Check for aliasing
AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
depPointer, depPointerSize);
@ -177,6 +188,8 @@ bool FDSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(1)))
possiblyDead.insert(D);
dependency->eraseFromParent();
NumFastStores++;
@ -216,23 +229,24 @@ bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead)
// If we find a store whose pointer is dead...
if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
if (deadPointers.count(S->getPointerOperand())){
Value* pointerOperand = S->getPointerOperand();
// See through pointer-to-pointer bitcasts
TranslatePointerBitCasts(pointerOperand);
if (deadPointers.count(pointerOperand)){
// Remove it!
MD.removeInstruction(S);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
possiblyDead.insert(D);
BBI++;
S->eraseFromParent();
NumFastStores++;
MadeChange = true;
// If we can't trivially delete this store, consider it undead
} else {
killPointer = S->getPointerOperand();
killPointerSize = TD.getTypeSize(S->getOperand(0)->getType());
}
// If we encounter a use of the pointer, it is no longer considered dead
@ -261,7 +275,7 @@ bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead)
// See if the call site touches it
AliasAnalysis::ModRefResult A = AA.getModRefInfo(CallSite::get(BBI),
*I, pointerSize);
if (A != AliasAnalysis::NoModRef)
if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
dead.push_back(*I);
}
@ -315,6 +329,8 @@ bool FDSE::RemoveUndeadPointers(Value* killPointer, unsigned killPointerSize,
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
possiblyDead.insert(D);
BBI++;
S->eraseFromParent();