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remove the "undead" terminology, which is nonstandard and never

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made sense to me.  We now have a set of dead stack objects, and
they become live when loaded.  Fix a theoretical problem where
we'd pass in the wrong pointer to the alias query.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120465 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-30 21:32:12 +00:00
parent 86dc6c08cf
commit 5fb0fb397c
1 changed files with 48 additions and 41 deletions
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89
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -64,9 +64,9 @@ namespace {
bool runOnBasicBlock(BasicBlock &BB);
bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 16> &deadPointers);
bool RemoveAccessedObjects(Value *Ptr, uint64_t killPointerSize,
BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 16> &deadPointers);
void DeleteDeadInstruction(Instruction *I,
SmallPtrSet<Value*, 16> *deadPointers = 0);
@ -399,21 +399,22 @@ bool DSE::HandleFree(CallInst *F) {
bool DSE::handleEndBlock(BasicBlock &BB) {
bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block
SmallPtrSet<Value*, 16> DeadPointers;
// Keep track of all of the stack objects that are dead at the end of the
// function.
SmallPtrSet<Value*, 16> DeadStackObjects;
// Find all of the alloca'd pointers in the entry block.
BasicBlock *Entry = BB.getParent()->begin();
for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
DeadPointers.insert(AI);
DeadStackObjects.insert(AI);
// Treat byval arguments the same, stores to them are dead at the end of the
// function.
for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
AE = BB.getParent()->arg_end(); AI != AE; ++AI)
if (AI->hasByValAttr())
DeadPointers.insert(AI);
DeadStackObjects.insert(AI);
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
@ -426,10 +427,10 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
// Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal.
if (DeadPointers.count(Pointer)) {
if (DeadStackObjects.count(Pointer)) {
// DCE instructions only used to calculate that store.
Instruction *Dead = BBI++;
DeleteDeadInstruction(Dead, &DeadPointers);
DeleteDeadInstruction(Dead, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
continue;
@ -439,14 +440,14 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(BBI)) {
Instruction *Inst = BBI++;
DeleteDeadInstruction(Inst, &DeadPointers);
DeleteDeadInstruction(Inst, &DeadStackObjects);
++NumFastOther;
MadeChange = true;
continue;
}
if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
DeadPointers.erase(A);
DeadStackObjects.erase(A);
continue;
}
@ -461,8 +462,8 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
// If the call might load from any of our allocas, then any store above
// the call is live.
SmallVector<Value*, 8> LiveAllocas;
for (SmallPtrSet<Value*, 16>::iterator I = DeadPointers.begin(),
E = DeadPointers.end(); I != E; ++I) {
for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
E = DeadStackObjects.end(); I != E; ++I) {
// If we detect that our AA is imprecise, it's not worth it to scan the
// rest of the DeadPointers set. Just assume that the AA will return
// ModRef for everything, and go ahead and bail out.
@ -484,11 +485,11 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
for (SmallVector<Value*, 8>::iterator I = LiveAllocas.begin(),
E = LiveAllocas.end(); I != E; ++I)
DeadPointers.erase(*I);
DeadStackObjects.erase(*I);
// If all of the allocas were clobbered by the call then we're not going
// to find anything else to process.
if (DeadPointers.empty())
if (DeadStackObjects.empty())
return MadeChange;
continue;
@ -511,41 +512,47 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
continue;
}
KillPointer = KillPointer->getUnderlyingObject();
// Remove any allocas from the DeadPointer set that are loaded, as this
// makes any stores above the access live.
MadeChange |= RemoveAccessedObjects(KillPointer, KillPointerSize, BBI,
DeadStackObjects);
// Deal with undead pointers
MadeChange |= RemoveUndeadPointers(KillPointer, KillPointerSize, BBI,
DeadPointers);
// If all of the allocas were clobbered by the access then we're not going
// to find anything else to process.
if (DeadStackObjects.empty())
break;
}
return MadeChange;
}
/// RemoveUndeadPointers - check for uses of a pointer that make it
/// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 16> &DeadPointers) {
// If the kill pointer can be easily reduced to an alloca,
// don't bother doing extraneous AA queries.
if (DeadPointers.count(killPointer)) {
DeadPointers.erase(killPointer);
/// RemoveAccessedObjects - Check to see if the specified location may alias any
/// of the stack objects in the DeadStackObjects set. If so, they become live
/// because the location is being loaded.
bool DSE::RemoveAccessedObjects(Value *KillPointer, uint64_t KillPointerSize,
BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 16> &DeadStackObjects) {
Value *UnderlyingPointer = KillPointer->getUnderlyingObject();
// A constant can't be in the dead pointer set.
if (isa<Constant>(UnderlyingPointer))
return false;
// If the kill pointer can be easily reduced to an alloca, don't bother doing
// extraneous AA queries.
if (DeadStackObjects.count(UnderlyingPointer)) {
DeadStackObjects.erase(UnderlyingPointer);
return false;
}
// A global can't be in the dead pointer set.
if (isa<GlobalValue>(killPointer))
return false;
bool MadeChange = false;
SmallVector<Value*, 16> NowLive;
SmallVector<Value*, 16> undead;
for (SmallPtrSet<Value*, 64>::iterator I = DeadPointers.begin(),
E = DeadPointers.end(); I != E; ++I) {
for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
E = DeadStackObjects.end(); I != E; ++I) {
// See if this pointer could alias it
AliasAnalysis::AliasResult A = AA->alias(*I, getPointerSize(*I, *AA),
killPointer, killPointerSize);
KillPointer, KillPointerSize);
// If it must-alias and a store, we can delete it
if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
@ -553,7 +560,7 @@ bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
// Remove it!
++BBI;
DeleteDeadInstruction(S, &DeadPointers);
DeleteDeadInstruction(S, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
@ -561,12 +568,12 @@ bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
// Otherwise, it is undead
} else if (A != AliasAnalysis::NoAlias)
undead.push_back(*I);
NowLive.push_back(*I);
}
for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
for (SmallVector<Value*, 16>::iterator I = NowLive.begin(), E = NowLive.end();
I != E; ++I)
DeadPointers.erase(*I);
DeadStackObjects.erase(*I);
return MadeChange;
}