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various cleanups and code simplification

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llvm-svn: 120454
This commit is contained in:
Chris Lattner 2010-11-30 19:48:15 +00:00
parent 3512297c58
commit ac17f2b483
1 changed files with 62 additions and 86 deletions
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128
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -400,104 +400,88 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block
SmallPtrSet<Value*, 64> deadPointers;
SmallPtrSet<Value*, 64> DeadPointers;
// 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);
DeadPointers.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);
DeadPointers.insert(AI);
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
// If we find a store whose pointer is dead.
if (hasMemoryWrite(BBI)) {
if (isRemovable(BBI)) {
// If we find a store, check to see if it points into a dead stack value.
if (hasMemoryWrite(BBI) && isRemovable(BBI)) {
// See through pointer-to-pointer bitcasts
Value *pointerOperand = getPointerOperand(BBI)->getUnderlyingObject();
Value *Pointer = getPointerOperand(BBI)->getUnderlyingObject();
// Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal.
if (deadPointers.count(pointerOperand)) {
if (DeadPointers.count(Pointer)) {
// DCE instructions only used to calculate that store.
Instruction *Dead = BBI;
++BBI;
DeleteDeadInstruction(Dead, &deadPointers);
Instruction *Dead = BBI++;
DeleteDeadInstruction(Dead, &DeadPointers);
++NumFastStores;
MadeChange = true;
continue;
}
}
// Because a memcpy or memmove is also a load, we can't skip it if we
// didn't remove it.
if (!isa<MemTransferInst>(BBI))
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(BBI)) {
Instruction *Inst = BBI++;
DeleteDeadInstruction(Inst, &DeadPointers);
++NumFastOther;
MadeChange = true;
continue;
}
Value *killPointer = 0;
uint64_t killPointerSize = AliasAnalysis::UnknownSize;
if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
DeadPointers.erase(A);
continue;
}
Value *KillPointer = 0;
uint64_t KillPointerSize = AliasAnalysis::UnknownSize;
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
// However, if this load is unused and not volatile, we can go ahead and
// remove it, and not have to worry about it making our pointer undead!
if (L->use_empty() && !L->isVolatile()) {
++BBI;
DeleteDeadInstruction(L, &deadPointers);
++NumFastOther;
MadeChange = true;
continue;
}
killPointer = L->getPointerOperand();
KillPointer = L->getPointerOperand();
} else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
killPointer = V->getOperand(0);
} else if (isa<MemTransferInst>(BBI) &&
isa<ConstantInt>(cast<MemTransferInst>(BBI)->getLength())) {
killPointer = cast<MemTransferInst>(BBI)->getSource();
killPointerSize = cast<ConstantInt>(
cast<MemTransferInst>(BBI)->getLength())->getZExtValue();
} else if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
deadPointers.erase(A);
// Dead alloca's can be DCE'd when we reach them
if (A->use_empty()) {
++BBI;
DeleteDeadInstruction(A, &deadPointers);
++NumFastOther;
MadeChange = true;
}
continue;
KillPointer = V->getOperand(0);
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
KillPointer = cast<MemTransferInst>(BBI)->getSource();
if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
KillPointerSize = Len->getZExtValue();
} else if (CallSite CS = cast<Value>(BBI)) {
// If this call does not access memory, it can't
// be undeadifying any of our pointers.
// If this call does not access memory, it can't be loading any of our
// pointers.
if (AA->doesNotAccessMemory(CS))
continue;
unsigned modRef = 0;
unsigned other = 0;
unsigned NumModRef = 0;
unsigned NumOther = 0;
// Remove any pointers made undead by the call from the dead set
std::vector<Value*> dead;
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
E = deadPointers.end(); I != E; ++I) {
for (SmallPtrSet<Value*, 64>::iterator I = DeadPointers.begin(),
E = DeadPointers.end(); I != E; ++I) {
// HACK: 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.
if (modRef >= 16 && other == 0) {
deadPointers.clear();
if (NumModRef >= 16 && NumOther == 0) {
DeadPointers.clear();
return MadeChange;
}
@ -506,9 +490,9 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
AA->getModRefInfo(CS, *I, getPointerSize(*I, *AA));
if (A == AliasAnalysis::ModRef)
++modRef;
++NumModRef;
else
++other;
++NumOther;
if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
dead.push_back(*I);
@ -516,27 +500,19 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
for (std::vector<Value*>::iterator I = dead.begin(), E = dead.end();
I != E; ++I)
deadPointers.erase(*I);
DeadPointers.erase(*I);
continue;
} else if (isInstructionTriviallyDead(BBI)) {
// For any non-memory-affecting non-terminators, DCE them as we reach them
Instruction *Inst = BBI;
++BBI;
DeleteDeadInstruction(Inst, &deadPointers);
++NumFastOther;
MadeChange = true;
} else {
// Not a loading instruction.
continue;
}
if (!killPointer)
continue;
killPointer = killPointer->getUnderlyingObject();
KillPointer = KillPointer->getUnderlyingObject();
// Deal with undead pointers
MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
deadPointers);
MadeChange |= RemoveUndeadPointers(KillPointer, KillPointerSize, BBI,
DeadPointers);
}
return MadeChange;
@ -546,11 +522,11 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
/// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 64> &deadPointers) {
SmallPtrSet<Value*, 64> &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);
if (DeadPointers.count(killPointer)) {
DeadPointers.erase(killPointer);
return false;
}
@ -562,8 +538,8 @@ bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
SmallVector<Value*, 16> undead;
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
E = deadPointers.end(); I != E; ++I) {
for (SmallPtrSet<Value*, 64>::iterator I = DeadPointers.begin(),
E = DeadPointers.end(); I != E; ++I) {
// See if this pointer could alias it
AliasAnalysis::AliasResult A = AA->alias(*I, getPointerSize(*I, *AA),
killPointer, killPointerSize);
@ -574,7 +550,7 @@ bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
// Remove it!
++BBI;
DeleteDeadInstruction(S, &deadPointers);
DeleteDeadInstruction(S, &DeadPointers);
++NumFastStores;
MadeChange = true;
@ -587,7 +563,7 @@ bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
I != E; ++I)
deadPointers.erase(*I);
DeadPointers.erase(*I);
return MadeChange;
}