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Handle extremely trivial cases extremely efficiently. This speeds up 

SRoA/mem2reg from 41.2s to 27.5s on the testcase in PR209.

llvm-svn: 11099
This commit is contained in:
Chris Lattner 2004-02-03 22:00:33 +00:00
parent d1b1992495
commit 3784188620
1 changed files with 30 additions and 17 deletions
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47
llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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@ -400,25 +400,38 @@ void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
//
void PromoteMem2Reg::PromoteLocallyUsedAlloca(AllocaInst *AI) {
assert(!AI->use_empty() && "There are no uses of the alloca!");
// Uses of the uninitialized memory location shall get zero...
Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
BasicBlock *BB = cast<Instruction>(AI->use_back())->getParent();
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
if (LI->getOperand(0) == AI) {
// Loads just return the "current value"...
LI->replaceAllUsesWith(CurVal);
BB->getInstList().erase(LI);
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(1) == AI) {
// Loads just update the "current value"...
CurVal = SI->getOperand(0);
BB->getInstList().erase(SI);
// Handle degenerate cases quickly.
if (AI->hasOneUse()) {
Instruction *U = cast<Instruction>(AI->use_back());
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
// Must be a load of uninitialized value.
LI->replaceAllUsesWith(Constant::getNullValue(AI->getAllocatedType()));
} else {
// Otherwise it must be a store which is never read.
assert(isa<StoreInst>(U));
}
BB->getInstList().erase(U);
} else {
// Uses of the uninitialized memory location shall get zero...
Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
if (LI->getOperand(0) == AI) {
// Loads just return the "current value"...
LI->replaceAllUsesWith(CurVal);
BB->getInstList().erase(LI);
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(1) == AI) {
// Loads just update the "current value"...
CurVal = SI->getOperand(0);
BB->getInstList().erase(SI);
}
}
}
}