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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. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11099 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -400,25 +400,38 @@ void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
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//
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void PromoteMem2Reg::PromoteLocallyUsedAlloca(AllocaInst *AI) {
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assert(!AI->use_empty() && "There are no uses of the alloca!");
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// Uses of the uninitialized memory location shall get zero...
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Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
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BasicBlock *BB = cast<Instruction>(AI->use_back())->getParent();
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
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Instruction *Inst = I++;
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
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if (LI->getOperand(0) == AI) {
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// Loads just return the "current value"...
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LI->replaceAllUsesWith(CurVal);
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BB->getInstList().erase(LI);
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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if (SI->getOperand(1) == AI) {
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// Loads just update the "current value"...
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CurVal = SI->getOperand(0);
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BB->getInstList().erase(SI);
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// Handle degenerate cases quickly.
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if (AI->hasOneUse()) {
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Instruction *U = cast<Instruction>(AI->use_back());
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if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
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// Must be a load of uninitialized value.
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LI->replaceAllUsesWith(Constant::getNullValue(AI->getAllocatedType()));
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} else {
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// Otherwise it must be a store which is never read.
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assert(isa<StoreInst>(U));
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}
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BB->getInstList().erase(U);
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} else {
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// Uses of the uninitialized memory location shall get zero...
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Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
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Instruction *Inst = I++;
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
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if (LI->getOperand(0) == AI) {
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// Loads just return the "current value"...
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LI->replaceAllUsesWith(CurVal);
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BB->getInstList().erase(LI);
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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if (SI->getOperand(1) == AI) {
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// Loads just update the "current value"...
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CurVal = SI->getOperand(0);
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BB->getInstList().erase(SI);
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}
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}
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}
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}
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