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Move zext and sext casts fed by loads into the same block as the

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load, to help SelectionDAG fold them into the loads, unless
conditions are unfavorable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84271 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-10-16 20:59:35 +00:00
parent a43d46f523
commit b00f236b03
3 changed files with 63 additions and 3 deletions
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42
lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -73,6 +73,7 @@ namespace {
DenseMap<Value*,Value*> &SunkAddrs);
bool OptimizeInlineAsmInst(Instruction *I, CallSite CS,
DenseMap<Value*,Value*> &SunkAddrs);
bool MoveExtToFormExtLoad(Instruction *I);
bool OptimizeExtUses(Instruction *I);
void findLoopBackEdges(const Function &F);
};
@ -731,6 +732,43 @@ bool CodeGenPrepare::OptimizeInlineAsmInst(Instruction *I, CallSite CS,
return MadeChange;
}
/// MoveExtToFormExtLoad - Move a zext or sext fed by a load into the same
/// basic block as the load, unless conditions are unfavorable. This allows
/// SelectionDAG to fold the extend into the load.
///
bool CodeGenPrepare::MoveExtToFormExtLoad(Instruction *I) {
// Look for a load being extended.
LoadInst *LI = dyn_cast<LoadInst>(I->getOperand(0));
if (!LI) return false;
// If they're already in the same block, there's nothing to do.
if (LI->getParent() == I->getParent())
return false;
// If the load has other users and the truncate is not free, this probably
// isn't worthwhile.
if (!LI->hasOneUse() &&
TLI && !TLI->isTruncateFree(I->getType(), LI->getType()))
return false;
// Check whether the target supports casts folded into loads.
unsigned LType;
if (isa<ZExtInst>(I))
LType = ISD::ZEXTLOAD;
else {
assert(isa<SExtInst>(I) && "Unexpected ext type!");
LType = ISD::SEXTLOAD;
}
if (TLI && !TLI->isLoadExtLegal(LType, TLI->getValueType(LI->getType())))
return false;
// Move the extend into the same block as the load, so that SelectionDAG
// can fold it.
I->removeFromParent();
I->insertAfter(LI);
return true;
}
bool CodeGenPrepare::OptimizeExtUses(Instruction *I) {
BasicBlock *DefBB = I->getParent();
@ -846,8 +884,10 @@ bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) {
MadeChange |= Change;
}
if (!Change && (isa<ZExtInst>(I) || isa<SExtInst>(I)))
if (!Change && (isa<ZExtInst>(I) || isa<SExtInst>(I))) {
MadeChange |= MoveExtToFormExtLoad(I);
MadeChange |= OptimizeExtUses(I);
}
} else if (CmpInst *CI = dyn_cast<CmpInst>(I)) {
MadeChange |= OptimizeCmpExpression(CI);
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {