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Check for volatile loads only once.

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Implement load.ll:test7


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21645 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-05-01 04:24:53 +00:00
parent 45c2bdd2f9
commit 37366c1ba8
1 changed files with 35 additions and 9 deletions
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44
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -4750,13 +4750,34 @@ static bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom) {
Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
Value *Op = LI.getOperand(0);
// load (cast X) --> cast (load X) iff safe
if (CastInst *CI = dyn_cast<CastInst>(Op))
if (Instruction *Res = InstCombineLoadCast(*this, LI))
return Res;
// None of the following transforms are legal for volatile loads.
if (LI.isVolatile()) return 0;
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op))
if (isa<ConstantPointerNull>(GEPI->getOperand(0)) ||
isa<UndefValue>(GEPI->getOperand(0))) {
// Insert a new store to null instruction before the load to indicate
// that this code is not reachable. We do this instead of inserting
// an unreachable instruction directly because we cannot modify the
// CFG.
new StoreInst(UndefValue::get(LI.getType()),
Constant::getNullValue(Op->getType()), &LI);
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
}
if (Constant *C = dyn_cast<Constant>(Op)) {
if ((C->isNullValue() || isa<UndefValue>(C)) &&
!LI.isVolatile()) { // load null/undef -> undef
// load null/undef -> undef
if ((C->isNullValue() || isa<UndefValue>(C))) {
// Insert a new store to null instruction before the load to indicate that
// this code is not reachable. We do this instead of inserting an
// unreachable instruction directly because we cannot modify the CFG.
new StoreInst(UndefValue::get(LI.getType()), C, &LI);
new StoreInst(UndefValue::get(LI.getType()),
Constant::getNullValue(Op->getType()), &LI);
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
}
@ -4772,18 +4793,23 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
if (GV->isConstant() && !GV->isExternal())
if (Constant *V = GetGEPGlobalInitializer(GV->getInitializer(), CE))
return ReplaceInstUsesWith(LI, V);
if (CE->getOperand(0)->isNullValue()) {
// Insert a new store to null instruction before the load to indicate
// that this code is not reachable. We do this instead of inserting
// an unreachable instruction directly because we cannot modify the
// CFG.
new StoreInst(UndefValue::get(LI.getType()),
Constant::getNullValue(Op->getType()), &LI);
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
}
} else if (CE->getOpcode() == Instruction::Cast) {
if (Instruction *Res = InstCombineLoadCast(*this, LI))
return Res;
}
}
// load (cast X) --> cast (load X) iff safe
if (CastInst *CI = dyn_cast<CastInst>(Op))
if (Instruction *Res = InstCombineLoadCast(*this, LI))
return Res;
if (!LI.isVolatile() && Op->hasOneUse()) {
if (Op->hasOneUse()) {
// Change select and PHI nodes to select values instead of addresses: this
// helps alias analysis out a lot, allows many others simplifications, and
// exposes redundancy in the code.