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switch InstCombine::visitLoadInst to use

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FindAvailableLoadedValue


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60169 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2008-11-27 08:56:30 +00:00
parent e3a0884ddf
commit 4aebaee0e4
2 changed files with 54 additions and 45 deletions
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27
lib/Transforms/Utils/BasicBlockUtils.cpp
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@ -373,6 +373,29 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
return NewBB;
}
/// AreEquivalentAddressValues - Test if A and B will obviously have the same
/// value. This includes recognizing that %t0 and %t1 will have the same
/// value in code like this:
/// %t0 = getelementptr @a, 0, 3
/// store i32 0, i32* %t0
/// %t1 = getelementptr @a, 0, 3
/// %t2 = load i32* %t1
///
static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
// Test if the values are trivially equivalent.
if (A == B) return true;
// Test if the values come form identical arithmetic instructions.
if (isa<BinaryOperator>(A) || isa<CastInst>(A) ||
isa<PHINode>(A) || isa<GetElementPtrInst>(A))
if (const Instruction *BI = dyn_cast<Instruction>(B))
if (cast<Instruction>(A)->isIdenticalTo(BI))
return true;
// Otherwise they may not be equivalent.
return false;
}
/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
/// instruction before ScanFrom) checking to see if we have the value at the
/// memory address *Ptr locally available within a small number of instructions.
@ -407,12 +430,12 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
// If this is a load of Ptr, the loaded value is available.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
if (LI->getOperand(0) == Ptr)
if (AreEquivalentAddressValues(LI->getOperand(0), Ptr))
return LI;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// If this is a store through Ptr, the value is available!
if (SI->getOperand(1) == Ptr)
if (AreEquivalentAddressValues(SI->getOperand(1), Ptr))
return SI->getOperand(0);
// If Ptr is an alloca and this is a store to a different alloca, ignore