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InstCombine: Fold A-b == C --> b == A-C if A and C are constants.

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The backend already knew this trick.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132915 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2011-06-13 15:24:24 +00:00
parent aa99bea46f
commit e7fdcad2f2
3 changed files with 33 additions and 13 deletions
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lib/Transforms/InstCombine/InstCombineCompares.cpp
+17 -8
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@@ -1407,18 +1407,27 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
case Instruction::Xor:
// For the xor case, we can xor two constants together, eliminating
// the explicit xor.
if (Constant *BOC = dyn_cast<Constant>(BO->getOperand(1)))
return new ICmpInst(ICI.getPredicate(), BO->getOperand(0),
if (Constant *BOC = dyn_cast<Constant>(BO->getOperand(1))) {
return new ICmpInst(ICI.getPredicate(), BO->getOperand(0),
ConstantExpr::getXor(RHS, BOC));
// FALLTHROUGH
case Instruction::Sub:
// Replace (([sub|xor] A, B) != 0) with (A != B)
if (RHSV == 0)
} else if (RHSV == 0) {
// Replace ((xor A, B) != 0) with (A != B)
return new ICmpInst(ICI.getPredicate(), BO->getOperand(0),
BO->getOperand(1));
}
break;
case Instruction::Sub:
// Replace ((sub A, B) != C) with (B != A-C) if A & C are constants.
if (ConstantInt *BOp0C = dyn_cast<ConstantInt>(BO->getOperand(0))) {
if (BO->hasOneUse())
return new ICmpInst(ICI.getPredicate(), BO->getOperand(1),
ConstantExpr::getSub(BOp0C, RHS));
} else if (RHSV == 0) {
// Replace ((sub A, B) != 0) with (A != B)
return new ICmpInst(ICI.getPredicate(), BO->getOperand(0),
BO->getOperand(1));
}
break;
case Instruction::Or:
// If bits are being or'd in that are not present in the constant we
// are comparing against, then the comparison could never succeed!