Teach LLVM to unravel the "swap idiom". This implements:
Regression/Transforms/InstCombine/xor.ll:test20
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11492 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 15c8945..4deb4ed 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1086,7 +1086,7 @@
ConstantIntegral::getAllOnesValue(I.getType()));
if (Instruction *Op1I = dyn_cast<Instruction>(Op1))
- if (Op1I->getOpcode() == Instruction::Or)
+ if (Op1I->getOpcode() == Instruction::Or) {
if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B
cast<BinaryOperator>(Op1I)->swapOperands();
I.swapOperands();
@@ -1094,7 +1094,13 @@
} else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B
I.swapOperands();
std::swap(Op0, Op1);
- }
+ }
+ } else if (Op1I->getOpcode() == Instruction::Xor) {
+ if (Op0 == Op1I->getOperand(0)) // A^(A^B) == B
+ return ReplaceInstUsesWith(I, Op1I->getOperand(1));
+ else if (Op0 == Op1I->getOperand(1)) // A^(B^A) == B
+ return ReplaceInstUsesWith(I, Op1I->getOperand(0));
+ }
if (Instruction *Op0I = dyn_cast<Instruction>(Op0))
if (Op0I->getOpcode() == Instruction::Or && Op0I->hasOneUse()) {
@@ -1106,6 +1112,11 @@
return BinaryOperator::create(Instruction::And, Op0I->getOperand(0),
NotB);
}
+ } else if (Op0I->getOpcode() == Instruction::Xor) {
+ if (Op1 == Op0I->getOperand(0)) // (A^B)^A == B
+ return ReplaceInstUsesWith(I, Op0I->getOperand(1));
+ else if (Op1 == Op0I->getOperand(1)) // (B^A)^A == B
+ return ReplaceInstUsesWith(I, Op0I->getOperand(0));
}
// (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1^C2 == 0