diff options
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 7 | ||||
| -rw-r--r-- | test/Transforms/InstCombine/xor-undef.ll | 6 |
2 files changed, 12 insertions, 1 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 8ebd2cca61..35715fb8ca 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -4425,8 +4425,13 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) { bool Changed = SimplifyCommutative(I); Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); - if (isa<UndefValue>(Op1)) + if (isa<UndefValue>(Op1)) { + if (isa<UndefValue>(Op0)) + // Handle undef ^ undef -> 0 special case. This is a common + // idiom (misuse). + return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); return ReplaceInstUsesWith(I, Op1); // X ^ undef -> undef + } // xor X, X = 0, even if X is nested in a sequence of Xor's. if (Instruction *Result = AssociativeOpt(I, XorSelf(Op1))) { diff --git a/test/Transforms/InstCombine/xor-undef.ll b/test/Transforms/InstCombine/xor-undef.ll new file mode 100644 index 0000000000..c090223b53 --- /dev/null +++ b/test/Transforms/InstCombine/xor-undef.ll @@ -0,0 +1,6 @@ +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep zeroinitializer + +define <2 x i64> @f() { + %tmp = xor <2 x i64> undef, undef + ret <2 x i64> %tmp +} |