InstCombine: Combine (xor (or %a, %b) (xor %a, %b)) to (add %a, %b)

Correctness proof of the transform using CVC3-

$ cat t.cvc
A, B : BITVECTOR(32);
QUERY BVXOR(A | B, BVXOR(A,B) ) = A & B;

$ cvc3 t.cvc
Valid.

llvm-svn: 215524

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/or-xor.ll b/llvm/test/Transforms/InstCombine/or-xor.ll
index 5c15c456f8d..6984c44d9a3 100644
--- a/llvm/test/Transforms/InstCombine/or-xor.ll
+++ b/llvm/test/Transforms/InstCombine/or-xor.ll
@@ -136,3 +136,14 @@ define i32 @test13(i32 %x, i32 %y) {
 ; CHECK-NEXT: %and = and i32 %x, %y
 ; CHECK-NEXT: ret i32 %and
 }
+
+; ((x | y) ^ (x ^ y)) -> (x & y)
+define i32 @test15(i32 %x, i32 %y) {
+  %1 = xor i32 %y, %x
+  %2 = or i32 %y, %x
+  %3 = xor i32 %2, %1
+  ret i32 %3
+; CHECK-LABEL: @test15(
+; CHECK-NEXT: %1 = and i32 %y, %x
+; CHECK-NEXT: ret i32 %1
+}