InstCombine: Simplify (A ^ B) or/and (A ^ B ^ C)

While we can already transform A | (A ^ B) into A | B, things get bad
once we have (A ^ B) | (A ^ B ^ Cst) because reassociation will morph
this into (A ^ B) | ((A ^ Cst) ^ B).  Our existing patterns fail once
this happens.

To fix this, we add a new pattern which looks through the tree of xor
binary operators to see that, in fact, there exists a redundant xor
operation.

What follows bellow is a correctness proof of the transform using CVC3.

$ cat t.cvc
A, B, C : BITVECTOR(64);

QUERY BVXOR(A, B) | BVXOR(BVXOR(B, C), A) = BVXOR(A, B) | C;
QUERY BVXOR(BVXOR(A, C), B) | BVXOR(A, B) = BVXOR(A, B) | C;

QUERY BVXOR(A, B) & BVXOR(BVXOR(B, C), A) = BVXOR(A, B) & ~C;
QUERY BVXOR(BVXOR(A, C), B) & BVXOR(A, B) = BVXOR(A, B) & ~C;

$ cvc3 < t.cvc
Valid.
Valid.
Valid.
Valid.

llvm-svn: 214342

2 files changed, 40 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/or-xor.ll b/llvm/test/Transforms/InstCombine/or-xor.ll
index cec36f119a9..3f247e27522 100644
--- a/llvm/test/Transforms/InstCombine/or-xor.ll
+++ b/llvm/test/Transforms/InstCombine/or-xor.ll
@@ -92,3 +92,23 @@ define i32 @test9(i32 %x, i32 %y) nounwind {
 ; CHECK-NEXT: %z = or i32 %y.not, %x
 ; CHECK-NEXT: ret i32 %z
 }
+
+define i32 @test10(i32 %A, i32 %B) {
+  %xor1 = xor i32 %B, %A
+  %not = xor i32 %A, -1
+  %xor2 = xor i32 %not, %B
+  %or = or i32 %xor1, %xor2
+  ret i32 %or
+; CHECK-LABEL: @test10(
+; CHECK-NEXT: ret i32 -1
+}
+
+define i32 @test11(i32 %A, i32 %B) {
+  %xor1 = xor i32 %B, %A
+  %not = xor i32 %A, -1
+  %xor2 = xor i32 %not, %B
+  %or = or i32 %xor1, %xor2
+  ret i32 %or
+; CHECK-LABEL: @test11(
+; CHECK-NEXT: ret i32 -1
+}
diff --git a/llvm/test/Transforms/InstCombine/xor2.ll b/llvm/test/Transforms/InstCombine/xor2.ll
index 4ae50a140e1..6318afe51bf 100644
--- a/llvm/test/Transforms/InstCombine/xor2.ll
+++ b/llvm/test/Transforms/InstCombine/xor2.ll
@@ -125,3 +125,23 @@ define i32 @test10(i32 %b, i32 %c) {
 ; CHECK-LABEL: @test10(
 ; CHECK-NEXT: %xor2 = or i32 %b, %c
 }
+
+define i32 @test11(i32 %A, i32 %B) {
+  %xor1 = xor i32 %B, %A
+  %not = xor i32 %A, -1
+  %xor2 = xor i32 %not, %B
+  %and = and i32 %xor1, %xor2
+  ret i32 %and
+; CHECK-LABEL: @test11(
+; CHECK-NEXT: ret i32 0
+}
+
+define i32 @test12(i32 %A, i32 %B) {
+  %xor1 = xor i32 %B, %A
+  %not = xor i32 %A, -1
+  %xor2 = xor i32 %not, %B
+  %and = and i32 %xor1, %xor2
+  ret i32 %and
+; CHECK-LABEL: @test12(
+; CHECK-NEXT: ret i32 0
+}