InstCombine: ((A | ~B) ^ (~A | B)) to A ^ B

Proof using CVC3 follows:
$ cat t.cvc
A, B : BITVECTOR(32);
QUERY BVXOR((A | ~B),(~A |B)) = BVXOR(A,B);
$ cvc3 t.cvc
Valid.

Patch by Mayur Pandey!

Differential Revision: http://reviews.llvm.org/D4883

llvm-svn: 215621

2 files changed, 23 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 64708c4d4f7..063d4a799e4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2512,6 +2512,16 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
       if ((A == C && B == D) || (A == D && B == C))
         return BinaryOperator::CreateXor(A, B);
     }
+    // (A | ~B) ^ (~A | B) -> A ^ B
+    if (match(Op0I, m_Or(m_Value(A), m_Not(m_Value(B)))) &&
+        match(Op1I, m_Or(m_Not(m_Specific(A)), m_Specific(B)))) {
+      return BinaryOperator::CreateXor(A, B);
+    }
+    // (~A | B) ^ (A | ~B) -> A ^ B
+    if (match(Op0I, m_Or(m_Not(m_Value(A)), m_Value(B))) &&
+        match(Op1I, m_Or(m_Specific(A), m_Not(m_Specific(B))))) {
+      return BinaryOperator::CreateXor(A, B);
+    }
     // (A ^ B)^(A | B) -> A & B
     if (match(Op0I, m_Xor(m_Value(A), m_Value(B))) &&
         match(Op1I, m_Or(m_Value(C), m_Value(D)))) {
diff --git a/llvm/test/Transforms/InstCombine/or-xor.ll b/llvm/test/Transforms/InstCombine/or-xor.ll
index 6984c44d9a3..984178aeb34 100644
--- a/llvm/test/Transforms/InstCombine/or-xor.ll
+++ b/llvm/test/Transforms/InstCombine/or-xor.ll
@@ -147,3 +147,16 @@ define i32 @test15(i32 %x, i32 %y) {
 ; CHECK-NEXT: %1 = and i32 %y, %x
 ; CHECK-NEXT: ret i32 %1
 }
+
+; ((x | ~y) ^ (~x | y)) -> x ^ y
+define i32 @test16(i32 %x, i32 %y) {
+  %noty = xor i32 %y, -1
+  %notx = xor i32 %x, -1
+  %or1 = or i32 %x, %noty
+  %or2 = or i32 %notx, %y
+  %xor = xor i32 %or1, %or2
+  ret i32 %xor
+; CHECK-LABEL: @test16(
+; CHECK-NEXT: %xor = xor i32 %x, %y
+; CHECK-NEXT: ret i32 %xor
+}