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

Mayur Pandey · Mayur Pandey · commit 960507beb466 · 2014-08-19T08:19:19.000Z
Proof using CVC3 follows: $ cat t.cvc A, B : BITVECTOR(32); QUERY BVXOR((A & ~B),(~A & B)) = BVXOR(A,B); $ cvc3 t.cvc Valid. Differential Revision: http://reviews.llvm.org/D4898 llvm-svn: 215974
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2522,6 +2522,16 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
         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_And(m_Value(A), m_Not(m_Value(B)))) &&
+        match(Op1I, m_And(m_Not(m_Specific(A)), m_Specific(B)))) {
+      return BinaryOperator::CreateXor(A, B);
+    }
+    // (~A & B) ^ (A & ~B) -> A ^ B
+    if (match(Op0I, m_And(m_Not(m_Value(A)), m_Value(B))) &&
+        match(Op1I, m_And(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
@@ -160,3 +160,16 @@ define i32 @test16(i32 %x, i32 %y) {
 ; CHECK-NEXT: %xor = xor i32 %x, %y
 ; CHECK-NEXT: ret i32 %xor
 }
+
+; ((x & ~y) ^ (~x & y)) -> x ^ y
+define i32 @test17(i32 %x, i32 %y) {
+  %noty = xor i32 %y, -1
+  %notx = xor i32 %x, -1
+  %and1 = and i32 %x, %noty
+  %and2 = and i32 %notx, %y
+  %xor = xor i32 %and1, %and2
+  ret i32 %xor
+; CHECK-LABEL: @test17(
+; CHECK-NEXT: %xor = xor i32 %x, %y
+; CHECK-NEXT: ret i32 %xor
+}
