[llvm] r215974 - InstCombine: ((A & ~B) ^ (~A & B)) to A ^ B

[Mayur Pandey]

Author: mayurp
Date: Tue Aug 19 03:19:19 2014
New Revision: 215974

URL: http://llvm.org/viewvc/llvm-project?rev=215974&view=rev
Log:
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.

Differential Revision: http://reviews.llvm.org/D4898

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
    llvm/trunk/test/Transforms/InstCombine/or-xor.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=215974&r1=215973&r2=215974&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Tue Aug 19 03:19:19 2014
@@ -2522,6 +2522,16 @@ Instruction *InstCombiner::visitXor(Bina
         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)))) {

Modified: llvm/trunk/test/Transforms/InstCombine/or-xor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/or-xor.ll?rev=215974&r1=215973&r2=215974&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/or-xor.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/or-xor.ll Tue Aug 19 03:19:19 2014
@@ -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
+}