[PATCH] InstCombine ((x | ~y) ^ (~x ^ y)) to (x & ~y)

[Mayur Pandey]

Hi majnemer,

Hi David,

Another small patch in instcombine. Can you please review the patch.

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

Thanks,
Mayur

http://reviews.llvm.org/D4940

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/or-xor.ll

Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2542,6 +2542,14 @@
     if (match(Op0I, m_Xor(m_Value(A), m_Value(B))) &&
         match(Op1I, m_And(m_Specific(A), m_Specific(B))))
       return BinaryOperator::CreateOr(A, B);
+    // (A | ~B) ^ (~A ^ B) -> A & ~B
+    if (match(Op0I, m_Or(m_Value(A), m_Not(m_Value(B)))) &&
+        match(Op1I, m_Xor(m_Not(m_Specific(A)), m_Specific(B))))
+      return BinaryOperator::CreateAnd(A, Builder->CreateNot(B));
+    // (B ^ ~A) ^ (~B | A) -> A & ~B
+    if (match(Op0I, m_Xor(m_Value(B), m_Not(m_Value(A)))) &&
+        match(Op1I, m_Or(m_Not(m_Specific(B)), m_Specific(A))))
+      return BinaryOperator::CreateAnd(A, Builder->CreateNot(B));
   }
 
   // (A | B)^(~A) -> (A | ~B)
Index: test/Transforms/InstCombine/or-xor.ll
===================================================================
--- test/Transforms/InstCombine/or-xor.ll
+++ test/Transforms/InstCombine/or-xor.ll
@@ -160,3 +160,17 @@
 ; CHECK-NEXT: %xor = xor i32 %x, %y
 ; CHECK-NEXT: ret i32 %xor
 }
+
+; ((x | ~y) ^ (~x ^ y)) -> (x & ~y)
+define i32 @test18(i32 %x, i32 %y) {
+  %noty = xor i32 %y, -1
+  %or = or i32 %x, %noty
+  %notx = xor i32 %x, -1
+  %xor1 = xor i32 %notx, %y
+  %xor2 = xor i32 %or, %xor1
+  ret i32 %xor2
+; CHECK-LABEL: @test18(
+; CHECK-NEXT: %1 = xor i32 %y, -1
+; CHECK-NEXT: %xor2 = and i32 %x, %1
+; CHECK-NEXT: ret i32 %xor2
+}
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