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

[mayurp]

Summary

Hi,
A patch in instcombine to transform ((A | ~B) ^ (~A | B)) -> A ^ B.
Please review the patch.

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

[majnemer]

lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

2511–2538 ↗

(On Diff #12446)

You have what appear to be eight different patterns you are trying to match. Are you sure we need all of them? What happens if you ran a reassociate pass first?

[majnemer]

test/Transforms/InstCombine/or-xor.ll

153–161 ↗

(On Diff #12446)

Please give these better names.

[mayurp]

Hi David,
With reassociate, the comparisons can be reduced. Modified the patch accordingly. Also modified the test case.
Please review.

Thanks,
Mayur

[majnemer]

LGTM.

[mayurp]

Hi David,

Thanks a lot for the review. Can you please commit this on my behalf. I dont have commit access as of now.

Thanks,
Mayur

[majnemer]

Closed by commit rL215621 (authored by @majnemer).

llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

if (match(Op0I, m_And(m_Value(A), m_Value(B))) &&
         return BinaryOperator::CreateXor(A, B);
     }
     // (A | B)^(A & B) -> A ^ B
     if (match(Op0I, m_Or(m_Value(A), m_Value(B))) &&
         match(Op1I, m_And(m_Value(C), m_Value(D)))) {
       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)))) {
       if ((A == C && B == D) || (A == D && B == C))
         return BinaryOperator::CreateAnd(A, B);
     }
     // (A | B)^(A ^ B) -> A & B
     if (match(Op0I, m_Or(m_Value(A), m_Value(B))) &&

llvm/trunk/test/Transforms/InstCombine/or-xor.ll

define i32 @test15(i32 %x, i32 %y) {
   %1 = xor i32 %y, %x
   %2 = or i32 %y, %x
   %3 = xor i32 %2, %1
   ret i32 %3
 ; CHECK-LABEL: @test15(
 ; 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
+}