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

[Anton Korobeynikov]

I'm really curios - how often such patterns happen in real world code?

On Sat, Aug 16, 2014 at 12:14 PM, Mayur Pandey <mayur.p at samsung.com> wrote:
> 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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-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University