[llvm] r215524 - InstCombine: Combine (xor (or %a, %b) (xor %a, %b)) to (add %a, %b)

[Jonathan Roelofs]

On 8/13/14, 5:05 PM, David Majnemer wrote:
> On Tue, Aug 12, 2014 at 10:13 PM, Karthik Bhat <kv.bhat at samsung.com
> <mailto:kv.bhat at samsung.com>> wrote:
>
>     Author: karthik
>     Date: Wed Aug 13 00:13:14 2014
>     New Revision: 215524
>
>     URL: http://llvm.org/viewvc/llvm-project?rev=215524&view=rev
>     Log:
>     InstCombine: Combine (xor (or %a, %b) (xor %a, %b)) to (add %a, %b)
s/add/and/

Unfortunately too late to fix as it's in the commit message.
>
>     Correctness proof of the transform using CVC3-
>
>     $ cat t.cvc
>     A, B : BITVECTOR(32);
>     QUERY BVXOR(A | B, BVXOR(A,B) ) = A & B;
>
>     $ cvc3 t.cvc
>     Valid.
>
>
>     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=215524&r1=215523&r2=215524&view=diff
>     ==============================================================================
>     --- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
>     +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Wed Aug 13
>     00:13:14 2014
>     @@ -2508,6 +2508,18 @@ Instruction *InstCombiner::visitXor(Bina
>             if ((A == C && B == D) || (A == D && B == C))
>               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))) &&
>     +        match(Op1I, m_Xor(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_And(m_Value(A), m_Value(B))) &&
>               match(Op1I, m_Xor(m_Specific(A), m_Specific(B))))
>
>     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=215524&r1=215523&r2=215524&view=diff
>     ==============================================================================
>     --- llvm/trunk/test/Transforms/InstCombine/or-xor.ll (original)
>     +++ llvm/trunk/test/Transforms/InstCombine/or-xor.ll Wed Aug 13 00:13:14 2014
>     @@ -136,3 +136,14 @@ define i32 @test13(i32 %x, i32 %y) {
>       ; CHECK-NEXT: %and = and i32 %x, %y
>       ; CHECK-NEXT: ret i32 %and
>       }
>     +
>     +; ((x | y) ^ (x ^ y)) -> (x & y)
>     +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
>
>
> I LGTM'd this differential under the understanding that you would clean up the
> variable names used: http://reviews.llvm.org/D4866#inline-40056
>
> Please fix test15.
>
>     +}
>
>
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-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded