[Bug target/55803] New: SSE2 double negation less efficient than explicit xor

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55803



             Bug #: 55803

           Summary: SSE2 double negation less efficient than explicit xor

    Classification: Unclassified

           Product: gcc

           Version: 4.8.0

            Status: UNCONFIRMED

          Keywords: missed-optimization

          Severity: normal

          Priority: P3

         Component: target

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: gli...@gcc.gnu.org

            Target: x86_64-linux-gnu





Compiling the following code with -Os (-O3 or -O2 have the same with xorpd) on

x86_64-linux



#include <x86intrin.h>

double f(double d){

  return -d;

}

__m128d g(__m128d d){

  __m128d m={-0.,0.};

  return _mm_xor_pd(d,m);

}



gives for f:

    movsd    .LC0(%rip), %xmm1

    xorps    %xmm1, %xmm0



and for g:

    xorps    .LC0(%rip), %xmm0



-mavx doesn't help.