[Bug tree-optimization/52034] New: __builtin_copysign optimization suboptimal

[drepper.fsp at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52034

             Bug #: 52034
           Summary: __builtin_copysign optimization suboptimal
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: drepper.fsp@gmail.com


The most trivial __builtin_copysign optimization is not optimal:

double f(double a, double b)
{
  return __builtin_copysign(a,b);
}

With gcc 4.6.2 this gets compiled to

    movapd    %xmm1, %xmm2
    andpd    .LC0(%rip), %xmm0
    andpd    .LC1(%rip), %xmm2
    orpd    %xmm2, %xmm0
    ret

There is no reason for %xmm1 to be duplicated to %xmm2.  This is sufficient:

    andpd    .LC0(%rip), %xmm0
    andpd    .LC1(%rip), %xmm1
    orpd    %xmm1, %xmm0
    ret

The same happens with more complicated code sequences.