[Bug target/54400] New: recognize haddpd

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54400

             Bug #: 54400
           Summary: recognize haddpd
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: gli...@gcc.gnu.org
            Target: x86_64-linux-gnu


Hello,

for this program:

#include <x86intrin.h>
double f(__m128d v){return v[1]+v[0];}

gcc -O3 -msse4 (same with -Os) generates:

    movapd    %xmm0, %xmm2
    unpckhpd    %xmm2, %xmm2
    movapd    %xmm2, %xmm1
    addsd    %xmm0, %xmm1
    movapd    %xmm1, %xmm0

(yes, the number of mov instructions is a bit high...)

Looking at the x86 backend, it can expand reduc_splus_v2df and
__builtin_ia32_haddpd, but it doesn't provide any pattern that could be
recognized. hsubpd is even less present.

It seems to me that, considering only the low part of the result of haddpd, the
pattern should be small enough to be matched: (plus (vec_select (match_operand
1) const_a) (vec_select (match_dup 1) const_b)) where a and b are 0 and 1 in
any order.