[Bug rtl-optimization/43147] New: SSE shuffle merge

[Bug rtl-optimization/43147] New: SSE shuffle merge

[liranuna at gmail dot com]

I've noticed that GCC (my current version is 4.4.1) doesn't fully optimize SSE
shuffle merges, as seen in this example: 

#include <xmmintrin.h>

extern void printv(__m128 m);

int main()
{
        m = _mm_shuffle_ps(m, m, 0xC9); // Those two shuffles together swap
pairs
        m = _mm_shuffle_ps(m, m, 0x2D); // And could be optimized to 0x4E
        printv(m);

        return 0;
}

This code generates the following assembly:

        movaps  .LC1, %xmm1
        shufps  $201, %xmm1, %xmm1
        shufps  $45, %xmm1, %xmm1    ; <-- Both should merge to 78
        movaps  %xmm1, %xmm0
        movaps  %xmm1, -24(%ebp)

        .LC0:
                .long   1065353216 ; 1.0f
                .long   1073741824 ; 2.0f
                .long   1077936128 ; 3.0f
                .long   1082130432 ; 4.0f

Would be nice to see it as an enhancement!


-- 
           Summary: SSE shuffle merge
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: liranuna at gmail dot com
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43147

[Bug rtl-optimization/43147] SSE shuffle merge

[liranuna at gmail dot com]

------- Comment #1 from liranuna at gmail dot com  2010-02-23 01:37 -------
It appears I am missing a line in the code I posted:

#include <xmmintrin.h>

extern void printv(__m128 m);

int main()
{
        __m128 m = _mm_set_ps(1.0f, 2.0f, 3.0f, 4.0f);
        m = _mm_shuffle_ps(m, m, 0xC9); // Those two shuffles together swap
pairs
        m = _mm_shuffle_ps(m, m, 0x2D); // And could be optimized to 0x4E
        printv(m);

        return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43147

[Bug rtl-optimization/43147] SSE shuffle merge

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2010-02-23 01:42 -------
Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-02-23 01:42:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43147

[Bug rtl-optimization/43147] SSE shuffle merge

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2010-02-23 01:42 -------
I think that is because nothing simplifies:
    (vec_select:V4SF (vec_concat:V8SF (vec_select:V4SF (vec_concat:V8SF
(reg:V4SF 62)
                    (reg:V4SF 62))
                (parallel [
                        (const_int 1 [0x1])
                        (const_int 2 [0x2])
                        (const_int 4 [0x4])
                        (const_int 7 [0x7])
                    ]))
            (vec_select:V4SF (vec_concat:V8SF (reg:V4SF 62)
                    (reg:V4SF 62))
                (parallel [
                        (const_int 1 [0x1])
                        (const_int 2 [0x2])
                        (const_int 4 [0x4])
                        (const_int 7 [0x7])
                    ])))
        (parallel [
                (const_int 1 [0x1])
                (const_int 3 [0x3])
                (const_int 6 [0x6])
                (const_int 4 [0x4])
            ]))


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43147