[Bug target/26546] missed optimization with respect of vector intrinsics

[Bug target/26546] missed optimization with respect of vector intrinsics

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26546

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|meta-bug                    |
             Target|                            |x86_64-*-*, i?86-*-*
          Component|tree-optimization           |target
            Version|4.1.0                       |4.8.0
            Summary|[meta-bugs] couple of       |missed optimization with
                   |missed optimization with    |respect of vector
                   |respect of vector and       |intrinsics
                   |unions                      |

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-26 10:42:04 UTC ---
I get:

main:
.LFB518:
        .cfi_startproc
        xorps   %xmm0, %xmm0
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
        movl    $.LC0, %edi
        movl    $1, %eax
        unpcklps        %xmm0, %xmm0
        cvtps2pd        %xmm0, %xmm0
        call    printf
        xorl    %eax, %eax
        addq    $8, %rsp
        .cfi_def_cfa_offset 8
        ret

with 4.8 and the asm from the description with 4.7 (with -O2).  Leaving
the union uninitialized of course makes it a bad testcase and probably
makes it optimized in the first place.

With

#include <xmmintrin.h>

typedef union
{
  __m128 vec;
  float data[4];
  struct { float x,y,z,w; };
} vec4f_t;

static inline float __attribute__((__always_inline__))
acc(vec4f_t src)
{
  float a;
  src.vec = _mm_add_ps(src.vec, _mm_movehl_ps(src.vec, src.vec));
  _mm_store_ss(&a, _mm_add_ss(src.vec, _mm_shuffle_ps(src.vec, src.vec,
                                                      _MM_SHUFFLE(3,2,1,1))));
  return a;
}

vec4f_t b;

int
main(int argc, char *argv[])
{
  __builtin_printf("%f\n", acc(b));
  return 0;
}

we are back to the unoptimized assembly.  Tree optimizers have no chance
optimizing this because they see target builtins:

  __m128 src;
  float a;
  double _2;
  __m128 _4;
  __m128 _5;
  __m128 _6;
  __m128 _7;

  <bb 2>:
  src_9 = MEM[(union  *)&b];
  _4 = __builtin_ia32_movhlps (src_9, src_9);
  _5 = __builtin_ia32_addps (src_9, _4);
  _6 = __builtin_ia32_shufps (_5, _5, 229);
  _7 = __builtin_ia32_addss (_5, _6);
  a_8 = __builtin_ia32_vec_ext_v4sf (_7, 0);
  _2 = (double) a_8;
  printf ("%f\n", _2);

but in all this is now a target issue.

[Bug target/26546] missed optimization with respect of vector intrinsics

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26546

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Without the uninitialized variable even LLVM produces the same assembly code.
Is there really anything more to opimize here?