Re: [PATCH 28/42] i386: Make _mm_empty () as NOP when MMX is disabled

[Uros Bizjak]

On Fri, Feb 15, 2019 at 3:03 PM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> With SSE emulation of MMX intrinsics, we should make _mm_empty () as NOP
> when MMX is disabled.
>
>         PR target/89021
>         * config/i386/mmx.md (EMMS): Also allow TARGET_MMX_WITH_SSE.
>         (mmx_<emms>): Generate "<emms>" only when MMX is enabled.

Better rename the pattern to "*mmx_<emms>" and introduce a new expander:

(define_insn "mmx_<emms>"
  [(unspec_volatile [(const_int 0)] EMMS)
   (clobber (reg:XF ST0_REG))
   (clobber (reg:XF ST1_REG))
   (clobber (reg:XF ST2_REG))
   (clobber (reg:XF ST3_REG))
   (clobber (reg:XF ST4_REG))
   (clobber (reg:XF ST5_REG))
   (clobber (reg:XF ST6_REG))
   (clobber (reg:XF ST7_REG))
   (clobber (reg:DI MM0_REG))
   (clobber (reg:DI MM1_REG))
   (clobber (reg:DI MM2_REG))
   (clobber (reg:DI MM3_REG))
   (clobber (reg:DI MM4_REG))
   (clobber (reg:DI MM5_REG))
   (clobber (reg:DI MM6_REG))
   (clobber (reg:DI MM7_REG))]
  "TARGET_MMX || TARGET_MMX_WITH_SSE"
{
  if (!TARGET_MMX)
    {
      emit_insn (gen_nop ());
      DONE;
    }
})

This way, the compiler won't bother with {f,}emms when there are no
MMX registers.

Uros.

> ---
>  gcc/config/i386/mmx.md | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/config/i386/mmx.md b/gcc/config/i386/mmx.md
> index d662663a445..eaca71d5750 100644
> --- a/gcc/config/i386/mmx.md
> +++ b/gcc/config/i386/mmx.md
> @@ -1839,7 +1839,7 @@
>     (set_attr "mode" "DI")])
>
>  (define_int_iterator EMMS
> -  [(UNSPECV_EMMS "TARGET_MMX")
> +  [(UNSPECV_EMMS "TARGET_MMX || TARGET_MMX_WITH_SSE")
>     (UNSPECV_FEMMS "TARGET_3DNOW")])
>
>  (define_int_attr emms
> @@ -1865,7 +1865,9 @@
>     (clobber (reg:DI MM6_REG))
>     (clobber (reg:DI MM7_REG))]
>    ""
> -  "<emms>"
> +{
> +  return TARGET_MMX ? "<emms>" : "";
>
> +}
>    [(set_attr "type" "mmx")
>     (set_attr "modrm" "0")
>     (set_attr "memory" "none")])
> --
> 2.20.1
>