[PATCH] Ensure vcond* expansion doesn't fail on x86 (PR target/50310)

[Uros Bizjak]

On Wed, Sep 7, 2011 at 10:01 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Wed, Sep 07, 2011 at 09:54:03PM +0200, Uros Bizjak wrote:
>> > 2011-09-07  Jakub Jelinek  <jakub@redhat.com>
>> >
>> >        PR target/50310
>> >        * config/i386/i386.c (ix86_prepare_sse_fp_compare_args): For
>> >        TARGET_AVX return code for LTGT and UNEQ.
>> >        (ix86_expand_fp_vcond): Handle LTGT and UNEQ.
>> >
>> >        * gcc.c-torture/execute/ieee/pr50310.c: New test.
>> >        * gcc.dg/pr50310-2.c: New test.
>>
>> Please put early exit for TARGET_SSE at the beginning of
>> ix86_prepare_sse_fp_compare_args function. There is really no need to
>
> You mean for TARGET_AVX, right?
>
>> swap operands - and to help reload, since AVX instructions are
>> three-operand instructions.
>>
>> OK for mainline with this change.
>
> Here is the updated patch, I'll bootstrap/regtest it now.
>
> 2011-09-07  Jakub Jelinek  <jakub@redhat.com>
>
>        PR target/50310
>        * config/i386/i386.c (ix86_prepare_sse_fp_compare_args): Return
>        code early if TARGET_AVX.
>        (ix86_expand_fp_vcond): Handle LTGT and UNEQ.
>
>        * gcc.c-torture/execute/ieee/pr50310.c: New test.
>        * gcc.dg/pr50310-2.c: New test.
>
> --- gcc/config/i386/i386.c.jj   2011-09-02 16:29:38.000000000 +0200
> +++ gcc/config/i386/i386.c      2011-09-07 21:57:52.000000000 +0200
> @@ -18304,6 +18304,11 @@ ix86_prepare_sse_fp_compare_args (rtx de
>  {
>   rtx tmp;
>
> +  /* AVX supports all the needed comparisons, no need to swap arguments
> +     nor help reload.  */
> +  if (TARGET_AVX)
> +    return code;
> +

Unfortunately, this part prevents generation of vmin/vmax instructions
for TARGET_AVX. In ix86_expand_fp_movcc, we call
ix86_prepare_sse_fp_compare_args, where we previously converted GT
into LT. LT is recognized in ix86_expand_sse_fp_minmax as valid
operand for MIN/MAX, whereas GT is not.

I'm not sure if we can swap operands in ix86_expand_sse_fp_minmax,
there is a scary comment  in front of ix86_expand_sse_fp_minmax w.r.t.
to IEEE safety.

The test is gcc.target/i386/ssefp-?.c, please compile it with "-O2 -mavx".

Uros.