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Re: [PATCH 1/2, x86] Add palignr support for AVX2.


On Mon, Apr 28, 2014 at 9:08 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Apr 28, 2014 at 9:48 AM, Evgeny Stupachenko <evstupac@gmail.com> wrote:
>> Hi,
>>
>> The patch enables use of "palignr with perm" instead of "2 pshufb, or
>> and perm" at AVX2 for some cases.
>>
>> Bootstrapped and passes make check on x86.
>>
>> Is it ok?
>>
>> 2014-04-28  Evgeny Stupachenko  <evstupac@gmail.com>
>>
>>         * config/i386/i386.c (expand_vec_perm_1): Try AVX2 vpshufb.
>>         * config/i386/i386.c (expand_vec_perm_palignr): Extend to use AVX2
>>         PALINGR instruction.
>
> Can you add testcases to verify that AVX2 vpshufb and paligngr are
> properly generated?

One of next patches will have test case.

>
>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>> index 88142a8..ae80477 100644
>> --- a/gcc/config/i386/i386.c
>> +++ b/gcc/config/i386/i386.c
>> @@ -42807,6 +42807,8 @@ expand_vec_perm_pshufb (struct expand_vec_perm_d *d)
>>    return true;
>>  }
>>
>> +static bool expand_vec_perm_vpshufb2_vpermq (struct expand_vec_perm_d *d);
>> +
>>  /* A subroutine of ix86_expand_vec_perm_builtin_1.  Try to instantiate D
>>     in a single instruction.  */
>>
>> @@ -42946,6 +42948,10 @@ expand_vec_perm_1 (struct expand_vec_perm_d *d)
>>    if (expand_vec_perm_pshufb (d))
>>      return true;
>>
>> +  /* Try the AVX2 vpshufb.  */
>> +  if (expand_vec_perm_vpshufb2_vpermq (d))
>> +    return true;
>> +
>>    /* Try the AVX512F vpermi2 instructions.  */
>>    rtx vec[64];
>>    enum machine_mode mode = d->vmode;
>> @@ -43004,7 +43010,7 @@ expand_vec_perm_pshuflw_pshufhw (struct
>> expand_vec_perm_d *d)
>>  }
>>
>>  /* A subroutine of ix86_expand_vec_perm_builtin_1.  Try to simplify
>> -   the permutation using the SSSE3 palignr instruction.  This succeeds
>> +   the permutation using the SSSE3/AVX2 palignr instruction.  This succeeds
>>     when all of the elements in PERM fit within one vector and we merely
>>     need to shift them down so that a single vector permutation has a
>>     chance to succeed.  */
>> @@ -43015,14 +43021,20 @@ expand_vec_perm_palignr (struct expand_vec_perm_d *d)
>>    unsigned i, nelt = d->nelt;
>>    unsigned min, max;
>>    bool in_order, ok;
>> -  rtx shift, target;
>> +  rtx shift, shift1, target, tmp;
>>    struct expand_vec_perm_d dcopy;
>>
>> -  /* Even with AVX, palignr only operates on 128-bit vectors.  */
>> -  if (!TARGET_SSSE3 || GET_MODE_SIZE (d->vmode) != 16)
>> +  /* PALIGNR of 2 256-bits registers on AVX2 costs only 2 instructions:
>> +     PERM and PALIGNR.  It is more profitable than 2 PSHUFB and PERM.
>> +     PALIGNR of 2 128-bits registers takes only 1 instrucion.  */
>> +  if (!TARGET_SSSE3 || (GET_MODE_SIZE (d->vmode) != 16 &&
>
>                        ^^^ This should
> be only on the next lined.
>
>> +      GET_MODE_SIZE (d->vmode) != 32))
>> +    return false;
>> +  /* Only AVX2 or higher support PALIGNR on 256-bits registers.  */
>> +  if (!TARGET_AVX2 && (GET_MODE_SIZE (d->vmode) == 32))
>                                          ^ No need for '(' here.
>
> Or you can use
>
> if ((!TARGET_SSSE3 || GET_MODE_SIZE (d->vmode) != 16)
>      && (!TARGET_AVX2 || GET_MODE_SIZE (d->vmode) != 32))
>
>>      return false;
>>
>> -  min = nelt, max = 0;
>> +  min = 2 * nelt, max = 0;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^  Will this change 128bit vector code?

No. The only case when all elements in permutation constant are equal
or greater than "nelt" will lead to canonization to one operand case
with all elements less than "nelt". So the change actually affects
nothing, but still more accurate.

>
>>    for (i = 0; i < nelt; ++i)
>>      {
>>        unsigned e = d->perm[i];
>> @@ -43041,9 +43053,34 @@ expand_vec_perm_palignr (struct expand_vec_perm_d *d)
>>
>>    dcopy = *d;
>>    shift = GEN_INT (min * GET_MODE_BITSIZE (GET_MODE_INNER (d->vmode)));
>> -  target = gen_reg_rtx (TImode);
>> -  emit_insn (gen_ssse3_palignrti (target, gen_lowpart (TImode, d->op1),
>> -                                 gen_lowpart (TImode, d->op0), shift));
>> +  shift1 = GEN_INT ((min - nelt / 2) *
>> +          GET_MODE_BITSIZE (GET_MODE_INNER (d->vmode)));
>> +
>> +  if (GET_MODE_SIZE (d->vmode) != 32)
>> +    {
>> +      target = gen_reg_rtx (TImode);
>> +      emit_insn (gen_ssse3_palignrti (target, gen_lowpart (TImode, d->op1),
>> +                                     gen_lowpart (TImode, d->op0), shift));
>> +    }
>> +  else
>> +    {
>> +      target = gen_reg_rtx (V2TImode);
>> +      tmp = gen_reg_rtx (V4DImode);
>> +      emit_insn (gen_avx2_permv2ti (tmp,
>> +                                   gen_lowpart (V4DImode, d->op0),
>> +                                   gen_lowpart (V4DImode, d->op1),
>> +                                   GEN_INT (33)));
>> +      if (min < nelt / 2)
>> +        emit_insn (gen_avx2_palignrv2ti (target,
>> +                                        gen_lowpart (V2TImode, tmp),
>> +                                        gen_lowpart (V2TImode, d->op0),
>> +                                        shift));
>> +      else
>> +       emit_insn (gen_avx2_palignrv2ti (target,
>> +                                        gen_lowpart (V2TImode, d->op1),
>> +                                        gen_lowpart (V2TImode, tmp),
>> +                                        shift1));
>> +    }
>>
>>    dcopy.op0 = dcopy.op1 = gen_lowpart (d->vmode, target);
>>    dcopy.one_operand_p = true;
>>
>>
>> Evgeny
>
>
>
> --
> H.J.


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