Re: [PATCH] Optimize nested permutation to single VEC_PERM_EXPR [PR54346]

[Lulu Cheng <chenglulu@loongson.cn>]

在 2022/10/13 下午7:10, Richard Biener 写道:
> On Thu, Oct 13, 2022 at 10:16 AM Lulu Cheng <chenglulu@loongson.cn> wrote:
>>
>> 在 2022/10/13 下午2:44, Xi Ruoyao 写道:
>>> On Thu, 2022-10-13 at 14:15 +0800, Levy wrote:
>>>> Hi RuoYao
>>>>
>>>> It’s probably because loongarch64 doesn’t support
>>>> can_vec_perm_const_p(result_mode, op_mode, sel2, false)
>>>>
>>>> I’m not sure whether if loongarch will support it or should I just
>>>> limit the test target for pr54346.c?
>>> I'm not sure if we can add TARGET_VECTORIZE_VEC_PERM_CONST when we don't
>>> actually support vector.  (LoongArch has SIMD instructions but the
>>> support in GCC won't be added in a very recent future.)
>>>
>> If what I understand is correct, I think this might be a better solution.
>>
>>    /* { dg-do compile } */
>>
>> +/* { dg-require-effective-target vect_perm } */
>>    /* { dg-options "-O -fdump-tree-dse1" } */
> Btw, what forwprop does is check whether any of the original permutations are
> not supported and then elide the supportability check for the result.
> The reasoning
> is that the original permute(s) would be lowered during vectlower so we can as
> well do that for the result.  We should just never turn a supported permutation
> sequence into a not supported one.
>
> Richard.
>
Hi Richard:

I'm very sorry. I don't fully understand what you mean.

Could you give me some more details?


Thanks!

Lulu Cheng