Re: [PATCH] LoongArch: Rework bswap{hi,si,di}2 definition

[Lulu Cheng <chenglulu@loongson.cn>]

在 2024/7/31 下午6:25, Xi Ruoyao 写道:
> On Wed, 2024-07-31 at 16:57 +0800, Lulu Cheng wrote:
>> 在 2024/7/29 下午3:58, Xi Ruoyao 写道:
>>> Per a gcc-help thread we are generating sub-optimal code for
>>> __builtin_bswap{32,64}.  To fix it:
>>>
>>> - Use a single revb.d instruction for bswapdi2.
>>> - Use a single revb.2w instruction for bswapsi2 for TARGET_64BIT,
>>>      revb.2h + rotri.w for !TARGET_64BIT.
>>> - Use a single revb.2h instruction for bswapsi2 (x) r>> 16, and a single
>>>      revb.2w instruction for bswapdi2 (x) r>> 32.
>>>
>>> Unfortunately I cannot figure out a way to make the compiler generate
>>> revb.4h or revh.{2w,d} instructions.
>> This optimization is really ingenious and I have no problem.
>>
>> I also haven't figured out how to generate revb.4h or revh. {2w,d}.
>> I think we can merge this patch first.
> Pushed r15-2433.
Ok. Thanks!
>
> FWIW I tried a naive pattern for revh.2w:
>
> (set (match_operand:DI 0 "register_operand" "=r")
>       (ior:DI
>         (and:DI
>           (ashift:DI (match_operand:DI 1 "register_operand" "r")
>                      (const_int 16))
>           (const_int 18446462603027742720))
>         (and:DI
>           (lshiftrt:DI (match_dup 1)
>                        (const_int 16))
>           (const_int 281470681808895))))
> But it seems too complex to be recognized.

I think it needs to be recognized as a bswap operation in the tree-bswap 
phase,

but it seems a bit difficult to be recognized

>