Re: [PATCH] Vect: use a small step to calculate induction for the unrolled loop (PR tree-optimization/110449)

[Hao Liu OS <hliu@os.amperecomputing.com>]

Hi Jeff,

Thanks for your help.

Actually I have write access as I was added to the "contributor list". Anyway, that's very kind of you to help committing the patch.

Thanks,
-Hao
________________________________________
From: Jeff Law <jeffreyalaw@gmail.com>
Sent: Friday, July 7, 2023 0:06
To: Richard Biener; Hao Liu OS
Cc: GCC-patches@gcc.gnu.org
Subject: Re: [PATCH] Vect: use a small step to calculate induction for the unrolled loop (PR tree-optimization/110449)



On 7/6/23 06:44, Richard Biener via Gcc-patches wrote:
> On Wed, Jul 5, 2023 at 8:44 AM Hao Liu OS via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi,
>>
>> If a loop is unrolled by n times during vectoriation, two steps are used to
>> calculate the induction variable:
>>    - The small step for the unrolled ith-copy: vec_1 = vec_iv + (VF/n * Step)
>>    - The large step for the whole loop: vec_loop = vec_iv + (VF * Step)
>>
>> This patch calculates an extra vec_n to replace vec_loop:
>>    vec_n = vec_prev + (VF/n * S) = vec_iv + (VF/n * S) * n = vec_loop.
>>
>> So that we can save the large step register and related operations.
>
> OK.  It would be nice to avoid the dead stmts created earlier though.
>
> Thanks,
> Richard.
>
>> gcc/ChangeLog:
>>
>>          PR tree-optimization/110449
>>          * tree-vect-loop.cc (vectorizable_induction): use vec_n to replace
>>          vec_loop for the unrolled loop.
>>
>> gcc/testsuite/ChangeLog:
>>
>>          * gcc.target/aarch64/pr110449.c: New testcase.
I didn't see Hao Liu in the MAINTAINERS file, so probably doesn't have
write access.  Therefore I went ahead and pushed this for Hao.

jeff