[PATCH V14] VECT: Add decrement IV iteration loop control by variable amount support

[钟居哲]

Oh. I see. Thank you so much for pointing this.
Could you tell me what I should do in the codes?
It seems that I should adjust it in 
vect_adjust_loop_lens_control

muliply by some factor ? Is this correct multiply by max_nscalars_per_iter
?
Thanks.


juzhe.zhong@rivai.ai
 
From: Richard Sandiford
Date: 2023-05-24 23:47
To: 钟居哲
CC: gcc-patches; rguenther
Subject: Re: [PATCH V14] VECT: Add decrement IV iteration loop control by variable amount support
钟居哲 <juzhe.zhong@rivai.ai> writes:
> Hi, Richard. I still don't understand it. Sorry about that.
>
>>>  loop_len_48 = MIN_EXPR <loop_len_34 * 2, 4>;
>   >>   _74 = loop_len_34 * 2 - loop_len_48;
>
> I have the tests already tested.
> We have a MIN_EXPR to calculate the total elements:
> loop_len_34 = MIN_EXPR <ivtmp_72, 8>;
> I think "8" is already multiplied by 2?
>
> Why do we need loop_len_34 * 2 ?
> Could you give me more informations, The similiar tests you present we already have
> execution check and passed. I am not sure whether this patch has the issue that I didn't notice.
 
Think about the maximum values of each SSA name:
 
   loop_len_34 = MIN_EXPR <ivtmp_72, 8>;       // MAX 8
   loop_len_48 = MIN_EXPR <loop_len_34, 4>;    // MAX 4
   _74 = loop_len_34 - loop_len_48;            // MAX 4
   loop_len_49 = MIN_EXPR <_74, 4>;            // MAX 4 (always == _74)
   _75 = _74 - loop_len_49;                    // 0
   loop_len_50 = MIN_EXPR <_75, 4>;            // 0
   loop_len_51 = _75 - loop_len_50;            // 0
 
So the final two y vectors will always have 0 controls.
 
Thanks,
Richard