Hi, Richards.

Could you take a look at this patch:
https://gcc.gnu.org/pipermail/gcc-patches/2023-May/618241.html 

Thanks


juzhe.zhong@rivai.ai
 
From: Richard Sandiford
Date: 2023-05-11 20:42
To: juzhe.zhong\@rivai.ai
CC: gcc-patches; rguenther
Subject: Re: [PATCH V4] VECT: Add decrement IV iteration loop control by variable amount support
"juzhe.zhong@rivai.ai" <juzhe.zhong@rivai.ai> writes:
> Thanks. I have read rgroup descriptions again.
> Still I am not fully understand it clearly, bear with me :)
>
> I don't known how to differentiate Case 2 and Case 3.
>
> Case 2 is multiple rgroup for SLP.
> Case 3 is multiple rgroup for non-SLP (VEC_PACK_TRUNC)
>
> Is it correct:
> case 2: rgc->max_nscalarper_iter != 1
 
Yes.
 
> Case 3 : rgc->max_nscalarper_iter == 1 but rgc->factor != 1?
 
For case 3 it's:
 
rgc->max_nscalars_per_iter == 1 && rgc != &LOOP_VINFO_LENS (loop_vinfo)[0]
 
rgc->factor is controlled by the target and just says what units
IFN_LOAD_LEN works in.  E.g. if we're loading 16-byte elements,
but the underlying instruction measures bytes, the factor would be 2.
 
Thanks,
Richard