OK. Thanks. I am gonna refine the patch following Richard's idea and test it.
Thanks both Richard and Richi.



juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2023-05-24 20:51
To: Richard Sandiford
CC: 钟居哲; gcc-patches
Subject: Re: [PATCH V12] VECT: Add decrement IV iteration loop control by variable amount support
On Wed, 24 May 2023, Richard Sandiford wrote:
 
> Sorry, I realised later that I had an implicit assumption here:
> if there are multiple rgroups, it's better to have a single IV
> for the smallest rgroup and scale that up to bigger rgroups.
> 
> E.g. if the loop control IV is taken from an N-control rgroup
> and has a step S, an N*M-control rgroup would be based on M*S.
> 
> Of course, it's also OK to create multiple IVs if you prefer.
> It's just a question of which approach gives the best output
> in practice.
 
One thing to check is whether IVOPTs is ever able to eliminate
one such IV using another.  You can then also check whether
when presented with a single IV it already considers the
others you can create as candidates so you get the optimal
selection in the end.
 
Richard.