No, we didn't undo the optimization.

We just disallow move pattern for (set (reg) (VL_REGNUM)).




juzhe.zhong@rivai.ai
 
From: Robin Dapp
Date: 2024-01-22 19:25
To: Juzhe-Zhong; gcc-patches
CC: rdapp.gcc; kito.cheng; kito.cheng; jeffreyalaw
Subject: Re: [PATCH] RISC-V: Fix regressions due to 86de9b66480b710202a2898cf513db105d8c432f
 
Hi Juzhe,
 
in principle this seems ok to me but I wonder about:
 
> We shouldn't worry about subreg:...VL_REGNUM since it's impossible
> that we can have such situation,
 
I think we allow this in legitimize_move for situations like
(subreg:SI (reg:V4QI)).  That was not added for correctness but
optimization - are we sure we don't undo this optimization with
that change?
 
Regards
Robin