Re: [PATCH v1] RISC-V: Revert RVV wv instructions overlap and xfail tests

[Jeff Law <jeffreyalaw@gmail.com>]

On 4/22/24 4:07 PM, 钟居哲 wrote:
> Apologize that we didn't post our (me, kito and Li Pan) disscussions.
> 
> This is the story:
> We found that my previous patches which support highpart register 
> overlap with register filter for instructions like (vwadd.wv)
> cause ICE reported by:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114714 <https:// 
> gcc.gnu.org/bugzilla/show_bug.cgi?id=114714>
> and this is obviously a regression (No ICE on GCC 13.2, but ICE on GCC 14)
Just a note for the future, this wouldn't really be considered a 
regression since GCC-13 didn't have any vector support.  I'm happy to 
help with this kind of judgment call, as are many other GCC developers 
such as Jakub, Richi, etc.  We've been making these kinds of judgment 
calls for decades.

> 
> We have tried several fixes to work around this ICE, however, we failed.
> And also I found my previous patches are quite wrong which is not the 
> perfect solution to support register group overlap
> for vwadd.wv.
> So, finally we decide to revert those patches.
It would have been useful to bring others into the discussion.  Both 
Robin and I would have likely wanted to understand why disabling the 
alternative wasn't sufficient.

Looking at this more generally, we need to keep in mind that the closer 
we get to a release, the more careful we need to be.  We can take the 
time to bring more engineers into the technical discussion.  We can take 
the time to evaluate the pros/cons of different approaches and balance 
them against the needs of the upcoming release and other factors that 
may come into play.

So let's learn, adjust & move on.

Thanks,
jeff