I am wondering whether we do have some situations that
vec_pack/vec_unpack/vec_widen_xxx/dot_prod pattern can be beneficial for RVV ?
I have ever met some situation that vec_unpack can be beneficial when working
on SELECT_VL but I don't which case....
juzhe.zh...@rivai.ai
From: Robin Dapp
Date: 2023-08-30 16:06
To: Richard Biener; juzhe.zh...@rivai.ai
CC: rdapp.gcc; gcc
Subject: Re: Question about wrapv-vect-reduc-dot-s8b.c
>> To fix it, is it necessary to support 'vec_unpack' ?
>
> both same units would be sext, not vec_unpacks_{lo,hi} - the vectorizer
> ties its hands by choosing vector types early and based on the number
> of incoming/outgoing vectors it chooses one or the other method.
>
> More precise dumping would probably help here but somewhere earlier you
> should be able to see the vector type used for _2
We usually try with a "normal" mode like VNx4SI (RVVM1SI or so) and
then switch to VNx4QI (i.e. a mode that only determines the number of
units/elements) and have vectorize_related_mode return modes with the
same number of units. This will then result in the sext/zext patterns
matching. The first round where we try the normal mode will not match
those because the related mode has a different number of units.
So it's somewhat expected that the first try fails.
My dump shows that we vectorize, so IMHO no problem. I can take a look
at this but it doesn't look like a case for pack/unpack.
Regards
Robin
