https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96836
Bug ID: 96836
Summary: [MVE] Consider using define_subst for predicatable
operations
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: rsandifo at gcc dot gnu.org
CC: ktkachov at gcc dot gnu.org, ramana at gcc dot gnu.org,
rearnsha at gcc dot gnu.org
Target Milestone: ---
Target: arm*-*-*
Created attachment 49147
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49147&action=edit
Proof of concept patch.
[This is really just an idea rather than a PR.]
At the moment we use separate patterns for the predicated and
unpredicated forms of MVE instructions. The predicated ones
have a VPST instruction built in.
This works well, but we might want to consider using define_subst
to define both the predicated and unpredicated forms at the same
time. As well as shortening the definition, it could help when
making future optimisations, such as:
- putting more than one instruction in the same VPST block
- using VPT instead of a combination of a comparison and a VPST
- using loop predication
I've attached a proof of concept that does this for one arbitrarily-
chosen intrinsic (vorrq_n). It's not worth submitting on its own,
it would only be useful as part of a wider move to this style.
(Equally, I don't think it would be necessary to convert everything
at once. We'd just need some indication that the approach is going
somewhere and won't stop at this one intrinsic.)
