> -----Original Message-----
> From: Alex Coplan <[email protected]>
> Sent: 06 May 2026 15:06
> To: Tamar Christina <[email protected]>
> Cc: [email protected]; nd <[email protected]>; Richard Earnshaw
> <[email protected]>; [email protected];
> [email protected]; Wilco Dijkstra
> <[email protected]>; Alice Carlotti <[email protected]>
> Subject: Re: [PATCH]AArch64: Turn on GPR narrowing pass by default
>
> On 06/05/2026 14:39, Tamar Christina wrote:
> > > -----Original Message-----
> > > From: Alex Coplan <[email protected]>
> > > Sent: 06 May 2026 14:15
> > > To: Tamar Christina <[email protected]>
> > > Cc: [email protected]; nd <[email protected]>; Richard Earnshaw
> > > <[email protected]>; [email protected];
> > > [email protected]; Wilco Dijkstra
> > > <[email protected]>; Alice Carlotti <[email protected]>
> > > Subject: Re: [PATCH]AArch64: Turn on GPR narrowing pass by default
> > >
> > > On 06/05/2026 14:00, Tamar Christina wrote:
> > > > This turns on the GPR narrowing pass for all AArch64 targets.
> > >
> > > In principle this sounds good, although maybe it should go in after
> > > Soumya's fix for PR124895 to minimize noise for folks that are testing
> > > the trunk.
> >
> > Sure, I'll wait for that fix to be committed.
> >
> > >
> > > >
> > > > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> > > >
> > > > Any objections?
> > > >
> > > > Thanks,
> > > > Tamar
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * config/aarch64/aarch64-tuning-flags.def
> > > > (AARCH64_EXTRA_TUNE_BASE): Add
> > > AARCH64_EXTRA_TUNE_NARROW_GP_WRITES.
> > > >
> > > > ---
> > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def
> > > b/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > index
> > >
> 882daa4b4312039f96dcde1295179be3ab3da0d0..058dadecccaac458e30a
> > > 6585b558581a7bef6f54 100644
> > > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > @@ -67,7 +67,8 @@ AARCH64_EXTRA_TUNING_OPTION
> > > ("cheap_fpmr_write", CHEAP_FPMR_WRITE)
> > > >
> > > > /* Baseline tuning settings suitable for all modern cores. */
> > > > #define AARCH64_EXTRA_TUNE_BASE
> > > (AARCH64_EXTRA_TUNE_CHEAP_SHIFT_EXTEND \
> > > > - |
> > > AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA)
> > > > + |
> > > AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA \
> > > > + |
> > > AARCH64_EXTRA_TUNE_NARROW_GP_WRITES)
> > >
> > > Doesn't this render the tuning flag obsolete? Presumably we could remove
> > > the flag entirely and instead just adjust the default to 1 for
> > > -mnarrow-gp-writes in aarch64.opt (simplifying the logic in
> > > pass_narrow_gp_writes::gate accordingly)?
> >
> > I think we should remove `-mnarrow-gp-writes` entirely. With it on by
> default
> > It can be disabled with the pass manager's standard -fdisable-rtl-
> narrow_gp_writes
> > so there's no need to the target option anymore.
>
> I don't think the -m option can just be removed, since it is already present
> in
> the GCC 16 release.
Flags can always be deprecated and removed. We've done so before.
That said I had expected this flag to be marked with "Undocumented" as it has
no point as a user visible flag.
It's basically replicating -fenable-rtl-narrow_gp_writes would have worked fine
to
enable it, and that is already maintained... So next time I don't think we
should
add an m option that just turns on a pass..
>
> >
> > This would also be more inline with other generic passes. Or do you see a
> value in
> > having it?
> >
> > >
> > > Or would you prefer to keep it so that the pass can be turned off for
> > > particular cores if required / to minimize churn in case a reversion is
> > > needed?
> > >
> >
> > I wanted to keep a way to disable it since I don't know if it'll do anything
> > weird on partner cores. So I think I'd like the tune for now, but when/if
> > this moves to a middle-end pass to drop it.
>
> That's fair enough, let's keep the tune flag in that case, so the original
> patch
> is OK from my POV.
Cool,
Tamar
>
> Thanks,
> Alex
>
> >
> > So I'll respin dropping the `-m` flag if you agree.
>
> >
> > Thanks,
> > Tamar
> >
> > > Thanks,
> > > Alex
> > >
> > > >
> > > > /* Enables dispatch scheduling. */
> > > > AARCH64_EXTRA_TUNING_OPTION ("dispatch_sched",
> DISPATCH_SCHED)
> > > >
> > > >
> > > > --
> > >
> > > > diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def
> > > b/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > index
> > >
> 882daa4b4312039f96dcde1295179be3ab3da0d0..058dadecccaac458e30a
> > > 6585b558581a7bef6f54 100644
> > > > --- a/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > +++ b/gcc/config/aarch64/aarch64-tuning-flags.def
> > > > @@ -67,7 +67,8 @@ AARCH64_EXTRA_TUNING_OPTION
> > > ("cheap_fpmr_write", CHEAP_FPMR_WRITE)
> > > >
> > > > /* Baseline tuning settings suitable for all modern cores. */
> > > > #define AARCH64_EXTRA_TUNE_BASE
> > > (AARCH64_EXTRA_TUNE_CHEAP_SHIFT_EXTEND \
> > > > - |
> > > AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA)
> > > > + |
> > > AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA \
> > > > + |
> > > AARCH64_EXTRA_TUNE_NARROW_GP_WRITES)
> > > >
> > > > /* Enables dispatch scheduling. */
> > > > AARCH64_EXTRA_TUNING_OPTION ("dispatch_sched",
> DISPATCH_SCHED)
> > > >
> >
