Re: [PATCH v2] aarch64: Canonicalize halving-add builtins [PR122715]

On Sat, Aug 15, 2026 at 06:23:08PM -0700, Andrea Pinski wrote:
> On Sat, Aug 15, 2026 at 3:25 PM Odysseas Georgoudis <[email protected]> wrote:
> >
> > Thanks for pointing me to Eikansh's earlier patch and the SME issue.
> >
> > Would delaying the canonicalization until after inlining be an
> > acceptable way to handle it?  This keeps the target builtins visible
> > while AArch64 IPA records their PSTATE.SM requirements, after which
> > they can be converted to IFN_AVG_FLOOR or IFN_AVG_CEIL
> >
> > The attached v2 retains both the signed and unsigned canonicalizations
> > and implements that approach.  I also added a focused SME regression
> > test for the unsigned rounding-add path.
> >
> > Tested with an aarch64-linux-gnu cross compiler.  The targeted PR
> > tests, the new SME test, and the existing arm_neon_1.c,
> > arm_neon_2.c, and arm_neon_3.c tests pass.
> 
> I am ok with the addition of the after inlining check. Let's see if
> the other aarch64 maintainers are ok with adding the after inlining
> check too.
> 
> Thanks,
> Andrea

I believe I have a fix for the inlining bug, which I intend to post later once
I've gathered up a couple more test cases and written it up.  Perhaps we can
see if that's sufficient to exclude the proposed inlining check in this patch.

Thanks,
Alice

> 
> >
> > Thanks
> > Odysseas
> >
> > ________________________________
> > From: Andrea Pinski <[email protected]>
> > Sent: 15 August 2026 02:52
> > To: Odysseas Georgoudis <[email protected]>
> > Cc: [email protected] <[email protected]>
> > Subject: Re: [PATCH] aarch64: Canonicalize halving-add builtins [PR122715]
> >
> > On Fri, Aug 14, 2026 at 5:33 PM Odysseas Georgoudis <[email protected]> wrote:
> > >
> > > The first two patches for PR122715 have been committed.  This patch
> > > handles the remaining AArch64 case.
> > >
> > > Advanced SIMD halving-add intrinsics remain target builtins in GIMPLE,
> > > preventing generic average simplifications from seeing them.  Canonicalize
> > > SHADD and UHADD to IFN_AVG_FLOOR, and SRHADD and URHADD to
> > > IFN_AVG_CEIL.
> > >
> > > This allows equal operands to be folded by the existing match.pd rule
> > > while retaining optab-based instruction selection for other operands.
> > >
> > > Tested with an aarch64-linux-gnu cross compiler.  The targeted tests
> > > pass.
> >
> > This does not fully work.
> > In fact is is the same as Eikansh's patch (except adding the signed ones):
> > https://inbox.sourceware.org/gcc-patches/[email protected]/
> >
> > The reason why it does not work is mentioned here:
> > https://inbox.sourceware.org/gcc-patches/CALvbMcAPZu5dupGfA=3GtS8avmzzPScYMy8SrRRQxTQhakhpKw@mail.gmail.com/
> > Basically gcc.target/aarch64/sme/arm_neon_1.c is no longer rejected
> > when it should be.
> >
> > Eikansh was still looking into how to fix the issue mentioned but has
> > not yet come up with a patch. He has been busy working on other
> > things.
> > If you want to look into how to resolve that issue that would be nice.
> >
> > Note the compile farm has a few aarch64 machines which you can use to
> > do a bootstrap test.
> > See https://gcc.gnu.org/wiki/CompileFarm on how to sign up (this is
> > seperate from GCC but is used by many GCC developers and had been
> > associated with GCC development for a long time now).
> >
> > Thanks,
> > Andrea
> >
> >
> > >
> > > Thanks,
> > > Odysseas
> > >