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

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

>
> 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
> >