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
>