[Bug target/117850] GCC emits DUP, UMULL instead of UMULL2

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117850

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Spencer Abson <sab...@gcc.gnu.org>:

https://gcc.gnu.org/g:abf865732a7313cf79ffa325faed3467ed28d8b8

commit r16-2291-gabf865732a7313cf79ffa325faed3467ed28d8b8
Author: Spencer Abson <spencer.ab...@arm.com>
Date:   Tue Jul 15 10:12:08 2025 +0000

    aarch64: Fold builtins with highpart args to highpart equivalent [PR117850]

    Add a fold at gimple_fold_builtin to prefer the highpart variant of a
builtin
    if at least one argument is a vector highpart and all others are
VECTOR_CSTs
    that we can extend to 128-bits.

    For example, we prefer to duplicate f0 and use UMULL2 here over DUP+UMULL:

    uint16x8_t
    foo (const uint8x16_t s)
    {
        const uint8x8_t f0 = vdup_n_u8 (4);
        return vmull_u8 (vget_high_u8 (s), f0);
    }

    gcc/ChangeLog:
            PR target/117850
            * config/aarch64/aarch64-builtins.cc (LO_HI_PAIRINGS): New, group
the
            lo/hi pairs from aarch64-builtin-pairs.def.
            (aarch64_get_highpart_builtin): New function.
            (aarch64_v128_highpart_ref): New function, helper to look for
vector
            highparts.
            (aarch64_build_vector_cst): New function, helper to build
duplicated
            VECTOR_CSTs.
            (aarch64_fold_lo_call_to_hi): New function.
            (aarch64_general_gimple_fold_builtin): Add cases for the lo
builtins
            in aarch64-builtin-pairs.def.
            * config/aarch64/aarch64-builtin-pairs.def: New file, declare the
            parirs of lowpart-operating and highpart-operating builtins.

    gcc/testsuite/ChangeLog:
            PR target/117850
            * gcc.target/aarch64/simd/vabal_combine.c: Removed.  This is
            covered by fold_to_highpart_1.c
            * gcc.target/aarch64/simd/fold_to_highpart_1.c: New test.
            * gcc.target/aarch64/simd/fold_to_highpart_2.c: Likewise.
            * gcc.target/aarch64/simd/fold_to_highpart_3.c: Likewise.
            * gcc.target/aarch64/simd/fold_to_highpart_4.c: Likewise.
            * gcc.target/aarch64/simd/fold_to_highpart_5.c: Likewise.
            * gcc.target/aarch64/simd/fold_to_highpart_6.c: Likewise.