[Bug target/99293] Built-in vec_splat generates sub-optimal code for -mcpu=power10

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99293

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-15 branch has been updated by Michael Meissner
<meissner@gcc.gnu.org>:

https://gcc.gnu.org/g:9aabf931dde5120767b8ee60652489b6db95f41e

commit r15-11526-g9aabf931dde5120767b8ee60652489b6db95f41e
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Thu Aug 27 23:47:09 2026 -0400

    Backport PR target/99293

    We had optimizations for splat of a vector extract for the other vector
    types, but we missed having one for V2DI and V2DF.  This patch adds a
    combiner insn to do this optimization.

    In looking at the source, we had similar optimizations for V4SI and V4SF
    extract and splats, but we missed doing V2DI/V2DF.

    Without the patch for the code:

            vector long long splat_dup_l_0 (vector long long v)
            {
              return __builtin_vec_splats (__builtin_vec_extract (v, 0));
            }

    the compiler generates (on a little endian power9):

            splat_dup_l_0:
                    mfvsrld 9,34
                    mtvsrdd 34,9,9
                    blr

    Now it generates:

            splat_dup_l_0:
                    xxpermdi 34,34,34,3
                    blr

    This change was backported from the changes checked into the master
    branch on 2026-08-03.

    2026-08-27  Michael Meissner  <meissner@linux.ibm.com>

    gcc/

            PR target/99293
            * config/rs6000/vsx.md (vsx_splat_extract_<mode>): New insn.

    gcc/testsuite/

            PR target/99293
            * gcc.target/powerpc/pr99293.c: New test.
            * gcc.target/powerpc/builtins-1.c: Update instruction count.