[Bug tree-optimization/92822] [10 Regression] vfma_laneq_f32 and vmul_laneq_f32 are broken on aarch64 after r278938

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92822

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:1ee3b380dfb479b335f3b50039ce26abcbffe59a

commit r10-6280-g1ee3b380dfb479b335f3b50039ce26abcbffe59a
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Sat Jan 25 17:18:51 2020 +0000

    forwprop: Tweak choice of VEC_PERM_EXPR filler [PR92822]

    For the 2s failures in the PR, we have a V4SF VEC_PERM_EXPR in
    which the first two elements are duplicates of one element and
    the other two are don't-care:

        v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, ?, ? }>;

    The heuristic was to extend this with a blend:

        v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 2, 3 }>;

    but it seems better to extend a partial duplicate to a full duplicate:

        v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 1, 1 }>;

    Obviously this is still just a heuristic though.

    I wondered whether to restrict this to two elements or more
    but couldn't find any examples in which it made a difference.
    Either way should be fine for the purposes of fixing this PR.

    2020-01-28  Richard Sandiford  <richard.sandiford@arm.com>

    gcc/
        PR tree-optimization/92822
        * tree-ssa-forwprop.c (simplify_vector_constructor): When filling
        out the don't-care elements of a vector whose significant elements
        are duplicates, make the don't-care elements duplicates too.