[Bug tree-optimization/108724] [11/12 Regression] Poor codegen when summing two arrays without AVX or SSE

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108724

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:21e7145aaf582c263e69a3ee05dfa9d42bdbd1aa

commit r12-9258-g21e7145aaf582c263e69a3ee05dfa9d42bdbd1aa
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Feb 10 11:07:30 2023 +0100

    tree-optimization/108724 - vectorized code getting piecewise expanded

    This fixes an oversight to when removing the hard limits on using
    generic vectors for the vectorizer to enable both SLP and BB
    vectorization to use those.  The vectorizer relies on vector lowering
    to expand plus, minus and negate to bit operations but vector
    lowering has a hard limit on the minimum number of elements per
    work item.  Vectorizer costs for the testcase at hand work out
    to vectorize a loop with just two work items per vector and that
    causes element wise expansion and spilling.

    The fix for now is to re-instantiate the hard limit, matching what
    vector lowering does.  For the future the way to go is to emit the
    lowered sequence directly from the vectorizer instead.

            PR tree-optimization/108724
            * tree-vect-stmts.cc (vectorizable_operation): Avoid
            using word_mode vectors when vector lowering will
            decompose them to elementwise operations.

            * gcc.target/i386/pr108724.c: New testcase.

    (cherry picked from commit dc87e1391c55c666c7ff39d4f0dea87666f25468)