[Bug target/110625] [14 Regression][AArch64] Vect: SLP fails to vectorize a loop as the reduction_latency calculated by new costs is too large

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110625

--- Comment #22 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Bisected the remaining regression to:

dd86a5a69cbda40cf76388a65d3317c91cb2b501 is the first bad commit
commit dd86a5a69cbda40cf76388a65d3317c91cb2b501
Author: Richard Biener <rguent...@suse.de>
Date:   Thu Jun 22 11:40:46 2023 +0200

    tree-optimization/96208 - SLP of non-grouped loads

    The following extends SLP discovery to handle non-grouped loads
    in loop vectorization in the case the same load appears in all
    lanes.

It looks like our cost model doesn't handle this change correctly,
so we over-vectorize MorphologyApply.constprop.0.  The resulting
code is significantly slower due to all the lane shufflings to
prepare the vector.

Reducing a testcase...