[Bug tree-optimization/126099] BB vectorization SLP subgraphs are not merged

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126099

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <[email protected]>:

https://gcc.gnu.org/g:adc20f13b60f90c6a55d46fc6be37dfb9f4b86a0

commit r17-3222-gadc20f13b60f90c6a55d46fc6be37dfb9f4b86a0
Author: Richard Biener <[email protected]>
Date:   Mon Aug 3 19:54:47 2026 +0200

    tree-optimization/126099 - SLP subgraph merging with low/highpart extracts

    The following implements merging of SLP subgraphs that overlap in
    their vectors low or highparts or in full vector copies using VEC_PERM
    SLP nodes which know how to perform these extractions, but not more
    in general.

    The operation is to build a reverse mapping of scalar stmt to SLP node
    for possible extraction starts - without knowing the extraction vector
    type that's even lanes of SLP nodes with an even number of lanes.  And
    then for each SLP node lane zero checking whether it's fully contained
    in one of the candidates with the restrictions implied by
    vectorizable_slp_permutation.

    The motivating testcase is in PR126053 coming from 508.namd_r.  The
    testcases gcc.dg/vect/bb-slp-pr126099-{4,5}.c are cases where schedule
    verification strips one of the graph entries as subgraph merging
    otherwise causes SSA verification failures.

            PR tree-optimization/126099
            PR tree-optimization/126053
            * tree-vect-slp.cc (vect_cse_gather_part_starts): New function.
            (vect_cse_slp_node_parts): Likewise.
            (vect_optimize_slp): For BB SLP CSE to low/highparts of
            other nodes.

            * gcc.dg/vect/bb-slp-pr126099-1.c: New testcase.
            * gcc.dg/vect/bb-slp-pr126099-2.c: Likewise.
            * gcc.dg/vect/bb-slp-pr126099-3.c: Likewise.
            * gcc.dg/vect/bb-slp-pr126099-4.c: Likewise.
            * gcc.dg/vect/bb-slp-pr126099-5.c: Likewise.
            * gcc.dg/vect/costmodel/x86_64/costmodel-pr126053.c: Likewise.