[Bug target/116044] [15 Regression] GCN vs. rtl-ssa: Avoid using a stale splay tree root [PR116009]

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116044

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:72fbd3b2b2a497dbbe6599239bd61c5624203ed0

commit r15-2298-g72fbd3b2b2a497dbbe6599239bd61c5624203ed0
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Jul 25 08:54:22 2024 +0100

    rtl-ssa: Fix split_clobber_group tree insertion [PR116044]

    PR116044 is a regression in the testsuite on AMD GCN caused (again)
    by the split_clobber_group code.  The first patch in this area
    (g:71b31690a7c52413496e91bcc5ee4c68af2f366f) fixed a bug caused
    by carrying the old group over as one of the split ones.  That
    patch instead:

    - created two new groups
    - inserted them in the splay tree as neighbours of the old group
    - removed the old group, and
    - invalidated the old group (to force lazy recomputation when
      a clobber's parent group is queried)

    However, this left add_def trying to insert the new definition
    relative to a stale splay tree root.  The second patch
    (g:34f33ea801563e2eabb348e8d3e9344a91abfd48) attempted to fix
    that by inserting it relative to the new root.  But that's not
    always correct either.  We specifically want to insert it after
    the first of the two new groups, whether that group is the root
    or not.

    This patch does that, and tries to refactor the code to make
    it a bit less brittle.

    gcc/
            PR rtl-optimization/116044
            * rtl-ssa/functions.h (function_info::split_clobber_group): Return
            an array of two clobber_groups.
            * rtl-ssa/accesses.cc (function_info::split_clobber_group): Return
            the new clobber groups.  Don't modify the splay tree here.
            (function_info::add_def): Update call accordingly.  Generalize
            the splay tree insertion code so that the new definition can be
            inserted as a child of any existing node, not just the root.
            Fix the insertion used after calling split_clobber_group.