[Bug rtl-optimization/115928] [15 regression] ICE on valid code at -O2 with "-fgcse-sm" on x86_64-linux-gnu: in merge_clobber_groups, at rtl-ssa/accesses.cc:757

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115928

--- Comment #1 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:71b31690a7c52413496e91bcc5ee4c68af2f366f

commit r15-2110-g71b31690a7c52413496e91bcc5ee4c68af2f366f
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Wed Jul 17 19:38:11 2024 +0100

    rtl-ssa: Fix split_clobber_group [PR115928]

    One of the goals of the rtl-ssa representation was to allow a
    group of consecutive clobbers to be skipped in constant time,
    with amortised sublinear insertion and deletion.  This involves
    putting consecutive clobbers in groups.  Splitting or joining
    groups would be linear if we had to update every clobber on
    each update, so the operation to query a clobber's group is
    lazy and (again) amortised sublinear.

    This means that, when splitting a group into two, we cannot
    reuse the old group for one side.  We have to invalidate it,
    so that the lazy clobber_info::group query can tell that something
    has changed.  The ICE in the PR came from failing to do that.

    gcc/
            PR rtl-optimization/115928
            * rtl-ssa/accesses.h (clobber_group): Add a new constructor that
            takes the first, last and root clobbers.
            * rtl-ssa/internals.inl (clobber_group::clobber_group): Define it.
            * rtl-ssa/accesses.cc (function_info::split_clobber_group): Use it.
            Allocate a new group for both sides and invalidate the previous
group.
            (function_info::add_def): After calling split_clobber_group,
            remove the old group from the splay tree.

    gcc/testsuite/
            PR rtl-optimization/115928
            * gcc.dg/torture/pr115928.c: New test.