[Bug debug/103742] [12 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions --param=early-inlining-insns=82 since r12-5301-g045206450386bcd7

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103742

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:e5acfcad98f3fa33e141f4e6bc06f7d7c13496e1

commit r12-6146-ge5acfcad98f3fa33e141f4e6bc06f7d7c13496e1
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Dec 29 21:46:21 2021 +0100

    tree-ssa-dce: Fix up -fcompare-debug failures in
make_forwarders_with_degenerate_phis [PR103742]

    make_forwarders_with_degenerate_phis causes a -fcompare-debug failure on
the
    following testcase.
    The problem is that on:
      # iftmp.4_8 = PHI <&D.2582(6), &D.2583(4), &D.2582(7), &D.2583(5)>
    the exact DECL_UIDs are different between -g and -g0 (which is ok, with -g
    the decls can have larger gaps in between the uids), which means
    iterative_hash_expr is different and because there are 2 pairs of edges
    with matching phi arguments, the function processes them in different
    orders.
    The following patch fixes it by using the iterative_hash_expr order
    only to determine which arguments are the same, then replaces the hashes
    with the minimum dest_idx in the set of matching arguments and qsorts
    again (which makes it stable for -fcompare-debug) and only splits edges
etc.
    on that stable order.
    As a small optimization, if no arguments are equal, it doesn't do the
    second qsort and continues, and if all arguments of the PHI are
    constants or SSA_NAMEs (I think that is a pretty common case for many
    PHIs), then it doesn't do the second qsort either, because in that case
    the hash values will be stable, only computed from the constant values or
    SSA_NAME_VERSIONs.

    2021-12-29  Jakub Jelinek  <jakub@redhat.com>

            PR debug/103742
            * tree-ssa-dce.c (make_forwarders_with_degenerate_phis): If any phi
            argument is not CONSTANT_CLASS_P or SSA_NAME and any arguments are
            equal, change second from hash value to lowest dest_idx from the
            edges which have equal argument and resort to ensure
-fcompare-debug
            stability.

            * g++.dg/opt/pr103742.C: New test.