[Bug rtl-optimization/103756] [12 Regression] -fcompare-debug failure (length) with -O -fconserve-stack -frename-registers -fno-tree-ch -fira-algorithm=priority since r12-5978-ga888259a71fbbb7f

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103756

--- Comment #3 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:6c684aa50d4eef28bb59ebb4664f362662845cd6

commit r12-6156-g6c684aa50d4eef28bb59ebb4664f362662845cd6
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Dec 30 22:25:34 2021 +0100

    regrename: Fix -fcompare-debug issue in find_rename_reg [PR103756]

    The r12-5978 change caused a -fcompare-debug issue, because without
    -g a chain might start with a noop move, but with -g there could be
    one or more DEBUG_INSNs in the chain before the noop move and so
    regrename could make different decisions between -g and -g0.

    Note, I must say I don't really understand the original change much,
    if we want to make sure the noop moves are removed, couldn't regrename
    during building of those du chains simply remove the noop moves instead?

    2021-12-30  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/103756
            * regrename.c (find_rename_reg): Test noop_move_p on the first
            non-debug insn in the chain rather than on the first insn.

            * g++.dg/opt/pr103756.C: New test.