[Bug tree-optimization/94329] [8/9/10 Regression] error: use_only.f90: ‘-fcompare-debug’ failure (length)

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94329

--- 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:679becf175c5d7f6b323cd3af0a09c6039b4123d

commit r10-7437-g679becf175c5d7f6b323cd3af0a09c6039b4123d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Mar 28 10:21:52 2020 +0100

    reassoc: Fix -fcompare-debug bug in reassociate_bb [PR94329]

    The following testcase FAILs with -fcompare-debug, because reassociate_bb
    mishandles the case when the last stmt in a bb has zero uses.  In that case
    reassoc_remove_stmt (like gsi_remove) moves the iterator to the next stmt,
    i.e. gsi_end_p is true, which means the code sets the iterator back to
    gsi_last_bb.  The problem is that the for loop does gsi_prev on that before
    handling the next statement, which means the former penultimate stmt, now
    last one, is not processed by reassociate_bb.
    Now, with -g, if there is at least one debug stmt at the end of the bb,
    reassoc_remove_stmt moves the iterator to that following debug stmt and we
    just do gsi_prev and continue with the former penultimate non-debug stmt,
    now last non-debug stmt.

    The following patch fixes that by not doing the gsi_prev in this case;
there
    are too many continue; cases, so I didn't want to copy over the gsi_prev to
    all of them, so this patch uses a bool for that instead.  The second
    gsi_end_p check isn't needed anymore, because when we don't do the
    undesirable gsi_prev after gsi = gsi_last_bb, the loop !gsi_end_p (gsi)
    condition will catch the removal of the very last stmt from a bb.

    2020-03-28  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/94329
            * tree-ssa-reassoc.c (reassociate_bb): When calling
reassoc_remove_stmt
            on the last stmt in a bb, make sure gsi_prev isn't done immediately
            after gsi_last_bb.

            * gfortran.dg/pr94329.f90: New test.