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Subject: [Bug c++/98126] -Wsequence-point is non-linear for certain cases
Date: Mon, 07 Dec 2020 16:56:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98126

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:1cac89da2cb1f2a7c2d93f7f325484c2d1619ca8

commit r11-5826-g1cac89da2cb1f2a7c2d93f7f325484c2d1619ca8
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Dec 3 18:35:00 2020 -0500

    c-family: Fix hang with -Wsequence-point [PR98126]

    verify_sequence_points uses verify_tree to recursively walk the
    subexpressions of an expression, and while recursing, it also
    keeps lists of expressions found after/before a sequence point.
    For a large expression, the list can grow significantly.  And
    merge_tlist is at least N(n^2): for a list of length n it will
    iterate n(n -1) times, and call candidate_equal_p each time, and
    that can recurse further.  warn_for_collision also has to go
    through the whole list.  With a large-enough expression, the
    compilation can easily get stuck here for 24 hours.

    This patch is a simple kludge: if we see that the expression is
    overly complex, don't even try.

    gcc/c-family/ChangeLog:

            PR c++/98126
            * c-common.c (verify_tree_lim_r): New function.
            (verify_sequence_points): Use it.  Use nullptr instead of 0.

    gcc/testsuite/ChangeLog:

            PR c++/98126
            * g++.dg/warn/Wsequence-point-4.C: New test.=