[Bug c++/99831] [10/11 Regression] ICE: in reshape_init, at cp/decl.c:6720

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99831

--- Comment #10 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:6a60ffc297b9d4903543a25538e62e7fb39420a9

commit r11-7954-g6a60ffc297b9d4903543a25538e62e7fb39420a9
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Apr 1 10:42:43 2021 -0400

    c++: GC collects live data when synthesizing operator== [PR99831]

    Here we crash in reshape_init because we're accessing ggc_freed
    & poisoned data: since r277865 in defaulted_late_check we call
    synthesize_method here:

      if (kind == sfk_comparison)
        {
          /* If the function was declared constexpr, check that the definition
             qualifies.  Otherwise we can define the function lazily.  */
          if (DECL_DECLARED_CONSTEXPR_P (fn) && !DECL_INITIAL (fn))
            synthesize_method (fn);
          return;
        }

    which in this test triggers when we're processing the string<"a">{} in
    the static_assert.  First, we create a CONSTRUCTOR for the "{}" in
    cp_parser_functional_cast, then we call finish_compound_literal which
    calls complete_type and that results in garbage collection, which then
    frees the CONSTRUCTOR {} we created when parsing the braced-list in
    string<"a">{} -- at this point, it's not referenced by anything.
    (That's not the case for 'type' in finish_compound_literal: the symbol
    table contains a node for operator==, so ggc_mark_roots goes and marks
    the fn decl, its type, its arguments etc., as used, so we don't collect
    it.)

    We could just bump function_depth around the new call to synthesize_method
    to prevent GC.

    gcc/cp/ChangeLog:

            PR c++/99831
            * method.c (defaulted_late_check): ++ and -- function_depth around
            the call to synthesize_method.
            * pt.c: Remove the saved_trees global.

    gcc/testsuite/ChangeLog:

            PR c++/99831
            * g++.dg/other/gc6.C: New test.