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Subject: [Bug c++/107065] GCC treats rvalue as an lvalue
Date: Fri, 10 Feb 2023 17:44:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107065

--- Comment #16 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:bc1ee711eeab4b0d55463cd153747d30c69225c7

commit r12-9127-gbc1ee711eeab4b0d55463cd153747d30c69225c7
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Dec 15 19:17:45 2022 +0100

    c++: Ensure !!var is not an lvalue [PR107065]

    The TRUTH_NOT_EXPR case in cp_build_unary_op is one of the spots where
    we somewhat fold immediately using invert_truthvalue_loc.
    I've tried using
      return build1_loc (location, TRUTH_NOT_EXPR, boolean_type_node, arg);
    in there instead, but unfortunately that regressed
    Wlogical-not-parentheses-*.c pr49706.c pr62199.c pr65120.c sequence-pt-=
1.C
    tests, so at least for backporting that doesn't seem to be a way to go.

    So, this patch instead wraps it into NON_LVALUE_EXPR if needed (which a=
lso
    need a tweak for some tests in the pr47906.c test, but nothing major),
    with the intent to make it backportable, and later I'll try to do furth=
er
    steps to avoid folding here prematurely.  Most of the problems with
    build1 TRUTH_NOT_EXPR are that it doesn't even invert comparisons as mo=
st
    common case and lots of warning code isn't able to deal with ! around
    comparisons; so perhaps one way to do this would be fold by hand only
    invertable comparisons and for the rest create TRUTH_NOT_EXPR.

    2022-12-15  Jakub Jelinek  <jakub@redhat.com>

            PR c++/107065
    gcc/cp/
            * typeck.cc (cp_build_unary_op) <case TRUTH_NOT_EXPR>: If
            invert_truthvalue_loc returns obvalue_p, wrap it into
NON_LVALUE_EXPR.
            * parser.cc (cp_parser_binary_expression): Don't call
            warn_logical_not_parentheses if current.lhs is a NON_LVALUE_EXPR
            of a decl with boolean type.
    gcc/testsuite/
            * g++.dg/cpp0x/pr107065.C: New test.

    (cherry picked from commit 8b775b4c48a3cc4ef5c50e56144aea02da2e9cc6)=