[Bug c++/99362] [10 Regression] invalid unused result

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99362

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:01edf2031461b558f630afea382a813e41b631e6

commit r10-9481-g01edf2031461b558f630afea382a813e41b631e6
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Mar 4 16:04:48 2021 +0100

    c++: Fix up [[nodiscard]] on ctors on targetm.cxx.cdtor_returns_this
targets [PR99362]

    In the P1771R1 changes JeanHeyd reverted part of Alex' PR88146 fix,
    but that seems to be incorrect to me.
    Where P1771R1 suggests warnings for [[nodiscard]] on constructors is
    handled in a different place - in particular the TARGET_EXPR handling
    of convert_to_void.  When we have CALL_EXPR of a ctor, on most arches
    that call has void return type and so returns early, and on arm where
    the ctor returns the this pointer it is undesirable to warn as it warns
    about all ctor calls, not just the ones where it should warn.

    The P1771R1 changes added a test for this, but as it was given *.c
    extension rather than *.C, the test was never run and so this didn't get
    spotted immediately.  The test also had a bug, (?n) can't be used
    in dg-warning/dg-error because those are implemented by prepending
    some regexp before the user provided one and (?n) must come at the start
    of the regexp.  Furthermore, while -ftrack-macro-expansion=0 is useful
    in one nodiscard test which uses macros, I don't see how it would be
    relevant to all the other cpp2a/nodiscard* tests which don't use any
    macros.

    2021-03-04  Jakub Jelinek  <jakub@redhat.com>

            PR c++/88146
            PR c++/99362
    gcc/cp/
            * cvt.c (convert_to_void): Revert 2019-10-17 changes.  Clarify
            comment.
    gcc/testsuite/
            * g++.dg/cpp2a/nodiscard-constructor.c: Renamed to ...
            * g++.dg/cpp2a/nodiscard-constructor1.C: ... this.  Remove
            -ftrack-macro-expansion=0 from dg-options.  Don't use (?n) in
            dg-warning regexps, instead replace .* with \[^\n\r]*.
            * g++.dg/cpp2a/nodiscard-constructor2.C: New test.
            * g++.dg/cpp2a/nodiscard-reason-only-one.C: Remove
            -ftrack-macro-expansion=0 from dg-options.
            * g++.dg/cpp2a/nodiscard-reason-nonstring.C: Likewise.
            * g++.dg/cpp2a/nodiscard-once.C: Likewise.

    (cherry picked from commit c9816196328a4f4b927f08cf2f66cf255849da0b)