[Bug libstdc++/93628] ranges::equal_to doesn't work for types convertible to function pointers

[Bug libstdc++/93628] ranges::equal_to doesn't work for types convertible to function pointers

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93628

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-04-15
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

[Bug libstdc++/93628] ranges::equal_to doesn't work for types convertible to function pointers

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93628

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
LWG 3530 should mean we don't have to support such silly types.
https://wg21.link/lwg3530

However, we are still required to impose a total order on function pointers,
which means ranges::less/greater/less_equal/greater_equal are still
(potentially) broken, as for object pointers in PR 78420. We might get away
with it if the compiler doesn't do similar optimizations for function pointers,
but we used to say that about object pointers too, and it stopped being true.

As noted above, we don't have a way to detect that a relational comparison
would call a built-in operator on function pointers. Maybe what we want is a
__builtin_less_than(t, u) which is t < u but with a total order.

[Bug libstdc++/93628] ranges::equal_to doesn't work for types convertible to function pointers

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93628

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

https://gcc.gnu.org/g:dddd011113b6ceede733d7ae33eca695c06b181b

commit r11-7603-gdddd011113b6ceede733d7ae33eca695c06b181b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 10 15:27:06 2021 +0000

    libstdc++: Implement LWG 3530 for concept-constrained comparisons

    The proposed resolution for this library issue simplifies the
    constraints for compare_three_way, ranges::equal_to, ranges::less etc.
    so that they do not work with types which are convertible to pointers
    but which fail to meet the usual syntactic requirements for the
    comparisons.

    This affects the example in PR libstdc++/93628 but doesn't fix the
    problem described in that report.

    libstdc++-v3/ChangeLog:

            * include/bits/ranges_cmp.h (__eq_builtin_ptr_cmp): Remove.
            (ranges::equal_to, ranges::not_equal_to): Do not constrain
            with __eq_builtin_ptr_cmp.
            (ranges::less, ranges::greater, ranges::less_equal)
            (ranges::greater_equal): Do not constrain with
            __less_builtin_ptr_cmp.
            * libsupc++/compare (compare_three_way): Do not constrain with
            __3way_builtin_ptr_cmp.
            * testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc:
Moved to...
            * testsuite/18_support/comparisons/object/lwg3530.cc: ...here.
            * testsuite/20_util/function_objects/range.cmp/lwg3530.cc: New
test.

[Bug libstdc++/93628] ranges::equal_to doesn't work for types convertible to function pointers

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93628

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:913312de92522e9e6696331fc3018e1020845c26

commit r10-9591-g913312de92522e9e6696331fc3018e1020845c26
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 10 15:27:06 2021 +0000

    libstdc++: Implement LWG 3530 for concept-constrained comparisons

    The proposed resolution for this library issue simplifies the
    constraints for compare_three_way, ranges::equal_to, ranges::less etc.
    so that they do not work with types which are convertible to pointers
    but which fail to meet the usual syntactic requirements for the
    comparisons.

    This affects the example in PR libstdc++/93628 but doesn't fix the
    problem described in that report.

    libstdc++-v3/ChangeLog:

            * include/bits/range_cmp.h (__eq_builtin_ptr_cmp): Remove.
            (ranges::equal_to, ranges::not_equal_to): Do not constrain
            with __eq_builtin_ptr_cmp.
            (ranges::less, ranges::greater, ranges::less_equal)
            (ranges::greater_equal): Do not constrain with
            __less_builtin_ptr_cmp.
            * libsupc++/compare (compare_three_way): Do not constrain with
            __3way_builtin_ptr_cmp.
            * testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc:
Moved to...
            * testsuite/18_support/comparisons/object/lwg3530.cc: ...here.
            * testsuite/20_util/function_objects/range.cmp/lwg3530.cc: New
test.

    (cherry picked from commit dddd011113b6ceede733d7ae33eca695c06b181b)