[Bug c++/67038] New: [c++-concepts] Viable function template despite unsatisfied constraints

["Casey at Carter dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67038

            Bug ID: 67038
           Summary: [c++-concepts] Viable function template despite
                    unsatisfied constraints
           Product: gcc
           Version: c++-concepts
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Casey at Carter dot net
  Target Milestone: ---

Created attachment 36077
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36077&action=edit
Preprocessed test case

r226205 fails to compile this correct program:

#include <stl2/iterator.hpp>

template <stl2::WeakOutputIterator<int> I>
  requires !stl2::WeakInputIterator<I>()
constexpr bool dispatch() { return false; }

template <stl2::WeakInputIterator I>
constexpr bool dispatch() { return true; }

template <stl2::WeakOutputIterator<int> I>
constexpr bool is_weak_out() { return true; }

template <stl2::WeakInputIterator I>
constexpr bool is_weak_in() { return true; }

int main() {
  static_assert(is_weak_out<int*>());
  static_assert(is_weak_in<int*>());
  static_assert(dispatch<int*>());
}

with error:

~/concept-gcc/bin/g++ -std=gnu++1z -I ~/cmcstl2/include -I
~/cmcstl2/meta/include foo.cpp -c
foo.cpp: In function ‘int main()’:
foo.cpp:19:32: error: call of overloaded ‘dispatch()’ is ambiguous
   static_assert(dispatch<int*>());
                                ^
foo.cpp:5:16: note: candidate: constexpr bool dispatch() [with I = int*]
 constexpr bool dispatch() { return false; }
                ^
foo.cpp:8:16: note: candidate: constexpr bool dispatch() [with I = int*]
 constexpr bool dispatch() { return true; }
                ^

The compiler apparently considers both overloads of dispatch to be viable
despite that the first overload's constraint !stl2::WeakInputIterator<I>() is
clearly not satisfied when I is int*.
>From gcc-bugs-return-493517-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jul 27 23:45:21 2015
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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/66846] parloops does not always mark loops for fixup if needed
Date: Mon, 27 Jul 2015 23:45:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf846

--- Comment #4 from vries at gcc dot gnu.org ---
Author: vries
Date: Mon Jul 27 23:44:43 2015
New Revision: 226279

URL: https://gcc.gnu.org/viewcvs?rev"6279&root=gcc&view=rev
Log:
Don't cancel loop tree in parloops

2015-07-28  Tom de Vries  <tom@codesourcery.com>

        PR tree-optimization/66846
        * omp-low.c (expand_omp_taskreg) [ENABLE_CHECKING]: Call
        verify_loop_structure for child_cfun if !LOOPS_NEED_FIXUP.
        (expand_omp_target) [ENABLE_CHECKING]: Same.
        (execute_expand_omp): Reinstate LOOPS_HAVE_SIMPLE_LATCHES if in ssa.
        [ENABLE_CHECKING]: Call verify_loop_structure for cfun if
        !LOOPS_NEED_FIXUP.
        (expand_omp_for_static_nochunk): Handle case that omp_for already has
        its own loop struct.
        * tree-parloops.c (create_parallel_loop): Add comment about breaking
        LOOPS_HAVE_SIMPLE_LATCHES.  Record new exit.
        (gen_parallel_loop): Remove call to cancel_loop_tree.
        (parallelize_loops): Skip loops that are inner loops of parallelized
        loops.
        (pass_parallelize_loops::execute): Clear LOOPS_HAVE_SIMPLE_LATCHES on
        loop state.
        [ENABLE_CHECKING]: Call verify_loop_structure.

Modified:
    branches/gomp-4_0-branch/gcc/ChangeLog.gomp
    branches/gomp-4_0-branch/gcc/omp-low.c
    branches/gomp-4_0-branch/gcc/tree-parloops.c