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[Bug c++/79592] incomplete diagnostic "is not usable as a constexpr function because:"
- From: "egallager at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 21 Aug 2017 17:00:05 +0000
- Subject: [Bug c++/79592] incomplete diagnostic "is not usable as a constexpr function because:"
- Auto-submitted: auto-generated
- References: <bug-79592-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79592
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |accepts-invalid
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-08-21
CC| |egallager at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> struct pthread_mutex {
> void *m_ptr;
> };
>
> struct M {
> pthread_mutex m = { ((void *) 1LL) };
> };
>
> constexpr M m;
>
> pt.cc:9:13: error: ‘constexpr M::M()’ called in a constant expression
> constexpr M m;
> ^
> pt.cc:5:8: note: ‘constexpr M::M()’ is not usable as a constexpr function
> because:
> struct M {
> ^
>
> It just says "because:" without saying what the problem is (the cast is not
> allowed in a constant expression).
>
> If the expression is (void*)1 rather than (void*)1LL then it is incorrectly
> accepted.
On a 32-bit target, it is always incorrectly accepted; adding -m64 is necessary
to get the incomplete diagnostic:
$ /usr/local/bin/g++ -c -Wall -Wextra -pedantic -std=c++11 79592.cc
$ /usr/local/bin/g++ -c -Wall -Wextra -pedantic -std=c++11 -m64 79592.cc
79592.cc:9:13: error: ‘constexpr M::M()’ called in a constant expression
constexpr M m;
^
79592.cc:5:8: note: ‘constexpr M::M()’ is not usable as a constexpr function
because:
struct M {
^
$
Confirmed.