[Bug c++/99985] New: [11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[Bug c++/99985] New: [11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

            Bug ID: 99985
           Summary: [11 Regression] bits/hashtable.h:483:9: error: body of
                    ‘constexpr’ function ... not a return-statement since
                    g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
  Target Milestone: ---

I noticed that in botan, inkscape and mariadb packages:

$ cat oid.C
#include <string>
#include <unordered_map>
struct OID {};
std::unordered_map< std::string, OID > load_str2oid_map() {
  return std::unordered_map< std::string, OID >{};
}

$ cat oid.C
#include <string>
#include <unordered_map>
struct OID {};
std::unordered_map< std::string, OID > load_str2oid_map() {
  return std::unordered_map< std::string, OID >{};
}

$ g++ oid.C -c -std=c++11
In file included from /home/marxin/bin/gcc/include/c++/11.0.1/unordered_map:46,
                 from oid.C:2:
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h: In instantiation of
‘static constexpr bool std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey,
_Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_S_nothrow_move()
[with bool _No_realloc = true; _Key = std::__cxx11::basic_string<char>; _Value
= std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’:
oid.C:5:49:   recursively required from ‘std::unordered_map<_Key, _Tp, _Hash,
_Pred, _Alloc>::unordered_map(std::unordered_map<_Key, _Tp, _Hash, _Pred,
_Alloc>&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = OID; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _Pred =
std::equal_to<std::__cxx11::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >]’
oid.C:5:49:   required from here
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h:483:9: error: body of
‘constexpr’ function ‘static constexpr bool std::_Hashtable<_Key, _Value,
_Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy,
_Traits>::_S_nothrow_move() [with bool _No_realloc = true; _Key =
std::__cxx11::basic_string<char>; _Value = std::pair<const
std::__cxx11::basic_string<char>, OID>; _Alloc = std::allocator<std::pair<const
std::__cxx11::basic_string<char>, OID> >; _ExtractKey =
std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’ not a return-statement
  483 |         }
      |         ^
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h: In instantiation of
‘std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash,
_Unused, _RehashPolicy, _Traits>::_Hashtable(std::_Hashtable<_Key, _Value,
_Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy,
_Traits>&&) [with _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’:
oid.C:5:49:   recursively required from ‘std::unordered_map<_Key, _Tp, _Hash,
_Pred, _Alloc>::unordered_map(std::unordered_map<_Key, _Tp, _Hash, _Pred,
_Alloc>&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = OID; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _Pred =
std::equal_to<std::__cxx11::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >]’
oid.C:5:49:   required from here
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h:520:33: error: ‘static
constexpr bool std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_S_nothrow_move() [with
bool _No_realloc = true; _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’ called in a constant
expression
  520 |         noexcept(_S_nothrow_move())
      |                  ~~~~~~~~~~~~~~~^~
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h:477:9: note: ‘static
constexpr bool std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_S_nothrow_move() [with
bool _No_realloc = true; _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’ is not usable as a
‘constexpr’ function because:
  477 |         _S_nothrow_move()
      |         ^~~~~~~~~~~~~~~
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h: In instantiation of
‘std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash,
_Unused, _RehashPolicy, _Traits>::_Hashtable(std::_Hashtable<_Key, _Value,
_Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy,
_Traits>&&, std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash,
_RangeHash, _Unused, _RehashPolicy, _Traits>::__node_alloc_type&&,
std::true_type) [with _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>; std::_Hashtable<_Key,
_Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy,
_Traits>::__node_alloc_type = std::_Hashtable<std::__cxx11::basic_string<char>,
std::pair<const std::__cxx11::basic_string<char>, OID>,
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >,
std::__detail::_Select1st, std::equal_to<std::__cxx11::basic_string<char> >,
std::hash<std::__cxx11::basic_string<char> >,
std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash,
std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true,
false, true> >::__node_alloc_type; std::true_type =
std::integral_constant<bool, true>]’:
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h:522:17:   required
from ‘std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash,
_RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable(std::_Hashtable<_Key,
_Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy,
_Traits>&&) [with _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’
/home/marxin/bin/gcc/include/c++/11.0.1/bits/unordered_map.h:184:7:   required
from here
/home/marxin/bin/gcc/include/c++/11.0.1/bits/hashtable.h:487:33: error: ‘static
constexpr bool std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_S_nothrow_move() [with
bool _No_realloc = true; _Key = std::__cxx11::basic_string<char>; _Value =
std::pair<const std::__cxx11::basic_string<char>, OID>; _Alloc =
std::allocator<std::pair<const std::__cxx11::basic_string<char>, OID> >;
_ExtractKey = std::__detail::_Select1st; _Equal =
std::equal_to<std::__cxx11::basic_string<char> >; _Hash =
std::hash<std::__cxx11::basic_string<char> >; _RangeHash =
std::__detail::_Mod_range_hashing; _Unused =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<true, false, true>]’ called in a constant
expression
  487 |         noexcept(_S_nothrow_move());
      |                  ~~~~~~~~~~~~~~~^~

[Bug c++/99985] [11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |redi at gcc dot gnu.org
           Priority|P3                          |P1
      Known to fail|                            |11.0
      Known to work|                            |10.2.0
   Target Milestone|---                         |11.0

[Bug c++/99985] [11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So do we need
#if __cplusplus < 201402L
         return _No_realloc
                && is_nothrow_copy_constructible<_Hash>()
                && is_nothrow_copy_constructible<_Equal>();
#else
         if _GLIBCXX17_CONSTEXPR (_No_realloc)
           if _GLIBCXX17_CONSTEXPR (is_nothrow_copy_constructible<_Hash>())
             return is_nothrow_copy_constructible<_Equal>();
#endif
?

[Bug c++/99985] [10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11 Regression]             |[10/11 Regression]
                   |bits/hashtable.h:483:9:     |bits/hashtable.h:483:9:
                   |error: body of ‘constexpr’  |error: body of ‘constexpr’
                   |function ... not a          |function ... not a
                   |return-statement since      |return-statement since
                   |g:1cbba49e3417d9b0661e70301 |g:1cbba49e3417d9b0661e70301
                   |d6fb7a7f52fd360             |d6fb7a7f52fd360
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
   Last reconfirmed|                            |2021-04-09
             Status|UNCONFIRMED                 |ASSIGNED
   Target Milestone|11.0                        |10.4

[Bug c++/99985] [10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Aside: is there a good reason those packages use -std=c++11? Did they just add
it ten years ago to enable "new" C++ features? Because now they're *disabling*
features by not using the compiler's default -std mode. I see -std=c++0x or
-std=c++11 in the build for lots of fedora packages.

[Bug c++/99985] [10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Bet they want C++11 or newer and aren't aware there could be compilers that
would default to C++14, C++17 or C++20...

[Bug c++/99985] [10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We can still make it short circuit (and so not instantiate class templates
unnecessarily) like this:

#if __cplusplus <= 201402L
          return __and_<__bool_constant<_No_realloc>,
                 is_nothrow_copy_constructible<_Hash>,
                 is_nothrow_copy_constructible<_Equal>>::value;
#else
          if constexpr (_No_realloc)
            if constexpr (is_nothrow_copy_constructible<_Hash>())
              return is_nothrow_copy_constructible<_Equal>();
          return false;
#endif

I didn't use __and_<> because that has to be instantiated too (although it's
cheaper than the is_xxx_constructible ones), and for C++17 the if-constexpr
version avoids that. But if we need a #if to work for C++11 anyway, we might as
well use __and_ for C++11 and C++14, and if-constexpr for everything later.

[Bug libstdc++/99985] [9/10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #5 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:40ccb47b505b528244ee305923681c0ae3b6f4d5

commit r11-8085-g40ccb47b505b528244ee305923681c0ae3b6f4d5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 9 12:05:39 2021 +0100

    libstdc++: Fix invalid constexpr function in C++11 mode [PR 99985]

    I keep forgetting that a constexpr function in C++11 has to be a single
    return statement.

    libstdc++-v3/ChangeLog:

            PR libstdc++/99985
            * include/bits/hashtable.h (_Hashtable::_S_nothrow_move()): Fix
            to be a valid constexpr function in C++11.
            * testsuite/23_containers/unordered_set/cons/99985.cc: New test.

[Bug libstdc++/99985] [9/10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #6 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:637418ec2c6f559d4fac074db3bafc34a728484b

commit r10-9679-g637418ec2c6f559d4fac074db3bafc34a728484b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 9 12:05:39 2021 +0100

    libstdc++: Fix invalid constexpr function in C++11 mode [PR 99985]

    I keep forgetting that a constexpr function in C++11 has to be a single
    return statement.

    libstdc++-v3/ChangeLog:

            PR libstdc++/99985
            * include/bits/hashtable.h (_Hashtable::_S_nothrow_move()): Fix
            to be a valid constexpr function in C++11.
            * testsuite/23_containers/unordered_set/cons/99985.cc: New test.

    (cherry picked from commit 40ccb47b505b528244ee305923681c0ae3b6f4d5)

[Bug libstdc++/99985] [9/10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:6b66d162835621c81a78f361416149d914d31de8

commit r9-9335-g6b66d162835621c81a78f361416149d914d31de8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 9 12:05:39 2021 +0100

    libstdc++: Fix invalid constexpr function in C++11 mode [PR 99985]

    I keep forgetting that a constexpr function in C++11 has to be a single
    return statement.

    libstdc++-v3/ChangeLog:

            PR libstdc++/99985
            * include/bits/hashtable.h (_Hashtable::_S_nothrow_move()): Fix
            to be a valid constexpr function in C++11.
            * testsuite/23_containers/unordered_set/cons/99985.cc: New test.

    (cherry picked from commit 40ccb47b505b528244ee305923681c0ae3b6f4d5)

[Bug libstdc++/99985] [9/10/11 Regression] bits/hashtable.h:483:9: error: body of ‘constexpr’ function ... not a return-statement since g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Should be fixed everywhere.