[Bug c++/65042] New: gcc5 has a template depth problem that was fine in gcc4

["karl at kleinpaste dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65042

            Bug ID: 65042
           Summary: gcc5 has a template depth problem that was fine in
                    gcc4
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: karl at kleinpaste dot org

Created attachment 34740
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34740&action=edit
class description employing layered string- and int-indexed maps-within-maps

Attached is modulecache.hh, part of Xiphos, which was recently involved in a
Fedora gcc5 mass rebuild test for upcoming Fedora 22.  This file exhibits a
template complaint regarding nested std::map usage.  The nesting provides an
intuitive access to data content by allowing subscripting at any map level to
obtain all subordinate content.

The plain fact is that this code has been compiling in gcc4 since approximately
2008.  It was then found that using -ftemplate-depth=128 makes the gcc5
compilation survive, but I don't see why this should be necessary, considering
that the code has been fine for 7 years preceding, without use of any such
modifiers.  Has the default depth limit changed in gcc5?

FYI recommended to file this report by an involved Fedora engineer; I am Xiphos
project admin.

In file included from /usr/include/c++/5.0.0/map:60:0,
                 from ../src/main/modulecache.hh:45,
                 from ../src/main/modulecache.cc:30:
/usr/include/c++/5.0.0/bits/stl_tree.h: In instantiation of 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_destroy_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = int; _Val = std::pair<const int,
ModuleCache::CacheVerse>; _KeyOfValue = std::_Select1st<std::pair<const int,
ModuleCache::CacheVerse> >; _Compare = std::less<int>; _Alloc =
std::allocator<std::pair<const int, ModuleCache::CacheVerse> >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const int, ModuleCache::CacheVerse> >*]':
/usr/include/c++/5.0.0/bits/stl_tree.h:562:17:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_drop_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = int; _Val = std::pair<const int,
ModuleCache::CacheVerse>; _KeyOfValue = std::_Select1st<std::pair<const int,
ModuleCache::CacheVerse> >; _Compare = std::less<int>; _Alloc =
std::allocator<std::pair<const int, ModuleCache::CacheVerse> >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const int, ModuleCache::CacheVerse> >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:1493:16:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_erase(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = int; _Val = std::pair<const int,
ModuleCache::CacheVerse>; _KeyOfValue = std::_Select1st<std::pair<const int,
ModuleCache::CacheVerse> >; _Compare = std::less<int>; _Alloc =
std::allocator<std::pair<const int, ModuleCache::CacheVerse> >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const int, ModuleCache::CacheVerse> >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:859:17:   required from
'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::~_Rb_tree() [with
_Key = int; _Val = std::pair<const int, ModuleCache::CacheVerse>; _KeyOfValue =
std::_Select1st<std::pair<const int, ModuleCache::CacheVerse> >; _Compare =
std::less<int>; _Alloc = std::allocator<std::pair<const int,
ModuleCache::CacheVerse> >]'
/usr/include/c++/5.0.0/bits/stl_map.h:96:11:   required from 'void
__gnu_cxx::new_allocator<_Tp>::destroy(__gnu_cxx::new_allocator<_Tp>::pointer)
[with _Tp = std::pair<const int, std::map<int, ModuleCache::CacheVerse> >;
__gnu_cxx::new_allocator<_Tp>::pointer = std::pair<const int, std::map<int,
ModuleCache::CacheVerse> >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:521:9:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_destroy_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = int; _Val = std::pair<const int,
std::map<int, ModuleCache::CacheVerse> >; _KeyOfValue =
std::_Select1st<std::pair<const int, std::map<int, ModuleCache::CacheVerse> >
>; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int,
std::map<int, ModuleCache::CacheVerse> > >; std::_Rb_tree<_Key, _Val,
_KeyOfValue, _Compare, _Alloc>::_Link_type = std::_Rb_tree_node<std::pair<const
int, std::map<int, ModuleCache::CacheVerse> > >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:562:17:   [ skipping 14 instantiation
contexts, use -ftemplate-backtrace-limit=0 to disable ]
/usr/include/c++/5.0.0/bits/stl_tree.h:521:9:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_destroy_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = const std::basic_string<char>; _Val =
std::pair<const std::basic_string<char>, std::map<int, std::map<int,
std::map<int, std::map<int, ModuleCache::CacheVerse> > > > >; _KeyOfValue =
std::_Select1st<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
_Compare = std::less<const std::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:562:17:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_drop_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = const std::basic_string<char>; _Val =
std::pair<const std::basic_string<char>, std::map<int, std::map<int,
std::map<int, std::map<int, ModuleCache::CacheVerse> > > > >; _KeyOfValue =
std::_Select1st<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
_Compare = std::less<const std::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:1493:16:   required from 'void
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_erase(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_Link_type) [with _Key = const std::basic_string<char>; _Val =
std::pair<const std::basic_string<char>, std::map<int, std::map<int,
std::map<int, std::map<int, ModuleCache::CacheVerse> > > > >; _KeyOfValue =
std::_Select1st<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
_Compare = std::less<const std::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >*]'
/usr/include/c++/5.0.0/bits/stl_tree.h:859:17:   required from
'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::~_Rb_tree() [with
_Key = const std::basic_string<char>; _Val = std::pair<const
std::basic_string<char>, std::map<int, std::map<int, std::map<int,
std::map<int, ModuleCache::CacheVerse> > > > >; _KeyOfValue =
std::_Select1st<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >;
_Compare = std::less<const std::basic_string<char> >; _Alloc =
std::allocator<std::pair<const std::basic_string<char>, std::map<int,
std::map<int, std::map<int, std::map<int, ModuleCache::CacheVerse> > > > > >]'
/usr/include/c++/5.0.0/bits/stl_map.h:163:14:   required from 'std::map<_Key,
_Tp, _Compare, _Alloc>::map() [with _Key = const std::basic_string<char>; _Tp =
std::map<int, std::map<int, std::map<int, std::map<int,
ModuleCache::CacheVerse> > > >; _Compare = std::less<const
std::basic_string<char> >; _Alloc = std::allocator<std::pair<const
std::basic_string<char>, std::map<int, std::map<int, std::map<int,
std::map<int, ModuleCache::CacheVerse> > > > > >]'
../src/main/modulecache.cc:34:23:   required from here
/usr/include/c++/5.0.0/bits/stl_tree.h:521:22: fatal error: template
instantiation depth exceeds maximum of 25 (use -ftemplate-depth= to increase
the maximum)
       { get_allocator().destroy(__p->_M_valptr()); }
                      ^