hashtable local iterator

[François Dumont]

On 12/19/2011 09:43 PM, Jonathan Wakely wrote:
> If you use std::tuple to store the members it will automatically use 
> EBO if possible. If two types might be the same use std::tuple<X,Y,X> 
> where X might be empty and Y is not empty, that ensures the two X 
> objects will not have the same address so can have zero size. 

Thanks for the proposition but it was not exactly what I needed. In fact 
I have this kind of use case:

struct A1
{};

struct A2
{};

struct A3
{};

struct B
{
   A1 m_a1;
   A2 m_a2;
   A3 m_a3;
};

struct C : B
{
   size_t m_size;
};

and I would like to have sizeof(C) == sizeof(size_t). I don't think 
tuple can do anything for me here. Only having B inheriting from A1, A2 
and A3 will give the expected result. And as I said there is no 
ambiguity problem here. The only ambiguity could come from using the 
same functor as a _Equal and _Hash functor but as I never inherit from 
both _Equal and _Hash there won't ever be any ambiguity.

So here is my final patch with sizeof(local_iterator) == 2 * 
size(size_t) + sizeof(void*).

2011-12-20  François Dumont <fdumont@gcc.gnu.org>

         * include/bits/hashtable_policy.h (_Equal_helper<>): New, 
change the
         way the _Equal functor is used depending on whether hash code 
is cache
         or not. (_Hash_code_base): Move _Equal functor management...
         (_Hashtable_base): ...here, new, use _Equal_helper.
         (_Local_iterator_base<>, _Locale_iterator<>, 
_Locale_const_iterator<>):
         New, use _Hash_code_base, implementation of...
         * include/bits/hashtable.h (_Hashtable<>::local_iterator,
         _Hashtable<>::const_local_iterator): ...those. Add static 
assertions
         checking that some functors are empty depending on whether hash 
code
         is cache or not. (_Hashtable<>::_M_bucket_index): New overloads 
using
         current bucket count, use through out the _Hastable<> 
implementation.
         * include/bits/unordered_set.h (__unordered_set<>,
         __unordered_multiset<>): Cache hash code if hash functor is not 
empty.
         * include/bits/unordere_map.H (__unordered_map<>,
         __unordered_multimap<>): Likewise.
         * include/debug/unordered_map
         (unordered_map<>::_S_to_local, unordered_multimap<>::_S_to_local):
         Adapt to match new local iterator implementation.
         * include/debug/unordered_set (unordered_set<>::_S_to_local,
         unordered_multiset<>::_S_to_local): Likewise.
         * include/profile/unordered_map 
(unordered_map<>::_M_profile_destruct,
         unordered_multimap<>::_M_profile_destruct): Enhance thanks to 
usage of
         local iterators.
         * include/profile/unordered_set 
(unordered_set<>::_M_profile_destruct,
         unordered_multiset<>::_M_profile_destruct): Likewise.

Tested under x86_64 linux, check, check-debug and check-profile.

Ok to commit ?

François

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