[Bug libstdc++/50257] [C++0x] unordered_map slow initialization due to huge __prime_list

["paolo.carlini at oracle dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50257

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011-09-01
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.7.0
     Ever Confirmed|0                           |1

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-01 17:54:14 UTC ---
Ah, very good. Thanks a lot for all your help. Indeed, I'm seeing similar
numbers on my machine. Thus, I would say, let's go with this kind of tweak for
now: indeed, it looks like an hack, but having default construction, move
constructor, faster is important, and as you noticed, it's also about having
the common case inline, vs the out of line lower_bound call. Also, I should
add, it's an hack, but I mild one, in my opinion, because we are doing it at an
abstraction level, _Prime_rehash_policy, which is exactly the same at which the
__prime_list is managed, thus we know for sure it begins by 2, etc. Only 10
it's a bit out of the blue at this level. Anyway, with another contributor, we
are also in the process of improving, streamlining, these _Prime_rehash_policy
functions for other reasons, I'll see later on if we can (re-)implement this
kind of tweak in a better way.