[Bug libstdc++/54075] [4.7.1] unordered_map insert still slower than 4.6.2

[Paolo Carlini]

Hi,

On 11/13/2012 10:40 PM, François Dumont wrote:
> 2012-11-13 François Dumont  <fdumont@gcc.gnu.org>
>
>     * include/bits/hashtable_policy.h (_Prime_rehash_policy): Remove
>     automatic shrink.
>     (_Prime_rehash_policy::_M_bkt_for_elements): Do not call
>     _M_next_bkt anymore.
>     (_Prime_rehash_policy::_M_next_bkt): Move usage of
>     _S_growth_factor ...
>     (_Prime_rehash_policy::_M_need_rehash): ... here.
>     * include/bits/hashtable.h (_Hashtable<>): Adapt.
>
> Tested under linux x86_64, normal and debug modes.
Patch is Ok with me, please wait another day or two for comments and 
then apply it.

You can also add the performance testcase, of course, note however that 
::random isn't a standard C function, thus we shouldn't use it 
unconditionally, either manage with std::rand from <cstdlib> or do 
something completely different (maybe even <random> since you are 
writing C++11 code anyway!). I would also recommend extending quite a 
bit the runtime, 10x would be still completely sensible (but I guess, 
without using much more memory)

Paolo.