Re: Enhance std::hash for pointers

["François Dumont" <frs.dumont@gmail.com>]

On 08/05/2015 10:02, Richard Biener wrote:
> On Wed, May 6, 2015 at 10:10 PM, François Dumont <frs.dumont@gmail.com> wrote:
>> Hi
>>
>>      Following Marc Glisse comment #4
>> on:https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65641 I would like to
>> propose this enhancement to the hash functor for pointers. It simply gets
>> rid of the irrelevant bits on pointers hash code based on memory alignment
>> of the pointed type. The only drawback I can think of is that the type needs
>> to be complete at std::hash instantiation time but is it really an issue ?
>>
>>      IMO it is quite obvious that the resulting hash code will be better but
> If you use a real hashing function that's not true.  That is, something
> else than GCCs pointer_hash (void *p) { return (uintptr_t)p >>3; }.

Sorry, I don't understand your remark. Do you mean that if someone is 
not using std::hash to hash its pointers he won't benefit from the 
enhancement ?

It is a good point however to see that gcc is using something similar 
internally.

François