Limit std::sort comparisons on small list

[François Dumont]

On 10/07/2013 02:56 PM, Christopher Jefferson wrote:
> I'm unconvinced by this optimisation. I have already heard the
> occasional complaint that libstdc++ is quite large, so even in this
> tiny case I would be unsure about producing a very small code size
> increase for a very small performance improvement.
>
> On 4 October 2013 21:44, François Dumont <frs.dumont@gmail.com> wrote:
>> so with a limited number of elements we can see the gain even if it looks
>> like for the sort algo it is limited to 1 comparison. For stable_sort it is
>> better.
>>
>> François
>>

I am surprised, code bloat is indeed the only drawback of this patch, 
but isn't sometimes the compiler unrolling loop itself ? You can even 
see in __find_if implementation that we sometimes unroll loops manually 
so I guess that in general it is rather good for performance. Especially 
in this case with the first iteration that is better taken care separately.

Of course it is a small optimization but also a rather trivial one. I am 
sorry that I can't check the result on the generated code but I am quite 
sure that the "code bloat" will be even smaller than the optimization.

François