[Nauty] Squeezing out another 10%...

[Chris Jefferson]

Gordon Royle wrote:
> Hi,
> 
> I have discovered through experimentation that I get an additional 10% 
> performance out of geng (and hence presumably) nauty by altering the 
> optimization flags from the supplied defaults... I am using a Pentium 4 
> machine, and if I put
> 
>     gcc -O2 -Dmarch=pentium4
> 
> then it is about 10% faster than
> 
>     gcc -O4
> 
> Interestingly, it proves better to use O1/O2 with the 
> architecture-specific flag than to use O3 or higher...
> 

Just one very minor note. There is no difference at all between -O3 and 
higher values, the higher values are just allowed for backwards 
compatability when they used to higher.

Chris