Dynamic array comparison optimization: check for equal pointers?

[Patrick Schluter]

On Tuesday, 2 June 2020 at 19:38:04 UTC, Johan wrote:
> Hi all,
>   I thought that we optimized dynamic array comparison with a 
> check to see if the pointers are equal, but I don't see it in 
> our array comparison implementation in druntime. Quick checking 
> of glibc memcmp also showed that there is no short circuit for 
> when the pointers of the slices are equal.
>
> I was expecting something like:
> ```
>   if ( sizes are not equal )
>      return false;
>   if ( pointers are equal  )
>      return true;
>   return memcmp;
> ```
>
> I am surprised that memcmp itself does not implement the 
> pointers are equal check. Is there a big impact of adding the 
> shortcircuit check to prevent scanning memory?

memcmp() doesn't implement the check to avoid memcmp(NULL, NULL, 
length) returning with 0 instead of segfaulting as it does if any 
of the 2 pointers in NULL.
It's a case of consistant behaviour, either you tolerate NULL 
pointers in all cases or you segfault in all cases.