Gcc builtin review: strcpy, stpcpy, strcat, stpcat?

[Ondřej Bílka]

On Thu, Jun 04, 2015 at 11:27:57AM +0100, Richard Earnshaw wrote:
> On 25/05/15 12:45, Ondřej Bílka wrote:
> > Replaces it with strcpy. One could argue that opposite way to replace
> > strcpy with stpcpy is faster.
> > 
> > Reason is register pressure. Strcpy needs extra register to save return
> > value while stpcpy has return value already in register used for writing
> > terminating zero.
> 
> 
> Depends on your architecture.  On aarch64 we have plenty of spare
> registers, so strcpy simply copies the destination register into a
> scratch.  It then doesn't have to carefully calculate the return value
> at the end of the function (making the tail code simpler - there are
> multiple return statements, but only one entry point).
> 
Thats correct, main saving you get is from return value is first register, that
forces needing extra copy which is suboptimal.

I don't have data how strcpy and stpcpy mix and want to know if few
extra cycles are worth it when these aren't called exactly often, I will
try to think how test these.