Re: [RFC PATCH v3 0/4] nolibc x86-64 string functions

[Willy Tarreau]

On Sun, Sep 03, 2023 at 08:38:22PM +0000, David Laight wrote:
> From: Ammar Faizi
> > Sent: 02 September 2023 14:35
> > 
> > This is an RFC patchset v3 for nolibc x86-64 string functions.
> > 
> > There are 4 patches in this series:
> > 
> > ## Patch 1-2: Use `rep movsb`, `rep stosb` for:
> >     - memcpy() and memmove()
> >     - memset()
> > respectively. They can simplify the generated ASM code.
> 
> It is worth pointing out that while the code size for 'rep xxxb'
> is smaller, the performance is terrible.
> The only time it is ever good is for the optimised forwards
> copies on cpu that support it.
> 
> reverse, stos and scas are always horrid.

It's terrible compared to other approaches but not *that* bad. Also we
absolutely don't care about performance here, rather about correctness
and compact size.

Regards,
Willy