Re: [PATCH] x86/boot: Avoid redundant address overlap tests in memcpy().

[Kuniyuki Iwashima <kuniyu@amazon.co.jp>]

From:   Dave Hansen <dave.hansen@intel.com>
Date:   Mon, 24 Jan 2022 09:38:40 -0800
> On 1/22/22 17:58, Kuniyuki Iwashima wrote:
> > -void *memmove(void *dest, const void *src, size_t n)
> > +void *____memmove(void *dest, const void *src, size_t n)
> >   {
> >   	unsigned char *d = dest;
> >   	const unsigned char *s = src;
> >   
> > -	if (d <= s || d - s >= n)
> > -		return ____memcpy(dest, src, n);
> > -
> >   	while (n-- > 0)
> >   		d[n] = s[n];
> >   
> >   	return dest;
> >   }
> 
> The ___ naming is pretty cruel.  Could we call it memmove_no_overlap() 
> or memmove_unsafe()?  Surely we can put some *useful* bytes in the name 
> rather than padding it out with _'s.  No need to perpetuate the 
> ____memcpy() naming.

Sure.  I will rename it to memmove_unsafe() because it supports another
overlap case. (d > s)


> 
> Also, is this worth the churn?  It probably saves less than 10 
> instructions, all of which are ridiculously cheap.  Is there a *reason* 
> for this other than being a pure cleanup?

This is just for cleanup.