Replacing C's memcpy with a D implementation

[Walter Bright]

On 6/10/2018 4:39 PM, David Nadlinger wrote:
> That's not entirely true. Intel started optimising some of the REP string 
> instructions again on Ivy Bridge and above. There is a CPUID bit to indicate 
> that (ERMS?); I'm sure the Optimization Manual has further details. From what I 
> remember, `rep movsb` is supposed to beat an AVX loop on most recent Intel 
> µarchs if the destination is aligned and the data is longer than a few cache 

The drama of which instruction mix is faster on which CPU never abates!