IA-64 strncpy

[Richard Henderson]

On Tue, Aug 21, 2001 at 10:46:30PM +0200, Jakub Jelinek wrote:
> The attached strncpy.S beats them all for small strings (or sizes) or for
> aligned strings, unfortunately for some strange reason strnlen+memcpy+memset
> is faster for long unaligned strings (unaligned is ((dst^src) & 0x7) != 0).
> Can any IA-64 assembly hacker look into it?


(p5)    ld1     c = [src], 1            // c = *src++
        ;;
        st1     [dest] = c, 1           // *dest++ = c

IA-64 won't write-combine smaller than 8 (or 4) bytes.  You'll
get something like a 6 cycle stall writing to sequential bytes
like this.

If you want to quickly copy unaligned data, you have to play
word shifting games.


r~