Re: [PATCH] powerpc: tiny memcpy_(to|from)io optimisation

[Albrecht Dreß]

Hi Jocke:

Am 29.05.09 08:31 schrieb(en) Joakim Tjernlund:

> No (and I wasn't aware of the PPC pre-inc vs. post-inc stuff) - I just

I think this is true for most RISC based CPU's. It is a pity as
post ops are a lot more common. The do {} while(--chunks) is also

chunks inside the loop).

better. Basically the "while(--chunks)" is free(but only if you don't use

<snip case="1">
  n >>= 2;
  do {
    *++dst = *++src;
  } while (--n);
<snip>

and

<snip case="2">
  n >>= 2;
  while (n--)
    *dst++ = *src++;
</snip>





Best, Albrecht.

Just a side note: I looked at the assembly output of gcc 4.3.3 coming with Ubuntu Jaunty/PowerPC for Using the gcc options "-O2 -mcpu=603e -mtune=603e" (same effect with "-O3" instead of "-O2") the loop core is *exactly* the same in both cases. With gcc 4.2.2 (coming with ELDK 4.2) the loop core in case 2 is indeed one statement longer, though...

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