https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88398
--- Comment #27 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
(In reply to Wilco from comment #13)
> So to add some real numbers to the discussion, the average number of
> iterations is 4.31. Frequency stats (16 includes all iterations > 16 too):
>
> 1: 29.0
> 2: 4.2
> 3: 1.0
> 4: 36.7
> 5: 8.7
> 6: 3.4
> 7: 3.0
> 8: 2.6
> 9: 2.1
> 10: 1.9
> 11: 1.6
> 12: 1.2
> 13: 0.9
> 14: 0.8
> 15: 0.7
> 16: 2.1
>
Find one interesting thing:
If using widen reading for the run which > 16 iterations, we can see the
performance is significantly improved(>18%) for xz_r in spec.
This means that the frequency is small for >16, while it still costs a big part
of the runtime.
if (len_limit - len > 16)
{
for(++len; len + sizeof(TYPEE) <= len_limit; len += sizeof(TYPEE))
{
long long a = *((TYPEE*)(cur+len));
long long b = *((TYPEE*)(pb+len));
if (a != b) {
int lz = __builtin_ctzll(a ^ b);
len += lz / 8;
goto found;
break;
}
}
for (;len != len_limit; ++len)
if (pb[len] != cur[len])
break;
found:;
}
else
{ xxxx original loop}
