On Thu, Mar 3, 2016 at 8:12 AM, David Laight <david.lai...@aculab.com> wrote:
>
> Did you try the asm loop that used 'leax %rcx..., jcxz... jmps..'
> without any unrolling?
Is that actually supposed to work ok these days? jcxz used to be quite
slow, and is historically *never* used.
Now, in theory, loop constructs can actually do better on branch
prediction etc, but Intel seems to have never really tried to push
them, and has instead pretty much discouraged them in favor of making
the normal jumps go faster (including all the instruction fusion etc)
>From what I have seen, the whole "don't use LOOP or JRCXZ" has not changed.
Linus
