>
> Dave Rivers wrote:
>
> > On a per-function basis - but not within functions; because
> > gcc points R13 at the literal pool; which can be quite large
> > (and different from the code location in sufficiently large
> > functions.)
>
> Separating code and literal pool would appear likely to cause
> a net win on machines with separate i-cache and d-cache (i.e.
> all zSeries machines). I don't have specific measurements to
> prove that point, though.
Yes - I would agree.
It was a rather surprising discovery to us as well (when
reported by some users of zSeries machines.)
I may, however, be mis-attributing the reason for the
performance benefit. There was some thought that
gcc's use of relative instructions (which should also
be fine in zSeries) might be the culprit...
Admittedly - this are all guesses, and could use
the watchful eye of some serious performance tester.
- Dave Rivers -
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