G'day all.
On Sun, Apr 28, 2002 at 11:44:04AM -0400, Dan Sugalski wrote:
> We're going caller-save. I think I made this declaration before, but
> now it's backed up with pure PDD goodness. :)
The first thing to realise is that this violates the principle of
"callee does everything important to it". :-)
More seriously, this is the opposite extreme, and IMO it's also not
a good idea.
OO code is full of subs which a) are called very often and b) look
like this:
sub code
{
my $self = shift;
return $self->{CODE};
}
sub body
{
my $self = shift;
if (@_) {
$self->{BODY} = shift;
}
return $self->{BODY};
}
Maybe half a dozen registers used in each one at the most. A caller is
obliged to save _all_ its registers in order to call these trivial
subs. Now admittedly we have a single op for this, so at least in the
interpreter it may not cost as much as a whole bunch of individual
register saves. For other targets (JIT), unnecessary caller saves will
almost certainly cause a measurable performance hit on OO-like code.
Cheers,
Andrew Bromage
