Random musings from a discussion I had yesterday. (And check me on my
assumptions, please.)
One of the more common lamentations is that a dynamic language (like Perl)
doesn't mix well with optimizations, because the majority of optimizations
are done at compile time, and the state at compile time isn't always the
state at runtime. A common declaration is, "We'd like to optimize that, but
we can't, because foo may change at runtime."
Perl 5 optimizations replace (or, more accurately, null out) a more complex
opcode stream [1] with a simpler one. Constant folding is one such example.
5 -> add -> 10 -> add -> 15 -> store
becomes
30 -> store
plus a bunch of null ops. (The null ops are faster than attempting to
splice the new opcode stream [1] in place of the old one, but I don't know
by how much.)
Consider the following:
Create an optimization op, which is more a less a very fancy branch operator.
Whenever you elect to do an aggressive optimization, place the opt op as a
branch between the newly created... [1] and the old, full one.
The op could decide ( From a switch or variable - turn on and off
optimizations while running. Or from state introspection, perhaps, since you
probably have a good idea of what changes would invalidate it. ) whether to
exercise the optimized code, or revert to the original, unoptimized version.
I supposed, if you were to implement an advanced JIT, you could replace an
invalidated optimization with its newly optimized variant.
That would also work with a couple of tie-ins with the language. First,
of course, the ubiquitous pragma, which could affect which optimizations
(assuming we categorized them) we should run, and which we shouldn't, based
on the suggestions from the programmer. And perhaps some hook into the
internals for the same reason.
sub foo {
no optimizations;
...
}
or
{
local $opt = (ref $obj eq "SomeNewObject");
# If the $obj has changed, don't run any optimizations
}
Is this possible? Feasible? Way out there?
[1] Chain? Branch? What's the correct terminology here?
--
Bryan C. Warnock
[EMAIL PROTECTED]
