[Vm-dev] Powerful JIT optimization

[Florin Mateoc]

Hi Eliot,

I am not sure if this is the right moment to bring this up, when you are so busy with the new garbage collector, but,
since you were also talking about powerful new optimizations and this seems a very good one... I was toying with the
idea before, but I did not have the right formulation for it - I was thinking of doing it on the image side, at the AST
level and then communicating somehow with the VM (this aspect becomes moot if the JIT code is generated from Smalltalk),
but now I stumbled upon it on the web and I think it would be better done inside the JIT. In Rémi Forax' formulation:

"On thing that trace based JIT has shown is that a loop or function are valid optimization entry points. So like you can
have an inlining cache for function at callsite, you should have a kind of inlining cache at the start of a loop."

This was in the context of a blog entry by Cliff Click:
http://www.azulsystems.com/blog/cliff/2011-04-04-fixing-the-inlining-problem
The comments also contain other useful suggestions.

And, the loop inlining cache could also specialize not just on the receiver block, but also on the types of the
arguments (this is true for methods as well, but, in the absence of profiling information, loops are more likely to be
"hot", plus we can easily detect nested loops which reinforce the "hotness")

Regards,
Florin