[Python-Dev] Optimization targets (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Fri Apr 16 02:00:12 EDT 2004

Jeremy Hylton wrote:

I'm not sure what you mean by the changes over standard JIT. Do you mean the difference between Hotspot and "standard JIT"? Your descriptions sounds a bit like the Deutsch and Schiffman inline method cache, which doesn't inline the method body but does inline the method lookup. Or does Hotspot actually inline methods?

I lost the link, but on some page describing it, they actually claimed they do inline methods. They went on explaining that you need "deoptimization" in case a different method should be called; I assume they generate a type check just before the inlined method body. I might be that they keep collecting statistics on how often the type guess was wrong to discard the inlining, and come up with a new one.

Hotspot operates by only compiling functions selectively, which have been invoked a number of times, and they claim they collect data on where virtual calls go to. So when they eventually do generate machine code, they have the data to do the inlining.

A "standard" JIT might chose to compile everything the first time it is invoked, and would then just replace the virtual-call bytecode with the necessary memory fetches and an indirect call.

Regards, Martin

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