Re: FYI: No JIT on Windows 8 for ARM
- From: Joshua Ballanco <jballanc@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Thu, 10 May 2012 20:02:27 +0300
On Thursday, May 10, 2012 at 6:44 PM, Mike Pall wrote:
> Joshua Ballanco wrote:
> > [...] but would it be possible (in theory) to combine something
> > like the trampolines from imp_implementationWithBlock with
> > Return-oriented Programming (possibly with the benefit of a
> > pre-built page containing common code sequences) to achieve
> > something like a JIT compiler?
> >
>
>
> Sure. But that's sort of the opposite of a call-threaded
> interpreter (call opcode_a; call opcode_b; ...). So it's really
> more like an interpreter, not a JIT compiler.
>
> And a terribly slow one, too: returns are only branch-predicted
> when there was a previous matching call (most CPUs have a small
> internal return address prediction stack). Otherwise, the return
> is mispredicted, which is very costly: a full pipeline flush costs
> about 7-20 cycles, depending on the CPU. You really, really don't
> want a full pipeline flush every other instruction. ;-)
>
>
Ah, totally makes sense. I hadn't even considered attempts to predict past
returns. Thanks for the information. (I see I still have a lot to learn!)
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