Re: [Lightning] On the benefits of inlining

[Paolo Bonzini]

> However,
> patching the `movi' instruction (in order to pass the input/output
> parameter) is done every time before the dynamically compiled code is
> used. I was assuming that patching was pretty lightweight, at least
> on RISC machines.
That's why a register would be preferable.  Patching is about as 
expensive as writing one instruction, or only slightly less.  That is, 
jit_movi + jit_patch_movi is about as expensive as writing 2 movs.

> > Instead of the goto you can put an asm ("jmp *%0" : : "r" (&&abc) : 
> > "eax", "ecx", "edx"); so you can avoid the push/pop and GCC does not 
> > think that no instruction will execute after the jump (which it does, if 
> > you have a goto).  It is unportable, however. :-(
> >    
> Right, hence the need for a mapping of register names.  And a mapping
> for some instructions (like `jmp') would come in handy as well.  ;-)
Yes... I have to think about it, I must admit I don't like the idea of 
providing asm statements within lightning.h.  Even though the way you'd 
be using it is indeed cute.

> > This would *not* make sense for very small pieces of code like this one, 
> > or did I miss something?
> >    
> Well, so long as the inlined code has to save registers and so on, this
> doesn't make much sense anyway.
... or it makes sense only for moderately large pieces of code.  I see 
your point now.,

Paolo