Re: [f-cpu] dynamic code reuse (fwd)

[Yann Guidon <whygee@f-cpu.org>]

hi,

Michael Riepe wrote:

> On Tue, Dec 09, 2003 at 10:47:07PM -0800, Raj Mahajan wrote:
>  
> > I read part of this paper... my main take-aways are as follows:
> >
> > 1) Instructions are often repeated verbatim.  This happens for many reasons
> > which are often difficult to address in the code or the compiler.
> >    
> As far as I remember, the address of the instruction is used to find
> the cache entry.  That is, caching won't work with repeated
> instructions (like function pro/epilogue boilerplate and such).
>
> But hey... I've found something to improve ;)
>  
such as ... ?

> > 2) Caching previous results of instructions can help by avoiding
> > re-computing complex instructions unnecessarily.
> >    
> Emphasis on _complex_, yes.
>
> The real problem -- and the reason why dynamic code reuse is not
> useful for FC0 -- is that you need an OOO core with all bells,
> whistles and gongs.  In our current design, we can't deal with the
> fact that a result may be available ahead of time.  Maybe later.
>  
F-CPU can't mandate that the core be OOO. Hence no standard F-CPU 
instruction can rely on a OOO core.

and, if one needs to repeat blocks of instructions, sub-functions exist 
for ages :-)

YG

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