Re: GCC + libJIT instead of LLVM

[Basile STARYNKEVITCH <basile at starynkevitch dot net>]

Andrew Haley wrote:
> > > Useful for what?  I think you have to tell us how this will improve the
> > > experience of gcc users .
> > >       
>
> Kirill Kononenko wrote:
>   
> > More useful in implementation of Just-In-Time compilation in Virtual
> > Machine runtimes. For example, for Microsoft Common Intermediate
> > Language (.NET).
> >     
>
> We already know what a JIT does, thank you.  I think you have to tell us how
> having libjit integrated in gcc will improve the experience of gcc users.
> As opposed to them, say, using libjit as a library separate from gcc.
>   

I still do not understand exactly what Kirill Kononenko is thinking about.

However, I see several interesting issues raised here:

the first is to [re-]use GCC for just in time compilation, for instance 
to JIT-compile CLI or JVM bytecode into machine code, or even C or some 
specialized gimple-like representation into machine code, or CLISP into 
machine code, all this using most of existing code in GCC (certainly the 
middle-end and a back-end). This might be doable, is certainly 
interesting (I heard even that some major GCC contributor[s] wanted that 
to happen), but remains difficult (because GCC was not designed for 
that). Note that libjit per se is not useful in that case, but GCC would 
be made as a server (or a library) which happens to deliver some of 
libjit or LLVM functionalities (the ability to generate code).

The second issue (which perhaps Kirill did not thought of) would be to 
accelerate some internal optimisations of GCC by using JIT-code 
generation techniques within the compiler itself. There are several 
occasions within GCC where complex internal processing happens, and one 
could imagine to "partially evaluate" them (w.r.t. to the compiled 
source program) by generating some code specifically tuned to that 
processing. BTW, the MELT branch was designed with such stuff in mind, 
and indeed can generate some code (currently, it generates C code, run 
the host compiler on it, dlopen it, and use it; in principle I could 
have used libjit instead of forking a compilation process from inside cc1).

I still don't understand what Kiril is thinking of exactly. In contrast 
to Andrew, I don't believe it is an April Fool's joke, but perhaps a 
language issue: both Kiril & me Basile are not native English speakers, 
and we may have difficulties in finding the right words & express 
ourself fluently in English. If it is the case please forgive us (or 
just try to interact on a french or russian mailing list!).

Regards.

--
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
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