Re: [Tinycc-devel] Re: C67 Support

[Fabrice Bellard]

Peter "Firefly" Lund wrote:
> On Sun, 16 Mar 2003, Fabrice Bellard wrote:
>
>
> > ELF is very simple if no relocation are done. All we need is to define a
> > correspondant machine id for TMS320C6xx.
>
>
> I know -- but if tcc is the only tool that uses ELF, what's the point ?

You are right :-) I made this proposal just to ensure that the ELF/COFF 
generator can be selected independantly from the CPU.

> > Ok for pointer and longs (it is needed for 64 bit CPUs). For ints I am
> > not sure it is useful and it would be more complicated.
>
>
> For easier portability testing using only one machine -- no, I don't know
> how hard it would be and of course it is not like I'm going to push
> patches for it to you tomorrow.  tcc needs many other things first.
>
>
> > Do you agree that only compile time selection is needed for that ?
>
>
> Errr... possibly yes.  Compile-time for what?  For the compiler?  No.
> For the compiled program?  Why, naturally.

Sorry, I meant compile time when compiling the compiler. It means that 
you won't have an option tcc -EL or tcc -EB to force little or big 
endian for example.

> > Bochs is incredibly slow and written in C++.
>
>
> Some of the slow speed is because it has to handle the hardware and it
> does that in a not so efficient way.  Some of it is because it has to
> handle memory mapping.  Some of it is due to a speed bug in the screen
> updating code.  And then some of it is due to it not being a JIT -- but
> that is not the most important part.

Right. From what I have seen in the code of bochs, it would be difficult 
to use it as a fast user space emulator (dispatching is done with 
functions, lazy flag evaluation is not optimal). Moreover, I find the 
code of bochs quite redundant - I factorized all the opcodes which gives 
a rather small and simple code.

> Let me guess...
>
> 1) You first write a main loop as an interpreter with a big switch in it.
> 2) when that works you compile (in the true sense of the word) snippets
> from that switch between the cases as the translation for a piece of code.
>
> I got that idea, too, about a year ago (I was playing with Moscow ML to
> see how I could speed it up).  Unfortunately, somebody else had invented
> that technique and published on it in 1998:
>
> http://citeseer.nj.nec.com/piumarta98optimizing.html
>
> (my actual implementation was somewhat different: it required less code
> and was slightly faster and tighter but you had to inspect the code the
> compiler generated -- but you really have to with Piumarta/Riccardi's
> implementation, too, because it is not as truly portable as it looks like)

Thank you for the reference - I'll add it in the documentation. I was 
sure I did not invent this method since 'executor' was also using 
similar ideas. But I went much further than explained in the article you 
mention, at the cost of slightly more CPU dependancy (the CPU dependancy 
is about the same as a dynamic linker such as ld.so). The goal was to 
achieve higher speed than just suppressing the dispatch stage.

Fabrice.