Re: [Sablevm-user] SableVM question

[Marcel A. <ma...@ca...>]

Etienne M. Gagnon wrote (eg...@j-...)
> Hi!
> 
> Marcel Ammerlaan wrote:
> >                         Name: benchmark.tar.bz2
> >    benchmark.tar.bz2    Type: unspecified type (application/octet-stream)
> >                     Encoding: base64
> 
> 
> I've looked at your test2.c.  You wrote:
> 
>  goto *code_addr[data[i]];
> 
> This should have been:
> 
>  goto *datap++; 
> 
> to correspond to your switch based test.c.
> 
> Mainly, you forgot the bytecode->address pre-interpretation phase. 
> Mainly, you don't have bytecodes anymnore; each bytecode is directly
> replaced by its address, which is why it is much quicker (no loop, no
> bound check [included in a switch], etc.) 

I've experimented with pre-interpretation but it doesn't seem to matter
much (ie. same results). A testing version of that code is in test2.c.
I've included the new version (test3.c) which uses the same testdata.h.
Maybe I'm wrong (could be, haven't slept) but I don't think using goto
is going to be faster than the switch. As for the bounds check; I
remember that C doesn't guarantee anything when there is no default
label, aka. bounds check is optional.

I'd liked to be proved wrong because using the goto table makes some
things possible in a JVM that I'd like to try in my own VM.

I've tried both gcc 2.95.2 and gcc 2.7.2.3 and both give comparable
results.

Marcel

ps. The var=i statement in the interpreter loop becomes a NOP because 'i'
isn't changed anymore. GCC doesn't seem to see this.
-- 
Don't let people drive you crazy
when you know it's in walking distance