--- John M McIntosh <johnmci at smalltalkconsulting.com> wrote:
> I was looking at CGeneratorEnhancements-ajh.cs with an eye towards 
> the statement about individual variables in each case statement 
> perhaps making things abit more optimizing friendly.
>
> But there is a problem
> You see if you just apply this change set, you can't get a runnable vm.
> why? well
> self sharedCodeNamed: 'commonReturn' inCase: 120.
> in Interpreter>>returnValue:to:
> 
> allows the code generator to build a common block of code within a 
> case statement (label commonReturn: in case 120), then other case 
> blocks can jump to the code, hint they share variables. But with 
> CGeneratorEnhancements-ajh.cs each case statement gets unique 
> variables like so:
> 
> (ack a goto aren't those evil?)
> 
>         case 121:
>             /* returnTrue */
>             cntx1 = longAt(((((char *) localHomeContext)) 
> + 4) + (0 << 2));
>             val1 = trueObj;
>             /* begin returnValue:to: */
>             goto commonReturn;
>         l4: /* end returnValue:to: */;
>             break;
>         case 122:
>             /* returnFalse */
>             cntx2 = longAt(((((char *) localHomeContext)) 
> + 4) + (0 << 2));
>             val2 = falseObj;
>             /* begin returnValue:to: */
>             goto commonReturn;
> 
> However in commonReturn the variables used are cntx and val, and of 
> course we fail to proceed.
> 
> Ah but the old code used t1 and t2, and you're right if you guessed 
> commonReturn: used
> t1 and t2 in the correct places. Design or accident?
> 
>         case 121:
>             /* returnTrue */
>             t2 = longAt(((((char *) localHomeContext)) + 
> 4) + (0 << 2));
>             t1 = trueObj;
>             /* begin returnValue:to: */
>             goto commonReturn;
>         l4: /* end returnValue:to: */;
>             break;
>         case 122:
>             /* returnFalse */
>             t2 = longAt(((((char *) localHomeContext)) + 
> 4) + (0 << 2));
>             t1 = falseObj;
>             /* begin returnValue:to: */
>             goto commonReturn;
> 
> 
> Mmm now I could hack something together, but thought I should look 
> for a more correct solution.

If you look at the comment in sharedCodeNamed:inCase: it says not to use this
in methods that take args.  The work around is to define a new global and use
it to pass the args.  You can make the global local to the interpret() function
the same way localSP and a few others are.  From John's subsequent posts it
looks like he figured this out already.

Cheers,
Anthony

__________________________________________________
Do You Yahoo!?
Yahoo! Tax Center - online filing with TurboTax
http://taxes.yahoo.com/