To the list & Anthony.

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.

Now for the 68K gcc version, this seems true, in many places 
addresses are moved into registers and manipulated, versus back and 
forth to the stack. Say 8 clock cycles instead of 32, and it also 
reduces the number of instructions by one or two, here and there. So 
I was quite excited to attempt to build a new VM today. Mmm if there 
is enought interest from the 68K mac folks, I might even build a new 
VM.

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.

-- 
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John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
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