There is also a SLANG optimization step involved. It's exploited by  
the GC code.

The smalltalk code for the GC logic consists of a number of methods,   
mark & sweep for example.
Normally these would be translated into individual C procedure calls,  
but the first optimization the
SLANG translator does is fold small methods that follow certain rules  
into the caller, and deletes the method
in question. There is a method in the image that notes methods it  
should not delete since an outside caller would
use them. So most of the GC logic which is spread over a few methods  
in Smalltalk get nicely folded into a single C procedure.
By doing this C optimizing compiler are more happy about you.

Now the 2nd optimization is that after folding all these smaller  
methods into a particular caller and we find that the
scope of variables that would be global actually are *ONLY* used by  
this method then we make the variables local
versus global in scope.   As a side effect this would make a global  
variable then become a local variable used in a
particular method.  Of course if you are depending on this variable to  
actually be global in scope you now have a problem

To defeat that optimization you need a dummy method that refers to the  
variable so that SLANG then
thinks the global variable is used in two different methods, thus it  
cann't be made into a local.


On 30-Jul-09, at 3:07 AM, Igor Stasenko wrote:

> 2009/7/30 Ang Beepeng <beepeng86 at yahoo.com>:
>>
>> I see this in SqueakVM souce, interp.c.
>>
>> sqInt dummyReferToProxy(void) {
>>        interpreterProxy = interpreterProxy;
>> }
>>
>> It looks strange to me. Can someone give me a clue?
>>
> it is a dummy function, referring to proxy :)
> It is done on purpose, because otherwise Code generator could decide
> to not declare the interpreterProxy variable, because it is not used
> anywhere.
> Of course, it would be better if we could tell this explicitly to
> codegen.. but dummy fn does the same..

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