[cfe-dev] PATCH: Cleanup function redeclaration representations

[Chris Lattner]

On May 4, 2008, at 2:37 PM, Argiris Kirtzidis wrote:

> Chris Lattner wrote:
>>> --Another suggestion is to not add to the scope chain the  
>>> redeclarations (at all 5 cases, Scope[foo] = 1), thus all calls to  
>>> 'foo' will refer to the same FunctionDecl node.
>>> One way to go about this would be to have a double linked list of  
>>> redeclarations, and the (V) case would be:
>>>
>>> A: foo [prevdecl=null, nextdecl=null]  void foo(int x = 12, int y  
>>> = 0);  // does the 'aggregate' need to point to #1 as nextdecl ?
>>> 1: foo [prevdecl=A, nextdecl=2]  void foo(int x, int y);  // this  
>>> is what all calls to 'foo' refer to
>>> 2: foo [prevdecl=1, nextdecl=3] void foo(int x, int y);
>>> 3: foo [prevdecl=2, nextdecl=4] void foo(int x, int y = 0);
>>> 4: foo [prevdecl=3, nextdecl=null] void foo(int x = 12, int y);
>>>
>>> following prevdecl, last one = #A = aggregate
>>>
>>> We could use two DenseMaps to store the redeclaration links,  
>>> similar to the way Doug is using one in his patch, thus not  
>>> bloating ScopeDecls.
>>> (just to be pedantic again, on the above case, if #A doesn't link  
>>> to #1 as nextdecl, we save a link :) )
>>
>> How about just storing the list in reverse order.  This means that  
>> adding a new redecl would have to walk the list (to add the redecl  
>> to the end of the singly linked list), but that the aggregate  
>> version would always be at the head of the list.  This would make  
>> redecls slower but would make references to the function constant  
>> time.  Given that there are usually not hundreds of redecls of  
>> functions, I think it would be ok.  If we find that walking the  
>> list *is* a problem, there are more complex/clever solutions  
>> possible too.
>
> The issue with the reverse order single list is that when the  
> consumer receives a redecl it cannot know if it's a redecl (the last  
> decl doesn't point to another decl), and even if we add a flag to  
> indicate it, the consumer will know that it's a redecl but it will  
> not be able to get the original decl and/or the aggregate one from  
> the latest redecl.

Do you mean that you can't tell if you are looking at the aggregate  
decl or a real decl?  If so, the aggregate decl could just have a null  
source location, to indicate that it is synthetic.

-Chris