[cfe-dev] PATCH: Cleanup function redeclaration representations

[Argiris Kirtzidis]

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.


-Argiris