[cfe-dev] annotation token documentation

[Argiris Kirtzidis]

Hi Chris & Doug,

Chris Lattner wrote:
> After my little fun hacking on annotation tokens, I decided to write 
> up some documentation so that I'd remember how they work the next time 
> around:
> http://clang.llvm.org/docs/InternalsManual.html#AnnotationToken

Thanks a lot for documenting it!

>
> Second, I think it would be interesting to consider handling the 
> "negative" case (when an identifier is not a type) by turning the 
> identifier into an annotation token as well, representing the variable 
> it resolves to (which could be null if it refers to nothing).  Right 
> now, if we see an identifier in the token stream, we don't know if 
> that means it is unresolved or whether it means that it is a variable 
> and backtracking already analyzed but did not change it.
>
> Argiris, do you think it would make sense to make a new annot_variable 
> that contains a (potentially null) pointer to a variable decl?  Even 
> without backtracking, this would reduce name lookups in C: right now 
> we try to decide if something is a type (which requires a lookup) then 
> decide its not, so we handle it as a variable (requiring another 
> lookup).  Specifically, things like:
>
> int x = sizeof(x);
>
> first call Sema::isTypeName then call Sema::LookupDecl.  If the parser 
> just called a "lookup the decl for this identifier" method, it could 
> annotate it once and avoid the second lookup.

This would work really well in combination with the suggestion by Doug 
about unifying the "identifier inquiring" methods in the Actions API. 
Something like "LookupIdentifier" which returns an enum describing it 
and optionally returning a void* through an out parameter ?


Douglas Gregor wrote:
> On Jan 5, 2009, at 10:13 PM, Chris Lattner wrote:
>
>   
> One thing we have to be careful of is that a given identifier can be  
> looked up in different ways in different contexts, so we have to know  
> when to throw away the results of a previous lookup. For example, and  
> identifier 'x' prior to a '::' is looked up differently that 'x' if it  
> is followed by something else.
>
>   

AFAIK an identifier followed by a '::' would always be looked up in a 
different context (using ActOnCXXNestedNameSpecifier) so there wouldn't 
be a need to change a previous annotation.

-Argiris