[cfe-dev] atomic builtins

[Chris Lattner]

Hi All,

I'm looking into implementing the atomic builtins correctly.  These  
are documented here:
http://gcc.gnu.org/onlinedocs/gcc/Atomic-Builtins.html#Atomic-Builtins

A funny thing of these is that they are overloaded (arg).  This means  
that code that calls __synch_fetch_and_add with an int ends up calling  
__synch_fetch_and_add_4, for example.  It also


I see a couple of ways to implement this:

1. Expand the attribute overloadable stuff to work from builtins.td  
somehow.  I'm not sure how to extend builtins.td to handle this, and  
I'm also not sure how overloading can reasonably handle insane cases  
like this (without enumerating every possible pointer type?):

int *test(int *A, int **P) {
   return __sync_fetch_and_add(P, A);
}

If we could get this resolved into a different builtin id for every  
width, the code generator could do the right thing.

2. Add all the versions (with the name suffixes) to the builtins.td  
file and have sema change the AST (introducing casts and a new callee)  
when it analyzes the call.

3. Add just the overloaded version of the builtin to the builtins.def  
file, and make sema change it into a new AtomicExpr node.  This would  
be better than #2 for representing the source level construct.

Does anyone have an opinion on this?  I'm not exactly sure what is  
required to get #1 working.  If that can't work, I tend to think that  
#3 is best.

-Chris