Is there a way to look for a tree by its UID?

[Erick Ochoa]

I think every SSA_NAME variable has a:

* ptr_info_def*
* which points to a pt_solution
* which points to a bitmap field vars

and I think this bitmap vars is set with 1 in the UID location of 
variables/references that an SSA_NAME variable might point to it.

So, I am just wondering is there an interface where I could do something 
like:

```
     // vars is the field in pt_solution of type bitmap
     EXECUTE_IF_SET_IN_BITMAP (vars, 0, uid, bi)
     {
        // uid is set
        tree pointed_to = get_tree_with_uid(uid);
     }
```

Thanks!