[cfe-dev] Validation of dependent expressions

[Douglas Gregor]

On Feb 25, 2009, at 8:37 AM, Sebastian Redl wrote:
> I've started some work on skipping validation of expressions that have
> dependent types and/or values. Am I doing it right?


Yes, you're on the right track. A few meta-comments:

   1) Whenever you have an expression 'E', prefer E->isTypeDependent()  
to E->getType()->isDependentType(). I think you're doing that already.

   2) In addition to updating Sema's type checking for value-dependent  
and type-dependent expressions, we also need to propagate those  
dependencies by updating the *Expr nodes themselves compute value- and  
type-dependence. For example, while updating the checking for array  
subscripting, we should also update ArraySubscriptExpr's constructor  
to accept (or compute) value- and type-dependence of the expression.  
For example, CallExpr has been updated to do this, and it uses


CallExpr::CallExpr(ASTContext& C, StmtClass SC, Expr *fn, Expr **args,
                    unsigned numargs, QualType t, SourceLocation  
rparenloc)
   : Expr(SC, t,
          fn->isTypeDependent() || hasAnyTypeDependentArguments(args,  
numargs),
          fn->isValueDependent() || hasAnyValueDependentArguments 
(args,numargs)),
     NumArgs(numargs) {

There's a big FIXME in the Expr class that will be addressed once  
*all* Expr nodes properly compute their type/value-dependence:

   // FIXME: Eventually, this constructor should go away and we should
   // require every subclass to provide type/value-dependence
   // information.
   Expr(StmtClass SC, QualType T)
     : Stmt(SC), TypeDependent(false), ValueDependent(false) {
     setType(T);
   }

Thanks for working on this!

	- Doug