Re: skip_evaluation

[Paolo Bonzini <paolo dot bonzini at gmail dot com>]

> In asking this, I'm particularly puzzled by code like this in
> build_base_path in cp/class.c:
>
>   /* Don't bother with the calculations inside sizeof; they'll ICE if the
>      source type is incomplete and the pointer value doesn't matter.  */
>   if (skip_evaluation)
>     {
>       expr = build_nop (build_pointer_type (target_type), expr);
>       if (!want_pointer)
> 	expr = build_indirect_ref (EXPR_LOCATION (expr), expr, NULL);
>       return expr;
>     }
>
> Presumably the early return is OK within a sizeof expression; it is OK
> within an expression like (0 ? x : y)?

From reading the code, I'd say yes.  The bug that Jason fixed is 
related to stuff that cannot appear within a constant expression except 
within sizeof -- for example

   struct B {};
   struct D : public B {
       static const int i = sizeof((B*)(D*)0);
   };

   struct Z {};
   struct A : Z {};
   Z* implicitToZ (Z*);
   struct B : A {
       static const int i = sizeof(implicitToZ((B*)0));
   };

   struct B {};
   struct D;
   D* p;
   struct D: public B {
       static const int i = sizeof ((B*)p);
   };

(see PR27177).  All of these would still be forbidden within (0?x:y).

Paolo