Re: `size_volatile' types

[Peter Gerwinski <peter at gerwinski dot de>]

Jeffrey A. Law wrote:
> I didn't understand the "or even for one and the same object within its scope".
> 
> Are you trying to say that the size/offsets can vary for two objects of the
> same type within the same scope?  Or are you trying to say that the 
> positions/types of the sam object can vary within the scope of the object?

Yes, the size of one variable (the target of a pointer) can
change within the scope of the variable.  To illustrate this,
here is a short example:

    Program Foo;

    Type
      A ( n: Integer ) = array [ 1..n ] of Integer;

    Var
      A42: A ( 42 );     (* an `array [ 1..42 ] of Integer' variable *)
      A137: A ( 137 );   (* an `array [ 1..137 ] of Integer' variable *)
      B: ^A;             (* a pointer do an `A' with arbitrary `n' *)

    begin
      B:= @A42;                   (* Assign the address of `A42' to `B' *)
      writeln ( SizeOf ( B^ ) );  (* Yields 172 on my machine *)
      B:= @A137;
      writeln ( SizeOf ( B^ ) )   (* Yields 552 on my machine *)
    end.

Since TYPE_SIZE (TREE_TYPE (B^)) (i.e. the size of the object
pointed to by `B') varies within the scope of `B', we must not
construct a SAVE_EXPR for this size.  Instead, the expression
for TYPE_SIZE (TREE_TYPE (B^)) contains `B^' as a PLACEHOLDER_EXPR.

   Peter