Re: Optimizing Boundary Checks

[Dale Stanbrough <dstanbro@bigpond.net.au>]

Preben Randhol wrote:

> After reading some posts here lately I have understood that the compiler
> can optimise out boundary checks on say arrays if you do this:
> 
>    type Index_Range is range 1 .. 10;
>    type Items is array (Index_Range) of Natural;
> 
> But if you write:
> 
>    type Items is array (1 .. 10) of Natural;
> 
> is boundary checks then on?

There are no boundary checks for a type declaration of course, so 
the question is

   "in which situations would a check be generated"

Clearly this depends on the compiler, and the code. For example the
code
  
   x : Items;

   for i in x'range loop
      put (x (i));
   end loop;

is quite easy for a compiler to know that no checks are needed.
There are increasingly more difficult levels of analysis for the
compiler depending on the situation.

Dale