Really, really const

[Andrew Haley <aph at redhat dot com>]

I'm trying to persuade gcc that a memory area is unchanging.  Consider
this:

extern const int a[];
extern void f();

int foo ()
{
  int n = a[0]; 
  f();
  n += a[0];
  return n;
}

Now, I know that a[0] can't change.  But is there any way to tell gcc
that i can't change?  const doesn't seem to do it:

        movl    a, %ebx
        call    f
        addl    a, %ebx

The memory a[0] is read twice.  Is there any attrribute I can use to
stop gcc from doing this?

Andrew.