Re: [named address] ice-on-valid: in postreload.c:reload_cse_simplify_operands

["Ulrich Weigand" <uweigand@de.ibm.com>]

Michael Matz wrote:
> On Fri, 5 Aug 2011, Ulrich Weigand wrote:
> > Instead, if you just have a address and you don't know ahead of time
> > whether it refers to Flash or RAM space, you ought to hold that number
> > in an "int" (or "short" or whatever integer type is most appropriate),
> > and then convert from that integer type to either a "char *" or a
> > "char __pgm *".
> 
> That would leave standard C.  You aren't allowed to construct pointers out 
> of random integers.

C leaves integer-to-pointer conversion *implementation-defined*,
not undefined, and GCC has always chosen to implement this by
(usually) keeping the value unchanged:
http://gcc.gnu.org/onlinedocs/gcc-4.6.1/gcc/Arrays-and-pointers-implementation.html
This works both for default and non-default address spaces.

Of course, my suggested implementation would therefore rely on
implementation-defined behaviour (but by simply using the __pgm
address space, it does so anyway).

> That would point to a third address space, call it "undef" :)  It would be 
> superset of default and pgm, conversions between undef to {default,pgm} 
> are allowed freely (and value preserving, i.e. trivial).

That would probably violate the named AS specification, since two different
entities in the undef space would share the same pointer value ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com