Re: [PATCH] pointer to integer conversion.

[Iain Buclaw <ibuclaw at gdcproject dot org>]

On 23 November 2013 10:46, Andreas Schwab <schwab@linux-m68k.org> wrote:
> Iain Buclaw <ibuclaw@gdcproject.org> writes:
>
>> Currently, GCC is converting the expression to a signed integer
>> instead of an unsigned one.  Does a test for the testsuite need to be
>> written for this?
>
> The C standard makes this implementation-defined, and GCC defines it
> like this (*Note (gcc) Arrays and pointers implementation::):
>
>      A cast from pointer to integer discards most-significant bits if
>      the pointer representation is larger than the integer type,
>      sign-extends(1) if the pointer representation is smaller than the
>      integer type, otherwise the bits are unchanged.
>  ---------- Footnotes ----------
>
>  (1) Future versions of GCC may zero-extend, or use a target-defined
> `ptr_extend' pattern.  Do not rely on sign extension.
>
> Andreas.
>

OK, I've checked that document, and there's also a comment with it.
Apparently someone spotted this before.

@c ??? We've always claimed that pointers were unsigned entities.
@c Shouldn't we therefore be doing zero-extension?  If so, the bug
@c is in convert_to_integer, where we call type_for_size and request
@c a signed integral type.  On the other hand, it might be most useful
@c for the target if we extend according to POINTERS_EXTEND_UNSIGNED.


So where does this leave languages that say that pointer to integer
conversions are clearly defined?

In any case, the comment in convert_to_integer is - in my eyes - wrong.

Iain.