Bug in loop optimize (invalid postinc to preinc transformation)

[Jamie Lokier]

Robert Dewar wrote:
> <<Overflow of unsigned integers has defined behaviour -- they wrap.  The
> question is, what rule applies to pointer comparisons?
> >>
> 
> This is a malformed question. Any pointer increment is constrained 
> to require that the resulting pointer be valid. Wrapping is simply
> not an issue.
> 
> If p points to a valid address in an allocated array, then P+1 is also
> valid, and there is no question of wrap. But P+2 may be beyond the
> array and therefore ill-defined, and this has nothing to do with wrapping.

Quite.  There's a pointer constant in the offending code.  It's not in
any array.  Do we offer implementation defined behaviour for numerical
pointer constants or not?  They do come in useful occasionally.

-- Jamie