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SubjectRe: [PATCH][2.6.6-rc3] gcc-3.4.0 fixes
H. Peter Anvin writes:
> Mikael Pettersson wrote:
> >
> > You're assuming pointers have uniform representation.
> > C makes no such guarantees, and machines _have_ had
> > different types of representations in the past.
> >
>
> By the way, I am not in any shape, way or form making that assumption -
> although that's presumably how it would be *implemented* in an architecture
> with sane pointers like, to the best of my knowledge ALL gcc targets.
>
> (foo *)bar++;
>
> ... should be implemented as ...
>
> ({
> foo *tmp1 = (foo *)bar;
> tmp2 = tmp1 + 1;
> bar = __typeof__(bar)tmp2;
> tmp1;
> })

I did an experiment with updating an unsigned short
via a cast-as-lvalue to unsigned char, and gcc did
in fact implement the temp + copy semantics you
describe above. That is,

unsigned short x = 0xaafe;
((unsigned char)x)++;

resulted in x == 0x00ff.

So cast-as-lvalue is at least reasonably correctly
implemented in gcc.

Whether it's useful and portable is a another matter :-)
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