Re: [PATCH 16/16] fix handling of integer constant expressions

[Segher Boessenkool <segher@kernel.crashing.org>]

> > Here are three independently invalid non-ICEs that sparse doesn't
> > diagnose.
> >
> > extern int f(void);
> > enum { cast_to_ptr = (int) (void *) 0 };
> > enum { cast_to_float = (int) (double) 1 };
>
> Those two *really* shouldn't fail. I don't care if the C standard says 
> so,
> that is *fine*.

GCC doesn't guarantee you this, either.

> In particular, "offsetof()" should be portably able to basically be the
> standard #define, which involves an integer cast from a constant 
> pointer.
> That had *better* be a valid constant integer expression, because it's
> very useful.

Yes it's useful.  That's why GCC gives you __builtin_offsetof()
for this purpose.

> And I think standards can go screw themselves, and you can make it an
> error with some "--standard-pedantic" switch or similar.
>
> Standards are just random pieces of paper, for crying out loud! They 
> have
> zero relevance in the end.

Sure, as long as you don't care about compatibility across
compilers, what matters is what the compilers you _do_ use
actually implement.  And note that GCC doesn't guarantee
you much over what the C standard does.  Almost everything
it allows extra is just an implementation side effect.


Segher

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