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


On Sun, 24 Jun 2007, Al Viro wrote:
>
> Heh... The first catches are lovely:
> struct fxsrAlignAssert {
> int _:!(offsetof(struct task_struct,
> thread.i387.fxsave) & 15);

Ok, that's a bit odd.

> as an idiotic way to do BUILD_BUG() and
> #define _IOC_TYPECHECK(t) \
> ((sizeof(t) == sizeof(t[1]) && \
> sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
> sizeof(t) : __invalid_size_argument_for_IOC)
> poisoning _IOW() et.al., so those who do something like
>
> static const char *v4l1_ioctls[] = {
> [_IOC_NR(VIDIOCGCAP)] = "VIDIOCGCAP",

On the other hand, this one really does seem to be "nice".

I don't think it's a misfeature to be able to do "obvious compile-time
constant optimizations" on initializer indexes. The bitfield size thing in
some ways does do the same thing - it's clearly _odd_, but if I had my
choice, I'd prefer a language that allows it over one that doesn't.

> Objections? The only reason that doesn't break gcc to hell and back is
> that gcc has unfixed bugs in that area. It certainly is not a valid C
> or even a remotely sane one.

I agree that it's obviously not "valid C", but I don't agree that it's not
remotely sane. Why not allow that extension?

Linus
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