Re: [PATCH] bitops: simplify generic bit finding functions

Linus Torvalds
2008-04-27T20:39:27Z

On Sun, 27 Apr 2008, Harvey Harrison wrote:
>
> Oh, I didn't realize, I only did this because sparse started spewing out
> lots of:
> include/linux/bitops.h:166:32: warning: shift too big (65536) for type unsigned long

Well, that's really just a sparse bug/misfeature that didn't matter
before.

It happens because the warning is done as part of constant expression
evaluation, but then the expression isn't actually *used*, so when we
optimize it away - at a later date - it's too late to undo the warning.

I don't rightly know how to fix it. We do want to do the constant
evaluation early (since all the optimizations that may then make it a
non-issue depends on constants being constants!), but in order to not
output the warning we'd have to turn the constant into a "constant with
warning 'xyz' if used".

Which we have no support for in sparse yet.

Linus