On Tue, Apr 23, 2013 at 1:59 AM, David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> If the narrower type is signed it is probably even more confusing!
> The high bits will be preserved unless you are masking off bit 31.
Yes. However, that case doesn't trigger with the normal case of small
values. So "~4" works fine with widening, in a way that "~4u" does
not.
Which doesn't mean that you aren't right, it only means that it's
harder to check for in sparse. The hacky little patch I sent out with
already resulted in a lot of noise for things like "~0u" (UINT_MAX)
and the "~4u" use in NLMSG_ALIGNTO, I'd dread to do the same for
signed values.
That said, with the most minimal value analysis (ie only looking at
constants), maybe it wouldn't be too bad. I started out just worrying
about the PAGE_MASK case, though, where we're talking about (somewhat
complicated) generated constants, and then the signed case is largely
irrelevant (although a signed "1 << 31" would - as you say - trigger
this same thing too).
Linus
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