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To: Alexander Best <arundel@FreeBSD.org>
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Cc: freebsd-toolchain@FreeBSD.org, Dimitry Andric <dim@FreeBSD.org>
Subject: Re: [poc] buildkernel + clang + -Werror
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On Nov 6, 2011, at 1:58 PM, Alexander Best wrote:

> On Sun Nov  6 11, Dimitry Andric wrote:
>> On 2011-11-06 21:33, Alexander Best wrote:
>> ...=20
>>> the problem is, something like
>>>=20
>>> uint x;
>>>=20
>>> if (x < 0) ...
>>>=20
>>> clang will warn about this, yet it is 100% valid code so my vote =
would be to
>>> make such an error into a warning.
>>=20
>> Sorry, but checking something unsigned to be smaller than zero is =
bogus,
>> or at the least superfluous, and it's perfectly sane to warn about =
this,
>> especially since the compiler is not going to emit code for it at =
all.
>=20
> there was a discussion with the topic
> "disable -Wtautological-compare for clang" on freebsd-toolchain@ and =
most of
> the devs considered this code *not* to be bogus. ;)

The code actually is bogus.  It may be masking a real problem, because =
often times it is a "sanity check" to make sure that you aren't doing =
something naughty, like passing -1 for the length.  However, if you then =
pass the unsigned through a signed value, it suddenly becomes negative, =
and you have a hard to spot bug.  IIR the the tread, there weren't too =
many people offering an opinion...

Warner=