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Date: Thu, 3 Nov 2011 11:01:52 +0000
From: Alexander Best <arundel@freebsd.org>
To: Gerald Pfeifer <gerald@pfeifer.com>,
	Matthias Andree <mandree@FreeBSD.org>, Warner Losh <imp@bsdimp.com>,
	Roman Divacky <rdivacky@freebsd.org>
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Cc: freebsd-toolchain@freebsd.org
Subject: Re: [toolchain] disable -Wtautological-compare for clang
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On Mon Oct 17 11, Gerald Pfeifer wrote:
> On Tue, 18 Oct 2011, Matthias Andree wrote:
> >> any chance we could disable -Wtautological-compare for clang? i don't 
> >> think comparing an unsigned int against < 0 is worth a warning. 
> >> actually it's always nice to have such a seatbelt, in case somebody 
> >> changes the type to int and forgets to introduce such a check.
> > If your code must be unclean in such a way that it uses deliberately 
> > dead code "just in case someone breaks the semantics", can you not use 
> > -Wno-tautological-compare in that situation?
> 
> It's not as straightforward, sadly, which is why I mentioned I am
> on the fence somehow.
> 
>   if (TYPE_MIN <= var && var <= TYPE_MAX)
> 
> or
> 
>   if (var < TYPE_MIN || var > TYPE_MAX)
> 
> are not that uncommon, in well written application, and if TYPE_MIN
> then evaluates to 0, we'll get a warning.
> 
> > Unless someone goes to paranoia mode and sprays unneeded checks like you
> > suggest all over the code like an ugly graffity, all such warnings are
> > worth investigating.  In code I've hand my eyes and/or hands on, the
> > better part of these warnings were pointing to true bugs.
> 
> In my experience some were, while others were of the class above.

however keeping these checks means that for gcc we can never turn on -Wextra,
since it enables these checks. while, running clang they can be turned off via
"-Wno-tautological-compare", there's no way of turning them off under gcc,
except for removing the -Wextra flag again.

cheers.
alex

> 
> Gerald