[cfe-commits] [Patch] Add new warning for logical not on LHS of comparison

[Chris Lattner]

On Oct 12, 2012, at 11:10 AM, Richard Trieu <rtrieu at google.com> wrote:

> On Fri, Oct 12, 2012 at 9:55 AM, Sean Silva <silvas at purdue.edu> wrote:
> How many lines of code have you compiled with this warning enabled?
> Millions. 
> How many bugs did it catch?
> Hundreds. 
> How many false positives did it have?
> I have only checked a few dozen so far.  No false positives so far.

This makes sense to me, use of a < comparison on a bool isn't something a "normal" person would write :)

-Chris

> Of course, there's some code like r165811 and r165812 that I just fixed, which technically works properly, but could be written in a different way.
> 
> -- Sean Silva
> 
> On Fri, Oct 12, 2012 at 12:38 PM, Richard Trieu <rtrieu at google.com> wrote:
> > This patch is for a new warning to Clang, called -Wlogical-not-compare.  It
> > is designed to catch the case where the user is attempting to negate a
> > comparison, but only manages to negate the LHS because of missing parens.
> > For instance, warn here:
> >
> >      if (!x < 5)
> >
> > The user probably meant:
> >
> >      if (!(x < 5))
> >
> > or
> >
> >      if (x >= 5)
> >
> > When emitted, the warning will have a note suggesting this as a fix-it (drop
> > the not and inverting the comparison operator).
> >
> > Also, a second note will be offer parenthesis around the LHS to silence this
> > warning.
> >
> >      if ((!x) < 5)
> >
> > This will not warn.
> >
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