[cfe-dev] Incomplete set of warnings in clang

[Marshall Clow]

On Mar 10, 2014, at 12:22 PM, Richard Trieu <rtrieu at google.com> wrote:

> Marshall,
> 
> Equality comparisons appear to have their own subset of -Wunused-value in -Wunused-comparison.  -Wunused-comparison checks both builtin and overloaded == and !=, which is the two warnings you saw.  For the relational operators, -Wunused-value does not check for overloaded operators.  So a < comparison of int's would trigger -Wunused-value warnings while a < comparison of iterators would not.  This looks like an oversight from when the warning was implemented.  I think the fix is to move the relational comparisons into -Wunused-comparison so that relational overloads will also be warned on.

Sounds good to me.
If you don’t want to do this, I will … in about a week.

— Marshall

> 
> Richard.
> 
> 
> On Mon, Mar 10, 2014 at 11:23 AM, Chandler Carruth <chandlerc at google.com> wrote:
> (CC-ing our local warnings expert...)
> 
> 
> On Mon, Mar 10, 2014 at 11:13 AM, Marshall Clow <mclow.lists at gmail.com> wrote:
> As I was working on a libc++ issue (
> 2263. Comparing iterators and allocator pointers with different const-character), if anyone cares, I wrote the following test program:
> 
> #include <string>
> 
> int main() {
>   std::string::iterator it;
>   std::string::const_iterator cit;
> 
>   it == cit;
>   it != cit;
>   it < cit;
>   it <= cit;
>   it > cit;
>   it >= cit;
> }
> 
> I wanted to make sure that these were all legal comparisons using libc++ (and they are).
> I kind of expected some compiler warnings about “unused results” or something.
> 
> What I didn’t expect was to get _two_ warnings. I figured either zero or some multiple of six.
> 
> Apparently clang doesn’t like it if you don’t use the result of == or !=, but is perfectly happy with ignoring the results of >, >=, <, <=.
> 
> Why is that?
> 
> — Marshall
> 
> 
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> 

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