[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[manu at gcc dot gnu.org]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62182

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-28
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
I'm going to confirm this because we obviously want it.
>From gcc-bugs-return-478827-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Feb 28 12:58:34 2015
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide249

Oleg Endo <olegendo at gcc dot gnu.org> changed:

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                 CC|                            |olegendo at gcc dot gnu.org

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
Created attachment 34901
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4901&actioníit
Reduced test case

[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[arnaud.bienner at ensimag dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62182

Arnaud Bienner <arnaud.bienner at ensimag dot fr> changed:

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                 CC|                            |arnaud.bienner at ensimag dot fr

--- Comment #2 from Arnaud Bienner <arnaud.bienner at ensimag dot fr> ---
Related bug: bug 53598.

[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[arnaud.bienner at ensimag dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62182

--- Comment #3 from Arnaud Bienner <arnaud.bienner at ensimag dot fr> ---
Created attachment 35324
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35324&action=edit
unused-comparison warning

I also believe it can be useful to have "unused comparison" warning (i.e.
something more specific than current "unused value" warning, because they are
likely to be typo.
Having a dedicated warning will allow people who want to activate this warning
specifically and/or to turn it into an error.

So I started to have a look at this and I would like to have some feedback from
someone more experienced.
It's my first patch to gcc, so it is probably not perfect.

One thing that doesn't work is turning on this warning using
-Wunused-comparison parameter. But surprisingly, turning it off with
-Wno-unused-comparison (when -Wunused or -Wall is used) works. Not sure what
I'm missing here.

The patch would just be a first step: the next step would be to also raise this
warning in the case of a "==" operator overloading in C++ (which seems to be
the case that doesn't raise a warning currently). Not sure yet how to do this.

[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62182

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Arnaud Bienner from comment #3)
> Created attachment 35324 [details]
> unused-comparison warning

You need testcases, and to run the testsuite. See point 4 at:
https://gcc.gnu.org/wiki/GettingStarted#Basics:_Contributing_to_GCC_in_10_easy_steps

> One thing that doesn't work is turning on this warning using
> -Wunused-comparison parameter. But surprisingly, turning it off with
> -Wno-unused-comparison (when -Wunused or -Wall is used) works. Not sure what
> I'm missing here.

That is very weird. I don't see anything wrong in your patch about this.

Nonetheless, please add the warning to c-family/c.opt not to common.opt since
it is a C/C++ warning.

Also watch out for the formatting (too long lines, incorrect indentation, etc.)
See point 6 in the link above.

> The patch would just be a first step: the next step would be to also raise
> this warning in the case of a "==" operator overloading in C++ (which seems
> to be the case that doesn't raise a warning currently). Not sure yet how to
> do this.

It is more than ok to do one patch per step. Try to get the first patch right
and committed, then worry about the next.
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Subject: [Bug c/65781] gcc-5.1.0-RC-20150412 thinks it is 5.0.1
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65781

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

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                 CC|                            |manu at gcc dot gnu.org

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
To be honest, it is pretty confusing even to me. If 5.0.1 denotes RC1, then why
not call it  5.0.1-20150412 ? Then RC2 would be denoted by 5.0.2, and so on. As
a general rule, X.0.N, where N > 0 could always be release candidate number N.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd921

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

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--- Comment #13 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
I still see this failure on trunk. 6.0

[Bug c++/62182] New warning wished: operator== and "equality comparison result unused [-Wunused-comparison]"/-Wunsed-value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62182

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Arnaud Bienner from comment #3)
> One thing that doesn't work is turning on this warning using
> -Wunused-comparison parameter. But surprisingly, turning it off with
> -Wno-unused-comparison (when -Wunused or -Wall is used) works. Not sure what
> I'm missing here.

Because the emit_side_effect_warnings calls are guarded by warn_unused_value.