[Bug c++/64383] New: missed warning for unused variable.

[Bug c++/64383] New: missed warning for unused variable.

[pluto at agmk dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

            Bug ID: 64383
           Summary: missed warning for unused variable.
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pluto at agmk dot net

#include <memory>
#include <vector>

int main()
{
    std::vector< std::shared_ptr< int > > v1;
    v1.push_back( std::make_shared< int >( 7 ) );
    for( auto p : v1 )
    {
    }
    std::vector< int > v2;
    v2.push_back( 7 );
    for( auto i : v2 )
    {
    }
}


the 'p' variable is not reported as unused.


% LANG=C g++ -Wall -g2 t.cpp -o t -std=c++1y
t.cpp: In function 'int main()':
t.cpp:13:15: warning: unused variable 'i' [-Wunused-variable]
     for( auto i : v2 )
               ^

[Bug c++/64383] missed warning for unused variable.

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
                 CC|                            |manu at gcc dot gnu.org

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
A minimized testcase would be helpful. Using delta would probably remove
already a lot: https://gcc.gnu.org/wiki/A_guide_to_testcase_reduction
>From gcc-bugs-return-471668-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Dec 23 20:55:35 2014
Return-Path: <gcc-bugs-return-471668-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Delivered-To: listarch-gcc-bugs@gcc.gnu.org
Received: (qmail 15693 invoked by alias); 23 Dec 2014 20:55:34 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Delivered-To: mailing list gcc-bugs@gcc.gnu.org
Received: (qmail 15669 invoked by uid 48); 23 Dec 2014 20:55:31 -0000
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/64396] Missed optimization in post-loop register handling
Date: Tue, 23 Dec 2014 20:55:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 4.9.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: minor
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields:
Message-ID: <bug-64396-4-8TRno2tHgb@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-64396-4@http.gcc.gnu.org/bugzilla/>
References: <bug-64396-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2014-12/txt/msg02675.txt.bz2
Content-length: 374

https://gcc.gnu.org/bugzilla/show_bug.cgi?idd396

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The reason is GCC tries to be smart of calculating s4 outside of the loop
because the iv that might be selected is not related at all to s4.  That is it
might do:
int limit = es4-s4;
int i = 0;

  for(i=0;i<limit;i++) {
    add_carry32(sum, *s4[i]);
  }

[Bug c++/64383] missed warning for unused variable.

[pluto at agmk dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

--- Comment #2 from Pawel Sikora <pluto at agmk dot net> ---
(In reply to Manuel López-Ibáñez from comment #1)
> A minimized testcase would be helpful. Using delta would probably remove
> already a lot: https://gcc.gnu.org/wiki/A_guide_to_testcase_reduction


one more small testcase w/o stl with missed warning.

struct Y
{
    ~Y(); // comment this line to get proper warning about 'unused y variable'
};
struct X
{
    static Y& get();
};
int main()
{
    Y& y = X::get();
}

clang 3.5.0 warns in both (w/ and w/o Y dtor) variants.
>From gcc-bugs-return-472796-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jan 12 12:07:34 2015
Return-Path: <gcc-bugs-return-472796-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Delivered-To: listarch-gcc-bugs@gcc.gnu.org
Received: (qmail 18674 invoked by alias); 12 Jan 2015 12:07:34 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Delivered-To: mailing list gcc-bugs@gcc.gnu.org
Received: (qmail 18636 invoked by uid 48); 12 Jan 2015 12:07:25 -0000
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/64383] missed warning for unused variable.
Date: Mon, 12 Jan 2015 12:07:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 4.9.2
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: cc
Message-ID: <bug-64383-4-gBMQlOZLn4@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-64383-4@http.gcc.gnu.org/bugzilla/>
References: <bug-64383-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-01/txt/msg00790.txt.bz2
Content-length: 593

https://gcc.gnu.org/bugzilla/show_bug.cgi?idd383

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
clang generally doesn't care about false positives.
And, the variable can be present just so that the dtor action is performed on
it (similarly to how other variables are there just to perform the ctor action
on it).

[Bug c++/64383] missed warning for unused variable.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On the #c2 testcase, gcc trunk now warns, starting with r217957.

[Bug c++/64383] missed warning for unused variable.

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Yes, this is already fixed by the patch for c++/63657. The testcases are
slightly different thus I'm going to add the reduced testcase before closing
the bug.

[Bug c++/64383] missed warning for unused variable.

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

--- Comment #7 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Tue Jan 20 14:19:32 2015
New Revision: 219896

URL: https://gcc.gnu.org/viewcvs?rev=219896&root=gcc&view=rev
Log:
2015-01-20  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/64383
    * g++.dg/warn/Wunused-var-23.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wunused-var-23.C
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug c++/64383] missed warning for unused variable.

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64383

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|paolo.carlini at oracle dot com    |
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.9.3

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done.