[Bug c++/56930] New: regression: pointless -Wconversion warning with sizeof

[Bug c++/56930] New: regression: pointless -Wconversion warning with sizeof

[jens.maurer at gmx dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

             Bug #: 56930
           Summary: regression: pointless -Wconversion warning with sizeof
    Classification: Unclassified
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jens.maurer@gmx.net


int main()
{
  int x = sizeof(int);
  int y { sizeof(int) };
}

$ g++ -Wconversion -std=c++11 conv.cc 
conv.cc: In function ‘int main()’:
conv.cc:3:17: warning: conversion to ‘int’ from ‘long unsigned int’ may alter
its value [-Wconversion]
   int x = sizeof(int);
                 ^


gcc 4.7.x didn't warn about this case, and rightly so: There should be no
conversion warnings triggered if the compiler can detect that the value in
question is constant and no narrowing actually happens.


conv.cc:4:17: warning: conversion to ‘int’ from ‘long unsigned int’ may alter
its value [-Wconversion]
   int y { sizeof(int) };
                 ^

The warning in this case is even more confusing: The compiler should generate a
language-mandated diagnostic if narrowing a non-constant, but the warning is
just besides the point at all.
>From gcc-bugs-return-419890-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Apr 12 07:22:25 2013
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From: "zeratul976 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/52748] [4.9 Regression][C++11] N3276 changes to decltype
Date: Fri, 12 Apr 2013 07:22:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idR748

--- Comment #16 from Nathan Ridge <zeratul976 at hotmail dot com> 2013-04-12 07:22:20 UTC ---
(In reply to comment #15)
> (In reply to comment #14)
> > Here is a related example that still fails to compile:
>
> Fixed.

It still fails if we make S a template:


template <int> struct A;

template <typename T> struct B : A<sizeof(T)> {};

template <typename F>
B<typename F::type> operator-(F);

template <typename T>
struct S
{
    struct F
    {
        typedef S type;
    };

    auto foo() -> decltype(-F());
};

int main()
{
    S<int> s;
}


test.cpp: In instantiation of 'struct B<S<int> >':
test.cpp:16:28:   required from 'struct S<int>'
test.cpp:21:12:   required from here
test.cpp:3:42: error: invalid application of 'sizeof' to incomplete type
'S<int>'
 template <typename T> struct B : A<sizeof(T)> {};
                                          ^

Tested with r197837.

[Bug c++/56930] [4.8/4.9 regression] pointless -Wconversion warning with sizeof

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-05-22
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Target Milestone|---                         |4.8.1
            Summary|regression: pointless       |[4.8/4.9 regression]
                   |-Wconversion warning with   |pointless -Wconversion
                   |sizeof                      |warning with sizeof
     Ever confirmed|0                           |1

[Bug c++/56930] [4.8/4.9 regression] pointless -Wconversion warning with sizeof

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

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

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So perhaps for the purposes of the -Wconversion warning we also want to
t = fold_nondependent_expr_sfinae (expr, tf_none);
t = maybe_const_value (t);
before warnings_for_convert_and_check call and pass the result of that instead
of expr?

[Bug c++/56930] [4.8 regression] pointless -Wconversion warning with sizeof

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.8/4.9 regression]        |[4.8 regression] pointless
                   |pointless -Wconversion      |-Wconversion warning with
                   |warning with sizeof         |sizeof

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 4.9 so far.

[Bug c++/56930] [4.8 regression] pointless -Wconversion warning with sizeof

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

Bug 56930 depends on bug 57391, which changed state.

Bug 57391 Summary: [4.9 Regression] ICE compiling AIX math.h caused by PR c++/56930
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57391

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |FIXED

[Bug c++/56930] [4.8 regression] pointless -Wconversion warning with sizeof

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.1                       |4.8.2

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.1 has been released.

[Bug c++/56930] [4.8 regression] pointless -Wconversion warning with sizeof

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 4.8.2.

[Bug c++/56930] [4.8 regression] pointless -Wconversion warning with sizeof

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56930

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Wed May  7 16:09:41 2014
New Revision: 210178

URL: http://gcc.gnu.org/viewcvs?rev=210178&root=gcc&view=rev
Log:
    Backported from mainline
    2013-11-28  Jakub Jelinek  <jakub@redhat.com>

    PR c++/59297
    * semantics.c (finish_omp_atomic): Call finish_expr_stmt
    rather than add_stmt.

    * g++.dg/gomp/pr59297.C: New test.

    2013-05-31  Jason Merrill  <jason@redhat.com>

    PR c++/56930
    * semantics.c (potential_constant_expression_1): Handle OMP_ATOMIC*.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/gomp/pr59297.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/semantics.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog