[Bug c/53661] New: Wrong narrowing conversion warning with -std=c++11

[Bug c/53661] New: Wrong narrowing conversion warning with -std=c++11

[tmsriram at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

             Bug #: 53661
           Summary: Wrong narrowing conversion warning with -std=c++11
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tmsriram@google.com


test.cc

enum Code {
  SUCCESS = 0
};

Code a;

int r[] = {a};

$ g++ test.cc -c -std=c++11
test.cc:7:13:warning: narrowing conversion of ‘a’ from ‘Code’ to ‘int’ inside {
} [-Wnarrowing]
 int r[] = {a};

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[tmsriram at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

Sriraman Tallam <tmsriram at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |c++
            Summary|Wrong narrowing conversion  |[gcc-4.7/4.8 regression]
                   |warning with -std=c++11     |Wrong narrowing conversion
                   |                            |warning with -std=c++11

--- Comment #1 from Sriraman Tallam <tmsriram at google dot com> 2012-08-07 22:33:58 UTC ---
Tip of trunk still fails.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-13 23:40:22 UTC ---
Manuel, what do you think about this? I see the warning happening because the
underlying type of Code is unsigned int.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

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

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-13 23:43:01 UTC ---
Actually adding Manuel in CC.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-09-14 06:05:09 UTC ---
(In reply to comment #2)
> Manuel, what do you think about this? I see the warning happening because the
> underlying type of Code is unsigned int.

Isn't this a warning mandated by the standard?

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

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

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-14 09:37:00 UTC ---
Indeed, I think it is, unless something says that the underlying type must be
int, but I don't think how. I think this PR is invalid. Let's ask Jason, to be
safe.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-09-14
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-14 13:46:12 UTC ---
This is a bug.  The values of Code (as per 7.2p7) are { 0, 1 }, and int can
represent both values, so the conversion is not a narrowing conversion.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

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

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-14 13:49:00 UTC ---
Ah, ah, I see, thanks.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-09-14 14:07:21 UTC ---
Wconversion does not warn either, but it also does not warn for:

enum Code {
  SUCCESS=-1
};

Code a;
void foo(void)
{
  unsigned int r;
  r = a;
}

Perhaps the code for handling this could be shared between Wconversion and
Wnarrowing (they warn in different cases but finding out these cases probably
requires similar code).

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #9 from Harald van Dijk <harald at gigawatt dot nl> 2012-09-14 16:28:40 UTC ---
Sorry for butting in, but is this really a bug?

7.2p5 says "Each enumeration defines a type that is different from all other
types. Each enumeration also has an underlying type. The underlying type can be
explicitly specified using enum-base; if not explicitly specified, the
underlying type of a scoped enumeration type is int. In these cases, the
underlying type is said to be fixed."

This is an unscoped enumeration type without an enum-base, so the underlying
type is not fixed. 7.2p7 starts as "For an enumeration whose underlying type is
fixed,", so does not apply. 7.2p6 does apply, but the relevant text of 7.2p7
that would make this code valid isn't present there.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 15:42:41 UTC ---
(In reply to comment #9)
> 7.2p7 starts as "For an enumeration whose underlying type is
> fixed,", so does not apply.

That's just the first sentence; the rest of p7 does apply.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 16:06:10 UTC ---
Author: jason
Date: Mon Sep 17 16:06:03 2012
New Revision: 191395

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191395
Log:
    PR c++/53661
    * typeck2.c (check_narrowing): Avoid false positives on conversion
    from enumeral type.

Added:
    trunk/gcc/testsuite/g++.dg/init/aggr9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck2.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #12 from Harald van Dijk <harald at gigawatt dot nl> 2012-09-17 16:25:09 UTC ---
Oops, quite right, sorry about that.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 16:41:49 UTC ---
Author: jason
Date: Mon Sep 17 16:41:41 2012
New Revision: 191398

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191398
Log:
    PR c++/53661
    * typeck2.c (check_narrowing): Avoid false positives on conversion
    from enumeral type.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/init/aggr9.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/typeck2.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.2

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 16:41:49 UTC ---
Author: jason
Date: Mon Sep 17 16:41:41 2012
New Revision: 191398

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191398
Log:
    PR c++/53661
    * typeck2.c (check_narrowing): Avoid false positives on conversion
    from enumeral type.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/init/aggr9.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/typeck2.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

--- Comment #14 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 16:42:44 UTC ---
Fixed for 4.7.2.

[Bug c++/53661] [gcc-4.7/4.8 regression] Wrong narrowing conversion warning with -std=c++11

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53661

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.2

--- Comment #14 from Jason Merrill <jason at gcc dot gnu.org> 2012-09-17 16:42:44 UTC ---
Fixed for 4.7.2.