[Bug c++/51253] New: [C++11][DR 1030] Evaluation order (sequenced-before relation) among intializer-clauses in braced-init-list

[Bug c++/51253] New: [C++11][DR 1030] Evaluation order (sequenced-before relation) among intializer-clauses in braced-init-list

[ai.azuma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

             Bug #: 51253
           Summary: [C++11][DR 1030] Evaluation order (sequenced-before
                    relation) among intializer-clauses in braced-init-list
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ai.azuma@gmail.com


Since DR 1030 http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1030
was accepted, I expect that the following code is well-defined and exits with
the status code 0. However, GCC 4.7.0 20111112 (experimental) with -std=c++11
produces a wrong executable. In addition, it spuriously warns about undefined
operations with -Wsequence-point option.

//////////////////////////////////
struct swallow{
  template<typename... Types>
  swallow(Types &&...){}
};

template<int... IS>
int f()
{
  int i = 2;
  swallow{ i = i * IS + IS... };
  return i;
}

int main()
{
  // `i = i * 2 + 2' should be sequenced before `i = i * 3 + 3'
  return f<2, 3>() == 21 ? 0 : 1;
}
//////////////////////////////////

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-10
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-10-10 09:24:08 UTC ---
Confirming.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

Akim Demaille <akim.demaille at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |akim.demaille at gmail dot com

--- Comment #2 from Akim Demaille <akim.demaille at gmail dot com> ---
Ping.  Still there with released 4.8.1 on GNU/Linux.  Using initializer lists
this way is a very handy way to handle variadic templates.

Cheers, and thanks for all the good work!

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[broes.decat at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

Broes De Cat <broes.decat at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |broes.decat at gmail dot com

--- Comment #3 from Broes De Cat <broes.decat at gmail dot com> ---
Confirmed, hit the bug with 4.7.3 in c++11 mode.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[st at quanttec dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

Stephan Tolksdorf <st at quanttec dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |st at quanttec dot com

--- Comment #4 from Stephan Tolksdorf <st at quanttec dot com> ---
I just stumbled over this bug with the current trunk version of GCC. It's a
pretty ugly bug.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #5 from Akim Demaille <akim.demaille at gmail dot com> ---
Happy two-year birthday, bug!  Sorry I'm (slightly more that) off-by-one.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #6 from Akim Demaille <akim.demaille at gmail dot com> ---
FWIW, because of this issue, I no longer use g++ for my project, which saddens
me.  If there were a means to put money on some bugs, I'd be happy to drop say
$50.  I do not pretend that should suffice, but maybe other people would be
happy to put money on their bugs, and maybe in end some bugs might be worth
shooting at.  Sort of crowd-funding.  Of course it would require some
infrastructure to support this, but maybe this would be worth considering?

Best regards.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #7 from Akim Demaille <akim.demaille at gmail dot com> ---
Hi all,

I'd really love to have some feedback on this issue.  It looks like nobody is
having a look at this.

Thanks for all the good work, and sorry for insisting.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

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

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

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Let's add Jason in CC.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

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

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

--- Comment #9 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Akim Demaille from comment #6)
> FWIW, because of this issue, I no longer use g++ for my project, which
> saddens me.  If there were a means to put money on some bugs, I'd be happy
> to drop say $50.  I do not pretend that should suffice, but maybe other
> people would be happy to put money on their bugs, and maybe in end some bugs
> might be worth shooting at.  Sort of crowd-funding.  Of course it would
> require some infrastructure to support this, but maybe this would be worth
> considering?

It would be nice if such infrastructure existed. Perhaps it would motivate more
people to contribute to GCC (current contributors have their hands pretty full
already). I know of: https://www.bountysource.com/trackers/384568-gcc
but I have never used it, so I don't know how it works.
>From gcc-bugs-return-446210-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Mar 13 17:49:48 2014
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Subject: [Bug c/60455] Imprecise column number of -Woverflow in array initializers
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`455

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-03-13
                 CC|                            |mpolacek at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Mine.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #10 from Akim Demaille <akim.demaille at gmail dot com> ---
Well, I have finally found a simple workaround for some of the cases: GCC seems
to be right in the order of evaluation when initializing an array so:

template<int... IS>
int f1()
{
  int i = 0;
  swallow{ i = 10 * i + IS... };
  return i;
}

fails, but

template<int... IS>
int f2()
{
  using swallow = int[];
  int i = 0;
  (void) swallow{ i = 10 * i + IS... };
  return i;
}

succeeds.  However, GCC's own libstdc++ is exposed to this bug, for instance
make_tuple.

$ cat foo.cc
#include <iostream>
#include <tuple>

struct swallow
{
  template<typename... Types>
  swallow(Types &&...){}
};

int incr()
{
  static int res = 2;
  return res++;
}

template<int... IS>
int f1()
{
  int i = 0;
  swallow{ i = 10 * i + IS... };
  return i;
}

template<int... IS>
int f2()
{
  using swallow = int[];
  int i = 0;
  (void) swallow{ i = 10 * i + IS... };
  return i;
}

int main()
{
  // `i = i * 2 + 2' should be sequenced before `i = i * 3 + 3'
  std::cerr << f1<2, 3>() << '\t';
  std::cerr << f2<2, 3>() << '\t';
  auto t = std::make_tuple(incr(), incr());
  std::cerr << std::get<0>(t) << std::get<1>(t) << '\n';
}

$ ./a.32
23    23    23
$ ./a.33
23    23    23
$ ./a.34
23    23    23
$ ./a.35
23    23    23
$ ./a.48
32    23    32
$ ./a.49
32    23    32

where 32...35 is clang++, and 48,49 is gcc.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Apr 11 17:08:47 2014
New Revision: 209309

URL: http://gcc.gnu.org/viewcvs?rev=209309&root=gcc&view=rev
Log:
    DR 1030
    PR c++/51253
    * cp-tree.h (CALL_EXPR_LIST_INIT_P): New.
    * call.c (struct z_candidate): Add flags field.
    (add_candidate): Add flags parm.
    (add_function_candidate, add_conv_candidate, build_builtin_candidate)
    (add_template_candidate_real): Pass it.
    (build_over_call): Set CALL_EXPR_LIST_INIT_P.
    * tree.c (build_aggr_init_expr): Copy it.
    * semantics.c (simplify_aggr_init_expr): Preevaluate args if it's set.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/semantics.c
    trunk/gcc/cp/tree.c

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Akim Demaille from comment #10)
>   auto t = std::make_tuple(incr(), incr());

That's not an initializer-list, it's a function call, so the order of
evaluation is not specified and that example is not relevant AFAICT.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Trunk still gives -Wsequence-point warnings, and PR 61382 has an example that
still fails

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[akim.demaille at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #15 from Akim Demaille <akim.demaille at gmail dot com> ---
(In reply to Jonathan Wakely from comment #13)
> (In reply to Akim Demaille from comment #10)
> >   auto t = std::make_tuple(incr(), incr());
> 
> That's not an initializer-list, it's a function call, so the order of
> evaluation is not specified and that example is not relevant AFAICT.

Yes, you are right, I had also realized that afterwards.  It would be
nice though if the standard could ensure that perfect forwarding could
preserve the guarantee on left-to-right "upward": convenience functions,
that wrap constructors for instance, could still be used safely.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #16 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Jun  4 15:51:01 2014
New Revision: 211235

URL: http://gcc.gnu.org/viewcvs?rev=211235&root=gcc&view=rev
Log:
    PR c++/51253
    PR c++/61382
gcc/
    * gimplify.c (gimplify_arg): Non-static.
    * gimplify.h: Declare it.
gcc/cp/
    * cp-gimplify.c (cp_gimplify_expr): Handle CALL_EXPR_LIST_INIT_P here.
    * semantics.c (simplify_aggr_init_expr): Not here, just copy it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/initlist86.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-gimplify.c
    trunk/gcc/cp/semantics.c
    trunk/gcc/gimplify.c
    trunk/gcc/gimplify.h

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #17 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Jun 30 14:25:21 2014
New Revision: 212150

URL: https://gcc.gnu.org/viewcvs?rev=212150&root=gcc&view=rev
Log:
    DR 1030
    PR c++/51253
    PR c++/61382
    * cp-tree.h (CALL_EXPR_LIST_INIT_P): New.
    * call.c (struct z_candidate): Add flags field.
    (add_candidate): Add flags parm.
    (add_function_candidate, add_conv_candidate, build_builtin_candidate)
    (add_template_candidate_real): Pass it.
    (build_over_call): Set CALL_EXPR_LIST_INIT_P.
    * tree.c (build_aggr_init_expr): Copy it.
    * semantics.c (simplify_aggr_init_expr): Copy it.
    * cp-gimplify.c (cp_gimplify_expr): Handle it.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/cpp0x/initlist86.C
Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/call.c
    branches/gcc-4_9-branch/gcc/cp/cp-gimplify.c
    branches/gcc-4_9-branch/gcc/cp/cp-tree.h
    branches/gcc-4_9-branch/gcc/cp/semantics.c
    branches/gcc-4_9-branch/gcc/cp/tree.c
    branches/gcc-4_9-branch/gcc/gimplify.c
    branches/gcc-4_9-branch/gcc/gimplify.h

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[christophe.lyon at st dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

christophe.lyon at st dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |christophe.lyon at st dot com

--- Comment #18 from christophe.lyon at st dot com ---
On 4.9 branch, I've noticed that commit 212150 adds new FAILs on some
configurations. g++.dg/cpp0x/initlist86.C fails at execution in the following
cases (tested with qemu):
target                     mode  cpu
arm-none-eabi              arm   cortex-a9
arm-none-linux-gnueabi     arm   cortex-a9
arm-none-linux-gnueabi     thumb cortex-a9
arm-none-linux-gnueabihf   arm   cortex-a9
arm-none-linux-gnueabihf   thumb cortex-a9
arm-none-linux-gnueabihf   arm   cortex-a9
armeb-none-linux-gnueabihf arm   cortex-a9
armeb-none-linux-gnueabihf thumb cortex-a9
aarch64-none-linux

the same test passes when:
target                     mode  cpu
arm-none-eabi              thumb cortex-a9
aarch64-none-elf
aarch64_be-none-elf

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #19 from Jason Merrill <jason at gcc dot gnu.org> ---
That's odd.  Can you investigate further?

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[christophe.lyon at st dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

--- Comment #20 from christophe.lyon at st dot com ---
The problem was fixed by Jakub's commit 212289.
Thanks.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|4.10.0                      |4.9.1

--- Comment #21 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed in 4.9.1.

[Bug c++/51253] [C++11][DR 1030] Evaluation order (sequenced-before relation) among initializer-clauses in braced-init-list

[dacamara.cameron at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253

Cameron <dacamara.cameron at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dacamara.cameron at gmail dot com

--- Comment #22 from Cameron <dacamara.cameron at gmail dot com> ---
*** Bug 62036 has been marked as a duplicate of this bug. ***