[Bug c++/52363] New: Presence/absence of -pedantic compilation affects run-time behavior

[Bug c++/52363] New: Presence/absence of -pedantic compilation affects run-time behavior

[wb at fnal dot gov]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

             Bug #: 52363
           Summary: Presence/absence of -pedantic compilation affects
                    run-time behavior
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: wb@fnal.gov


Created attachment 26738
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26738
C++11 source program whose behavior differs w/ -pedantic.

The run-time behavior of the attached C++11 program differs according to the
presence or absence of -pedantic during compilation.

MacPorts compiler version: g++-mp-4.7 (GCC) 4.7.0 20120218 (experimental)
System:  MacBook Pro with 2.8GHz Intel Core 2 Duo running OS X 10.6.8
Command line 1:   g++-mp-4.7 -O3 -std=c++0x           pedantic_t.cc
Command line 2:   g++-mp-4.7 -O3 -std=c++0x -pedantic pedantic_t.cc

* Using command line 1, the program builds with no diagnostic and runs to
successful completion.
* Using command line 2, the program builds with no diagnostic, but the
assertion fails during execution.

The principal concern is the inconsistent run-time behavior.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-02-23
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-23 19:08:28 UTC ---
confirmed

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

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

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 11:03:18 UTC ---
Jason, this is the -pedantic issue I was referring too.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 12:52:04 UTC ---
Interestingly, removing the const from the move assignment avoids the issue
with -pedantic.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 13:01:37 UTC ---
And this is enough to see the inconsistency vs -pedantic:

#include <type_traits>
#include <cassert>

struct proxy
{
  void operator=(int const&);
  void operator=(int &&) const;
};

int main()
{
  assert( (std::is_assignable<proxy, int>::value) );
}

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 13:56:23 UTC ---
This block of code in joust changes the behavior without -pedantic:

Index: call.c
===================================================================
--- call.c      (revision 186565)
+++ call.c      (working copy)
@@ -8305,7 +8305,7 @@ tweak:

   /* Extension: If the worst conversion for one candidate is worse than the
      worst conversion for the other, take the first.  */
-  if (!pedantic)
+  if (0 && !pedantic)
     {
       conversion_rank rank1 = cr_identity, rank2 = cr_identity;
       struct z_candidate *w = 0, *l = 0;

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 14:08:45 UTC ---
Daniel, can you have a look to snippet in Comment #5? Should it compile or not?

Because, if it should not, then it seems we should simply arrange for joust to
know about sfinae-mode and in that case behave as-if pedantic were always set.
Would be doable, I think.  On the other hand, if it should compile, things
seems a bit more fuzzy to me, it's as if the behavior due to the piece of code
at the end of joust is what we really want, even in -pedantic mode?!?

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 13:29:10 UTC ---
Oh, and isn't really a run-time issue:

#include <type_traits>

struct proxy
{
  void operator=(int const&);
  void operator=(int &&) const;
};

static_assert( std::is_assignable<proxy, int>::value, "" );

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #8 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2012-04-18 14:41:38 UTC ---
(In reply to comment #7)
> Daniel, can you have a look to snippet in Comment #5? Should it compile or not?

It needed a while until I recognized that the second operator= overload is a
const function: With this fact my *tentative* interpretation is that the static
assertion should fire, because we have a non-const proxy rvalue and a non-const
int rvalue. The non-const proxy argument has a better match with the non-const
object parameter of the first function, but the int rvalue has a better match
with the int&& argument of the second function. The corresponding C++03 problem
would be described by

struct proxy
{
  void operator=(int const&);
  void operator=(int &) const;
};

template<class T>
T& create();

int v = sizeof(create<proxy>() = create<int>(), 0);

and is ambiguous as well. The alternative fix (instead of removing the const
from the function) is to *add* a const to left hand type (i.e. use "const
proxy" instead).

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #9 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 14:59:02 UTC ---
Ah, thanks Daniel. Therefore the situation is becoming more clear.

Then - assuming this interpretation is correct - I'm not sure what we want to
do from a practical point of view: should we arrange the front-end to always
have the static_assertion triggered (thus, even without -pedantic) or we really
want that only when -pedantic is passed? I'm not clear whether the user may
like to see the value is std::is_assignable changing depending on -pedantic?!?
I never pondered that possibility in the past.

I guess Jason should give a direction, here.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> 2012-04-18 15:14:58 UTC ---
std::is_assignable uses SFINAE, so it should always act pedantic, and the
assert should fail.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|paolo.carlini at oracle dot |
                   |com                         |
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-18 15:20:57 UTC ---
Good. Then, let's see if my idea of tweaking joust to know about sfinae works.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

--- Comment #12 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-04-24 16:25:33 UTC ---
Author: paolo
Date: Tue Apr 24 16:25:15 2012
New Revision: 186774

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=186774
Log:
/cp
2012-04-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/52363
    * call.c (tourney, perform_overload_resolution,
    build_operator_new_call, build_user_type_conversion_1,
    build_user_type_conversion, perform_overload_resolution,
    add_template_candidate, add_template_candidate_real,
    add_template_conv_candidate, add_builtin_candidates,
    add_builtin_candidate, build_builtin_candidate,
    add_conv_candidate, add_function_candidate, implicit_conversion,
    reference_binding, build_list_conv, conditional_conversion,
    add_candidates, can_convert_array, build_aggr_conv,
    build_array_conv, build_complex_conv, conditional_conversion):
    Add tsubst_flags_t parameter.
    (joust): Likewise, use it to handle SFINAE as if pedantic.
    (add_list_candidates, build_integral_nontype_arg_conv,
    perform_overload_resolution, build_new_function_call,
    build_operator_new_call, build_op_call_1,
    build_conditional_expr_1, build_new_op_1, convert_like_real,
    convert_arg_to_ellipsis, convert_default_arg,
    convert_for_arg_passing, build_over_call,
    build_new_method_call_1, can_convert_arg, can_convert_arg_bad,
    perform_implicit_conversion_flags,
    perform_direct_initialization_if_possible,
    initialize_reference): Adjust.
    * typeck.c (casts_away_constness, casts_away_constness_r):
    Add tsubst_flags_t parameter.
    (convert_arguments, check_for_casting_away_constness,
    build_static_cast_1, build_ptrmemfunc, convert_for_assignment):
    Adjust.
    * decl.c (reshape_init_r, check_default_argument): Likewise.
    * cp-gimplify.c (cxx_omp_clause_apply_fn): Likewise.
    * pt.c (convert_nontype_argument, check_non_deducible_conversion):
    Likewise.
    * init.c (build_new_1): Likewise.
    * cvt.c (convert_to_reference, ocp_convert, build_type_conversion,
    build_expr_type_conversion, ): Likewise.
    * search.c (check_final_overrider): Likewise.
    * cp-tree.h (build_user_type_conversion,
    build_operator_new_call, can_convert, can_convert_arg,
    can_convert_arg_bad, convert_default_arg,
    convert_arg_to_ellipsis, convert_for_arg_passing):
    Adjust declaration.

/testsuite
2012-04-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/52363
    * g++.dg/cpp0x/sfinae35.C: New.
    * g++.dg/cpp0x/sfinae36.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae35.C
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae36.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-gimplify.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/cvt.c
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/init.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/search.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.8.0

--- Comment #13 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-24 16:27:58 UTC ---
Fixed for 4.8.0.

[Bug c++/52363] Presence/absence of -pedantic compilation affects run-time behavior

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hstong at ca dot ibm.com

--- Comment #14 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-06-08 00:47:47 UTC ---
*** Bug 53606 has been marked as a duplicate of this bug. ***