[Bug c++/33916] New: Default constructor fails to initialize array members

[Bug c++/33916] New: Default constructor fails to initialize array members

[mec at google dot com]

(This may be related to PR 30111 )

In this program, a default constructor fails to initialize the given array
members to zero.  Results are shown with several versions of gcc.

===

#include <string.h>
#include <iostream>

namespace {

class Stats {
  friend void alpha();
  private:
    int a_[12];
    int b_[12];
};

void dirty_stack() {
  char array[4096];
  memset(array, 0x11, 4096);
}

void alpha() {
  Stats my_stats = Stats();
  for (int i = 0; i < 12; ++i) {
    std::cout << my_stats.a_[i] << " ";
  }
  std::cout << std::endl;
}

}

int main() {
  dirty_stack();
  alpha();
  return 0;
}

===

mec@hollerith:~/exp-array-default$ /home/mec/gcc-4.1.2/install/bin/g++ z3.cc &&
./a.out
0 0 0 0 0 0 0 0 0 0 0 0 

mec@hollerith:~/exp-array-default$ /home/mec/gcc-4.2.2/install/bin/g++ z3.cc &&
./a.out
286331153 286331153 286331153 286331153 286331153 286331153 286331153 286331153
286331153 286331153 286331153 286331153 

mec@hollerith:~/exp-array-default$ /home/mec/gcc-4.3-20071019/install/bin/g++
z3.cc && ./a.out
286331153 286331153 286331153 286331153 286331153 286331153 286331153 286331153
286331153 286331153 286331153 286331153


-- 
           Summary: Default constructor fails to initialize array members
           Product: gcc
           Version: 4.2.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mec at google dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] Default constructor fails to initialize array members

[crowl at google dot com]

------- Comment #1 from crowl at google dot com  2007-10-31 20:08 -------
The wording in the C++ standard working paper is as follows:

8.5 Initializers [dcl.init]

-8- An object whose initializer is an empty set of parentheses, i.e.,
   (), shall be value-initialized.

Therefore, in <<< Stats my_stats = Stats(); >>>, the temporary object
is value-initialized and then my_stats is copy-constructed.

-5- To value-initialize an object of type T means:
   -- if T is a non-union class type without a user-provided
      constructor, then every non-static data member and base-class
      component of T is value-initialized;93)

   93) Value-initialization for such a class object may be
       implemented by zero-initializing the object and then calling
       the default constructor.

   -- if T is an array type, then each element is value-initialized;

   -- otherwise, the object is zero-initialized

Therefore, the temporary should be zero-initialized and the resulting
copy should copy zeros.  So, I conclude that gcc 4.2.1 is in error.
(I suspect the compiler already eliminates the copy.)

I suspect the problem arose in someone thinking that the zero
initialization in front of a call to a default constructor was
redundant.  Alas, it is not.  It is redundant only if the constructor
initializes all fields, which is generally unknowable, though the
compiler could determine so for many types and constructors.


-- 

crowl at google dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |crowl at google dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] Default constructor fails to initialize array members

[gdr at gcc dot gnu dot org]

------- Comment #2 from gdr at gcc dot gnu dot org  2007-11-01 02:16 -------
I concur with Lawrence' analysis.
I was bitten by this bug myself in my own code.


-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gdr at gcc dot gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-11-01 02:16:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[janis at gcc dot gnu dot org]

------- Comment #3 from janis at gcc dot gnu dot org  2007-12-11 00:03 -------
A regression hunt on powerpc-linux identified this patch:

    http://gcc.gnu.org/viewcvs?view=rev&rev=117834

    r117834 | mmitchel | 2006-10-17 22:35:29 +0000 (Tue, 17 Oct 2006)


-- 

janis at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mmitchel at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
   Target Milestone|---                         |4.2.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |mmitchel at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-12-10 18:15:07         |2008-01-02 23:32:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[mmitchel at gcc dot gnu dot org]

------- Comment #4 from mmitchel at gcc dot gnu dot org  2008-01-07 18:13 -------
I still agree that we should fix this -- but it is worth noting that
value-initialization did not exist in C++98.  I believe that the current G++
behavior conforms to the original C++98 specification.

Does anyone know if this change was in C++98 TC1?  Or not until C++0x?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[crowl at google dot com]

------- Comment #5 from crowl at google dot com  2008-01-07 18:58 -------
Subject: Re:  [4.2/4.3 Regression] Default constructor fails to initialize
array members

Value initialization was in C++98 TC1 (2003) as a result of core issue 178.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[steven at gcc dot gnu dot org]

------- Comment #6 from steven at gcc dot gnu dot org  2008-01-22 21:01 -------
There is some discussion about this bug in the following thread on gcc-patches:
http://gcc.gnu.org/ml/gcc-patches/2008-01/msg00326.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2008-01-25 15:46 -------
Jason, can you coordinate with Mark and help with the remaining P1 C++
regressions?


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[jsm28 at gcc dot gnu dot org]

------- Comment #8 from jsm28 at gcc dot gnu dot org  2008-02-01 16:55 -------
4.2.3 is being released now, changing milestones of open bugs to 4.2.4.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.2.3                       |4.2.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2/4.3 Regression] Default constructor fails to initialize array members

[jason at gcc dot gnu dot org]

------- Comment #9 from jason at gcc dot gnu dot org  2008-02-04 03:29 -------
Subject: Bug 33916

Author: jason
Date: Mon Feb  4 03:28:53 2008
New Revision: 132088

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=132088
Log:
        PR c++/33916
        * cp/init.c (build_value_init_1): New function.
        (build_value_init): New function.
        * cp/typeck2.c (build_functional_cast): Call it.
        * cp/cp-gimplify.c (cp_gimplify_init_expr): Handle its output.

        * cp/cp-tree.h (TYPE_HAS_USER_CONSTRUCTOR): Rename from
        TYPE_HAS_CONSTRUCTOR.
        * cp/class.c (finish_struct_bits,
maybe_warn_about_overly_private_class,
        add_implicitly_declared_members): Adjust.
        (check_field_decls): Adjust. Remove warnings about reference/const
        in class without constructor.
        (check_bases_and_members): Adjust.  Give those warnings here instead.
        * cp/decl.c (fixup_anonymous_aggr): Adjust.
        (check_initializer): Adjust, clarify logic slightly.
        (grok_special_member_properties): Adjust, only set if user-provided.
        * cp/rtti.c (create_tinfo_types): Don't set.
        * cp/cvt.c (ocp_convert): Remove exception for vtable_entry_type et al.
        Use same_type_ignoring_top_level_qualifiers_p.
        * cp/pt.c (check_explicit_specialization): Adjust.
        (instantiate_class_template): Adjust.

        * print-tree.c (print_node) [CONSTRUCTOR]: Print elements.

Added:
    trunk/gcc/testsuite/g++.dg/init/value1.C
    trunk/gcc/testsuite/g++.dg/warn/Wextra-1.C
    trunk/gcc/testsuite/g++.dg/warn/Wextra-2.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.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/rtti.c
    trunk/gcc/cp/typeck2.c
    trunk/gcc/print-tree.c
    trunk/gcc/testsuite/g++.dg/init/ctor8.C


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2 Regression] Default constructor fails to initialize array members

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2008-02-04 12:15 -------
Fixed on the trunk.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.3.0
            Summary|[4.2/4.3 Regression] Default|[4.2 Regression] Default
                   |constructor fails to        |constructor fails to
                   |initialize array members    |initialize array members


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2 Regression] Default constructor fails to initialize array members

[jason at gcc dot gnu dot org]

------- Comment #11 from jason at gcc dot gnu dot org  2008-02-12 06:38 -------
Subject: Bug 33916

Author: jason
Date: Tue Feb 12 06:37:34 2008
New Revision: 132254

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=132254
Log:
        PR c++/34094
        * decl2.c (cp_write_global_declarations): Don't write out static
        data members with DECL_IN_AGGR_P set.

        PR c++/33916
        * Revert:
        2006-10-17  Mark Mitchell  <mark@codesourcery.com>
        PR c++/29039
        * typeck2.c (build_functional_cast): Don't zero-initialize
        non-PODs; instead, call their constructors.

Removed:
    branches/gcc-4_2-branch/gcc/testsuite/g++.dg/init/ctor8.C
Modified:
    branches/gcc-4_2-branch/gcc/cp/ChangeLog
    branches/gcc-4_2-branch/gcc/cp/decl2.c
    branches/gcc-4_2-branch/gcc/cp/typeck2.c
    branches/gcc-4_2-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916

[Bug c++/33916] [4.2 Regression] Default constructor fails to initialize array members

[jason at gcc dot gnu dot org]

------- Comment #12 from jason at gcc dot gnu dot org  2008-02-12 06:41 -------
Fixed for 4.2.4 by reverting part of Mark's patch for PR 29039.


-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916