[Bug c++/67104] New: Constant expression factory function initializes std::array with static storage duration strangely

[Bug c++/67104] New: Constant expression factory function initializes std::array with static storage duration strangely

[moritz at klammler dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

            Bug ID: 67104
           Summary: Constant expression factory function initializes
                    std::array with static storage duration strangely
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: moritz at klammler dot eu
  Target Milestone: ---

Created attachment 36110
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36110&action=edit
Source code to reproduce the problem

The following program -- that, to my best knowledge, is valid C++14 -- if
compiled with GCC fails at the marked assertion.  If compiled with Clang, both
assertions hold.

    #include <array>
    #include <cassert>

    namespace /* anonymous */
    {

      constexpr auto
      make_array(const int val) noexcept
      {
        std::array<int, 2> result = { { val, 0 } };
        return result;
      }

      // Replacing `constexpr` by `const` doesn't change anything.
      constexpr auto numbers_static = make_array(42);

    }

    int
    main()
    {
      const auto numbers_automatic = make_array(42);
      assert(numbers_automatic[0] == 42);  // okay
      assert(numbers_static[0] == 42);     // fails
    }

Attached are the source code, preprocessor output and standard error output
when compiling with GCC 5.1.0 using this command:

    $ g++ -std=c++14 -v -save-temps -Wall -Wextra -Werror -pedantic main.cxx

There are no warnings or errors reported by the compiler.

This issue has already been discussed on Stack Overflow where I have posted a
more complicated example to trigger the behavior.

   
https://stackoverflow.com/questions/31762429/initializing-stdarray-with-static-storage-duration-with-a-parameter-pack-expan

The reduced example included in this report is courtesy of Stack Overflow user
Columbo who has also tried different versions of GCC that reproduced the
behavior.

[Bug c++/67104] Constant expression factory function initializes std::array with static storage duration strangely

[moritz at klammler dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #1 from Moritz Klammler <moritz at klammler dot eu> ---
Created attachment 36111
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36111&action=edit
Preprocessed source file

[Bug c++/67104] Constant expression factory function initializes std::array with static storage duration strangely

[moritz at klammler dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #2 from Moritz Klammler <moritz at klammler dot eu> ---
Created attachment 36112
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36112&action=edit
Compiler standard error output

[Bug c++/67104] Constant expression factory function initializes std::array with static storage duration strangely

[moritz at klammler dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #3 from Moritz Klammler <moritz at klammler dot eu> ---
Note that the following slightly modified program passes all assertions and
behaves identical when compiled with either GCC or Clang.

    #include <array>
    #include <cassert>

    namespace /* anonymous */
    {

      constexpr auto
      make_array(const int val1, const int val2) noexcept
      {
        std::array<int, 2> result = { { val1, val2 } };
        return result;
      }

      constexpr auto numbers_static = make_array(42, 0);

    }

    int
    main()
    {
      const auto numbers_automatic = make_array(42, 0);
      assert(numbers_automatic[0] == 42);  // okay
      assert(numbers_static[0] == 42);     // okay
    }

[Bug c++/67104] Constant expression factory function initializes std::array with static storage duration strangely

[trippels at gcc dot gnu.org]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="UTF-8", Size: 3958 bytes --]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-08-03
                 CC|                            |trippels at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #4 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
markus@x4 tmp % cat te3.ii
namespace std
{
typedef int size_t;
template <typename _Tp, int _Nm> struct A
{
  typedef int _Type[_Nm];
  static constexpr _Tp
  _S_ref (const _Type __t, size_t)
  {
    return __t[0];
  }
};
template <typename, int _Nm> struct array
{
  typedef int const_reference;
  typedef int size_type;
  typedef A<int, _Nm> _AT_Type;
  typename _AT_Type::_Type _M_elems;
  constexpr const_reference operator[](size_type) const
  {
    return _AT_Type::_S_ref (_M_elems, 0);
  }
};
}

constexpr auto make_array (int val)
{
  std::array<int, 2> result{ val, 0 };
  return result;
}

constexpr auto numbers_static = make_array (1);
int
main ()
{
  static_assert (numbers_static[0], "");
}

markus@x4 tmp % clang++ -std=c++14 te3.ii
markus@x4 tmp % g++ -std=c++14 te3.ii
te3.ii: In function ‘int main()’:
te3.ii:36:3: error: static assertion failed: 
   static_assert (numbers_static[0], "");
   ^
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf079

--- Comment #8 from Paul Thomas <pault at gcc dot gnu.org> ---
Created attachment 36113
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id6113&actioníit
Patch for th 5 branch

Before closing this PR, I checked and found that the 5 branch now leaks memory.

The attached fixes the memory leak but does not fix the ICEs for which the
tests have been commented out. There is already too much divergence in
trans_allocate between 5 and 6 to do any more.

What do you think about applying this patch, which bootstraps and regtests?

Paul

[Bug c++/67104] [5/6 regression] Constant expression factory function initializes std::array with static storage duration strangely

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
                 CC|                            |jason at gcc dot gnu.org
            Summary|Constant expression factory |[5/6 regression] Constant
                   |function initializes        |expression factory function
                   |std::array with static      |initializes std::array with
                   |storage duration strangely  |static storage duration
                   |                            |strangely

--- Comment #5 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Started with r217663 (C++14 constexpr support).

[Bug c++/67104] [5/6 regression] Constant expression factory function initializes std::array with static storage duration strangely

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #6 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Another example
http://stackoverflow.com/questions/31878796/removing-constexpr-changes-values-of-array-on-gcc

markus@x4 tmp % cat test.ii
template <typename T, int N> struct array
{
  constexpr T &operator[](int index) { return data[index]; }
  constexpr T operator[](int index) const { return data[index]; }
  T data[N];
};

constexpr array<long unsigned, 1001>
make_bottle_count ()
{
  array<long unsigned, 1001> a{};
  a[65] = 1;
  return a;
}

constexpr auto bottle_count = make_bottle_count ();
static_assert (bottle_count[65], "");

markus@x4 tmp % clang++ -c -std=c++14 test.ii
markus@x4 tmp % g++ -c -std=c++14 test.ii
test.ii:17:1: error: static assertion failed: 
 static_assert (bottle_count[65], "");
 ^

[Bug c++/67104] [5/6 regression] Constant expression factory function initializes std::array with static storage duration strangely

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Aug 12 18:02:43 2015
New Revision: 226830

URL: https://gcc.gnu.org/viewcvs?rev=226830&root=gcc&view=rev
Log:
        PR c++/67104
        * constexpr.c (cxx_eval_array_reference): Handle sparse
        CONSTRUCTORs.

Added:
    trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-array1.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c

[Bug c++/67104] [5/6 regression] Constant expression factory function initializes std::array with static storage duration strangely

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Aug 12 18:08:45 2015
New Revision: 226833

URL: https://gcc.gnu.org/viewcvs?rev=226833&root=gcc&view=rev
Log:
        PR c++/67104
        * constexpr.c (cxx_eval_array_reference): Fix typo.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c

[Bug c++/67104] [5/6 regression] Constant expression factory function initializes std::array with static storage duration strangely

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

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

--- Comment #9 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
fixed.

[Bug c++/67104] [5 regression] Constant expression factory function initializes std::array with static storage duration strangely

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---
            Summary|[5/6 regression] Constant   |[5 regression] Constant
                   |expression factory function |expression factory function
                   |initializes std::array with |initializes std::array with
                   |static storage duration     |static storage duration
                   |strangely                   |strangely

--- Comment #10 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Actually the gcc-5 backport is still pending.

[Bug c++/67104] [5 regression] Constant expression factory function initializes std::array with static storage duration strangely

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Aug 17 15:44:29 2015
New Revision: 226940

URL: https://gcc.gnu.org/viewcvs?rev=226940&root=gcc&view=rev
Log:
        PR c++/67104
        * constexpr.c (cxx_eval_array_reference): Handle sparse
        CONSTRUCTORs.

Added:
    branches/gcc-5-branch/gcc/testsuite/g++.dg/cpp1y/constexpr-array1.C
Modified:
    branches/gcc-5-branch/gcc/cp/ChangeLog
    branches/gcc-5-branch/gcc/cp/constexpr.c

[Bug c++/67104] [5 regression] Constant expression factory function initializes std::array with static storage duration strangely

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Target Milestone|---                         |5.3

--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 5.3 as well.

[Bug c++/67104] [5 regression] Constant expression factory function initializes std::array with static storage duration strangely

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Aug 17 18:42:04 2015
New Revision: 226949

URL: https://gcc.gnu.org/viewcvs?rev=226949&root=gcc&view=rev
Log:
        PR c++/67104
        * constexpr.c (array_index_cmp, find_array_ctor_elt): New.
        (cxx_eval_array_reference, cxx_eval_store_expression): Use them.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c