[Bug c++/48911] New: [C++0x]An error that a valid array subscript

[Bug c++/48911] New: [C++0x]An error that a valid array subscript

[sscrisk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

           Summary: [C++0x]An error that a valid array subscript
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sscrisk@gmail.com


Source:

int main()
{
 {
  constexpr int array[1] = {0};
  constexpr int i = array[0]; // OK.
 }
 {
  constexpr int array[1] = {};
  constexpr int i = array[0]; // error: array subscript out of bound. Why?
 }
}


Compile errors:

a.cpp: In function 'int main()':
a.cpp:5:17: warning: unused variable 'i' [-Wunused-variable]
a.cpp:9:28: error: array subscript out of bound
a.cpp:9:17: warning: unused variable 'i' [-Wunused-variable]


Access to array[0] is valid. But, compiler says "that's an error."

[Bug c++/48911] [C++0x] Error for valid array subscript

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.06 09:27:51
                 CC|                            |jason at gcc dot gnu.org
            Summary|[C++0x]An error that a      |[C++0x] Error for valid
                   |valid array subscript       |array subscript
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-06 09:27:51 UTC ---
Confirmed mainline and 4_6-branch.

[Bug c++/48911] [C++0x] Error for valid array subscript

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-06 11:00:19 UTC ---
Better testcase:

// PR c++/48911
// { dg-do compile }
// { dg-options "-std=c++0x" }

struct A
{
  constexpr A () : a (6) {}
  int a;
};

int
main ()
{
  constexpr int a[1] = { 0 };
  constexpr int i = a[0];
  constexpr int b[1] = { };
  constexpr int j = b[0];
  constexpr char c[2] = "a";
  constexpr char k = c[1];
  constexpr char d[2] = "";
  constexpr char l = d[1];
  constexpr wchar_t e[2] = L"a";
  constexpr wchar_t m = e[1];
  constexpr wchar_t f[2] = L"";
  constexpr wchar_t n = f[1];
  constexpr A g[2] = { A () };
  constexpr A o = g[0];
  constexpr A p = g[1];
}

which covers also the case where ary is not CONSTRUCTOR, but STRING_CST.
I think we want to to the len check as done right now, but if index is above
len, we shouldn't error or set non-constant unconditionally, instead we should
check domain of TREE_TYPE (oldary).  If it is within the range, we want to
return zero of the appropriate type for PODs, not sure what exactly for
constexpr non-PODs.

[Bug c++/48911] [C++0x] Error for valid array subscript

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |

[Bug c++/48911] [C++0x] Error for valid array subscript

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-06 21:57:45 UTC ---
Author: jason
Date: Fri May  6 21:57:41 2011
New Revision: 173510

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173510
Log:
    PR c++/48911
    * semantics.c (cxx_eval_array_reference): Handle implicit
    initializers.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-missing.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/semantics.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/48911] [C++0x] Error for valid array subscript

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-06 21:58:40 UTC ---
Author: jason
Date: Fri May  6 21:58:37 2011
New Revision: 173515

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173515
Log:
    PR c++/48911
    * semantics.c (cxx_eval_array_reference): Handle implicit
    initializers.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/constexpr-missing.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/semantics.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c++/48911] [C++0x] Error for valid array subscript

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48911

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.1

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-06 22:01:27 UTC ---
Fixed for 4.6.1.