[Bug c++/60771] New: rejects-valid: static constexpr const reference initialization

[Bug c++/60771] New: rejects-valid: static constexpr const reference initialization

[filip.roseen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

            Bug ID: 60771
           Summary: rejects-valid: static constexpr const reference
                    initialization
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: filip.roseen at gmail dot com

Created attachment 32550
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32550&action=edit
testcase.cpp

struct A { 
  static constexpr int const& ref = 5;
};

int main () { } 

------------------------------------------------------------------

testcase.cpp:2:37: error: non-constant in-class initialization invalid for
static member ‘A::ref’
   static constexpr int const& ref = 5;
                                     ^
testcase.cpp:2:37: error: (an out of class initialization is required)
testcase.cpp:2:37: error: ‘A::ref’ cannot be initialized by a non-constant
expression when being declared


------------------------------------------------------------------

The snippet should be accepted, `int const&` is a literal-type and `5` sure is
a constant expression suitable for initializing `ref` in the written context.

[ Note: `gcc` correctly accepts `static constexpr int const& ref = 5;` if it
appears outside of a class definition. ]

[ Note: `clang` shows the correct behavior. ]

------------------------------------------------------------------

[basic.start.init]p2:

  > Variables with static storage duration (3.7.1) or thread storage
  > duration (3.7.2) shall be zero-initialized (8.5) before any other
  > initialization takes place. A constant initializer for an object o is
  > an expression that is a constant expression, except that it may also
  > invoke constexpr constructors for o and its subobjects even if those
  > objects are of non-literal class types [ Note: such a class may have a
  > non-trivial destructor — end note ].
  > 
  > Constant initialization is performed:
  > 
  >   — if each full-expression (including implicit conversions) that
  >     appears in the initializer of a reference with static or
  >     thread storage duration is a constant expression (5.19) and
  >     the reference is bound to an lvalue designating an object
  >     with static storage duration or to a temporary (see 12.2);
  >
  > </snip>
>From gcc-bugs-return-448381-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Apr 06 04:40:09 2014
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From: "andi-gcc at firstfloor dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/60469] simple cilk plus program ICEs
Date: Sun, 06 Apr 2014 04:40:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`469

--- Comment #1 from Andi Kleen <andi-gcc at firstfloor dot org> ---
I investigated this a bit.


The problem is in get_chain_decl() in the nested function lowering because Cilk
creates nested functions.

info->outer is NULL

created_nesting_tree does this


 for (cgn = cgn->nested; cgn ; cgn = cgn->next_nested)
    {
      struct nesting_info *sub = create_nesting_tree (cgn);
      sub->outer = info;
      sub->next = info->inner;
      info->inner = sub;
    }

So it would only set ->outer for any inner functions and it is expected to be
NULL on the outer most nesting level


$6 = {outer = 0x0, inner = 0x329b590, next = 0x0, field_map = 0x329c780,
var_map = 0x329dc70, mem_refs = 0x329e850, suppress_expansion = 0x32f8d20,
  context = <function_decl 0x7fe4297b7e00 main>, new_local_var_chain = <tree
0x0>, debug_var_chain = <tree 0x0>, frame_type = <tree 0x0>, frame_decl = <tree
0x0>,
  chain_field = <tree 0x0>, chain_decl = <tree 0x0>, nl_goto_field = <tree
0x0>, any_parm_remapped = false, any_tramp_created = false, static_chain_added
= 0 '\000'}


So this whole code is invoked on the most outer most context, which it cannot
deal with


This seems to be related to the decl_function_context farther up the callstack:


static tree
convert_nonlocal_reference_op (tree *tp, int *walk_subtrees, void *data)
{
  struct walk_stmt_info *wi = (struct walk_stmt_info *) data;
  struct nesting_info *const info = (struct nesting_info *) wi->info;
  tree t = *tp;

  *walk_subtrees = 0;
  switch (TREE_CODE (t))
    {
    case VAR_DECL:
      /* Non-automatic variables are never processed.  */
      if (TREE_STATIC (t) || DECL_EXTERNAL (t))
    break;
      /* FALLTHRU */

    case PARM_DECL:
      if (decl_function_context (t) != info->context)


(gdb) p t->decl_minimal.context
$11 = <tree 0x0>

(gdb) p info->context
$12 = <function_decl 0x7fe4297b7e00 main>

This means the VAR_DECL doesn't have the correct context

Looking at c-common/cilk.c it seems to copy VAR_DECLs.
So it somehow doesn't set up the context correctly?

[Bug c++/60771] rejects-valid: static in-class constexpr const reference initialization

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-06-06
             Blocks|                            |55004
     Ever confirmed|0                           |1

[Bug c++/60771] static in-class constexpr const reference initialization

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed by the commit which fixed c++/50473 (r217672). I'm adding the
testcase and closing the bug.

[Bug c++/60771] static in-class constexpr const reference initialization

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

--- Comment #2 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Tue Nov 18 11:25:47 2014
New Revision: 217708

URL: https://gcc.gnu.org/viewcvs?rev=217708&root=gcc&view=rev
Log:
2014-11-18  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/60771
    * g++.dg/cpp0x/constexpr-ref6.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-ref6.C
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug c++/60771] static in-class constexpr const reference initialization

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.0

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done.