[Bug c++/51222] New: [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[Bug c++/51222] New: [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

             Bug #: 51222
           Summary: [C++11][SFINAE] Unevaluated combined delete new
                    expression completely broken
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com
                CC: jason@gcc.gnu.org


The following problem became obvious to me when I recently tried to provide a
both simpler and more general library emulation of is_constructible.

gcc 4.7 20111112 (experimental) in C++11 mode rejects the following code:

//---
template<class T>
struct add_rref {
  typedef T&& type;
};

template<>
struct add_rref<void> {
  typedef void type;
};

template<class T>
typename add_rref<T>::type declval();

template<class T, class U, class =
  decltype(::delete ::new T(declval<U>()))
>
auto f(int) -> char;

template<class, class>
auto f(...) -> char(&)[2];

template<class T, class =
  decltype(::delete ::new T())
>
auto g(int) -> char;

template<class>
auto g(...) -> char(&)[2];

struct C { };

struct A {
  virtual ~A() = 0;
};

struct D1 {
  D1() = delete;
};

struct D2 {
  ~D2() = delete;
};

static_assert(sizeof(g<void>(0)) == 2, "Ouch");
static_assert(sizeof(g<void()>(0)) == 2, "Ouch");
static_assert(sizeof(g<void() const>(0)) == 2, "Ouch");
static_assert(sizeof(g<A>(0)) == 2, "Ouch");
static_assert(sizeof(g<D1>(0)) == 2, "Ouch");
static_assert(sizeof(g<D2>(0)) == 2, "Ouch");
static_assert(sizeof(g<int&>(0)) == 2, "Ouch");
static_assert(sizeof(g<int&&>(0)) == 2, "Ouch");
static_assert(sizeof(g<void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(g<void(&&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(), void()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void() const, void() const>(0)) == 2, "Ouch");
static_assert(sizeof(f<int, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<void, int>(0)) == 2, "Ouch");
static_assert(sizeof(f<C, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<C, int>(0)) == 2, "Ouch");
static_assert(sizeof(f<int&, int&>(0)) == 2, "Ouch");
static_assert(sizeof(f<int&&, int&&>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(&)(), void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(&&)(), void(&&)()>(0)) == 2, "Ouch");
//---

All static assertions fail, but they shouldn't. This is very unfortunate,
because above test expressions are extremely useful for emulating an effective
variable definition including destruction semantics.

The test code should be accepted.

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |51185

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-11-19 23:36:59 UTC ---
Ouch, indeed. Then let's mark this as blocking the library issue (if Daniel in
the meanwhile you can figure out a workaround we can remove the blockage)

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

--- Comment #2 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2011-11-21 07:51:49 UTC ---
When fixing this problem, I suggest to add the following tests as well, which
also fail currently (In previous builds sometimes one of these forms worked
when the other failed):

//---
template<class T>
struct add_rref {
  typedef T&& type;
};

template<>
struct add_rref<void> {
  typedef void type;
};

template<class T>
typename add_rref<T>::type declval();

template<class T, class U>
auto f2(int) -> decltype(::delete ::new T(declval<U>()), char());

template<class, class>
auto f2(...) -> char(&)[2];

template<class T>
auto g2(int) -> decltype(::delete ::new T(), char());

template<class>
auto g2(...) -> char(&)[2];

struct C { };

struct A {
  virtual ~A() = 0;
};

struct D1 {
  D1() = delete;
};

struct D2 {
  ~D2() = delete;
};

static_assert(sizeof(g2<void>(0)) == 2, "Ouch");
static_assert(sizeof(g2<void()>(0)) == 2, "Ouch");
static_assert(sizeof(g2<void() const>(0)) == 2, "Ouch");
static_assert(sizeof(g2<A>(0)) == 2, "Ouch");
static_assert(sizeof(g2<D1>(0)) == 2, "Ouch");
static_assert(sizeof(g2<D2>(0)) == 2, "Ouch");
static_assert(sizeof(g2<int&>(0)) == 2, "Ouch");
static_assert(sizeof(g2<int&&>(0)) == 2, "Ouch");
static_assert(sizeof(g2<void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(g2<void(&&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void, void>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void(), void()>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void() const, void() const>(0)) == 2, "Ouch");
static_assert(sizeof(f2<int, void>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void, int>(0)) == 2, "Ouch");
static_assert(sizeof(f2<C, void>(0)) == 2, "Ouch");
static_assert(sizeof(f2<C, int>(0)) == 2, "Ouch");
static_assert(sizeof(f2<int&, int&>(0)) == 2, "Ouch");
static_assert(sizeof(f2<int&&, int&&>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void(&)(), void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f2<void(&&)(), void(&&)()>(0)) == 2, "Ouch");
//---

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-11-22
             Blocks|51185                       |
     Ever Confirmed|0                           |1

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-11-22 21:50:48 UTC ---
Confirmed indeed (and cleared Blocks field, PR51185 is fixed anyway).

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.8.0

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-05-24 12:16:54 UTC ---
I worked on this and a patch is essentially ready, AFAICS. But there are ABI
implications waiting to be resolved, if I understand correctly.

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-06-11 16:02:40 UTC ---
Last posted version:

  http://gcc.gnu.org/ml/gcc-patches/2012-05/msg00157.html

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2012-08-31 02:50:35 UTC ---
Author: jason
Date: Fri Aug 31 02:50:28 2012
New Revision: 190830

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=190830
Log:
    PR c++/50545
    PR c++/51222
    * pt.c (instantiation_dependent_r): New.
    (instantiation_dependent_expression_p): New.
    (value_dependent_expression_p): Use it.  SCOPE_REF is always dependent.
    * semantics.c (finish_decltype_type): Use it.
    * cp-tree.h: Declare it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype40.C
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype41.C
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype42.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/semantics.c

[Bug c++/51222] [C++11][SFINAE] Unevaluated combined delete new expression completely broken

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222

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

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

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2012-08-31 15:03:09 UTC ---
Fixed.