Add support for "fancy" pointers to shared_ptr. Fixes PR20616

Summary:
This patch add support for "fancy pointers/allocators" as well as fixing support for shared_pointer and "minimal" allocators.

Fancy pointers are class types that meet the NullablePointer requirements. In our case they are created by fancy allocators. `support/min_allocator.h` is an archetype for these types.

There are three types of changes made in this patch:
1. `_Alloc::template rebind<T>::other` -> `__allocator_traits_rebind<_Alloc, T>::type`. This change was made because allocators don't need a rebind template. `__allocator_traits_rebind` is used instead of `allocator_traits::rebind` because use of `allocator_traits::rebind` requires a workaround for when template aliases are unavailable.
2. `a.deallocate(this, 1)` -> `a.deallocate(pointer_traits<self>::pointer_to(*this), 1)`. This change change is made because fancy pointers aren't always constructible from raw pointers. 
3. `p.get()` -> `addressof(*p.get())`. Fancy pointers aren't actually a pointer. When we need a "real" pointer we take the address of dereferencing the fancy pointer. This should give us the actual raw pointer.

Test Plan: Tests were added using `support/min_allocator.h` to each affected shared_ptr overload and creation function. These tests can only be executed in C++11 or greater since min_allocator is only available then. A extra test was added for the non-variadic versions of allocate_shared. 

Reviewers: danalbert, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4859

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@220469 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.create/allocate_shared.pass.cpp

@@ -19,6 +19,7 @@
 #include <cstdlib>
 #include <cassert>
 #include "test_allocator.h"
+#include "min_allocator.h"
 
 int new_count = 0;
 
@@ -54,4 +55,24 @@ int main()
     }
     assert(A::count == 0);
     assert(test_allocator<A>::alloc_count == 0);
+#if __cplusplus >= 201103L
+    {
+    int i = 67;
+    char c = 'e';
+    std::shared_ptr<A> p = std::allocate_shared<A>(min_allocator<void>(), i, c);
+    assert(A::count == 1);
+    assert(p->get_int() == 67);
+    assert(p->get_char() == 'e');
+    }
+    assert(A::count == 0);
+    {
+    int i = 68;
+    char c = 'f';
+    std::shared_ptr<A> p = std::allocate_shared<A>(bare_allocator<void>(), i, c);
+    assert(A::count == 1);
+    assert(p->get_int() == 68);
+    assert(p->get_char() == 'f');
+    }
+    assert(A::count == 0);
+#endif
 }

test/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.create/allocate_shared_no_variadics.pass.cpp

@@ -0,0 +1,118 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+
+// shared_ptr
+
+// template<class T, class A, class... Args>
+//    shared_ptr<T> allocate_shared(const A& a, Args&&... args);
+
+#define _LIBCPP_HAS_NO_VARIADICS
+#include <memory>
+#include <new>
+#include <cstdlib>
+#include <cassert>
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+struct Zero
+{
+    static int count;
+    Zero() {++count;}
+    Zero(Zero const &) {++count;}
+    ~Zero() {--count;}
+};
+
+int Zero::count = 0;
+
+struct One
+{
+    static int count;
+    int value;
+    explicit One(int v) : value(v) {++count;}
+    One(One const & o) : value(o.value) {++count;}
+    ~One() {--count;}
+};
+
+int One::count = 0;
+
+
+struct Two
+{
+    static int count;
+    int value;
+    Two(int v, int) : value(v) {++count;}
+    Two(Two const & o) : value(o.value) {++count;}
+    ~Two() {--count;}
+};
+
+int Two::count = 0;
+
+struct Three
+{
+    static int count;
+    int value;
+    Three(int v, int, int) : value(v) {++count;}
+    Three(Three const & o) : value(o.value) {++count;}
+    ~Three() {--count;}
+};
+
+int Three::count = 0;
+
+template <class Alloc>
+void test()
+{
+    int const bad = -1;
+    {
+    std::shared_ptr<Zero> p = std::allocate_shared<Zero>(Alloc());
+    assert(Zero::count == 1);
+    }
+    assert(Zero::count == 0);
+    {
+    int const i = 42;
+    std::shared_ptr<One> p = std::allocate_shared<One>(Alloc(), i);
+    assert(One::count == 1);
+    assert(p->value == i);
+    }
+    assert(One::count == 0);
+    {
+    int const i = 42;
+    std::shared_ptr<Two> p = std::allocate_shared<Two>(Alloc(), i, bad);
+    assert(Two::count == 1);
+    assert(p->value == i);
+    }
+    assert(Two::count == 0);
+    {
+    int const i = 42;
+    std::shared_ptr<Three> p = std::allocate_shared<Three>(Alloc(), i, bad, bad);
+    assert(Three::count == 1);
+    assert(p->value == i);
+    }
+    assert(Three::count == 0);
+}
+
+int main()
+{
+    {
+    int i = 67;
+    int const bad = -1;
+    std::shared_ptr<Two> p = std::allocate_shared<Two>(test_allocator<Two>(54), i, bad);
+    assert(test_allocator<Two>::alloc_count == 1);
+    assert(Two::count == 1);
+    assert(p->value == 67);
+    }
+    assert(Two::count == 0);
+    assert(test_allocator<Two>::alloc_count == 0);
+
+    test<bare_allocator<void> >();
+#if __cplusplus >= 201103L
+    test<min_allocator<void> >();
+#endif
+}