C++ DR1611, 1658, 2180: implement "potentially constructed subobject" rules for special member functions.

Essentially, as a base class constructor does not construct virtual bases, such
a constructor for an abstract class does not need the corresponding base class
construction to be valid, and likewise for destructors.

This creates an awkward situation: clang will sometimes generate references to
the complete object and deleting destructors for an abstract class (it puts
them in the construction vtable for a derived class). But we can't generate a
"correct" version of these because we can't generate references to base class
constructors any more (if they're template specializations, say, we might not
have instantiated them and can't assume any other TU will emit a copy).
Fortunately, we don't need to, since no correct program can ever invoke them,
so instead emit symbols that just trap.

We should stop emitting references to these symbols, but still need to emit
definitions for compatibility.

llvm-svn: 296275

5 files changed, 277 insertions, 1 deletions

diff --git a/clang/test/CXX/drs/dr16xx.cpp b/clang/test/CXX/drs/dr16xx.cpp
index c9f084db73a..08ae92570ce 100644
--- a/clang/test/CXX/drs/dr16xx.cpp
+++ b/clang/test/CXX/drs/dr16xx.cpp
@@ -3,6 +3,13 @@
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++1z -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 
+namespace dr1611 { // dr1611: dup 1658
+  struct A { A(int); };
+  struct B : virtual A { virtual void f() = 0; };
+  struct C : B { C() : A(0) {} void f(); };
+  C c;
+}
+
 namespace dr1684 { // dr1684: 3.6
 #if __cplusplus >= 201103L
   struct NonLiteral { // expected-note {{because}}
@@ -101,3 +108,114 @@ namespace dr1653 { // dr1653: 4 c++17
     b -= 1; // ok
   }
 }
+
+namespace dr1658 { // dr1658: 5
+  namespace DefCtor {
+    class A { A(); }; // expected-note 0-2{{here}}
+    class B { ~B(); }; // expected-note 0-2{{here}}
+
+    // The stars align! An abstract class does not construct its virtual bases.
+    struct C : virtual A { C(); virtual void foo() = 0; };
+    C::C() = default; // ok, not deleted, expected-error 0-1{{extension}}
+    struct D : virtual B { D(); virtual void foo() = 0; };
+    D::D() = default; // ok, not deleted, expected-error 0-1{{extension}}
+
+    // In all other cases, we are not so lucky.
+    struct E : A { E(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    E::E() = default; // expected-error {{private default constructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    E::E() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible default constructor}}
+#endif
+    struct F : virtual A { F(); };
+#if __cplusplus < 201103L
+    F::F() = default; // expected-error {{private default constructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    F::F() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible default constructor}}
+#endif
+
+    struct G : B { G(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    G::G() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    G::G() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+    struct H : virtual B { H(); };
+#if __cplusplus < 201103L
+    H::H() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    H::H() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+  }
+
+  namespace Dtor {
+    class B { ~B(); }; // expected-note 0-2{{here}}
+
+    struct D : virtual B { ~D(); virtual void foo() = 0; };
+    D::~D() = default; // ok, not deleted, expected-error 0-1{{extension}}
+
+    struct G : B { ~G(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    G::~G() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    G::~G() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+    struct H : virtual B { ~H(); };
+#if __cplusplus < 201103L
+    H::~H() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    H::~H() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+  }
+
+  namespace MemInit {
+    struct A { A(int); }; // expected-note {{here}}
+    struct B : virtual A {
+      B() {}
+      virtual void f() = 0;
+    };
+    struct C : virtual A {
+      C() {} // expected-error {{must explicitly initialize}}
+    };
+  }
+
+  namespace CopyCtorParamType {
+    struct A { A(A&); };
+    struct B : virtual A { virtual void f() = 0; };
+    struct C : virtual A { virtual void f(); };
+    struct D : A { virtual void f() = 0; };
+
+    struct X {
+      friend B::B(const B&) throw();
+      friend C::C(C&);
+      friend D::D(D&);
+    };
+  }
+
+  namespace CopyCtor {
+    class A { A(const A&); A(A&&); }; // expected-note 0-4{{here}} expected-error 0-1{{extension}}
+
+    struct C : virtual A { C(const C&); C(C&&); virtual void foo() = 0; }; // expected-error 0-1{{extension}}
+    C::C(const C&) = default; // expected-error 0-1{{extension}}
+    C::C(C&&) = default; // expected-error 0-2{{extension}}
+
+    struct E : A { E(const E&); E(E&&); virtual void foo() = 0; }; // expected-error 0-1{{extension}}
+#if __cplusplus < 201103L
+    E::E(const E&) = default; // expected-error {{private copy constructor}} expected-error {{extension}} expected-note {{here}}
+    E::E(E&&) = default; // expected-error {{private move constructor}} expected-error 2{{extension}} expected-note {{here}}
+#else
+    E::E(const E&) = default; // expected-error {{would delete}} expected-note@-5{{inaccessible copy constructor}}
+    E::E(E&&) = default; // expected-error {{would delete}} expected-note@-6{{inaccessible move constructor}}
+#endif
+    struct F : virtual A { F(const F&); F(F&&); }; // expected-error 0-1{{extension}}
+#if __cplusplus < 201103L
+    F::F(const F&) = default; // expected-error {{private copy constructor}} expected-error {{extension}} expected-note {{here}}
+    F::F(F&&) = default; // expected-error {{private move constructor}} expected-error 2{{extension}} expected-note {{here}}
+#else
+    F::F(const F&) = default; // expected-error {{would delete}} expected-note@-5{{inaccessible copy constructor}}
+    F::F(F&&) = default; // expected-error {{would delete}} expected-note@-6{{inaccessible move constructor}}
+#endif
+  }
+
+  // assignment case is superseded by dr2180
+}
diff --git a/clang/test/CXX/drs/dr21xx.cpp b/clang/test/CXX/drs/dr21xx.cpp
new file mode 100644
index 00000000000..78fc0bec40b
--- /dev/null
+++ b/clang/test/CXX/drs/dr21xx.cpp
@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++1z -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+
+namespace dr2180 { // dr2180: yes
+  class A {
+    A &operator=(const A &); // expected-note 0-2{{here}}
+    A &operator=(A &&); // expected-note 0-2{{here}} expected-error 0-1{{extension}}
+  };
+
+  struct B : virtual A {
+    B &operator=(const B &);
+    B &operator=(B &&); // expected-error 0-1{{extension}}
+    virtual void foo() = 0;
+  };
+#if __cplusplus < 201103L
+  B &B::operator=(const B&) = default; // expected-error {{private member}} expected-error {{extension}} expected-note {{here}}
+  B &B::operator=(B&&) = default; // expected-error {{private member}} expected-error 2{{extension}} expected-note {{here}}
+#else
+  B &B::operator=(const B&) = default; // expected-error {{would delete}} expected-note@-9{{inaccessible copy assignment}}
+  B &B::operator=(B&&) = default; // expected-error {{would delete}} expected-note@-10{{inaccessible move assignment}}
+#endif
+}
diff --git a/clang/test/CodeGenCXX/constructors.cpp b/clang/test/CodeGenCXX/constructors.cpp
index ecbe5bb45b6..a8981403834 100644
--- a/clang/test/CodeGenCXX/constructors.cpp
+++ b/clang/test/CodeGenCXX/constructors.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - | FileCheck %s --implicit-check-not=should_not_appear_in_output
 
 struct Member { int x; Member(); Member(int); Member(const Member &); };
 struct VBase { int x; VBase(); VBase(int); VBase(const VBase &); };
@@ -109,3 +109,57 @@ namespace test1 {
   // CHECK:      [[THIS:%.*]] = load [[B:%.*]]*, [[B:%.*]]**
   // CHECK-NEXT: ret void
 }
+
+// Ensure that we
+// a) emit the ABI-required but useless complete object and deleting destructor
+//    symbols for an abstract class, and 
+// b) do *not* emit references to virtual base destructors for an abstract class
+//
+// Our approach to this is to give these functions a body that simply traps.
+//
+// FIXME: We should ideally not create these symbols at all, but Clang can
+// actually generate references to them in other TUs in some cases, so we can't
+// stop emitting them without breaking ABI. See:
+//
+//   https://github.com/itanium-cxx-abi/cxx-abi/issues/10
+namespace abstract {
+  // Note, the destructor of this class is not instantiated here.
+  template<typename T> struct should_not_appear_in_output {
+    ~should_not_appear_in_output() { int arr[-(int)sizeof(T)]; }
+  };
+
+  struct X { ~X(); };
+
+  struct A : virtual should_not_appear_in_output<int>, X {
+    virtual ~A() = 0;
+  };
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD2Ev(
+  // CHECK: call {{.*}}@_ZN8abstract1XD2Ev(
+  // CHECK: ret
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD1Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD0Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+  A::~A() {}
+
+  struct B : virtual should_not_appear_in_output<int>, X {
+    virtual void f() = 0;
+    ~B();
+  };
+
+  // CHECK-LABEL: define void @_ZN8abstract1BD2Ev(
+  // CHECK: call {{.*}}@_ZN8abstract1XD2Ev(
+  // CHECK: ret
+
+  // CHECK-LABEL: define void @_ZN8abstract1BD1Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+
+  // CHECK-NOT: @_ZN8abstract1BD0Ev(
+  B::~B() {}
+}
diff --git a/clang/test/CodeGenCXX/implicit-exception-spec.cpp b/clang/test/CodeGenCXX/implicit-exception-spec.cpp
new file mode 100644
index 00000000000..cf363bd685a
--- /dev/null
+++ b/clang/test/CodeGenCXX/implicit-exception-spec.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -emit-llvm -std=c++11 -o - -fcxx-exceptions -fexceptions | FileCheck -check-prefix=CHECK %s
+
+struct A {
+  A();
+  A(const A&);
+  A(A&&);
+};
+struct B : virtual A {
+  virtual void f() = 0;
+};
+struct C : B {
+  void f();
+};
+
+// CHECK-DAG: define {{.*}} @_ZN1BC2Ev({{.*}} #[[NOUNWIND:[0-9]*]]
+C c1;
+// CHECK-DAG: define {{.*}} @_ZN1BC2ERKS_({{.*}} #[[NOUNWIND]]
+C c2(c1);
+// CHECK-DAG: define {{.*}} @_ZN1BC2EOS_({{.*}} #[[NOUNWIND]]
+C c3(static_cast<C&&>(c1));
+
+// CHECK-DAG: #[[NOUNWIND]] = {{{.*}} nounwind
diff --git a/clang/test/SemaCXX/implicit-exception-spec.cpp b/clang/test/SemaCXX/implicit-exception-spec.cpp
index fc86d1810ba..f400c222de8 100644
--- a/clang/test/SemaCXX/implicit-exception-spec.cpp
+++ b/clang/test/SemaCXX/implicit-exception-spec.cpp
@@ -92,3 +92,61 @@ namespace ImplicitDtorExceptionSpec {
     } e;
   };
 }
+
+struct nothrow_t {} nothrow;
+void *operator new(decltype(sizeof(0)), nothrow_t) noexcept;
+
+namespace PotentiallyConstructed {
+  template<bool NE> struct A {
+    A() noexcept(NE);
+    A(const A&) noexcept(NE);
+    A(A&&) noexcept(NE);
+    A &operator=(const A&) noexcept(NE);
+    A &operator=(A&&) noexcept(NE);
+    ~A() noexcept(NE);
+  };
+
+  template<bool NE> struct B : virtual A<NE> {};
+
+  template<bool NE> struct C : virtual A<NE> {
+    virtual void f() = 0; // expected-note 2{{unimplemented}}
+  };
+
+  template<bool NE> struct D final : C<NE> {
+    void f();
+  };
+
+  template<typename T, bool A, bool B, bool C, bool D, bool E, bool F> void check() {
+    T *p = nullptr;
+    T &a = *p;
+    static_assert(noexcept(a = a) == D, "");
+    static_assert(noexcept(a = static_cast<T&&>(a)) == E, "");
+    static_assert(noexcept(delete &a) == F, ""); // expected-warning 2{{abstract}}
+
+    // These are last because the first failure here causes instantiation to bail out.
+    static_assert(noexcept(new (nothrow) T()) == A, ""); // expected-error 2{{abstract}}
+    static_assert(noexcept(new (nothrow) T(a)) == B, "");
+    static_assert(noexcept(new (nothrow) T(static_cast<T&&>(a))) == C, "");
+  }
+
+  template void check<A<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<A<true >, 1, 1, 1, 1, 1, 1>();
+  template void check<B<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<B<true >, 1, 1, 1, 1, 1, 1>();
+  template void check<C<false>, 1, 1, 1, 0, 0, 0>(); // expected-note {{instantiation}}
+  template void check<C<true >, 1, 1, 1, 1, 1, 1>(); // expected-note {{instantiation}}
+  template void check<D<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<D<true >, 1, 1, 1, 1, 1, 1>();
+
+  // ... the above trick doesn't work for this case...
+  struct Cfalse : virtual A<false> {
+    virtual void f() = 0;
+
+    Cfalse() noexcept;
+    Cfalse(const Cfalse&) noexcept;
+    Cfalse(Cfalse&&) noexcept;
+  };
+  Cfalse::Cfalse() noexcept = default;
+  Cfalse::Cfalse(const Cfalse&) noexcept = default;
+  Cfalse::Cfalse(Cfalse&&) noexcept = default;
+}