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

1 files changed, 58 insertions, 0 deletions

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;
+}