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, 55 insertions, 1 deletions

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() {}
+}