PR22763: if a defaulted (non-user-provided) special member function is

explicitly instantiated, still emit it with each use.

We don't emit a definition of the member with an explicit instantiation
definition (and indeed it appears that we're not allowed to, since an explicit
instantiation definition does not constitute an odr-use and only odr-use
permits definition for defaulted special members). So we still need to emit a
weak definition with each use.

This also makes defaulted-in-class declarations behave more like
implicitly-declared special members, which matches their design intent.
And it matches the way this problem was solved in GCC.

llvm-svn: 318474

1 files changed, 19 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/explicit-instantiation.cpp b/clang/test/CodeGenCXX/explicit-instantiation.cpp
index 85857fb6fb8..ad20abde8f1 100644
--- a/clang/test/CodeGenCXX/explicit-instantiation.cpp
+++ b/clang/test/CodeGenCXX/explicit-instantiation.cpp
@@ -170,3 +170,22 @@ void use() {
   f<int>();
 }
 }
+
+namespace DefaultedMembers {
+  struct B { B(); B(const B&); ~B(); };
+  template<typename T> struct A : B {
+    A() = default;
+    ~A() = default;
+  };
+  extern template struct A<int>;
+
+  // CHECK-LABEL: define {{.*}} @_ZN16DefaultedMembers1AIiEC2Ev
+  // CHECK-LABEL: define {{.*}} @_ZN16DefaultedMembers1AIiED2Ev
+  A<int> ai;
+
+  // CHECK-LABEL: define {{.*}} @_ZN16DefaultedMembers1AIiEC2ERKS1_
+  A<int> ai2(ai);
+
+  // CHECK-NOT: @_ZN16DefaultedMembers1AIcE
+  template struct A<char>;
+}