[interop] ensure IRGen traverses inherited C++ constructors correctly

Author: hyp

lib/IRGen/GenClangDecl.cpp

@@ -95,6 +95,12 @@ class ClangDeclFinder
     return true;
   }
 
+  bool VisitCXXInheritedCtorInitExpr(clang::CXXInheritedCtorInitExpr *CIE) {
+    if (auto ctor = CIE->getConstructor())
+      callback(ctor);
+    return true;
+  }
+
   // Do not traverse unevaluated expressions. Doing to might result in compile
   // errors if we try to instantiate an un-instantiatable template.
 

test/Interop/Cxx/class/constructor-inherited-from-base-irgen.swift

@@ -0,0 +1,50 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: %target-swiftxx-frontend -emit-ir -I %t/Inputs -validate-tbd-against-ir=none %t/test.swift | %FileCheck %s
+
+//--- Inputs/module.modulemap
+module BaseConstructor {
+  header "test.h"
+  requires cplusplus
+}
+//--- Inputs/test.h
+
+extern void referencedSymbol();
+inline void emittedIntoSwiftObject() { referencedSymbol(); }
+
+class BaseClass {
+public:
+    inline BaseClass() : x(0) {}
+    inline BaseClass(bool v, const BaseClass &) {
+        if (v)
+          emittedIntoSwiftObject();
+    }
+
+    int x;
+};
+
+class DerivedClass: public BaseClass {
+    int y;
+public:
+    using BaseClass::BaseClass;
+
+    inline DerivedClass(int y) : y(y) {}
+
+    inline int test() const {
+        DerivedClass m(true, *this);
+        return m.x;
+    }
+};
+
+//--- test.swift
+
+import BaseConstructor
+
+public func test() {
+  let i = DerivedClass(0)
+  let v = i.test()
+}
+
+// Make sure we reach clang declarations accessible from base constructors:
+
+// CHECK: define linkonce_odr{{( dso_local)?}} void @{{_Z22emittedIntoSwiftObjectv|"\?emittedIntoSwiftObject@@YAXXZ"}}