[DebugInfo] Add types from constructor homing to the retained types list.

[akhuang]

Summary

Add class types to the retained types list to make sure they
don't get dropped if the constructor is optimized out later.

[dblaikie]

Looks good - thanks!

clang/lib/CodeGen/CGDebugInfo.cpp

if (Method->getRefQualifier() == RQ_RValue)
     Flags |= llvm::DINode::FlagRValueReference;
   if (CGM.getLangOpts().Optimize)
     SPFlags |= llvm::DISubprogram::SPFlagOptimized;
 
   // In this debug mode, emit type info for a class when its constructor type
   // info is emitted.
   if (DebugKind == codegenoptions::DebugInfoConstructor)
     if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(Method))
-      completeClass(CD->getParent());
+      completeUnusedClass(*CD->getParent());
 
   llvm::DINodeArray TParamsArray = CollectFunctionTemplateParams(Method, Unit);
   llvm::DISubprogram *SP = DBuilder.createMethod(
       RecordTy, MethodName, MethodLinkageName, MethodDefUnit, MethodLine,
       MethodTy, VIndex, ThisAdjustment, ContainingType, Flags, SPFlags,
       TParamsArray.get());
 
   SPCache[Method->getCanonicalDecl()].reset(SP);

clang/test/CodeGenCXX/debug-info-limited-ctor.cpp

 // RUN: %clang -cc1 -debug-info-kind=constructor -emit-llvm %s -o - | FileCheck %s
 
 // CHECK-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "A"{{.*}}DIFlagTypePassByValue
 struct A {
 } TestA;
 
 // CHECK-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "B"{{.*}}flags: DIFlagFwdDecl
 struct B {
   B();
 } TestB;
 
-// CHECK-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "C"{{.*}}DIFlagTypePassByValue
+// CHECK-DAG: ![[C:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "C"{{.*}}DIFlagTypePassByValue
 struct C {
   C() {}
 } TestC;
 
 // CHECK-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "D"{{.*}}DIFlagTypePassByValue
 struct D {
   D();
 };

 void f(K k) {}
 
 // Test that we don't use constructor homing on lambdas.
 // CHECK-DAG: ![[L:.*]] ={{.*}}!DISubprogram({{.*}}name: "L"
 // CHECK-DAG: !DICompositeType({{.*}}scope: ![[L]], {{.*}}DIFlagTypePassByValue
 void L() {
   auto func = [&]() {};
 }
+
+// Check that types are being added to retained types list.
+// CHECK-DAG: !DICompileUnit{{.*}}retainedTypes: ![[RETAINED:[0-9]+]]
+// CHECK-DAG: ![[RETAINED]] = {{.*}}![[C]]