When emitting the destructor for a class with a vtable, if we can determine

that the destructor body is trivial and that all member variables also have either
trivial destructors or trivial destructor bodies, we don't need to initialize the
vtable pointers since no virtual member functions will be called on the destructor.

Fixes PR9181.

llvm-svn: 131368

3 files changed, 49 insertions, 13 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index b57c6ab7d76..d4df017383d 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -1422,6 +1422,20 @@ bool FunctionDecl::hasBody(const FunctionDecl *&Definition) const {
   return false;
 }
 
+bool FunctionDecl::hasTrivialBody() const
+{
+  Stmt *S = getBody();
+  if (!S) {
+    // Since we don't have a body for this function, we don't know if it's
+    // trivial or not.
+    return false;
+  }
+
+  if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
+    return true;
+  return false;
+}
+
 bool FunctionDecl::isDefined(const FunctionDecl *&Definition) const {
   for (redecl_iterator I = redecls_begin(), E = redecls_end(); I != E; ++I) {
     if (I->IsDeleted || I->Body || I->IsLateTemplateParsed) {
diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 4390f3a3e3e..f6fc202eaae 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -28,17 +28,6 @@
 using namespace clang;
 using namespace CodeGen;
 
-/// Determines whether the given function has a trivial body that does
-/// not require any specific codegen.
-static bool HasTrivialBody(const FunctionDecl *FD) {
-  Stmt *S = FD->getBody();
-  if (!S)
-    return true;
-  if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
-    return true;
-  return false;
-}
-
 /// Try to emit a base destructor as an alias to its primary
 /// base-class destructor.
 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
@@ -47,7 +36,7 @@ bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
 
   // If the destructor doesn't have a trivial body, we have to emit it
   // separately.
-  if (!HasTrivialBody(D))
+  if (!D->hasTrivialBody())
     return true;
 
   const CXXRecordDecl *Class = D->getParent();
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 4172948b602..785b9e129a1 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -741,6 +741,38 @@ void CodeGenFunction::EmitCtorPrologue(const CXXConstructorDecl *CD,
     EmitMemberInitializer(*this, ClassDecl, MemberInitializers[I], CD, Args);
 }
 
+/// CanSkipVTablePointerInitialization - Check whether we need to initialize
+/// any vtable pointers before calling this destructor.
+static bool CanSkipVTablePointerInitialization(ASTContext &Context,
+                                           const CXXDestructorDecl *Dtor) {
+  if (!Dtor->hasTrivialBody())
+    return false;
+
+  // Check the fields.
+  const CXXRecordDecl *ClassDecl = Dtor->getParent();
+  for (CXXRecordDecl::field_iterator I = ClassDecl->field_begin(),
+       E = ClassDecl->field_end(); I != E; ++I) {
+    const FieldDecl *Field = *I;
+    
+    QualType FieldBaseElementType = 
+      Context.getBaseElementType(Field->getType());
+
+    const RecordType *RT = FieldBaseElementType->getAs<RecordType>();
+    if (!RT)
+      continue;
+    
+    CXXRecordDecl *FieldClassDecl = cast<CXXRecordDecl>(RT->getDecl());
+    if (FieldClassDecl->hasTrivialDestructor())
+      continue;
+    if (FieldClassDecl->getDestructor()->hasTrivialBody())
+      continue;
+
+    return false;
+  }
+
+  return true;
+}
+
 /// EmitDestructorBody - Emits the body of the current destructor.
 void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   const CXXDestructorDecl *Dtor = cast<CXXDestructorDecl>(CurGD.getDecl());
@@ -792,7 +824,8 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
     EnterDtorCleanups(Dtor, Dtor_Base);
 
     // Initialize the vtable pointers before entering the body.
-    InitializeVTablePointers(Dtor->getParent());
+    if (!CanSkipVTablePointerInitialization(getContext(), Dtor))
+        InitializeVTablePointers(Dtor->getParent());
 
     if (isTryBody)
       EmitStmt(cast<CXXTryStmt>(Body)->getTryBlock());