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.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@131368 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 35 insertions, 13 deletions

diff --git a/lib/CodeGen/CGCXX.cpp b/lib/CodeGen/CGCXX.cpp
index 4390f3a3e3..f6fc202eaa 100644
--- a/lib/CodeGen/CGCXX.cpp
+++ b/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/lib/CodeGen/CGClass.cpp b/lib/CodeGen/CGClass.cpp
index 4172948b60..785b9e129a 100644
--- a/lib/CodeGen/CGClass.cpp
+++ b/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());