AST: Introduce ClassDecl::hasResilientMetadata()

Author: slavapestov

include/swift/AST/Decl.h

@@ -3584,6 +3584,17 @@ class ClassDecl final : public NominalTypeDecl {
     return SourceRange(ClassLoc, getBraces().End);
   }
 
+  /// Determine whether the member area of this class's metadata (which consists
+  /// of field offsets and vtable entries) is to be considered opaque by clients.
+  ///
+  /// Note that even @_fixed_layout classes have resilient metadata if they are
+  /// in a resilient module.
+  bool hasResilientMetadata() const;
+
+  /// Determine whether this class has resilient metadata when accessed from the
+  /// given module and resilience expansion.
+  bool hasResilientMetadata(ModuleDecl *M, ResilienceExpansion expansion) const;
+
   /// Determine whether this class has a superclass.
   bool hasSuperclass() const { return (bool)getSuperclassDecl(); }
 

lib/AST/Decl.cpp

@@ -3314,6 +3314,36 @@ ClassDecl::ClassDecl(SourceLoc ClassLoc, Identifier Name, SourceLoc NameLoc,
   Bits.ClassDecl.HasMissingVTableEntries = 0;
 }
 
+bool ClassDecl::hasResilientMetadata() const {
+  // Imported classes don't have a vtable, etc, at all.
+  if (hasClangNode())
+    return false;
+
+  // If the module is not resilient, neither is the class metadata.
+  if (getParentModule()->getResilienceStrategy()
+          != ResilienceStrategy::Resilient)
+    return false;
+
+  // If the class is not public, we can't use it outside the module at all.
+  if (!getFormalAccessScope(/*useDC=*/nullptr,
+                            /*treatUsableFromInlineAsPublic=*/true).isPublic())
+    return false;
+
+  // Otherwise we access metadata members, such as vtable entries, resiliently.
+  return true;
+}
+
+bool ClassDecl::hasResilientMetadata(ModuleDecl *M,
+                                     ResilienceExpansion expansion) const {
+  switch (expansion) {
+  case ResilienceExpansion::Minimal:
+    return hasResilientMetadata();
+  case ResilienceExpansion::Maximal:
+    return M != getModuleContext() && hasResilientMetadata();
+  }
+  llvm_unreachable("bad resilience expansion");
+}
+
 DestructorDecl *ClassDecl::getDestructor() {
   auto results = lookupDirect(DeclBaseName::createDestructor());
   assert(!results.empty() && "Class without destructor?");

lib/IRGen/GenDecl.cpp

@@ -3859,6 +3859,20 @@ bool IRGenModule::isResilient(NominalTypeDecl *D, ResilienceExpansion expansion)
   return D->isResilient(getSwiftModule(), expansion);
 }
 
+/// Do we have to use resilient access patterns when working with this
+/// class?
+///
+/// For classes, this means that virtual method calls use dispatch thunks
+/// rather than accessing metadata members directly.
+bool IRGenModule::hasResilientMetadata(ClassDecl *D,
+                                       ResilienceExpansion expansion) {
+  if (expansion == ResilienceExpansion::Maximal &&
+      Types.getLoweringMode() == TypeConverter::Mode::CompletelyFragile) {
+    return false;
+  }
+  return D->hasResilientMetadata(getSwiftModule(), expansion);
+}
+
 // The most general resilience expansion where the given declaration is visible.
 ResilienceExpansion
 IRGenModule::getResilienceExpansionForAccess(NominalTypeDecl *decl) {

lib/IRGen/IRGenModule.h

@@ -784,6 +784,7 @@ class IRGenModule {
   clang::CodeGen::CodeGenModule &getClangCGM() const;
 
   bool isResilient(NominalTypeDecl *decl, ResilienceExpansion expansion);
+  bool hasResilientMetadata(ClassDecl *decl, ResilienceExpansion expansion);
   ResilienceExpansion getResilienceExpansionForAccess(NominalTypeDecl *decl);
   ResilienceExpansion getResilienceExpansionForLayout(NominalTypeDecl *decl);
   ResilienceExpansion getResilienceExpansionForLayout(SILGlobalVariable *var);