Directly access @_objcImpl stored props sometimes

Accessing a stored property from a normal method should send a selector, but accessing it from an initializer or accessor should use the field offset.

Author: beccadax

lib/AST/Decl.cpp

@@ -3761,10 +3761,13 @@ static bool checkAccess(const DeclContext *useDC, const ValueDecl *VD,
                         bool forConformance,
                         bool includeInlineable,
                         llvm::function_ref<AccessLevel()> getAccessLevel) {
-  // If this is an @_objcImplementation member implementation, unconditionally
-  // forbid access. Name lookups will instead find and use the matching
-  // interface decl.
-  if (isObjCMemberImplementation(VD, getAccessLevel))
+  // If this is an @_objcImplementation member implementation, and we aren't in
+  // a context where we would access its storage directly, forbid access. Name
+  // lookups will instead find and use the matching interface decl.
+  // FIXME: Passing `true` for `isAccessOnSelf` may cause false positives.
+  if (isObjCMemberImplementation(VD, getAccessLevel) &&
+      VD->getAccessSemanticsFromContext(useDC, /*isAccessOnSelf=*/true)
+          != AccessSemantics::DirectToStorage)
     return false;
 
   if (VD->getASTContext().isAccessControlDisabled())

lib/Sema/TypeCheckDecl.cpp

@@ -448,7 +448,7 @@ InitKindRequest::evaluate(Evaluator &evaluator, ConstructorDecl *decl) const {
       // (or the same file) to add vtable entries, we can re-evaluate this
       // restriction.
       if (!decl->isSynthesized() &&
-          isa<ExtensionDecl>(decl->getDeclContext()) &&
+          isa<ExtensionDecl>(decl->getDeclContext()->getImplementedObjCContext()) &&
           !(decl->getAttrs().hasAttribute<DynamicReplacementAttr>())) {
 
         if (classDcl->getForeignClassKind() == ClassDecl::ForeignKind::CFType) {

test/IRGen/Inputs/objc_implementation.h

@@ -2,6 +2,8 @@
 
 @interface ImplClass: NSObject
 
+- (nonnull instancetype)init;
+
 @property (assign) int implProperty;
 
 - (void)mainMethod:(int)param;