[Clang][ObjC] Add optionality to property attribute strings.

Add a new attribute, "?", to the property attribute string for
properties of protocols that are declared @optional.

(Previously https://reviews.llvm.org/D135273)

rdar://100463524

Author: al45tair

clang/lib/AST/ASTContext.cpp

@@ -7824,6 +7824,7 @@ ASTContext::getObjCPropertyImplDeclForPropertyDecl(
 /// kPropertyWeak = 'W'              // 'weak' property
 /// kPropertyStrong = 'P'            // property GC'able
 /// kPropertyNonAtomic = 'N'         // property non-atomic
+/// kPropertyOptional = '?'          // property optional
 /// };
 /// @endcode
 std::string
@@ -7849,6 +7850,9 @@ ASTContext::getObjCEncodingForPropertyDecl(const ObjCPropertyDecl *PD,
   // closely resembles encoding of ivars.
   getObjCEncodingForPropertyType(PD->getType(), S);
 
+  if (PD->isOptional())
+    S += ",?";
+
   if (PD->isReadOnly()) {
     S += ",R";
     if (PD->getPropertyAttributes() & ObjCPropertyAttribute::kind_copy)

clang/test/CodeGenObjC/objc-asm-attribute-test.m

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm -triple x86_64-apple-darwin %s -o - | FileCheck %s
+// RUN: %clang_cc1 -Wno-objc-root-class -no-opaque-pointers -emit-llvm -triple x86_64-apple-darwin %s -o - | FileCheck %s
 // rdar://16462586
 
 __attribute__((objc_runtime_name("MySecretNamespace.Protocol")))
@@ -11,6 +11,10 @@ + (void) ClsMethodP;
 @protocol Protocol2
 - (void) MethodP2;
 + (void) ClsMethodP2;
+
+@optional
+@property(retain) id optionalProp;
+
 @end
 
 __attribute__((objc_runtime_name("MySecretNamespace.Protocol3")))
@@ -59,6 +63,10 @@ id Test16877359(void) {
 // CHECK: @"OBJC_CLASS_$_MySecretNamespace.Message" ={{.*}} global %struct._class_t
 // CHECK: @"OBJC_METACLASS_$_MySecretNamespace.Message" ={{.*}} global %struct._class_t
 
+// CHECK: @OBJC_PROP_NAME_ATTR_ = private unnamed_addr constant [13 x i8] c"optionalProp\00"
+// CHECK-NEXT: @OBJC_PROP_NAME_ATTR_.11 = private unnamed_addr constant [7 x i8] c"T@,?,&\00"
+// CHECK: @"_OBJC_$_PROP_LIST_MySecretNamespace.Protocol2" ={{.*}} [%struct._prop_t { ptr @OBJC_PROP_NAME_ATTR_, ptr @OBJC_PROP_NAME_ATTR_.11 }]
+
 // CHECK: private unnamed_addr constant [42 x i8] c"T@\22MySecretNamespace.Message\22,&,V_msgProp\00"
 // CHECK: private unnamed_addr constant [76 x i8] c"T@\22MySecretNamespace.Message<MySecretNamespace.Protocol3>\22,&,V_msgProtoProp\00"
 // CHECK: private unnamed_addr constant [50 x i8] c"T@\22<MySecretNamespace.Protocol3>\22,&,V_idProtoProp\00"