[IRGen] Do not emit ObjC property ivar field for non-trivially-representable types. (#21976)

This patch prevents writing ivar field for ObjC property whose type
is not trivially representable in ObjC within its DeclContext.
For example, in the case of the property `@objc var foo: String`,
it is accessed as an NSString on the ObjC side. Without this patch,
this property is backed with an ivar, to which direct accesses would
fail.

Resolves: SR-9557.

Author: dingobye

lib/IRGen/GenClass.cpp

@@ -1867,6 +1867,7 @@ namespace {
       llvm::raw_svector_ostream outs(out);
 
       auto propTy = prop->getValueInterfaceType();
+      auto propDC = prop->getDeclContext();
 
       // Emit the type encoding for the property.
       outs << 'T';
@@ -1884,13 +1885,13 @@ namespace {
       if (prop->getAttrs().hasAttribute<NSManagedAttr>())
         outs << ",D";
 
-      auto isObject = prop->getDeclContext()->mapTypeIntoContext(propTy)
+      auto isObject = propDC->mapTypeIntoContext(propTy)
           ->hasRetainablePointerRepresentation();
       auto hasObjectEncoding = typeEnc[0] == '@';
 
       // Determine the assignment semantics.
       // Get-only properties are (readonly).
-      if (!prop->isSettable(prop->getDeclContext()))
+      if (!prop->isSettable(propDC))
         outs << ",R";
       // Weak and Unowned properties are (weak).
       else if (prop->getAttrs().hasAttribute<ReferenceOwnershipAttr>())
@@ -1908,9 +1909,12 @@ namespace {
       else
         (void)0;
 
-      // If the property is an instance property and has storage, emit the ivar
-      // name last.
-      if (!prop->isStatic() && prop->hasStorage())
+      // If the property is an instance property and has storage, and meanwhile
+      // its type is trivially representable in ObjC, emit the ivar name last.
+      bool isTriviallyRepresentable =
+          propTy->isTriviallyRepresentableIn(ForeignLanguage::ObjectiveC,
+                                             propDC);
+      if (!prop->isStatic() && prop->hasStorage() && isTriviallyRepresentable)
         outs << ",V" << prop->getName();
     }
 

test/IRGen/objc_bridge.swift

@@ -100,7 +100,7 @@ import Foundation
 
 // CHECK: @_PROPERTIES__TtC11objc_bridge3Bas = private constant { i32, i32, [5 x { i8*, i8* }] } {
 
-// CHECK: [[OBJC_BLOCK_PROPERTY:@.*]] = private unnamed_addr constant [11 x i8] c"T@?,N,C,Vx\00"
+// CHECK: [[OBJC_BLOCK_PROPERTY:@.*]] = private unnamed_addr constant [8 x i8] c"T@?,N,C\00"
 // CHECK: @_PROPERTIES__TtC11objc_bridge21OptionalBlockProperty = private constant {{.*}} [[OBJC_BLOCK_PROPERTY]]
 
 func getDescription(_ o: NSObject) -> String {

test/IRGen/objc_property_attrs.swift

@@ -50,11 +50,11 @@ class Foo: NSManagedObject {
 
   // -- Bridged value types
 
-  // nonatomic, copy, ivar k
-  // CHECK: private unnamed_addr constant {{.*}} c"T@\22NSString\22,N,C,Vk\00"
+  // nonatomic, copy
+  // CHECK: private unnamed_addr constant {{.*}} c"T@\22NSString\22,N,C\00"
   @objc var k: String = ""
-  // nonatomic, readonly, ivar l
-  // CHECK: private unnamed_addr constant {{.*}} c"T@\22NSString\22,N,R,Vl\00"
+  // nonatomic, readonly
+  // CHECK: private unnamed_addr constant {{.*}} c"T@\22NSString\22,N,R\00"
   @objc let l: String? = nil
 
   // -- Protocol types: