RequirementMachine: Use the correct predicate to determine if a class uses Objective-C reference counting

Also, introduce the layout requirement implied by a superclass requirement
when lowering requirements, instead of when building the property map.

Right now this is functionally equivalent, but if we ever start to
test properties by checking for joinability of T with T.[p] instead of
looking at the property map entry of T, this new formulation is the
right one.

Author: slavapestov

lib/AST/RequirementMachine/PropertyMap.cpp

@@ -493,17 +493,6 @@ void PropertyBag::addProperty(
     return;
 
   case Symbol::Kind::Superclass: {
-    auto superclass = property.getSuperclass();
-
-    // A superclass requirement implies a layout requirement.
-    auto layout =
-      LayoutConstraint::getLayoutConstraint(
-        superclass->getClassOrBoundGenericClass()->isObjC()
-          ? LayoutConstraintKind::Class
-          : LayoutConstraintKind::NativeClass,
-        ctx.getASTContext());
-    addProperty(Symbol::forLayout(layout, ctx), ctx, inducedRules, debug);
-
     // FIXME: This needs to find the most derived subclass and also call
     // unifyConcreteTypes()
     Superclass = property;

lib/AST/RequirementMachine/RequirementMachine.cpp

@@ -171,6 +171,13 @@ void RewriteSystemBuilder::addRequirement(const Requirement &req,
     // A superclass requirement T : C<X, Y> becomes a rewrite rule
     //
     //   T.[superclass: C<X, Y>] => T
+    //
+    // Together with a rewrite rule
+    //
+    //   T.[layout: L] => T
+    //
+    // Where 'L' is either AnyObject or _NativeObject, depending on the
+    // ancestry of C.
     auto otherType = CanType(req.getSecondType());
 
     SmallVector<Term, 1> substitutions;
@@ -180,6 +187,16 @@ void RewriteSystemBuilder::addRequirement(const Requirement &req,
     constraintTerm = subjectTerm;
     constraintTerm.add(Symbol::forSuperclass(otherType, substitutions,
                                              Context));
+    Rules.emplace_back(subjectTerm, constraintTerm);
+
+    constraintTerm = subjectTerm;
+    auto layout =
+      LayoutConstraint::getLayoutConstraint(
+        otherType->getClassOrBoundGenericClass()->usesObjCObjectModel()
+          ? LayoutConstraintKind::Class
+          : LayoutConstraintKind::NativeClass,
+        Context.getASTContext());
+    constraintTerm.add(Symbol::forLayout(layout, Context));
     break;
   }
 

test/Generics/generic_objc_superclass.swift

@@ -0,0 +1,21 @@
+// RUN: %target-typecheck-verify-swift %clang-importer-sdk -requirement-machine=verify -debug-requirement-machine 2>&1 | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+import Foundation
+
+class Generic<T> : NSObject {}
+
+func foo<T : Generic<U>, U>(_: T, _: U) {
+  _ = T.self
+  _ = U.self
+}
+
+// CHECK-LABEL: Requirement machine for <τ_0_0, τ_0_1 where τ_0_0 : Generic<τ_0_1>>
+// CHECK-NEXT: Rewrite system: {
+// CHECK-NEXT: - τ_0_0.[superclass: Generic<τ_0_0> with <τ_0_1>] => τ_0_0
+// CHECK-NEXT: - τ_0_0.[layout: AnyObject] => τ_0_0
+// CHECK-NEXT: }
+// CHECK-NEXT: Property map: {
+// CHECK-NEXT:   τ_0_0 => { layout: AnyObject superclass: [superclass: Generic<τ_0_0> with <τ_0_1>] }
+// CHECK-NEXT: }