SIL: Fix type lowering of unowned reference to class-bound generic parameter

Unowned references lower as address-only or loadable, depending on
whether the underlying class type is known to be native Swift or
not.

In the case where we were lowering an interface type, we would
unconditionally erase the type to AnyObject, producing an incorrect
lowering when the generic signature constrained the type parameter
to a native Swift class.

Fixes <rdar://problem/73083179>.

Author: slavapestov

lib/SIL/IR/TypeLowering.cpp

@@ -414,8 +414,15 @@ namespace {
       return visitAbstractTypeParamType(type, origType, isSensitive);
     }
 
-    Type getConcreteReferenceStorageReferent(Type type) {
+    Type getConcreteReferenceStorageReferent(Type type,
+                                             AbstractionPattern origType) {
       if (type->isTypeParameter()) {
+        auto genericSig = origType.getGenericSignature();
+        if (auto concreteType = genericSig->getConcreteType(type))
+          return concreteType;
+        if (auto superclassType = genericSig->getSuperclassBound(type))
+          return superclassType;
+        assert(genericSig->requiresClass(type));
         return TC.Context.getAnyObjectType();
       }
 
@@ -460,7 +467,7 @@ namespace {
                                    IsTypeExpansionSensitive_t isSensitive) { \
       auto referentType = \
         type->getReferentType()->lookThroughSingleOptionalType(); \
-      auto concreteType = getConcreteReferenceStorageReferent(referentType); \
+      auto concreteType = getConcreteReferenceStorageReferent(referentType, origType); \
       if (Name##StorageType::get(concreteType, TC.Context) \
             ->isLoadable(Expansion.getResilienceExpansion())) { \
         return asImpl().visitLoadable##Name##StorageType(type, origType, \

test/SILGen/unowned-class-bound-generic-parameter.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-emit-silgen %s -enable-objc-interop | %FileCheck %s
+
+protocol ClassProtocol: AnyObject {}
+
+class BaseClass {}
+
+func makeGenericClosureWithUnknownClass<T>(t: T) where T : ClassProtocol {
+  _ = { [unowned t] in _ = t }
+}
+
+// CHECK-LABEL: sil private [ossa] @$s4main34makeGenericClosureWithUnknownClass1tyx_tAA0G8ProtocolRzlFyycfU_ : $@convention(thin) <T where T : ClassProtocol> (@guaranteed <τ_0_0 where τ_0_0 : ClassProtocol> { var @sil_unowned τ_0_0 } <T>) -> () {
+
+func makeGenericClosureWithNativeClass1<T>(t: T) where T : BaseClass {
+  _ = { [unowned t] in _ = t }
+}
+
+// CHECK-LABEL: sil private [ossa] @$s4main34makeGenericClosureWithNativeClass11tyx_tAA9BaseClassCRbzlFyycfU_ : $@convention(thin) <T where T : BaseClass> (@guaranteed @sil_unowned T) -> () {
+
+func makeGenericClosureWithNativeClass2<T>(t: T) where T : ClassProtocol, T : BaseClass {
+  _ = { [unowned t] in _ = t }
+}
+
+// CHECK-LABEL: sil private [ossa] @$s4main34makeGenericClosureWithNativeClass21tyx_tAA9BaseClassCRbzAA0I8ProtocolRzlFyycfU_ : $@convention(thin) <T where T : BaseClass, T : ClassProtocol> (@guaranteed @sil_unowned T) -> () {