SILGen: Allocating entry points for @objc dynamic inits should use alloc_ref_dynamic

If the initializer witnesses a protocol requirement, the protocol witness
thunk references the allocating entry point directly, since it has no
vtable entry. For this reason we must use alloc_ref_dynamic and not
alloc_ref to ensure the right type of instance is allocated.

Fixes <rdar://problem/49560721>, <https://bugs.swift.org/browse/SR-10285>.

Author: slavapestov

lib/SILGen/SILGenConstructor.cpp

@@ -530,7 +530,9 @@ void SILGenFunction::emitClassConstructorAllocator(ConstructorDecl *ctor) {
   // Allocate the 'self' value.
   bool useObjCAllocation = usesObjCAllocator(selfClassDecl);
 
-  if (ctor->hasClangNode() || ctor->isConvenienceInit()) {
+  if (ctor->hasClangNode() ||
+      ctor->isObjCDynamic() ||
+      ctor->isConvenienceInit()) {
     assert(ctor->hasClangNode() || ctor->isObjC());
     // For an allocator thunk synthesized for an @objc convenience initializer
     // or imported Objective-C init method, allocate using the metatype.

test/Interpreter/objc_metatypes.swift

@@ -0,0 +1,32 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import StdlibUnittest
+import Foundation
+
+protocol Horse {
+  init()
+}
+
+class Pony : NSObject, Horse {
+  override required init() {}
+}
+
+class ChincoteaguePony : Pony {}
+
+var ObjCMetatypesTest = TestSuite("ObjCMetatypes")
+
+ObjCMetatypesTest.test("ClassInit") {
+  let metatype: Pony.Type = ChincoteaguePony.self
+  let instance = metatype.init()
+  expectEqual(type(of: instance), ChincoteaguePony.self)
+}
+
+ObjCMetatypesTest.test("ProtocolInit") {
+  let metatype: Horse.Type = ChincoteaguePony.self
+  let instance = metatype.init()
+  expectEqual(type(of: instance), ChincoteaguePony.self)
+}
+
+runAllTests()

test/SILGen/objc_dynamic_init.swift

@@ -17,6 +17,16 @@ class Gadget: NSObject, Hoozit {
     }
 }
 
+// CHECK-LABEL: sil hidden [ossa] @$s17objc_dynamic_init6GadgetCACycfC : $@convention(method) (@thick Gadget.Type) -> @owned Gadget
+// CHECK: [[OBJC_METATYPE:%.*]] = thick_to_objc_metatype %0 : $@thick Gadget.Type to $@objc_metatype Gadget.Type
+// CHECK: [[SELF:%.*]] = alloc_ref_dynamic [objc] %1 : $@objc_metatype Gadget.Type, $Gadget
+// CHECK: [[INIT:%.*]] = function_ref @$s17objc_dynamic_init6GadgetCACycfcTD : $@convention(method) (@owned Gadget) -> @owned Gadget
+// CHECK: [[NEW_SELF:%.*]] = apply [[INIT]]([[SELF]]) : $@convention(method) (@owned Gadget) -> @owned Gadget
+// CHECK: return [[NEW_SELF]]
+
+// CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s17objc_dynamic_init6GadgetCAA6HoozitA2aDPxycfCTW : $@convention(witness_method: Hoozit) (@thick Gadget.Type) -> @out Gadget {
+// CHECK:         function_ref @$s17objc_dynamic_init6GadgetCACycfC
+
 class Gizmo: Gadget, Wotsit {
     required init() {
         super.init()
@@ -35,8 +45,7 @@ final class Bobamathing: Thingamabob {
     }
 }
 
-// CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s{{.*}}GadgetC{{.*}}CTW
-// CHECK:         function_ref @{{.*}}Gadget{{.*}}fC :
+
 
 // CHECK-LABEL: sil_vtable Gadget {
 // CHECK-NOT:     #Gadget.init!allocator.1