IRGen: Disable eager initialization of NSCoding adopters on newer targets

If a class does not have a custom @objc name, objc_getClass() can find
it at runtime by calling the Swift runtime's metadata demangler hook.

This avoids the static initializer on startup. If the class has a
custom runtime name we still need the static initializer unfortunately.

Fixes <rdar://problem/49660515>.

Author: slavapestov

include/swift/Basic/LangOptions.h

@@ -394,6 +394,15 @@ namespace swift {
     // - watchOS 5.2
     bool doesTargetSupportObjCMetadataUpdateCallback() const;
 
+    // The following deployment targets ship an Objective-C runtime supporting
+    // the objc_getClass() hook:
+    //
+    // - macOS 10.14.4
+    // - iOS 12.2
+    // - tvOS 12.2
+    // - watchOS 5.2
+    bool doesTargetSupportObjCGetClassHook() const;
+
     /// Returns true if the given platform condition argument represents
     /// a supported target operating system.
     ///

lib/Basic/LangOptions.cpp

@@ -288,3 +288,7 @@ bool LangOptions::doesTargetSupportObjCMetadataUpdateCallback() const {
   // tests that -enable-objc-interop.
   return false;
 }
+
+bool LangOptions::doesTargetSupportObjCGetClassHook() const {
+  return doesTargetSupportObjCMetadataUpdateCallback();
+}

lib/Sema/TypeCheckProtocol.cpp

@@ -4839,6 +4839,12 @@ static void inferStaticInitializeObjCMetadata(TypeChecker &tc,
   if (classDecl->getAttrs().hasAttribute<StaticInitializeObjCMetadataAttr>())
     return;
 
+  // If the class does not have a custom @objc name and the deployment target
+  // supports the objc_getClass() hook, the workaround is unnecessary.
+  if (tc.Context.LangOpts.doesTargetSupportObjCGetClassHook() &&
+      !hasExplicitObjCName(classDecl))
+    return;
+
   // If we know that the Objective-C metadata will be statically registered,
   // there's nothing to do.
   if (!classDecl->checkAncestry(AncestryFlags::Generic)) {

test/IRGen/eager-class-initialization.swift

@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: %build-irgen-test-overlays
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -emit-ir | %FileCheck %s -DINT=i%target-ptrsize --check-prefix=CHECK --check-prefix=CHECK-OLD
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -target x86_64-apple-macosx10.14.4 -emit-ir | %FileCheck %s -DINT=i%target-ptrsize --check-prefix=CHECK
+// REQUIRES: CPU=x86_64
+// REQUIRES: OS=macosx
+
+import Foundation
+
+class BaseWithCoding : NSObject, NSCoding {
+  required init(coder: NSCoder) { fatalError() }
+
+  func encode(coder: NSCoder) { fatalError() }
+}
+
+class Generic<T> : BaseWithCoding {}
+
+class GenericAncestry : Generic<Int> {}
+
+@objc(custom_name)
+class GenericAncestryWithCustomName : Generic<Double> {}
+
+// CHECK-LABEL: define {{.*}} @_swift_eager_class_initialization
+// CHECK-NEXT:  entry:
+// CHECK-OLD-NEXT: [[RESPONSE:%.*]] = call swiftcc %swift.metadata_response @"$s4main15GenericAncestryCMa"([[INT]] 0)
+// CHECK-OLD-NEXT: [[METADATA:%.*]] = extractvalue %swift.metadata_response [[RESPONSE]], 0
+// CHECK-OLD-NEXT: call void asm sideeffect "", "r"(%swift.type* [[METADATA]])
+// CHECK-NEXT:     [[RESPONSE:%.*]] = call swiftcc %swift.metadata_response @"$s4main29GenericAncestryWithCustomNameCMa"([[INT]] 0)
+// CHECK-NEXT:     [[METADATA:%.*]] = extractvalue %swift.metadata_response [[RESPONSE]], 0
+// CHECK-NEXT:     call void asm sideeffect "", "r"(%swift.type* [[METADATA]])
+// CHECK-NEXT:     ret

test/Interpreter/SDK/archive_attributes.swift

@@ -1,18 +1,20 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-build-swift %s -module-name=test -DENCODE -o %t/encode
-// RUN: %target-build-swift %s -module-name=test -o %t/decode
-// RUN: %target-build-swift %s -module-name=test -Xfrontend -disable-llvm-optzns -emit-ir | %FileCheck -check-prefix=CHECK-IR %s
 // RUN: %target-run %t/encode %t/test.arc
 // RUN: plutil -p %t/test.arc | %FileCheck -check-prefix=CHECK-ARCHIVE %s
-// RUN: %target-run %t/decode %t/test.arc | %FileCheck %s
+
+// RUN: %target-build-swift %s -module-name=test -o %t/decode
+// RUN: %target-run %t/decode %t/test.arc --stdlib-unittest-in-process
+
+// RUN: %target-build-swift %s -module-name=test -o %t/decode -target x86_64-apple-macosx10.14.4
+// RUN: %target-run %t/decode %t/test.arc NEW --stdlib-unittest-in-process
 
 // REQUIRES: executable_test
 // REQUIRES: objc_interop
-// REQUIRES: CPU=i386 || CPU=x86_64
-// UNSUPPORTED: OS=tvos
-// UNSUPPORTED: OS=watchos
+// REQUIRES: OS=macosx
 
 import Foundation
+import StdlibUnittest
 
 struct ABC {
   // CHECK-ARCHIVE-DAG: "$classname" => "nested_class_coding"
@@ -133,59 +135,37 @@ class TopLevel : NSObject, NSCoding {
   }
 }
 
-func main() {
-
-  let args = CommandLine.arguments
-
 #if ENCODE
-  let c = TopLevel(27)
-  c.nested = ABC.NestedClass(28)
-  c.priv = PrivateClass(29)
-  c.intc = IntClass(ii: 42)
-  c.doublec = DoubleClass(dd: 3.14)
+let c = TopLevel(27)
+c.nested = ABC.NestedClass(28)
+c.priv = PrivateClass(29)
+c.intc = IntClass(ii: 42)
+c.doublec = DoubleClass(dd: 3.14)
 
-  NSKeyedArchiver.archiveRootObject(c, toFile: args[1])
+NSKeyedArchiver.archiveRootObject(c, toFile: CommandLine.arguments[1])
 #else
-  if let u = NSKeyedUnarchiver.unarchiveObject(withFile: args[1]) {
-    if let x = u as? TopLevel {
-      // CHECK: top-level: 27
-      print("top-level: \(x.tli)")
-      if let n = x.nested {
-        // CHECK: nested: 28
-        print("nested: \(n.i)")
-      }
-      if let p = x.priv {
-        // CHECK: private: 29
-        print("private: \(p.pi)")
-      }
-      if let g = x.intc {
-        // CHECK: int: 42
-        print("int: \(g.gi!)")
-      }
-      if let d = x.doublec {
-        // CHECK: double: 3.14
-        print("double: \(d.gi!)")
-      }
-    } else {
-      print(u)
+var DecodeTestSuite = TestSuite("Decode")
+
+DecodeTestSuite.test("Decode") {
+  func doIt() {
+    let u = NSKeyedUnarchiver.unarchiveObject(withFile: CommandLine.arguments[1])!
+    let x = u as! TopLevel
+    expectEqual(27, x.tli)
+    expectEqual(28, x.nested!.i)
+    expectEqual(29, x.priv!.pi)
+    expectEqual(42, x.intc!.gi!)
+    expectEqual(3.14, x.doublec!.gi!)
+  }
+
+  if CommandLine.arguments[2] == "NEW" {
+    if #available(macOS 10.14.4, *) {
+      doIt()
     }
-  } else {
-    print("nil")
+    return
   }
-#endif
-}
-
-main()
 
-// Check that we eagerly create metadata of generic classes, but not for nested classes.
-
-// CHECK-IR-LABEL: define {{.*}} @_swift_eager_class_initialization
-// CHECK-IR-NEXT:  entry:
-// CHECK-IR-NEXT:    call {{.*}}IntClassCMa
-// CHECK-IR-NEXT:    extractvalue
-// CHECK-IR-NEXT:    call void asm
-// CHECK-IR-NEXT:    call {{.*}}DoubleClassCMa
-// CHECK-IR-NEXT:    extractvalue
-// CHECK-IR-NEXT:    call void asm
-// CHECK-IR-NEXT:    ret
+  doIt()
+}
 
+runAllTests()
+#endif