[IRGen] Use Singleton metadata strategy in JIT mode [5.1]

lib/IRGen/GenClass.cpp

@@ -2317,6 +2317,11 @@ IRGenModule::getClassMetadataStrategy(const ClassDecl *theClass) {
   // If we have resiliently-sized fields, we might be able to use the
   // update pattern.
   if (resilientLayout.doesMetadataRequireUpdate()) {
+
+    // FixedOrUpdate strategy does not work in JIT mode
+    if (IRGen.Opts.UseJIT)
+      return ClassMetadataStrategy::Singleton;
+
     // The update pattern only benefits us on platforms with an Objective-C
     // runtime, otherwise just use the singleton pattern.
     if (!Context.LangOpts.EnableObjCInterop)

test/IRGen/Inputs/legacy_type_info/jit_metadata_strategy.yaml

@@ -0,0 +1,6 @@
+Name:            resilient_struct
+Decls:
+  - Name:            16resilient_struct15ResilientDoubleV
+    Size:            8
+    Alignment:       8
+    ExtraInhabitants: 0

test/IRGen/jit_metadata_strategy.swift

@@ -0,0 +1,40 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -enable-library-evolution %S/../Inputs/resilient_struct.swift -emit-module-path %t/resilient_struct.swiftmodule
+// RUN: %target-swift-frontend -use-jit %s -emit-ir -lresilient_struct -L %t -I %t -enable-objc-interop -read-legacy-type-info-path=%S/Inputs/legacy_type_info/jit_metadata_strategy.yaml | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+import resilient_struct
+
+// ClassMetadataStrategy::Fixed
+class FixedSizeClass {
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+// ClassMetadataStrategy::Singleton
+class GenericSuperclass<T> { }
+class ClassWithGenericSuperclass: GenericSuperclass<Int> {
+    var v1: ResilientDouble?
+    var v2: ResilientDouble?
+    var v3: ResilientDouble?
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+// ClassMetadataStrategy::FixedOrUpdate when compiling
+// ClassMetadataStrategy::Singleton when interpreting
+class ClassNeedingUpdate {
+    var v1: ResilientDouble?
+    var v2: ResilientDouble?
+    var v3: ResilientDouble?
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+// CHECK-LABEL: define{{( protected)?}} private void @runtime_registration
+// CHECK:             call void @swift_instantiateObjCClass({{.*}} @"$s21jit_metadata_strategy14FixedSizeClassCN")
+// CHECK-NOT:         call void @swift_instantiateObjCClass({{.*}} @"$s21jit_metadata_strategy18ClassNeedingUpdateCN")

test/Interpreter/Inputs/legacy_type_info/jit_metadata_strategy.yaml

@@ -0,0 +1,6 @@
+Name:            resilient_struct
+Decls:
+  - Name:            16resilient_struct15ResilientDoubleV
+    Size:            8
+    Alignment:       8
+    ExtraInhabitants: 0

test/Interpreter/jit_metadata_strategy.swift

@@ -0,0 +1,44 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift-dylib(%t/%target-library-name(resilient_struct)) -enable-library-evolution %S/../Inputs/resilient_struct.swift -emit-module -emit-module-path %t/resilient_struct.swiftmodule -module-name resilient_struct
+
+// RUN: %target-swift-frontend -interpret %s -lresilient_struct -L %t -I %t -enable-objc-interop -read-legacy-type-info-path=%S/Inputs/legacy_type_info/jit_metadata_strategy.yaml
+
+// REQUIRES: objc_interop
+// REQUIRES: swift_interpreter
+
+import resilient_struct
+
+@_optimize(none) func blackHole<T>(_: T) {}
+
+// ClassMetadataStrategy::Fixed
+class FixedSizeClass {
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+// ClassMetadataStrategy::Singleton
+class GenericSuperclass<T> { }
+class ClassWithGenericSuperclass: GenericSuperclass<Int> {
+    var v1: ResilientDouble?
+    var v2: ResilientDouble?
+    var v3: ResilientDouble?
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+// ClassMetadataStrategy::FixedOrUpdate when compiling
+// ClassMetadataStrategy::Singleton when interpreting
+class ClassNeedingUpdate {
+    var v1: ResilientDouble?
+    var v2: ResilientDouble?
+    var v3: ResilientDouble?
+    var v4: String?
+    var v5: Int?
+    var v6: String?
+}
+
+blackHole(FixedSizeClass())
+blackHole(ClassWithGenericSuperclass())
+blackHole(ClassNeedingUpdate())