[SUA] Add test for allocation of classes without metadata (#63759)

Add test for allocating classes with pruned metadata and refactor
`computeMallocTypeSummary()` to make it easier to understand:

* Use early returns for error (metadata absent) conditions
* Remove reliance on implicit dependency---having a type descriptor
  currently implies that there is also class metadata---in case this
  ever changes

Co-authored-by: Julian Lettner <julian.lettner@apple.com>

stdlib/public/runtime/HeapObject.cpp

@@ -125,25 +125,23 @@ computeMallocTypeSummary(const HeapMetadata *heapMetadata) {
   auto *classMetadata = heapMetadata->getClassObject();
   auto *typeDesc = heapMetadata->getTypeContextDescriptor();
 
-  malloc_type_summary_t summary = {};
+  // Pruned metadata or unclassified
+  if (!classMetadata || !typeDesc)
+    return {.type_kind = MALLOC_TYPE_KIND_SWIFT};
 
   // Objc
-  if (classMetadata && classMetadata->isPureObjC()) {
-    summary.type_kind = MALLOC_TYPE_KIND_OBJC;
-    return summary;
-  }
+  if (classMetadata->isPureObjC())
+    return {.type_kind = MALLOC_TYPE_KIND_OBJC};
 
-  // Runtime internal and unclassified
-  if (!typeDesc) {
-    summary.type_kind = MALLOC_TYPE_KIND_CXX;
-    return summary;
-  }
+  malloc_type_summary_t summary = {.type_kind = MALLOC_TYPE_KIND_SWIFT};
+  summary.layout_semantics.reference_count =
+      (classMetadata->getFlags() & ClassFlags::UsesSwiftRefcounting);
 
-  // Swift
-  summary.type_kind = MALLOC_TYPE_KIND_SWIFT;
+  auto *fieldDesc = typeDesc->Fields.get();
+  if (!fieldDesc)
+    return summary;
 
   bool isGenericData = true;
-  if (auto *fieldDesc = typeDesc->Fields.get()) {
   for (auto &field : *fieldDesc) {
     if (field.isIndirectCase()) {
       isGenericData = false;
@@ -153,13 +151,7 @@ computeMallocTypeSummary(const HeapMetadata *heapMetadata) {
         summary.layout_semantics.immutable_pointer = true;
     }
   }
-  }
-
-  if (classMetadata->Flags & ClassFlags::UsesSwiftRefcounting) {
-    summary.layout_semantics.reference_count = true;
-  } else {
   summary.layout_semantics.generic_data = isGenericData;
-  }
 
   return summary;
 

test/stdlib/MetadataPruning.swift

@@ -0,0 +1,133 @@
+// RUN: %target-run-simple-swift
+// RUN: %target-run-simple-swift(-Xfrontend -disable-reflection-metadata)
+// RUN: %target-run-simple-swift(-Xfrontend -reflection-metadata-for-debugger-only)
+// RUN: %target-run-simple-swift(-Xfrontend -disable-reflection-names)
+//
+// REQUIRES: executable_test
+
+import StdlibUnittest
+
+var tests = TestSuite("MetadataPruning")
+
+struct TestStruct {
+  var int = 0
+  var double = 0.0
+  var bool = false
+}
+
+struct GenericStruct<T> {
+  var int = 0
+  var first: T
+  var second: T
+}
+
+enum TestEnum {
+  case one
+  case two
+  case three(TestStruct)
+}
+
+class BaseClass {
+  var superInt = 0
+  init() {}
+}
+
+class TestClass: BaseClass {
+  var int = 0
+  var double = 0.0
+  var bool = false
+  override init() {}
+}
+
+class TestSubclass: TestClass {
+  var strings: [String] = []
+  override init() {}
+}
+
+class GenericClass<T, U>: BaseClass {
+  var first: T
+  var second: U
+
+  init(_ t: T, _ u: U) {
+    self.first = t
+    self.second = u
+  }
+}
+
+class GenericSubclass<V, W>: GenericClass<V, Bool> {
+  var third: W
+
+  init(_ v: V, _ w: W) {
+    self.third = w
+    super.init(v, false)
+  }
+}
+
+class OwnershipTestClass: BaseClass {
+  weak var test1: TestClass?
+  unowned var test2: TestClass
+  unowned(unsafe) var test3: TestClass
+
+  init(_ t: TestClass) {
+    self.test1 = t
+    self.test2 = t
+    self.test3 = t
+  }
+}
+
+struct ContainsObject {
+  var obj: TestClass
+}
+
+#if _runtime(_ObjC)
+import Foundation
+
+class NSObjectSubclass: NSObject {
+  var point: (Double, Double)
+
+  init(x: Double, y: Double) {
+    self.point = (x, y)
+  }
+}
+
+class EmptyNSObject: NSObject {}
+#endif
+
+
+func printAddress(_ obj: AnyObject) {
+  print("\(obj) address: \(Unmanaged.passUnretained(obj).toOpaque())")
+}
+
+tests.test("Allocate types without metadata") {
+  let testStruct = TestStruct()
+  let genericStruct = GenericStruct<Double>(first: 1.3, second: 3.7)
+  let testEnum = TestEnum.three(testStruct)
+  let baseClass = BaseClass()
+  let testClass = TestClass()
+  let testSubclass = TestSubclass()
+  let genericClass = GenericClass<Int, String>(5, "bla")
+  let genericSubclass = GenericSubclass<Double, TestClass>(1.1, testClass)
+  let ownershipTestClass = OwnershipTestClass(testClass)
+  let containsObject = ContainsObject(obj: testClass)
+
+  print("\(testStruct)")
+  print("\(genericStruct)")
+  print("\(testEnum)")
+  printAddress(baseClass)
+  printAddress(testClass)
+  printAddress(testSubclass)
+  printAddress(genericClass)
+  printAddress(genericSubclass)
+  printAddress(ownershipTestClass)
+  print("\(containsObject)")
+
+#if _runtime(_ObjC)
+  let nsObjectSubclass = NSObjectSubclass(x: 1.2, y: 3.4)
+  let emptyNSObject = EmptyNSObject()
+
+  printAddress(nsObjectSubclass)
+  printAddress(emptyNSObject)
+#endif
+}
+
+runAllTests()