IRGen: fix the superclass pointer for generic classes in embedded swift

fixes in IRGen crash

Author: eeckstein

lib/IRGen/ClassMetadataVisitor.h

@@ -67,6 +67,18 @@ template <class Impl> class ClassMetadataVisitor
     : super(IGM), Target(target), VTable(vtable) {}
 
 public:
+
+  // Layout in embedded mode while considering the class type.
+  // This is important for adding the right superclass pointer.
+  // The regular `layout` method can be used for layout tasks for which the
+  // actual superclass pointer is not relevant.
+  void layoutEmbedded(CanType classTy) {
+    asImpl().noteAddressPoint();
+    asImpl().addEmbeddedSuperclass(classTy);
+    asImpl().addDestructorFunction();
+    addEmbeddedClassMembers(Target);
+  }
+
   void layout() {
     static_assert(MetadataAdjustmentIndex::Class == 3,
                   "Adjustment index must be synchronized with this layout");

lib/IRGen/GenMeta.cpp

@@ -3903,6 +3903,16 @@ namespace {
       llvm_unreachable("covered switch");
     }
 
+    void addEmbeddedSuperclass(CanType classTy) {
+      CanType superclass = asImpl().getSuperclassTypeForMetadata();
+      if (!superclass) {
+        B.addNullPointer(IGM.TypeMetadataPtrTy);
+        return;
+      }
+      CanType superTy = classTy->getSuperclass()->getCanonicalType();
+      B.add(IGM.getAddrOfTypeMetadata(superTy));
+    }
+
     void addSuperclass() {
       if (asImpl().shouldAddNullSuperclass()) {
         B.addNullPointer(IGM.TypeMetadataPtrTy);
@@ -5025,7 +5035,7 @@ static void emitEmbeddedVTable(IRGenModule &IGM, CanType classTy,
 
   FixedClassMetadataBuilder builder(IGM, classDecl, init, fragileLayout,
                                     vtable);
-  builder.layout();
+  builder.layoutEmbedded(classTy);
   bool canBeConstant = builder.canBeConstant();
 
   StringRef section{};

test/embedded/generic-classes.swift

@@ -0,0 +1,36 @@
+// RUN: %target-run-simple-swift(%S/Inputs/print.swift -enable-experimental-feature Embedded -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: optimized_stdlib
+// REQUIRES: VENDOR=apple
+// REQUIRES: OS=macosx
+
+protocol Fooable {
+  func foo()
+}
+
+class GenericFooableClass<T>: Fooable {
+  func foo() { print("GenericFooableClass<T>.foo") }
+}
+
+class GenericFooableSubClass<T>: GenericFooableClass<T> {
+  override func foo() { print("GenericFooableSubClass<T>.foo") }
+}
+
+func makeItFoo<F: Fooable>(f: F) {
+  f.foo()
+}
+
+@main
+struct Main {
+  static func main() {
+    let f = GenericFooableClass<Int>()
+    makeItFoo(f: f)
+    let g: GenericFooableClass = GenericFooableSubClass<Int>()
+    makeItFoo(f: g)
+  }
+}
+
+// CHECK: GenericFooableClass<T>.foo
+// CHECK: GenericFooableSubClass<T>.foo
+