JBR-7523 fix ClassUnloading support in DCEVM

src/hotspot/share/prims/jvmtiEnhancedRedefineClasses.cpp

@@ -106,6 +106,7 @@ u8        VM_EnhancedRedefineClasses::_id_counter = 0;
 // @param class_load_kind always jvmti_class_load_kind_redefine
 VM_EnhancedRedefineClasses::VM_EnhancedRedefineClasses(jint class_count, const jvmtiClassDefinition *class_defs, JvmtiClassLoadKind class_load_kind) :
         VM_GC_Operation(Universe::heap()->total_collections(), GCCause::_heap_inspection, Universe::heap()->total_full_collections(), true) {
+  _new_classes = nullptr;
   _affected_klasses = nullptr;
   _class_count = class_count;
   _class_defs = class_defs;
@@ -717,12 +718,6 @@ void VM_EnhancedRedefineClasses::doit() {
     Universe::objectArrayKlassObj()->append_to_sibling_list();
   }
 
-  if (_object_klass_redefined) {
-    // TODO: This is a hack; it keeps old mirror instances on the heap. A correct solution could be to hold the old mirror class in the new mirror class.
-    ClassUnloading = false;
-    ClassUnloadingWithConcurrentMark = false;
-  }
-
   if (needs_instance_update) {
     // Do a full garbage collection to update the instance sizes accordingly
     log_trace(redefine, class, redefine, metadata)("Before redefinition full GC run");
@@ -788,6 +783,10 @@ void VM_EnhancedRedefineClasses::doit() {
 
   Universe::set_inside_redefinition(false);
   _timer_vm_op_doit.stop();
+
+  if (log_is_enabled(Trace, redefine, class, codecache)) {
+    CodeCache::print();
+  }
 }
 
 // Cleanup - runs in JVM thread
@@ -1027,9 +1026,11 @@ jvmtiError VM_EnhancedRedefineClasses::load_new_class_versions_single_step(TRAPS
         // The hidden class loader data has been artificially been kept alive to
         // this point. The mirror and any instances of this class have to keep
         // it alive afterwards.
-        if (the_class->class_loader_data()->keep_alive_cnt() > 0) {
-          the_class->class_loader_data()->dec_keep_alive();
-        }
+
+        // Keep old classloader data alive otherwise it crashes with ClassUnloading=true
+//        if (the_class->class_loader_data()->keep_alive_cnt() > 0) {
+//          the_class->class_loader_data()->dec_keep_alive();
+//        }
       }
 
     } else {

src/hotspot/share/runtime/arguments.cpp

@@ -4021,15 +4021,6 @@ jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
 
   setup_hotswap_agent();
 
-  if (AllowEnhancedClassRedefinition) {
-    if (!FLAG_IS_CMDLINE(ClassUnloading)) {
-      ClassUnloading = false;
-      ClassUnloadingWithConcurrentMark = false;
-    } else {
-      warning("The JVM is unstable when using -XX:+AllowEnhancedClassRedefinition and -XX:+ClassUnloading together!");
-    }
-  }
-
 #if !INCLUDE_CDS
   if (DumpSharedSpaces || RequireSharedSpaces) {
     jio_fprintf(defaultStream::error_stream(),