8330699: Obsolete -XX:+UseEmptySlotsInSupers

src/hotspot/share/classfile/fieldLayoutBuilder.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -137,7 +137,7 @@ void FieldLayout::initialize_instance_layout(const InstanceKlass* super_klass) {
   } else {
     bool has_fields = reconstruct_layout(super_klass);
     fill_holes(super_klass);
-    if ((UseEmptySlotsInSupers && !super_klass->has_contended_annotations()) || !has_fields) {
+    if (!super_klass->has_contended_annotations() || !has_fields) {
       _start = _blocks;  // start allocating fields from the first empty block
     } else {
       _start = _last;    // append fields at the end of the reconstructed layout
@@ -364,20 +364,6 @@ void FieldLayout::fill_holes(const InstanceKlass* super_klass) {
     b = p;
   }
 
-  if (!UseEmptySlotsInSupers) {
-    // Add an empty slots to align fields of the subclass on a heapOopSize boundary
-    // in order to emulate the behavior of the previous algorithm
-    int align = (b->offset() + b->size()) % heapOopSize;
-    if (align != 0) {
-      int sz = heapOopSize - align;
-      LayoutRawBlock* p = new LayoutRawBlock(LayoutRawBlock::EMPTY, sz);
-      p->set_offset(b->offset() + b->size());
-      b->set_next_block(p);
-      p->set_prev_block(b);
-      b = p;
-    }
-  }
-
   LayoutRawBlock* last = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
   last->set_offset(b->offset() + b->size());
   assert(last->offset() > 0, "Sanity check");

src/hotspot/share/runtime/arguments.cpp

@@ -505,14 +505,14 @@ static SpecialFlag const special_jvm_flags[] = {
   { "DontYieldALot",                JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
   { "PreserveAllAnnotations",       JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
   { "UseNotificationThread",        JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
-  { "UseEmptySlotsInSupers",        JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
   // --- Deprecated alias flags (see also aliased_jvm_flags) - sorted by obsolete_in then expired_in:
   { "CreateMinidumpOnCrash",        JDK_Version::jdk(9),  JDK_Version::undefined(), JDK_Version::undefined() },
 
   // -------------- Obsolete Flags - sorted by expired_in --------------
 
   { "MetaspaceReclaimPolicy",       JDK_Version::undefined(), JDK_Version::jdk(21), JDK_Version::undefined() },
 
+  { "UseEmptySlotsInSupers",        JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
   { "OldSize",                      JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },
 #if defined(X86)
   { "UseRTMLocking",                JDK_Version::jdk(23), JDK_Version::jdk(24), JDK_Version::jdk(25) },

src/hotspot/share/runtime/globals.hpp

@@ -1948,10 +1948,6 @@ const int ObjectAlignmentInBytes = 8;
   product(bool, UseFastUnorderedTimeStamps, false, EXPERIMENTAL,            \
           "Use platform unstable time where supported for timestamps only") \
                                                                             \
-  product(bool, UseEmptySlotsInSupers, true,                                \
-          "(Deprecated) Allow allocating fields in empty slots of "         \
-          "super-classes")                                                  \
-                                                                            \
   product(bool, DeoptimizeNMethodBarriersALot, false, DIAGNOSTIC,           \
                 "Make nmethod barriers deoptimise a lot.")                  \
                                                                             \