Faster Klass* access

src/hotspot/share/oops/klassMode.cpp

@@ -0,0 +1,39 @@
+/*
+ * Copyright Amazon.com Inc. 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "oops/klassMode.hpp"
+
+KlassMode::Mode KlassMode::_klass_mode = KlassMode::Undefined;
+
+void KlassMode::init_klass_mode() {
+  assert(_klass_mode == Undefined, "KlassMode initialized twice");
+  if (UseCompactObjectHeaders) {
+    _klass_mode = Compact;
+  } else if (UseCompressedClassPointers) {
+    _klass_mode = Compressed;
+  } else {
+    _klass_mode = Uncompressed;
+  }
+}

src/hotspot/share/oops/klassMode.hpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright Amazon.com Inc. 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_OOPS_KLASSMODE_HPP
+#define SHARE_OOPS_KLASSMODE_HPP
+
+/*
+ * This class helps to avoid loading more than one flag when
+ * accessing the Klass* in oopDesc::klass(). This is important
+ * on some performance critical paths where the Klass* is
+ * accessed frequently, especially by GC oop iterators.
+ *
+ * Instead of doing:
+ * if (UseCompactObjectHeaders) { // Load first flag
+ *   ..
+ * } else if (UseCompressedClassPointers) { // Load second flag
+ *   ..
+ * } else {
+ *   ..
+ * }
+ *
+ * we can do:
+ * switch (KlassMode::klass_mode()) {
+ * case Compact:
+ *   ..
+ * case Compressed:
+ *   ..
+ * case Uncompressed:
+ *   ..
+ * }
+ */
+class KlassMode {
+public:
+  enum Mode {
+    // +UseCompactObjectHeaders (implies +UseCompressedClassPointers)
+    Compact,
+    // +UseCompressedClassPointers (-UseCompactObjectHeaders)
+    Compressed,
+    // -UseCompressedClassPointers (-UseCompactObjectHeaders)
+    Uncompressed,
+    // Not yet initialized
+    Undefined
+  };
+
+private:
+  static Mode _klass_mode;
+
+public:
+  static void init_klass_mode();
+  static inline Mode klass_mode();
+};
+
+#endif // SHARE_OOPS_KLASSMODE_HPP

src/hotspot/share/oops/klassMode.inline.hpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright Amazon.com Inc. 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_OOPS_KLASSMODE_INLINE_HPP
+#define SHARE_OOPS_KLASSMODE_INLINE_HPP
+
+#include "oops/klassMode.hpp"
+
+inline KlassMode::Mode KlassMode::klass_mode() {
+#ifdef ASSERT
+  assert(_klass_mode != Undefined, "KlassMode not yet initialized");
+  if (UseCompactObjectHeaders) {
+    assert(_klass_mode == Compact, "Klass mode does not match flags");
+  } else if (UseCompressedClassPointers) {
+    assert(_klass_mode == Compressed, "Klass mode does not match flags");
+  } else {
+    assert(_klass_mode == Uncompressed, "Klass mode does not match flags");
+  }
+#endif
+#ifdef _LP64
+  return _klass_mode;
+#else
+  return Uncompressed;
+#endif
+}
+
+#endif // SHARE_OOPS_KLASSMODE_INLINE_HPP

src/hotspot/share/oops/oop.inline.hpp

@@ -34,6 +34,7 @@
 #include "oops/arrayOop.hpp"
 #include "oops/compressedKlass.inline.hpp"
 #include "oops/instanceKlass.hpp"
+#include "oops/klassMode.inline.hpp"
 #include "oops/markWord.inline.hpp"
 #include "oops/oopsHierarchy.hpp"
 #include "runtime/atomic.hpp"
@@ -95,43 +96,48 @@ void oopDesc::init_mark() {
 }
 
 Klass* oopDesc::klass() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass();
-  } else if (UseCompressedClassPointers) {
-     return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (KlassMode::klass_mode()) {
+    case KlassMode::Compact:
+      return mark().klass();
+    case KlassMode::Compressed:
+      return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 
 Klass* oopDesc::klass_or_null() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass_or_null();
-  } else if (UseCompressedClassPointers) {
-    return CompressedKlassPointers::decode(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (KlassMode::klass_mode()) {
+    case KlassMode::Compact:
+      return mark().klass_or_null();
+    case KlassMode::Compressed:
+      return CompressedKlassPointers::decode(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 
 Klass* oopDesc::klass_or_null_acquire() const {
-  if (UseCompactObjectHeaders) {
-    return mark_acquire().klass();
-  } else if (UseCompressedClassPointers) {
-    narrowKlass narrow_klass = Atomic::load_acquire(&_metadata._compressed_klass);
-    return CompressedKlassPointers::decode(narrow_klass);
-  } else {
-    return Atomic::load_acquire(&_metadata._klass);
+  switch (KlassMode::klass_mode()) {
+    case KlassMode::Compact:
+      return mark_acquire().klass();
+    case KlassMode::Compressed: {
+      narrowKlass narrow_klass = Atomic::load_acquire(&_metadata._compressed_klass);
+      return CompressedKlassPointers::decode(narrow_klass);
+    }
+    default:
+      return Atomic::load_acquire(&_metadata._klass);
   }
 }
 
 Klass* oopDesc::klass_without_asserts() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass_without_asserts();
-  } else if (UseCompressedClassPointers) {
-    return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (KlassMode::klass_mode()) {
+    case KlassMode::Compact:
+      return mark().klass_without_asserts();
+    case KlassMode::Compressed:
+      return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 

src/hotspot/share/runtime/arguments.cpp

@@ -46,6 +46,7 @@
 #include "nmt/nmtCommon.hpp"
 #include "oops/compressedKlass.hpp"
 #include "oops/instanceKlass.hpp"
+#include "oops/klassMode.hpp"
 #include "oops/oop.inline.hpp"
 #include "prims/jvmtiAgentList.hpp"
 #include "prims/jvmtiExport.hpp"
@@ -3670,6 +3671,7 @@ jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
   if (UseCompactObjectHeaders && !UseCompressedClassPointers) {
     FLAG_SET_DEFAULT(UseCompressedClassPointers, true);
   }
+  KlassMode::init_klass_mode();
 #endif
 
   return JNI_OK;