8203339: Add oopDesc::field_offset()

Reviewed-by: rkennke, eosterlund

src/hotspot/share/oops/oop.hpp

@@ -131,6 +131,8 @@ class oopDesc {
   // Need this as public for garbage collection.
   template <class T> inline T* obj_field_addr_raw(int offset) const;
 
+  template <typename T> inline size_t field_offset(T* p) const;
+
   // Standard compare function returns negative value if o1 < o2
   //                                   0              if o1 == o2
   //                                   positive value if o1 > o2

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

@@ -266,6 +266,9 @@ void*    oopDesc::field_addr(int offset)         const { return Access<>::resolv
 template <class T>
 T*       oopDesc::obj_field_addr_raw(int offset) const { return (T*) field_addr_raw(offset); }
 
+template <typename T>
+size_t   oopDesc::field_offset(T* p) const { return pointer_delta((void*)p, (void*)this, 1); }
+
 template <DecoratorSet decorators>
 inline oop  oopDesc::obj_field_access(int offset) const             { return HeapAccess<decorators>::oop_load_at(as_oop(), offset); }
 inline oop  oopDesc::obj_field(int offset) const                    { return HeapAccess<>::oop_load_at(as_oop(), offset);  }

test/hotspot/gtest/oops/test_oop.cpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2018, 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
+ * 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/oop.inline.hpp"
+#include "unittest.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+static char memory[32];
+
+oop fake_object() {
+  return cast_to_oop(memory);
+}
+
+template <typename T>
+T* fake_field_addr() {
+  return reinterpret_cast<T*>(&memory[16]);
+}
+
+TEST_VM(oopDesc, field_offset_oop) {
+  // Fake object
+  oop obj = fake_object();
+
+  // Fake oop field
+  oop* oop_field_addr = fake_field_addr<oop>();
+
+  // Check offset
+  size_t oop_offset = obj->field_offset(oop_field_addr);
+  ASSERT_EQ(16u, oop_offset);
+}
+
+TEST_VM(oopDesc, field_offset_narrowOop) {
+  // Fake object
+  oop obj = fake_object();
+
+  // Fake narrowOop field
+  narrowOop* narrowOop_field_addr = fake_field_addr<narrowOop>();
+
+  size_t narrowOop_offset = obj->field_offset(narrowOop_field_addr);
+  ASSERT_EQ(16u, narrowOop_offset);
+}
+
+TEST_VM(oopDesc, field_offset_primitive) {
+  // Fake object
+  oop obj = fake_object();
+
+  // Fake primitive field
+  char* char_field_addr = fake_field_addr<char>();
+
+  size_t char_offset = obj->field_offset(char_field_addr);
+  ASSERT_EQ(16u, char_offset);
+}