diff -r 349843ebb209 -r f344a0c6e19e src/hotspot/share/gc/z/zForwarding.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/z/zForwarding.cpp	Mon Mar 18 11:50:39 2019 +0100
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2015, 2019, 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 "gc/z/zForwarding.inline.hpp"
+#include "gc/z/zUtils.inline.hpp"
+#include "memory/allocation.hpp"
+#include "utilities/debug.hpp"
+
+ZForwarding::ZForwarding(uintptr_t start, size_t object_alignment_shift, uint32_t nentries) :
+    _start(start),
+    _object_alignment_shift(object_alignment_shift),
+    _nentries(nentries),
+    _refcount(1),
+    _pinned(false) {}
+
+ZForwarding* ZForwarding::create(uintptr_t start, size_t object_alignment_shift, uint32_t live_objects) {
+  assert(live_objects > 0, "Invalid value");
+
+  // Allocate table for linear probing. The size of the table must be
+  // a power of two to allow for quick and inexpensive indexing/masking.
+  // The table is sized to have a load factor of 50%, i.e. sized to have
+  // double the number of entries actually inserted.
+  const uint32_t nentries = ZUtils::round_up_power_of_2(live_objects * 2);
+
+  const size_t size = sizeof(ZForwarding) + (sizeof(ZForwardingEntry) * nentries);
+  uint8_t* const addr = NEW_C_HEAP_ARRAY(uint8_t, size, mtGC);
+  ZForwardingEntry* const entries = ::new (addr + sizeof(ZForwarding)) ZForwardingEntry[nentries];
+  ZForwarding* const forwarding = ::new (addr) ZForwarding(start, object_alignment_shift, nentries);
+  return forwarding;
+}
+
+void ZForwarding::destroy(ZForwarding* forwarding) {
+  FREE_C_HEAP_ARRAY(uint8_t, forwarding);
+}
+
+void ZForwarding::verify(uint32_t object_max_count, uint32_t live_objects) const {
+  uint32_t count = 0;
+
+  for (ZForwardingCursor i = 0; i < _nentries; i++) {
+    const ZForwardingEntry entry = at(&i);
+    if (entry.is_empty()) {
+      // Skip empty entries
+      continue;
+    }
+
+    // Check from index
+    guarantee(entry.from_index() < object_max_count, "Invalid from index");
+
+    // Check for duplicates
+    for (ZForwardingCursor j = i + 1; j < _nentries; j++) {
+      const ZForwardingEntry other = at(&j);
+      guarantee(entry.from_index() != other.from_index(), "Duplicate from");
+      guarantee(entry.to_offset() != other.to_offset(), "Duplicate to");
+    }
+
+    count++;
+  }
+
+  // Check number of non-null entries
+  guarantee(live_objects == count, "Count mismatch");
+}