--- /dev/null	2017-01-22 10:16:57.869617664 -0800
+++ new/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.replacements.aarch64/src/org/graalvm/compiler/replacements/aarch64/AArch64LongSubstitutions.java	2017-02-15 17:08:42.327047485 -0800
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2013, 2016, 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.
+ */
+package org.graalvm.compiler.replacements.aarch64;
+
+import org.graalvm.compiler.api.replacements.ClassSubstitution;
+import org.graalvm.compiler.api.replacements.MethodSubstitution;
+
+/**
+ * Aarch64 ISA offers a count leading zeros instruction which can be used to implement
+ * numberOfLeadingZeros more efficiently than using BitScanReverse.
+ */
+@ClassSubstitution(Long.class)
+public class AArch64LongSubstitutions {
+
+    @MethodSubstitution
+    public static int bitCount(long value) {
+        // Based on Warren, Hacker's Delight, slightly adapted to profit from Aarch64 add + shift
+        // instruction.
+        // Assuming the peephole optimizer optimizes all x - y >>> z into a single instruction
+        // this takes 11 instructions.
+        long x = value;
+        x = x - ((x & 0xaaaaaaaaaaaaaaaaL) >>> 1);
+        x = (x & 0x3333333333333333L) + ((x & 0xccccccccccccccccL) >>> 2);
+        x = (x + (x >>> 4)) & 0x0f0f0f0f0f0f0f0fL;
+        x = x + (x >>> 8);
+        x = x + (x >>> 16);
+        x = x + (x >>> 32);
+        return (int) x & 0x7f;
+    }
+
+}