6859338: amd64 native unverified entry point pushes values before implicit null check

Reviewed-by: kvn, twisti

src/cpu/x86/vm/sharedRuntime_x86_64.cpp

@@ -1302,22 +1302,19 @@ nmethod *SharedRuntime::generate_native_wrapper(MacroAssembler *masm,
 
   const Register ic_reg = rax;
   const Register receiver = j_rarg0;
-  const Register tmp = rdx;
 
   Label ok;
   Label exception_pending;
 
+  assert_different_registers(ic_reg, receiver, rscratch1);
   __ verify_oop(receiver);
-  __ push(tmp); // spill (any other registers free here???)
-  __ load_klass(tmp, receiver);
-  __ cmpq(ic_reg, tmp);
+  __ load_klass(rscratch1, receiver);
+  __ cmpq(ic_reg, rscratch1);
   __ jcc(Assembler::equal, ok);
 
-  __ pop(tmp);
   __ jump(RuntimeAddress(SharedRuntime::get_ic_miss_stub()));
 
   __ bind(ok);
-  __ pop(tmp);
 
   // Verified entry point must be aligned
   __ align(8);

test/compiler/6859338/Test6859338.java

+/*
+ * Copyright 2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+/**
+ * @test
+ * @bug 6859338
+ * @summary Assertion failure in sharedRuntime.cpp
+ *
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions  -XX:-InlineObjectHash -Xbatch -XX:-ProfileInterpreter Test6859338
+ */
+
+public class Test6859338 {
+    static Object[] o = new Object[] { new Object(), null };
+    public static void main(String[] args) {
+        int total = 0;
+        try {
+            // Exercise the implicit null check in the unverified entry point
+            for (int i = 0; i < 40000; i++) {
+                int limit = o.length;
+                if (i < 20000) limit = 1;
+                for (int j = 0; j < limit; j++) {
+                    total += o[j].hashCode();
+                }
+            }
+
+        } catch (NullPointerException e) {
+            // this is expected.  A true failure causes a crash
+        }
+    }
+}