6866651: Regression: simple int sum crashes jvm (build 1.6.0_14-b08 and 1.7.0-ea-b59)

Summary: delay dead code elimination in set_req_X to make it safe
Reviewed-by: kvn, never

src/share/vm/opto/phaseX.cpp

@@ -1622,9 +1622,11 @@ void Node::set_req_X( uint i, Node *n, PhaseIterGVN *igvn ) {
   // old goes dead?
   if( old ) {
     switch (old->outcnt()) {
-    case 0:      // Kill all his inputs, and recursively kill other dead nodes.
+    case 0:
+      // Put into the worklist to kill later. We do not kill it now because the
+      // recursive kill will delete the current node (this) if dead-loop exists
       if (!old->is_top())
-        igvn->remove_dead_node( old );
+        igvn->_worklist.push( old );
       break;
     case 1:
       if( old->is_Store() || old->has_special_unique_user() )

test/compiler/6866651/Test.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 6866651
+ * @summary delay dead node elimination in set_req_X to prevent killing the current node when it is in use
+ *
+ * @run main Test
+ */
+
+public class Test {
+
+    static int sum() {
+        int s = 0;
+        for (int x = 1, y = 0; x != 0; x++, y--) {
+            s ^= y;
+        }
+        return s;
+    }
+
+    public static void main(final String[] args) {
+        for (int k = 0; k < 2; k++) {
+            System.err.println(String.valueOf(sum()));
+        }
+    }
+}