# HG changeset patch
# User thartmann
# Date 1408426571 -7200
# Node ID 91cb3b8aac2b2be0d538341da735abd32318b77a
# Parent  7ff83df6c85a3f8f6edad38fb6d9bb3a220d6f4b
8048879: "unexpected yanked node" opto/postaloc.cpp:139
Summary: MemBarAcquireNode prevents deletion of dead LoadNNode. Added condition to 'has_special_unique_user' to trigger deletion.
Reviewed-by: kvn, iveresov

diff -r 7ff83df6c85a -r 91cb3b8aac2b src/share/vm/opto/node.cpp
--- a/src/share/vm/opto/node.cpp	Fri Sep 05 15:10:41 2014 -0700
+++ b/src/share/vm/opto/node.cpp	Tue Aug 19 07:36:11 2014 +0200
@@ -1093,6 +1093,9 @@
   if( this->is_Store() ) {
     // Condition for back-to-back stores folding.
     return n->Opcode() == op && n->in(MemNode::Memory) == this;
+  } else if (this->is_Load()) {
+    // Condition for removing an unused LoadNode from the MemBarAcquire precedence input
+    return n->Opcode() == Op_MemBarAcquire;
   } else if( op == Op_AddL ) {
     // Condition for convL2I(addL(x,y)) ==> addI(convL2I(x),convL2I(y))
     return n->Opcode() == Op_ConvL2I && n->in(1) == this;
diff -r 7ff83df6c85a -r 91cb3b8aac2b test/compiler/membars/TestMemBarAcquire.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/compiler/membars/TestMemBarAcquire.java	Tue Aug 19 07:36:11 2014 +0200
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2014, 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.
+ */
+
+/*
+ * @test TestMemBarAcquire
+ * @bug 8048879
+ * @summary "Tests optimization of MemBarAcquireNodes"
+ * @run main/othervm -XX:-TieredCompilation -XX:-BackgroundCompilation TestMemBarAcquire
+ */
+public class TestMemBarAcquire {
+  private volatile static Object defaultObj = new Object();
+  private Object obj;
+
+  public TestMemBarAcquire(Object param) {
+    // Volatile load. MemBarAcquireNode is added after the
+    // load to prevent following loads from floating up past.
+    // StoreNode is added to store result of load in 'obj'.
+    this.obj = defaultObj;
+    // Overrides 'obj' and therefore makes previous StoreNode
+    // and the corresponding LoadNode useless. However, the
+    // LoadNode is still connected to the MemBarAcquireNode
+    // that should now release the reference.
+    this.obj = param;
+  }
+
+  public static void main(String[] args) throws Exception {
+    // Make sure TestMemBarAcquire::<init> is compiled
+    for (int i = 0; i < 100000; ++i) {
+      TestMemBarAcquire p = new TestMemBarAcquire(new Object());
+    }
+  }
+}
+