--- a/src/share/vm/c1/c1_InstructionPrinter.cpp	Thu May 05 21:06:14 2011 -0700
+++ b/src/share/vm/c1/c1_InstructionPrinter.cpp	Fri May 06 12:12:29 2011 -0700
@@ -132,17 +132,22 @@
     if (value->is_null_object()) {
       output()->print("null");
     } else if (!value->is_loaded()) {
-      output()->print("<unloaded object 0x%x>", value);
+      output()->print("<unloaded object " PTR_FORMAT ">", value);
     } else if (value->is_method()) {
       ciMethod* m = (ciMethod*)value;
       output()->print("<method %s.%s>", m->holder()->name()->as_utf8(), m->name()->as_utf8());
     } else {
-      output()->print("<object 0x%x>", value->constant_encoding());
+      output()->print("<object " PTR_FORMAT ">", value->constant_encoding());
     }
   } else if (type->as_InstanceConstant() != NULL) {
-    output()->print("<instance 0x%x>", type->as_InstanceConstant()->value()->constant_encoding());
+    ciInstance* value = type->as_InstanceConstant()->value();
+    if (value->is_loaded()) {
+      output()->print("<instance " PTR_FORMAT ">", value->constant_encoding());
+    } else {
+      output()->print("<unloaded instance " PTR_FORMAT ">", value);
+    }
   } else if (type->as_ArrayConstant() != NULL) {
-    output()->print("<array 0x%x>", type->as_ArrayConstant()->value()->constant_encoding());
+    output()->print("<array " PTR_FORMAT ">", type->as_ArrayConstant()->value()->constant_encoding());
   } else if (type->as_ClassConstant() != NULL) {
     ciInstanceKlass* klass = type->as_ClassConstant()->value();
     if (!klass->is_loaded()) {

--- a/src/share/vm/c1/c1_Optimizer.cpp	Thu May 05 21:06:14 2011 -0700
+++ b/src/share/vm/c1/c1_Optimizer.cpp	Fri May 06 12:12:29 2011 -0700
@@ -252,26 +252,28 @@
         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 
-        guarantee(t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable, "incomparable constants in IfOp");
-
-        Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
-        Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
+        // not_comparable here is a valid return in case we're comparing unloaded oop constants
+        if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
+          Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
+          Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 
-        _ifop_count++;
-        if (new_tval == new_fval) {
-          return new_tval;
-        } else {
-          return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
+          _ifop_count++;
+          if (new_tval == new_fval) {
+            return new_tval;
+          } else {
+            return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
+          }
         }
       }
     } else {
       Constant* x_const = x->as_Constant();
       if (x_const != NULL) {         // x and y are constants
         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
-        guarantee(x_compare_res != Constant::not_comparable, "incomparable constants in IfOp");
-
-        _ifop_count++;
-        return x_compare_res == Constant::cond_true ? tval : fval;
+        // not_comparable here is a valid return in case we're comparing unloaded oop constants
+        if (x_compare_res != Constant::not_comparable) {
+          _ifop_count++;
+          return x_compare_res == Constant::cond_true ? tval : fval;
+        }
       }
     }
   }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/compiler/7042153/Test7042153.java	Fri May 06 12:12:29 2011 -0700
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2011, 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
+ * @bug 7042153
+ * @summary Bad folding of IfOps with unloaded constant arguments in C1
+ *
+ * @run main/othervm -Xcomp Test7042153
+ */
+
+import java.lang.reflect.*;
+
+public class Test7042153 {
+  static public class Bar { }
+  static public class Foo { }
+
+  static volatile boolean z;
+  public static void main(String [] args) {
+    Class cx = Bar.class;
+    Class cy = Foo.class;
+    z = (cx == cy);
+  }
+}