diff -r 5a297ea605c7 -r fcbb92a1ab3b src/share/vm/runtime/arguments.cpp
--- a/src/share/vm/runtime/arguments.cpp	Sat Jun 26 00:19:55 2010 -0700
+++ b/src/share/vm/runtime/arguments.cpp	Tue Jun 29 16:09:57 2010 -0700
@@ -1508,6 +1508,9 @@
   if (AggressiveOpts && FLAG_IS_DEFAULT(BiasedLockingStartupDelay)) {
     FLAG_SET_DEFAULT(BiasedLockingStartupDelay, 500);
   }
+  if (AggressiveOpts && FLAG_IS_DEFAULT(OptimizeStringConcat)) {
+    FLAG_SET_DEFAULT(OptimizeStringConcat, true);
+  }
 #endif
 
   if (AggressiveOpts) {