diff -r d6ec2737186c -r 6d700b859b3e hotspot/src/share/vm/opto/memnode.cpp
--- a/hotspot/src/share/vm/opto/memnode.cpp	Fri Nov 27 07:56:58 2009 -0800
+++ b/hotspot/src/share/vm/opto/memnode.cpp	Thu Nov 12 09:24:21 2009 -0800
@@ -1503,6 +1503,8 @@
       }
     }
   } else if (tp->base() == Type::InstPtr) {
+    const TypeInstPtr* tinst = tp->is_instptr();
+    ciKlass* klass = tinst->klass();
     assert( off != Type::OffsetBot ||
             // arrays can be cast to Objects
             tp->is_oopptr()->klass()->is_java_lang_Object() ||
@@ -1510,6 +1512,25 @@
             phase->C->has_unsafe_access(),
             "Field accesses must be precise" );
     // For oop loads, we expect the _type to be precise
+    if (OptimizeStringConcat && klass == phase->C->env()->String_klass() &&
+        adr->is_AddP() && off != Type::OffsetBot) {
+      // For constant Strings treat the fields as compile time constants.
+      Node* base = adr->in(AddPNode::Base);
+      if (base->Opcode() == Op_ConP) {
+        const TypeOopPtr* t = phase->type(base)->isa_oopptr();
+        ciObject* string = t->const_oop();
+        ciConstant constant = string->as_instance()->field_value_by_offset(off);
+        if (constant.basic_type() == T_INT) {
+          return TypeInt::make(constant.as_int());
+        } else if (constant.basic_type() == T_ARRAY) {
+          if (adr->bottom_type()->is_ptr_to_narrowoop()) {
+            return TypeNarrowOop::make_from_constant(constant.as_object());
+          } else {
+            return TypeOopPtr::make_from_constant(constant.as_object());
+          }
+        }
+      }
+    }
   } else if (tp->base() == Type::KlassPtr) {
     assert( off != Type::OffsetBot ||
             // arrays can be cast to Objects