6810653: Change String cache class used by Hotspot from String to StringValue

Summary: Change create_vm() to load and initialize StringValue rather than String.
Reviewed-by: kvn

src/share/vm/classfile/vmSymbols.hpp

@@ -49,6 +49,7 @@
   template(java_lang_Object,                          "java/lang/Object")                         \
   template(java_lang_Class,                           "java/lang/Class")                          \
   template(java_lang_String,                          "java/lang/String")                         \
+  template(java_lang_StringValue,                     "java/lang/StringValue")                    \
   template(java_lang_Thread,                          "java/lang/Thread")                         \
   template(java_lang_ThreadGroup,                     "java/lang/ThreadGroup")                    \
   template(java_lang_Cloneable,                       "java/lang/Cloneable")                      \

src/share/vm/runtime/thread.cpp

@@ -3007,20 +3007,22 @@ jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {
       }
 
       if (UseStringCache) {
-        // Forcibly initialize java/lang/String and mutate the private
+        // Forcibly initialize java/lang/StringValue and mutate the private
         // static final "stringCacheEnabled" field before we start creating instances
-        klassOop k_o = SystemDictionary::resolve_or_null(vmSymbolHandles::java_lang_String(), Handle(), Handle(), CHECK_0);
+        klassOop k_o = SystemDictionary::resolve_or_null(vmSymbolHandles::java_lang_StringValue(), Handle(), Handle(), CHECK_0);
+        // Possible that StringValue isn't present: if so, silently don't break
+        if (k_o != NULL) {
           KlassHandle k = KlassHandle(THREAD, k_o);
-        guarantee(k.not_null(), "Must find java/lang/String");
           instanceKlassHandle ik = instanceKlassHandle(THREAD, k());
           ik->initialize(CHECK_0);
           fieldDescriptor fd;
-        // Possible we might not find this field; if so, don't break
+          // Possible we might not find this field: if so, silently don't break
           if (ik->find_local_field(vmSymbols::stringCacheEnabled_name(), vmSymbols::bool_signature(), &fd)) {
             k()->bool_field_put(fd.offset(), true);
           }
         }
       }
+    }
 
     // Initialize java_lang.System (needed before creating the thread)
     if (InitializeJavaLangSystem) {