Improve C++ code for string splittig (Dromaeo benchmark).

runtime/lib/string.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/symbols.h"
@@ skipping 56 matching lines @@
   ASSERT(receiver.IsOneByteString());
   GET_NATIVE_ARGUMENT(Smi, start_obj, arguments->NativeArgAt(1));
   GET_NATIVE_ARGUMENT(Smi, end_obj, arguments->NativeArgAt(2));
 
   const intptr_t start = start_obj.Value();
   const intptr_t end = end_obj.Value();
   return OneByteString::New(receiver, start, end - start, Heap::kNew);
 }
 
 
+// This is high-performance code.
 DEFINE_NATIVE_ENTRY(OneByteString_splitWithCharCode, 2) {
-  const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
+  const String& receiver = String::CheckedHandle(isolate,
+                                                 arguments->NativeArgAt(0));
   ASSERT(receiver.IsOneByteString());
   GET_NATIVE_ARGUMENT(Smi, smi_split_code, arguments->NativeArgAt(1));
   const intptr_t len = receiver.Length();
   const intptr_t split_code = smi_split_code.Value();
   const GrowableObjectArray& result = GrowableObjectArray::Handle(
-      GrowableObjectArray::New(4, Heap::kNew));
-  String& str = String::Handle();
+      isolate,
+      GrowableObjectArray::New(16, Heap::kNew));
+  String& str = String::Handle(isolate);
   intptr_t start = 0;
   intptr_t i = 0;
   for (; i < len; i++) {
-    if (split_code == receiver.CharAt(i)) {
-      str = String::SubString(receiver, start, (i - start));
-      result.Add(str);
+    if (split_code == OneByteString::CharAt(receiver, i)) {
+      str = OneByteString::SubStringUnchecked(receiver,
+                                              start,
+                                              (i - start),
+                                              Heap::kNew);
+      result.Add(isolate, str);
       start = i + 1;
     }
   }
-  str = String::SubString(receiver, start, (i - start));
-  result.Add(str);
+  str = OneByteString::SubStringUnchecked(receiver,
+                                          start,
+                                          (i - start),
+                                          Heap::kNew);
+  result.Add(isolate, str);
   return result.raw();
 }
 
 
 DEFINE_NATIVE_ENTRY(String_getHashCode, 1) {
   const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   intptr_t hash_val = receiver.Hash();
   ASSERT(hash_val > 0);
   ASSERT(Smi::IsValid(hash_val));
   return Smi::New(hash_val);
@@ skipping 77 matching lines @@
     if (!elem.IsString()) {
       GrowableArray<const Object*> args;
       args.Add(&elem);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
   }
   return String::ConcatAll(strings);
 }
 
 }  // namespace dart