Improve scanner performance by remembering string's CharAt function as the string type does not cha…

runtime/vm/object.cc

 // Copyright (c) 2012, 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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 15980 matching lines @@
     return *TwoByteString::CharAddr(*this, index);
   }
   if (class_id == kExternalOneByteStringCid) {
     return *ExternalOneByteString::CharAddr(*this, index);
   }
   ASSERT(class_id == kExternalTwoByteStringCid);
   return *ExternalTwoByteString::CharAddr(*this, index);
 }
 
 
+Scanner::CharAtFunc String::CharAtFunc() const {
+  intptr_t class_id = raw()->GetClassId();
+  ASSERT(RawObject::IsStringClassId(class_id));
+  NoGCScope no_gc;

[zra, 2014/06/05 20:49:46]

What is the reason for the NoGCScope?

[srdjan, 2014/06/05 21:16:38]

Copy and paste error: removed.

+  if (class_id == kOneByteStringCid) {
+    return &OneByteString::CharAt;
+  }
+  if (class_id == kTwoByteStringCid) {
+    return &TwoByteString::CharAt;
+  }
+  if (class_id == kExternalOneByteStringCid) {
+    return &ExternalOneByteString::CharAt;
+  }
+  ASSERT(class_id == kExternalTwoByteStringCid);
+  return &ExternalTwoByteString::CharAt;
+}
+
+
 intptr_t String::CharSize() const {
   intptr_t class_id = raw()->GetClassId();
   if (class_id == kOneByteStringCid || class_id == kExternalOneByteStringCid) {
     return kOneByteChar;
   }
   ASSERT(class_id == kTwoByteStringCid ||
          class_id == kExternalTwoByteStringCid);
   return kTwoByteChar;
 }
 
@@ skipping 2978 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart