Don't flatten every time we call CharCodeAt

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 724a734a2145d6b682725a6b9b7e9d5b7c2f26af..00b391edcb7963a3e78202c9d569b4b45e0e5fc5 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5182,7 +5182,7 @@ uint16_t ConsString::ConsStringGet(int index) {
   // Check for a flattened cons string
   if (second()->length() == 0) {
     String* left = first();
-    return left->Get(index);
+    return FlatString::cast(left)->FlatStringGet(index);
   }
 
   String* string = String::cast(this);
@@ -5198,7 +5198,7 @@ uint16_t ConsString::ConsStringGet(int index) {
         string = cons_string->second();
       }
     } else {
-      return string->Get(index);
+      return FlatString::cast(string)->FlatStringGet(index);
     }
   }
 
@@ -5207,6 +5207,44 @@ uint16_t ConsString::ConsStringGet(int index) {
 }
 
 
+MaybeObject* ConsString::ConsStringGetMayFlatten(int index) {
+  ASSERT(index >= 0);
+  ASSERT(index < this->length());
+
+  String* string = this;
+  if (this->GetIsolate()->ShouldFlattenString()) {
+    MaybeObject* flatten_result = this->TryFlatten();
+    if (flatten_result->IsFailure()) return flatten_result;
+    string = String::cast(flatten_result->ToObjectUnchecked());
+  } else {
+    int recurse_limit = 7;

[Vitaly Repeshko, 2011/05/12 15:54:53]

Make this a (documented) constant in ConsString.

+    String* cursor = string;
+    int index_in_cursor = index;
+    while (cursor->IsConsString()) {
+      ConsString* cons = ConsString::cast(cursor);
+      String* first = cons->first();
+      int first_length = first->length();
+      if (index_in_cursor < first_length) {
+        cursor = first;
+      } else {
+        cursor = cons->second();
+        index_in_cursor -= first_length;
+      }
+      if (--recurse_limit <= 0) {
+        MaybeObject* flatten_result = this->TryFlatten();
+        if (flatten_result->IsFailure()) return flatten_result;
+        cursor = String::cast(flatten_result->ToObjectUnchecked());

[Vitaly Repeshko, 2011/05/12 15:54:53]

It's more straightforward to simply return 
Smi::FromInt(String::cast(flatten_result->ToObjectUnchecked())->Get(index))
here.

+        index_in_cursor = index;
+        break;
+      }
+    }
+    string = cursor;
+    index = index_in_cursor;
+  }
+  return Smi::FromInt(string->Get(index));
+}
+
+
 template <typename sinkchar>
 void String::WriteToFlat(String* src,
                          sinkchar* sink,