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 519909c914185aa899860cb77ee185304db815d9..177febb00a0d8ebef88eb199f0b7f39bbb1a01e1 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5181,7 +5181,7 @@ 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);
@@ -5197,7 +5197,7 @@ uint16_t ConsString::ConsStringGet(int index) {
         string = cons_string->second();
       }
     } else {
-      return string->Get(index);
+      return FlatString::cast(string)->FlatStringGet(index);
     }
   }
 
@@ -5206,6 +5206,20 @@ 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()) {

[Vitaly Repeshko, 2011/05/10 13:07:02]

Here "this" can already be a flat cons (i.e. with empty second). We shouldn't
update the isolate counter in this case. Maybe ShouldFlattenString() should take
a string argument.

[Lasse Reichstein, 2011/05/10 16:27:46]

Good point. We should probably not get here for a flat string.

+    MaybeObject* flatten_result = this->TryFlatten();
+    if (flatten_result->IsFailure()) return flatten_result;
+    string = String::cast(flatten_result->ToObjectUnchecked());
+  }
+  return Smi::FromInt(string->Get(index));
+}
+
+
 template <typename sinkchar>
 void String::WriteToFlat(String* src,
                          sinkchar* sink,