Don't flatten every time we call CharCodeAt

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index e3d21cc658ea6d2445c22ebab33fedc3033bb969..2e3aaf4968c436b1f898c1c88ec44c7eaadf34a3 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -178,6 +178,13 @@ bool Object::IsConsString() {
 }
 
 
+bool Object::IsFlatString() {
+  if (!this->IsHeapObject()) return false;
+  uint32_t type = HeapObject::cast(this)->map()->instance_type();
+  return (type & (kIsNotStringMask | kStringRepresentationMask)) == kStringTag;
+}
+
+
 bool Object::IsSeqString() {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsSequential();
@@ -1875,6 +1882,7 @@ CAST_ACCESSOR(CompilationCacheTable)
 CAST_ACCESSOR(CodeCacheHashTable)
 CAST_ACCESSOR(MapCache)
 CAST_ACCESSOR(String)
+CAST_ACCESSOR(FlatString)
 CAST_ACCESSOR(SeqString)
 CAST_ACCESSOR(SeqAsciiString)
 CAST_ACCESSOR(SeqTwoByteString)
@@ -1974,6 +1982,26 @@ String* String::TryFlattenGetString(PretenureFlag pretenure) {
 }
 
 
+uint16_t FlatString::FlatStringGet(int index) {
+  ASSERT(index >= 0 && index < length());
+  switch (StringShape(this).full_representation_tag()) {
+    case kSeqStringTag | kAsciiStringTag:
+      return SeqAsciiString::cast(this)->SeqAsciiStringGet(index);
+    case kSeqStringTag | kTwoByteStringTag:
+      return SeqTwoByteString::cast(this)->SeqTwoByteStringGet(index);
+    case kExternalStringTag | kAsciiStringTag:
+      return ExternalAsciiString::cast(this)->ExternalAsciiStringGet(index);
+    case kExternalStringTag | kTwoByteStringTag:
+      return ExternalTwoByteString::cast(this)->ExternalTwoByteStringGet(index);
+    default:
+      break;
+  }
+
+  UNREACHABLE();
+  return 0;
+}
+
+
 uint16_t String::Get(int index) {
   ASSERT(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {
@@ -1991,12 +2019,19 @@ uint16_t String::Get(int index) {
     default:
       break;
   }
-
   UNREACHABLE();
   return 0;
 }
 
 
+MaybeObject* String::GetMayFlatten(int index) {
+  if (this->IsConsString()) {
+    return ConsString::cast(this)->ConsStringGetMayFlatten(index);
+  }
+  return Smi::FromInt(FlatString::cast(this)->FlatStringGet(index));
+}
+
+
 void String::Set(int index, uint16_t value) {
   ASSERT(index >= 0 && index < length());
   ASSERT(StringShape(this).IsSequential());