Remove unnecessary buffer doubling and content copying.

src/scanner.cc

Index: src/scanner.cc
diff --git a/src/scanner.cc b/src/scanner.cc
index 23b8aff9c41488001bf12fb475aaf6ff46a91963..a834150c04788878f71f9b3bf1ee4679112e265c 100644
--- a/src/scanner.cc
+++ b/src/scanner.cc
@@ -49,13 +49,7 @@ StaticResource<Scanner::Utf8Decoder> Scanner::utf8_decoder_;
 // ----------------------------------------------------------------------------
 // UTF8Buffer
 
-UTF8Buffer::UTF8Buffer() {
-  static const int kInitialCapacity = 1 * KB;
-  data_ = NewArray<char>(kInitialCapacity);
-  limit_ = ComputeLimit(data_, kInitialCapacity);
-  Reset();
-  ASSERT(Capacity() == kInitialCapacity && pos() == 0);
-}
+UTF8Buffer::UTF8Buffer() : data_(NULL), limit_(NULL) { }
 
 
 UTF8Buffer::~UTF8Buffer() {
@@ -69,7 +63,7 @@ void UTF8Buffer::AddCharSlow(uc32 c) {
     int old_capacity = Capacity();
     int old_position = pos();
     int new_capacity =
-        Min(old_capacity * 2, old_capacity + kCapacityGrowthLimit);
+        Min(old_capacity * 3, old_capacity + kCapacityGrowthLimit);
     char* new_data = NewArray<char>(new_capacity);
     memcpy(new_data, data_, old_position);
     DeleteArray(data_);
@@ -346,9 +340,6 @@ void Scanner::Init(Handle<String> source, unibrow::CharacterStream* stream,
 
   position_ = position;
 
-  // Reset literals buffer
-  literals_.Reset();
-
   // Set c0_ (one character ahead)
   ASSERT(kCharacterLookaheadBufferSize == 1);
   Advance();
@@ -376,6 +367,7 @@ Token::Value Scanner::Next() {
   if (check.HasOverflowed()) {
     stack_overflow_ = true;
     next_.token = Token::ILLEGAL;
+    next_.literal_buffer = NULL;
   } else {
     Scan();
   }
@@ -384,17 +376,23 @@ Token::Value Scanner::Next() {
 
 
 void Scanner::StartLiteral() {
-  next_.literal_pos = literals_.pos();
+  // Use the first buffer, unless it's currently in use by the current_ token.
+  // In most cases, we won't have two literals/identifiers in a row, so
+  // the second buffer won't be used very often and is unlikely to grow much.
+  UTF8Buffer* free_buffer =
+      (current_.literal_buffer != &literal_buffer_1_) ? &literal_buffer_1_
+                                                      : &literal_buffer_2_;
+  next_.literal_buffer = free_buffer;
+  free_buffer->Reset();
 }
 
 
 void Scanner::AddChar(uc32 c) {
-  literals_.AddChar(c);
+  next_.literal_buffer->AddChar(c);
 }
 
 
 void Scanner::TerminateLiteral() {
-  next_.literal_end = literals_.pos();
   AddChar(0);
 }