Optimized scanner to avoid virtual calls for every character read.

src/scanner-base.cc

Index: src/scanner-base.cc
diff --git a/src/scanner-base.cc b/src/scanner-base.cc
index 9e58c4e6371d746fe4ef523701c14015390be70f..a01e75efe0eafde283461db7152b2ba2d6225628 100644
--- a/src/scanner-base.cc
+++ b/src/scanner-base.cc
@@ -35,12 +35,6 @@ namespace v8 {
 namespace internal {
 
 // ----------------------------------------------------------------------------
-// UTF16Buffer
-
-UTF16Buffer::UTF16Buffer()
-    : pos_(0), end_(kNoEndPosition) { }
-
-// ----------------------------------------------------------------------------
 // LiteralCollector
 
 LiteralCollector::LiteralCollector()
@@ -92,7 +86,7 @@ bool ScannerConstants::IsIdentifier(unibrow::CharacterStream* buffer) {
 // ----------------------------------------------------------------------------
 // Scanner
 
-Scanner::Scanner() : source_(NULL) {}
+Scanner::Scanner() { }
 
 
 uc32 Scanner::ScanHexEscape(uc32 c, int length) {
@@ -142,8 +136,7 @@ uc32 Scanner::ScanOctalEscape(uc32 c, int length) {
 // ----------------------------------------------------------------------------
 // JavaScriptScanner
 
-JavaScriptScanner::JavaScriptScanner()
-    : has_line_terminator_before_next_(false) {}
+JavaScriptScanner::JavaScriptScanner() : Scanner() {}
 
 
 Token::Value JavaScriptScanner::Next() {
@@ -503,13 +496,23 @@ void JavaScriptScanner::Scan() {
 
 
 void JavaScriptScanner::SeekForward(int pos) {
-  source_->SeekForward(pos - 1);
-  Advance();
-  // This function is only called to seek to the location
-  // of the end of a function (at the "}" token). It doesn't matter
-  // whether there was a line terminator in the part we skip.
-  has_line_terminator_before_next_ = false;
+  // After this call, we will have the token at the given position as
+  // the "next" token. The "current" token will be invalid.
+  if (pos == next_.location.beg_pos) return;
+  int current_pos = source_pos();
+  ASSERT_EQ(next_.location.end_pos, current_pos);
+  // Positions inside the lookahead token aren't supported.
+  ASSERT(pos >= current_pos);
+  if (pos != current_pos) {
+    source_->SeekForward(pos - source_->pos());
+    Advance();
+    // This function is only called to seek to the location
+    // of the end of a function (at the "}" token). It doesn't matter
+    // whether there was a line terminator in the part we skip.
+    has_line_terminator_before_next_ = false;
+  }
   Scan();
+  ASSERT_EQ(Token::RBRACE, next_.token);
 }