[parser] Use Back2() where appropriate.

src/parsing/scanner.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Features shared by parsing and pre-parsing scanners.
 
 #include "src/parsing/scanner.h"
 
 #include <stdint.h>
 
@@ skipping 322 matching lines @@
   // The Unicode value U+FFFE is guaranteed never to be assigned as a
   // Unicode character; this implies that in a Unicode context the
   // 0xFF, 0xFE byte pattern can only be interpreted as the U+FEFF
   // character expressed in little-endian byte order (since it could
   // not be a U+FFFE character expressed in big-endian byte
   // order). Nevertheless, we check for it to be compatible with
   // Spidermonkey.
   return c == 0xFFFE;
 }
 
-
 bool Scanner::SkipWhiteSpace() {
   int start_position = source_pos();
 
   while (true) {
     while (true) {
-      // The unicode cache accepts unsigned inputs.
+      // Don't skip behind the end of input.
       if (c0_ == kEndOfInput) break;
+
       // Advance as long as character is a WhiteSpace or LineTerminator.
       // Remember if the latter is the case.
       if (unicode_cache_->IsLineTerminator(c0_)) {
         has_line_terminator_before_next_ = true;
       } else if (!unicode_cache_->IsWhiteSpace(c0_) &&
                  !IsLittleEndianByteOrderMark(c0_)) {
         break;
       }
       Advance();
     }
 
     // If there is an HTML comment end '-->' at the beginning of a
     // line (with only whitespace in front of it), we treat the rest
     // of the line as a comment. This is in line with the way
     // SpiderMonkey handles it.
-    if (c0_ == '-' && has_line_terminator_before_next_) {
-      Advance();
-      if (c0_ == '-') {
-        Advance();
-        if (c0_ == '>') {
-          // Treat the rest of the line as a comment.
-          SkipSingleLineComment();
-          // Continue skipping white space after the comment.
-          continue;
-        }
-        PushBack('-');  // undo Advance()
-      }
+    if (c0_ != '-' || !has_line_terminator_before_next_) break;
+
+    Advance();
+    if (c0_ != '-') {
       PushBack('-');  // undo Advance()
+      break;
     }
-    // Return whether or not we skipped any characters.
-    return source_pos() != start_position;
+
+    Advance();
+    if (c0_ != '>') {
+      PushBack2('-', '-');  // undo 2x Advance();
+      break;
+    }
+
+    // Treat the rest of the line as a comment.
+    SkipSingleLineComment();
   }
+
+  // Return whether or not we skipped any characters.
+  return source_pos() != start_position;
 }
 
-
 Token::Value Scanner::SkipSingleLineComment() {
   Advance();
 
   // The line terminator at the end of the line is not considered
   // to be part of the single-line comment; it is recognized
   // separately by the lexical grammar and becomes part of the
   // stream of input elements for the syntactic grammar (see
   // ECMA-262, section 7.4).
   while (c0_ != kEndOfInput && !unicode_cache_->IsLineTerminator(c0_)) {
     Advance();
@@ skipping 82 matching lines @@
     if (ch == '*' && c0_ == '/') {
       c0_ = ' ';
       return Token::WHITESPACE;
     }
   }
 
   // Unterminated multi-line comment.
   return Token::ILLEGAL;
 }
 
-
 Token::Value Scanner::ScanHtmlComment() {
   // Check for <!-- comments.
   DCHECK(c0_ == '!');
   Advance();
-  if (c0_ == '-') {
-    Advance();
-    if (c0_ == '-') {
-      found_html_comment_ = true;
-      return SkipSingleLineComment();
-    }
-    PushBack('-');  // undo Advance()
+  if (c0_ != '-') {
+    PushBack('!');  // undo Advance()
+    return Token::LT;
   }
-  PushBack('!');  // undo Advance()
-  DCHECK(c0_ == '!');
-  return Token::LT;
+
+  Advance();
+  if (c0_ != '-') {
+    PushBack2('-', '!');  // undo 2x Advance()
+    return Token::LT;
+  }
+
+  found_html_comment_ = true;
+  return SkipSingleLineComment();
 }
 
-
 void Scanner::Scan() {
   next_.literal_chars = NULL;
   next_.raw_literal_chars = NULL;
   Token::Value token;
   do {
     // Remember the position of the next token
     next_.location.beg_pos = source_pos();
 
     switch (c0_) {
       case ' ':
@@ skipping 1117 matching lines @@
   // 2, reset the source to the desired position,
   source_->Seek(position);
   // 3, re-scan, by scanning the look-ahead char + 1 token (next_).
   c0_ = source_->Advance();
   Next();
   DCHECK_EQ(next_.location.beg_pos, position);
 }
 
 }  // namespace internal
 }  // namespace v8