[scanner] Faster SkipMultiLineComment by avoiding a copy.

Avoid copying the last character to a local variable, by checking the parsing
state in a different order.

BUG=v8:7926

Change-Id: Ifb722dd3864737dc66d8e0885adbeba1376a059e
Reviewed-on: https://chromium-review.googlesource.com/1148569Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#54680}

src/parsing/scanner.cc

@@ -181,6 +181,9 @@ Scanner::Scanner(UnicodeCache* unicode_cache)
     : unicode_cache_(unicode_cache),
       octal_pos_(Location::invalid()),
       octal_message_(MessageTemplate::kNone),
+      has_line_terminator_before_next_(false),
+      has_multiline_comment_before_next_(false),
+      has_line_terminator_after_next_(false),
       found_html_comment_(false),
       allow_harmony_bigint_(false),
       allow_harmony_numeric_separator_(false) {}
@@ -555,27 +558,29 @@ void Scanner::TryToParseSourceURLComment() {
   }
 }
 
-
 Token::Value Scanner::SkipMultiLineComment() {
   DCHECK_EQ(c0_, '*');
   Advance();
 
   while (c0_ != kEndOfInput) {
-    uc32 ch = c0_;
-    Advance();
     DCHECK(!unibrow::IsLineTerminator(kEndOfInput));
-    if (unibrow::IsLineTerminator(ch)) {
+    if (!has_multiline_comment_before_next_ && unibrow::IsLineTerminator(c0_)) {
       // Following ECMA-262, section 7.4, a comment containing
       // a newline will make the comment count as a line-terminator.
       has_multiline_comment_before_next_ = true;
     }
-    // If we have reached the end of the multi-line comment, we
-    // consume the '/' and insert a whitespace. This way all
-    // multi-line comments are treated as whitespace.
-    if (ch == '*' && c0_ == '/') {
-      c0_ = ' ';
-      return Token::WHITESPACE;
+
+    while (V8_UNLIKELY(c0_ == '*')) {
+      Advance();
+      // If we have reached the end of the multi-line comment, we
+      // consume the '/' and insert a whitespace. This way all
+      // multi-line comments are treated as whitespace.
+      if (c0_ == '/') {
+        c0_ = ' ';
+        return Token::WHITESPACE;
+      }
     }
+    Advance();
   }
 
   // Unterminated multi-line comment.