Scanner: remove PushBack calls when we're going to return ILLEGAL.

src/scanner.cc

Index: src/scanner.cc
diff --git a/src/scanner.cc b/src/scanner.cc
index 0709939dbac8b142a3ad81a2ea948fa681179b34..dc15e37e9a7c1087e56b7e3a57ca26a2703911d4 100644
--- a/src/scanner.cc
+++ b/src/scanner.cc
@@ -57,20 +57,10 @@ void Scanner::Initialize(Utf16CharacterStream* source) {
 uc32 Scanner::ScanHexNumber(int expected_length) {
   DCHECK(expected_length <= 4);  // prevent overflow
 
-  uc32 digits[4] = { 0, 0, 0, 0 };
   uc32 x = 0;
   for (int i = 0; i < expected_length; i++) {
-    digits[i] = c0_;
     int d = HexValue(c0_);
     if (d < 0) {
-      // According to ECMA-262, 3rd, 7.8.4, page 18, these hex escapes
-      // should be illegal, but other JS VMs just return the
-      // non-escaped version of the original character.
-
-      // Push back digits that we have advanced past.
-      for (int j = i-1; j >= 0; j--) {
-        PushBack(digits[j]);
-      }
       return -1;
     }
     x = x * 16 + d;
@@ -894,9 +884,7 @@ uc32 Scanner::ScanIdentifierUnicodeEscape() {
   Advance();
   if (c0_ != 'u') return -1;
   Advance();
-  uc32 result = ScanHexNumber(4);
-  if (result < 0) PushBack('u');
-  return result;
+  return ScanHexNumber(4);
 }
 
 
@@ -1145,31 +1133,19 @@ bool Scanner::ScanRegExpPattern(bool seen_equal) {
 
 bool Scanner::ScanLiteralUnicodeEscape() {
   DCHECK(c0_ == '\\');
-  uc32 chars_read[6] = {'\\', 'u', 0, 0, 0, 0};
+  AddLiteralChar(c0_);
   Advance();
-  int i = 1;
+  int hex_digits_read = 0;
   if (c0_ == 'u') {
-    i++;
-    while (i < 6) {
+    AddLiteralChar(c0_);
+    while (hex_digits_read < 4) {
       Advance();
       if (!IsHexDigit(c0_)) break;
-      chars_read[i] = c0_;
-      i++;
-    }
-  }
-  if (i < 6) {
-    // Incomplete escape. Undo all advances and return false.
-    while (i > 0) {
-      i--;
-      PushBack(chars_read[i]);
+      AddLiteralChar(c0_);
+      ++hex_digits_read;
     }
-    return false;
-  }
-  // Complete escape. Add all chars to current literal buffer.
-  for (int i = 0; i < 6; i++) {
-    AddLiteralChar(chars_read[i]);
   }
-  return true;
+  return hex_digits_read == 4;
 }
 
 
@@ -1181,7 +1157,7 @@ bool Scanner::ScanRegExpFlags() {
       AddLiteralCharAdvance();
     } else {
       if (!ScanLiteralUnicodeEscape()) {
-        break;
+        return false;
       }
       Advance();
     }