Add fast cases for flat comparison to String::Is{Ascii,TwoByte}EqualTo.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 52b7add58f4f75409c947070bfb2a8e74add2fef..bd544963a590c9a5eff1ed4e869b57b02a2262df 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5509,6 +5509,9 @@ bool String::IsEqualTo(Vector<const char> str) {
 bool String::IsAsciiEqualTo(Vector<const char> str) {
   int slen = length();
   if (str.length() != slen) return false;
+  if (IsFlat() && IsAsciiRepresentation()) {

[Erik Corry, 2011/05/24 07:14:07]

CompareChars doesn't require that the two strings have the same width, so you
can speed up the operation for ASCII-UC16 and UC16-ASCII comparisons too.

+    return CompareChars(ToAsciiVector().start(), str.start(), slen) == 0;
+  }
   for (int i = 0; i < slen; i++) {
     if (Get(i) != static_cast<uint16_t>(str[i])) return false;
   }
@@ -5519,6 +5522,9 @@ bool String::IsAsciiEqualTo(Vector<const char> str) {
 bool String::IsTwoByteEqualTo(Vector<const uc16> str) {
   int slen = length();
   if (str.length() != slen) return false;
+  if (IsFlat() && IsTwoByteRepresentation()) {
+    return CompareChars(ToUC16Vector().start(), str.start(), slen) == 0;
+  }
   for (int i = 0; i < slen; i++) {
     if (Get(i) != str[i]) return false;
   }