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

src/objects.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5491 matching lines @@
     uc32 r = decoder->GetNext();
     if (Get(i) != r) return false;
   }
   return i == slen && !decoder->has_more();
 }
 
 
 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;
   }
   return true;
 }
 
 
 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;
   }
   return true;
 }
 
 
 uint32_t String::ComputeAndSetHash() {
   // Should only be called if hash code has not yet been computed.
   ASSERT(!HasHashCode());
@@ skipping 4962 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 
 } }  // namespace v8::internal