Some string optimizations:

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index a1fbc9927701388f1f2300847c3b33fc7d52e1b5..02ea5b0455deee01a3c2fe33d7f476fd3bb562ec 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -4660,13 +4660,38 @@ bool String::IsEqualTo(Vector<const char> str) {
 }
 
 
+template <typename schar>
+static inline uint32_t HashSequentialString(const schar* chars, int length) {
+  StringHasher hasher(length);
+  if (!hasher.has_trivial_hash()) {
+    int i;
+    for (i = 0; hasher.is_array_index() && (i < length); i++) {
+      hasher.AddCharacter(chars[i]);
+    }
+    for (; i < length; i++) {
+      hasher.AddCharacterNoIndex(chars[i]);
+    }
+  }
+  return hasher.GetHashField();
+}
+
+
 uint32_t String::ComputeAndSetHash() {
   // Should only be called if hash code has not yet been computed.
   ASSERT(!(hash_field() & kHashComputedMask));
 
+  const int len = length();
+
   // Compute the hash code.
-  StringInputBuffer buffer(this);
-  uint32_t field = ComputeHashField(&buffer, length());
+  uint32_t field = 0;
+  if (StringShape(this).IsSequentialAscii()) {
+    field = HashSequentialString(SeqAsciiString::cast(this)->GetChars(), len);
+  } else if (StringShape(this).IsSequentialTwoByte()) {
+    field = HashSequentialString(SeqTwoByteString::cast(this)->GetChars(), len);
+  } else {
+    StringInputBuffer buffer(this);
+    field = ComputeHashField(&buffer, len);
+  }
 
   // Store the hash code in the object.
   set_hash_field(field);