Some string optimizations:

src/objects.cc

 // Copyright 2006-2009 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 4642 matching lines @@
   decoder->Reset(str.start(), str.length());
   int i;
   for (i = 0; i < slen && decoder->has_more(); i++) {
     uc32 r = decoder->GetNext();
     if (Get(i) != r) return false;
   }
   return i == slen && !decoder->has_more();
 }
 
 
+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);
 
   // Check the hash code is there.
   ASSERT(hash_field() & kHashComputedMask);
   uint32_t result = field >> kHashShift;
   ASSERT(result != 0);  // Ensure that the hash value of 0 is never computed.
   return result;
 }
@@ skipping 3833 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