add fast path for hashing small cons strings

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 6810 matching lines @@
   if (!hasher.has_trivial_hash()) hasher.AddCharacters(chars, length);
   return hasher.GetHashField();
 }
 
 
 uint32_t IteratingStringHasher::Hash(String* string, uint32_t seed) {
   IteratingStringHasher hasher(string->length(), seed);
   // Nothing to do.
   if (hasher.has_trivial_hash()) return hasher.GetHashField();
   ConsString* cons_string = String::VisitFlat(&hasher, string);
-  if (cons_string != nullptr) {
-    hasher.VisitConsString(cons_string);
-  }
+  if (cons_string == nullptr) return hasher.GetHashField();
+  hasher.VisitConsString(cons_string);
   return hasher.GetHashField();
 }
 
 
 void IteratingStringHasher::VisitOneByteString(const uint8_t* chars,
                                                int length) {
   AddCharacters(chars, length);
 }
 
 
@@ skipping 671 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_