Use a random seed for the string hash algorithm.

src/x64/code-stubs-x64.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 4940 matching lines @@
   if (!result.is(rax)) {
     __ movq(rax, result);
   }
 }
 
 
 void StringHelper::GenerateHashInit(MacroAssembler* masm,
                                     Register hash,
                                     Register character,
                                     Register scratch) {
-  // hash = character + (character << 10);
-  __ movl(hash, character);
-  __ shll(hash, Immediate(10));
-  __ addl(hash, character);
+  int32_t seed = masm->isolate()->HasherSeed();
+  if (seed != 0) {
+    ASSERT(FLAG_randomize_string_hashes);
+    // hash = (seed + character) + ((seed + character) << 10);
+    __ leal(scratch, Operand(character, seed));
+    __ shll(scratch, Immediate(10));
+    __ leal(hash, Operand(scratch, character, times_1, seed));
+  } else {
+    ASSERT(!FLAG_randomize_string_hashes);
+    // hash = character + (character << 10);
+    __ movl(hash, character);
+    __ shll(hash, Immediate(10));
+    __ addl(hash, character);
+  }
   // hash ^= hash >> 6;
   __ movl(scratch, hash);
   __ shrl(scratch, Immediate(6));
   __ xorl(hash, scratch);
 }
 
 
 void StringHelper::GenerateHashAddCharacter(MacroAssembler* masm,
                                             Register hash,
                                             Register character,
@@ skipping 1256 matching lines @@
                                  xmm0,
                                  &slow_elements);
   __ ret(0);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64