Backport hash collision workaround to 3.6.

src/mips/code-stubs-mips.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 5559 matching lines @@
   __ jmp(not_found);
 
   // Scratch register contains result when we fall through to here.
   Register result = candidate;
   __ bind(&found_in_symbol_table);
   __ mov(v0, result);
 }
 
 
 void StringHelper::GenerateHashInit(MacroAssembler* masm,
-                                      Register hash,
-                                      Register character) {
-  // hash = character + (character << 10);
-  __ sll(hash, character, 10);
+                                    Register hash,
+                                    Register character) {
+  // hash = seed + character + ((seed + character) << 10);
+  __ LoadRoot(hash, Heap::kStringHashSeedRootIndex);
+  // Untag smi seed and add the character.
+  __ SmiUntag(hash);
   __ addu(hash, hash, character);
+  __ sll(at, hash, 10);
+  __ addu(hash, hash, at);
   // hash ^= hash >> 6;
   __ sra(at, hash, 6);
   __ xor_(hash, hash, at);
 }
 
 
 void StringHelper::GenerateHashAddCharacter(MacroAssembler* masm,
-                                              Register hash,
-                                              Register character) {
+                                            Register hash,
+                                            Register character) {
   // hash += character;
   __ addu(hash, hash, character);
   // hash += hash << 10;
   __ sll(at, hash, 10);
   __ addu(hash, hash, at);
   // hash ^= hash >> 6;
   __ sra(at, hash, 6);
   __ xor_(hash, hash, at);
 }
 
 
 void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
                                          Register hash) {
   // hash += hash << 3;
   __ sll(at, hash, 3);
   __ addu(hash, hash, at);
   // hash ^= hash >> 11;
   __ sra(at, hash, 11);
   __ xor_(hash, hash, at);
   // hash += hash << 15;
   __ sll(at, hash, 15);
   __ addu(hash, hash, at);
 
   // if (hash == 0) hash = 27;

[Vyacheslav Egorov (Chromium), 2012/01/09 19:09:33]

should not there be some special masking here?

[Erik Corry, 2012/01/10 00:18:44]

As noted in the description I wasn't able to get MIPS working correctly, so
there may be a followup patch for MIPS (it was already broken in this branch if
I understand correctly, the external MIPS git repo is apparently the place to go
for 3.6).

   __ ori(at, zero_reg, 27);
   __ movz(hash, at, hash);
 }
 
 
 void SubStringStub::Generate(MacroAssembler* masm) {
   Label sub_string_runtime;
   // Stack frame on entry.
   //  ra: return address
   //  sp[0]: to
@@ skipping 1330 matching lines @@
   __ mov(result, zero_reg);
   __ Ret();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS