Fix zero hash handling on ARM.

Some cleanup.
Review URL: http://codereview.chromium.org/9169010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10362 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/code-stubs-arm.cc

@@ -5759,13 +5759,12 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
   // hash ^= hash >> 11;
   __ eor(hash, hash, Operand(hash, LSR, 11));
   // hash += hash << 15;
-  __ add(hash, hash, Operand(hash, LSL, 15), SetCC);
+  __ add(hash, hash, Operand(hash, LSL, 15));
 
-  uint32_t kHashShiftCutOffMask = (1 << (32 - String::kHashShift)) - 1;
-  __ and_(hash, hash, Operand(kHashShiftCutOffMask));
+  __ and_(hash, hash, Operand(String::kHashBitMask), SetCC);
 
   // if (hash == 0) hash = 27;
-  __ mov(hash, Operand(27), LeaveCC, eq);
+  __ mov(hash, Operand(StringHasher::kZeroHash), LeaveCC, eq);
 }
 
 

src/ia32/code-stubs-ia32.cc

@@ -6091,14 +6091,12 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
   __ shl(scratch, 15);
   __ add(hash, scratch);
 
-  uint32_t kHashShiftCutOffMask = (1 << (32 - String::kHashShift)) - 1;
-  __ and_(hash, kHashShiftCutOffMask);
+  __ and_(hash, String::kHashBitMask);
 
   // if (hash == 0) hash = 27;
   Label hash_not_zero;
-  __ test(hash, hash);
   __ j(not_zero, &hash_not_zero, Label::kNear);
-  __ mov(hash, Immediate(27));
+  __ mov(hash, Immediate(StringHasher::kZeroHash));
   __ bind(&hash_not_zero);
 }
 

src/mips/code-stubs-mips.cc

@@ -5954,7 +5954,7 @@ void StringHelper::GenerateHashAddCharacter(MacroAssembler* masm,
 
 
 void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
-                                         Register hash) {
+                                       Register hash) {
   // hash += hash << 3;
   __ sll(at, hash, 3);
   __ addu(hash, hash, at);
@@ -5965,12 +5965,11 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
   __ sll(at, hash, 15);
   __ addu(hash, hash, at);
 
-  uint32_t kHashShiftCutOffMask = (1 << (32 - String::kHashShift)) - 1;
-  __ li(at, Operand(kHashShiftCutOffMask));
+  __ li(at, Operand(String::kHashBitMask));
   __ and_(hash, hash, at);
 
   // if (hash == 0) hash = 27;
-  __ ori(at, zero_reg, 27);
+  __ ori(at, zero_reg, StringHasher::kZeroHash);
   __ movz(hash, at, hash);
 }
 

src/objects.cc

@@ -11577,7 +11577,7 @@ class TwoCharHashTableKey : public HashTableKey {
     hash += hash << 3;
     hash ^= hash >> 11;
     hash += hash << 15;
-    if ((hash & String::kHashBitMask) == 0) hash = 27;
+    if ((hash & String::kHashBitMask) == 0) hash = String::kZeroHash;
 #ifdef DEBUG
     StringHasher hasher(2, seed);
     hasher.AddCharacter(c1);

src/objects.h

@@ -6210,6 +6210,11 @@ class StringHasher {
   // value is represented decimal value.
   static uint32_t MakeArrayIndexHash(uint32_t value, int length);
 
+  // No string is allowed to have a hash of zero.  That value is reserved
+  // for internal properties.  If the hash calculation yields zero then we
+  // use 27 instead.
+  static const int kZeroHash = 27;
+
  private:
   uint32_t array_index() {
     ASSERT(is_array_index());

src/x64/code-stubs-x64.cc

@@ -5003,13 +5003,12 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
   __ shll(scratch, Immediate(15));
   __ addl(hash, scratch);
 
-  uint32_t kHashShiftCutOffMask = (1 << (32 - String::kHashShift)) - 1;
-  __ andl(hash, Immediate(kHashShiftCutOffMask));
+  __ andl(hash, Immediate(String::kHashBitMask));
 
   // if (hash == 0) hash = 27;
   Label hash_not_zero;
   __ j(not_zero, &hash_not_zero);
-  __ Set(hash, 27);
+  __ Set(hash, StringHasher::kZeroHash);
   __ bind(&hash_not_zero);
 }