Changed hash table to use more of the hash value when probing.

Review URL: http://codereview.chromium.org/155350

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2486 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/ic-arm.cc

@@ -103,16 +103,20 @@ static void GenerateDictionaryLoad(MacroAssembler* masm,
   // Generate an unrolled loop that performs a few probes before
   // giving up. Measurements done on Gmail indicate that 2 probes
   // cover ~93% of loads from dictionaries.
-  static const int kProbes = 4;
-  for (int i = 0; i < kProbes; i++) {
-    // Compute the masked index: (hash + i + i * i) & mask.
+  static const uint32_t kProbes =
+      HashTable<StringDictionaryShape, String*>::kNofFastProbes;
+  static const uint32_t kShift =
+      HashTable<StringDictionaryShape, String*>::kHashRotateShift;
+
+  for (uint32_t i = 0; i < kProbes; i++) {
+    // Compute the masked index.
     __ ldr(t1, FieldMemOperand(r2, String::kLengthOffset));
     __ mov(t1, Operand(t1, LSR, String::kHashShift));
     if (i > 0) {
-      __ add(t1, t1, Operand(StringDictionary::GetProbeOffset(i)));
+      __ and_(t1, r3, Operand(t1, ROR, (kShift * i) % kBitsPerInt));
+    } else {
+      __ and_(t1, t1, Operand(r3));
     }
-    __ and_(t1, t1, Operand(r3));
-
     // Scale the index by multiplying by the element size.
     ASSERT(StringDictionary::kEntrySize == 3);
     __ add(t1, t1, Operand(t1, LSL, 1));  // t1 = t1 * 3

src/arm/simulator-arm.cc

@@ -45,6 +45,7 @@ using ::v8::internal::PrintF;
 using ::v8::internal::OS;
 using ::v8::internal::ReadLine;
 using ::v8::internal::DeleteArray;
+using ::v8::internal::RotateRight;
 
 // This macro provides a platform independent use of sscanf. The reason for
 // SScanF not being implemented in a platform independent was through
@@ -817,7 +818,12 @@ int32_t Simulator::GetShiftRm(Instr* instr, bool* carry_out) {
       }
 
       case ROR: {
-        UNIMPLEMENTED();
+        ASSERT(shift_amount > 0);
+        uint32_t uresult = static_cast<uint32_t>(result);
+        uresult = RotateRight(uresult, shift_amount - 1);
+        *carry_out = (uresult & 1) == 1;
+        uresult = RotateRight(uresult, 1);
+        result = static_cast<int32_t>(uresult);
         break;
       }
 

src/ia32/assembler-ia32.cc

@@ -1240,6 +1240,16 @@ void Assembler::xor_(const Operand& dst, const Immediate& x) {
 }
 
 
+void Assembler::ror(Register dst, uint32_t count) {
+  EnsureSpace ensure_space(this);
+  last_pc_ = pc_;
+  EMIT(0xC1);
+  emit_operand(ecx, Operand(dst));
+  ASSERT(count < 32);
+  EMIT(count);
+}
+
+
 void Assembler::bt(const Operand& dst, Register src) {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;

src/ia32/assembler-ia32.h

@@ -597,6 +597,9 @@ class Assembler : public Malloced {
   void xor_(const Operand& src, Register dst);
   void xor_(const Operand& dst, const Immediate& x);
 
+  // Rotate dist right count times, asserts count < 32.
+  void ror(Register dst, uint32_t count);
+
   // Bit operations.
   void bt(const Operand& dst, Register src);
   void bts(const Operand& dst, Register src);

src/ia32/ic-ia32.cc

@@ -97,15 +97,20 @@ static void GenerateDictionaryLoad(MacroAssembler* masm, Label* miss_label,
   // Generate an unrolled loop that performs a few probes before
   // giving up. Measurements done on Gmail indicate that 2 probes
   // cover ~93% of loads from dictionaries.
-  static const int kProbes = 4;
   const int kElementsStartOffset =
       Array::kHeaderSize + StringDictionary::kElementsStartIndex * kPointerSize;
-  for (int i = 0; i < kProbes; i++) {
-    // Compute the masked index: (hash + i + i * i) & mask.
+
+  static const uint32_t kProbes =
+      HashTable<StringDictionaryShape, String*>::kNofFastProbes;
+  static const uint32_t kShift =
+      HashTable<StringDictionaryShape, String*>::kHashRotateShift;
+
+  for (uint32_t i = 0; i < kProbes; i++) {
+    // Compute the masked index.
     __ mov(r1, FieldOperand(name, String::kLengthOffset));
     __ shr(r1, String::kHashShift);
     if (i > 0) {
-      __ add(Operand(r1), Immediate(StringDictionary::GetProbeOffset(i)));
+      __ ror(r1, (kShift * i) % kBitsPerInt);
     }
     __ and_(r1, Operand(r2));
 

src/objects.cc

@@ -6502,7 +6502,8 @@ template<typename Shape, typename Key>
 Object* HashTable<Shape, Key>::Allocate(
     int at_least_space_for) {
   int capacity = RoundUpToPowerOf2(at_least_space_for);
-  if (capacity < 4) capacity = 4;  // Guarantee min capacity.
+  static const int kMinCapacity = 16;
+  if (capacity < kMinCapacity) capacity = kMinCapacity;
   Object* obj = Heap::AllocateHashTable(EntryToIndex(capacity));
   if (!obj->IsFailure()) {
     HashTable::cast(obj)->SetNumberOfElements(0);
@@ -6516,26 +6517,25 @@ Object* HashTable<Shape, Key>::Allocate(
 // Find entry for key otherwise return -1.
 template<typename Shape, typename Key>
 int HashTable<Shape, Key>::FindEntry(Key key) {
-  uint32_t nof = NumberOfElements();
-  if (nof == 0) return kNotFound;  // Bail out if empty.
-
-  uint32_t capacity = Capacity();
+  uint32_t mask = Capacity() - 1;
   uint32_t hash = Shape::Hash(key);
-  uint32_t entry = GetProbe(hash, 0, capacity);
 
-  Object* element = KeyAt(entry);
-  uint32_t passed_elements = 0;
-  if (!element->IsNull()) {
-    if (!element->IsUndefined() && Shape::IsMatch(key, element)) return entry;
-    if (++passed_elements == nof) return kNotFound;
+  // For the first probes rotate the hash to ensure a proper spread.
+  for (uint32_t i = 0; i < kNofFastProbes; i++) {
+    int entry = hash & mask;
+    Object* element = KeyAt(entry);
+    if (element->IsUndefined()) return kNotFound;
+    if (!element->IsNull() && Shape::IsMatch(key, element)) return entry;
+    hash = RotateRight(hash, kHashRotateShift);
   }
-  for (uint32_t i = 1; !element->IsUndefined(); i++) {
-    entry = GetProbe(hash, i, capacity);
-    element = KeyAt(entry);
-    if (!element->IsNull()) {
-      if (!element->IsUndefined() && Shape::IsMatch(key, element)) return entry;
-      if (++passed_elements == nof) return kNotFound;
-    }
+
+
+  // In this unlikely event, do a linear scan.
+  for (uint32_t i = 1; i <= mask; i++) {
+    int entry = ++hash & mask;
+    Object* element = KeyAt(entry);
+    if (element->IsUndefined()) return kNotFound;
+    if (!element->IsNull() && Shape::IsMatch(key, element)) return entry;
   }
   return kNotFound;
 }
@@ -6579,15 +6579,23 @@ Object* HashTable<Shape, Key>::EnsureCapacity(int n, Key key) {
 
 template<typename Shape, typename Key>
 uint32_t HashTable<Shape, Key>::FindInsertionEntry(uint32_t hash) {
-  uint32_t capacity = Capacity();
-  uint32_t entry = GetProbe(hash, 0, capacity);
-  Object* element = KeyAt(entry);
+  uint32_t mask = Capacity() - 1;
+  int entry;
+  Object* element;
 
-  for (uint32_t i = 1; !(element->IsUndefined() || element->IsNull()); i++) {
-    entry = GetProbe(hash, i, capacity);
+  // For the first probes rotate the hash to ensure a proper spread.
+  for (uint32_t i = 0; i < kNofFastProbes; i++) {
+    entry = hash & mask;
     element = KeyAt(entry);
+    if (element->IsUndefined() || element->IsNull()) return entry;
+    hash = RotateRight(hash, kHashRotateShift);
   }
 
+  do {
+    entry = ++hash & mask;
+    element = KeyAt(entry);
+  } while(!(element->IsUndefined() || element->IsNull()));
+
   return entry;
 }
 
@@ -6666,6 +6674,10 @@ int Dictionary<NumberDictionaryShape, uint32_t>::NumberOfEnumElements();
 template
 int Dictionary<StringDictionaryShape, String*>::NumberOfEnumElements();
 
+template
+int HashTable<NumberDictionaryShape, uint32_t>::FindEntry(uint32_t key);
+
+
 // Collates undefined and unexisting elements below limit from position
 // zero of the elements. The object stays in Dictionary mode.
 Object* JSObject::PrepareSlowElementsForSort(uint32_t limit) {
@@ -7021,7 +7033,7 @@ class SymbolsKey : public HashTableKey {
   uint32_t HashForObject(Object* obj) {
     FixedArray* symbols = FixedArray::cast(obj);
     int len = symbols->length();
-    uint32_t hash = 0;
+    uint32_t hash = 40617523; // In case the array is empty.
     for (int i = 0; i < len; i++) {
       hash ^= String::cast(symbols->get(i))->Hash();
     }

src/objects.h

@@ -2051,11 +2051,6 @@ class HashTable: public FixedArray {
   // Casting.
   static inline HashTable* cast(Object* obj);
 
-  // Compute the probe offset (quadratic probing).
-  INLINE(static uint32_t GetProbeOffset(uint32_t n)) {
-    return (n + n * n) >> 1;
-  }
-
   static const int kNumberOfElementsIndex = 0;
   static const int kCapacityIndex         = 1;
   static const int kPrefixStartIndex      = 2;
@@ -2071,6 +2066,9 @@ class HashTable: public FixedArray {
   // Find entry for key otherwise return -1.
   int FindEntry(Key key);
 
+  static const uint32_t kNofFastProbes = 4;
+  static const uint32_t kHashRotateShift = 3;
+
  protected:
 
   // Find the entry at which to insert element with the given key that
@@ -2096,13 +2094,6 @@ class HashTable: public FixedArray {
     fast_set(this, kCapacityIndex, Smi::FromInt(capacity));
   }
 
-
-  // Returns probe entry.
-  static uint32_t GetProbe(uint32_t hash, uint32_t number, uint32_t size) {
-    ASSERT(IsPowerOf2(size));
-    return (hash + GetProbeOffset(number)) & (size - 1);
-  }
-
   // Ensure enough space for n additional elements.
   Object* EnsureCapacity(int n, Key key);
 };

src/utils.h

@@ -211,6 +211,21 @@ inline byte* DecodeUnsignedIntBackward(byte* p, unsigned int* x) {
 uint32_t ComputeIntegerHash(uint32_t key);
 
 
+// ----------------------------------------------------------------------------
+// Bitwise rotate word
+
+inline uint32_t RotateRight(uint32_t value, uint32_t n) {
+  ASSERT(n < 31);
+  return (value >> n) | (value << (32-n));
+}
+
+
+inline uint32_t RotateLeft(uint32_t value, uint32_t n) {
+  ASSERT(n < 31);
+  return (value << n) | (value >> (32-n));
+}
+
+
 // ----------------------------------------------------------------------------
 // I/O support.