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
This commit is contained in:
bak@chromium.org 2009-07-16 12:56:50 +00:00
parent 263acb4d02
commit e0047e4331
8 changed files with 93 additions and 47 deletions

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@ -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

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@ -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;
}

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@ -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_;

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@ -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);

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@ -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));

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@ -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();
}

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@ -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);
};

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@ -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.