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//===--- StringMap.cpp - String Hash table map implementation -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the StringMap class.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/MathExtras.h"
using namespace llvm;
/// Returns the number of buckets to allocate to ensure that the DenseMap can
/// accommodate \p NumEntries without need to grow().
static inline unsigned getMinBucketToReserveForEntries(unsigned NumEntries) {
// Ensure that "NumEntries * 4 < NumBuckets * 3"
if (NumEntries == 0)
return 0;
// +1 is required because of the strict equality.
// For example if NumEntries is 48, we need to return 401.
return NextPowerOf2(NumEntries * 4 / 3 + 1);
}
static inline StringMapEntryBase **createTable(unsigned NewNumBuckets) {
auto **Table = static_cast<StringMapEntryBase **>(safe_calloc(
NewNumBuckets + 1, sizeof(StringMapEntryBase **) + sizeof(unsigned)));
// Allocate one extra bucket, set it to look filled so the iterators stop at
// end.
Table[NewNumBuckets] = (StringMapEntryBase *)2;
return Table;
}
static inline unsigned *getHashTable(StringMapEntryBase **TheTable,
unsigned NumBuckets) {
return reinterpret_cast<unsigned *>(TheTable + NumBuckets + 1);
}
StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
ItemSize = itemSize;
// If a size is specified, initialize the table with that many buckets.
if (InitSize) {
// The table will grow when the number of entries reach 3/4 of the number of
// buckets. To guarantee that "InitSize" number of entries can be inserted
// in the table without growing, we allocate just what is needed here.
init(getMinBucketToReserveForEntries(InitSize));
return;
}
// Otherwise, initialize it with zero buckets to avoid the allocation.
TheTable = nullptr;
NumBuckets = 0;
NumItems = 0;
NumTombstones = 0;
}
void StringMapImpl::init(unsigned InitSize) {
assert((InitSize & (InitSize - 1)) == 0 &&
"Init Size must be a power of 2 or zero!");
unsigned NewNumBuckets = InitSize ? InitSize : 16;
NumItems = 0;
NumTombstones = 0;
TheTable = createTable(NewNumBuckets);
// Set the member only if TheTable was successfully allocated
NumBuckets = NewNumBuckets;
}
/// LookupBucketFor - Look up the bucket that the specified string should end
/// up in. If it already exists as a key in the map, the Item pointer for the
/// specified bucket will be non-null. Otherwise, it will be null. In either
/// case, the FullHashValue field of the bucket will be set to the hash value
/// of the string.
unsigned StringMapImpl::LookupBucketFor(StringRef Name) {
// Hash table unallocated so far?
if (NumBuckets == 0)
init(16);
unsigned FullHashValue = djbHash(Name, 0);
unsigned BucketNo = FullHashValue & (NumBuckets - 1);
unsigned *HashTable = getHashTable(TheTable, NumBuckets);
unsigned ProbeAmt = 1;
int FirstTombstone = -1;
while (true) {
StringMapEntryBase *BucketItem = TheTable[BucketNo];
// If we found an empty bucket, this key isn't in the table yet, return it.
if (LLVM_LIKELY(!BucketItem)) {
// If we found a tombstone, we want to reuse the tombstone instead of an
// empty bucket. This reduces probing.
if (FirstTombstone != -1) {
HashTable[FirstTombstone] = FullHashValue;
return FirstTombstone;
}
HashTable[BucketNo] = FullHashValue;
return BucketNo;
}
if (BucketItem == getTombstoneVal()) {
// Skip over tombstones. However, remember the first one we see.
if (FirstTombstone == -1)
FirstTombstone = BucketNo;
} else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
// If the full hash value matches, check deeply for a match. The common
// case here is that we are only looking at the buckets (for item info
// being non-null and for the full hash value) not at the items. This
// is important for cache locality.
// Do the comparison like this because Name isn't necessarily
// null-terminated!
char *ItemStr = (char *)BucketItem + ItemSize;
if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
// We found a match!
return BucketNo;
}
}
// Okay, we didn't find the item. Probe to the next bucket.
BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
// Use quadratic probing, it has fewer clumping artifacts than linear
// probing and has good cache behavior in the common case.
++ProbeAmt;
}
}
/// FindKey - Look up the bucket that contains the specified key. If it exists
/// in the map, return the bucket number of the key. Otherwise return -1.
/// This does not modify the map.
int StringMapImpl::FindKey(StringRef Key) const {
if (NumBuckets == 0)
return -1; // Really empty table?
unsigned FullHashValue = djbHash(Key, 0);
unsigned BucketNo = FullHashValue & (NumBuckets - 1);
unsigned *HashTable = getHashTable(TheTable, NumBuckets);
unsigned ProbeAmt = 1;
while (true) {
StringMapEntryBase *BucketItem = TheTable[BucketNo];
// If we found an empty bucket, this key isn't in the table yet, return.
if (LLVM_LIKELY(!BucketItem))
return -1;
if (BucketItem == getTombstoneVal()) {
// Ignore tombstones.
} else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
// If the full hash value matches, check deeply for a match. The common
// case here is that we are only looking at the buckets (for item info
// being non-null and for the full hash value) not at the items. This
// is important for cache locality.
// Do the comparison like this because NameStart isn't necessarily
// null-terminated!
char *ItemStr = (char *)BucketItem + ItemSize;
if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
// We found a match!
return BucketNo;
}
}
// Okay, we didn't find the item. Probe to the next bucket.
BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
// Use quadratic probing, it has fewer clumping artifacts than linear
// probing and has good cache behavior in the common case.
++ProbeAmt;
}
}
/// RemoveKey - Remove the specified StringMapEntry from the table, but do not
/// delete it. This aborts if the value isn't in the table.
void StringMapImpl::RemoveKey(StringMapEntryBase *V) {
const char *VStr = (char *)V + ItemSize;
StringMapEntryBase *V2 = RemoveKey(StringRef(VStr, V->getKeyLength()));
(void)V2;
assert(V == V2 && "Didn't find key?");
}
/// RemoveKey - Remove the StringMapEntry for the specified key from the
/// table, returning it. If the key is not in the table, this returns null.
StringMapEntryBase *StringMapImpl::RemoveKey(StringRef Key) {
int Bucket = FindKey(Key);
if (Bucket == -1)
return nullptr;
StringMapEntryBase *Result = TheTable[Bucket];
TheTable[Bucket] = getTombstoneVal();
--NumItems;
++NumTombstones;
assert(NumItems + NumTombstones <= NumBuckets);
return Result;
}
/// RehashTable - Grow the table, redistributing values into the buckets with
/// the appropriate mod-of-hashtable-size.
unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
unsigned NewSize;
// If the hash table is now more than 3/4 full, or if fewer than 1/8 of
// the buckets are empty (meaning that many are filled with tombstones),
// grow/rehash the table.
if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
NewSize = NumBuckets * 2;
} else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
NumBuckets / 8)) {
NewSize = NumBuckets;
} else {
return BucketNo;
}
unsigned NewBucketNo = BucketNo;
auto **NewTableArray = createTable(NewSize);
unsigned *NewHashArray = getHashTable(NewTableArray, NewSize);
unsigned *HashTable = getHashTable(TheTable, NumBuckets);
// Rehash all the items into their new buckets. Luckily :) we already have
// the hash values available, so we don't have to rehash any strings.
for (unsigned I = 0, E = NumBuckets; I != E; ++I) {
StringMapEntryBase *Bucket = TheTable[I];
if (Bucket && Bucket != getTombstoneVal()) {
// If the bucket is not available, probe for a spot.
unsigned FullHash = HashTable[I];
unsigned NewBucket = FullHash & (NewSize - 1);
if (NewTableArray[NewBucket]) {
unsigned ProbeSize = 1;
do {
NewBucket = (NewBucket + ProbeSize++) & (NewSize - 1);
} while (NewTableArray[NewBucket]);
}
// Finally found a slot. Fill it in.
NewTableArray[NewBucket] = Bucket;
NewHashArray[NewBucket] = FullHash;
if (I == BucketNo)
NewBucketNo = NewBucket;
}
}
free(TheTable);
TheTable = NewTableArray;
NumBuckets = NewSize;
NumTombstones = 0;
return NewBucketNo;
}