LLVM 18.0.0git
StringMap.cpp
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1//===--- StringMap.cpp - String Hash table map implementation -------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the StringMap class.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/ADT/StringMap.h"
16#include "llvm/Support/xxhash.h"
17
18using namespace llvm;
19
20/// Returns the number of buckets to allocate to ensure that the DenseMap can
21/// accommodate \p NumEntries without need to grow().
22static inline unsigned getMinBucketToReserveForEntries(unsigned NumEntries) {
23 // Ensure that "NumEntries * 4 < NumBuckets * 3"
24 if (NumEntries == 0)
25 return 0;
26 // +1 is required because of the strict equality.
27 // For example if NumEntries is 48, we need to return 401.
28 return NextPowerOf2(NumEntries * 4 / 3 + 1);
29}
30
31static inline StringMapEntryBase **createTable(unsigned NewNumBuckets) {
32 auto **Table = static_cast<StringMapEntryBase **>(safe_calloc(
33 NewNumBuckets + 1, sizeof(StringMapEntryBase **) + sizeof(unsigned)));
34
35 // Allocate one extra bucket, set it to look filled so the iterators stop at
36 // end.
37 Table[NewNumBuckets] = (StringMapEntryBase *)2;
38 return Table;
39}
40
41static inline unsigned *getHashTable(StringMapEntryBase **TheTable,
42 unsigned NumBuckets) {
43 return reinterpret_cast<unsigned *>(TheTable + NumBuckets + 1);
44}
45
46StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
47 ItemSize = itemSize;
48
49 // If a size is specified, initialize the table with that many buckets.
50 if (InitSize) {
51 // The table will grow when the number of entries reach 3/4 of the number of
52 // buckets. To guarantee that "InitSize" number of entries can be inserted
53 // in the table without growing, we allocate just what is needed here.
55 return;
56 }
57
58 // Otherwise, initialize it with zero buckets to avoid the allocation.
59 TheTable = nullptr;
60 NumBuckets = 0;
61 NumItems = 0;
62 NumTombstones = 0;
63}
64
65void StringMapImpl::init(unsigned InitSize) {
66 assert((InitSize & (InitSize - 1)) == 0 &&
67 "Init Size must be a power of 2 or zero!");
68
69 unsigned NewNumBuckets = InitSize ? InitSize : 16;
70 NumItems = 0;
71 NumTombstones = 0;
72
73 TheTable = createTable(NewNumBuckets);
74
75 // Set the member only if TheTable was successfully allocated
76 NumBuckets = NewNumBuckets;
77}
78
79/// LookupBucketFor - Look up the bucket that the specified string should end
80/// up in. If it already exists as a key in the map, the Item pointer for the
81/// specified bucket will be non-null. Otherwise, it will be null. In either
82/// case, the FullHashValue field of the bucket will be set to the hash value
83/// of the string.
85 // Hash table unallocated so far?
86 if (NumBuckets == 0)
87 init(16);
88 unsigned FullHashValue = xxh3_64bits(Name);
90 FullHashValue = ~FullHashValue;
91 unsigned BucketNo = FullHashValue & (NumBuckets - 1);
92 unsigned *HashTable = getHashTable(TheTable, NumBuckets);
93
94 unsigned ProbeAmt = 1;
95 int FirstTombstone = -1;
96 while (true) {
97 StringMapEntryBase *BucketItem = TheTable[BucketNo];
98 // If we found an empty bucket, this key isn't in the table yet, return it.
99 if (LLVM_LIKELY(!BucketItem)) {
100 // If we found a tombstone, we want to reuse the tombstone instead of an
101 // empty bucket. This reduces probing.
102 if (FirstTombstone != -1) {
103 HashTable[FirstTombstone] = FullHashValue;
104 return FirstTombstone;
105 }
106
107 HashTable[BucketNo] = FullHashValue;
108 return BucketNo;
109 }
110
111 if (BucketItem == getTombstoneVal()) {
112 // Skip over tombstones. However, remember the first one we see.
113 if (FirstTombstone == -1)
114 FirstTombstone = BucketNo;
115 } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
116 // If the full hash value matches, check deeply for a match. The common
117 // case here is that we are only looking at the buckets (for item info
118 // being non-null and for the full hash value) not at the items. This
119 // is important for cache locality.
120
121 // Do the comparison like this because Name isn't necessarily
122 // null-terminated!
123 char *ItemStr = (char *)BucketItem + ItemSize;
124 if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
125 // We found a match!
126 return BucketNo;
127 }
128 }
129
130 // Okay, we didn't find the item. Probe to the next bucket.
131 BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
132
133 // Use quadratic probing, it has fewer clumping artifacts than linear
134 // probing and has good cache behavior in the common case.
135 ++ProbeAmt;
136 }
137}
138
139/// FindKey - Look up the bucket that contains the specified key. If it exists
140/// in the map, return the bucket number of the key. Otherwise return -1.
141/// This does not modify the map.
143 if (NumBuckets == 0)
144 return -1; // Really empty table?
145 unsigned FullHashValue = xxh3_64bits(Key);
147 FullHashValue = ~FullHashValue;
148 unsigned BucketNo = FullHashValue & (NumBuckets - 1);
149 unsigned *HashTable = getHashTable(TheTable, NumBuckets);
150
151 unsigned ProbeAmt = 1;
152 while (true) {
153 StringMapEntryBase *BucketItem = TheTable[BucketNo];
154 // If we found an empty bucket, this key isn't in the table yet, return.
155 if (LLVM_LIKELY(!BucketItem))
156 return -1;
157
158 if (BucketItem == getTombstoneVal()) {
159 // Ignore tombstones.
160 } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
161 // If the full hash value matches, check deeply for a match. The common
162 // case here is that we are only looking at the buckets (for item info
163 // being non-null and for the full hash value) not at the items. This
164 // is important for cache locality.
165
166 // Do the comparison like this because NameStart isn't necessarily
167 // null-terminated!
168 char *ItemStr = (char *)BucketItem + ItemSize;
169 if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
170 // We found a match!
171 return BucketNo;
172 }
173 }
174
175 // Okay, we didn't find the item. Probe to the next bucket.
176 BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
177
178 // Use quadratic probing, it has fewer clumping artifacts than linear
179 // probing and has good cache behavior in the common case.
180 ++ProbeAmt;
181 }
182}
183
184/// RemoveKey - Remove the specified StringMapEntry from the table, but do not
185/// delete it. This aborts if the value isn't in the table.
187 const char *VStr = (char *)V + ItemSize;
188 StringMapEntryBase *V2 = RemoveKey(StringRef(VStr, V->getKeyLength()));
189 (void)V2;
190 assert(V == V2 && "Didn't find key?");
191}
192
193/// RemoveKey - Remove the StringMapEntry for the specified key from the
194/// table, returning it. If the key is not in the table, this returns null.
196 int Bucket = FindKey(Key);
197 if (Bucket == -1)
198 return nullptr;
199
200 StringMapEntryBase *Result = TheTable[Bucket];
201 TheTable[Bucket] = getTombstoneVal();
202 --NumItems;
205
206 return Result;
207}
208
209/// RehashTable - Grow the table, redistributing values into the buckets with
210/// the appropriate mod-of-hashtable-size.
211unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
212 unsigned NewSize;
213 // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
214 // the buckets are empty (meaning that many are filled with tombstones),
215 // grow/rehash the table.
216 if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
217 NewSize = NumBuckets * 2;
219 NumBuckets / 8)) {
220 NewSize = NumBuckets;
221 } else {
222 return BucketNo;
223 }
224
225 unsigned NewBucketNo = BucketNo;
226 auto **NewTableArray = createTable(NewSize);
227 unsigned *NewHashArray = getHashTable(NewTableArray, NewSize);
228 unsigned *HashTable = getHashTable(TheTable, NumBuckets);
229
230 // Rehash all the items into their new buckets. Luckily :) we already have
231 // the hash values available, so we don't have to rehash any strings.
232 for (unsigned I = 0, E = NumBuckets; I != E; ++I) {
233 StringMapEntryBase *Bucket = TheTable[I];
234 if (Bucket && Bucket != getTombstoneVal()) {
235 // If the bucket is not available, probe for a spot.
236 unsigned FullHash = HashTable[I];
237 unsigned NewBucket = FullHash & (NewSize - 1);
238 if (NewTableArray[NewBucket]) {
239 unsigned ProbeSize = 1;
240 do {
241 NewBucket = (NewBucket + ProbeSize++) & (NewSize - 1);
242 } while (NewTableArray[NewBucket]);
243 }
244
245 // Finally found a slot. Fill it in.
246 NewTableArray[NewBucket] = Bucket;
247 NewHashArray[NewBucket] = FullHash;
248 if (I == BucketNo)
249 NewBucketNo = NewBucket;
250 }
251 }
252
253 free(TheTable);
254
255 TheTable = NewTableArray;
256 NumBuckets = NewSize;
257 NumTombstones = 0;
258 return NewBucketNo;
259}
This file defines the StringMap class.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
#define LLVM_UNLIKELY(EXPR)
Definition: Compiler.h:222
#define LLVM_LIKELY(EXPR)
Definition: Compiler.h:221
std::string Name
#define I(x, y, z)
Definition: MD5.cpp:58
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
static StringMapEntryBase ** createTable(unsigned NewNumBuckets)
Definition: StringMap.cpp:31
static unsigned * getHashTable(StringMapEntryBase **TheTable, unsigned NumBuckets)
Definition: StringMap.cpp:41
static unsigned getMinBucketToReserveForEntries(unsigned NumEntries)
Returns the number of buckets to allocate to ensure that the DenseMap can accommodate NumEntries with...
Definition: StringMap.cpp:22
StringMapEntryBase - Shared base class of StringMapEntry instances.
size_t getKeyLength() const
static StringMapEntryBase * getTombstoneVal()
Definition: StringMap.h:87
unsigned ItemSize
Definition: StringMap.h:41
int FindKey(StringRef Key) const
FindKey - Look up the bucket that contains the specified key.
Definition: StringMap.cpp:142
unsigned RehashTable(unsigned BucketNo=0)
RehashTable - Grow the table, redistributing values into the buckets with the appropriate mod-of-hash...
Definition: StringMap.cpp:211
unsigned NumItems
Definition: StringMap.h:39
unsigned LookupBucketFor(StringRef Key)
LookupBucketFor - Look up the bucket that the specified string should end up in.
Definition: StringMap.cpp:84
void RemoveKey(StringMapEntryBase *V)
RemoveKey - Remove the specified StringMapEntry from the table, but do not delete it.
Definition: StringMap.cpp:186
StringMapEntryBase ** TheTable
Definition: StringMap.h:37
StringMapImpl(unsigned itemSize)
Definition: StringMap.h:44
void init(unsigned Size)
Allocate the table with the specified number of buckets and otherwise setup the map as empty.
Definition: StringMap.cpp:65
unsigned NumBuckets
Definition: StringMap.h:38
unsigned NumTombstones
Definition: StringMap.h:40
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
uint64_t xxh3_64bits(ArrayRef< uint8_t > data)
Definition: xxhash.cpp:397
LLVM_ATTRIBUTE_RETURNS_NONNULL void * safe_calloc(size_t Count, size_t Sz)
Definition: MemAlloc.h:38
bool shouldReverseIterate()
constexpr uint64_t NextPowerOf2(uint64_t A)
Returns the next power of two (in 64-bits) that is strictly greater than A.
Definition: MathExtras.h:349