LLVM  16.0.0git
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"
14 #include "llvm/Support/DJB.h"
16 
17 using namespace llvm;
18 
19 /// Returns the number of buckets to allocate to ensure that the DenseMap can
20 /// accommodate \p NumEntries without need to grow().
21 static inline unsigned getMinBucketToReserveForEntries(unsigned NumEntries) {
22  // Ensure that "NumEntries * 4 < NumBuckets * 3"
23  if (NumEntries == 0)
24  return 0;
25  // +1 is required because of the strict equality.
26  // For example if NumEntries is 48, we need to return 401.
27  return NextPowerOf2(NumEntries * 4 / 3 + 1);
28 }
29 
30 static inline StringMapEntryBase **createTable(unsigned NewNumBuckets) {
31  auto **Table = static_cast<StringMapEntryBase **>(safe_calloc(
32  NewNumBuckets + 1, sizeof(StringMapEntryBase **) + sizeof(unsigned)));
33 
34  // Allocate one extra bucket, set it to look filled so the iterators stop at
35  // end.
36  Table[NewNumBuckets] = (StringMapEntryBase *)2;
37  return Table;
38 }
39 
40 static inline unsigned *getHashTable(StringMapEntryBase **TheTable,
41  unsigned NumBuckets) {
42  return reinterpret_cast<unsigned *>(TheTable + NumBuckets + 1);
43 }
44 
45 StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
46  ItemSize = itemSize;
47 
48  // If a size is specified, initialize the table with that many buckets.
49  if (InitSize) {
50  // The table will grow when the number of entries reach 3/4 of the number of
51  // buckets. To guarantee that "InitSize" number of entries can be inserted
52  // in the table without growing, we allocate just what is needed here.
54  return;
55  }
56 
57  // Otherwise, initialize it with zero buckets to avoid the allocation.
58  TheTable = nullptr;
59  NumBuckets = 0;
60  NumItems = 0;
61  NumTombstones = 0;
62 }
63 
64 void StringMapImpl::init(unsigned InitSize) {
65  assert((InitSize & (InitSize - 1)) == 0 &&
66  "Init Size must be a power of 2 or zero!");
67 
68  unsigned NewNumBuckets = InitSize ? InitSize : 16;
69  NumItems = 0;
70  NumTombstones = 0;
71 
72  TheTable = createTable(NewNumBuckets);
73 
74  // Set the member only if TheTable was successfully allocated
75  NumBuckets = NewNumBuckets;
76 }
77 
78 /// LookupBucketFor - Look up the bucket that the specified string should end
79 /// up in. If it already exists as a key in the map, the Item pointer for the
80 /// specified bucket will be non-null. Otherwise, it will be null. In either
81 /// case, the FullHashValue field of the bucket will be set to the hash value
82 /// of the string.
84  // Hash table unallocated so far?
85  if (NumBuckets == 0)
86  init(16);
87  unsigned FullHashValue = djbHash(Name, 0);
88  unsigned BucketNo = FullHashValue & (NumBuckets - 1);
89  unsigned *HashTable = getHashTable(TheTable, NumBuckets);
90 
91  unsigned ProbeAmt = 1;
92  int FirstTombstone = -1;
93  while (true) {
94  StringMapEntryBase *BucketItem = TheTable[BucketNo];
95  // If we found an empty bucket, this key isn't in the table yet, return it.
96  if (LLVM_LIKELY(!BucketItem)) {
97  // If we found a tombstone, we want to reuse the tombstone instead of an
98  // empty bucket. This reduces probing.
99  if (FirstTombstone != -1) {
100  HashTable[FirstTombstone] = FullHashValue;
101  return FirstTombstone;
102  }
103 
104  HashTable[BucketNo] = FullHashValue;
105  return BucketNo;
106  }
107 
108  if (BucketItem == getTombstoneVal()) {
109  // Skip over tombstones. However, remember the first one we see.
110  if (FirstTombstone == -1)
111  FirstTombstone = BucketNo;
112  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
113  // If the full hash value matches, check deeply for a match. The common
114  // case here is that we are only looking at the buckets (for item info
115  // being non-null and for the full hash value) not at the items. This
116  // is important for cache locality.
117 
118  // Do the comparison like this because Name isn't necessarily
119  // null-terminated!
120  char *ItemStr = (char *)BucketItem + ItemSize;
121  if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
122  // We found a match!
123  return BucketNo;
124  }
125  }
126 
127  // Okay, we didn't find the item. Probe to the next bucket.
128  BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
129 
130  // Use quadratic probing, it has fewer clumping artifacts than linear
131  // probing and has good cache behavior in the common case.
132  ++ProbeAmt;
133  }
134 }
135 
136 /// FindKey - Look up the bucket that contains the specified key. If it exists
137 /// in the map, return the bucket number of the key. Otherwise return -1.
138 /// This does not modify the map.
140  if (NumBuckets == 0)
141  return -1; // Really empty table?
142  unsigned FullHashValue = djbHash(Key, 0);
143  unsigned BucketNo = FullHashValue & (NumBuckets - 1);
144  unsigned *HashTable = getHashTable(TheTable, NumBuckets);
145 
146  unsigned ProbeAmt = 1;
147  while (true) {
148  StringMapEntryBase *BucketItem = TheTable[BucketNo];
149  // If we found an empty bucket, this key isn't in the table yet, return.
150  if (LLVM_LIKELY(!BucketItem))
151  return -1;
152 
153  if (BucketItem == getTombstoneVal()) {
154  // Ignore tombstones.
155  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
156  // If the full hash value matches, check deeply for a match. The common
157  // case here is that we are only looking at the buckets (for item info
158  // being non-null and for the full hash value) not at the items. This
159  // is important for cache locality.
160 
161  // Do the comparison like this because NameStart isn't necessarily
162  // null-terminated!
163  char *ItemStr = (char *)BucketItem + ItemSize;
164  if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
165  // We found a match!
166  return BucketNo;
167  }
168  }
169 
170  // Okay, we didn't find the item. Probe to the next bucket.
171  BucketNo = (BucketNo + ProbeAmt) & (NumBuckets - 1);
172 
173  // Use quadratic probing, it has fewer clumping artifacts than linear
174  // probing and has good cache behavior in the common case.
175  ++ProbeAmt;
176  }
177 }
178 
179 /// RemoveKey - Remove the specified StringMapEntry from the table, but do not
180 /// delete it. This aborts if the value isn't in the table.
182  const char *VStr = (char *)V + ItemSize;
184  (void)V2;
185  assert(V == V2 && "Didn't find key?");
186 }
187 
188 /// RemoveKey - Remove the StringMapEntry for the specified key from the
189 /// table, returning it. If the key is not in the table, this returns null.
191  int Bucket = FindKey(Key);
192  if (Bucket == -1)
193  return nullptr;
194 
195  StringMapEntryBase *Result = TheTable[Bucket];
196  TheTable[Bucket] = getTombstoneVal();
197  --NumItems;
198  ++NumTombstones;
200 
201  return Result;
202 }
203 
204 /// RehashTable - Grow the table, redistributing values into the buckets with
205 /// the appropriate mod-of-hashtable-size.
206 unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
207  unsigned NewSize;
208  // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
209  // the buckets are empty (meaning that many are filled with tombstones),
210  // grow/rehash the table.
211  if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
212  NewSize = NumBuckets * 2;
213  } else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
214  NumBuckets / 8)) {
215  NewSize = NumBuckets;
216  } else {
217  return BucketNo;
218  }
219 
220  unsigned NewBucketNo = BucketNo;
221  auto **NewTableArray = createTable(NewSize);
222  unsigned *NewHashArray = getHashTable(NewTableArray, NewSize);
223  unsigned *HashTable = getHashTable(TheTable, NumBuckets);
224 
225  // Rehash all the items into their new buckets. Luckily :) we already have
226  // the hash values available, so we don't have to rehash any strings.
227  for (unsigned I = 0, E = NumBuckets; I != E; ++I) {
228  StringMapEntryBase *Bucket = TheTable[I];
229  if (Bucket && Bucket != getTombstoneVal()) {
230  // If the bucket is not available, probe for a spot.
231  unsigned FullHash = HashTable[I];
232  unsigned NewBucket = FullHash & (NewSize - 1);
233  if (NewTableArray[NewBucket]) {
234  unsigned ProbeSize = 1;
235  do {
236  NewBucket = (NewBucket + ProbeSize++) & (NewSize - 1);
237  } while (NewTableArray[NewBucket]);
238  }
239 
240  // Finally found a slot. Fill it in.
241  NewTableArray[NewBucket] = Bucket;
242  NewHashArray[NewBucket] = FullHash;
243  if (I == BucketNo)
244  NewBucketNo = NewBucket;
245  }
246  }
247 
248  free(TheTable);
249 
250  TheTable = NewTableArray;
251  NumBuckets = NewSize;
252  NumTombstones = 0;
253  return NewBucketNo;
254 }
llvm::StringMapImpl::RehashTable
unsigned RehashTable(unsigned BucketNo=0)
RehashTable - Grow the table, redistributing values into the buckets with the appropriate mod-of-hash...
Definition: StringMap.cpp:206
MathExtras.h
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
DJB.h
llvm::StringMapEntryBase::getKeyLength
size_t getKeyLength() const
Definition: StringMapEntry.h:32
llvm::StringMapImpl::NumTombstones
unsigned NumTombstones
Definition: StringMap.h:40
llvm::safe_calloc
LLVM_ATTRIBUTE_RETURNS_NONNULL void * safe_calloc(size_t Count, size_t Sz)
Definition: MemAlloc.h:38
getMinBucketToReserveForEntries
static unsigned getMinBucketToReserveForEntries(unsigned NumEntries)
Returns the number of buckets to allocate to ensure that the DenseMap can accommodate NumEntries with...
Definition: StringMap.cpp:21
llvm::StringMapImpl::NumBuckets
unsigned NumBuckets
Definition: StringMap.h:38
getHashTable
static unsigned * getHashTable(StringMapEntryBase **TheTable, unsigned NumBuckets)
Definition: StringMap.cpp:40
llvm::StringMapEntryBase
StringMapEntryBase - Shared base class of StringMapEntry instances.
Definition: StringMapEntry.h:26
createTable
static StringMapEntryBase ** createTable(unsigned NewNumBuckets)
Definition: StringMap.cpp:30
E
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
llvm::StringMapImpl::TheTable
StringMapEntryBase ** TheTable
Definition: StringMap.h:37
llvm::AMDGPU::PALMD::Key
Key
PAL metadata keys.
Definition: AMDGPUMetadata.h:486
llvm::NextPowerOf2
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:611
llvm::StringMapImpl::FindKey
int FindKey(StringRef Key) const
FindKey - Look up the bucket that contains the specified key.
Definition: StringMap.cpp:139
llvm::StringMapImpl::getTombstoneVal
static StringMapEntryBase * getTombstoneVal()
Definition: StringMap.h:87
llvm::StringMapImpl::init
void init(unsigned Size)
Allocate the table with the specified number of buckets and otherwise setup the map as empty.
Definition: StringMap.cpp:64
llvm::StringMapImpl::NumItems
unsigned NumItems
Definition: StringMap.h:39
I
#define I(x, y, z)
Definition: MD5.cpp:58
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::StringMapImpl::LookupBucketFor
unsigned LookupBucketFor(StringRef Key)
LookupBucketFor - Look up the bucket that the specified string should end up in.
Definition: StringMap.cpp:83
llvm::StringRef
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
llvm::NVPTX::PTXLdStInstCode::V2
@ V2
Definition: NVPTX.h:123
llvm::StringMapImpl::StringMapImpl
StringMapImpl(unsigned itemSize)
Definition: StringMap.h:44
llvm::StringMapImpl::RemoveKey
void RemoveKey(StringMapEntryBase *V)
RemoveKey - Remove the specified StringMapEntry from the table, but do not delete it.
Definition: StringMap.cpp:181
LLVM_LIKELY
#define LLVM_LIKELY(EXPR)
Definition: Compiler.h:209
StringMap.h
llvm::djbHash
uint32_t djbHash(StringRef Buffer, uint32_t H=5381)
The Bernstein hash function used by the DWARF accelerator tables.
Definition: DJB.h:21
LLVM_UNLIKELY
#define LLVM_UNLIKELY(EXPR)
Definition: Compiler.h:210
llvm::StringMapImpl::ItemSize
unsigned ItemSize
Definition: StringMap.h:41