LLVM  10.0.0svn
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/ADT/StringExtras.h"
15 #include "llvm/Support/Compiler.h"
16 #include "llvm/Support/DJB.h"
18 #include <cassert>
19 
20 using namespace llvm;
21 
22 /// Returns the number of buckets to allocate to ensure that the DenseMap can
23 /// accommodate \p NumEntries without need to grow().
24 static unsigned getMinBucketToReserveForEntries(unsigned NumEntries) {
25  // Ensure that "NumEntries * 4 < NumBuckets * 3"
26  if (NumEntries == 0)
27  return 0;
28  // +1 is required because of the strict equality.
29  // For example if NumEntries is 48, we need to return 401.
30  return NextPowerOf2(NumEntries * 4 / 3 + 1);
31 }
32 
33 StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
34  ItemSize = itemSize;
35 
36  // If a size is specified, initialize the table with that many buckets.
37  if (InitSize) {
38  // The table will grow when the number of entries reach 3/4 of the number of
39  // buckets. To guarantee that "InitSize" number of entries can be inserted
40  // in the table without growing, we allocate just what is needed here.
42  return;
43  }
44 
45  // Otherwise, initialize it with zero buckets to avoid the allocation.
46  TheTable = nullptr;
47  NumBuckets = 0;
48  NumItems = 0;
49  NumTombstones = 0;
50 }
51 
52 void StringMapImpl::init(unsigned InitSize) {
53  assert((InitSize & (InitSize-1)) == 0 &&
54  "Init Size must be a power of 2 or zero!");
55 
56  unsigned NewNumBuckets = InitSize ? InitSize : 16;
57  NumItems = 0;
58  NumTombstones = 0;
59 
60  TheTable = static_cast<StringMapEntryBase **>(
61  safe_calloc(NewNumBuckets+1,
62  sizeof(StringMapEntryBase **) + sizeof(unsigned)));
63 
64  // Set the member only if TheTable was successfully allocated
65  NumBuckets = NewNumBuckets;
66 
67  // Allocate one extra bucket, set it to look filled so the iterators stop at
68  // end.
70 }
71 
72 /// LookupBucketFor - Look up the bucket that the specified string should end
73 /// up in. If it already exists as a key in the map, the Item pointer for the
74 /// specified bucket will be non-null. Otherwise, it will be null. In either
75 /// case, the FullHashValue field of the bucket will be set to the hash value
76 /// of the string.
78  unsigned HTSize = NumBuckets;
79  if (HTSize == 0) { // Hash table unallocated so far?
80  init(16);
81  HTSize = NumBuckets;
82  }
83  unsigned FullHashValue = djbHash(Name, 0);
84  unsigned BucketNo = FullHashValue & (HTSize-1);
85  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
86 
87  unsigned ProbeAmt = 1;
88  int FirstTombstone = -1;
89  while (true) {
90  StringMapEntryBase *BucketItem = TheTable[BucketNo];
91  // If we found an empty bucket, this key isn't in the table yet, return it.
92  if (LLVM_LIKELY(!BucketItem)) {
93  // If we found a tombstone, we want to reuse the tombstone instead of an
94  // empty bucket. This reduces probing.
95  if (FirstTombstone != -1) {
96  HashTable[FirstTombstone] = FullHashValue;
97  return FirstTombstone;
98  }
99 
100  HashTable[BucketNo] = FullHashValue;
101  return BucketNo;
102  }
103 
104  if (BucketItem == getTombstoneVal()) {
105  // Skip over tombstones. However, remember the first one we see.
106  if (FirstTombstone == -1) FirstTombstone = BucketNo;
107  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
108  // If the full hash value matches, check deeply for a match. The common
109  // case here is that we are only looking at the buckets (for item info
110  // being non-null and for the full hash value) not at the items. This
111  // is important for cache locality.
112 
113  // Do the comparison like this because Name isn't necessarily
114  // null-terminated!
115  char *ItemStr = (char*)BucketItem+ItemSize;
116  if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
117  // We found a match!
118  return BucketNo;
119  }
120  }
121 
122  // Okay, we didn't find the item. Probe to the next bucket.
123  BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
124 
125  // Use quadratic probing, it has fewer clumping artifacts than linear
126  // probing and has good cache behavior in the common case.
127  ++ProbeAmt;
128  }
129 }
130 
131 /// FindKey - Look up the bucket that contains the specified key. If it exists
132 /// in the map, return the bucket number of the key. Otherwise return -1.
133 /// This does not modify the map.
135  unsigned HTSize = NumBuckets;
136  if (HTSize == 0) return -1; // Really empty table?
137  unsigned FullHashValue = djbHash(Key, 0);
138  unsigned BucketNo = FullHashValue & (HTSize-1);
139  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
140 
141  unsigned ProbeAmt = 1;
142  while (true) {
143  StringMapEntryBase *BucketItem = TheTable[BucketNo];
144  // If we found an empty bucket, this key isn't in the table yet, return.
145  if (LLVM_LIKELY(!BucketItem))
146  return -1;
147 
148  if (BucketItem == getTombstoneVal()) {
149  // Ignore tombstones.
150  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
151  // If the full hash value matches, check deeply for a match. The common
152  // case here is that we are only looking at the buckets (for item info
153  // being non-null and for the full hash value) not at the items. This
154  // is important for cache locality.
155 
156  // Do the comparison like this because NameStart isn't necessarily
157  // null-terminated!
158  char *ItemStr = (char*)BucketItem+ItemSize;
159  if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
160  // We found a match!
161  return BucketNo;
162  }
163  }
164 
165  // Okay, we didn't find the item. Probe to the next bucket.
166  BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
167 
168  // Use quadratic probing, it has fewer clumping artifacts than linear
169  // probing and has good cache behavior in the common case.
170  ++ProbeAmt;
171  }
172 }
173 
174 /// RemoveKey - Remove the specified StringMapEntry from the table, but do not
175 /// delete it. This aborts if the value isn't in the table.
177  const char *VStr = (char*)V + ItemSize;
179  (void)V2;
180  assert(V == V2 && "Didn't find key?");
181 }
182 
183 /// RemoveKey - Remove the StringMapEntry for the specified key from the
184 /// table, returning it. If the key is not in the table, this returns null.
186  int Bucket = FindKey(Key);
187  if (Bucket == -1) return nullptr;
188 
189  StringMapEntryBase *Result = TheTable[Bucket];
190  TheTable[Bucket] = getTombstoneVal();
191  --NumItems;
192  ++NumTombstones;
194 
195  return Result;
196 }
197 
198 /// RehashTable - Grow the table, redistributing values into the buckets with
199 /// the appropriate mod-of-hashtable-size.
200 unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
201  unsigned NewSize;
202  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
203 
204  // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
205  // the buckets are empty (meaning that many are filled with tombstones),
206  // grow/rehash the table.
207  if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
208  NewSize = NumBuckets*2;
209  } else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
210  NumBuckets / 8)) {
211  NewSize = NumBuckets;
212  } else {
213  return BucketNo;
214  }
215 
216  unsigned NewBucketNo = BucketNo;
217  // Allocate one extra bucket which will always be non-empty. This allows the
218  // iterators to stop at end.
219  auto NewTableArray = static_cast<StringMapEntryBase **>(
220  safe_calloc(NewSize+1, sizeof(StringMapEntryBase *) + sizeof(unsigned)));
221 
222  unsigned *NewHashArray = (unsigned *)(NewTableArray + NewSize + 1);
223  NewTableArray[NewSize] = (StringMapEntryBase*)2;
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  // Fast case, bucket available.
231  unsigned FullHash = HashTable[I];
232  unsigned NewBucket = FullHash & (NewSize-1);
233  if (!NewTableArray[NewBucket]) {
234  NewTableArray[FullHash & (NewSize-1)] = Bucket;
235  NewHashArray[FullHash & (NewSize-1)] = FullHash;
236  if (I == BucketNo)
237  NewBucketNo = NewBucket;
238  continue;
239  }
240 
241  // Otherwise probe for a spot.
242  unsigned ProbeSize = 1;
243  do {
244  NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
245  } while (NewTableArray[NewBucket]);
246 
247  // Finally found a slot. Fill it in.
248  NewTableArray[NewBucket] = Bucket;
249  NewHashArray[NewBucket] = FullHash;
250  if (I == BucketNo)
251  NewBucketNo = NewBucket;
252  }
253  }
254 
255  free(TheTable);
256 
257  TheTable = NewTableArray;
258  NumBuckets = NewSize;
259  NumTombstones = 0;
260  return NewBucketNo;
261 }
StringMapImpl(unsigned itemSize)
Definition: StringMap.h:61
This class represents lattice values for constants.
Definition: AllocatorList.h:23
#define LLVM_UNLIKELY(EXPR)
Definition: Compiler.h:199
#define LLVM_LIKELY(EXPR)
Definition: Compiler.h:198
amdgpu Simplify well known AMD library false FunctionCallee Value const Twine & Name
unsigned RehashTable(unsigned BucketNo=0)
RehashTable - Grow the table, redistributing values into the buckets with the appropriate mod-of-hash...
Definition: StringMap.cpp:200
unsigned LookupBucketFor(StringRef Key)
LookupBucketFor - Look up the bucket that the specified string should end up in.
Definition: StringMap.cpp:77
static unsigned getMinBucketToReserveForEntries(unsigned NumEntries)
Returns the number of buckets to allocate to ensure that the DenseMap can accommodate NumEntries with...
Definition: StringMap.cpp:24
Key
PAL metadata keys.
int FindKey(StringRef Key) const
FindKey - Look up the bucket that contains the specified key.
Definition: StringMap.cpp:134
unsigned NumItems
Definition: StringMap.h:56
StringMapEntryBase ** TheTable
Definition: StringMap.h:54
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
void init(unsigned Size)
Allocate the table with the specified number of buckets and otherwise setup the map as empty...
Definition: StringMap.cpp:52
uint64_t NextPowerOf2(uint64_t A)
Returns the next power of two (in 64-bits) that is strictly greater than A.
Definition: MathExtras.h:644
uint32_t djbHash(StringRef Buffer, uint32_t H=5381)
The Bernstein hash function used by the DWARF accelerator tables.
Definition: DJB.h:21
unsigned ItemSize
Definition: StringMap.h:58
void RemoveKey(StringMapEntryBase *V)
RemoveKey - Remove the specified StringMapEntry from the table, but do not delete it...
Definition: StringMap.cpp:176
static StringMapEntryBase * getTombstoneVal()
Definition: StringMap.h:101
unsigned NumBuckets
Definition: StringMap.h:55
size_t getKeyLength() const
Definition: StringMap.h:44
#define I(x, y, z)
Definition: MD5.cpp:58
unsigned NumTombstones
Definition: StringMap.h:57
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
StringMapEntryBase - Shared base class of StringMapEntry instances.
Definition: StringMap.h:38
LLVM_ATTRIBUTE_RETURNS_NONNULL void * safe_calloc(size_t Count, size_t Sz)
Definition: MemAlloc.h:38
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48