LLVM  4.0.0
StringMap.cpp
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1 //===--- StringMap.cpp - String Hash table map implementation -------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the StringMap class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/ADT/StringMap.h"
15 #include "llvm/ADT/StringExtras.h"
16 #include "llvm/Support/Compiler.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  NumBuckets = InitSize ? InitSize : 16;
56  NumItems = 0;
57  NumTombstones = 0;
58 
59  TheTable = (StringMapEntryBase **)calloc(NumBuckets+1,
60  sizeof(StringMapEntryBase **) +
61  sizeof(unsigned));
62 
63  // Allocate one extra bucket, set it to look filled so the iterators stop at
64  // end.
66 }
67 
68 /// LookupBucketFor - Look up the bucket that the specified string should end
69 /// up in. If it already exists as a key in the map, the Item pointer for the
70 /// specified bucket will be non-null. Otherwise, it will be null. In either
71 /// case, the FullHashValue field of the bucket will be set to the hash value
72 /// of the string.
74  unsigned HTSize = NumBuckets;
75  if (HTSize == 0) { // Hash table unallocated so far?
76  init(16);
77  HTSize = NumBuckets;
78  }
79  unsigned FullHashValue = HashString(Name);
80  unsigned BucketNo = FullHashValue & (HTSize-1);
81  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
82 
83  unsigned ProbeAmt = 1;
84  int FirstTombstone = -1;
85  while (true) {
86  StringMapEntryBase *BucketItem = TheTable[BucketNo];
87  // If we found an empty bucket, this key isn't in the table yet, return it.
88  if (LLVM_LIKELY(!BucketItem)) {
89  // If we found a tombstone, we want to reuse the tombstone instead of an
90  // empty bucket. This reduces probing.
91  if (FirstTombstone != -1) {
92  HashTable[FirstTombstone] = FullHashValue;
93  return FirstTombstone;
94  }
95 
96  HashTable[BucketNo] = FullHashValue;
97  return BucketNo;
98  }
99 
100  if (BucketItem == getTombstoneVal()) {
101  // Skip over tombstones. However, remember the first one we see.
102  if (FirstTombstone == -1) FirstTombstone = BucketNo;
103  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
104  // If the full hash value matches, check deeply for a match. The common
105  // case here is that we are only looking at the buckets (for item info
106  // being non-null and for the full hash value) not at the items. This
107  // is important for cache locality.
108 
109  // Do the comparison like this because Name isn't necessarily
110  // null-terminated!
111  char *ItemStr = (char*)BucketItem+ItemSize;
112  if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
113  // We found a match!
114  return BucketNo;
115  }
116  }
117 
118  // Okay, we didn't find the item. Probe to the next bucket.
119  BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
120 
121  // Use quadratic probing, it has fewer clumping artifacts than linear
122  // probing and has good cache behavior in the common case.
123  ++ProbeAmt;
124  }
125 }
126 
127 /// FindKey - Look up the bucket that contains the specified key. If it exists
128 /// in the map, return the bucket number of the key. Otherwise return -1.
129 /// This does not modify the map.
131  unsigned HTSize = NumBuckets;
132  if (HTSize == 0) return -1; // Really empty table?
133  unsigned FullHashValue = HashString(Key);
134  unsigned BucketNo = FullHashValue & (HTSize-1);
135  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
136 
137  unsigned ProbeAmt = 1;
138  while (true) {
139  StringMapEntryBase *BucketItem = TheTable[BucketNo];
140  // If we found an empty bucket, this key isn't in the table yet, return.
141  if (LLVM_LIKELY(!BucketItem))
142  return -1;
143 
144  if (BucketItem == getTombstoneVal()) {
145  // Ignore tombstones.
146  } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
147  // If the full hash value matches, check deeply for a match. The common
148  // case here is that we are only looking at the buckets (for item info
149  // being non-null and for the full hash value) not at the items. This
150  // is important for cache locality.
151 
152  // Do the comparison like this because NameStart isn't necessarily
153  // null-terminated!
154  char *ItemStr = (char*)BucketItem+ItemSize;
155  if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
156  // We found a match!
157  return BucketNo;
158  }
159  }
160 
161  // Okay, we didn't find the item. Probe to the next bucket.
162  BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
163 
164  // Use quadratic probing, it has fewer clumping artifacts than linear
165  // probing and has good cache behavior in the common case.
166  ++ProbeAmt;
167  }
168 }
169 
170 /// RemoveKey - Remove the specified StringMapEntry from the table, but do not
171 /// delete it. This aborts if the value isn't in the table.
173  const char *VStr = (char*)V + ItemSize;
175  (void)V2;
176  assert(V == V2 && "Didn't find key?");
177 }
178 
179 /// RemoveKey - Remove the StringMapEntry for the specified key from the
180 /// table, returning it. If the key is not in the table, this returns null.
182  int Bucket = FindKey(Key);
183  if (Bucket == -1) return nullptr;
184 
185  StringMapEntryBase *Result = TheTable[Bucket];
186  TheTable[Bucket] = getTombstoneVal();
187  --NumItems;
188  ++NumTombstones;
190 
191  return Result;
192 }
193 
194 /// RehashTable - Grow the table, redistributing values into the buckets with
195 /// the appropriate mod-of-hashtable-size.
196 unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
197  unsigned NewSize;
198  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
199 
200  // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
201  // the buckets are empty (meaning that many are filled with tombstones),
202  // grow/rehash the table.
203  if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
204  NewSize = NumBuckets*2;
205  } else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
206  NumBuckets / 8)) {
207  NewSize = NumBuckets;
208  } else {
209  return BucketNo;
210  }
211 
212  unsigned NewBucketNo = BucketNo;
213  // Allocate one extra bucket which will always be non-empty. This allows the
214  // iterators to stop at end.
215  StringMapEntryBase **NewTableArray =
216  (StringMapEntryBase **)calloc(NewSize+1, sizeof(StringMapEntryBase *) +
217  sizeof(unsigned));
218  unsigned *NewHashArray = (unsigned *)(NewTableArray + NewSize + 1);
219  NewTableArray[NewSize] = (StringMapEntryBase*)2;
220 
221  // Rehash all the items into their new buckets. Luckily :) we already have
222  // the hash values available, so we don't have to rehash any strings.
223  for (unsigned I = 0, E = NumBuckets; I != E; ++I) {
224  StringMapEntryBase *Bucket = TheTable[I];
225  if (Bucket && Bucket != getTombstoneVal()) {
226  // Fast case, bucket available.
227  unsigned FullHash = HashTable[I];
228  unsigned NewBucket = FullHash & (NewSize-1);
229  if (!NewTableArray[NewBucket]) {
230  NewTableArray[FullHash & (NewSize-1)] = Bucket;
231  NewHashArray[FullHash & (NewSize-1)] = FullHash;
232  if (I == BucketNo)
233  NewBucketNo = NewBucket;
234  continue;
235  }
236 
237  // Otherwise probe for a spot.
238  unsigned ProbeSize = 1;
239  do {
240  NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
241  } while (NewTableArray[NewBucket]);
242 
243  // Finally found a slot. Fill it in.
244  NewTableArray[NewBucket] = Bucket;
245  NewHashArray[NewBucket] = FullHash;
246  if (I == BucketNo)
247  NewBucketNo = NewBucket;
248  }
249  }
250 
251  free(TheTable);
252 
253  TheTable = NewTableArray;
254  NumBuckets = NewSize;
255  NumTombstones = 0;
256  return NewBucketNo;
257 }
StringMapImpl(unsigned itemSize)
Definition: StringMap.h:62
static unsigned HashString(StringRef Str, unsigned Result=0)
HashString - Hash function for strings.
Definition: StringExtras.h:129
#define LLVM_UNLIKELY(EXPR)
Definition: Compiler.h:182
#define LLVM_LIKELY(EXPR)
Definition: Compiler.h:181
unsigned RehashTable(unsigned BucketNo=0)
RehashTable - Grow the table, redistributing values into the buckets with the appropriate mod-of-hash...
Definition: StringMap.cpp:196
int FindKey(StringRef Key) const
FindKey - Look up the bucket that contains the specified key.
Definition: StringMap.cpp:130
unsigned LookupBucketFor(StringRef Key)
LookupBucketFor - Look up the bucket that the specified string should end up in.
Definition: StringMap.cpp:73
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
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
unsigned NumItems
Definition: StringMap.h:57
StringMapEntryBase ** TheTable
Definition: StringMap.h:55
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)
NextPowerOf2 - Returns the next power of two (in 64-bits) that is strictly greater than A...
Definition: MathExtras.h:619
unsigned ItemSize
Definition: StringMap.h:59
void RemoveKey(StringMapEntryBase *V)
RemoveKey - Remove the specified StringMapEntry from the table, but do not delete it...
Definition: StringMap.cpp:172
static StringMapEntryBase * getTombstoneVal()
Definition: StringMap.h:104
unsigned NumBuckets
Definition: StringMap.h:56
#define I(x, y, z)
Definition: MD5.cpp:54
unsigned getKeyLength() const
Definition: StringMap.h:45
unsigned NumTombstones
Definition: StringMap.h:58
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
StringMapEntryBase - Shared base class of StringMapEntry instances.
Definition: StringMap.h:39
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:47