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Fix a really subtle bug where the entire hash table could fill with

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tombstones, causing subsequent insertions to infinitely loop.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33972 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-02-07 00:55:59 +00:00
parent 8e59ea998f
commit 04a3115e61
1 changed files with 23 additions and 2 deletions
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25
include/llvm/ADT/DenseMap.h
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@ -28,6 +28,7 @@ struct DenseMapKeyInfo {
//static bool isPod()
};
// Provide DenseMapKeyInfo for all pointers.
template<typename T>
struct DenseMapKeyInfo<T*> {
static inline T* getEmptyKey() { return (T*)-1; }
@ -51,6 +52,7 @@ class DenseMap {
BucketT *Buckets;
unsigned NumEntries;
unsigned NumTombstones;
DenseMap(const DenseMap &); // not implemented.
public:
explicit DenseMap(unsigned NumInitBuckets = 64) {
@ -96,6 +98,7 @@ public:
}
}
assert(NumEntries == 0 && "Node count imbalance!");
NumTombstones = 0;
}
/// count - Return true if the specified key is in the map.
@ -129,6 +132,7 @@ public:
TheBucket->second.~ValueT();
TheBucket->first = getTombstoneKey();
--NumEntries;
++NumTombstones;
return true;
}
bool erase(iterator I) {
@ -136,6 +140,7 @@ public:
TheBucket->second.~ValueT();
TheBucket->first = getTombstoneKey();
--NumEntries;
++NumTombstones;
return true;
}
@ -150,12 +155,26 @@ public:
private:
BucketT *InsertIntoBucket(const KeyT &Key, const ValueT &Value,
BucketT *TheBucket) {
// If the load of the hash table is more than 3/4, grow it.
if (NumEntries*4 >= NumBuckets*3) {
// If the load of the hash table is more than 3/4, or if fewer than 1/8 of
// the buckets are empty (meaning that many are filled with tombstones),
// grow the table.
//
// The later case is tricky. For example, if we had one empty bucket with
// tons of tombstones, failing lookups (e.g. for insertion) would have to
// probe almost the entire table until it found the empty bucket. If the
// table completely filled with tombstones, no lookup would ever succeed,
// causing infinite loops in lookup.
if (NumEntries*4 >= NumBuckets*3 ||
NumBuckets-(NumEntries+NumTombstones) < NumBuckets/8) {
this->grow();
LookupBucketFor(Key, TheBucket);
}
++NumEntries;
// If we are writing over a tombstone, remember this.
if (TheBucket->first != getEmptyKey())
--NumTombstones;
TheBucket->first = Key;
new (&TheBucket->second) ValueT(Value);
return TheBucket;
@ -218,6 +237,7 @@ private:
void init(unsigned InitBuckets) {
NumEntries = 0;
NumTombstones = 0;
NumBuckets = InitBuckets;
assert(InitBuckets && (InitBuckets & InitBuckets-1) == 0 &&
"# initial buckets must be a power of two!");
@ -234,6 +254,7 @@ private:
// Double the number of buckets.
NumBuckets <<= 1;
NumTombstones = 0;
Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
// Initialize all the keys to EmptyKey.