[llvm-commits] CVS: llvm/include/llvm/ADT/DenseMap.h
Chris Lattner
sabre at nondot.org
Tue Feb 6 16:56:15 PST 2007
Changes in directory llvm/include/llvm/ADT:
DenseMap.h updated: 1.16 -> 1.17
---
Log message:
Fix a really subtle bug where the entire hash table could fill with
tombstones, causing subsequent insertions to infinitely loop.
---
Diffs of the changes: (+23 -2)
DenseMap.h | 25 +++++++++++++++++++++++--
1 files changed, 23 insertions(+), 2 deletions(-)
Index: llvm/include/llvm/ADT/DenseMap.h
diff -u llvm/include/llvm/ADT/DenseMap.h:1.16 llvm/include/llvm/ADT/DenseMap.h:1.17
--- llvm/include/llvm/ADT/DenseMap.h:1.16 Sat Feb 3 18:42:41 2007
+++ llvm/include/llvm/ADT/DenseMap.h Tue Feb 6 18:55:59 2007
@@ -28,6 +28,7 @@
//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 @@
BucketT *Buckets;
unsigned NumEntries;
+ unsigned NumTombstones;
DenseMap(const DenseMap &); // not implemented.
public:
explicit DenseMap(unsigned NumInitBuckets = 64) {
@@ -96,6 +98,7 @@
}
}
assert(NumEntries == 0 && "Node count imbalance!");
+ NumTombstones = 0;
}
/// count - Return true if the specified key is in the map.
@@ -129,6 +132,7 @@
TheBucket->second.~ValueT();
TheBucket->first = getTombstoneKey();
--NumEntries;
+ ++NumTombstones;
return true;
}
bool erase(iterator I) {
@@ -136,6 +140,7 @@
TheBucket->second.~ValueT();
TheBucket->first = getTombstoneKey();
--NumEntries;
+ ++NumTombstones;
return true;
}
@@ -150,12 +155,26 @@
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 @@
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 @@
// Double the number of buckets.
NumBuckets <<= 1;
+ NumTombstones = 0;
Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
// Initialize all the keys to EmptyKey.
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