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Prevent infinite growth of SmallMap instances.

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Rehash but don't grow when full of tombstones.

Patch by José Fonseca!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128565 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-03-30 18:32:44 +00:00
parent 414fdbdb01
commit aea4fe2862
2 changed files with 15 additions and 15 deletions
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16
include/llvm/ADT/StringMap.h
View File

@ -81,16 +81,6 @@ protected:
StringMapImpl(unsigned InitSize, unsigned ItemSize); StringMapImpl(unsigned InitSize, unsigned ItemSize);
void RehashTable(); void RehashTable();
/// ShouldRehash - Return true if the table should be rehashed after a new
/// element was recently inserted.
bool ShouldRehash() const {
// If the hash table is now more than 3/4 full, or if fewer than 1/8 of
// the buckets are empty (meaning that many are filled with tombstones),
// grow the table.
return NumItems*4 > NumBuckets*3 ||
NumBuckets-(NumItems+NumTombstones) < NumBuckets/8;
}
/// LookupBucketFor - Look up the bucket that the specified string should end /// LookupBucketFor - Look up the bucket that the specified string should end
/// up in. If it already exists as a key in the map, the Item pointer for the /// up in. If it already exists as a key in the map, the Item pointer for the
/// specified bucket will be non-null. Otherwise, it will be null. In either /// specified bucket will be non-null. Otherwise, it will be null. In either
@ -340,8 +330,7 @@ public:
Bucket.Item = KeyValue; Bucket.Item = KeyValue;
++NumItems; ++NumItems;
if (ShouldRehash()) RehashTable();
RehashTable();
return true; return true;
} }
@ -383,8 +372,7 @@ public:
// filled in by LookupBucketFor. // filled in by LookupBucketFor.
Bucket.Item = NewItem; Bucket.Item = NewItem;
if (ShouldRehash()) RehashTable();
RehashTable();
return *NewItem; return *NewItem;
} }

14
lib/Support/StringMap.cpp
View File

@ -177,7 +177,19 @@ StringMapEntryBase *StringMapImpl::RemoveKey(StringRef Key) {
/// RehashTable - Grow the table, redistributing values into the buckets with /// RehashTable - Grow the table, redistributing values into the buckets with
/// the appropriate mod-of-hashtable-size. /// the appropriate mod-of-hashtable-size.
void StringMapImpl::RehashTable() { void StringMapImpl::RehashTable() {
unsigned NewSize = NumBuckets*2; unsigned NewSize;
// If the hash table is now more than 3/4 full, or if fewer than 1/8 of
// the buckets are empty (meaning that many are filled with tombstones),
// grow/rehash the table.
if (NumItems*4 > NumBuckets*3) {
NewSize = NumBuckets*2;
} else if (NumBuckets-(NumItems+NumTombstones) < NumBuckets/8) {
NewSize = NumBuckets;
} else {
return;
}
// Allocate one extra bucket which will always be non-empty. This allows the // Allocate one extra bucket which will always be non-empty. This allows the
// iterators to stop at end. // iterators to stop at end.
ItemBucket *NewTableArray =(ItemBucket*)calloc(NewSize+1, sizeof(ItemBucket)); ItemBucket *NewTableArray =(ItemBucket*)calloc(NewSize+1, sizeof(ItemBucket));