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Fix nasty performance bug in rehash() that could lead to rehashing everything into one giant bucket, but only for tables with >256K elements, so we never saw it in regression.

This commit is contained in:
John Coiner 2018-06-13 08:20:19 -04:00
parent 3e739db7fa
commit 8b5dc0b678
1 changed files with 13 additions and 14 deletions
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27
include/verilated_unordered_set_map.h
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@ -180,7 +180,7 @@ private:
// MEMBERS
size_type m_numElements; // Number of entries present.
size_type m_log2Buckets; // Log-base-2 of the number of buckets.
mutable Bucket *m_bucketsp; // Hash table buckets. May be NULL;
mutable Bucket* m_bucketsp; // Hash table buckets. May be NULL;
// // we'll allocate it on the fly when
// // the first entries are created.
Bucket m_emptyBucket; // A fake bucket, used to construct end().
@ -266,10 +266,10 @@ public:
size_type hash = m_hash.operator()(key);
bucketIdxOut = hash & ((VL_ULL(1) << m_log2Buckets) - 1);
initBuckets();
Bucket *bucket = &m_bucketsp[bucketIdxOut];
Bucket* bucketp = &m_bucketsp[bucketIdxOut];
for (typename Bucket::iterator it = bucket->begin();
it != bucket->end(); ++it) {
for (typename Bucket::iterator it = bucketp->begin();
it != bucketp->end(); ++it) {
if (m_equal.operator()(*it, key)) {
return iterator(bucketIdxOut, it, this);
}
@ -346,9 +346,6 @@ public:
}
private:
// numBuckets() and getBucket() are only public so that
// vl_unordered_map can see them. Do not call from outside
// this file.
size_type numBuckets() const { return (VL_ULL(1) << m_log2Buckets); }
Bucket* getBucket(size_type idx) {
@ -356,7 +353,6 @@ private:
return &m_bucketsp[idx];
}
private:
void initBuckets() const {
if (!m_bucketsp) m_bucketsp = new Bucket[numBuckets()];
}
@ -364,16 +360,19 @@ private:
bool needToRehash() const { return ((4 * numBuckets()) < m_numElements); }
void rehash() {
size_type new_log2Buckets = m_log2Buckets << 2;
size_type new_log2Buckets = m_log2Buckets + 2;
size_type new_num_buckets = VL_ULL(1) << new_log2Buckets;
Bucket *new_bucketsp = new Bucket[new_num_buckets];
Bucket* new_bucketsp = new Bucket[new_num_buckets];
for (size_type i=0; i<numBuckets(); i++) {
for (typename Bucket::iterator bit = m_bucketsp[i].begin();
bit != m_bucketsp[i].end(); ++bit) {
while (!m_bucketsp[i].empty()) {
typename Bucket::iterator bit = m_bucketsp[i].begin();
size_type hash = m_hash.operator()(*bit);
size_type new_idx = hash & ((VL_ULL(1) << new_log2Buckets) - 1);
new_bucketsp[new_idx].push_back(*bit);
// Avoid mallocing one list elem and freeing another;
// splice just moves it over.
new_bucketsp[new_idx].splice(new_bucketsp[new_idx].begin(),
m_bucketsp[i], bit);
}
}
@ -442,7 +441,7 @@ template <class Key,
Equal mapEq;
size_type hash = mapHash.operator()(k);
size_type bucketIdxOut = hash & (m_set.numBuckets() - 1);
typename MapSet::Bucket *bucketp = m_set.getBucket(bucketIdxOut);
typename MapSet::Bucket* bucketp = m_set.getBucket(bucketIdxOut);
for (typename MapSet::Bucket::iterator it = bucketp->begin();
it != bucketp->end(); ++it) {