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QHash: Return void from QHashPrivate::Data::erase()

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This removes some calculations that are not required in
80% of the cases where d->erase() is being called (as
the return value is ignored). When removing lots of
elements from the hash, the ++it could loop quite a
bit until it found the next valid item in the hash.

This chain of changes combined improve the overall performance of
QHash by 10-50% depending on the operation. Deletes are twice
as fast, reads around 20% faster, inserts around 10% faster.

Task-number: QTBUG-91739
Fixes: QTBUG-98436
Change-Id: I2d82a7c9dd1dd0a4da8402e6d95bfd620caeff3a
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
This commit is contained in:
Lars Knoll 2021-03-15 08:39:51 +01:00 committed by Mårten Nordheim
parent 46dc8e453a
commit 1cc5948839
1 changed files with 11 additions and 9 deletions
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20
src/corelib/tools/qhash.h
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@ -746,21 +746,19 @@ struct Data
return { it.toIterator(this), false };
}
iterator erase(Bucket bucket) noexcept(std::is_nothrow_destructible<Node>::value)
void erase(Bucket bucket) noexcept(std::is_nothrow_destructible<Node>::value)
{
Q_ASSERT(bucket.span->hasNode(bucket.index));
bucket.span->erase(bucket.index);
--size;
Bucket originalBucket = bucket;
// re-insert the following entries to avoid holes
Bucket next = bucket;
while (true) {
next.advanceWrapped(this);
size_t offset = next.offset();
if (offset == SpanConstants::UnusedEntry)
break;
return;
size_t hash = QHashPrivate::calculateHash(next.nodeAtOffset(offset).key, seed);
Bucket newBucket(this, GrowthPolicy::bucketForHash(numBuckets, hash));
while (true) {
@ -781,9 +779,6 @@ struct Data
newBucket.advanceWrapped(this);
}
}
if (originalBucket.toBucketIndex(this) == numBuckets - 1 || originalBucket.isUnused())
return ++(originalBucket.toIterator(this));
return originalBucket.toIterator(this);
}
~Data()
@ -1242,7 +1237,10 @@ public:
iterator i = iterator{d->detachedIterator(it.i)};
typename Data::Bucket bucket(i.i);
return iterator(d->erase(bucket));
d->erase(bucket);
if (bucket.toBucketIndex(d) == d->numBuckets - 1 || bucket.isUnused())
++i;
return i;
}
QPair<iterator, iterator> equal_range(const Key &key)
@ -1880,7 +1878,11 @@ public:
if (i.e == &i.i.node()->value) {
// last remaining entry, erase
typename Data::Bucket bucket(i.i);
i = iterator(d->erase(bucket));
d->erase(bucket);
if (bucket.toBucketIndex(d) == d->numBuckets - 1 || bucket.isUnused())
i = iterator(++iter.i);
else // 'i' currently has a nullptr chain. So, we must recreate it
i = iterator(bucket.toIterator(d));
} else {
i = iterator(++iter.i);
}