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QCborValue: optimize the array-to-map conversion

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Yes, this is a cold function, but we can do it in-place if we want to.

Done in three separate passes so the autovectorizer can do its thing, if
it wants to.

Change-Id: I5e52dc5b093c43a3b678fffd16b6eb34d02fc40b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
This commit is contained in:
Thiago Macieira 2021-11-12 13:55:26 -08:00
parent f4d49910be
commit ccea344640
2 changed files with 35 additions and 21 deletions
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1
src/corelib/serialization/qcborarray.h
View File

@ -275,7 +275,6 @@ public:
private:
void detach(qsizetype reserve = 0);
friend QCborContainerPrivate;
friend QCborValue;
friend QCborValueRef;
friend class QJsonPrivate::Variant;

55
src/corelib/serialization/qcborvalue.cpp
View File

@ -2237,19 +2237,36 @@ static bool shouldArrayRemainArray(qint64 key, QCborValue::Type t, QCborContaine
/*!
\internal
*/
static Q_DECL_COLD_FUNCTION QCborMap arrayAsMap(const QCborArray &array)
static void convertArrayToMap(QCborContainerPrivate *&array)
{
if (array.size())
qWarning("Using CBOR array as map forced conversion");
QCborMap map;
for (qsizetype i = array.size(); i-- > 0; ) {
QCborValue entry = array.at(i);
// Ignore padding entries that may have been added to grow the array
// when inserting past its end:
if (!entry.isInvalid())
map[i] = entry;
if (Q_LIKELY(!array || array->elements.isEmpty()))
return;
// The Q_LIKELY and the qWarning mark the rest of this function as unlikely
qWarning("Using CBOR array as map forced conversion");
qsizetype size = array->elements.size();
QCborContainerPrivate *map = QCborContainerPrivate::detach(array, size * 2);
map->elements.resize(size * 2);
// this may be an in-place copy, so we have to do it from the end
auto dst = map->elements.begin();
auto src = array->elements.constBegin();
for (qsizetype i = size - 1; i >= 0; --i) {
Q_ASSERT(src->type != QCborValue::Invalid);
dst[i * 2 + 1] = src[i];
}
return map;
for (qsizetype i = 0; i < size; ++i)
dst[i * 2] = { i, QCborValue::Integer };
// only do this last portion if we're not modifying in-place
for (qsizetype i = 0; src != dst && i < size; ++i) {
if (dst[i * 2 + 1].flags & QtCbor::Element::IsContainer)
dst[i * 2 + 1].container->ref.ref();
}
// update reference counts
assignContainer(array, map);
}
/*!
@ -2276,9 +2293,11 @@ QCborContainerPrivate::findOrAddMapKey(QCborValue &self, KeyType key)
{
// we need a map, so convert if necessary
if (self.isArray())
self = arrayAsMap(self.toArray());
convertArrayToMap(self.container);
else if (!self.isMap())
self = QCborValue(QCborValue::Map);
self.t = QCborValue::Map;
self.n = -1;
QCborValueRef result = findOrAddMapKey<KeyType>(self.container, key);
assignContainer(self.container, result.d);
@ -2291,15 +2310,11 @@ QCborContainerPrivate::findOrAddMapKey(QCborValueRef self, KeyType key)
auto &e = self.d->elements[self.i];
// we need a map, so convert if necessary
if (e.flags & QtCbor::Element::IsContainer) {
if (e.type == QCborValue::Array) {
QCborValue repack = QCborValue(arrayAsMap(QCborArray(*e.container)));
qSwap(e.container, repack.container);
} else if (e.type != QCborValue::Map) {
if (e.type == QCborValue::Array) {
convertArrayToMap(e.container);
} else if (e.type != QCborValue::Map) {
if (e.flags & QtCbor::Element::IsContainer)
e.container->deref();
e.container = nullptr;
}
} else {
e.container = nullptr;
}
e.flags = QtCbor::Element::IsContainer;