diff options
author | Olivier Goffart <ogoffart@woboq.com> | 2015-11-10 11:04:20 +0100 |
---|---|---|
committer | Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com> | 2018-04-08 08:03:15 +0000 |
commit | 488c4932366dcba8f6acf56091bd74ff04c5695b (patch) | |
tree | 2efc702eb26d7b2f53c536ce9944c5b709f1a2c4 /src/corelib/kernel/qvariant.cpp | |
parent | 800119509837f4dfe3b4de1ecd88938ae6b18b71 (diff) |
QVariant: Avoid a memory allocation with custom types
Store big or un-movable custom type within the same memory region as
the QVariant::PrivateShared.
Makes tst_qvariant::bigClassVariantCreation 33% faster
Change-Id: I60a757d1f0a9a02cf9ac36fb53a72426b2f8cfa8
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>
Diffstat (limited to 'src/corelib/kernel/qvariant.cpp')
-rw-r--r-- | src/corelib/kernel/qvariant.cpp | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/src/corelib/kernel/qvariant.cpp b/src/corelib/kernel/qvariant.cpp index b3a86576af..369405c7cd 100644 --- a/src/corelib/kernel/qvariant.cpp +++ b/src/corelib/kernel/qvariant.cpp @@ -1175,9 +1175,16 @@ static void customConstruct(QVariant::Private *d, const void *copy) type.construct(&d->data.ptr, copy); d->is_shared = false; } else { - void *ptr = type.create(copy); + // Private::Data contains long long, and long double is the biggest standard type. + const size_t maxAlignment = + qMax(Q_ALIGNOF(QVariant::Private::Data), Q_ALIGNOF(long double)); + const size_t s = sizeof(QVariant::PrivateShared); + const size_t offset = s + ((s * maxAlignment - s) % maxAlignment); + void *data = operator new(offset + size); + void *ptr = static_cast<char *>(data) + offset; + type.construct(ptr, copy); d->is_shared = true; - d->data.shared = new QVariant::PrivateShared(ptr); + d->data.shared = new (data) QVariant::PrivateShared(ptr); } } @@ -1186,7 +1193,7 @@ static void customClear(QVariant::Private *d) if (!d->is_shared) { QMetaType::destruct(d->type, &d->data.ptr); } else { - QMetaType::destroy(d->type, d->data.shared->ptr); + QMetaType::destruct(d->type, d->data.shared->ptr); delete d->data.shared; } } |