From 488c4932366dcba8f6acf56091bd74ff04c5695b Mon Sep 17 00:00:00 2001 From: Olivier Goffart Date: Tue, 10 Nov 2015 11:04:20 +0100 Subject: QVariant: Avoid a memory allocation with custom types MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- src/corelib/kernel/qvariant.cpp | 13 ++++++++++--- 1 file 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(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; } } -- cgit v1.2.3