Improve QUrl constructing performance by making empty URLs have d==0.

One major cost is that QUrl::d is never 0 (even for default
constructor). While this simplifies the code, it has a real
performance impact, since QUrlPrivate is quite expensive to create (14
QString/QByteArray members, plus others). In a simple test of the QML
flickr demo, 1 in 3 QUrlPrivate objects that were created were never
used before being deleted.

According to callgrind, this reduces cost of QUrl+QUrlPrivate by 25%
in the case tested.

Patch-by: Warwick Allison
Reviewed-by: Thiago Macieira

0 files changed, 0 insertions, 0 deletions