For non-point geometry subclasses (points are always valid!) we
now cache the results of a geometry validity check. Subsequent
checks utilise the cached result wherever possible.
Because QgsGeometry/QgsFeature objects are implicitly shared, this
means that we avoid a *lot* of duplicate validity checks as
features and geometries are thrown around during processing model
execution.
All your uses of toUtf8().data() actually just need a const char*
So use constData() that is semantically more correct, and documented
to be faster.
From http://doc.qt.io/qt-5/qbytearray.html#data
"For read-only access, constData() is faster because it never
causes a deep copy to occur."
