QIcon has increased memory usage because pixmaps are not loaded on demand

There is a significant increase of runtime memory consumption of up to 300% more memory when using QIcon in Qt 5.7 compared to Qt 5.2.1.

The documentation says that images for an icon given from a file are loaded on demand, but it seems that this is not the case anymore.

I attaches a zip file with a buildable example that creates a widget containing some comboboxes with the same icons for every item. It has two boolean command line options:

• -i or --icon : use the QIcon constructor
• -p or --pixmap : use the QPixmap constructor
  If you set both, the QIcon constructor will be used, if you set none no icons will be loaded.

I measured the memory usage with the windows task manager. The results are the following:

• QIcon Constructor (-i):
  • Qt 5.2.1: 5740 KB
  • Qt 5.7: 46472 KB
• QPixmap Constructor (-p):
  • Qt 5.2.1: 7184 KB
  • Qt 5.7: 9712 KB
• No Icons (no options):
  • Qt 5.2.1: 4636 KB
  • Qt 5.7: 8096 KB