Further reading

There are several books about specific C++ performance techniques. We already mentioned two:  the slightly older Efficient C++ Performance Programming Techniques by Dov Bulka and David Mayhew (Addison Wesley, 1999) and Optimized C++ by Kurt Guntheroth (O'Reilly, 2013). Both books discuss basic C++ optimizations in more detail than we are doing here and contain a fair number of general performance techniques. There are also example implementations of custom memory management techniques and, in the second book, there are also STL allocators.

There is also a newer book focused more on the recent C++17 language version: C++ High Performance by Viktor Sehr and Björn Andrist (Packt Publishing, 2018). These books focus more on C+ usage in a standard setting, that is, without using Qt. 

The two-part article What Every Programmer Should Know About Compiler Optimizations (2015) by Hadi Brais, available on  https://msdn.microsoft.com/en-us/magazine/dn904673.aspx and https://msdn.microsoft.com/en-us/magazine/dn973015.aspx, discusses some compiler optimization techniques used by Microsoft C++ compiler in more depth.

"Optimizing software in C++: An optimization guide for Windows, Linux and Mac platforms by Agner Fog (2018), available on http://www.agner.org/optimize/optimizing_cpp.pdf, contains an in-depth discussion of general performance, compiler optimizations, and the efficiency of different C++ language constructs.