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...
