C++ High Performance

Instruction reordering

To understand the importance of the memory model, we first need some background about how programs we write are actually being executed.

When we write and run a program, it would be reasonable to assume that the instructions in the source code are being executed in the same order as they appear in the source code. This is not true though—the code we write will be optimized in multiple stages before it is finally executed. Both the compiler and the hardware will reorder instructions with the goal of executing the program more efficiently. This is not new technology: compilers have done this for a long time, and this is one reason why an optimized build runs faster than a non-optimized build. The compiler (and hardware) ...