C++ Optimized Compilation Ways

The very common way we know to compile a C++ program is by running the following command: g++ filename.cpp -o filename Talking in terms of stages of optimized compilation, this method is the basic one — we can say stage 0, also written as: g++ -O0 filename.cpp -o filename There are a few more, from zero to three. Let's talk about these ways of compilation. 1] -O0 : No Optimization (Default) Fast compile time. Every variable gets a real stack slot; nothing gets reordered or removed. 2] -O1 : Basic Optimization Some dead code elimination. Simple register allocation. 3] -O2 : 'Standard' Optimization Register allocation. Dead code elimination. Inlining small functions. Loop unrolling and vectorization. Constant folding/propagation. Does not enable optimizations that trade accuracy/safety for speed. 4] -O3 : More Aggressive than -O2 Sometimes faster, sometimes not. Can hurt cache performance. Other than this, there is also a space-optimization option. 5] -Os : Optimization for Size Instead of Speed The command to use these optimizations is as follows: g++ -O2 filename.cpp -o filename Remember, in -O2 the "O" is a capital letter, not a zero — the same applies to the other optimization levels. If you don't know what's going on, or you just wish to compile C++ files the way developers do, use the following standard command: g++ -O2 filename.cpp -o filename