Notes on using D for performance-efficient code
dmd -O -release -inline -noboundscheck ldc -O5 -release -inline -boundscheck=off gdc -O3 -frelease -finline -fno-bounds-check
0a. Use LDC or GDC
1. Profile first; then optimize. For DMD: dmd -profile; also perf on Linux and AMD CodeAnalyst
2. Do foreach (y; 0 .. height) not foreach(y; (iota(height)))
3. Be careful with foreach on arrays of structs, because it performs copies that are slow if the structs aren't very small.
4. Sometimes in inner loops it's better to use a classic for instead of a foreach.
5. Be careful with classes, because on default their methods are virtual. Sometimes in D you want to use structs for performance reasons. Otherwise make all methods final
6. GC: Minimize situations where there's a lot of allocations going on while the GC is enabled because that will fire up the GC more often than is required and it can slow down your app significantly; A 2x or more performance penalty is certainly possible. It can also make performance unpredictable with large delays at inappropriate points in the execution.