Using Assembly Language in C/C++

Question

I remember reading somewhere that to really optimize & speed up certain section of the code, programmers write that section in Assembly language. My questions are -

Answer 1

You should read the classic book Zen of Code Optimization and the followup Zen of Graphics Programming by Michael Abrash.

Summarily in the first book he explained how to use assembly programming pushed to the limits. In the followup he explained that programmers should rather use some higher level language like C and only try to optimize very specific spots using assembly, if necessary at all.

One motivation of this change of mind was that he saw that highly optimized programs for one generation of processor could become (somewhat) slow in the next generation of the same processor familly compared to code compiled from a high level language (maybe compiler using new instructions for instance, or performance and behavior of existing ones changing from a processor generation to another).

Another reason is that compilers are quite good and optimize aggressively nowaday, there is usually much more performance to gain working on algorithms that converting C code to assembly. Even for GPU (Graphic Cards processors) programming you can do it with C using cuda or OpenCL.

There are still some (rare) cases when you should/have to use assembly, usually to get very fine control on the hardware. But even in OS kernel code it's usually very small parts and not that much code.