So if you're here, I'm going to take a lucky guess and say you feel shader compilation is slow and you want to speed it up.
Well, I'm happy to say that you're in luck! Speeding up the Shader Compiler is as easy as changing one number, seriously, ONE NUMBER!
I've had this "problem" a few times, I put "problem" in quotes as its actually a feature of the engine! One of the most demanding things is compiling shaders so Shader Compiler is set up to run at a lower priority so it doesn't cause issues with anything else, causing other programs to lag or freeze.
Before we get into it; I wouldn't recommend doing this on a low spec system due to the mentioned reasons. Also; it's only possible on the source version of the engine.
Before I begin, I should mention that I'm doing this on Ubuntu however Windows is the exact same process. I'm not even sure if this does anything on Linux.
3) Open ShaderCompiler.cpp in your favourite text editor, for now, I'm using the default text editor in Ubuntu, and search for "PriorityModifier".
4) As you can see; its set to -1 which is below normal. Increase that to "above normal" which would be 1.
You can set it higher or lower depending on your system performance.
And that's it! Just build the engine again and see a massive improvement in shader compile times. Remember that performance gains will vary from machine to machine. I saw an insane improvement on my main development machine, nearly cutting shader compilation times in half!