Link collection for the Compile C++ faster talk

faster_compiles.md

This is a link collection for the talk I held at stockholm c++ meetup where I talked about how to compile c++ faster.

The slides can be found here: https://docs.google.com/presentation/d/e/2PACX-1vQnImhVyHCiZka4wRmnhISq7O8wl6wvf0zmja2HNsiBDF4l6xBL6fXwFXHjdEpIsvZkiRhNNQBXmNuP/pub?start=false&loop=false&delayms=3000

Our environment

• We are using Conan as our package manager and we talked about this setup in another talk.
• We use LLVM/Clang 8.0.1 as our compiler
• CMake and Ninja is our build system

Easy methods

• Switch linker to gold or lld - With clang you can pass -fuse-ld=gold and -fuse-ld=lld. If you are using gcc you need to update default ld symlink to point to gold instead. See this for an example: https://gist.github.com/daniel-j-h/ed3bf9e5cb458b012b5a
• Precompiled headers with CMake 3.16: target_precompile_headers()
• Cache objects with ccache

Harder methods

• Unity builds in CMake 3.16: CMAKE_UNITY_BUILD=ON
• PMIPL - Restructure your code according to the rules of pointer to implementation.

Make Clang Faster!

• Rebuild clang with LTO, the relevant flag is LLVM_ENABLE_LTO but I think this document is requuired to read more about building llvm/clang: https://llvm.org/docs/CMake.html
• Rebuild clang with PGO. This document gives a good overview: https://llvm.org/docs/HowToBuildWithPGO.html
• Post-link optimizitaion of clang with llvm-bolt and llvm-propeller

Grab bag

• -fvisibility=hidden - https://gcc.gnu.org/wiki/Visibility
• -fexperimental-new-pass-mananger - This should be combined with the Make Clang Faster topic above. Not so experimental any more - google is using it by default for example.
• distcc - distributed compiler
• -ftime-trace get flame graphs for your own code!