C++ Build Speed

Recommendation for includes

• Refactor massive header files
• Forward declarations
• Include what you use

Templates recommendation

• Consider whether you need to use template metaprogramming (constexpr, consteval)
• Re-evaluate your API

Why do modules help?

• Eliminate redundant parsing
• Precompiled headers ~ Modules

Translation unit recommendations

• Precompiled headers
• Modules

Dependency Management

• Builds should be purely functional
• Avoid large dependency bottlenecks
• Prefer smaller targets
• Explicitly expressed dependencies enables efficient hardware utilization while maintaining build correctness

Tools

• https://github.com/aras-p/ClangBuildAnalyzer
• https://github.com/nico/ninjatracing
• Perfetto
• https://github.com/google/perfetto

Takeaways

• Profile your builds
• Compilation requires parsing which isn’t free
• Better hardware won’t always save us from ourselves
• We are all stewards of our build times

Reference

• Why Is My C++ Build So Slow? Compilation Profiling and Visualization - Samuel Privett - CppCon 2024
• Code examples
• Clang -ftime-trace