Reduce Compilation Times C++

Build system

• cmake -G Ninja

Linkers

• lld much faster than the default linker ld or gold
• -fuse-ld=lld
• mold is even faster than lld

Compiler Caching

• CCache
• ln -s ccache /usr/local/bin/g++

Open Source Tooling

• clang -ftime-trace flag creates a flame chart JSON file of each translation unit
• Open tracing output with chrome://tracing
• ClangBuildAnalyzer parses and summarizes these files
• GCC -ftime-report makes the compiler print some statistics to stderr about the time consumed by each pass when it finishes.

Techniques

• Forward Declarations - <iosfwd>, dedicated headers with forward declarations
• Removing unused includes - https://include-what-you-use.org/, Graphviz
• Splitting Protocol and Implementation - Fundamental Theorem of Software Engineering, PIMPL
• Object Libraries
• Precompiled Headers - since CMake 3.16, headers that are often included bu not changed often, use profiling to determine headers to pre-compile
• Unity Build - since CMake 3.16

Main Takeaways

• Profile your build to determine where to focus your effort
• Forward declarations
• Remove unused includes
• Split Protocol from Implementation
• Merge executables
• Tune precompiled headers
• Unity build and reducing number of files

References

• Reducing C++ Compilation Times Through Good Design - Andrew Pearcy - ACCU 2024
• Ninja Build system
• LLD - The LLVM Linker
• Gold Linker
• ld linker
• mold linker
• Ccache — a fast C/C++ compiler cache
• time-trace: timeline / flame chart profiler for Clang
• Clang command line argument reference
• https://github.com/aras-p/ClangBuildAnalyzer
• GCC Developer Options
• Google C++ Style Guide : Forward Declarations
• https://include-what-you-use.org/
• Graphviz
• CMake CMakeGraphVizOptions
• Fundamental Theorem of Software Engineering
• PIMPL
• CMake target_precompile_headers
• CMake UNITY_BUILD