Tools

• prefer ninja over make when possible.

• if using make, use the flags -r and -j`nproc`.
  • -r greatly improves “do nothing” build speed.
    When I started using it “do nothing” went from 0.6 seconds to 0.02, eliminating
    an annoying lag when launching via IDE.
    
    
• use LLVM’s LLD linker.
  compiler flag: -fuse-ld=lld
  • if you’re using precompiled headers it only works with Clang’s precompiled headers.
    • if GCC gives you better performance, you can use Clang for development only.
  • if you can’t use LLD, alternatively you can use GOLD linker, which slower than LLD but faster than the default LD.
    compiler flag: -fuse-ld=gold
    
    
• use Clang ThinLTO with caching.
  In my testing it’s faster than not using LTO at all.
  compiler flags: -flto=thin -Wl,--thinlto-cache-dir=...
  • in my project it resulted x2.3 speedup.
    
    
• use -pipe compiler flag.
  make sure you have enough RAM for big projects.

Code

• use forward declarations to move #includes from headers to .cpp files.
  This can help eliminate dependencies and reduce incremental build time.

Hardware

• Fast storage can make compilation several times faster.
  In my experience switching from HDD to SSD resulted ~x10 speedup.

• More cores for parallel builds.

• RAM consumption can scale up with parallel builds, especially when using -pipe.
  I’ve reached ~30GB RAM usage while compiling a medium sized project, with 16c/32t CPU.
  So at least 1GB per CPU thread should be a good heuristic.