faster compile

profile

• clang -ftime-trace would output one json file, that can generate flame graph
• gcc -ftime-report would output the phase time and percent

speed up

do not change the code

1. faster linker lld faster than gnu bsd linker
2. PCH(pre-compiled header) target_precompile_headers(<target> PUBLIC <headers>)
3. cache compile result
   • ccache
   • sccache(cache shareing)
4. unity builds cmake -DCMAKE_UNITY_BUILD=ON when cmake 3.16+
5. LTO (link time optimization) cmake -DLLVM_ENABLE_LTO=Thin for clang
6. PGO(profile guided optimization)

   build clang with cmake -DLLVM_BUILD_INSTRUMENTED=IR
   use this to train the compiler
     - we build some application
     - generate a profraw file
   merge all profraw files with llvm-prodata
   feed output to clang cmake with -DLLVM_PROFDATA_FILE=<path>
   combine with LTO for best results

7. Post link optimization
   • LLVM-BOLT
   • LLVM-Propeller

Grab bag

1. -fvisibility=hidden
2. -fexperimental-new-pass-manager
3. distcc
4. LTO on your code
5. -ftime-trace

bloaty a size profiler for binaries

change the code

1. split one large file into many small file , so that is benefit from parallel compiling
2. PIMPL
3. fwd class instead of include header

reference

• youtube
• cmake3.16 introduce and something