Analyze configure times with CMake

With clang it is possible to analyze the build times in great detail thanks to -ftime-trace.

But while building a program, the compiler (and linker), are not the only processes that can take a lot of time.

Configuring a project, executing custom scripts for generating code, or simply detecting dependencies between targets, can be time-consuming.

While most pieces of advice written for Clang are also true for CMake (verify if antivirus is interfering, remove dead code, …​), it does not change the fact that it is hard to know in advance how useful they are.

Since cmake 3.18 ^🗄️ CMake supports the switches --profiling-format and --profiling-output.

For most use cases, when configuring a CMake project, adding --profiling-format=google-trace --profiling-output=perfcmake.json as parameters will let CMake generate a file named perfcmake.json.

This file contains a detailed overview of how much time is spent executing the configuration step. As CMake is mostly single-threaded (and it is by design ^🗄️), the data is easy to analyze. This makes it possible to understand where it makes sense to spend some time to try to optimize your configure time.