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c++g++llvmclang++compile-time

Is there a way to make G++/clang++ compile times as fast as MSVC?

For my tests I need to compile some thousand C++ files which have a lot of code in common. Because not all compilers are conformant (or more permissive) I execute all my tests with g++, clang++ and msvc on windows and linux.

To improve compile times I use already precompiled headers for common code. Additionally I wrote a small preprocessor app to allow "unity builds" (combine *.cpp files into a single *.cpp file).

Currently I get the following compile times (random test case):

  • MSVC with PCH: 0.573 secs
  • MSVC without PCH: 5.367 secs

(approx 10 times)

  • Clang with PCH: 5.221 secs
  • Clang without PCH: 7.225 secs

(approx 1.4 times)

  • G++ with PCH: 3.099 secs
  • G++ without PCH: 5.826 secs

(approx 1.9 times)

Unfortunately my code contains a lot of templates / template instantiations which seem to be only "saved" in the Microsoft PCH.

Do you know any way to get similar compile times for g++ and clang++? Do you have any suggestion how to improve my compile times?

Here you can see the chrome/clang trace (-ftime-trace and pch): Clang time trace with precompiled header

Solution

  • I see at least in the current clang trunk that there is some notable progress to improve compile times in combination with templates and precompiled headers / modules.

    Perhaps gcc implements something similar - we will see. But thanks for your comments.