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zapcc C++ compilation speed against gcc 5.4 and clang 3.9

A week ago, I compared the compilation time performance of zapcc against gcc-4.9.3 and clang-3.7. On debug builds, zapcc was about 2 times faster than gcc and 3 times faster than clang. In this post, I'm going to try some more recent compilers, namely gcc 5.4 and clang 3.9 on the same project. If you want more information on zapcc, read the previous posts, this post will concentrate on results.

Again, I use my Expression Template Library (ETL). This is a purely header-only library with lots of templates. I'm going to compile the full test cases.

The results of the two articles are not directly comparable, since they were obtained on two different computers. The one on which the present results are done has a less powerful and only 16Go of RAM compared to the 32Go of RAM of my build machine. Also take into account that that the present results were obtained on a Desktop machine, there can be some perturbations from background tasks.

Just like on the previous results, it does not help using more threads than physical cores, therefore, the results were only computed on up to 4 cores on this machine.

The link time is not taken into account on the results.

Debug build

Let's start with the result of the debug build.

Compiler -j1 -j2 -j4
g++-5.4.0 469s 230s 130s
clang++-3.9 710s 371s 218s
zapcc++ 214s 112s 66s
Speedup VS Clang 3.31 3.31 3.3
Speedup VS GCC 2.19 2.05 1.96

The results are almost the same as the previous test. zapcc is 3.3 times faster to compile than Clang and around 2 times faster than GCC. It seems that GCC 5.4 is a bit faster than GCC 4.9.3 while clang 3.9 is a bit slower than clang 3.7, but nothing terribly significant.

Overall, for debug builds, zapcc can bring a very significant improvement to your compile times.

Release build

Let's see what is the status of Release builds. Since the results are comparable between the numbers of threads, the results here are just for one thread.

This is more time consuming since a lot of optimizations are enabled and more features from ETL are enabled as well.

Compiler -j1
g++-5.4.0 782s
clang++-3.9 960s
zapcc++ 640s
Speedup VS Clang 1.5
Speedup VS GCC 1.22

On a release build, the speedups are much less interesting. Nevertheless, they are still significant. zapcc is still 1.2 times faster than gcc and 1.5 times faster than clang. Then speedup against clang 3.9 is significantly higher than it was on my experiment with clang 3.7, it's possible that clang 3.9 is slower or simply has new optimization passes.


The previous conclusion still holds with modern version of compilers: zapcc is much faster than other compilers on Debug builds of template heavy code. More than 3 times faster than clang-3.9 and about 2 times faster than gcc-5.4. Since it's based on clang, there should not be any issue compiling projects that already compile with a recent clang. Even though the speedups are less interesting on a release build, it is still significantly, especially compared against clang.

I'm really interested in finding out what will be the pricing for zapcc once out of the beta or if they will be able to get even faster!

For the comparison with gcc 4.9.3 and clang 3.7, you can have a look at this article.

If you want more information about zapcc, you can go to the official website of zapcc


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