How fast is D compilation compared to C++?

[Krzysztof Jajeśnica]

On Tuesday, 20 September 2022 at 16:13:30 UTC, Ali Çehreli wrote:
> D's CTFE can make D compilation infinitely slow. Let's put 
> anomalous cases aside...
>
> We say D compiles much faster than C++. Does anyone have any 
> measurement or a gut feeling about the same program written in 
> idiomatic C++ vs. idiomatic D? I think it may be 30 seconds vs. 
> 5 seconds. I that a fair guess?
>
> Although a ballpark figure is good enough, precise measurements 
> would be useful as well.
>
> Thank you,
> Ali

Out of curiosity I tried comparing build times for 2 personal 
projects (one written in C++, the other written in D).

The C++ project is ~3k lines of code (including header files) and 
takes ~8s to do a clean debug build with GCC+CMake (~2s for a 
parallel build).

The D project is ~8k lines of code, takes ~1.4s to build with 
DMD+DUB and ~3.6s to build with LDC. Unfortunately DUB seems to 
be much worse than CMake at parallelising the build (or maybe my 
spaghetti is a bit difficult to build in parallel) because 
building with `dub --parallel` takes basically the same amount of 
time.

Both projects are small video games using GLFW+OpenGL and very 
few dependencies beyond that. The D project has 2-3 cases of 
horrible CTFE/template abuse which is absent in the C++ project 
and uses templates a bit more extensively. The C++ project has 
more low level code.

Overall it seems that for single threaded debug builds D compiles 
~15-20 times faster (per line of code) than C++ with DMD and ~5-7 
times faster with LDC.

You should only treat these numbers as very rough estimates, 
since I'm not exactly comparing apples to apples here.