The Fed says this is a cube of $1M. They're off by half a million (calvin.sh)

Thanks to author for doing some solid work in providing data points for modules. For those like me looking for the headline metric, here it is in the conclusion

  While the evidence shown above is pretty clear that building a software package as a module provides the claimed benefits in terms of compile time (a reduction by around 10%, see Section 5.1.1) and perhaps better code structure (Section 5.1.4), the data shown in Section 5.1.2 also make clear that the effect on compile time of downstream projects is at best unclear.

So, alas, underwhelming in this iteration and perhaps speaks to 'module-fication' of existing source code (deal.II, dates from the '90s I believe), rather than doing it from scratch. More work might be needed in structuring the source code into modules as I have known good speedup with just pch, forward decls etc. (more than 10%). Good data point and rich analysis, nevertheless.

trostaft · 1h ago

Oh, it’s Wolfgang. In computational math, he has a focus on research software that few others are able to do, he (the deal.ii team more generally) got an award for it last SIAMCSE. Generally a great writer, looking forward to reading this.

Asooka · 1h ago

I would like to see a comparison between modules and precompiled headers. I have a suspicion that using precompiled headers could provide the same build time gains with much less work.

w4rh4wk5 · 35m ago

From my experience, compile times ain't an issue if you pay a little attention. Precompiled header, thoughtful forward declarations, and not abusing templates get you a long way.

We are commonly working with games that come with a custom engine and tooling. Compiling everything from scratch (around 1M lines of modern C++ code) takes about 30-40 seconds on my desktop. Rebuilding 1 source file + linking comes in typically under 2 seconds (w/o LTO). We might get this even lower by introducing unity builds, but there's no need for that right now.

ttoinou · 19m ago

40 seconds for 1M lines seems super fast, do you have a fast computer and/or did you spend a lot of time optimizing the compilation pipeline ?

vblanco · 5m ago

The modern cryengine compiles very fast. Their trick is that they have architected everything to go through interfaces that are on very thin headers, and thus their headers end very light and they dont compile the class properties over and over. But its a shame we need to do tricks like this for compile speed as they harm runtime performance.

dataflow · 40m ago

Precompiled headers are generally better for system/3rd-party headers. Module are better than PCHs for headers you own, although in some cases you may be better off not using them at all. (I say these because the benefit depends on the frequency with which you need to recompile them, and the relative coupling etc.) Depending on how heavy each one is in your codebase, and how often you modify global build settings, you may have a different experience. And neither is a substitute for keeping headers lightweight and decoupled.

pjmlp · 1h ago

As per Office team, modules are much faster, especially if you also make use of C++ standard library as module, available since C++23.

See VC++ devblogs and CppCon/C++Now talks from the team.

Pre-compiled headers have only worked well on Windows, and OS/2 back in the day.

For whatever reason UNIX compilers never had a great implementation of it.

With exception of clang header maps, which is anyway one of the first approaches to C++ modules.