Added support ccache for speedup compilation on Linux

[GermanAizek]

@sfan5 more information:
https://ccache.dev/
https://en.wikipedia.org/wiki/Ccache

[wsor4035]

duplicate/alternate of #13111 ? - if nothing else, #11667 should be linked @Zughy

[GermanAizek]

I did not measure CI build speed, I was interested in local build on computer.

[lhofhansl]

A complete rebuild takes 2m12s on my 2019 laptop. Do we really need to add complexity to this?
Not opposed, but at least "neutral".

[Desour]

I've already been using ccache for years (I have /usr/lib/ccache/bin/ in my $PATH), and I consider it essential. Waiting minutes at rebuilding each time you checkout a different branch is awful.
=> I support this.

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Please add a build option to enable this. One might still want to compile without ccache every now and then, e.g. for benchmarking build speed.

[Desour]

duplicate/alternate of #13111 ?

Probably not. The cached build artifacts needs to be stored somewhere, you won't get this without modifying the CI stuff.

[appgurueu]

What's the benefit of making changes to our CMakeLists.txt for this? According to https://github.com/ccache/ccache/wiki/CMake, I can just do -D CMAKE_CXX_COMPILER_LAUNCHER=ccache, and this seems to work just fine; I can switch branches and recompile efficiently.

Maybe we should just recommend ccache in the docs?

[GermanAizek]

What's the benefit of making changes to our CMakeLists.txt for this? According to https://github.com/ccache/ccache/wiki/CMake, I can just do -D CMAKE_CXX_COMPILER_LAUNCHER=ccache, and this seems to work just fine; I can switch branches and recompile efficiently.

Maybe we should just recommend ccache in the docs?

Do you suggest entering -D parameter every time? I think most people will forget.

[appgurueu]

Do you suggest entering -D parameter every time? I think most people will forget.

This is just needed at "configure time", e.g. when invoking cmake. Subsequent make invocations do not require this to be passed. Using ccache should be an explicit choice; it comes at a cost (disk space and, apparently, a minuscule risk of broken builds) and is only really relevant to developers who frequently recompile anyways.

And if people do "forget" to use ccache, it's not much of an issue; their build will just be slightly slower.

(BTW, I removed the linked issue, since that concerned CI, and this PR does not make necessary CI changes.)

[Desour]

A simple -DENABLE_CCACHE=1 is easier than something like -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DCMAKE_C_COMPILER_LAUNCHER=ccache (if you also want to enable it for C files). (And this doesn't even include the sloppiness yet.)

Either way, we should have some doc explaining how one can compile minetest with ccache.

[appgurueu]

A simple -DENABLE_CCACHE=1 is easier than something like -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DCMAKE_C_COMPILER_LAUNCHER=ccache (if you also want to enable it for C files). (And this doesn't even include the sloppiness yet.)

(Nitpick: The C files aren't really relevant for performance. We have only one C file (sha256.c). But it's nice for consistency, I suppose.)

What I like about -DCMAKE_CXX_COMPILER_LAUNCHER=ccache is that it should work for pretty much any CMake C++ project. No need to deal with any project-specific flags there.

Anyways, if it's such a trivial shorthand I wouldn't mind; there is virtually no risk in merging that, though I'd be wary of a default of 1.

Either way, we should have some doc explaining how one can compile minetest with ccache.

Agreed.

[Desour]

The option is still missing.