Added ccache speedup compilation

[GermanAizek]

Description

More effective helped after compilation checkout branches.
More information on https://ccache.dev

• I have read the CONTRIBUTING document.
• I have squashed my commits to have one significant change per commit.
• I have signed my commits before making this PR
• My code follows the code style of this project. See GREP1.md.
• I have updated the documentation where necessary.
• I have added tests to cover my changes, and all previous tests pass.

[willcode]

Please sign your commit (git commit -S --amend) and force push, to acknowledge the DCO (contributor agreement).

[willcode]

What kind of speedup did you see? Was there any speedup on an initial build, or only on subsequent builds?

[GermanAizek]

What kind of speedup did you see? Was there any speedup on an initial build, or only on subsequent builds?

Yep, more effective recompilation after checkout branches.

[willcode]

How much speedup?

Our CI does not have ccache installed, based on the cmake output in the logs. It wouldn't have any effect on CI anyway since that's a single compilation.

[GermanAizek]

How much speedup?

Our CI does not have ccache installed, based on the cmake output in the logs. It wouldn't have any effect on CI anyway since that's a single compilation.

You're right, it doesn't apply to CI, it's convenience for developers.

[marcusmueller]

on most Linux distros where ccache is installed, it does get used automatically:

git clone https://github.com/gnuradio/gnuradio
mkdir gnuradio/build-defaultconfig
cd gnuradio/build-defaultconfig
cmake ..
grep CMAKE_CXX_COMPILER CMakeCache.txt

yields

CMAKE_CXX_COMPILER:FILEPATH=/usr/lib64/ccache/c++
CMAKE_CXX_COMPILER_AR:FILEPATH=/usr/bin/gcc-ar
CMAKE_CXX_COMPILER_RANLIB:FILEPATH=/usr/bin/gcc-ranlib
//ADVANCED property for variable: CMAKE_CXX_COMPILER
CMAKE_CXX_COMPILER-ADVANCED:INTERNAL=1
//ADVANCED property for variable: CMAKE_CXX_COMPILER_AR
CMAKE_CXX_COMPILER_AR-ADVANCED:INTERNAL=1
//ADVANCED property for variable: CMAKE_CXX_COMPILER_RANLIB
CMAKE_CXX_COMPILER_RANLIB-ADVANCED:INTERNAL=1

without any further ado (on Fedora).

You also want to have a definitive way to disable it, as well. I'm not sure on which systems this is actually needed, so I'm kind of sceptical it's generally a good idea; we'd really need a killswitch to disable it in the face of compiler and linker trouble, or when you just don't want to use ccache, because you know this is going to be a modified one-off build.

[marcusmueller]

By the way, @willcode:

Our CI does not have ccache installed, based on the cmake output in the logs. It wouldn't have any effect on CI anyway since that's a single compilation.

Definitely on my to-do list, we could (after adding ccache to the CI builders) have a CI run that we execute once per push to maint-3.10 or main, which then gets pushed as artifact; all the regular CI runs would first download and extract the ccache before running the build.

[willcode]

I've seen it get picked up automatically in the past, too. @GermanAizek ccache is not used automatically on your distro? Which one is that?

I actually stopped using ccache when SSDs first came out and were pretty small, since the cache was always using up a lot of space. Haven't tried it again recently.

[mbr0wn]

I have been also using ccache for almost a decade now with no CMake mods required. I'm not sure how this changeset will work for cases where ccache is available, but not desired (currently, you can simply do CXX=/usr/bin/g++ cmake .....). @GermanAizek what's your dev setup? Fedora/Ubuntu users certainly won't need this, but what system are you on? Maybe we're making things unnecessarily complicated for some OSs.

[willcode]

Unclear whether this is needed on most systems, and DCO (git signoff) missing, so changing to draft for now.

[GermanAizek]

@GermanAizek what's your dev setup? Fedora/Ubuntu users certainly won't need this, but what system are you on? Maybe we're making things unnecessarily complicated for some OSs.

Debian and FreeBSD

[marcusmueller]

Debian? Interesting! So, we're now a bit on a crossroads:

1. We change nothing, and ccache is opt-in on debian, and opt-out on Fedora, Ubuntu, it seems, through setting -DCMAKE_CXX_COMPILER_LAUNCHER (to empty string to opt out and to ccache to opt in)
2. We generally adopt the direction of the PR, and fix the PR to at least honor an already defined CMAKE_CXX_COMPILER_LAUNCHER, even and especially when set to empty, thus making ccache opt-out.

In both cases the current form of the PR isn't going to get us where we want!

[marcusmueller]

Sorry, won't do; this needs to respect an already defined CMAKE_{LANGUAGE}_COMPILER_LAUNCHER