Speed up CI builds with ccache (seeded from develop)

[marcocastignoli]

Depends on #16384

• This PR enables ccache for the main CMake build in CircleCI and stores the cache between runs.
• CircleCI now restores ~/.ccache on most branches from the latest cache produced on develop, so builds can reuse compiled objects.
• Runs on develop start from an empty cache and then save a fresh ~/.ccache snapshot (one per revision) to keep the seed cache updated.
• The build step also resets and prints ccache stats (ccache -z / ccache -s) so we can see cache hits in the logs.

For the purpose of testing instead of creating the cache from develop, the cache is created by this branch ci-ccache. We can later create another PR starting from this branch to see if the builds are indeed using the cache generated by ci-ccache, before merging this PR let's remember to fix the occurrences of ci-ccache in the code.

Results

In this PR, I edited a single file and the CI is successfully using ccache for all build job. These are the results of the speedup:

Job	ccache disabled	ccache enabled	speedup
b_ubu_force_release	10:52	01:02	11×
b_ubu_static_arm	20:55	01:09	18×
b_ubu_min_req	17:25	01:39	11×
b_ubu_ossfuzz	22:05	02:13	10×
b_ubu_min_req_clang	12:15	01:29	8×
b_ubu_clang	12:54	01:32	8×
b_win	23:06	05:47	4×
b_ubu	11:22	00:42	16×
b_ems	07:18	03:15	2×
b_osx	09:25	01:14	8×
b_ubu_static	11:16	00:42	16×
b_archlinux	18:49	01:29	13×

In total we save ~23 minutes (or around 2$) each run.

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[clonker]

won't that very easily break?

[marcocastignoli]

You mean the hard-coded path?

I cannot find a reliable way to find that path.

[clonker]

vswhere.exe might be able to do that for you (or vcvarsall or something)

[marcocastignoli]

This is the solution I found:

https://github.com/argotorg/solidity/pull/16385/changes#diff-269e9853066c3b757fe5118f39a0330b0fa38daa20092bb30657dbf79058f866R19-R25

[clonker]

some preliminary comments. very nice work altogether! i was thinking whether we should perhaps have another environment variable that globally enables or disables ccache entirely. that way, if there are problems, we can quickly switch it off.

[r0qs]

We already have ccache detection in place, I’m wondering whether it would be better to let CMake handle this automatically and remove -DCMAKE_C_COMPILER_LAUNCHER=ccache and -DCMAKE_CXX_COMPILER_LAUNCHER=ccache from here. See: https://github.com/argotorg/solidity/blob/develop/cmake/EthCcache.cmake).

[r0qs]

We would probably need to add set(CMAKE_C_COMPILER_LAUNCHER ${CCACHE}) on the cmake ccache config as well.

[clonker]

I kinda like that it's explicit. Never understood why we need this EthCcache.cmake in the first place.

[r0qs]

Haha sure. We can keep it as it is then, and don't change the cake cmake config.

[clonker]

Never change the cake config

[r0qs]

Suggested change

	- ~/.ccache
	run_with_ccache_unless_tag:
	- ~/.ccache
	run_with_ccache_unless_tag:

[r0qs]

I think that for build.sh and build_ossfuzz.sh we can remove this and let cmake set it. For Windows, it seems that we may need to explicitly set using CMAKE_VS_GLOBALS

[r0qs]

Can this be done by cmake? See: https://github.com/ccache/ccache/wiki/MS-Visual-Studio#usage-with-cmake

Maybe we can add that you our cmake ccache config.

[r0qs]

Since #16385 (comment) is @clonker’s preference, and I don’t have a strong opinion either way, I’m okay with keeping some configurations out of CMake and explicitly defining them in the build scripts.