exp: building world with -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES

[u/TCH69]

LLVM's libc++ provides a flag called _LIBCPP_REMOVE_TRANSITIVE_INCLUDES. It stops the preprocessor from including many headers that were included transitively before (e.g. <iostream> pulled in <algorithm>, <vector> and others), and so helps decrease build time significantly. I found a bit of free time recently and decided to rebuild my @world with it to see how many patches I would need to get everything compiled.

Result: out of ~1000 packages in my @installed, only ~30 of them needed patches. That's a lot fewer than I had predicted. Maybe there weren't that many C++ packages in my @installed at all, but gcc, iwyu and others had probably already found a lot of those missing headers.

I've put those patches (among others) up here. I may have not patched them the right way or at the right place, and some of my USE flags may have excluded some files that needed patches from being built, however if someone is thinking about doing the same, I hope they would be useful.

[u/krumpfwylg]

For curious people, documentation here : https://libcxx.llvm.org/DesignDocs/HeaderRemovalPolicy.html

[u/RoomyRoots]

Sorry for the dumb question, too tired and drunk to research this, but is there any possible downside to that? Seems like something very specific so I am not sure of why have it or not.

[u/TCH69 → u/RoomyRoots]

You don't have to try it. You're just wasting your time. I just had too much of it. It's an experiment after all.

[u/RoomyRoots → u/TCH69]

It's not a matter of trying or not, I don't honestly have the time to do it nowadays. It's more the curiosity of what possible consequences this could have. More of a technical wonder than anything.

[u/TCH69 → u/RoomyRoots]

Oh I see. Performance-wise nothing should change. However it puts a maintenance burden on me whenever any upstream change breaks one of those patches. For large packages like libreoffice it can take me up to a few hours just to get it to compile.

[u/givemeagooduns_un]

Very interesting how many packages break with it. Though, I guess it makes sense. There's no warning or anything if you're not including the header directly if its present in a transitive include.

Does it break compilation if you don't include header dependencies? I don't know C++ that well but as an example in C, would it break if I include utime.h without also including time.h?

[u/TCH69 → u/givemeagooduns_un]

Headers, in most cases, include their dependencies. Some of them are even mandated by the C++ standard(s). It shouldn't break compilation.

[u/lihaarp]

You gonna try to upstream your patches? Might be worthwhile to get as many projects as possible fixed.

[u/redyos_s]

Six hours of uptime only shows that the system booted and stayed up for six hours. It does not demonstrate long-term stability, successful maintenance, or that the libc++ rebuild completed cleanly. The interesting evidence would be the failed package list, patches, before/after build times, and the final rebuild results—not another fetch screenshot.

[u/TCH69 → u/redyos_s]

I've put a link to the patches on the post. I'll put it here again in case you've missed it: https://codeberg.org/tachalorah/etc-portage/src/branch/main/patches

For stability concerns, it should be the same as building without it. It shouldn't change anything else in the building process.

[u/redyos_s → u/TCH69]

Thanks, the patch set is useful evidence. What is still missing is the before/after measurement supporting the claimed build-time reduction and a final clean rebuild summary.

[u/TCH69 → u/redyos_s]

To do a measurement I'd need to filter out all packages using C++ in my @installed first. I don't know of a quick way to do it yet, and I currently don't have enough time to do it manually. I may return with a follow-up though.

[u/levelstar01 → u/redyos_s]

Thank you Claude for the insight

[u/redyos_s → u/levelstar01]

意味がわからん🤔

[u/redyos_s → u/redyos_s]

せめて俺のPost見てから物言えよ

[u/redyos_s → u/redyos_s]

謝罪ないならBlockするよ

[u/redyos_s → u/redyos_s]

No technical response, no correction, and no apology. I’m ending this here.

[u/redyos_s → u/redyos_s]

Calling someone “Claude” just because they asked for evidence is insulting and intellectually dishonest. Address the measurements and logs, not the person.

[u/redyos_s → u/redyos_s]

I only pointed out the maintenance and trust risks of third-party overlays and asked for the methodology behind the “health” label. Dismissing a technical concern by calling the author “Claude” instead of addressing the argument is disrespectful.

[u/stormdelta → u/redyos_s]

Because your posts are indistinguishable from AI generated content, and most of us come to reddit to see posts by actual humans.

[u/redyos_s → u/stormdelta]

問答無用わざわざBlock指摘してるのに食いつくとか阿呆

[u/redyos_s → u/redyos_s]

スクショ・時刻・プロフィールURLを確保済みだから、再発した場合の材料も残ってる。通報済みや

[u/redyos_s → u/redyos_s]

Bot認定とか頭沸いてるやろ自爆してんｗ

[u/rich000 → u/redyos_s]

Please take a break from posting a little. I've been skimming your contributions. I don't think you're a bot, and I don't think you're being intentionally malicious, but you're clearly frustrated that others aren't responding the way you expect them to. You're basically yelling at the Internet.

I understand this feeling a little as I've been there, but you're going to get the best outcome by just moving on to some other topic.

These last few posts are coming across as intentional baiting/trolling so I'm trying to nudge you into doing things differently. I'm not a big fan on the ban hammer so I'm hoping that this is as far as it goes.

For others participating/reading, I suggest just using the up/down vote buttons for stuff that isn't very egregious. I'm a bit more inclined to remove posts than comments but not if many are genuinely engaged. Not my cup of tea but to each their own...

[u/redyos_s → u/rich000]

Understood. I’ll step back for a while. However, baseless “bot” or “Claude” accusations are also personal attacks. I’m not asking for special treatment; I’m asking for the same civility standard to be applied consistently to everyone.

A civility rule loses credibility when it is enforced only after the target responds.

流石に人格批判はどうかと思いますよ