Assorted bootstrap LLVM refactors (part 2/N) by Kobzol · Pull Request #160916 · rust-lang/rust

Kobzol · 2026-08-11T14:49:27Z

Continuation of #160645.

This PR removes dependence on implicit LLVM CI paths, and generally tries to make depending on various LLVM things more explicit wherever possible. One nice outcome of that is that we no longer override the LLVM config during config parsing when using download-ci-llvm 🎉 We also no longer dynamically download LLVM from CI when someone asks what is the LLVM linkage mode, lol (well, we still need to do it in a few places, but now at least it is explicit).

I tried to ensure that x check compiler does not build or even checkout the LLVM submodule. That being said, there might be some cases where calling get_llvm_build_status might now checkout the LLVM submodule (but it shouldn't happen for x test mir-opt --bless, which was fixed in #130918 - that PR introduced a boolean flag, but it was difficult to understand where it should be set to false/true).

The next thing after this is to try getting rid of the llvm_out function, though that will be probably quite painful. And also explicitly depending on the output of LlvmFromCi, rather than reading llvm_ci_mode.

I printed some step traces using commands like this:

BOOTSTRAP_TRACING=STEP=trace BOOTSTRAP_TRACING_SKIP_TIME=1 ./x build compiler 2> post-cg_default-build-compiler.txt

with this PR and on main.

The BOOTSTRAP_TRACING_SKIP_TIME thing was added in the first commit to make it easier to compare step traces. But later I realized that we should also normalize source code locations of the steps, otherwise if you modify something in a given file with the step, its location will change and it will perturb the diff. Anyway, I can drop the first commit if you want.

Best reviewed commit-by-commit (in fact I don't think it can be really reviewed in another way, lol).

r? jieyouxu

rustbot · 2026-08-11T14:49:32Z

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

To make it easier to compare tracing step outputs.

…m CI

This allows explicitly depending on LLVM from CI in other parts of bootstrap.

…ally

…sing

So that the function can run steps.

To avoid implicitly depending on the directory where LLVM CI is extracted.

So that we can later introduce `prebuilt_llvm_config` again, which will never try to checkout the LLVM submodule.

… available Without checking the LLVM submodule.

The `llvm_out_behaviour` test wasn't very useful. It was just depending on LLVM being downloaded from CI, even if it wasn't really.

rustbot · 2026-08-12T19:41:09Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

jieyouxu

Makes sense to me overall, just a few nits
@rustbot author

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jieyouxu · 2026-08-12T08:35:19Z

+        // FIXME: llvm_ci_mode should eventually represent what was used in the config, not the
+        // dynamic value used for determining whether it is actually available.
+        let llvm_ci_mode =
+            if llvm_from_ci { LlvmCiMode::DownloadFromCi } else { LlvmCiMode::BuildLocally };


Remark: hm, right, there's two concerns here:

What LLVM CI mode was requested via config

Whether CI LLVM is actually elligble wrt. the config

Yeah there are even more of those :D

What did you request?

Is it compatible with your config?

Is LLVM CI available for your target?

Is LLVM CI available for your value of assertions?

Is the LLVM target the host target? (if not, download-ci-llvm doesn't do anything right now)

Was it actually possible to download it from the servers?

If you have if-unchanged, do you have local modifications?

rustbot · 2026-08-15T19:20:34Z

rustc-dev-guide is developed in its own repository. If possible, consider making this change to rust-lang/rustc-dev-guide instead.

cc @BoxyUwU, @tshepang

Kobzol · 2026-08-15T19:20:34Z

@rustbot ready

jieyouxu

Thanks
@bors r+ rollup=never note="CI LLVM refactors"

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rust-bors · 2026-08-16T04:21:02Z

📌 Commit a0b57de has been approved by jieyouxu

It is now in the queue for this repository.

rust-bors · 2026-08-16T17:41:30Z

☀️ Test successful - CI
Approved by: jieyouxu
Duration: 3h 7m 17s
Pushing bf063f1 to main...

rustbot added the A-testsuite Area: The testsuite used to check the correctness of rustc label Aug 11, 2026

rustbot assigned jieyouxu Aug 11, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Aug 11, 2026

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Kobzol force-pushed the bootstrap-llvm-2 branch from 7c61c77 to 7caa3d5 Compare August 11, 2026 18:25

Kobzol mentioned this pull request Aug 12, 2026

2026/08/12 -- hrsraiden -- bootstrap: warn when download-ci-llvm is unavailable with assertions #160959

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Kobzol added 19 commits August 12, 2026 21:36

Add environment variable to skip printing time in bootstrap tracing logs

9169785

To make it easier to compare tracing step outputs.

Use LlvmCiMode to distinguish whether LLVM should be downloaded fro…

33271bd

…m CI

Add explicit LlvmFromCi step

8f2c2bb

This allows explicitly depending on LLVM from CI in other parts of bootstrap.

Explicitly store in LlvmOutput whether we should link to it dynamic…

ab49dc4

…ally

Reduce dependency on the Builder::llvm_link_shared function

8ddf956

Store the name of the link-type.txt file in a shared constant

79cf1e7

Add LlvmKind to distinguish how was LLVM provided

adbcc9e

Centralize handling of LLVM linkage mode

f535c14

Only call maybe_download_ci_llvm in try_download_ci_llvm

41f54f7

Stop overriding llvm-config when using download-ci-llvm in config par…

da2de27

…sing

Move llvm_out from Build to Builder

952d4be

So that the function can run steps.

Fix downloading LLVM from CI in dry run

e3a4831

Remove the ci_llvm_root function

b095a44

To avoid implicitly depending on the directory where LLVM CI is extracted.

Rename prebuilt_llvm_config to get_llvm_build_status

653cca2

So that we can later introduce `prebuilt_llvm_config` again, which will never try to checkout the LLVM submodule.

Add prebuilt_llvm_output function to check whether prebuilt LLVM is…

299d6f1

… available Without checking the LLVM submodule.

Fix tracing compilation errors

f8403e5

Fix tests

0896a61

The `llvm_out_behaviour` test wasn't very useful. It was just depending on LLVM being downloaded from CI, even if it wasn't really.

Fix checking of compiler-rt sources in dry run

6b5cad6

Fix Clippy

53bd738

Kobzol force-pushed the bootstrap-llvm-2 branch from 02c1b49 to 53bd738 Compare August 12, 2026 19:41

jieyouxu reviewed Aug 15, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 15, 2026

jieyouxu reviewed Aug 15, 2026

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Comment thread src/bootstrap/src/core/build_steps/llvm.rs

Kobzol added 3 commits August 15, 2026 21:14

Document BOOTSTRAP_TRACING_SKIP_TIME in the rustc-dev-guide

0a92a1f

Rename TracingPrinter field to avoid double negative

6644179

Rename maybe_download_ci_llvm to maybe_download_host_ci_llvm

a0b57de

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 15, 2026

jieyouxu approved these changes Aug 16, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 16, 2026

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rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 16, 2026

rust-bors Bot merged commit bf063f1 into rust-lang:main Aug 16, 2026
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rustbot added this to the 1.100.0 milestone Aug 16, 2026

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