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Assorted bootstrap LLVM refactors (part 3/N) - #161247

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Assorted bootstrap LLVM refactors (part 3/N)#161247
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@Kobzol Kobzol commented Aug 17, 2026 •
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Continuation of #160916.

This PR removes the llvm_out function, and makes it explicit when we need to build the host LLVM.

Before, bootstrap used to just arbitrarily run a llvm-config binary, even though it might not have been executable on the given host. Now, if we need to execute it, the host LLVM will always be explicitly built. It is possible that there are some cases where this will build LLVM where it didn't before, but that should only happen if you were on a target A, built LLVM for target B, and by sheer luck A could execute code for B (where A != B).
In any case, it is now explicit, so if we encounter such situation, we can fix it without depending on implicit assumptions (well, there are still thousands of other assumptions, but you get my point).

After this, I'll work on centralizing the sanity checking of downloading LLVM inside the LlvmFromCi step, which will allow us to log the exact reason why download-ci-llvm might not have been applied, and also enable downloading LLVM from CI for non-host targets.

r? jieyouxu

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

@rustbot rustbot added A-testsuite Area: The testsuite used to check the correctness of rustc 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 17, 2026
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fbstj
fbstj reviewed Aug 17, 2026
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Comment thread src/bootstrap/src/core/builder/mod.rs Outdated
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@Kobzol
Remove the llvm_out function
cf840fa 
And explicitly depend on building the host LLVM when we need to invoke its `llvm-config` binary.
jieyouxu
jieyouxu reviewed Aug 18, 2026
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AFAICT this generally looks good. One question on the test change.

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Comment thread src/bootstrap/src/core/builder/tests.rs Outdated
jieyouxu
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Comment thread src/bootstrap/src/core/build_steps/compile.rs
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jieyouxu approved these changes Aug 18, 2026
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Thanks, r=me after pr ci green
@bors rollup=never note="bootstrap llvm rework just in case"

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@Kobzol Kobzol mentioned this pull request Aug 18, 2026
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Kobzol commented Aug 18, 2026

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@bors r=jieyouxu

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📌 Commit 781ef03 has been approved by jieyouxu

It is now in the queue for this repository.

@rust-bors 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 18, 2026
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JonathanBrouwer commented Aug 19, 2026

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@bors p=6 scheduling

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rust-bors Bot pushed a commit that referenced this pull request Aug 19, 2026
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Auto merge of #161247 - Kobzol:bootstrap-llvm-3, r=jieyouxu
55e7b47 
Assorted bootstrap LLVM refactors (part 3/N)

Continuation of #160916.

This PR removes the `llvm_out` function, and makes it explicit when we need to build the host LLVM.

Before, bootstrap used to just arbitrarily run a `llvm-config` binary, even though it might not have been executable on the given host. Now, if we need to execute it, the host LLVM will always be explicitly built. It is possible that there are some cases where this will build LLVM where it didn't before, but that should only happen if you were on a target A, built LLVM for target B, and by sheer luck A could execute code for B (where A != B).
In any case, it is now explicit, so if we encounter such situation, we can fix it without depending on implicit assumptions (well, there are still thousands of other assumptions, but you get my point).

After this, I'll work on centralizing the sanity checking of downloading LLVM inside the `LlvmFromCi` step, which will allow us to log the exact reason why `download-ci-llvm` might not have been applied, and also enable downloading LLVM from CI for non-host targets.

r? jieyouxu
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@rust-bors rust-bors Bot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 19, 2026
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💔 Test for 55e7b47 failed: CI. Failed job:

@rust-bors rust-bors Bot 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 20, 2026
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Kobzol commented Aug 20, 2026

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@bors try jobs=dist-aarch64-freebsd

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rust-bors Bot pushed a commit that referenced this pull request Aug 20, 2026
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Auto merge of #161247 - Kobzol:bootstrap-llvm-3, r=<try>
969b4ee 
Assorted bootstrap LLVM refactors (part 3/N)


try-job: dist-aarch64-freebsd
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💔 Test for 969b4ee failed: CI. Failed job:

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Kobzol commented Aug 20, 2026

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Hmm, for some reason rustc_llvm was claiming that llvm-config doesn't exist on disk, even though it does. Probably just a wrong error message... In any case, we should be passing the host llvm-config to rustc_llvm, which the last commit does.

@bors try jobs=dist-aarch64-freebsd

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rust-bors Bot pushed a commit that referenced this pull request Aug 20, 2026
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Auto merge of #161247 - Kobzol:bootstrap-llvm-3, r=<try>
66740f0 
Assorted bootstrap LLVM refactors (part 3/N)


try-job: dist-aarch64-freebsd
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💔 Test for 66740f0 failed: CI. Failed job:

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@bors try jobs=dist-aarch64-freebsd

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rust-bors Bot pushed a commit that referenced this pull request Aug 20, 2026
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Auto merge of #161247 - Kobzol:bootstrap-llvm-3, r=<try>
6d78a74 
Assorted bootstrap LLVM refactors (part 3/N)


try-job: dist-aarch64-freebsd
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☀️ Try build successful (CI)
Build commit: 6d78a74 (6d78a745f3fe588cc1054964ebe9d36f5fd0ab1c)
Base parent: f7d782a (f7d782a3be46d6bb4b9792fe69a61db389ba1769)

@Kobzol

Kobzol commented Aug 20, 2026

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Ok, hopefully that did the trick.

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@rustbot 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 20, 2026
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