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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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rustbot commented Aug 17, 2026

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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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jieyouxu is currently at their maximum review capacity.
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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Comment thread src/bootstrap/src/core/builder/mod.rs Outdated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
jieyouxu reviewed Aug 18, 2026
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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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@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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The job dist-aarch64-freebsd failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot) 

Caused by:
  process didn't exit successfully: `/checkout/obj/build/aarch64-unknown-linux-gnu/stage2-rustc/release/build/rustc_llvm/8f14eb7a04190b5d/out/build_script_build` (exit status: 1)
  --- stdout
  cargo:rustc-check-cfg=cfg(llvm_component,values("ipo"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("bitreader"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("bitwriter"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("linker"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("asmparser"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("lto"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("coverage"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("instrumentation"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("x86"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("arm"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("aarch64"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("amdgpu"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("avr"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("loongarch"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("m68k"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("csky"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("mips"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("powerpc"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("systemz"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("webassembly"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("msp430"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("sparc"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("nvptx"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("hexagon"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("riscv"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("xtensa"))
  cargo:rustc-check-cfg=cfg(llvm_component,values("bpf"))
  cargo:rerun-if-env-changed=RUST_CHECK
  cargo:rerun-if-env-changed=REAL_LIBRARY_PATH_VAR
  cargo:rerun-if-env-changed=REAL_LIBRARY_PATH
  cargo:rerun-if-env-changed=LLVM_CONFIG
  cargo:rerun-if-changed=/checkout/obj/build/aarch64-unknown-freebsd/llvm/bin/llvm-config


  failed to execute command: "/checkout/obj/build/aarch64-unknown-freebsd/llvm/bin/llvm-config" "--help"
  error: No such file or directory (os error 2)

@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:

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