The LLVM we ship in rust-dev doesn't match the LLVM we ship in the rustc component

I tried this code:

; rustc +stage2 --print=target-spec-json --target loongarch64-unknown-linux-gnu -Zunstable-options

I expected to see this happen: rustc prints the target spec successfully, because it knows it exists:

; rustc +stage2 --print=target-list | grep loong
loongarch64-unknown-linux-gnu

Instead, this happened: rustc fails to load the LLVM specification:

; rustc +stage2 --print=target-spec-json --target loongarch64-unknown-linux-gnu -Zunstable-options
error: could not create LLVM TargetMachine for triple: loongarch64-unknown-linux-gnu: No available targets are compatible with triple "loongarch64-unknown-linux-gnu"

Note that this is different from the error we emit for an unrecognized target:

; rustc +stage2 --print=target-spec-json --target unknown -Zunstable-options
error: Error loading target specification: Could not find specification for target "unknown". Run `rustc --print target-list` for a list of built-in targets

Also, this only happens for local builds, because we don't use the LLVM in the rust-dev component in rustup, only when building rustc from source.

... wtf ???

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HEAD is branched from ce1073b

@zhaixiaojuan

cc @zhaixiaojuan @heiher, do you know what could be going wrong here?

@jyn514

@jyn514 Thank you for bringing this to my attention. It is possible that the locally builds has enabled llvm.download-ci-llvm, and that prebuilt LLVM does not support LoongArch architecture. It would be great if you could provide specific steps to reproduce. Thank you.

Yes, that's exactly what's happened, I have download-ci-llvm enabled and the prebuilt LLVM differs.

Here's steps to reproduce:

rm config.toml  # download-ci-llvm is on by default
x build --stage 0 rustc
build/host/stage1/bin/rustc --print=target-spec-json --target loongarch64-unknown-linux-gnu -Zunstable-options

The RustDev component builds LLVM here:

rust/src/bootstrap/dist.rs

Line 2239 in 276fa29

builder.ensure(crate::llvm::Llvm { target });

but I'm not sure how that differs from the Rustc component?

rust/src/bootstrap/dist.rs

Lines 456 to 461 in 276fa29

    
           // Copy libLLVM.so to the lib dir as well, if needed. While not 
        
           // technically needed by rustc itself it's needed by lots of other 
        
           // components like the llvm tools and LLD. LLD is included below and 
        
           // tools/LLDB come later, so let's just throw it in the rustc 
        
           // component for now. 
        
           maybe_install_llvm_runtime(builder, host, image);

I think the difference is that the llvm.targets of ci-llvm does not contain LoongArch, but locally it does. Is it time to update ci-llvm?

Maybe need to bump download-ci-llvm-stamp to pick up the LoongArch enablement?

Rollup merge of rust-lang#110490 - jyn514:bump-llvm, r=nikic

@jyn514

@jyn514 @nikic Thank you for catching that. I was mistaken to think that the cached prebuilt ci-llvm would automatically update over time.

@heiher

@heiher no worries :) it updates every six weeks when we make a new release, or if the submodule is updated, but it's cached until then so it's not constantly re-uploaded on every change to bootstrap.

Is there any way CI could help prevent such problems? Like, complain if compiler/rustc_llvm gets changed but the stamp file does not, or something like that?

@RalfJung

@RalfJung we can use heuristics, but they're only heuristics and I wouldn't want to fail CI on them. That said, having rustbot leave a comment if you touch rustc_llvm or src/bootstrap/llvm.rs seems reasonable, so the PR author can make a judgement call but also doesn't forget about the stamp.

Rollup merge of rust-lang#112619 - jyn514:llvm-reminder, r=Mark-Simul…

Rollup merge of #112619 - jyn514:llvm-reminder, r=Mark-Simulacrum

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The LLVM we ship in `rust-dev` doesn't match the LLVM we ship in the `rustc` component #110474

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	// Copy libLLVM.so to the lib dir as well, if needed. While not
	// technically needed by rustc itself it's needed by lots of other
	// components like the llvm tools and LLD. LLD is included below and
	// tools/LLDB come later, so let's just throw it in the rustc
	// component for now.
	maybe_install_llvm_runtime(builder, host, image);

The LLVM we ship in rust-dev doesn't match the LLVM we ship in the rustc component #110474

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jyn514 commented on Apr 18, 2023

heiher commented on Apr 18, 2023

jyn514 commented on Apr 18, 2023

jyn514 commented on Apr 18, 2023

heiher commented on Apr 18, 2023

nikic commented on Apr 18, 2023

heiher commented on Apr 18, 2023

jyn514 commented on Apr 18, 2023

RalfJung commented on Apr 20, 2023

jyn514 commented on Apr 20, 2023

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The LLVM we ship in `rust-dev` doesn't match the LLVM we ship in the `rustc` component #110474