`rustc-LLVM ERROR: Cannot select` with `-C code-model=large`

[konstin]

Unfortunately this is far from an MRE, but I wanted to report it anyway in case anyone else has the same problem.

Code

uv in https://github.com/astral-sh/uv at ae880c6d48671fbe84d304d3f86b9666ee89ad54

When compiling in CI in a 32-bit docker container, we were experiencing out-of-memory errors ("rustc-LLVM ERROR: out of memory" - the build was using more than 4GB of RAM), so we tried adding -C code-model=large to reduce the memory usage. Doing so, we instead got an error with llvm internals when compiling the final binary (https://github.com/astral-sh/uv/actions/runs/14040533118/job/39309313189):

# Start a 32-bit docker container
$ docker run -it --rm -v $(pwd):/io quay.io/pypa/manylinux2014_i686:latest
# Install Rust
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
# Compie the program
$ cargo rustc --release --features self-update --bin uv -p uv -- -Ccode-model=large
[...]
rustc-LLVM ERROR: Cannot select: 0x876befa0: i32,ch = load<(load (s64) from jump-table, align 4), sext from i64> 0x99d77300, 0x876bef50, undef:i32
  0x876bef50: i32 = add 0x876be690, 0x876bed70
    0x876be690: i32 = shl 0x876e0910, Constant:i8<3>
      0x876e0910: i32,ch = CopyFromReg 0x99d77300, Register:i32 %27
        0x876beb90: i32 = Register %27
      0x876e01e0: i8 = Constant<3>
    0x876bed70: i32 = add X86ISD::GlobalBaseReg:i32, 0x876be230
      0x876bee10: i32 = X86ISD::GlobalBaseReg
      0x876be230: i32 = X86ISD::Wrapper TargetJumpTable:i32<0> [TF=4]
        0x876e0dc0: i32 = TargetJumpTable<0> [TF=4]
  0x876bea00: i32 = undef
In function: _ZN10axoupdater7release16get_release_list28_$u7b$$u7b$closure$u7d$$u7d$17hf4e3434edf50ffdeE

Meta

rustc --version --verbose:

rustc 1.85.1 (4eb161250 2025-03-15)
binary: rustc
commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181
commit-date: 2025-03-15
host: i686-unknown-linux-gnu
release: 1.85.1
LLVM version: 19.1.7

Error output

rustc-LLVM ERROR: Cannot select: 0x876befa0: i32,ch = load<(load (s64) from jump-table, align 4), sext from i64> 0x99d77300, 0x876bef50, undef:i32
  0x876bef50: i32 = add 0x876be690, 0x876bed70
    0x876be690: i32 = shl 0x876e0910, Constant:i8<3>
      0x876e0910: i32,ch = CopyFromReg 0x99d77300, Register:i32 %27
        0x876beb90: i32 = Register %27
      0x876e01e0: i8 = Constant<3>
    0x876bed70: i32 = add X86ISD::GlobalBaseReg:i32, 0x876be230
      0x876bee10: i32 = X86ISD::GlobalBaseReg
      0x876be230: i32 = X86ISD::Wrapper TargetJumpTable:i32<0> [TF=4]
        0x876e0dc0: i32 = TargetJumpTable<0> [TF=4]
  0x876bea00: i32 = undef
In function: _ZN10axoupdater7release16get_release_list28_$u7b$$u7b$closure$u7d$$u7d$17hf4e3434edf50ffdeE

[moxian]

@rustbot label: +E-needs-mcve +A-llvm +O-x86_32

[moxian]

I am unable to reproduce this with --target i686-pc-windows-msvc
I am also unable to build the project for --target i686-unknown-linux-gnu due to dependencies build script reliant on cc and i686-linux-gnu-gcc being available on the system. I don't have a linux machine available to test there.

@konstin (or anyone with 32-bit system available) the error message points to axoupdater crate. Can you check whether you can reproduce the problem with that, smaller, crate? (Would likely need to build it as a binary, test, or at least as cdylib to invoke that codegen path)

Separately, it would be useful to run something like https://github.com/Noratrieb/cargo-minimize on the codebase to bring it down to a more minimal size that's easier to reason about.

[workingjubilee]

@konstin You probably should first try to skip lto = "fat" on 32-bit: https://github.com/astral-sh/uv/blob/664c77a6e12b4735c0000bbb44f895c892c62aa0/Cargo.toml#L230-L232