[ICE]: place local already assigned to

Code

Run Gankra/abi-cafe@94d3803 on x86_64-pc-windows-msvc

https://github.com/rust-lang/rustc_codegen_cranelift/actions/runs/38254284770/job/114828214547

Error output

error: internal compiler error: /rustc-dev/080cc27146389dbb5c8772c476b1937be9c6110f/compiler/rustc_codegen_ssa\src\mir\block.rs:2482:21: place local already assigned to

Backtrace

thread 'rustc' (8124) panicked at /rustc-dev/080cc27146389dbb5c8772c476b1937be9c6110f/compiler/rustc_codegen_ssa\src\mir\block.rs:2482:21:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_span::macros::ExplicitBug>
   1: rustc_span::macros::bug_impl
   2: <alloc::raw_vec::RawVec<&rustc_codegen_llvm::llvm::ffi::Type>>::grow_one
   3: <hashbrown::raw::RawTable<((&rustc_codegen_llvm::llvm::ffi::Metadata, usize), &rustc_codegen_llvm::llvm::ffi::Metadata)>>::reserve_rehash::<hashbrown::map::make_hasher<(&rustc_codegen_llvm::llvm::ffi::Metadata, usize), &rustc_codegen_llvm::llvm::ffi::Metadata, rustc_hash::FxBuildHasher>::{closure#0}>
   4: <alloc::raw_vec::RawVec<&rustc_codegen_llvm::llvm::ffi::Type>>::grow_one
   5: <rustc_codegen_llvm::back::llvm_backend::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::compile_codegen_unit
   6: <rustc_interface::passes::LintStoreExpandImpl as rustc_expand::base::LintStoreExpand>::pre_expansion_lint
   7: <rustc_codegen_llvm::back::llvm_backend::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
   8: <rustc_interface::queries::Linker>::codegen_and_build_linker
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: please make sure that you have updated to the latest nightly

note: please attach the file at `D:\a\rustc_codegen_cranelift\rustc_codegen_cranelift\build\abi-cafe\rustc-ice-2026-10-12T13_20_42-6808.txt` to your bug report

note: rustc 1.101.0-nightly (080cc2714 2026-10-11) running on x86_64-pc-windows-msvc

note: compiler flags: --crate-type staticlib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: aborting due to 1 previous error; 197 warnings emitted

@Jules-Bertholet

#[repr(C)]
pub struct A { }

unsafe extern "C" {
    fn g(_: A) -> A;
}

 pub unsafe fn f(a: A) -> A {
    g(a)
}

Potentially related to changes from #156112 (cc @Jules-Bertholet)

@rustbot

Smaller:

#[repr(C)]
pub struct A {}

unsafe extern "C" {
    fn g() -> A;
}

pub unsafe fn f() -> A {
    g()
}

Yes, #156112 is the culprit. Apparently rustc_codegen_ssa doesn't support returning a ZST by pointer. I do not know that part of the codebase at all, so no idea how to fix it :(

We are ICEing where we would previously generate a function with the wrong ABI, so I don't think this is too urgent to fix.

@rustbot label A-ABI

Possibly related issue: #161117

Worked around this in rust-lang/rustc_codegen_cranelift@2582170 by ignoring the respective test on MSVC.

Assigning P-high (discussion on Zulip).

@Jules-Bertholet

@Jules-Bertholet @oli-obk would it make sense reverting temporarily #156112?

I don't think so. Again, this isn't "works → ICE", but "silently broken ABI → ICE". If we do revert, it should be a partial revert affecting only return types

@rustbot

understood, thanks (sorry I missed the full context in your previous comment). we can then downgrade to

@rustbot label -p-high p-medium

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[ICE]: place local already assigned to #164207

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tmiasko commented on Oct 12, 2026

Jules-Bertholet commented on Oct 13, 2026

theemathas commented on Oct 13, 2026

bjorn3 commented on Oct 13, 2026

rustbot commented on Oct 13, 2026

apiraino commented on Oct 15, 2026

Jules-Bertholet commented on Oct 15, 2026

apiraino commented on Oct 15, 2026

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