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Only allow PassMode::Direct for aggregates on wasm when using the C ABI #133931

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Merged
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Dec 6, 2024
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Only allow PassMode::Direct for aggregates on wasm when using the C ABI #133931

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30 changes: 20 additions & 10 deletions compiler/rustc_ty_utils/src/abi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -473,20 +473,30 @@ fn fn_abi_sanity_check<'tcx>(
// This really shouldn't happen even for sized aggregates, since
// `immediate_llvm_type` will use `layout.fields` to turn this Rust type into an
// LLVM type. This means all sorts of Rust type details leak into the ABI.
// However wasm sadly *does* currently use this mode so we have to allow it --
// but we absolutely shouldn't let any more targets do that.
// (Also see <https://github.com/rust-lang/rust/issues/115666>.)
// However wasm sadly *does* currently use this mode for it's "C" ABI so we
// have to allow it -- but we absolutely shouldn't let any more targets do
// that. (Also see <https://github.com/rust-lang/rust/issues/115666>.)
//
// The unstable abi `PtxKernel` also uses Direct for now.
// It needs to switch to something else before stabilization can happen.
// (See issue: https://github.com/rust-lang/rust/issues/117271)
assert!(
matches!(&*tcx.sess.target.arch, "wasm32" | "wasm64")
|| matches!(spec_abi, ExternAbi::PtxKernel | ExternAbi::Unadjusted),
"`PassMode::Direct` for aggregates only allowed for \"unadjusted\" and \"ptx-kernel\" functions and on wasm\n\
Problematic type: {:#?}",
arg.layout,
);
//
// And finally the unadjusted ABI is ill specified and uses Direct for all
// args, but unfortunately we need it for calling certain LLVM intrinsics.

match spec_abi {
ExternAbi::Unadjusted => {}
ExternAbi::PtxKernel => {}
ExternAbi::C { unwind: _ }
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Should the C-abi-only aspect also be mentioned in the comment above?

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It could be something like

Suggested change
ExternAbi::C { unwind: _ }
// wasm targets currently implement a dysfunctional C ABI
ExternAbi::C { unwind: _ }

if matches!(&*tcx.sess.target.arch, "wasm32" | "wasm64") => {}
_ => {
panic!(
"`PassMode::Direct` for aggregates only allowed for \"unadjusted\" and \"ptx-kernel\" functions and on wasm\n\
Problematic type: {:#?}",
arg.layout,
);
}
}
}
}
}
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