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Documents that `BikeshedIntrinsicFrom` models transmute-via-union, which is slightly more expressive than the transmute-via-cast implemented by `transmute_copy`. Additionally, we provide an implementation of transmute-via-union as a method on the `BikeshedIntrinsicFrom` trait with additional documentation on the boundary between trait invariants and caller obligations. Whether or not transmute-via-union is the right kind of transmute to model remains up for discussion [1]. Regardless, it seems wise to document the present behavior. [1] https://rust-lang.zulipchat.com/#narrow/stream/216762-project-safe-transmute/topic/What.20'kind'.20of.20transmute.20to.20model.3F/near/426331967
24 lines
594 B
Diff
24 lines
594 B
Diff
- // MIR for `transmute_to_ref_uninhabited` before LowerIntrinsics
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+ // MIR for `transmute_to_ref_uninhabited` after LowerIntrinsics
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fn transmute_to_ref_uninhabited() -> ! {
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let mut _0: !;
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let _1: &Never;
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scope 1 {
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debug x => _1;
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}
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bb0: {
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StorageLive(_1);
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- _1 = std::intrinsics::transmute::<usize, &Never>(const 1_usize) -> [return: bb1, unwind unreachable];
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+ _1 = const 1_usize as &Never (Transmute);
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+ goto -> bb1;
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}
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bb1: {
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PlaceMention((*_1));
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unreachable;
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}
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}
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