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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
50 lines
1.2 KiB
Rust
50 lines
1.2 KiB
Rust
// MIR for `main` after built
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| User Type Annotations
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| 0: user_ty: Canonical { value: Ty(Void), max_universe: U0, variables: [], defining_opaque_types: [] }, span: $DIR/issue_72181_1.rs:17:12: 17:16, inferred_ty: Void
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| 1: user_ty: Canonical { value: Ty(Void), max_universe: U0, variables: [], defining_opaque_types: [] }, span: $DIR/issue_72181_1.rs:17:12: 17:16, inferred_ty: Void
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fn main() -> () {
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let mut _0: ();
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let mut _1: !;
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let _2: Void as UserTypeProjection { base: UserType(0), projs: [] };
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let mut _3: ();
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let _4: !;
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let mut _5: Void;
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scope 1 {
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debug v => _2;
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}
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bb0: {
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StorageLive(_2);
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StorageLive(_3);
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_3 = ();
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_2 = std::intrinsics::transmute::<(), Void>(move _3) -> bb4;
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}
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bb1: {
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StorageDead(_3);
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FakeRead(ForLet(None), _2);
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AscribeUserType(_2, o, UserTypeProjection { base: UserType(1), projs: [] });
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StorageLive(_4);
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StorageLive(_5);
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_5 = move _2;
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_4 = f(move _5) -> bb4;
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}
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bb2: {
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StorageDead(_5);
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StorageDead(_4);
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StorageDead(_2);
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unreachable;
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}
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bb3: {
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return;
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}
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bb4 (cleanup): {
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resume;
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}
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}
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