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Rollup merge of #110706 - scottmcm:transmute_unchecked, r=oli-obk

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Add `intrinsics::transmute_unchecked`

This takes a whole 3 lines in `compiler/` since it lowers to `CastKind::Transmute` in MIR *exactly* the same as the existing `intrinsics::transmute` does, it just doesn't have the fancy checking in `hir_typeck`.

Added to enable experimenting with the request in <https://github.com/rust-lang/rust/pull/106281#issuecomment-1496648190> and because the portable-simd folks might be interested for dependently-sized array-vector conversions.

It also simplifies a couple places in `core`.

See also https://github.com/rust-lang/rust/pull/108442#issuecomment-1474777273, where `CastKind::Transmute` was added having exactly these semantics before the lang meeting (which I wasn't in) independently expressed interest.
This commit is contained in:
Matthias Krüger 2023-04-24 07:53:25 +02:00 • committed by GitHub
commit 3ecae2932c
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7 changed files with 43 additions and 54 deletions
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2
compiler/rustc_mir_transform/src/lower_intrinsics.rs
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@ -221,7 +221,7 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
terminator.kind = TerminatorKind::Goto { target };
}
}
sym::transmute => {
sym::transmute | sym::transmute_unchecked => {
let dst_ty = destination.ty(local_decls, tcx).ty;
let Ok([arg]) = <[_; 1]>::try_from(std::mem::take(args)) else {
span_bug!(