bjoernager/rust
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Lower discriminant_value intrinsic

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This allows const propagation to evaluate comparisons involving
field-less enums using derived implementations of `PartialEq` (after
inlining `eq`).
This commit is contained in:
Tomasz Miąsko 2020-12-11 00:00:00 +00:00
parent d32c320d7e
commit 686237c49a
5 changed files with 191 additions and 6 deletions
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39
compiler/rustc_middle/src/ty/sty.rs
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@ -2213,13 +2213,44 @@ impl<'tcx> TyS<'tcx> {
}
/// Returns the type of the discriminant of this type.
pub fn discriminant_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
pub fn discriminant_ty(&'tcx self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
match self.kind() {
ty::Adt(adt, _) if adt.is_enum() => adt.repr.discr_type().to_ty(tcx),
ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
_ => {
// This can only be `0`, for now, so `u8` will suffice.
tcx.types.u8
ty::Param(_) | ty::Projection(_) | ty::Opaque(..) | ty::Infer(ty::TyVar(_)) => {
let assoc_items =
tcx.associated_items(tcx.lang_items().discriminant_kind_trait().unwrap());
let discriminant_def_id = assoc_items.in_definition_order().next().unwrap().def_id;
tcx.mk_projection(discriminant_def_id, tcx.mk_substs([self.into()].iter()))
}
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(..)
| ty::Foreign(_)
| ty::Str
| ty::Array(..)
| ty::Slice(_)
| ty::RawPtr(_)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Dynamic(..)
| ty::Closure(..)
| ty::GeneratorWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Error(_)
| ty::Infer(IntVar(_) | FloatVar(_)) => tcx.types.u8,
ty::Bound(..)
| ty::Placeholder(_)
| ty::Infer(FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
bug!("`discriminant_ty` applied to unexpected type: {:?}", self)
}
}
}