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Stable hash tag (discriminant) of GenericArg #110622

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merged 1 commit into from
Apr 22, 2023
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Stable hash tag (discriminant) of GenericArg #110622

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28 changes: 0 additions & 28 deletions compiler/rustc_middle/src/ty/impls_ty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,34 +73,6 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::subst::GenericArg<'t
}
}

impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::subst::GenericArgKind<'tcx> {
fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
match self {
// WARNING: We dedup cache the `HashStable` results for `List`
// while ignoring types and freely transmute
// between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
// See `fn mk_type_list` for more details.
//
// We therefore hash types without adding a hash for their discriminant.
//
// In order to make it very unlikely for the sequence of bytes being hashed for
// a `GenericArgKind::Type` to be the same as the sequence of bytes being
// hashed for one of the other variants, we hash some very high number instead
// of their actual discriminant since `TyKind` should never start with anything
// that high.
ty::subst::GenericArgKind::Type(ty) => ty.hash_stable(hcx, hasher),
ty::subst::GenericArgKind::Const(ct) => {
0xF3u8.hash_stable(hcx, hasher);
ct.hash_stable(hcx, hasher);
}
ty::subst::GenericArgKind::Lifetime(lt) => {
0xF5u8.hash_stable(hcx, hasher);
lt.hash_stable(hcx, hasher);
}
}
}
}

// AllocIds get resolved to whatever they point to (to be stable)
impl<'a> HashStable<StableHashingContext<'a>> for mir::interpret::AllocId {
fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
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2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/subst.rs
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Expand Up @@ -48,7 +48,7 @@ const TYPE_TAG: usize = 0b00;
const REGION_TAG: usize = 0b01;
const CONST_TAG: usize = 0b10;

#[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord)]
#[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord, HashStable)]
pub enum GenericArgKind<'tcx> {
Lifetime(ty::Region<'tcx>),
Type(Ty<'tcx>),
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