Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

no more transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>> #94841

Closed
wants to merge 2 commits into from
Closed

no more transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>> #94841

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
c004f8c
Revert "safely `transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>>`"
lcnr Mar 11, 2022
0ed0fce
fix fallout
lcnr Mar 11, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
37 changes: 5 additions & 32 deletions compiler/rustc_middle/src/ty/context.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,7 @@ pub struct CtxtInterners<'tcx> {
// Specifically use a speedy hash algorithm for these hash sets, since
// they're accessed quite often.
type_: InternedSet<'tcx, TyS<'tcx>>,
type_list: InternedSet<'tcx, List<Ty<'tcx>>>,
substs: InternedSet<'tcx, InternalSubsts<'tcx>>,
canonical_var_infos: InternedSet<'tcx, List<CanonicalVarInfo<'tcx>>>,
region: InternedSet<'tcx, RegionKind>,
Expand All @@ -123,6 +124,7 @@ impl<'tcx> CtxtInterners<'tcx> {
CtxtInterners {
arena,
type_: Default::default(),
type_list: Default::default(),
substs: Default::default(),
region: Default::default(),
poly_existential_predicates: Default::default(),
Expand Down Expand Up @@ -1670,25 +1672,6 @@ macro_rules! nop_lift {
};
}

// Can't use the macros as we have reuse the `substs` here.
//
// See `intern_type_list` for more info.
impl<'a, 'tcx> Lift<'tcx> for &'a List<Ty<'a>> {
type Lifted = &'tcx List<Ty<'tcx>>;
fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
if self.is_empty() {
return Some(List::empty());
}
if tcx.interners.substs.contains_pointer_to(&InternedInSet(self.as_substs())) {
// SAFETY: `self` is interned and therefore valid
// for the entire lifetime of the `TyCtxt`.
Some(unsafe { mem::transmute::<&'a List<Ty<'a>>, &'tcx List<Ty<'tcx>>>(self) })
} else {
None
}
}
}

macro_rules! nop_list_lift {
($set:ident; $ty:ty => $lifted:ty) => {
impl<'a, 'tcx> Lift<'tcx> for &'a List<$ty> {
Expand All @@ -1713,6 +1696,7 @@ nop_lift! {const_; Const<'a> => Const<'tcx>}
nop_lift! {const_allocation; ConstAllocation<'a> => ConstAllocation<'tcx>}
nop_lift! {predicate; Predicate<'a> => Predicate<'tcx>}

nop_list_lift! {type_list; Ty<'a> => Ty<'tcx>}
nop_list_lift! {poly_existential_predicates; ty::Binder<'a, ExistentialPredicate<'a>> => ty::Binder<'tcx, ExistentialPredicate<'tcx>>}
nop_list_lift! {predicates; Predicate<'a> => Predicate<'tcx>}
nop_list_lift! {canonical_var_infos; CanonicalVarInfo<'a> => CanonicalVarInfo<'tcx>}
Expand Down Expand Up @@ -2203,6 +2187,7 @@ macro_rules! slice_interners {
}

slice_interners!(
type_list: _intern_type_list(Ty<'tcx>),
substs: _intern_substs(GenericArg<'tcx>),
canonical_var_infos: _intern_canonical_var_infos(CanonicalVarInfo<'tcx>),
poly_existential_predicates:
Expand Down Expand Up @@ -2620,19 +2605,7 @@ impl<'tcx> TyCtxt<'tcx> {
}

pub fn intern_type_list(self, ts: &[Ty<'tcx>]) -> &'tcx List<Ty<'tcx>> {
if ts.is_empty() {
List::empty()
} else {
// Actually intern type lists as lists of `GenericArg`s.
//
// Transmuting from `Ty<'tcx>` to `GenericArg<'tcx>` is sound
// as explained in ty_slice_as_generic_arg`. With this,
// we guarantee that even when transmuting between `List<Ty<'tcx>>`
// and `List<GenericArg<'tcx>>`, the uniqueness requirement for
// lists is upheld.
let substs = self._intern_substs(ty::subst::ty_slice_as_generic_args(ts));
substs.try_as_type_list().unwrap()
}
if ts.is_empty() { List::empty() } else { self._intern_type_list(ts) }
}

pub fn intern_substs(self, ts: &[GenericArg<'tcx>]) -> &'tcx List<GenericArg<'tcx>> {
Expand Down
30 changes: 0 additions & 30 deletions compiler/rustc_middle/src/ty/impls_ty.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -61,36 +61,6 @@ 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 intern_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 a `0xFF` byte before hashing
// their discriminant (since the discriminant of `TyKind` is unlikely to ever start
// with 0xFF).
ty::subst::GenericArgKind::Type(ty) => ty.hash_stable(hcx, hasher),
ty::subst::GenericArgKind::Const(ct) => {
0xFFu8.hash_stable(hcx, hasher);
mem::discriminant(self).hash_stable(hcx, hasher);
ct.hash_stable(hcx, hasher);
}
ty::subst::GenericArgKind::Lifetime(lt) => {
0xFFu8.hash_stable(hcx, hasher);
mem::discriminant(self).hash_stable(hcx, hasher);
lt.hash_stable(hcx, hasher);
}
}
}
}

impl<'a> HashStable<StableHashingContext<'a>> for ty::RegionKind {
fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
mem::discriminant(self).hash_stable(hcx, hasher);
Expand Down
39 changes: 1 addition & 38 deletions compiler/rustc_middle/src/ty/subst.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,6 @@ use std::marker::PhantomData;
use std::mem;
use std::num::NonZeroUsize;
use std::ops::ControlFlow;
use std::slice;

/// An entity in the Rust type system, which can be one of
/// several kinds (types, lifetimes, and consts).
Expand All @@ -41,38 +40,13 @@ 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>),
Const(ty::Const<'tcx>),
}

/// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]`
///
/// This is sound as, for types, `GenericArg` is just
/// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as
/// long as we use `0` for the `TYPE_TAG`.
pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] {
assert_eq!(TYPE_TAG, 0);
// SAFETY: the whole slice is valid and immutable.
// `Ty` and `GenericArg` is explained above.
unsafe { slice::from_raw_parts(ts.as_ptr().cast(), ts.len()) }
}

impl<'tcx> List<Ty<'tcx>> {
/// Allows to freely switch betwen `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
///
/// As lists are interned, `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` have
/// be interned together, see `intern_type_list` for more details.
#[inline]
pub fn as_substs(&'tcx self) -> SubstsRef<'tcx> {
assert_eq!(TYPE_TAG, 0);
// SAFETY: `List<T>` is `#[repr(C)]`. `Ty` and `GenericArg` is explained above.
unsafe { &*(self as *const List<Ty<'tcx>> as *const List<GenericArg<'tcx>>) }
}
}

impl<'tcx> GenericArgKind<'tcx> {
#[inline]
fn pack(self) -> GenericArg<'tcx> {
Expand Down Expand Up @@ -234,17 +208,6 @@ pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;

impl<'a, 'tcx> InternalSubsts<'tcx> {
/// Checks whether all elements of this list are types, if so, transmute.
pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
assert_eq!(TYPE_TAG, 0);
// SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
} else {
None
}
}

/// Interpret these substitutions as the substitutions of a closure type.
/// Closure substitutions have a particular structure controlled by the
/// compiler that encodes information like the signature and closure kind;
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/walk.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -178,7 +178,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
| ty::FnDef(_, substs) => {
stack.extend(substs.iter().rev());
}
ty::Tuple(ts) => stack.extend(ts.as_substs().iter().rev()),
ty::Tuple(ts) => stack.extend(ts.iter().map(|ty| ty.into()).rev()),
ty::GeneratorWitness(ts) => {
stack.extend(ts.skip_binder().iter().rev().map(|ty| ty.into()));
}
Expand Down
16 changes: 10 additions & 6 deletions compiler/rustc_traits/src/chalk/lowering.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -329,9 +329,13 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
),
ty::GeneratorWitness(_) => unimplemented!(),
ty::Never => chalk_ir::TyKind::Never,
ty::Tuple(types) => {
chalk_ir::TyKind::Tuple(types.len(), types.as_substs().lower_into(interner))
}
ty::Tuple(types) => chalk_ir::TyKind::Tuple(
types.len(),
chalk_ir::Substitution::from_iter(
interner,
types.iter().map(|ty| ty::subst::GenericArg::from(ty).lower_into(interner)),
),
),
ty::Projection(proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
ty::Opaque(def_id, substs) => {
chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
Expand Down Expand Up @@ -403,9 +407,9 @@ impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
TyKind::Generator(..) => unimplemented!(),
TyKind::GeneratorWitness(..) => unimplemented!(),
TyKind::Never => ty::Never,
TyKind::Tuple(_len, substitution) => {
ty::Tuple(substitution.lower_into(interner).try_as_type_list().unwrap())
}
TyKind::Tuple(_len, substitution) => ty::Tuple(interner.tcx.mk_type_list(
substitution.iter(interner).map(|subst| subst.lower_into(interner).expect_ty()),
)),
TyKind::Slice(ty) => ty::Slice(ty.lower_into(interner)),
TyKind::Raw(mutbl, ty) => ty::RawPtr(ty::TypeAndMut {
ty: ty.lower_into(interner),
Expand Down