Rollup merge of #104898 - oli-obk:group_all_the_things, r=wesleywiser

Put all cached values into a central struct instead of just the stable hash

cc `@nnethercote`

this allows re-use of the type for Predicate without duplicating all the logic for the non-hash cached fields

compiler/rustc_data_structures/src/intern.rs

@@ -4,8 +4,6 @@ use std::hash::{Hash, Hasher};
 use std::ops::Deref;
 use std::ptr;
 
-use crate::fingerprint::Fingerprint;
-
 mod private {
     #[derive(Clone, Copy, Debug)]
     pub struct PrivateZst;
@@ -110,86 +108,5 @@ where
     }
 }
 
-/// A helper type that you can wrap round your own type in order to automatically
-/// cache the stable hash on creation and not recompute it whenever the stable hash
-/// of the type is computed.
-/// This is only done in incremental mode. You can also opt out of caching by using
-/// StableHash::ZERO for the hash, in which case the hash gets computed each time.
-/// This is useful if you have values that you intern but never (can?) use for stable
-/// hashing.
-#[derive(Copy, Clone)]
-pub struct WithStableHash<T> {
-    pub internee: T,
-    pub stable_hash: Fingerprint,
-}
-
-impl<T: PartialEq> PartialEq for WithStableHash<T> {
-    #[inline]
-    fn eq(&self, other: &Self) -> bool {
-        self.internee.eq(&other.internee)
-    }
-}
-
-impl<T: Eq> Eq for WithStableHash<T> {}
-
-impl<T: Ord> PartialOrd for WithStableHash<T> {
-    fn partial_cmp(&self, other: &WithStableHash<T>) -> Option<Ordering> {
-        Some(self.internee.cmp(&other.internee))
-    }
-}
-
-impl<T: Ord> Ord for WithStableHash<T> {
-    fn cmp(&self, other: &WithStableHash<T>) -> Ordering {
-        self.internee.cmp(&other.internee)
-    }
-}
-
-impl<T> Deref for WithStableHash<T> {
-    type Target = T;
-
-    #[inline]
-    fn deref(&self) -> &T {
-        &self.internee
-    }
-}
-
-impl<T: Hash> Hash for WithStableHash<T> {
-    #[inline]
-    fn hash<H: Hasher>(&self, s: &mut H) {
-        if self.stable_hash != Fingerprint::ZERO {
-            self.stable_hash.hash(s)
-        } else {
-            self.internee.hash(s)
-        }
-    }
-}
-
-impl<T: HashStable<CTX>, CTX> HashStable<CTX> for WithStableHash<T> {
-    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        if self.stable_hash == Fingerprint::ZERO || cfg!(debug_assertions) {
-            // No cached hash available. This can only mean that incremental is disabled.
-            // We don't cache stable hashes in non-incremental mode, because they are used
-            // so rarely that the performance actually suffers.
-
-            // We need to build the hash as if we cached it and then hash that hash, as
-            // otherwise the hashes will differ between cached and non-cached mode.
-            let stable_hash: Fingerprint = {
-                let mut hasher = StableHasher::new();
-                self.internee.hash_stable(hcx, &mut hasher);
-                hasher.finish()
-            };
-            if cfg!(debug_assertions) && self.stable_hash != Fingerprint::ZERO {
-                assert_eq!(
-                    stable_hash, self.stable_hash,
-                    "cached stable hash does not match freshly computed stable hash"
-                );
-            }
-            stable_hash.hash_stable(hcx, hasher);
-        } else {
-            self.stable_hash.hash_stable(hcx, hasher);
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests;

compiler/rustc_lint/src/pass_by_value.rs

@@ -10,7 +10,7 @@ declare_tool_lint! {
     /// The `rustc_pass_by_value` lint marks a type with `#[rustc_pass_by_value]` requiring it to
     /// always be passed by value. This is usually used for types that are thin wrappers around
     /// references, so there is no benefit to an extra layer of indirection. (Example: `Ty` which
-    /// is a reference to an `Interned<TyS>`)
+    /// is a reference to an `Interned<TyKind>`)
     pub rustc::PASS_BY_VALUE,
     Warn,
     "pass by reference of a type flagged as `#[rustc_pass_by_value]`",

compiler/rustc_middle/src/arena.rs

@@ -1,3 +1,5 @@
+#![allow(rustc::usage_of_ty_tykind)]
+
 /// This higher-order macro declares a list of types which can be allocated by `Arena`.
 ///
 /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]` where `T` is the type
@@ -89,8 +91,8 @@ macro_rules! arena_types {
             [] hir_id_set: rustc_hir::HirIdSet,
 
             // Interned types
-            [] tys: rustc_data_structures::intern::WithStableHash<rustc_middle::ty::TyS<'tcx>>,
+            [] tys: rustc_type_ir::WithCachedTypeInfo<rustc_middle::ty::TyKind<'tcx>>,
-            [] predicates: rustc_data_structures::intern::WithStableHash<rustc_middle::ty::PredicateS<'tcx>>,
+            [] predicates: rustc_type_ir::WithCachedTypeInfo<rustc_middle::ty::PredicateKind<'tcx>>,
             [] consts: rustc_middle::ty::ConstS<'tcx>,
 
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -103,7 +103,7 @@ impl hash::Hash for Allocation {
 /// Interned types generally have an `Outer` type and an `Inner` type, where
 /// `Outer` is a newtype around `Interned<Inner>`, and all the operations are
 /// done on `Outer`, because all occurrences are interned. E.g. `Ty` is an
-/// outer type and `TyS` is its inner type.
+/// outer type and `TyKind` is its inner type.
 ///
 /// Here things are different because only const allocations are interned. This
 /// means that both the inner type (`Allocation`) and the outer type

compiler/rustc_middle/src/ty/context.rs

@@ -1,5 +1,7 @@
 //! Type context book-keeping.
 
+#![allow(rustc::usage_of_ty_tykind)]
+
 use crate::arena::Arena;
 use crate::dep_graph::{DepGraph, DepKindStruct};
 use crate::hir::place::Place as HirPlace;
@@ -19,15 +21,15 @@ use crate::ty::{
     self, AdtDef, AdtDefData, AdtKind, Binder, BindingMode, BoundVar, CanonicalPolyFnSig,
     ClosureSizeProfileData, Const, ConstS, DefIdTree, FloatTy, FloatVar, FloatVid,
     GenericParamDefKind, InferTy, IntTy, IntVar, IntVid, List, ParamConst, ParamTy,
-    PolyExistentialPredicate, PolyFnSig, Predicate, PredicateKind, PredicateS, ProjectionTy,
+    PolyExistentialPredicate, PolyFnSig, Predicate, PredicateKind, ProjectionTy, Region,
-    Region, RegionKind, ReprOptions, TraitObjectVisitor, Ty, TyKind, TyS, TyVar, TyVid, TypeAndMut,
+    RegionKind, ReprOptions, TraitObjectVisitor, Ty, TyKind, TyVar, TyVid, TypeAndMut, UintTy,
-    UintTy, Visibility,
+    Visibility,
 };
 use crate::ty::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef, UserSubsts};
 use rustc_ast as ast;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_data_structures::intern::{Interned, WithStableHash};
+use rustc_data_structures::intern::Interned;
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
@@ -68,6 +70,7 @@ use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::{Layout, LayoutS, TargetDataLayout, VariantIdx};
 use rustc_target::spec::abi;
 use rustc_type_ir::sty::TyKind::*;
+use rustc_type_ir::WithCachedTypeInfo;
 use rustc_type_ir::{DynKind, InternAs, InternIteratorElement, Interner, TypeFlags};
 
 use std::any::Any;
@@ -137,13 +140,13 @@ pub struct CtxtInterners<'tcx> {
 
     // Specifically use a speedy hash algorithm for these hash sets, since
     // they're accessed quite often.
-    type_: InternedSet<'tcx, WithStableHash<TyS<'tcx>>>,
+    type_: InternedSet<'tcx, WithCachedTypeInfo<TyKind<'tcx>>>,
     const_lists: InternedSet<'tcx, List<ty::Const<'tcx>>>,
     substs: InternedSet<'tcx, InternalSubsts<'tcx>>,
     canonical_var_infos: InternedSet<'tcx, List<CanonicalVarInfo<'tcx>>>,
     region: InternedSet<'tcx, RegionKind<'tcx>>,
     poly_existential_predicates: InternedSet<'tcx, List<PolyExistentialPredicate<'tcx>>>,
-    predicate: InternedSet<'tcx, WithStableHash<PredicateS<'tcx>>>,
+    predicate: InternedSet<'tcx, WithCachedTypeInfo<ty::Binder<'tcx, PredicateKind<'tcx>>>>,
     predicates: InternedSet<'tcx, List<Predicate<'tcx>>>,
     projs: InternedSet<'tcx, List<ProjectionKind>>,
     place_elems: InternedSet<'tcx, List<PlaceElem<'tcx>>>,
@@ -194,15 +197,12 @@ impl<'tcx> CtxtInterners<'tcx> {
                     let stable_hash =
                         self.stable_hash(&flags, sess, definitions, cstore, source_span, &kind);
 
-                    let ty_struct = TyS {
+                    InternedInSet(self.arena.alloc(WithCachedTypeInfo {
-                        kind,
+                        internee: kind,
+                        stable_hash,
                         flags: flags.flags,
                         outer_exclusive_binder: flags.outer_exclusive_binder,
-                    };
+                    }))
-
-                    InternedInSet(
-                        self.arena.alloc(WithStableHash { internee: ty_struct, stable_hash }),
-                    )
                 })
                 .0,
         ))
@@ -246,16 +246,12 @@ impl<'tcx> CtxtInterners<'tcx> {
                     let stable_hash =
                         self.stable_hash(&flags, sess, definitions, cstore, source_span, &kind);
 
-                    let predicate_struct = PredicateS {
+                    InternedInSet(self.arena.alloc(WithCachedTypeInfo {
-                        kind,
+                        internee: kind,
+                        stable_hash,
                         flags: flags.flags,
                         outer_exclusive_binder: flags.outer_exclusive_binder,
-                    };
+                    }))
-
-                    InternedInSet(
-                        self.arena
-                            .alloc(WithStableHash { internee: predicate_struct, stable_hash }),
-                    )
                 })
                 .0,
         ))
@@ -2104,7 +2100,7 @@ macro_rules! sty_debug_print {
                 let shards = tcx.interners.type_.lock_shards();
                 let types = shards.iter().flat_map(|shard| shard.keys());
                 for &InternedInSet(t) in types {
-                    let variant = match t.kind {
+                    let variant = match t.internee {
                         ty::Bool | ty::Char | ty::Int(..) | ty::Uint(..) |
                             ty::Float(..) | ty::Str | ty::Never => continue,
                         ty::Error(_) => /* unimportant */ continue,
@@ -2214,51 +2210,26 @@ impl<'tcx, T: 'tcx + ?Sized> IntoPointer for InternedInSet<'tcx, T> {
 }
 
 #[allow(rustc::usage_of_ty_tykind)]
-impl<'tcx> Borrow<TyKind<'tcx>> for InternedInSet<'tcx, WithStableHash<TyS<'tcx>>> {
+impl<'tcx, T> Borrow<T> for InternedInSet<'tcx, WithCachedTypeInfo<T>> {
-    fn borrow<'a>(&'a self) -> &'a TyKind<'tcx> {
+    fn borrow<'a>(&'a self) -> &'a T {
-        &self.0.kind
+        &self.0.internee
     }
 }
 
-impl<'tcx> PartialEq for InternedInSet<'tcx, WithStableHash<TyS<'tcx>>> {
+impl<'tcx, T: PartialEq> PartialEq for InternedInSet<'tcx, WithCachedTypeInfo<T>> {
-    fn eq(&self, other: &InternedInSet<'tcx, WithStableHash<TyS<'tcx>>>) -> bool {
+    fn eq(&self, other: &InternedInSet<'tcx, WithCachedTypeInfo<T>>) -> bool {
         // The `Borrow` trait requires that `x.borrow() == y.borrow()` equals
         // `x == y`.
-        self.0.kind == other.0.kind
+        self.0.internee == other.0.internee
     }
 }
 
-impl<'tcx> Eq for InternedInSet<'tcx, WithStableHash<TyS<'tcx>>> {}
+impl<'tcx, T: Eq> Eq for InternedInSet<'tcx, WithCachedTypeInfo<T>> {}
 
-impl<'tcx> Hash for InternedInSet<'tcx, WithStableHash<TyS<'tcx>>> {
+impl<'tcx, T: Hash> Hash for InternedInSet<'tcx, WithCachedTypeInfo<T>> {
     fn hash<H: Hasher>(&self, s: &mut H) {
         // The `Borrow` trait requires that `x.borrow().hash(s) == x.hash(s)`.
-        self.0.kind.hash(s)
+        self.0.internee.hash(s)
-    }
-}
-
-impl<'tcx> Borrow<Binder<'tcx, PredicateKind<'tcx>>>
-    for InternedInSet<'tcx, WithStableHash<PredicateS<'tcx>>>
-{
-    fn borrow<'a>(&'a self) -> &'a Binder<'tcx, PredicateKind<'tcx>> {
-        &self.0.kind
-    }
-}
-
-impl<'tcx> PartialEq for InternedInSet<'tcx, WithStableHash<PredicateS<'tcx>>> {
-    fn eq(&self, other: &InternedInSet<'tcx, WithStableHash<PredicateS<'tcx>>>) -> bool {
-        // The `Borrow` trait requires that `x.borrow() == y.borrow()` equals
-        // `x == y`.
-        self.0.kind == other.0.kind
-    }
-}
-
-impl<'tcx> Eq for InternedInSet<'tcx, WithStableHash<PredicateS<'tcx>>> {}
-
-impl<'tcx> Hash for InternedInSet<'tcx, WithStableHash<PredicateS<'tcx>>> {
-    fn hash<H: Hasher>(&self, s: &mut H) {
-        // The `Borrow` trait requires that `x.borrow().hash(s) == x.hash(s)`.
-        self.0.kind.hash(s)
     }
 }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -9,6 +9,8 @@
 //!
 //! ["The `ty` module: representing types"]: https://rustc-dev-guide.rust-lang.org/ty.html
 
+#![allow(rustc::usage_of_ty_tykind)]
+
 pub use self::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeSuperFoldable};
 pub use self::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
 pub use self::AssocItemContainer::*;
@@ -32,7 +34,7 @@ use rustc_ast::node_id::NodeMap;
 use rustc_attr as attr;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_data_structures::intern::{Interned, WithStableHash};
+use rustc_data_structures::intern::Interned;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::tagged_ptr::CopyTaggedPtr;
 use rustc_hir as hir;
@@ -50,6 +52,7 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{ExpnId, Span};
 use rustc_target::abi::{Align, Integer, IntegerType, VariantIdx};
 pub use rustc_target::abi::{ReprFlags, ReprOptions};
+use rustc_type_ir::WithCachedTypeInfo;
 pub use subst::*;
 pub use vtable::*;
 
@@ -445,86 +448,22 @@ pub struct CReaderCacheKey {
     pub pos: usize,
 }
 
-/// Represents a type.
+/// Use this rather than `TyKind`, whenever possible.
-///
-/// IMPORTANT:
-/// - This is a very "dumb" struct (with no derives and no `impls`).
-/// - Values of this type are always interned and thus unique, and are stored
-///   as an `Interned<TyS>`.
-/// - `Ty` (which contains a reference to a `Interned<TyS>`) or `Interned<TyS>`
-///   should be used everywhere instead of `TyS`. In particular, `Ty` has most
-///   of the relevant methods.
-#[derive(PartialEq, Eq, PartialOrd, Ord)]
-#[allow(rustc::usage_of_ty_tykind)]
-pub(crate) struct TyS<'tcx> {
-    /// This field shouldn't be used directly and may be removed in the future.
-    /// Use `Ty::kind()` instead.
-    kind: TyKind<'tcx>,
-
-    /// This field provides fast access to information that is also contained
-    /// in `kind`.
-    ///
-    /// This field shouldn't be used directly and may be removed in the future.
-    /// Use `Ty::flags()` instead.
-    flags: TypeFlags,
-
-    /// This field provides fast access to information that is also contained
-    /// in `kind`.
-    ///
-    /// This is a kind of confusing thing: it stores the smallest
-    /// binder such that
-    ///
-    /// (a) the binder itself captures nothing but
-    /// (b) all the late-bound things within the type are captured
-    ///     by some sub-binder.
-    ///
-    /// So, for a type without any late-bound things, like `u32`, this
-    /// will be *innermost*, because that is the innermost binder that
-    /// captures nothing. But for a type `&'D u32`, where `'D` is a
-    /// late-bound region with De Bruijn index `D`, this would be `D + 1`
-    /// -- the binder itself does not capture `D`, but `D` is captured
-    /// by an inner binder.
-    ///
-    /// We call this concept an "exclusive" binder `D` because all
-    /// De Bruijn indices within the type are contained within `0..D`
-    /// (exclusive).
-    outer_exclusive_binder: ty::DebruijnIndex,
-}
-
-/// Use this rather than `TyS`, whenever possible.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
 #[rustc_diagnostic_item = "Ty"]
 #[rustc_pass_by_value]
-pub struct Ty<'tcx>(Interned<'tcx, WithStableHash<TyS<'tcx>>>);
+pub struct Ty<'tcx>(Interned<'tcx, WithCachedTypeInfo<TyKind<'tcx>>>);
 
 impl<'tcx> TyCtxt<'tcx> {
     /// A "bool" type used in rustc_mir_transform unit tests when we
     /// have not spun up a TyCtxt.
-    pub const BOOL_TY_FOR_UNIT_TESTING: Ty<'tcx> = Ty(Interned::new_unchecked(&WithStableHash {
+    pub const BOOL_TY_FOR_UNIT_TESTING: Ty<'tcx> =
-        internee: TyS {
+        Ty(Interned::new_unchecked(&WithCachedTypeInfo {
-            kind: ty::Bool,
+            internee: ty::Bool,
+            stable_hash: Fingerprint::ZERO,
             flags: TypeFlags::empty(),
             outer_exclusive_binder: DebruijnIndex::from_usize(0),
-        },
+        }));
-        stable_hash: Fingerprint::ZERO,
-    }));
-}
-
-impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TyS<'tcx> {
-    #[inline]
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let TyS {
-            kind,
-
-            // The other fields just provide fast access to information that is
-            // also contained in `kind`, so no need to hash them.
-            flags: _,
-
-            outer_exclusive_binder: _,
-        } = self;
-
-        kind.hash_stable(hcx, hasher)
-    }
 }
 
 impl ty::EarlyBoundRegion {
@@ -535,28 +474,18 @@ impl ty::EarlyBoundRegion {
     }
 }
 
-/// Represents a predicate.
+/// Use this rather than `PredicateKind`, whenever possible.
-///
-/// See comments on `TyS`, which apply here too (albeit for
-/// `PredicateS`/`Predicate` rather than `TyS`/`Ty`).
-#[derive(Debug)]
-pub(crate) struct PredicateS<'tcx> {
-    kind: Binder<'tcx, PredicateKind<'tcx>>,
-    flags: TypeFlags,
-    /// See the comment for the corresponding field of [TyS].
-    outer_exclusive_binder: ty::DebruijnIndex,
-}
-
-/// Use this rather than `PredicateS`, whenever possible.
 #[derive(Clone, Copy, PartialEq, Eq, Hash, HashStable)]
 #[rustc_pass_by_value]
-pub struct Predicate<'tcx>(Interned<'tcx, WithStableHash<PredicateS<'tcx>>>);
+pub struct Predicate<'tcx>(
+    Interned<'tcx, WithCachedTypeInfo<ty::Binder<'tcx, PredicateKind<'tcx>>>>,
+);
 
 impl<'tcx> Predicate<'tcx> {
     /// Gets the inner `Binder<'tcx, PredicateKind<'tcx>>`.
     #[inline]
     pub fn kind(self) -> Binder<'tcx, PredicateKind<'tcx>> {
-        self.0.kind
+        self.0.internee
     }
 
     #[inline(always)]
@@ -631,21 +560,6 @@ impl<'tcx> Predicate<'tcx> {
     }
 }
 
-impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for PredicateS<'tcx> {
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let PredicateS {
-            ref kind,
-
-            // The other fields just provide fast access to information that is
-            // also contained in `kind`, so no need to hash them.
-            flags: _,
-            outer_exclusive_binder: _,
-        } = self;
-
-        kind.hash_stable(hcx, hasher);
-    }
-}
-
 impl rustc_errors::IntoDiagnosticArg for Predicate<'_> {
     fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
         rustc_errors::DiagnosticArgValue::Str(std::borrow::Cow::Owned(self.to_string()))
@@ -1028,7 +942,7 @@ impl<'tcx> Term<'tcx> {
         unsafe {
             match ptr & TAG_MASK {
                 TYPE_TAG => TermKind::Ty(Ty(Interned::new_unchecked(
-                    &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>),
+                    &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::TyKind<'tcx>>),
                 ))),
                 CONST_TAG => TermKind::Const(ty::Const(Interned::new_unchecked(
                     &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>),
@@ -1072,7 +986,7 @@ impl<'tcx> TermKind<'tcx> {
             TermKind::Ty(ty) => {
                 // Ensure we can use the tag bits.
                 assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0);
-                (TYPE_TAG, ty.0.0 as *const WithStableHash<ty::TyS<'tcx>> as usize)
+                (TYPE_TAG, ty.0.0 as *const WithCachedTypeInfo<ty::TyKind<'tcx>> as usize)
             }
             TermKind::Const(ct) => {
                 // Ensure we can use the tag bits.
@@ -2692,8 +2606,7 @@ mod size_asserts {
     use super::*;
     use rustc_data_structures::static_assert_size;
     // tidy-alphabetical-start
-    static_assert_size!(PredicateS<'_>, 48);
+    static_assert_size!(PredicateKind<'_>, 32);
-    static_assert_size!(TyS<'_>, 40);
+    static_assert_size!(WithCachedTypeInfo<TyKind<'_>>, 56);
-    static_assert_size!(WithStableHash<TyS<'_>>, 56);
     // tidy-alphabetical-end
 }

compiler/rustc_middle/src/ty/sty.rs

@@ -1611,7 +1611,7 @@ impl<'tcx> Region<'tcx> {
 impl<'tcx> Ty<'tcx> {
     #[inline(always)]
     pub fn kind(self) -> &'tcx TyKind<'tcx> {
-        &self.0.0.kind
+        &self.0.0
     }
 
     #[inline(always)]

compiler/rustc_middle/src/ty/subst.rs

@@ -6,10 +6,11 @@ use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts};
 use crate::ty::visit::{TypeVisitable, TypeVisitor};
 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
 
-use rustc_data_structures::intern::{Interned, WithStableHash};
+use rustc_data_structures::intern::Interned;
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
 use rustc_serialize::{self, Decodable, Encodable};
+use rustc_type_ir::WithCachedTypeInfo;
 use smallvec::SmallVec;
 
 use core::intrinsics;
@@ -84,7 +85,7 @@ impl<'tcx> GenericArgKind<'tcx> {
             GenericArgKind::Type(ty) => {
                 // Ensure we can use the tag bits.
                 assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0);
-                (TYPE_TAG, ty.0.0 as *const WithStableHash<ty::TyS<'tcx>> as usize)
+                (TYPE_TAG, ty.0.0 as *const WithCachedTypeInfo<ty::TyKind<'tcx>> as usize)
             }
             GenericArgKind::Const(ct) => {
                 // Ensure we can use the tag bits.
@@ -162,7 +163,7 @@ impl<'tcx> GenericArg<'tcx> {
                     &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>),
                 ))),
                 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
-                    &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>),
+                    &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::TyKind<'tcx>>),
                 ))),
                 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
                     &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>),

compiler/rustc_type_ir/src/lib.rs

@@ -19,9 +19,11 @@ use std::mem::discriminant;
 
 pub mod codec;
 pub mod sty;
+pub mod ty_info;
 
 pub use codec::*;
 pub use sty::*;
+pub use ty_info::*;
 
 /// Needed so we can use #[derive(HashStable_Generic)]
 pub trait HashStableContext {}

compiler/rustc_type_ir/src/ty_info.rs

@@ -0,0 +1,122 @@
+use std::{
+    cmp::Ordering,
+    hash::{Hash, Hasher},
+    ops::Deref,
+};
+
+use rustc_data_structures::{
+    fingerprint::Fingerprint,
+    stable_hasher::{HashStable, StableHasher},
+};
+
+use crate::{DebruijnIndex, TypeFlags};
+
+/// A helper type that you can wrap round your own type in order to automatically
+/// cache the stable hash, type flags and debruijn index on creation and
+/// not recompute it whenever the information is needed.
+/// This is only done in incremental mode. You can also opt out of caching by using
+/// StableHash::ZERO for the hash, in which case the hash gets computed each time.
+/// This is useful if you have values that you intern but never (can?) use for stable
+/// hashing.
+#[derive(Copy, Clone)]
+pub struct WithCachedTypeInfo<T> {
+    pub internee: T,
+    pub stable_hash: Fingerprint,
+
+    /// This field provides fast access to information that is also contained
+    /// in `kind`.
+    ///
+    /// This field shouldn't be used directly and may be removed in the future.
+    /// Use `Ty::flags()` instead.
+    pub flags: TypeFlags,
+
+    /// This field provides fast access to information that is also contained
+    /// in `kind`.
+    ///
+    /// This is a kind of confusing thing: it stores the smallest
+    /// binder such that
+    ///
+    /// (a) the binder itself captures nothing but
+    /// (b) all the late-bound things within the type are captured
+    ///     by some sub-binder.
+    ///
+    /// So, for a type without any late-bound things, like `u32`, this
+    /// will be *innermost*, because that is the innermost binder that
+    /// captures nothing. But for a type `&'D u32`, where `'D` is a
+    /// late-bound region with De Bruijn index `D`, this would be `D + 1`
+    /// -- the binder itself does not capture `D`, but `D` is captured
+    /// by an inner binder.
+    ///
+    /// We call this concept an "exclusive" binder `D` because all
+    /// De Bruijn indices within the type are contained within `0..D`
+    /// (exclusive).
+    pub outer_exclusive_binder: DebruijnIndex,
+}
+
+impl<T: PartialEq> PartialEq for WithCachedTypeInfo<T> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.internee.eq(&other.internee)
+    }
+}
+
+impl<T: Eq> Eq for WithCachedTypeInfo<T> {}
+
+impl<T: Ord> PartialOrd for WithCachedTypeInfo<T> {
+    fn partial_cmp(&self, other: &WithCachedTypeInfo<T>) -> Option<Ordering> {
+        Some(self.internee.cmp(&other.internee))
+    }
+}
+
+impl<T: Ord> Ord for WithCachedTypeInfo<T> {
+    fn cmp(&self, other: &WithCachedTypeInfo<T>) -> Ordering {
+        self.internee.cmp(&other.internee)
+    }
+}
+
+impl<T> Deref for WithCachedTypeInfo<T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        &self.internee
+    }
+}
+
+impl<T: Hash> Hash for WithCachedTypeInfo<T> {
+    #[inline]
+    fn hash<H: Hasher>(&self, s: &mut H) {
+        if self.stable_hash != Fingerprint::ZERO {
+            self.stable_hash.hash(s)
+        } else {
+            self.internee.hash(s)
+        }
+    }
+}
+
+impl<T: HashStable<CTX>, CTX> HashStable<CTX> for WithCachedTypeInfo<T> {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        if self.stable_hash == Fingerprint::ZERO || cfg!(debug_assertions) {
+            // No cached hash available. This can only mean that incremental is disabled.
+            // We don't cache stable hashes in non-incremental mode, because they are used
+            // so rarely that the performance actually suffers.
+
+            // We need to build the hash as if we cached it and then hash that hash, as
+            // otherwise the hashes will differ between cached and non-cached mode.
+            let stable_hash: Fingerprint = {
+                let mut hasher = StableHasher::new();
+                self.internee.hash_stable(hcx, &mut hasher);
+                hasher.finish()
+            };
+            if cfg!(debug_assertions) && self.stable_hash != Fingerprint::ZERO {
+                assert_eq!(
+                    stable_hash, self.stable_hash,
+                    "cached stable hash does not match freshly computed stable hash"
+                );
+            }
+            stable_hash.hash_stable(hcx, hasher);
+        } else {
+            self.stable_hash.hash_stable(hcx, hasher);
+        }
+    }
+}