Auto merge of #118189 - compiler-errors:cache-flags-for-const, r=nnethercote

Cache flags for `ty::Const`

Not sure if this has been attempted yet, but worth a shot. It does make the code simpler in `rustc_type_ir`, since we can assume that consts have a `flags` method that is no-cost.

r? `@ghost`

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -9,7 +9,6 @@ use crate::infer::canonical::{
     Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, OriginalQueryValues,
 };
 use crate::infer::InferCtxt;
-use rustc_middle::ty::flags::FlagComputation;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::GenericArg;
 use rustc_middle::ty::{self, BoundVar, InferConst, List, Ty, TyCtxt, TypeFlags, TypeVisitableExt};
@@ -550,8 +549,11 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
             _ => {}
         }
 
-        let flags = FlagComputation::for_const(ct);
-        if flags.intersects(self.needs_canonical_flags) { ct.super_fold_with(self) } else { ct }
+        if ct.flags().intersects(self.needs_canonical_flags) {
+            ct.super_fold_with(self)
+        } else {
+            ct
+        }
     }
 }
 

compiler/rustc_middle/src/arena.rs

@@ -94,7 +94,7 @@ macro_rules! arena_types {
 
             // Interned types
             [] tys: rustc_type_ir::WithCachedTypeInfo<rustc_middle::ty::TyKind<'tcx>>,
-            [] consts: rustc_middle::ty::ConstData<'tcx>,
+            [] consts: rustc_type_ir::WithCachedTypeInfo<rustc_middle::ty::ConstData<'tcx>>,
 
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,
             // since we need to allocate this type on both the `rustc_hir` arena

compiler/rustc_middle/src/ty/consts.rs

@@ -7,6 +7,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::LocalDefId;
 use rustc_macros::HashStable;
+use rustc_type_ir::{TypeFlags, WithCachedTypeInfo};
 
 mod int;
 mod kind;
@@ -23,7 +24,7 @@ use super::sty::ConstKind;
 /// Use this rather than `ConstData`, whenever possible.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
 #[rustc_pass_by_value]
-pub struct Const<'tcx>(pub(super) Interned<'tcx, ConstData<'tcx>>);
+pub struct Const<'tcx>(pub(super) Interned<'tcx, WithCachedTypeInfo<ConstData<'tcx>>>);
 
 /// Typed constant value.
 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
@@ -46,6 +47,16 @@ impl<'tcx> Const<'tcx> {
         self.0.kind.clone()
     }
 
+    #[inline]
+    pub fn flags(self) -> TypeFlags {
+        self.0.flags
+    }
+
+    #[inline]
+    pub fn outer_exclusive_binder(self) -> ty::DebruijnIndex {
+        self.0.outer_exclusive_binder
+    }
+
     #[inline]
     pub fn new(tcx: TyCtxt<'tcx>, kind: ty::ConstKind<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
         tcx.mk_ct_from_kind(kind, ty)

compiler/rustc_middle/src/ty/context.rs

@@ -151,7 +151,7 @@ pub struct CtxtInterners<'tcx> {
     clauses: InternedSet<'tcx, List<Clause<'tcx>>>,
     projs: InternedSet<'tcx, List<ProjectionKind>>,
     place_elems: InternedSet<'tcx, List<PlaceElem<'tcx>>>,
-    const_: InternedSet<'tcx, ConstData<'tcx>>,
+    const_: InternedSet<'tcx, WithCachedTypeInfo<ConstData<'tcx>>>,
     const_allocation: InternedSet<'tcx, Allocation>,
     bound_variable_kinds: InternedSet<'tcx, List<ty::BoundVariableKind>>,
     layout: InternedSet<'tcx, LayoutS<FieldIdx, VariantIdx>>,
@@ -212,6 +212,32 @@ impl<'tcx> CtxtInterners<'tcx> {
         ))
     }
 
+    /// Interns a const. (Use `mk_*` functions instead, where possible.)
+    #[allow(rustc::usage_of_ty_tykind)]
+    #[inline(never)]
+    fn intern_const(
+        &self,
+        data: ty::ConstData<'tcx>,
+        sess: &Session,
+        untracked: &Untracked,
+    ) -> Const<'tcx> {
+        Const(Interned::new_unchecked(
+            self.const_
+                .intern(data, |data: ConstData<'_>| {
+                    let flags = super::flags::FlagComputation::for_const(&data.kind, data.ty);
+                    let stable_hash = self.stable_hash(&flags, sess, untracked, &data);
+
+                    InternedInSet(self.arena.alloc(WithCachedTypeInfo {
+                        internee: data,
+                        stable_hash,
+                        flags: flags.flags,
+                        outer_exclusive_binder: flags.outer_exclusive_binder,
+                    }))
+                })
+                .0,
+        ))
+    }
+
     fn stable_hash<'a, T: HashStable<StableHashingContext<'a>>>(
         &self,
         flags: &ty::flags::FlagComputation,
@@ -418,11 +444,17 @@ impl<'tcx> CommonLifetimes<'tcx> {
 }
 
 impl<'tcx> CommonConsts<'tcx> {
-    fn new(interners: &CtxtInterners<'tcx>, types: &CommonTypes<'tcx>) -> CommonConsts<'tcx> {
+    fn new(
+        interners: &CtxtInterners<'tcx>,
+        types: &CommonTypes<'tcx>,
+        sess: &Session,
+        untracked: &Untracked,
+    ) -> CommonConsts<'tcx> {
         let mk_const = |c| {
-            Const(Interned::new_unchecked(
-                interners.const_.intern(c, |c| InternedInSet(interners.arena.alloc(c))).0,
-            ))
+            interners.intern_const(
+                c, sess, // This is only used to create a stable hashing context.
+                untracked,
+            )
         };
 
         CommonConsts {
@@ -714,7 +746,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let interners = CtxtInterners::new(arena);
         let common_types = CommonTypes::new(&interners, s, &untracked);
         let common_lifetimes = CommonLifetimes::new(&interners);
-        let common_consts = CommonConsts::new(&interners, &common_types);
+        let common_consts = CommonConsts::new(&interners, &common_types, s, &untracked);
 
         GlobalCtxt {
             sess: s,
@@ -1533,7 +1565,6 @@ macro_rules! direct_interners {
 // crate only, and have a corresponding `mk_` function.
 direct_interners! {
     region: pub(crate) intern_region(RegionKind<'tcx>): Region -> Region<'tcx>,
-    const_: intern_const(ConstData<'tcx>): Const -> Const<'tcx>,
     const_allocation: pub mk_const_alloc(Allocation): ConstAllocation -> ConstAllocation<'tcx>,
     layout: pub mk_layout(LayoutS<FieldIdx, VariantIdx>): Layout -> Layout<'tcx>,
     adt_def: pub mk_adt_def_from_data(AdtDefData): AdtDef -> AdtDef<'tcx>,
@@ -1710,7 +1741,12 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_ct_from_kind(self, kind: ty::ConstKind<'tcx>, ty: Ty<'tcx>) -> Const<'tcx> {
-        self.intern_const(ty::ConstData { kind, ty })
+        self.interners.intern_const(
+            ty::ConstData { kind, ty },
+            self.sess,
+            // This is only used to create a stable hashing context.
+            &self.untracked,
+        )
     }
 
     // Avoid this in favour of more specific `Ty::new_*` methods, where possible.

compiler/rustc_middle/src/ty/flags.rs

@@ -28,10 +28,11 @@ impl FlagComputation {
         result
     }
 
-    pub fn for_const(c: ty::Const<'_>) -> TypeFlags {
+    pub fn for_const(c: &ty::ConstKind<'_>, t: Ty<'_>) -> FlagComputation {
         let mut result = FlagComputation::new();
-        result.add_const(c);
-        result.flags
+        result.add_const_kind(c);
+        result.add_ty(t);
+        result
     }
 
     fn add_flags(&mut self, flags: TypeFlags) {
@@ -297,8 +298,12 @@ impl FlagComputation {
     }
 
     fn add_const(&mut self, c: ty::Const<'_>) {
-        self.add_ty(c.ty());
-        match c.kind() {
+        self.add_flags(c.flags());
+        self.add_exclusive_binder(c.outer_exclusive_binder());
+    }
+
+    fn add_const_kind(&mut self, c: &ty::ConstKind<'_>) {
+        match *c {
             ty::ConstKind::Unevaluated(uv) => {
                 self.add_args(uv.args);
                 self.add_flags(TypeFlags::HAS_CT_PROJECTION);

compiler/rustc_middle/src/ty/generic_args.rs

@@ -70,7 +70,7 @@ impl<'tcx> GenericArgKind<'tcx> {
             GenericArgKind::Const(ct) => {
                 // Ensure we can use the tag bits.
                 assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0);
-                (CONST_TAG, ct.0.0 as *const ty::ConstData<'tcx> as usize)
+                (CONST_TAG, ct.0.0 as *const WithCachedTypeInfo<ty::ConstData<'tcx>> as usize)
             }
         };
 
@@ -136,7 +136,7 @@ impl<'tcx> GenericArg<'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::ConstData<'tcx>),
+                    &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::ConstData<'tcx>>),
                 ))),
                 _ => intrinsics::unreachable(),
             }

compiler/rustc_middle/src/ty/mod.rs

@@ -900,7 +900,7 @@ impl<'tcx> Term<'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::ConstData<'tcx>),
+                    &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::ConstData<'tcx>>),
                 ))),
                 _ => core::intrinsics::unreachable(),
             }
@@ -967,7 +967,7 @@ impl<'tcx> TermKind<'tcx> {
             TermKind::Const(ct) => {
                 // Ensure we can use the tag bits.
                 assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0);
-                (CONST_TAG, ct.0.0 as *const ty::ConstData<'tcx> as usize)
+                (CONST_TAG, ct.0.0 as *const WithCachedTypeInfo<ty::ConstData<'tcx>> as usize)
             }
         };
 

compiler/rustc_middle/src/ty/visit.rs

@@ -1,4 +1,4 @@
-use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
+use crate::ty::{self, Binder, Ty, TyCtxt, TypeFlags};
 use rustc_errors::ErrorGuaranteed;
 
 use rustc_data_structures::fx::FxHashSet;
@@ -440,16 +440,15 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasEscapingVarsVisitor {
     }
 
     fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // we don't have a `visit_infer_const` callback, so we have to
-        // hook in here to catch this case (annoying...), but
-        // otherwise we do want to remember to visit the rest of the
-        // const, as it has types/regions embedded in a lot of other
-        // places.
-        match ct.kind() {
-            ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
-                ControlFlow::Break(FoundEscapingVars)
-            }
-            _ => ct.super_visit_with(self),
+        // If the outer-exclusive-binder is *strictly greater* than
+        // `outer_index`, that means that `ct` contains some content
+        // bound at `outer_index` or above (because
+        // `outer_exclusive_binder` is always 1 higher than the
+        // content in `t`). Therefore, `t` has some escaping vars.
+        if ct.outer_exclusive_binder() > self.outer_index {
+            ControlFlow::Break(FoundEscapingVars)
+        } else {
+            ControlFlow::Continue(())
         }
     }
 
@@ -529,9 +528,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
     #[inline]
     fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         // Note: no `super_visit_with` call.
-        let flags = FlagComputation::for_const(c);
-        trace!(r.flags=?flags);
-        if flags.intersects(self.flags) {
+        if c.flags().intersects(self.flags) {
             ControlFlow::Break(FoundFlags)
         } else {
             ControlFlow::Continue(())

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -160,14 +160,12 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxEscapingBoundVarVisitor {
     }
 
     fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        match ct.kind() {
-            ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
-                self.escaping =
-                    self.escaping.max(debruijn.as_usize() - self.outer_index.as_usize());
-                ControlFlow::Continue(())
-            }
-            _ => ct.super_visit_with(self),
+        if ct.outer_exclusive_binder() > self.outer_index {
+            self.escaping = self
+                .escaping
+                .max(ct.outer_exclusive_binder().as_usize() - self.outer_index.as_usize());
         }
+        ControlFlow::Continue(())
     }
 }