Auto merge of rust-lang#118742 - lcnr:infer-var-cleanup, r=compiler-errors

refactor infer var storage

cleanup the code, discovered while working on rust-lang#118725

Author: bors

compiler/rustc_hir_typeck/src/fallback.rs

@@ -24,9 +24,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             self.fulfillment_cx.borrow_mut().pending_obligations()
         );
 
-        let fallback_occured = self.fallback_types() | self.fallback_effects();
+        let fallback_occurred = self.fallback_types() | self.fallback_effects();
 
-        if !fallback_occured {
+        if !fallback_occurred {
             return;
         }
 
@@ -57,24 +57,25 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     }
 
     fn fallback_types(&self) -> bool {
-        // Check if we have any unsolved variables. If not, no need for fallback.
-        let unsolved_variables = self.unsolved_variables();
+        // Check if we have any unresolved variables. If not, no need for fallback.
+        let unresolved_variables = self.unresolved_variables();
 
-        if unsolved_variables.is_empty() {
+        if unresolved_variables.is_empty() {
             return false;
         }
 
-        let diverging_fallback = self.calculate_diverging_fallback(&unsolved_variables);
+        let diverging_fallback = self.calculate_diverging_fallback(&unresolved_variables);
 
         // We do fallback in two passes, to try to generate
         // better error messages.
         // The first time, we do *not* replace opaque types.
-        for ty in unsolved_variables {
+        let mut fallback_occurred = false;
+        for ty in unresolved_variables {
             debug!("unsolved_variable = {:?}", ty);
-            self.fallback_if_possible(ty, &diverging_fallback);
+            fallback_occurred |= self.fallback_if_possible(ty, &diverging_fallback);
         }
 
-        true
+        fallback_occurred
     }
 
     fn fallback_effects(&self) -> bool {
@@ -84,9 +85,8 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             return false;
         }
 
-        // not setting `fallback_has_occured` here because that field is only used for type fallback
-        // diagnostics.
-
+        // not setting the `fallback_has_occured` field here because
+        // that field is only used for type fallback diagnostics.
         for effect in unsolved_effects {
             let expected = self.tcx.consts.true_;
             let cause = self.misc(rustc_span::DUMMY_SP);
@@ -122,7 +122,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         &self,
         ty: Ty<'tcx>,
         diverging_fallback: &UnordMap<Ty<'tcx>, Ty<'tcx>>,
-    ) {
+    ) -> bool {
         // Careful: we do NOT shallow-resolve `ty`. We know that `ty`
         // is an unsolved variable, and we determine its fallback
         // based solely on how it was created, not what other type
@@ -147,7 +147,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             ty::Infer(ty::FloatVar(_)) => self.tcx.types.f64,
             _ => match diverging_fallback.get(&ty) {
                 Some(&fallback_ty) => fallback_ty,
-                None => return,
+                None => return false,
             },
         };
         debug!("fallback_if_possible(ty={:?}): defaulting to `{:?}`", ty, fallback);
@@ -159,6 +159,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             .unwrap_or(rustc_span::DUMMY_SP);
         self.demand_eqtype(span, ty, fallback);
         self.fallback_has_occurred.set(true);
+        true
     }
 
     /// The "diverging fallback" system is rather complicated. This is
@@ -230,17 +231,17 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     ///   any variable that has an edge into `D`.
     fn calculate_diverging_fallback(
         &self,
-        unsolved_variables: &[Ty<'tcx>],
+        unresolved_variables: &[Ty<'tcx>],
     ) -> UnordMap<Ty<'tcx>, Ty<'tcx>> {
-        debug!("calculate_diverging_fallback({:?})", unsolved_variables);
+        debug!("calculate_diverging_fallback({:?})", unresolved_variables);
 
         // Construct a coercion graph where an edge `A -> B` indicates
         // a type variable is that is coerced
         let coercion_graph = self.create_coercion_graph();
 
         // Extract the unsolved type inference variable vids; note that some
         // unsolved variables are integer/float variables and are excluded.
-        let unsolved_vids = unsolved_variables.iter().filter_map(|ty| ty.ty_vid());
+        let unsolved_vids = unresolved_variables.iter().filter_map(|ty| ty.ty_vid());
 
         // Compute the diverging root vids D -- that is, the root vid of
         // those type variables that (a) are the target of a coercion from

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

@@ -166,10 +166,7 @@ impl<'tcx> InferCtxt<'tcx> {
     }
 
     fn take_opaque_types_for_query_response(&self) -> Vec<(ty::OpaqueTypeKey<'tcx>, Ty<'tcx>)> {
-        std::mem::take(&mut self.inner.borrow_mut().opaque_type_storage.opaque_types)
-            .into_iter()
-            .map(|(k, v)| (k, v.hidden_type.ty))
-            .collect()
+        self.take_opaque_types().into_iter().map(|(k, v)| (k, v.hidden_type.ty)).collect()
     }
 
     /// Given the (canonicalized) result to a canonical query,

compiler/rustc_infer/src/infer/generalize.rs

@@ -295,7 +295,7 @@ where
                                 ty::Covariant | ty::Contravariant => (),
                             }
 
-                            let origin = *inner.type_variables().var_origin(vid);
+                            let origin = inner.type_variables().var_origin(vid);
                             let new_var_id =
                                 inner.type_variables().new_var(self.for_universe, origin);
                             let u = Ty::new_var(self.tcx(), new_var_id);

compiler/rustc_infer/src/infer/mod.rs

@@ -98,6 +98,8 @@ pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
 /// call to `start_snapshot` and `rollback_to`.
 #[derive(Clone)]
 pub struct InferCtxtInner<'tcx> {
+    undo_log: InferCtxtUndoLogs<'tcx>,
+
     /// Cache for projections.
     ///
     /// This cache is snapshotted along with the infcx.
@@ -162,18 +164,17 @@ pub struct InferCtxtInner<'tcx> {
     /// that all type inference variables have been bound and so forth.
     region_obligations: Vec<RegionObligation<'tcx>>,
 
-    undo_log: InferCtxtUndoLogs<'tcx>,
-
     /// Caches for opaque type inference.
     opaque_type_storage: OpaqueTypeStorage<'tcx>,
 }
 
 impl<'tcx> InferCtxtInner<'tcx> {
     fn new() -> InferCtxtInner<'tcx> {
         InferCtxtInner {
+            undo_log: InferCtxtUndoLogs::default(),
+
             projection_cache: Default::default(),
             type_variable_storage: type_variable::TypeVariableStorage::new(),
-            undo_log: InferCtxtUndoLogs::default(),
             const_unification_storage: ut::UnificationTableStorage::new(),
             int_unification_storage: ut::UnificationTableStorage::new(),
             float_unification_storage: ut::UnificationTableStorage::new(),
@@ -783,7 +784,7 @@ impl<'tcx> InferCtxt<'tcx> {
     pub fn type_var_origin(&self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
         match *ty.kind() {
             ty::Infer(ty::TyVar(vid)) => {
-                Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
+                Some(self.inner.borrow_mut().type_variables().var_origin(vid))
             }
             _ => None,
         }
@@ -793,11 +794,11 @@ impl<'tcx> InferCtxt<'tcx> {
         freshen::TypeFreshener::new(self)
     }
 
-    pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
+    pub fn unresolved_variables(&self) -> Vec<Ty<'tcx>> {
         let mut inner = self.inner.borrow_mut();
         let mut vars: Vec<Ty<'_>> = inner
             .type_variables()
-            .unsolved_variables()
+            .unresolved_variables()
             .into_iter()
             .map(|t| Ty::new_var(self.tcx, t))
             .collect();
@@ -1306,12 +1307,7 @@ impl<'tcx> InferCtxt<'tcx> {
     pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
         let mut inner = self.inner.borrow_mut();
         let inner = &mut *inner;
-        inner
-            .region_constraint_storage
-            .as_mut()
-            .expect("regions already resolved")
-            .with_log(&mut inner.undo_log)
-            .var_origin(vid)
+        inner.unwrap_region_constraints().var_origin(vid)
     }
 
     /// Clone the list of variable regions. This is used only during NLL processing

compiler/rustc_infer/src/infer/resolve.rs

@@ -134,7 +134,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for UnresolvedTypeOrConstFinder<'a, 'tc
                 if let TypeVariableOrigin {
                     kind: TypeVariableOriginKind::TypeParameterDefinition(_, _),
                     span,
-                } = *ty_vars.var_origin(ty_vid)
+                } = ty_vars.var_origin(ty_vid)
                 {
                     Some(span)
                 } else {

compiler/rustc_infer/src/infer/type_variable.rs

@@ -1,4 +1,5 @@
 use rustc_hir::def_id::DefId;
+use rustc_index::IndexVec;
 use rustc_middle::ty::{self, Ty, TyVid};
 use rustc_span::symbol::Symbol;
 use rustc_span::Span;
@@ -11,14 +12,13 @@ use std::cmp;
 use std::marker::PhantomData;
 use std::ops::Range;
 
-use rustc_data_structures::undo_log::{Rollback, UndoLogs};
+use rustc_data_structures::undo_log::Rollback;
 
 /// Represents a single undo-able action that affects a type inference variable.
 #[derive(Clone)]
 pub(crate) enum UndoLog<'tcx> {
     EqRelation(sv::UndoLog<ut::Delegate<TyVidEqKey<'tcx>>>),
     SubRelation(sv::UndoLog<ut::Delegate<ty::TyVid>>),
-    Values(sv::UndoLog<Delegate>),
 }
 
 /// Convert from a specific kind of undo to the more general UndoLog
@@ -35,34 +35,19 @@ impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::TyVid>>> for UndoLog<'tcx> {
     }
 }
 
-/// Convert from a specific kind of undo to the more general UndoLog
-impl<'tcx> From<sv::UndoLog<Delegate>> for UndoLog<'tcx> {
-    fn from(l: sv::UndoLog<Delegate>) -> Self {
-        UndoLog::Values(l)
-    }
-}
-
-/// Convert from a specific kind of undo to the more general UndoLog
-impl<'tcx> From<Instantiate> for UndoLog<'tcx> {
-    fn from(l: Instantiate) -> Self {
-        UndoLog::Values(sv::UndoLog::Other(l))
-    }
-}
-
 impl<'tcx> Rollback<UndoLog<'tcx>> for TypeVariableStorage<'tcx> {
     fn reverse(&mut self, undo: UndoLog<'tcx>) {
         match undo {
             UndoLog::EqRelation(undo) => self.eq_relations.reverse(undo),
             UndoLog::SubRelation(undo) => self.sub_relations.reverse(undo),
-            UndoLog::Values(undo) => self.values.reverse(undo),
         }
     }
 }
 
 #[derive(Clone)]
 pub struct TypeVariableStorage<'tcx> {
-    values: sv::SnapshotVecStorage<Delegate>,
-
+    /// The origins of each type variable.
+    values: IndexVec<TyVid, TypeVariableData>,
     /// Two variables are unified in `eq_relations` when we have a
     /// constraint `?X == ?Y`. This table also stores, for each key,
     /// the known value.
@@ -168,15 +153,10 @@ impl<'tcx> TypeVariableValue<'tcx> {
     }
 }
 
-#[derive(Clone)]
-pub(crate) struct Instantiate;
-
-pub(crate) struct Delegate;
-
 impl<'tcx> TypeVariableStorage<'tcx> {
     pub fn new() -> TypeVariableStorage<'tcx> {
         TypeVariableStorage {
-            values: sv::SnapshotVecStorage::new(),
+            values: Default::default(),
             eq_relations: ut::UnificationTableStorage::new(),
             sub_relations: ut::UnificationTableStorage::new(),
         }
@@ -194,15 +174,20 @@ impl<'tcx> TypeVariableStorage<'tcx> {
     pub(crate) fn eq_relations_ref(&self) -> &ut::UnificationTableStorage<TyVidEqKey<'tcx>> {
         &self.eq_relations
     }
+
+    pub(super) fn finalize_rollback(&mut self) {
+        debug_assert!(self.values.len() >= self.eq_relations.len());
+        self.values.truncate(self.eq_relations.len());
+    }
 }
 
 impl<'tcx> TypeVariableTable<'_, 'tcx> {
     /// Returns the origin that was given when `vid` was created.
     ///
     /// Note that this function does not return care whether
     /// `vid` has been unified with something else or not.
-    pub fn var_origin(&self, vid: ty::TyVid) -> &TypeVariableOrigin {
-        &self.storage.values.get(vid.as_usize()).origin
+    pub fn var_origin(&self, vid: ty::TyVid) -> TypeVariableOrigin {
+        self.storage.values[vid].origin
     }
 
     /// Records that `a == b`, depending on `dir`.
@@ -237,11 +222,6 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
             self.eq_relations().probe_value(vid)
         );
         self.eq_relations().union_value(vid, TypeVariableValue::Known { value: ty });
-
-        // Hack: we only need this so that `types_escaping_snapshot`
-        // can see what has been unified; see the Delegate impl for
-        // more details.
-        self.undo_log.push(Instantiate);
     }
 
     /// Creates a new type variable.
@@ -262,14 +242,14 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
         let eq_key = self.eq_relations().new_key(TypeVariableValue::Unknown { universe });
 
         let sub_key = self.sub_relations().new_key(());
-        assert_eq!(eq_key.vid, sub_key);
+        debug_assert_eq!(eq_key.vid, sub_key);
 
-        let index = self.values().push(TypeVariableData { origin });
-        assert_eq!(eq_key.vid.as_u32(), index as u32);
+        let index = self.storage.values.push(TypeVariableData { origin });
+        debug_assert_eq!(eq_key.vid, index);
 
         debug!("new_var(index={:?}, universe={:?}, origin={:?})", eq_key.vid, universe, origin);
 
-        eq_key.vid
+        index
     }
 
     /// Returns the number of type variables created thus far.
@@ -329,13 +309,6 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
         }
     }
 
-    #[inline]
-    fn values(
-        &mut self,
-    ) -> sv::SnapshotVec<Delegate, &mut Vec<TypeVariableData>, &mut InferCtxtUndoLogs<'tcx>> {
-        self.storage.values.with_log(self.undo_log)
-    }
-
     #[inline]
     fn eq_relations(&mut self) -> super::UnificationTable<'_, 'tcx, TyVidEqKey<'tcx>> {
         self.storage.eq_relations.with_log(self.undo_log)
@@ -354,16 +327,14 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
         let range = TyVid::from_usize(value_count)..TyVid::from_usize(self.num_vars());
         (
             range.start..range.end,
-            (range.start.as_usize()..range.end.as_usize())
-                .map(|index| self.storage.values.get(index).origin)
-                .collect(),
+            (range.start..range.end).map(|index| self.var_origin(index)).collect(),
         )
     }
 
     /// Returns indices of all variables that are not yet
     /// instantiated.
-    pub fn unsolved_variables(&mut self) -> Vec<ty::TyVid> {
-        (0..self.storage.values.len())
+    pub fn unresolved_variables(&mut self) -> Vec<ty::TyVid> {
+        (0..self.num_vars())
             .filter_map(|i| {
                 let vid = ty::TyVid::from_usize(i);
                 match self.probe(vid) {
@@ -375,26 +346,6 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     }
 }
 
-impl sv::SnapshotVecDelegate for Delegate {
-    type Value = TypeVariableData;
-    type Undo = Instantiate;
-
-    fn reverse(_values: &mut Vec<TypeVariableData>, _action: Instantiate) {
-        // We don't actually have to *do* anything to reverse an
-        // instantiation; the value for a variable is stored in the
-        // `eq_relations` and hence its rollback code will handle
-        // it. In fact, we could *almost* just remove the
-        // `SnapshotVec` entirely, except that we would have to
-        // reproduce *some* of its logic, since we want to know which
-        // type variables have been instantiated since the snapshot
-        // was started, so we can implement `types_escaping_snapshot`.
-        //
-        // (If we extended the `UnificationTable` to let us see which
-        // values have been unified and so forth, that might also
-        // suffice.)
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////
 
 /// These structs (a newtyped TyVid) are used as the unification key