Auto merge of #155443 - jdonszelmann:canonical, r=lcnr

Improve caching by introducing `TypingMode::ErasedNotCoherence`



r? @lcnr


This introduces `TypingMode::ErasedNotCoherence`. Most typing modes contain a list of opaque types, which are quite often unused during canonicalization. With this change, any time we try canonicalization, we replace whichever typing mode we're currently in with `ErasedNotcoherence`, attempt to canonicalize, and if that fails *retry* in the original typing mode. If erased mode succeeds, this is beneficial because that way the opaque types don't end up in the cache key, allowing more cache reuse.

This seems to have a small (0.5%) slowdown on most programs, but a dramatic (>60%) speedup in specific cases like the rustc-perf `wg-grammar` benchmark. Some more improvements are expected with "eager normalization", which is work that's under way right now.

Author: bors

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -374,7 +374,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     assert!(key.value.promoted.is_some() || !tcx.is_static(key.value.instance.def_id()));
 
     if cfg!(debug_assertions) {
-        match key.typing_env.typing_mode() {
+        match key.typing_env.typing_mode().assert_not_erased() {
             ty::TypingMode::PostAnalysis => {}
             ty::TypingMode::Coherence
             | ty::TypingMode::Analysis { .. }

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -237,7 +237,7 @@ pub(crate) fn eval_to_valtree<'tcx>(
     cid: GlobalId<'tcx>,
 ) -> EvalToValTreeResult<'tcx> {
     if cfg!(debug_assertions) {
-        match typing_env.typing_mode() {
+        match typing_env.typing_mode().assert_not_erased() {
             ty::TypingMode::PostAnalysis => {}
             ty::TypingMode::Coherence
             | ty::TypingMode::Analysis { .. }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -243,7 +243,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // types that are not specified in the opaque type. We also use MIR bodies whose opaque types have
         // already been revealed, so we'd be able to at least partially observe the hidden types anyways.
         if cfg!(debug_assertions) {
-            match typing_env.typing_mode() {
+            match typing_env.typing_mode().assert_not_erased() {
                 TypingMode::PostAnalysis => {}
                 TypingMode::Coherence
                 | TypingMode::Analysis { .. }

compiler/rustc_hir_typeck/src/callee.rs

@@ -62,6 +62,7 @@ enum CallStep<'tcx> {
 }
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    #[tracing::instrument(skip(self))]
     pub(crate) fn check_expr_call(
         &self,
         call_expr: &'tcx hir::Expr<'tcx>,

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -17,7 +17,9 @@ use rustc_hir_analysis::hir_ty_lowering::{
 };
 use rustc_infer::infer::{self, RegionVariableOrigin};
 use rustc_infer::traits::{DynCompatibilityViolation, Obligation};
-use rustc_middle::ty::{self, Const, Flags, Ty, TyCtxt, TypeVisitableExt, Unnormalized};
+use rustc_middle::ty::{
+    self, CantBeErased, Const, Flags, Ty, TyCtxt, TypeVisitableExt, TypingMode, Unnormalized,
+};
 use rustc_session::Session;
 use rustc_span::{self, DUMMY_SP, ErrorGuaranteed, Ident, Span};
 use rustc_trait_selection::error_reporting::TypeErrCtxt;
@@ -161,6 +163,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    pub(crate) fn typing_mode(&self) -> TypingMode<'tcx, CantBeErased> {
+        // `FnCtxt` is never constructed in the trait solver, so we can safely use
+        // `assert_not_erased`.
+        self.infcx.typing_mode_raw().assert_not_erased()
+    }
+
     pub(crate) fn dcx(&self) -> DiagCtxtHandle<'a> {
         self.root_ctxt.infcx.dcx()
     }

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

@@ -72,7 +72,7 @@ impl<'tcx> InferCtxt<'tcx> {
             query_state,
         )
         .unchecked_map(|(param_env, value)| param_env.and(value));
-        CanonicalQueryInput { canonical, typing_mode: TypingModeEqWrapper(self.typing_mode()) }
+        CanonicalQueryInput { canonical, typing_mode: TypingModeEqWrapper(self.typing_mode_raw()) }
     }
 
     /// Canonicalizes a query *response* `V`. When we canonicalize a

compiler/rustc_infer/src/infer/context.rs

@@ -26,8 +26,8 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
         self.disable_trait_solver_fast_paths()
     }
 
-    fn typing_mode(&self) -> ty::TypingMode<'tcx> {
-        self.typing_mode()
+    fn typing_mode_raw(&self) -> ty::TypingMode<'tcx> {
+        self.typing_mode_raw()
     }
 
     fn universe(&self) -> ty::UniverseIndex {

compiler/rustc_infer/src/infer/mod.rs

@@ -34,6 +34,7 @@ use rustc_middle::ty::{
     TypeSuperFoldable, TypeVisitable, TypeVisitableExt, TypingEnv, TypingMode, fold_regions,
 };
 use rustc_span::{DUMMY_SP, Span, Symbol};
+use rustc_type_ir::MayBeErased;
 use snapshot::undo_log::InferCtxtUndoLogs;
 use tracing::{debug, instrument};
 use type_variable::TypeVariableOrigin;
@@ -640,14 +641,34 @@ impl<'tcx> InferCtxt<'tcx> {
         self.next_trait_solver
     }
 
+    /// This method is deliberately called `..._raw`,
+    /// since the output may possibly include [`TypingMode::ErasedNotCoherence`](TypingMode::ErasedNotCoherence).
+    /// `ErasedNotCoherence` is an implementation detail of the next trait solver, see its docs for
+    /// more information.
+    ///
+    /// `InferCtxt` has two uses: the trait solver calls some methods on it, because the `InferCtxt`
+    /// works as a kind of store for for example type unification information.
+    /// `InferCtxt` is also often used outside the trait solver during typeck.
+    /// There, we don't care about the `ErasedNotCoherence` case and should never encounter it.
+    /// To make sure these two uses are never confused, we want to statically encode this information.
+    ///
+    /// The `FnCtxt`, for example, is only used in the outside-trait-solver case. It has a non-raw
+    /// version of the `typing_mode` method available that asserts `ErasedNotCoherence` is
+    /// impossible, and returns a `TypingMode` where `ErasedNotCoherence` is made uninhabited using
+    /// the [`CantBeErased`](rustc_type_ir::CantBeErased) enum. That way you don't even have to
+    /// match on the variant and can safely ignore it.
+    ///
+    /// Prefer non-raw apis if available. e.g.,
+    /// - On the `FnCtxt`
+    /// - on the `SelectionCtxt`
     #[inline(always)]
-    pub fn disable_trait_solver_fast_paths(&self) -> bool {
-        self.tcx.disable_trait_solver_fast_paths()
+    pub fn typing_mode_raw(&self) -> TypingMode<'tcx> {
+        self.typing_mode
     }
 
     #[inline(always)]
-    pub fn typing_mode(&self) -> TypingMode<'tcx> {
-        self.typing_mode
+    pub fn disable_trait_solver_fast_paths(&self) -> bool {
+        self.tcx.disable_trait_solver_fast_paths()
     }
 
     /// Returns the origin of the type variable identified by `vid`.
@@ -1071,7 +1092,7 @@ impl<'tcx> InferCtxt<'tcx> {
     #[inline(always)]
     pub fn can_define_opaque_ty(&self, id: impl Into<DefId>) -> bool {
         debug_assert!(!self.next_trait_solver());
-        match self.typing_mode() {
+        match self.typing_mode_raw().assert_not_erased() {
             TypingMode::Analysis {
                 defining_opaque_types_and_generators: defining_opaque_types,
             }
@@ -1402,7 +1423,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// which contains the necessary information to use the trait system without
     /// using canonicalization or carrying this inference context around.
     pub fn typing_env(&self, param_env: ty::ParamEnv<'tcx>) -> ty::TypingEnv<'tcx> {
-        let typing_mode = match self.typing_mode() {
+        let typing_mode = match self.typing_mode_raw() {
             // FIXME(#132279): This erases the `defining_opaque_types` as it isn't possible
             // to handle them without proper canonicalization. This means we may cause cycle
             // errors and fail to reveal opaques while inside of bodies. We should rename this
@@ -1414,6 +1435,7 @@ impl<'tcx> InferCtxt<'tcx> {
             mode @ (ty::TypingMode::Coherence
             | ty::TypingMode::PostBorrowckAnalysis { .. }
             | ty::TypingMode::PostAnalysis) => mode,
+            ty::TypingMode::ErasedNotCoherence(MayBeErased) => unreachable!(),
         };
         ty::TypingEnv::new(param_env, typing_mode)
     }

compiler/rustc_infer/src/infer/opaque_types/mod.rs

@@ -89,7 +89,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 if def_id.is_local() =>
             {
                 let def_id = def_id.expect_local();
-                if self.typing_mode().is_coherence() {
+                if self.typing_mode_raw().is_coherence() {
                     // See comment on `insert_hidden_type` for why this is sufficient in coherence
                     return Some(self.register_hidden_type(
                         OpaqueTypeKey { def_id, args },
@@ -229,7 +229,9 @@ impl<'tcx> InferCtxt<'tcx> {
         // value being folded. In simple cases like `-> impl Foo`,
         // these are the same span, but not in cases like `-> (impl
         // Foo, impl Bar)`.
-        match self.typing_mode() {
+        //
+        // Note: we don't use this function in the next solver so we can safely call `assert_not_erased`
+        match self.typing_mode_raw().assert_not_erased() {
             ty::TypingMode::Coherence => {
                 // During intercrate we do not define opaque types but instead always
                 // force ambiguity unless the hidden type is known to not implement

compiler/rustc_infer/src/infer/relate/generalize.rs

@@ -604,7 +604,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Generalizer<'_, 'tcx> {
                             //
                             // cc trait-system-refactor-initiative#108
                             if self.infcx.next_trait_solver()
-                                && !self.infcx.typing_mode().is_coherence()
+                                && !self.infcx.typing_mode_raw().is_coherence()
                                 && self.in_alias
                             {
                                 inner.type_variables().equate(vid, new_var_id);
@@ -736,7 +736,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Generalizer<'_, 'tcx> {
                             // See the comment for type inference variables
                             // for more details.
                             if self.infcx.next_trait_solver()
-                                && !self.infcx.typing_mode().is_coherence()
+                                && !self.infcx.typing_mode_raw().is_coherence()
                                 && self.in_alias
                             {
                                 variable_table.union(vid, new_var_id);