new solver: add a separate cache for coherence

compiler/rustc_middle/src/ty/context.rs

@@ -569,6 +569,7 @@ pub struct GlobalCtxt<'tcx> {
 
     /// Caches the results of goal evaluation in the new solver.
     pub new_solver_evaluation_cache: solve::EvaluationCache<'tcx>,
+    pub new_solver_coherence_evaluation_cache: solve::EvaluationCache<'tcx>,
 
     /// Data layout specification for the current target.
     pub data_layout: TargetDataLayout,
@@ -680,10 +681,12 @@ impl<'tcx> TyCtxt<'tcx> {
         value.lift_to_tcx(self)
     }
 
-    /// Creates a type context and call the closure with a `TyCtxt` reference
-    /// to the context. The closure enforces that the type context and any interned
-    /// value (types, args, etc.) can only be used while `ty::tls` has a valid
-    /// reference to the context, to allow formatting values that need it.
+    /// Creates a type context. To use the context call `fn enter` which
+    /// provides a `TyCtxt`.
+    ///
+    /// By only providing the `TyCtxt` inside of the closure we enforce that the type
+    /// context and any interned alue (types, args, etc.) can only be used while `ty::tls`
+    /// has a valid reference to the context, to allow formatting values that need it.
     pub fn create_global_ctxt(
         s: &'tcx Session,
         lint_store: Lrc<dyn Any + sync::DynSend + sync::DynSync>,
@@ -721,6 +724,7 @@ impl<'tcx> TyCtxt<'tcx> {
             selection_cache: Default::default(),
             evaluation_cache: Default::default(),
             new_solver_evaluation_cache: Default::default(),
+            new_solver_coherence_evaluation_cache: Default::default(),
             data_layout,
             alloc_map: Lock::new(interpret::AllocMap::new()),
         }

compiler/rustc_trait_selection/src/solve/search_graph/mod.rs

@@ -9,7 +9,9 @@ use cache::ProvisionalCache;
 use overflow::OverflowData;
 use rustc_index::IndexVec;
 use rustc_middle::dep_graph::DepKind;
-use rustc_middle::traits::solve::{CanonicalInput, Certainty, MaybeCause, QueryResult};
+use rustc_middle::traits::solve::{
+    CanonicalInput, Certainty, EvaluationCache, MaybeCause, QueryResult,
+};
 use rustc_middle::ty::TyCtxt;
 use std::{collections::hash_map::Entry, mem};
 
@@ -58,10 +60,10 @@ impl<'tcx> SearchGraph<'tcx> {
     ///
     /// We could add another global cache for coherence instead,
     /// but that's effort so let's only do it if necessary.
-    pub(super) fn should_use_global_cache(&self) -> bool {
+    pub(super) fn global_cache(&self, tcx: TyCtxt<'tcx>) -> &'tcx EvaluationCache<'tcx> {
         match self.mode {
-            SolverMode::Normal => true,
-            SolverMode::Coherence => false,
+            SolverMode::Normal => &tcx.new_solver_evaluation_cache,
+            SolverMode::Coherence => &tcx.new_solver_coherence_evaluation_cache,
         }
     }
 
@@ -213,8 +215,8 @@ impl<'tcx> SearchGraph<'tcx> {
         inspect: &mut ProofTreeBuilder<'tcx>,
         mut loop_body: impl FnMut(&mut Self, &mut ProofTreeBuilder<'tcx>) -> QueryResult<'tcx>,
     ) -> QueryResult<'tcx> {
-        if self.should_use_global_cache() && inspect.use_global_cache() {
-            if let Some(result) = tcx.new_solver_evaluation_cache.get(&canonical_input, tcx) {
+        if inspect.use_global_cache() {
+            if let Some(result) = self.global_cache(tcx).get(&canonical_input, tcx) {
                 debug!(?canonical_input, ?result, "cache hit");
                 inspect.cache_hit(CacheHit::Global);
                 return result;
@@ -278,13 +280,10 @@ impl<'tcx> SearchGraph<'tcx> {
             // dependencies, our non-root goal may no longer appear as child of the root goal.
             //
             // See https://github.com/rust-lang/rust/pull/108071 for some additional context.
-            let can_cache = !self.overflow_data.did_overflow() || self.stack.is_empty();
-            if self.should_use_global_cache() && can_cache {
-                tcx.new_solver_evaluation_cache.insert(
-                    current_goal.input,
-                    dep_node,
-                    current_goal.response,
-                );
+            let can_cache = inspect.use_global_cache()
+                && (!self.overflow_data.did_overflow() || self.stack.is_empty());
+            if can_cache {
+                self.global_cache(tcx).insert(current_goal.input, dep_node, current_goal.response)
             }
         }