resuse eagerly resolved goal from previous iteration

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs

@@ -53,17 +53,14 @@ where
 {
     /// Canonicalizes the goal remembering the original values
     /// for each bound variable.
+    ///
+    /// This expects `goal` and `opaque_types` to be eager resolved.
     pub(super) fn canonicalize_goal(
         &self,
         is_hir_typeck_root_goal: bool,
         goal: Goal<I, I::Predicate>,
+        opaque_types: Vec<(ty::OpaqueTypeKey<I>, I::Ty)>,
     ) -> (Vec<I::GenericArg>, CanonicalInput<I, I::Predicate>) {
-        // We only care about one entry per `OpaqueTypeKey` here,
-        // so we only canonicalize the lookup table and ignore
-        // duplicate entries.
-        let opaque_types = self.delegate.clone_opaque_types_lookup_table();
-        let (goal, opaque_types) = eager_resolve_vars(self.delegate, (goal, opaque_types));
-
         let mut orig_values = Default::default();
         let canonical = Canonicalizer::canonicalize_input(
             self.delegate,

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -20,6 +20,7 @@ use super::has_only_region_constraints;
 use crate::coherence;
 use crate::delegate::SolverDelegate;
 use crate::placeholder::BoundVarReplacer;
+use crate::resolve::eager_resolve_vars;
 use crate::solve::inspect::{self, ProofTreeBuilder};
 use crate::solve::search_graph::SearchGraph;
 use crate::solve::ty::may_use_unstable_feature;
@@ -440,6 +441,7 @@ where
             return Ok((
                 NestedNormalizationGoals::empty(),
                 GoalEvaluation {
+                    goal,
                     certainty: Certainty::Maybe(stalled_on.stalled_cause),
                     has_changed: HasChanged::No,
                     stalled_on: Some(stalled_on),
@@ -447,10 +449,16 @@ where
             ));
         }
 
+        // We only care about one entry per `OpaqueTypeKey` here,
+        // so we only canonicalize the lookup table and ignore
+        // duplicate entries.
+        let opaque_types = self.delegate.clone_opaque_types_lookup_table();
+        let (goal, opaque_types) = eager_resolve_vars(self.delegate, (goal, opaque_types));
+
         let is_hir_typeck_root_goal = matches!(goal_evaluation_kind, GoalEvaluationKind::Root)
             && self.delegate.in_hir_typeck();
-
-        let (orig_values, canonical_goal) = self.canonicalize_goal(is_hir_typeck_root_goal, goal);
+        let (orig_values, canonical_goal) =
+            self.canonicalize_goal(is_hir_typeck_root_goal, goal, opaque_types);
         let mut goal_evaluation =
             self.inspect.new_goal_evaluation(goal, &orig_values, goal_evaluation_kind);
         let canonical_result = self.search_graph.evaluate_goal(
@@ -528,7 +536,10 @@ where
             },
         };
 
-        Ok((normalization_nested_goals, GoalEvaluation { certainty, has_changed, stalled_on }))
+        Ok((
+            normalization_nested_goals,
+            GoalEvaluation { goal, certainty, has_changed, stalled_on },
+        ))
     }
 
     pub(super) fn compute_goal(&mut self, goal: Goal<I, I::Predicate>) -> QueryResult<I> {
@@ -664,7 +675,7 @@ where
 
                 let (
                     NestedNormalizationGoals(nested_goals),
-                    GoalEvaluation { certainty, stalled_on, has_changed: _ },
+                    GoalEvaluation { goal, certainty, stalled_on, has_changed: _ },
                 ) = self.evaluate_goal_raw(
                     GoalEvaluationKind::Nested,
                     source,
@@ -702,7 +713,15 @@ where
                 // FIXME: Do we need to eagerly resolve here? Or should we check
                 // if the cache key has any changed vars?
                 let with_resolved_vars = self.resolve_vars_if_possible(goal);
-                if pred.alias != goal.predicate.as_normalizes_to().unwrap().skip_binder().alias {
+                if pred.alias
+                    != with_resolved_vars
+                        .predicate
+                        .as_normalizes_to()
+                        .unwrap()
+                        .no_bound_vars()
+                        .unwrap()
+                        .alias
+                {
                     unchanged_certainty = None;
                 }
 
@@ -714,7 +733,7 @@ where
                     }
                 }
             } else {
-                let GoalEvaluation { certainty, has_changed, stalled_on } =
+                let GoalEvaluation { goal, certainty, has_changed, stalled_on } =
                     self.evaluate_goal(GoalEvaluationKind::Nested, source, goal, stalled_on)?;
                 if has_changed == HasChanged::Yes {
                     unchanged_certainty = None;

compiler/rustc_next_trait_solver/src/solve/mod.rs

@@ -386,6 +386,10 @@ fn response_no_constraints_raw<I: Interner>(
 
 /// The result of evaluating a goal.
 pub struct GoalEvaluation<I: Interner> {
+    /// The goal we've evaluated. This is the input goal, but potentially with its
+    /// inference variables resolved. This never applies any inference constraints
+    /// from evaluating the goal.
+    pub goal: Goal<I, I::Predicate>,
     pub certainty: Certainty,
     pub has_changed: HasChanged,
     /// If the [`Certainty`] was `Maybe`, then keep track of whether the goal has changed

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -207,7 +207,7 @@ where
 
                 let result = delegate.evaluate_root_goal(goal, obligation.cause.span, stalled_on);
                 self.inspect_evaluated_obligation(infcx, &obligation, &result);
-                let GoalEvaluation { certainty, has_changed, stalled_on } = match result {
+                let GoalEvaluation { goal, certainty, has_changed, stalled_on } = match result {
                     Ok(result) => result,
                     Err(NoSolution) => {
                         errors.push(E::from_solver_error(
@@ -218,6 +218,10 @@ where
                     }
                 };
 
+                // We've resolved the goal in `evaluate_root_goal`, avoid redoing this work
+                // in the next iteration. This does not resolve the inference variables
+                // constrained by evaluating the goal.
+                obligation.predicate = goal.predicate;
                 if has_changed == HasChanged::Yes {
                     // We increment the recursion depth here to track the number of times
                     // this goal has resulted in inference progress. This doesn't precisely