Auto merge of rust-lang#128746 - compiler-errors:cache-super-outlives, r=lcnr

Cache supertrait outlives of impl header for soundness check

This caches the results of computing the transitive supertraits of an impl and filtering it to its outlives obligations. This is purely an optimization to improve rust-lang#124336.

Author: bors

compiler/rustc_hir_analysis/src/collect.rs

@@ -67,6 +67,7 @@ pub fn provide(providers: &mut Providers) {
         item_super_predicates: item_bounds::item_super_predicates,
         explicit_item_super_predicates: item_bounds::explicit_item_super_predicates,
         item_non_self_assumptions: item_bounds::item_non_self_assumptions,
+        impl_super_outlives: item_bounds::impl_super_outlives,
         generics_of: generics_of::generics_of,
         predicates_of: predicates_of::predicates_of,
         predicates_defined_on,

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -212,6 +212,8 @@ pub(super) fn item_super_predicates(
     })
 }
 
+/// This exists as an optimization to compute only the item bounds of the item
+/// that are not `Self` bounds.
 pub(super) fn item_non_self_assumptions(
     tcx: TyCtxt<'_>,
     def_id: DefId,
@@ -226,6 +228,25 @@ pub(super) fn item_non_self_assumptions(
     }
 }
 
+/// This exists as an optimization to compute only the supertraits of this impl's
+/// trait that are outlives bounds.
+pub(super) fn impl_super_outlives(
+    tcx: TyCtxt<'_>,
+    def_id: DefId,
+) -> ty::EarlyBinder<'_, ty::Clauses<'_>> {
+    tcx.impl_trait_header(def_id).expect("expected an impl of trait").trait_ref.map_bound(
+        |trait_ref| {
+            let clause: ty::Clause<'_> = trait_ref.upcast(tcx);
+            tcx.mk_clauses_from_iter(util::elaborate(tcx, [clause]).filter(|clause| {
+                matches!(
+                    clause.kind().skip_binder(),
+                    ty::ClauseKind::TypeOutlives(_) | ty::ClauseKind::RegionOutlives(_)
+                )
+            }))
+        },
+    )
+}
+
 struct AssocTyToOpaque<'tcx> {
     tcx: TyCtxt<'tcx>,
     fn_def_id: DefId,

compiler/rustc_middle/src/query/mod.rs

@@ -407,6 +407,10 @@ rustc_queries! {
         desc { |tcx| "elaborating item assumptions for `{}`", tcx.def_path_str(key) }
     }
 
+    query impl_super_outlives(key: DefId) -> ty::EarlyBinder<'tcx, ty::Clauses<'tcx>> {
+        desc { |tcx| "elaborating supertrait outlives for trait of `{}`", tcx.def_path_str(key) }
+    }
+
     /// Look up all native libraries this crate depends on.
     /// These are assembled from the following places:
     /// - `extern` blocks (depending on their `link` attributes)

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -17,7 +17,6 @@ use rustc_hir::LangItem;
 use rustc_infer::infer::relate::TypeRelation;
 use rustc_infer::infer::BoundRegionConversionTime::{self, HigherRankedType};
 use rustc_infer::infer::DefineOpaqueTypes;
-use rustc_infer::traits::util::elaborate;
 use rustc_infer::traits::TraitObligation;
 use rustc_middle::bug;
 use rustc_middle::dep_graph::{dep_kinds, DepNodeIndex};
@@ -2801,31 +2800,22 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         }
 
         // Register any outlives obligations from the trait here, cc #124336.
-        if matches!(self.tcx().def_kind(def_id), DefKind::Impl { of_trait: true })
-            && let Some(header) = self.tcx().impl_trait_header(def_id)
-        {
-            let trait_clause: ty::Clause<'tcx> =
-                header.trait_ref.instantiate(self.tcx(), args).upcast(self.tcx());
-            for clause in elaborate(self.tcx(), [trait_clause]) {
-                if matches!(
-                    clause.kind().skip_binder(),
-                    ty::ClauseKind::TypeOutlives(..) | ty::ClauseKind::RegionOutlives(..)
-                ) {
-                    let clause = normalize_with_depth_to(
-                        self,
-                        param_env,
-                        cause.clone(),
-                        recursion_depth,
-                        clause,
-                        &mut obligations,
-                    );
-                    obligations.push(Obligation {
-                        cause: cause.clone(),
-                        recursion_depth,
-                        param_env,
-                        predicate: clause.as_predicate(),
-                    });
-                }
+        if matches!(tcx.def_kind(def_id), DefKind::Impl { of_trait: true }) {
+            for clause in tcx.impl_super_outlives(def_id).iter_instantiated(tcx, args) {
+                let clause = normalize_with_depth_to(
+                    self,
+                    param_env,
+                    cause.clone(),
+                    recursion_depth,
+                    clause,
+                    &mut obligations,
+                );
+                obligations.push(Obligation {
+                    cause: cause.clone(),
+                    recursion_depth,
+                    param_env,
+                    predicate: clause.as_predicate(),
+                });
             }
         }