Auto merge of #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 https://github.com/rust-lang/rust/pull/124336.

1 files changed, 16 insertions, 26 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 1d9a90f0300..1b2767a6a62 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/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(),
+                });
             }
         }