Delegation: second attempt to improve perf

compiler/rustc_hir/src/hir.rs

@@ -2952,6 +2952,17 @@ pub struct FnDecl<'hir> {
     pub lifetime_elision_allowed: bool,
 }
 
+impl<'hir> FnDecl<'hir> {
+    pub fn opt_delegation_sig_id(&self) -> Option<DefId> {
+        if let FnRetTy::Return(ty) = self.output
+            && let TyKind::InferDelegation(sig_id, _) = ty.kind
+        {
+            return Some(sig_id);
+        }
+        None
+    }
+}
+
 /// Represents what type of implicit self a function has, if any.
 #[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub enum ImplicitSelfKind {

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -54,13 +54,6 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         };
     }
 
-    // For a delegation item inherit generics from callee.
-    if let Some(sig_id) = tcx.hir().opt_delegation_sig_id(def_id)
-        && let Some(generics) = inherit_generics_for_delegation_item(tcx, def_id, sig_id)
-    {
-        return generics;
-    }
-
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
 
     let node = tcx.hir_node(hir_id);
@@ -234,6 +227,16 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 // inherit the generics of the item.
                 Some(parent.to_def_id())
             }
+            ItemKind::Fn(sig, _, _) => {
+                // For a delegation item inherit generics from callee.
+                if let Some(sig_id) = sig.decl.opt_delegation_sig_id()
+                    && let Some(generics) =
+                        inherit_generics_for_delegation_item(tcx, def_id, sig_id)
+                {
+                    return generics;
+                }
+                None
+            }
             _ => None,
         },
         _ => None,

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -115,13 +115,6 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
         None => {}
     }
 
-    // For a delegation item inherit predicates from callee.
-    if let Some(sig_id) = tcx.hir().opt_delegation_sig_id(def_id)
-        && let Some(predicates) = inherit_predicates_for_delegation_item(tcx, def_id, sig_id)
-    {
-        return predicates;
-    }
-
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
     let node = tcx.hir_node(hir_id);
 
@@ -151,6 +144,16 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             ItemKind::Trait(_, _, _, self_bounds, ..) | ItemKind::TraitAlias(_, self_bounds) => {
                 is_trait = Some(self_bounds);
             }
+
+            ItemKind::Fn(sig, _, _) => {
+                // For a delegation item inherit predicates from callee.
+                if let Some(sig_id) = sig.decl.opt_delegation_sig_id()
+                    && let Some(predicates) =
+                        inherit_predicates_for_delegation_item(tcx, def_id, sig_id)
+                {
+                    return predicates;
+                }
+            }
             _ => {}
         }
     };

compiler/rustc_hir_analysis/src/delegation.rs

@@ -242,7 +242,7 @@ pub(crate) fn inherit_sig_for_delegation_item<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
 ) -> &'tcx [Ty<'tcx>] {
-    let sig_id = tcx.hir().delegation_sig_id(def_id);
+    let sig_id = tcx.hir().opt_delegation_sig_id(def_id).unwrap();
     let caller_sig = tcx.fn_sig(sig_id);
     if let Err(err) = check_constraints(tcx, def_id, sig_id) {
         let sig_len = caller_sig.instantiate_identity().skip_binder().inputs().len() + 1;

compiler/rustc_middle/src/hir/map/mod.rs

@@ -747,18 +747,7 @@ impl<'hir> Map<'hir> {
     }
 
     pub fn opt_delegation_sig_id(self, def_id: LocalDefId) -> Option<DefId> {
-        if let Some(ret) = self.get_fn_output(def_id)
-            && let FnRetTy::Return(ty) = ret
-            && let TyKind::InferDelegation(sig_id, _) = ty.kind
-        {
-            return Some(sig_id);
-        }
-        None
-    }
-
-    #[inline]
-    pub fn delegation_sig_id(self, def_id: LocalDefId) -> DefId {
-        self.opt_delegation_sig_id(def_id).unwrap()
+        self.tcx.opt_hir_owner_node(def_id)?.fn_decl()?.opt_delegation_sig_id()
     }
 
     #[inline]