lang-items: Store NodeId mappings for lang items

gcc/rust/ChangeLog:

	* util/rust-hir-map.h: Keep a NodeId mappings for lang items.
	* util/rust-hir-map.cc (Mappings::insert_lang_item_node): New function.
	(Mappings::lookup_lang_item_node): Likewise.

gcc/rust/util/rust-hir-map.cc

@@ -1241,6 +1241,9 @@ Mappings::lookup_builtin_marker ()
   return builtinMarker;
 }
 
+// FIXME: Before merging: Should we remove the `locus` parameter here? since
+// lang items are looked up mostly for code generation, it doesn't make sense to
+// error out on the locus of the node trying to access an inexistant lang item
 DefId
 Mappings::get_lang_item (LangItem::Kind item_type, location_t locus)
 {
@@ -1277,5 +1280,24 @@ Mappings::lookup_lang_item (LangItem::Kind item_type)
   return it->second;
 }
 
+void
+Mappings::insert_lang_item_node (LangItem::Kind item_type, NodeId node_id)
+{
+  auto it = lang_item_nodes.find (item_type);
+  rust_assert (it == lang_item_nodes.end ());
+
+  lang_item_nodes.insert ({item_type, node_id});
+}
+
+tl::optional<NodeId &>
+Mappings::lookup_lang_item_node (LangItem::Kind item_type)
+{
+  auto it = lang_item_nodes.find (item_type);
+  if (it == lang_item_nodes.end ())
+    return tl::nullopt;
+
+  return it->second;
+}
+
 } // namespace Analysis
 } // namespace Rust

gcc/rust/util/rust-hir-map.h

@@ -259,6 +259,9 @@ class Mappings
   void insert_lang_item (LangItem::Kind item_type, DefId id);
   tl::optional<DefId &> lookup_lang_item (LangItem::Kind item_type);
 
+  void insert_lang_item_node (LangItem::Kind item_type, NodeId node_id);
+  tl::optional<NodeId &> lookup_lang_item_node (LangItem::Kind item_type);
+
   // This will fatal_error when this lang item does not exist
   DefId get_lang_item (LangItem::Kind item_type, location_t locus);
 
@@ -375,7 +378,12 @@ class Mappings
   std::map<HirId, HIR::GenericParam *> hirGenericParamMappings;
   std::map<HirId, HIR::Trait *> hirTraitItemsToTraitMappings;
   std::map<HirId, HIR::Pattern *> hirPatternMappings;
+
+  // We need to have two maps here, as lang-items need to be used for both AST
+  // passes and HIR passes. Thus those two maps are created at different times.
   std::map<LangItem::Kind, DefId> lang_item_mappings;
+  std::map<LangItem::Kind, NodeId> lang_item_nodes;
+
   std::map<NodeId, Resolver::CanonicalPath> paths;
   std::map<NodeId, location_t> locations;
   std::map<NodeId, HirId> nodeIdToHirMappings;