Optimize TyCtxt::adjust_ident.

It's a hot function that returns a 2-tuple, but the hottest call site
(`hygienic_eq`) discards the second element.

This commit renames `adjust_ident` as `adjust_ident_and_get_scope`, and
then introduces a new `adjust_ident` that only computes the first
element. This change also avoids the need to pass in an unused
`DUMMY_HIR_ID` argument in a couple of places, which is nice.

src/librustc/ty/mod.rs

@@ -3089,20 +3089,28 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // comparison fails frequently, and we want to avoid the expensive
         // `modern()` calls required for the span comparison whenever possible.
         use_name.name == def_name.name &&
-        self.adjust_ident(use_name, def_parent_def_id, hir::DUMMY_HIR_ID).0.span.ctxt() ==
-            def_name.modern().span.ctxt()
+        self.adjust_ident(use_name, def_parent_def_id).span.ctxt() == def_name.modern().span.ctxt()
     }
 
-    pub fn adjust_ident(self, mut ident: Ident, scope: DefId, block: hir::HirId) -> (Ident, DefId) {
-        ident = ident.modern();
-        let target_expansion = match scope.krate {
+    fn expansion_that_defined(self, scope: DefId) -> Mark {
+        match scope.krate {
             LOCAL_CRATE => self.hir().definitions().expansion_that_defined(scope.index),
             _ => Mark::root(),
-        };
-        let scope = match ident.span.adjust(target_expansion) {
+        }
+    }
+
+    pub fn adjust_ident(self, mut ident: Ident, scope: DefId) -> Ident {
+        ident = ident.modern();
+        ident.span.adjust(self.expansion_that_defined(scope));
+        ident
+    }
+
+    pub fn adjust_ident_and_get_scope(self, mut ident: Ident, scope: DefId, block: hir::HirId)
+                                      -> (Ident, DefId) {
+        ident = ident.modern();
+        let scope = match ident.span.adjust(self.expansion_that_defined(scope)) {
             Some(actual_expansion) =>
                 self.hir().definitions().parent_module_of_macro_def(actual_expansion),
-            None if block == hir::DUMMY_HIR_ID => DefId::local(CRATE_DEF_INDEX), // Dummy DefId
             None => self.hir().get_module_parent_by_hir_id(block),
         };
         (ident, scope)

src/librustc_privacy/lib.rs

@@ -845,7 +845,7 @@ impl<'a, 'tcx> NamePrivacyVisitor<'a, 'tcx> {
                    field: &'tcx ty::FieldDef) { // definition of the field
         let ident = Ident::new(kw::Invalid, use_ctxt);
         let current_hir = self.current_item;
-        let def_id = self.tcx.adjust_ident(ident, def.did, current_hir).1;
+        let def_id = self.tcx.adjust_ident_and_get_scope(ident, def.did, current_hir).1;
         if !def.is_enum() && !field.vis.is_accessible_from(def_id, self.tcx) {
             struct_span_err!(self.tcx.sess, span, E0451, "field `{}` of {} `{}` is private",
                              field.ident, def.variant_descr(), self.tcx.def_path_str(def.did))

src/librustc_typeck/astconv.rs

@@ -903,7 +903,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         }?;
 
         let (assoc_ident, def_scope) =
-            tcx.adjust_ident(binding.item_name, candidate.def_id(), hir_ref_id);
+            tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
         let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
             i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident
         }).expect("missing associated type");
@@ -1433,7 +1433,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         };
 
         let trait_did = bound.def_id();
-        let (assoc_ident, def_scope) = tcx.adjust_ident(assoc_ident, trait_did, hir_ref_id);
+        let (assoc_ident, def_scope) =
+            tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
         let item = tcx.associated_items(trait_did).find(|i| {
             Namespace::from(i.kind) == Namespace::Type &&
                 i.ident.modern() == assoc_ident

src/librustc_typeck/check/_match.rs

@@ -1184,7 +1184,7 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
         let mut inexistent_fields = vec![];
         // Typecheck each field.
         for &Spanned { node: ref field, span } in fields {
-            let ident = tcx.adjust_ident(field.ident, variant.def_id, self.body_id).0;
+            let ident = tcx.adjust_ident(field.ident, variant.def_id);
             let field_ty = match used_fields.entry(ident) {
                 Occupied(occupied) => {
                     struct_span_err!(tcx.sess, span, E0025,

src/librustc_typeck/check/method/probe.rs

@@ -510,7 +510,8 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
     {
         let is_accessible = if let Some(name) = self.method_name {
             let item = candidate.item;
-            let def_scope = self.tcx.adjust_ident(name, item.container.id(), self.body_id).1;
+            let def_scope =
+                self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
             item.vis.is_accessible_from(def_scope, self.tcx)
         } else {
             true

src/librustc_typeck/check/mod.rs

@@ -3339,7 +3339,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
                     debug!("struct named {:?}",  base_t);
                     let (ident, def_scope) =
-                        self.tcx.adjust_ident(field, base_def.did, self.body_id);
+                        self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
                     let fields = &base_def.non_enum_variant().fields;
                     if let Some(index) = fields.iter().position(|f| f.ident.modern() == ident) {
                         let field = &fields[index];
@@ -3510,7 +3510,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
         variant.fields.iter().filter(|field| {
-            let def_scope = self.tcx.adjust_ident(field.ident, variant.def_id, self.body_id).1;
+            let def_scope =
+                self.tcx.adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id).1;
             field.vis.is_accessible_from(def_scope, self.tcx)
         })
         .map(|field| field.ident.name)
@@ -3628,7 +3629,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         // Type-check each field.
         for field in ast_fields {
-            let ident = tcx.adjust_ident(field.ident, variant.def_id, self.body_id).0;
+            let ident = tcx.adjust_ident(field.ident, variant.def_id);
             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
                 seen_fields.insert(ident, field.span);
                 self.write_field_index(field.hir_id, i);