Avoid interning in resolve_place_op.

This function is hot for `keccak`.

src/librustc_typeck/check/mod.rs

@@ -2698,16 +2698,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
     fn resolve_place_op(&self, op: PlaceOp, is_mut: bool) -> (Option<DefId>, ast::Ident) {
         let (tr, name) = match (op, is_mut) {
-            (PlaceOp::Deref, false) =>
-                (self.tcx.lang_items().deref_trait(), "deref"),
-            (PlaceOp::Deref, true) =>
-                (self.tcx.lang_items().deref_mut_trait(), "deref_mut"),
-            (PlaceOp::Index, false) =>
-                (self.tcx.lang_items().index_trait(), "index"),
-            (PlaceOp::Index, true) =>
-                (self.tcx.lang_items().index_mut_trait(), "index_mut"),
+            (PlaceOp::Deref, false) => (self.tcx.lang_items().deref_trait(), sym::deref),
+            (PlaceOp::Deref, true) => (self.tcx.lang_items().deref_mut_trait(), sym::deref_mut),
+            (PlaceOp::Index, false) => (self.tcx.lang_items().index_trait(), sym::index),
+            (PlaceOp::Index, true) => (self.tcx.lang_items().index_mut_trait(), sym::index_mut),
         };
-        (tr, ast::Ident::from_str(name))
+        (tr, ast::Ident::with_empty_ctxt(name))
     }
 
     fn try_overloaded_place_op(&self,

src/libsyntax_pos/symbol.rs

@@ -204,6 +204,8 @@ symbols! {
         default_type_params,
         deny,
         deprecated,
+        deref,
+        deref_mut,
         derive,
         doc,
         doc_alias,
@@ -291,6 +293,8 @@ symbols! {
         impl_header_lifetime_elision,
         impl_trait_in_bindings,
         import_shadowing,
+        index,
+        index_mut,
         in_band_lifetimes,
         include,
         inclusive_range_syntax,