check_doc_keyword: don't alloc string for emptiness check

check_doc_alias_value: get argument as Symbol to prevent needless string convertions

check_doc_attrs: don't alloc vec, iterate over slice. Vec introduced in #83149, but no perf run posted on merge

replace as_str() check with symbol check

get_single_str_from_tts: don't prealloc string

trivial string to str replace

LifetimeScopeForPath::NonElided use Vec<Symbol> instead of Vec<String>

AssertModuleSource use BTreeSet<Symbol> instead of BTreeSet<String>

CrateInfo.crate_name replace FxHashMap<CrateNum, String> with FxHashMap<CrateNum, Symbol>

compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs

@@ -497,7 +497,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
                             param_names
                                 .iter()
                                 .take(num_params_to_take)
-                                .map(|p| (*p).clone())
+                                .map(|p| p.as_str())
                                 .collect::<Vec<_>>()
                                 .join(", ")
                         } else {