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_builtin_macros/src/compile_error.rs

@@ -13,7 +13,7 @@ pub fn expand_compile_error<'cx>(
         return DummyResult::any(sp);
     };
 
-    cx.span_err(sp, &var);
+    cx.span_err(sp, var.as_str());
 
     DummyResult::any(sp)
 }

compiler/rustc_builtin_macros/src/env.rs

@@ -21,8 +21,8 @@ pub fn expand_option_env<'cx>(
     };
 
     let sp = cx.with_def_site_ctxt(sp);
-    let value = env::var(&var.as_str()).ok().as_deref().map(Symbol::intern);
+    let value = env::var(var.as_str()).ok().as_deref().map(Symbol::intern);
-    cx.sess.parse_sess.env_depinfo.borrow_mut().insert((Symbol::intern(&var), value));
+    cx.sess.parse_sess.env_depinfo.borrow_mut().insert((var, value));
     let e = match value {
         None => {
             let lt = cx.lifetime(sp, Ident::new(kw::StaticLifetime, sp));

compiler/rustc_builtin_macros/src/source_util.rs

@@ -104,7 +104,7 @@ pub fn expand_include<'cx>(
         return DummyResult::any(sp);
     };
     // The file will be added to the code map by the parser
-    let file = match resolve_path(cx, file, sp) {
+    let file = match resolve_path(cx, file.as_str(), sp) {
         Ok(f) => f,
         Err(mut err) => {
             err.emit();
@@ -173,7 +173,7 @@ pub fn expand_include_str(
     let Some(file) = get_single_str_from_tts(cx, sp, tts, "include_str!") else {
         return DummyResult::any(sp);
     };
-    let file = match resolve_path(cx, file, sp) {
+    let file = match resolve_path(cx, file.as_str(), sp) {
         Ok(f) => f,
         Err(mut err) => {
             err.emit();
@@ -207,7 +207,7 @@ pub fn expand_include_bytes(
     let Some(file) = get_single_str_from_tts(cx, sp, tts, "include_bytes!") else {
         return DummyResult::any(sp);
     };
-    let file = match resolve_path(cx, file, sp) {
+    let file = match resolve_path(cx, file.as_str(), sp) {
         Ok(f) => f,
         Err(mut err) => {
             err.emit();

compiler/rustc_codegen_cranelift/src/driver/jit.rs

@@ -288,8 +288,8 @@ fn load_imported_symbols_for_jit(
         match data[cnum.as_usize() - 1] {
             Linkage::NotLinked | Linkage::IncludedFromDylib => {}
             Linkage::Static => {
-                let name = &crate_info.crate_name[&cnum];
+                let name = crate_info.crate_name[&cnum];
-                let mut err = sess.struct_err(&format!("Can't load static lib {}", name.as_str()));
+                let mut err = sess.struct_err(&format!("Can't load static lib {}", name));
                 err.note("rustc_codegen_cranelift can only load dylibs in JIT mode.");
                 err.emit();
             }

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -216,7 +216,7 @@ pub fn each_linked_rlib(
             Some(_) => {}
             None => return Err("could not find formats for rlibs".to_string()),
         }
-        let name = &info.crate_name[&cnum];
+        let name = info.crate_name[&cnum];
         let used_crate_source = &info.used_crate_source[&cnum];
         if let Some((path, _)) = &used_crate_source.rlib {
             f(cnum, &path);
@@ -467,7 +467,7 @@ fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
     let mut all_native_libs = vec![];
 
     let res = each_linked_rlib(&codegen_results.crate_info, &mut |cnum, path| {
-        let name = &codegen_results.crate_info.crate_name[&cnum];
+        let name = codegen_results.crate_info.crate_name[&cnum];
         let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
 
         // Here when we include the rlib into our staticlib we need to make a

compiler/rustc_codegen_ssa/src/base.rs

@@ -861,7 +861,7 @@ impl CrateInfo {
         for &cnum in crates.iter() {
             info.native_libraries
                 .insert(cnum, tcx.native_libraries(cnum).iter().map(Into::into).collect());
-            info.crate_name.insert(cnum, tcx.crate_name(cnum).to_string());
+            info.crate_name.insert(cnum, tcx.crate_name(cnum));
             info.used_crate_source.insert(cnum, tcx.used_crate_source(cnum).clone());
             if tcx.is_compiler_builtins(cnum) {
                 info.compiler_builtins = Some(cnum);

compiler/rustc_codegen_ssa/src/lib.rs

@@ -146,7 +146,7 @@ pub struct CrateInfo {
     pub profiler_runtime: Option<CrateNum>,
     pub is_no_builtins: FxHashSet<CrateNum>,
     pub native_libraries: FxHashMap<CrateNum, Vec<NativeLib>>,
-    pub crate_name: FxHashMap<CrateNum, String>,
+    pub crate_name: FxHashMap<CrateNum, Symbol>,
     pub used_libraries: Vec<NativeLib>,
     pub used_crate_source: FxHashMap<CrateNum, Lrc<CrateSource>>,
     pub used_crates: Vec<CrateNum>,

compiler/rustc_expand/src/base.rs

@@ -1215,7 +1215,7 @@ pub fn get_single_str_from_tts(
     sp: Span,
     tts: TokenStream,
     name: &str,
-) -> Option<String> {
+) -> Option<Symbol> {
     let mut p = cx.new_parser_from_tts(tts);
     if p.token == token::Eof {
         cx.span_err(sp, &format!("{} takes 1 argument", name));
@@ -1227,7 +1227,7 @@ pub fn get_single_str_from_tts(
     if p.token != token::Eof {
         cx.span_err(sp, &format!("{} takes 1 argument", name));
     }
-    expr_to_string(cx, ret, "argument must be a string literal").map(|(s, _)| s.to_string())
+    expr_to_string(cx, ret, "argument must be a string literal").map(|(s, _)| s)
 }
 
 /// Extracts comma-separated expressions from `tts`.

compiler/rustc_incremental/src/assert_module_sources.rs

@@ -22,12 +22,12 @@
 //! was re-used.
 
 use rustc_ast as ast;
+use rustc_data_structures::stable_set::FxHashSet;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::mir::mono::CodegenUnitNameBuilder;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::cgu_reuse_tracker::*;
 use rustc_span::symbol::{sym, Symbol};
-use std::collections::BTreeSet;
 
 #[allow(missing_docs)]
 pub fn assert_module_sources(tcx: TyCtxt<'_>) {
@@ -36,12 +36,8 @@ pub fn assert_module_sources(tcx: TyCtxt<'_>) {
             return;
         }
 
-        let available_cgus = tcx
+        let available_cgus =
-            .collect_and_partition_mono_items(())
+            tcx.collect_and_partition_mono_items(()).1.iter().map(|cgu| cgu.name()).collect();
-            .1
-            .iter()
-            .map(|cgu| cgu.name().to_string())
-            .collect::<BTreeSet<String>>();
 
         let ams = AssertModuleSource { tcx, available_cgus };
 
@@ -53,7 +49,7 @@ pub fn assert_module_sources(tcx: TyCtxt<'_>) {
 
 struct AssertModuleSource<'tcx> {
     tcx: TyCtxt<'tcx>,
-    available_cgus: BTreeSet<String>,
+    available_cgus: FxHashSet<Symbol>,
 }
 
 impl<'tcx> AssertModuleSource<'tcx> {
@@ -124,18 +120,17 @@ impl<'tcx> AssertModuleSource<'tcx> {
 
         debug!("mapping '{}' to cgu name '{}'", self.field(attr, sym::module), cgu_name);
 
-        if !self.available_cgus.contains(cgu_name.as_str()) {
+        if !self.available_cgus.contains(&cgu_name) {
+            let mut cgu_names: Vec<&str> =
+                self.available_cgus.iter().map(|cgu| cgu.as_str()).collect();
+            cgu_names.sort();
             self.tcx.sess.span_err(
                 attr.span,
                 &format!(
                     "no module named `{}` (mangled: {}). Available modules: {}",
                     user_path,
                     cgu_name,
-                    self.available_cgus
+                    cgu_names.join(", ")
-                        .iter()
-                        .map(|cgu| cgu.to_string())
-                        .collect::<Vec<_>>()
-                        .join(", ")
                 ),
             );
         }

compiler/rustc_middle/src/middle/resolve_lifetime.rs

@@ -6,6 +6,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::ItemLocalId;
 use rustc_macros::HashStable;
+use rustc_span::symbol::Symbol;
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable, Debug, HashStable)]
 pub enum Region {
@@ -23,7 +24,7 @@ pub enum Region {
 pub enum LifetimeScopeForPath {
     // Contains all lifetime names that are in scope and could possibly be used in generics
     // arguments of path.
-    NonElided(Vec<String>),
+    NonElided(Vec<Symbol>),
 
     // Information that allows us to suggest args of the form `<'_>` in case
     // no generic arguments were provided for a path.

compiler/rustc_middle/src/mir/pretty.rs

@@ -561,8 +561,7 @@ fn write_scope_tree(
         }
         indented_decl.push(';');
 
-        let local_name =
+        let local_name = if local == RETURN_PLACE { " return place" } else { "" };
-            if local == RETURN_PLACE { " return place".to_string() } else { String::new() };
 
         writeln!(
             w,

compiler/rustc_passes/src/check_attr.rs

@@ -20,7 +20,7 @@ use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, UNUSED_ATTRIBUTES,
 };
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::{sym, Symbol};
+use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use std::collections::hash_map::Entry;
 
@@ -536,7 +536,7 @@ impl CheckAttrVisitor<'_> {
     fn check_doc_alias_value(
         &self,
         meta: &NestedMetaItem,
-        doc_alias: &str,
+        doc_alias: Symbol,
         hir_id: HirId,
         target: Target,
         is_list: bool,
@@ -554,14 +554,17 @@ impl CheckAttrVisitor<'_> {
             );
             false
         };
-        if doc_alias.is_empty() {
+        if doc_alias == kw::Empty {
             return err_fn(
                 meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
                 "attribute cannot have empty value",
             );
         }
-        if let Some(c) =
+
-            doc_alias.chars().find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
+        let doc_alias_str = doc_alias.as_str();
+        if let Some(c) = doc_alias_str
+            .chars()
+            .find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
         {
             self.tcx.sess.span_err(
                 meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
@@ -573,7 +576,7 @@ impl CheckAttrVisitor<'_> {
             );
             return false;
         }
-        if doc_alias.starts_with(' ') || doc_alias.ends_with(' ') {
+        if doc_alias_str.starts_with(' ') || doc_alias_str.ends_with(' ') {
             return err_fn(
                 meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
                 "cannot start or end with ' '",
@@ -608,11 +611,11 @@ impl CheckAttrVisitor<'_> {
             return err_fn(meta.span(), &format!("isn't allowed on {}", err));
         }
         let item_name = self.tcx.hir().name(hir_id);
-        if item_name.as_str() == doc_alias {
+        if item_name == doc_alias {
             return err_fn(meta.span(), "is the same as the item's name");
         }
         let span = meta.span();
-        if let Err(entry) = aliases.try_insert(doc_alias.to_owned(), span) {
+        if let Err(entry) = aliases.try_insert(doc_alias_str.to_owned(), span) {
             self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, span, |lint| {
                 lint.build("doc alias is duplicated")
                     .span_label(*entry.entry.get(), "first defined here")
@@ -635,14 +638,7 @@ impl CheckAttrVisitor<'_> {
                 match v.literal() {
                     Some(l) => match l.kind {
                         LitKind::Str(s, _) => {
-                            if !self.check_doc_alias_value(
+                            if !self.check_doc_alias_value(v, s, hir_id, target, true, aliases) {
-                                v,
-                                s.as_str(),
-                                hir_id,
-                                target,
-                                true,
-                                aliases,
-                            ) {
                                 errors += 1;
                             }
                         }
@@ -670,8 +666,8 @@ impl CheckAttrVisitor<'_> {
                 }
             }
             errors == 0
-        } else if let Some(doc_alias) = meta.value_str().map(|s| s.to_string()) {
+        } else if let Some(doc_alias) = meta.value_str() {
-            self.check_doc_alias_value(meta, &doc_alias, hir_id, target, false, aliases)
+            self.check_doc_alias_value(meta, doc_alias, hir_id, target, false, aliases)
         } else {
             self.tcx
                 .sess
@@ -686,8 +682,8 @@ impl CheckAttrVisitor<'_> {
     }
 
     fn check_doc_keyword(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
-        let doc_keyword = meta.value_str().map(|s| s.to_string()).unwrap_or_else(String::new);
+        let doc_keyword = meta.value_str().unwrap_or(kw::Empty);
-        if doc_keyword.is_empty() {
+        if doc_keyword == kw::Empty {
             self.doc_attr_str_error(meta, "keyword");
             return false;
         }
@@ -718,7 +714,7 @@ impl CheckAttrVisitor<'_> {
                 return false;
             }
         }
-        if !rustc_lexer::is_ident(&doc_keyword) {
+        if !rustc_lexer::is_ident(doc_keyword.as_str()) {
             self.tcx
                 .sess
                 .struct_span_err(
@@ -911,20 +907,20 @@ impl CheckAttrVisitor<'_> {
     ) -> bool {
         let mut is_valid = true;
 
-        if let Some(list) = attr.meta().and_then(|mi| mi.meta_item_list().map(|l| l.to_vec())) {
+        if let Some(mi) = attr.meta() && let Some(list) = mi.meta_item_list() {
-            for meta in &list {
+            for meta in list {
                 if let Some(i_meta) = meta.meta_item() {
                     match i_meta.name_or_empty() {
                         sym::alias
-                            if !self.check_attr_not_crate_level(&meta, hir_id, "alias")
+                            if !self.check_attr_not_crate_level(meta, hir_id, "alias")
-                                || !self.check_doc_alias(&meta, hir_id, target, aliases) =>
+                                || !self.check_doc_alias(meta, hir_id, target, aliases) =>
                         {
                             is_valid = false
                         }
 
                         sym::keyword
-                            if !self.check_attr_not_crate_level(&meta, hir_id, "keyword")
+                            if !self.check_attr_not_crate_level(meta, hir_id, "keyword")
-                                || !self.check_doc_keyword(&meta, hir_id) =>
+                                || !self.check_doc_keyword(meta, hir_id) =>
                         {
                             is_valid = false
                         }
@@ -936,15 +932,15 @@ impl CheckAttrVisitor<'_> {
                         | sym::html_root_url
                         | sym::html_no_source
                         | sym::test
-                            if !self.check_attr_crate_level(&attr, &meta, hir_id) =>
+                            if !self.check_attr_crate_level(attr, meta, hir_id) =>
                         {
                             is_valid = false;
                         }
 
                         sym::inline | sym::no_inline
                             if !self.check_doc_inline(
-                                &attr,
+                                attr,
-                                &meta,
+                                meta,
                                 hir_id,
                                 target,
                                 specified_inline,
@@ -976,7 +972,7 @@ impl CheckAttrVisitor<'_> {
                         | sym::plugins => {}
 
                         sym::test => {
-                            if !self.check_test_attr(&meta, hir_id) {
+                            if !self.check_test_attr(meta, hir_id) {
                                 is_valid = false;
                             }
                         }

compiler/rustc_passes/src/stability.rs

@@ -696,7 +696,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
             hir::ItemKind::ExternCrate(_) => {
                 // compiler-generated `extern crate` items have a dummy span.
                 // `std` is still checked for the `restricted-std` feature.
-                if item.span.is_dummy() && item.ident.as_str() != "std" {
+                if item.span.is_dummy() && item.ident.name != sym::std {
                     return;
                 }
 

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -587,7 +587,7 @@ fn get_lifetime_scopes_for_path(mut scope: &Scope<'_>) -> LifetimeScopeForPath {
         match scope {
             Scope::Binder { lifetimes, s, .. } => {
                 available_lifetimes.extend(lifetimes.keys().filter_map(|p| match p {
-                    hir::ParamName::Plain(ident) => Some(ident.name.to_string()),
+                    hir::ParamName::Plain(ident) => Some(ident.name),
                     _ => None,
                 }));
                 scope = s;

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 {