mbe: Change unused_macro_rules to a DenseBitSet

Now that it only contains indexes, and no other information, a bitset
provides a more compact and simpler representation.

Author: joshtriplett

Cargo.lock

@@ -4461,6 +4461,7 @@ dependencies = [
  "rustc_feature",
  "rustc_fluent_macro",
  "rustc_hir",
+ "rustc_index",
  "rustc_macros",
  "rustc_metadata",
  "rustc_middle",

compiler/rustc_resolve/Cargo.toml

@@ -19,6 +19,7 @@ rustc_expand = { path = "../rustc_expand" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_hir = { path = "../rustc_hir" }
+rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_metadata = { path = "../rustc_metadata" }
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -18,6 +18,7 @@ use rustc_expand::base::ResolverExpand;
 use rustc_expand::expand::AstFragment;
 use rustc_hir::def::{self, *};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
+use rustc_index::bit_set::DenseBitSet;
 use rustc_metadata::creader::LoadedMacro;
 use rustc_middle::metadata::ModChild;
 use rustc_middle::ty::Feed;
@@ -1202,9 +1203,8 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
     fn insert_unused_macro(&mut self, ident: Ident, def_id: LocalDefId, node_id: NodeId) {
         if !ident.as_str().starts_with('_') {
             self.r.unused_macros.insert(def_id, (node_id, ident));
-            for rule_i in 0..self.r.macro_map[&def_id.to_def_id()].nrules {
-                self.r.unused_macro_rules.entry(node_id).or_default().insert(rule_i);
-            }
+            let nrules = self.r.macro_map[&def_id.to_def_id()].nrules;
+            self.r.unused_macro_rules.insert(node_id, DenseBitSet::new_filled(nrules));
         }
     }
 

compiler/rustc_resolve/src/lib.rs

@@ -46,7 +46,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::FreezeReadGuard;
-use rustc_data_structures::unord::{UnordMap, UnordSet};
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{Applicability, Diag, ErrCode, ErrorGuaranteed};
 use rustc_expand::base::{DeriveResolution, SyntaxExtension, SyntaxExtensionKind};
 use rustc_feature::BUILTIN_ATTRIBUTES;
@@ -57,6 +57,7 @@ use rustc_hir::def::{
 use rustc_hir::def_id::{CRATE_DEF_ID, CrateNum, DefId, LOCAL_CRATE, LocalDefId, LocalDefIdMap};
 use rustc_hir::definitions::DisambiguatorState;
 use rustc_hir::{PrimTy, TraitCandidate};
+use rustc_index::bit_set::DenseBitSet;
 use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::middle::privacy::EffectiveVisibilities;
@@ -1135,7 +1136,7 @@ pub struct Resolver<'ra, 'tcx> {
     ast_transform_scopes: FxHashMap<LocalExpnId, Module<'ra>>,
     unused_macros: FxIndexMap<LocalDefId, (NodeId, Ident)>,
     /// A map from the macro to all its potentially unused arms.
-    unused_macro_rules: FxIndexMap<NodeId, UnordSet<usize>>,
+    unused_macro_rules: FxIndexMap<NodeId, DenseBitSet<usize>>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
     single_segment_macro_resolutions:

compiler/rustc_resolve/src/macros.rs

@@ -334,7 +334,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
 
     fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
         if let Some(rules) = self.unused_macro_rules.get_mut(&id) {
-            rules.remove(&rule_i);
+            rules.remove(rule_i);
         }
     }
 
@@ -359,7 +359,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
             let SyntaxExtensionKind::LegacyBang(ref ext) = m.ext.kind else {
                 continue;
             };
-            for &arm_i in unused_arms.to_sorted_stable_ord() {
+            for arm_i in unused_arms.iter() {
                 if let Some((ident, rule_span)) = ext.get_unused_rule(arm_i) {
                     self.lint_buffer.buffer_lint(
                         UNUSED_MACRO_RULES,