Auto merge of #98841 - Kobzol:hir-validator-bitset, r=cjgillot

Use a bitset instead of a hash map in HIR ID validator

The hashset insertion was slightly hot in incr patched runs, but it seems unnecessary to use a hashset here, as it just checks that a dense set of N integers was seen.

I'm not sure if it's possible to know the amount of items beforehand to preallocate the bitset? I suppose not.

compiler/rustc_index/src/bit_set.rs

@@ -1546,6 +1546,16 @@ impl<T: Idx> GrowableBitSet<T> {
         let (word_index, mask) = word_index_and_mask(elem);
         self.bit_set.words.get(word_index).map_or(false, |word| (word & mask) != 0)
     }
+
+    #[inline]
+    pub fn iter(&self) -> BitIter<'_, T> {
+        self.bit_set.iter()
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.bit_set.count()
+    }
 }
 
 impl<T: Idx> From<BitSet<T>> for GrowableBitSet<T> {

compiler/rustc_passes/src/hir_id_validator.rs

@@ -1,9 +1,9 @@
-use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lock;
 use rustc_hir as hir;
 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::intravisit;
 use rustc_hir::{HirId, ItemLocalId};
+use rustc_index::bit_set::GrowableBitSet;
 use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::TyCtxt;
@@ -15,6 +15,8 @@ pub fn check_crate(tcx: TyCtxt<'_>) {
         crate::hir_stats::print_hir_stats(tcx);
     }
 
+    #[cfg(debug_assertions)]
+    {
         let errors = Lock::new(Vec::new());
         let hir_map = tcx.hir();
 
@@ -35,12 +37,13 @@ pub fn check_crate(tcx: TyCtxt<'_>) {
             let message = errors.iter().fold(String::new(), |s1, s2| s1 + "\n" + s2);
             tcx.sess.delay_span_bug(rustc_span::DUMMY_SP, &message);
         }
+    }
 }
 
 struct HirIdValidator<'a, 'hir> {
     hir_map: Map<'hir>,
     owner: Option<LocalDefId>,
-    hir_ids_seen: FxHashSet<ItemLocalId>,
+    hir_ids_seen: GrowableBitSet<ItemLocalId>,
     errors: &'a Lock<Vec<String>>,
 }
 
@@ -80,7 +83,7 @@ impl<'a, 'hir> HirIdValidator<'a, 'hir> {
         if max != self.hir_ids_seen.len() - 1 {
             // Collect the missing ItemLocalIds
             let missing: Vec<_> = (0..=max as u32)
-                .filter(|&i| !self.hir_ids_seen.contains(&ItemLocalId::from_u32(i)))
+                .filter(|&i| !self.hir_ids_seen.contains(ItemLocalId::from_u32(i)))
                 .collect();
 
             // Try to map those to something more useful
@@ -106,7 +109,7 @@ impl<'a, 'hir> HirIdValidator<'a, 'hir> {
                     missing_items,
                     self.hir_ids_seen
                         .iter()
-                        .map(|&local_id| HirId { owner, local_id })
+                        .map(|local_id| HirId { owner, local_id })
                         .map(|h| format!("({:?} {})", h, self.hir_map.node_to_string(h)))
                         .collect::<Vec<_>>()
                 )