[experiment, do not merge!] rewrite the DenseBitSet structure to only use 1 word on the stack

Cargo.lock

@@ -3855,6 +3855,7 @@ dependencies = [
 name = "rustc_index"
 version = "0.0.0"
 dependencies = [
+ "itertools",
  "rustc_index_macros",
  "rustc_macros",
  "rustc_serialize",

compiler/rustc_abi/src/layout/coroutine.rs

@@ -120,7 +120,7 @@ fn coroutine_saved_local_eligibility<VariantIdx: Idx, FieldIdx: Idx, LocalIdx: I
             for assignment in assignments.iter_mut() {
                 *assignment = Ineligible(None);
             }
-            ineligible_locals.insert_all();
+            ineligible_locals.insert_all(nb_locals);
         }
     }
 

compiler/rustc_data_structures/src/stable_hasher/tests.rs

@@ -14,16 +14,6 @@ fn hash<T: HashStable<()>>(t: &T) -> Hash128 {
     h.finish()
 }
 
-// Check that bit set hash includes the domain size.
-#[test]
-fn test_hash_bit_set() {
-    use rustc_index::bit_set::DenseBitSet;
-    let a: DenseBitSet<usize> = DenseBitSet::new_empty(1);
-    let b: DenseBitSet<usize> = DenseBitSet::new_empty(2);
-    assert_ne!(a, b);
-    assert_ne!(hash(&a), hash(&b));
-}
-
 // Check that bit matrix hash includes the matrix dimensions.
 #[test]
 fn test_hash_bit_matrix() {

compiler/rustc_index/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+itertools = "0.12"
 rustc_index_macros = { path = "../rustc_index_macros" }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }