Rewrite the DenseBitSet structure to only use one word on the stack.

This commit modifies DenseBitSet so that it only uses one word on the
stack instead of 4 words as before, allowing for faster clones. The
downside is that it may at most store 63 elements on the stack as aposed
to 128 for the previous implementation.

Author: Tage Johansson

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_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 }