Auto merge of rust-lang#141325 - tage64:thin_bit_set, r=<try>

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

Modify DenseBitSet in the rustc_index crate 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.

r? lqd

This is experimental so far and I mostly want a perf run to measure
the performance.

Author: bors

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 }