Rollup merge of #135205 - lqd:bitsets, r=Mark-Simulacrum

Rename `BitSet` to `DenseBitSet`

r? `@Mark-Simulacrum` as you requested this in https://github.com/rust-lang/rust/pull/134438#discussion_r1890659739 after such a confusion.

This PR renames `BitSet` to `DenseBitSet` to make it less obvious as the go-to solution for bitmap needs, as well as make its representation (and positives/negatives) clearer. It also expands the comments there to hopefully make it clearer when it's not a good fit, with some alternative bitsets types.

(This migrates the subtrees cg_gcc and clippy to use the new name in separate commits, for easier review by their respective owners, but they can obvs be squashed)

1 files changed, 7 insertions, 4 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/counters.rs b/compiler/rustc_mir_transform/src/coverage/counters.rs
index 9e80f1f1c4a..a9111a5ef9b 100644
--- a/compiler/rustc_mir_transform/src/coverage/counters.rs
+++ b/compiler/rustc_mir_transform/src/coverage/counters.rs
@@ -5,7 +5,7 @@ use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::IndexVec;
-use rustc_index::bit_set::BitSet;
+use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
 use tracing::{debug, debug_span, instrument};
 
@@ -77,7 +77,7 @@ impl CoverageCounters {
     /// counters or counter expressions for nodes and edges as required.
     pub(super) fn make_bcb_counters(
         graph: &CoverageGraph,
-        bcb_needs_counter: &BitSet<BasicCoverageBlock>,
+        bcb_needs_counter: &DenseBitSet<BasicCoverageBlock>,
     ) -> Self {
         let mut builder = CountersBuilder::new(graph, bcb_needs_counter);
         builder.make_bcb_counters();
@@ -220,13 +220,16 @@ fn sibling_out_edge_targets(
 /// the set of nodes that need counters.
 struct CountersBuilder<'a> {
     graph: &'a CoverageGraph,
-    bcb_needs_counter: &'a BitSet<BasicCoverageBlock>,
+    bcb_needs_counter: &'a DenseBitSet<BasicCoverageBlock>,
 
     site_counters: FxHashMap<Site, SiteCounter>,
 }
 
 impl<'a> CountersBuilder<'a> {
-    fn new(graph: &'a CoverageGraph, bcb_needs_counter: &'a BitSet<BasicCoverageBlock>) -> Self {
+    fn new(
+        graph: &'a CoverageGraph,
+        bcb_needs_counter: &'a DenseBitSet<BasicCoverageBlock>,
+    ) -> Self {
         assert_eq!(graph.num_nodes(), bcb_needs_counter.domain_size());
         Self { graph, bcb_needs_counter, site_counters: FxHashMap::default() }
     }