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, 2 insertions, 2 deletions

diff --git a/compiler/rustc_pattern_analysis/src/constructor.rs b/compiler/rustc_pattern_analysis/src/constructor.rs
index 8fce4266345..4ce868f014f 100644
--- a/compiler/rustc_pattern_analysis/src/constructor.rs
+++ b/compiler/rustc_pattern_analysis/src/constructor.rs
@@ -182,7 +182,7 @@ use std::iter::once;
 
 use rustc_apfloat::ieee::{DoubleS, HalfS, IeeeFloat, QuadS, SingleS};
 use rustc_index::IndexVec;
-use rustc_index::bit_set::{BitSet, GrowableBitSet};
+use rustc_index::bit_set::{DenseBitSet, GrowableBitSet};
 use smallvec::SmallVec;
 
 use self::Constructor::*;
@@ -1072,7 +1072,7 @@ impl<Cx: PatCx> ConstructorSet<Cx> {
                 }
             }
             ConstructorSet::Variants { variants, non_exhaustive } => {
-                let mut seen_set = BitSet::new_empty(variants.len());
+                let mut seen_set = DenseBitSet::new_empty(variants.len());
                 for idx in seen.iter().filter_map(|c| c.as_variant()) {
                     seen_set.insert(idx);
                 }