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, 14 insertions, 14 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index edaec3c7965..3e7cf8541c2 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -1,5 +1,5 @@
 use rustc_data_structures::captures::Captures;
-use rustc_index::bit_set::BitSet;
+use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::{
     CounterId, CovTerm, CoverageIdsInfo, CoverageKind, Expression, ExpressionId,
@@ -92,13 +92,13 @@ fn coverage_ids_info<'tcx>(
 
     let Some(fn_cov_info) = mir_body.function_coverage_info.as_deref() else {
         return CoverageIdsInfo {
-            counters_seen: BitSet::new_empty(0),
-            zero_expressions: BitSet::new_empty(0),
+            counters_seen: DenseBitSet::new_empty(0),
+            zero_expressions: DenseBitSet::new_empty(0),
         };
     };
 
-    let mut counters_seen = BitSet::new_empty(fn_cov_info.num_counters);
-    let mut expressions_seen = BitSet::new_filled(fn_cov_info.expressions.len());
+    let mut counters_seen = DenseBitSet::new_empty(fn_cov_info.num_counters);
+    let mut expressions_seen = DenseBitSet::new_filled(fn_cov_info.expressions.len());
 
     // For each expression ID that is directly used by one or more mappings,
     // mark it as not-yet-seen. This indicates that we expect to see a
@@ -148,23 +148,23 @@ fn is_inlined(body: &Body<'_>, statement: &Statement<'_>) -> bool {
     scope_data.inlined.is_some() || scope_data.inlined_parent_scope.is_some()
 }
 
-/// Identify expressions that will always have a value of zero, and note
-/// their IDs in a `BitSet`. Mappings that refer to a zero expression
-/// can instead become mappings to a constant zero value.
+/// Identify expressions that will always have a value of zero, and note their
+/// IDs in a `DenseBitSet`. Mappings that refer to a zero expression can instead
+/// become mappings to a constant zero value.
 ///
 /// This function mainly exists to preserve the simplifications that were
 /// already being performed by the Rust-side expression renumbering, so that
 /// the resulting coverage mappings don't get worse.
 fn identify_zero_expressions(
     fn_cov_info: &FunctionCoverageInfo,
-    counters_seen: &BitSet<CounterId>,
-    expressions_seen: &BitSet<ExpressionId>,
-) -> BitSet<ExpressionId> {
+    counters_seen: &DenseBitSet<CounterId>,
+    expressions_seen: &DenseBitSet<ExpressionId>,
+) -> DenseBitSet<ExpressionId> {
     // The set of expressions that either were optimized out entirely, or
     // have zero as both of their operands, and will therefore always have
     // a value of zero. Other expressions that refer to these as operands
     // can have those operands replaced with `CovTerm::Zero`.
-    let mut zero_expressions = BitSet::new_empty(fn_cov_info.expressions.len());
+    let mut zero_expressions = DenseBitSet::new_empty(fn_cov_info.expressions.len());
 
     // Simplify a copy of each expression based on lower-numbered expressions,
     // and then update the set of always-zero expressions if necessary.
@@ -228,8 +228,8 @@ fn identify_zero_expressions(
 /// into account knowledge of which counters are unused and which expressions
 /// are always zero.
 fn is_zero_term(
-    counters_seen: &BitSet<CounterId>,
-    zero_expressions: &BitSet<ExpressionId>,
+    counters_seen: &DenseBitSet<CounterId>,
+    zero_expressions: &DenseBitSet<ExpressionId>,
     term: CovTerm,
 ) -> bool {
     match term {