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)

2 files changed, 6 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
index 43b8230c679..23baab3124e 100644
--- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
@@ -2,7 +2,7 @@
 //! which do not.
 
 use rustc_data_structures::graph::dominators::Dominators;
-use rustc_index::bit_set::BitSet;
+use rustc_index::bit_set::DenseBitSet;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{self, DefLocation, Location, TerminatorKind, traversal};
@@ -16,7 +16,7 @@ use crate::traits::*;
 pub(crate) fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     fx: &FunctionCx<'a, 'tcx, Bx>,
     traversal_order: &[mir::BasicBlock],
-) -> BitSet<mir::Local> {
+) -> DenseBitSet<mir::Local> {
     let mir = fx.mir;
     let dominators = mir.basic_blocks.dominators();
     let locals = mir
@@ -44,7 +44,7 @@ pub(crate) fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         analyzer.visit_basic_block_data(bb, data);
     }
 
-    let mut non_ssa_locals = BitSet::new_empty(analyzer.locals.len());
+    let mut non_ssa_locals = DenseBitSet::new_empty(analyzer.locals.len());
     for (local, kind) in analyzer.locals.iter_enumerated() {
         if matches!(kind, LocalKind::Memory) {
             non_ssa_locals.insert(local);
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 62f69af3f2f..3a896071bc6 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -1,7 +1,7 @@
 use std::iter;
 
 use rustc_index::IndexVec;
-use rustc_index::bit_set::BitSet;
+use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::{UnwindTerminateReason, traversal};
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, TyAndLayout};
@@ -293,7 +293,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     // So drop the builder of `start_llbb` to avoid having two at the same time.
     drop(start_bx);
 
-    let mut unreached_blocks = BitSet::new_filled(mir.basic_blocks.len());
+    let mut unreached_blocks = DenseBitSet::new_filled(mir.basic_blocks.len());
     // Codegen the body of each reachable block using our reverse postorder list.
     for bb in traversal_order {
         fx.codegen_block(bb);
@@ -316,7 +316,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     bx: &mut Bx,
     fx: &mut FunctionCx<'a, 'tcx, Bx>,
-    memory_locals: &BitSet<mir::Local>,
+    memory_locals: &DenseBitSet<mir::Local>,
 ) -> Vec<LocalRef<'tcx, Bx::Value>> {
     let mir = fx.mir;
     let mut idx = 0;