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Auto merge of rust-lang#116152 - cjgillot:unchunck, r=nnethercote
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Only use dense bitsets in dataflow analyses

When a dataflow state has the size close to the number of locals, we should prefer a dense bitset, like we already store locals in a dense vector.
Other occurrences of `ChunkedBitSet` need to be justified by the size of the dataflow state.
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bors committed Jan 23, 2024
2 parents 8b94152 + e07ffe9 commit 0e42435
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Showing 7 changed files with 24 additions and 17 deletions.
6 changes: 3 additions & 3 deletions compiler/rustc_borrowck/src/type_check/liveness/trace.rs
Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
use rustc_data_structures::graph::WithSuccessors;
use rustc_index::bit_set::HybridBitSet;
use rustc_index::bit_set::BitSet;
use rustc_index::interval::IntervalSet;
use rustc_infer::infer::canonical::QueryRegionConstraints;
use rustc_infer::infer::outlives::for_liveness;
Expand Down Expand Up @@ -135,7 +135,7 @@ struct LivenessResults<'me, 'typeck, 'flow, 'tcx> {
cx: LivenessContext<'me, 'typeck, 'flow, 'tcx>,

/// Set of points that define the current local.
defs: HybridBitSet<PointIndex>,
defs: BitSet<PointIndex>,

/// Points where the current variable is "use live" -- meaning
/// that there is a future "full use" that may use its value.
Expand All @@ -158,7 +158,7 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
let num_points = cx.elements.num_points();
LivenessResults {
cx,
defs: HybridBitSet::new_empty(num_points),
defs: BitSet::new_empty(num_points),
use_live_at: IntervalSet::new(num_points),
drop_live_at: IntervalSet::new(num_points),
drop_locations: vec![],
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_index/src/bit_set.rs
Original file line number Diff line number Diff line change
Expand Up @@ -284,7 +284,7 @@ impl<T: Idx> BitSet<T> {
not_already
}

fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
pub fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
let (start, end) = inclusive_start_end(range, self.domain_size)?;
let (start_word_index, _) = word_index_and_mask(start);
let (end_word_index, end_mask) = word_index_and_mask(end);
Expand Down Expand Up @@ -1299,7 +1299,7 @@ impl<T: Idx> SparseBitSet<T> {
}

impl<T: Idx + Ord> SparseBitSet<T> {
fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
pub fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
let mut last_leq = None;
for e in self.iter() {
if range.contains(e) {
Expand Down
7 changes: 7 additions & 0 deletions compiler/rustc_mir_dataflow/src/impls/initialized.rs
Original file line number Diff line number Diff line change
Expand Up @@ -305,7 +305,10 @@ impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
}

impl<'tcx> AnalysisDomain<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
/// There can be many more `MovePathIndex` than there are locals in a MIR body.
/// We use a chunked bitset to avoid paying too high a memory footprint.
type Domain = MaybeReachable<ChunkedBitSet<MovePathIndex>>;

const NAME: &'static str = "maybe_init";

fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
Expand Down Expand Up @@ -437,6 +440,8 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
}

impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
/// There can be many more `MovePathIndex` than there are locals in a MIR body.
/// We use a chunked bitset to avoid paying too high a memory footprint.
type Domain = ChunkedBitSet<MovePathIndex>;

const NAME: &'static str = "maybe_uninit";
Expand Down Expand Up @@ -636,6 +641,8 @@ impl<'tcx> GenKillAnalysis<'tcx> for DefinitelyInitializedPlaces<'_, 'tcx> {
}

impl<'tcx> AnalysisDomain<'tcx> for EverInitializedPlaces<'_, 'tcx> {
/// There can be many more `InitIndex` than there are locals in a MIR body.
/// We use a chunked bitset to avoid paying too high a memory footprint.
type Domain = ChunkedBitSet<InitIndex>;

const NAME: &'static str = "ever_init";
Expand Down
10 changes: 5 additions & 5 deletions compiler/rustc_mir_dataflow/src/impls/liveness.rs
Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use rustc_index::bit_set::{BitSet, ChunkedBitSet};
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::{
self, CallReturnPlaces, Local, Location, Place, StatementKind, TerminatorEdges,
Expand Down Expand Up @@ -26,14 +26,14 @@ use crate::{Analysis, AnalysisDomain, Backward, GenKill, GenKillAnalysis};
pub struct MaybeLiveLocals;

impl<'tcx> AnalysisDomain<'tcx> for MaybeLiveLocals {
type Domain = ChunkedBitSet<Local>;
type Domain = BitSet<Local>;
type Direction = Backward;

const NAME: &'static str = "liveness";

fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
// bottom = not live
ChunkedBitSet::new_empty(body.local_decls.len())
BitSet::new_empty(body.local_decls.len())
}

fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
Expand Down Expand Up @@ -233,14 +233,14 @@ impl<'a> MaybeTransitiveLiveLocals<'a> {
}

impl<'a, 'tcx> AnalysisDomain<'tcx> for MaybeTransitiveLiveLocals<'a> {
type Domain = ChunkedBitSet<Local>;
type Domain = BitSet<Local>;
type Direction = Backward;

const NAME: &'static str = "transitive liveness";

fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
// bottom = not live
ChunkedBitSet::new_empty(body.local_decls.len())
BitSet::new_empty(body.local_decls.len())
}

fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
Expand Down
6 changes: 3 additions & 3 deletions compiler/rustc_mir_dataflow/src/points.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use crate::framework::{visit_results, ResultsVisitable, ResultsVisitor};
use rustc_index::bit_set::ChunkedBitSet;
use rustc_index::bit_set::BitSet;
use rustc_index::interval::SparseIntervalMatrix;
use rustc_index::Idx;
use rustc_index::IndexVec;
Expand Down Expand Up @@ -102,7 +102,7 @@ pub fn save_as_intervals<'tcx, N, R>(
) -> SparseIntervalMatrix<N, PointIndex>
where
N: Idx,
R: ResultsVisitable<'tcx, FlowState = ChunkedBitSet<N>>,
R: ResultsVisitable<'tcx, FlowState = BitSet<N>>,
{
let values = SparseIntervalMatrix::new(elements.num_points());
let mut visitor = Visitor { elements, values };
Expand All @@ -124,7 +124,7 @@ impl<'mir, 'tcx, R, N> ResultsVisitor<'mir, 'tcx, R> for Visitor<'_, N>
where
N: Idx,
{
type FlowState = ChunkedBitSet<N>;
type FlowState = BitSet<N>;

fn visit_statement_after_primary_effect(
&mut self,
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_mir_dataflow/src/rustc_peek.rs
Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use crate::MoveDataParamEnv;
use crate::{Analysis, JoinSemiLattice, ResultsCursor};
use rustc_ast::MetaItem;
use rustc_hir::def_id::DefId;
use rustc_index::bit_set::ChunkedBitSet;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::MirPass;
use rustc_middle::mir::{self, Body, Local, Location};
use rustc_middle::ty::{self, Ty, TyCtxt};
Expand Down Expand Up @@ -275,7 +275,7 @@ impl<'tcx> RustcPeekAt<'tcx> for MaybeLiveLocals {
&self,
tcx: TyCtxt<'tcx>,
place: mir::Place<'tcx>,
flow_state: &ChunkedBitSet<Local>,
flow_state: &BitSet<Local>,
call: PeekCall,
) {
info!(?place, "peek_at");
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_mir_transform/src/nrvo.rs
Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
//! See the docs for [`RenameReturnPlace`].

use rustc_hir::Mutability;
use rustc_index::bit_set::HybridBitSet;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::{MutVisitor, NonUseContext, PlaceContext, Visitor};
use rustc_middle::mir::{self, BasicBlock, Local, Location};
use rustc_middle::ty::TyCtxt;
Expand Down Expand Up @@ -123,7 +123,7 @@ fn find_local_assigned_to_return_place(
body: &mut mir::Body<'_>,
) -> Option<Local> {
let mut block = start;
let mut seen = HybridBitSet::new_empty(body.basic_blocks.len());
let mut seen = BitSet::new_empty(body.basic_blocks.len());

// Iterate as long as `block` has exactly one predecessor that we have not yet visited.
while seen.insert(block) {
Expand Down

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