From 9419f5f937ebdccf6cefea5d8a2bd193aab1e662 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Thu, 29 Aug 2024 11:47:00 +1000 Subject: [PATCH] Simplify `Candidate`. By making it own the index maps, instead of holding references to them. This requires moving the free function `find_candidate` into `Candidate::reset_and_find`. It lets the `'alloc` lifetime be removed everywhere that still has it. --- compiler/rustc_mir_transform/src/dest_prop.rs | 83 ++++++++----------- 1 file changed, 36 insertions(+), 47 deletions(-) diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs index f5f496acfcea0..d925d95700c3f 100644 --- a/compiler/rustc_mir_transform/src/dest_prop.rs +++ b/compiler/rustc_mir_transform/src/dest_prop.rs @@ -164,8 +164,7 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation { fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { let def_id = body.source.def_id(); - let mut candidates = FxIndexMap::default(); - let mut candidates_reverse = FxIndexMap::default(); + let mut candidates = Candidates::default(); let mut write_info = WriteInfo::default(); trace!(func = ?tcx.def_path_str(def_id)); @@ -194,12 +193,7 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation { loop { // PERF: Can we do something smarter than recalculating the candidates and liveness // results? - let mut candidates = find_candidates( - body, - &borrowed, - &mut candidates, - &mut candidates_reverse, - ); + candidates.reset_and_find(body, &borrowed); trace!(?candidates); dest_prop_mir_dump(tcx, body, &points, &live, round_count); @@ -256,8 +250,8 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation { } } -#[derive(Debug)] -struct Candidates<'alloc> { +#[derive(Debug, Default)] +struct Candidates { /// The set of candidates we are considering in this optimization. /// /// We will always merge the key into at most one of its values. @@ -272,11 +266,12 @@ struct Candidates<'alloc> { /// /// We will still report that we would like to merge `_1` and `_2` in an attempt to allow us to /// remove that assignment. - c: &'alloc mut FxIndexMap>, + c: FxIndexMap>, + /// A reverse index of the `c` set; if the `c` set contains `a => Place { local: b, proj }`, /// then this contains `b => a`. // PERF: Possibly these should be `SmallVec`s? - reverse: &'alloc mut FxIndexMap>, + reverse: FxIndexMap>, } ////////////////////////////////////////////////////////// @@ -349,11 +344,11 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Merger<'a, 'tcx> { // // This section enforces bullet point 2 -struct FilterInformation<'a, 'alloc, 'tcx> { +struct FilterInformation<'a, 'tcx> { body: &'a Body<'tcx>, points: &'a DenseLocationMap, live: &'a SparseIntervalMatrix, - candidates: &'a mut Candidates<'alloc>, + candidates: &'a mut Candidates, write_info: &'a mut WriteInfo, at: Location, } @@ -361,7 +356,28 @@ struct FilterInformation<'a, 'alloc, 'tcx> { // We first implement some utility functions which we will expose removing candidates according to // different needs. Throughout the liveness filtering, the `candidates` are only ever accessed // through these methods, and not directly. -impl<'alloc> Candidates<'alloc> { +impl Candidates { + /// Collects the candidates for merging + /// + /// This is responsible for enforcing the first and third bullet point. + fn reset_and_find<'tcx>(&mut self, body: &Body<'tcx>, borrowed: &BitSet) { + self.c.clear(); + self.reverse.clear(); + let mut visitor = FindAssignments { body, candidates: &mut self.c, borrowed }; + visitor.visit_body(body); + // Deduplicate candidates + for (_, cands) in self.c.iter_mut() { + cands.sort(); + cands.dedup(); + } + // Generate the reverse map + for (src, cands) in self.c.iter() { + for dest in cands.iter().copied() { + self.reverse.entry(dest).or_default().push(*src); + } + } + } + /// Just `Vec::retain`, but the condition is inverted and we add debugging output fn vec_filter_candidates( src: Local, @@ -436,7 +452,7 @@ enum CandidateFilter { Remove, } -impl<'a, 'alloc, 'tcx> FilterInformation<'a, 'alloc, 'tcx> { +impl<'a, 'tcx> FilterInformation<'a, 'tcx> { /// Filters the set of candidates to remove those that conflict. /// /// The steps we take are exactly those that are outlined at the top of the file. For each @@ -455,7 +471,7 @@ impl<'a, 'alloc, 'tcx> FilterInformation<'a, 'alloc, 'tcx> { /// statement/terminator to be live. We are additionally conservative by treating all written to /// locals as also being read from. fn filter_liveness( - candidates: &mut Candidates<'alloc>, + candidates: &mut Candidates, points: &DenseLocationMap, live: &SparseIntervalMatrix, write_info: &mut WriteInfo, @@ -725,40 +741,13 @@ fn places_to_candidate_pair<'tcx>( Some((a, b)) } -/// Collects the candidates for merging -/// -/// This is responsible for enforcing the first and third bullet point. -fn find_candidates<'alloc, 'tcx>( - body: &Body<'tcx>, - borrowed: &BitSet, - candidates: &'alloc mut FxIndexMap>, - candidates_reverse: &'alloc mut FxIndexMap>, -) -> Candidates<'alloc> { - candidates.clear(); - candidates_reverse.clear(); - let mut visitor = FindAssignments { body, candidates, borrowed }; - visitor.visit_body(body); - // Deduplicate candidates - for (_, cands) in candidates.iter_mut() { - cands.sort(); - cands.dedup(); - } - // Generate the reverse map - for (src, cands) in candidates.iter() { - for dest in cands.iter().copied() { - candidates_reverse.entry(dest).or_default().push(*src); - } - } - Candidates { c: candidates, reverse: candidates_reverse } -} - -struct FindAssignments<'a, 'alloc, 'tcx> { +struct FindAssignments<'a, 'tcx> { body: &'a Body<'tcx>, - candidates: &'alloc mut FxIndexMap>, + candidates: &'a mut FxIndexMap>, borrowed: &'a BitSet, } -impl<'tcx> Visitor<'tcx> for FindAssignments<'_, '_, 'tcx> { +impl<'tcx> Visitor<'tcx> for FindAssignments<'_, 'tcx> { fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) { if let StatementKind::Assign(box ( lhs,