1
Fork 0

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.
This commit is contained in:
Nicholas Nethercote 2024-08-29 11:47:00 +10:00
parent ad5a6e11c7
commit 1be2204363

View file

@ -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<Local, Vec<Local>>,
c: FxIndexMap<Local, Vec<Local>>,
/// 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<Local, Vec<Local>>,
reverse: FxIndexMap<Local, Vec<Local>>,
}
//////////////////////////////////////////////////////////
@ -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<Local, PointIndex>,
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<Local>) {
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<Local, PointIndex>,
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<Local>,
candidates: &'alloc mut FxIndexMap<Local, Vec<Local>>,
candidates_reverse: &'alloc mut FxIndexMap<Local, Vec<Local>>,
) -> 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<Local, Vec<Local>>,
candidates: &'a mut FxIndexMap<Local, Vec<Local>>,
borrowed: &'a BitSet<Local>,
}
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,