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Limit creation of tracked place directly.

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This commit is contained in:
Camille GILLOT 2023-01-28 11:23:18 +00:00
parent 9a6c04f5d0
commit c48756cdbf
2 changed files with 22 additions and 11 deletions
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22
compiler/rustc_mir_dataflow/src/value_analysis.rs
View File

@ -599,10 +599,11 @@ impl Map {
tcx: TyCtxt<'tcx>,
body: &Body<'tcx>,
filter: impl FnMut(Ty<'tcx>) -> bool,
place_limit: Option<usize>,
) -> Self {
let mut map = Self::new();
let exclude = excluded_locals(body);
map.register_with_filter(tcx, body, filter, exclude);
map.register_with_filter(tcx, body, filter, exclude, place_limit);
debug!("registered {} places ({} nodes in total)", map.value_count, map.places.len());
map
}
@ -614,12 +615,20 @@ impl Map {
body: &Body<'tcx>,
mut filter: impl FnMut(Ty<'tcx>) -> bool,
exclude: BitSet<Local>,
place_limit: Option<usize>,
) {
// We use this vector as stack, pushing and popping projections.
let mut projection = Vec::new();
for (local, decl) in body.local_decls.iter_enumerated() {
if !exclude.contains(local) {
self.register_with_filter_rec(tcx, local, &mut projection, decl.ty, &mut filter);
self.register_with_filter_rec(
tcx,
local,
&mut projection,
decl.ty,
&mut filter,
place_limit,
);
}
}
}
@ -634,7 +643,12 @@ impl Map {
projection: &mut Vec<PlaceElem<'tcx>>,
ty: Ty<'tcx>,
filter: &mut impl FnMut(Ty<'tcx>) -> bool,
place_limit: Option<usize>,
) {
if let Some(place_limit) = place_limit && self.value_count >= place_limit {
return
}
// We know that the projection only contains trackable elements.
let place = self.make_place(local, projection).unwrap();
@ -672,13 +686,13 @@ impl Map {
projection.push(PlaceElem::Downcast(None, variant));
let _ = self.make_place(local, projection);
projection.push(PlaceElem::Field(field, ty));
self.register_with_filter_rec(tcx, local, projection, ty, filter);
self.register_with_filter_rec(tcx, local, projection, ty, filter, place_limit);
projection.pop();
projection.pop();
return;
}
projection.push(PlaceElem::Field(field, ty));
self.register_with_filter_rec(tcx, local, projection, ty, filter);
self.register_with_filter_rec(tcx, local, projection, ty, filter, place_limit);
projection.pop();
});
}

11
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
View File

@ -37,9 +37,6 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
return;
}
// Decide which places to track during the analysis.
let map = Map::from_filter(tcx, body, Ty::is_scalar);
// We want to have a somewhat linear runtime w.r.t. the number of statements/terminators.
// Let's call this number `n`. Dataflow analysis has `O(h*n)` transfer function
// applications, where `h` is the height of the lattice. Because the height of our lattice
@ -48,10 +45,10 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
// `O(num_nodes * tracked_places * n)` in terms of time complexity. Since the number of
// map nodes is strongly correlated to the number of tracked places, this becomes more or
// less `O(n)` if we place a constant limit on the number of tracked places.
if tcx.sess.mir_opt_level() < 4 && map.tracked_places() > PLACE_LIMIT {
debug!("aborted dataflow const prop due to too many tracked places");
return;
}
let place_limit = if tcx.sess.mir_opt_level() < 4 { Some(PLACE_LIMIT) } else { None };
// Decide which places to track during the analysis.
let map = Map::from_filter(tcx, body, Ty::is_scalar, place_limit);
// Perform the actual dataflow analysis.
let analysis = ConstAnalysis::new(tcx, body, map);