Auto merge of #90637 - Mark-Simulacrum:liveness-btree, r=lqd

Store liveness in interval sets for region inference

On the 100,000 line test case from #90445, this reduces memory usage from 35 GB to 444 MB at peak (based on DHAT results, though with regular malloc), and yields a 9.4x speedup, with wall time going from 14.5 seconds to 1.5s. Performance results show that for the majority of real-world code this has little to no impact, but it's expected to generally scale better for auto-generated functions and other cases which stress this area of the compiler, as results on #90445 illustrate.

There may also be further room for improvement in future PRs making use of this data structures benefits over raw bitsets (which, at some level, are a less perfect fit for representing liveness, which is almost always composed of contiguous ranges, not point locations).

Fixes #90445.

Author: bors

Diff for: Cargo.lock

@@ -3976,6 +3976,7 @@ dependencies = [
  "arrayvec",
  "rustc_macros",
  "rustc_serialize",
+ "smallvec",
 ]
 
 [[package]]

Diff for: compiler/rustc_borrowck/src/region_infer/values.rs

@@ -1,5 +1,7 @@
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_index::bit_set::{HybridBitSet, SparseBitMatrix};
+use rustc_index::bit_set::SparseBitMatrix;
+use rustc_index::interval::IntervalSet;
+use rustc_index::interval::SparseIntervalMatrix;
 use rustc_index::vec::Idx;
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::{BasicBlock, Body, Location};
@@ -110,19 +112,19 @@ crate enum RegionElement {
     PlaceholderRegion(ty::PlaceholderRegion),
 }
 
-/// When we initially compute liveness, we use a bit matrix storing
-/// points for each region-vid.
+/// When we initially compute liveness, we use an interval matrix storing
+/// liveness ranges for each region-vid.
 crate struct LivenessValues<N: Idx> {
     elements: Rc<RegionValueElements>,
-    points: SparseBitMatrix<N, PointIndex>,
+    points: SparseIntervalMatrix<N, PointIndex>,
 }
 
 impl<N: Idx> LivenessValues<N> {
     /// Creates a new set of "region values" that tracks causal information.
     /// Each of the regions in num_region_variables will be initialized with an
     /// empty set of points and no causal information.
     crate fn new(elements: Rc<RegionValueElements>) -> Self {
-        Self { points: SparseBitMatrix::new(elements.num_points), elements }
+        Self { points: SparseIntervalMatrix::new(elements.num_points), elements }
     }
 
     /// Iterate through each region that has a value in this set.
@@ -140,7 +142,7 @@ impl<N: Idx> LivenessValues<N> {
 
     /// Adds all the elements in the given bit array into the given
     /// region. Returns whether any of them are newly added.
-    crate fn add_elements(&mut self, row: N, locations: &HybridBitSet<PointIndex>) -> bool {
+    crate fn add_elements(&mut self, row: N, locations: &IntervalSet<PointIndex>) -> bool {
         debug!("LivenessValues::add_elements(row={:?}, locations={:?})", row, locations);
         self.points.union_row(row, locations)
     }
@@ -153,7 +155,7 @@ impl<N: Idx> LivenessValues<N> {
     /// Returns `true` if the region `r` contains the given element.
     crate fn contains(&self, row: N, location: Location) -> bool {
         let index = self.elements.point_from_location(location);
-        self.points.contains(row, index)
+        self.points.row(row).map_or(false, |r| r.contains(index))
     }
 
     /// Returns an iterator of all the elements contained by the region `r`
@@ -221,7 +223,7 @@ impl PlaceholderIndices {
 crate struct RegionValues<N: Idx> {
     elements: Rc<RegionValueElements>,
     placeholder_indices: Rc<PlaceholderIndices>,
-    points: SparseBitMatrix<N, PointIndex>,
+    points: SparseIntervalMatrix<N, PointIndex>,
     free_regions: SparseBitMatrix<N, RegionVid>,
 
     /// Placeholders represent bound regions -- so something like `'a`
@@ -241,7 +243,7 @@ impl<N: Idx> RegionValues<N> {
         let num_placeholders = placeholder_indices.len();
         Self {
             elements: elements.clone(),
-            points: SparseBitMatrix::new(elements.num_points),
+            points: SparseIntervalMatrix::new(elements.num_points),
             placeholder_indices: placeholder_indices.clone(),
             free_regions: SparseBitMatrix::new(num_universal_regions),
             placeholders: SparseBitMatrix::new(num_placeholders),

Diff for: compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -1,5 +1,6 @@
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_index::bit_set::HybridBitSet;
+use rustc_index::interval::IntervalSet;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_middle::mir::{BasicBlock, Body, ConstraintCategory, Local, Location};
 use rustc_middle::ty::{Ty, TypeFoldable};
@@ -105,12 +106,12 @@ struct LivenessResults<'me, 'typeck, 'flow, 'tcx> {
 
     /// Points where the current variable is "use live" -- meaning
     /// that there is a future "full use" that may use its value.
-    use_live_at: HybridBitSet<PointIndex>,
+    use_live_at: IntervalSet<PointIndex>,
 
     /// Points where the current variable is "drop live" -- meaning
     /// that there is no future "full use" that may use its value, but
     /// there is a future drop.
-    drop_live_at: HybridBitSet<PointIndex>,
+    drop_live_at: IntervalSet<PointIndex>,
 
     /// Locations where drops may occur.
     drop_locations: Vec<Location>,
@@ -125,8 +126,8 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
         LivenessResults {
             cx,
             defs: HybridBitSet::new_empty(num_points),
-            use_live_at: HybridBitSet::new_empty(num_points),
-            drop_live_at: HybridBitSet::new_empty(num_points),
+            use_live_at: IntervalSet::new(num_points),
+            drop_live_at: IntervalSet::new(num_points),
             drop_locations: vec![],
             stack: vec![],
         }
@@ -165,7 +166,7 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
         drop_used: Vec<(Local, Location)>,
         live_locals: FxHashSet<Local>,
     ) {
-        let locations = HybridBitSet::new_empty(self.cx.elements.num_points());
+        let locations = IntervalSet::new(self.cx.elements.num_points());
 
         for (local, location) in drop_used {
             if !live_locals.contains(&local) {
@@ -456,7 +457,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
     fn add_use_live_facts_for(
         &mut self,
         value: impl TypeFoldable<'tcx>,
-        live_at: &HybridBitSet<PointIndex>,
+        live_at: &IntervalSet<PointIndex>,
     ) {
         debug!("add_use_live_facts_for(value={:?})", value);
 
@@ -473,7 +474,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
         dropped_local: Local,
         dropped_ty: Ty<'tcx>,
         drop_locations: &[Location],
-        live_at: &HybridBitSet<PointIndex>,
+        live_at: &IntervalSet<PointIndex>,
     ) {
         debug!(
             "add_drop_live_constraint(\
@@ -521,7 +522,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
         elements: &RegionValueElements,
         typeck: &mut TypeChecker<'_, 'tcx>,
         value: impl TypeFoldable<'tcx>,
-        live_at: &HybridBitSet<PointIndex>,
+        live_at: &IntervalSet<PointIndex>,
     ) {
         debug!("make_all_regions_live(value={:?})", value);
         debug!(

Diff for: compiler/rustc_index/Cargo.toml

@@ -10,3 +10,4 @@ doctest = false
 arrayvec = { version = "0.7", default-features = false }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_macros = { path = "../rustc_macros" }
+smallvec = "1"