Auto merge of #161938 - jackh726:polonius-lazy-liveness-final, r=lqd

Defer extra liveness calculation for Polonius Alpha



Best reviewed by commit.

This moves liveness calculation of NLL-boring/Polonius-relevant locals to be lazy. This allows us to skip unnecessary work.

r? lqd

Author: bors

compiler/rustc_borrowck/src/lib.rs

@@ -310,7 +310,7 @@ struct CollectRegionConstraintsResult<'tcx> {
     deferred_closure_requirements: DeferredClosureRequirements<'tcx>,
     deferred_opaque_type_errors: Vec<DeferredOpaqueTypeError<'tcx>>,
     polonius_facts: Option<AllFacts<RustcFacts>>,
-    polonius_context: Option<PoloniusContext>,
+    polonius_context: Option<PoloniusContext<'tcx>>,
 }
 
 /// Start borrow checking by collecting the region constraints for
@@ -797,7 +797,7 @@ pub(crate) struct MirBorrowckCtxt<'a, 'diag, 'tcx> {
     /// Results of Polonius analysis.
     polonius_output: Option<&'a PoloniusOutput>,
     /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics.
-    polonius_context: Option<&'a PoloniusContext>,
+    polonius_context: Option<&'a PoloniusContext<'tcx>>,
 }
 
 // Check that:

compiler/rustc_borrowck/src/nll.rs

@@ -46,7 +46,7 @@ pub(crate) struct NllOutput<'tcx> {
 
     /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics, e.g.
     /// localized typeck and liveness constraints.
-    pub polonius_context: Option<PoloniusContext>,
+    pub polonius_context: Option<PoloniusContext<'tcx>>,
 }
 
 /// Rewrites the regions in the MIR to use NLL variables, also scraping out the set of universal
@@ -121,7 +121,7 @@ pub(crate) fn compute_regions<'tcx>(
     universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
     constraints: MirTypeckRegionConstraints<'tcx>,
     mut polonius_facts: Option<AllFacts<RustcFacts>>,
-    mut polonius_context: Option<PoloniusContext>,
+    mut polonius_context: Option<PoloniusContext<'tcx>>,
 ) -> NllOutput<'tcx> {
     let polonius_output = root_cx.consumer.as_ref().map_or(false, |c| c.polonius_output())
         || infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled();
@@ -144,20 +144,20 @@ pub(crate) fn compute_regions<'tcx>(
         &lowered_constraints,
     );
 
-    let num_points = location_map.num_points();
-
     // If requested for `-Zpolonius=next`, compute loan liveness information.
     // This is done prior to `RegionInferenceContext::new`, because we may add
     // additional liveness constraints.
     if let Some(polonius_context) = polonius_context.as_mut() {
         let _timer = infcx.tcx.prof.generic_activity("borrowck_polonius_loan_liveness");
         polonius_context.compute_loan_liveness(
+            infcx,
             &mut lowered_constraints.liveness_constraints,
             lowered_constraints.outlives_constraints.outlives().iter().copied(),
             &universal_region_relations.universal_regions,
             body,
+            move_data,
+            &location_map,
             borrow_set,
-            num_points,
         );
     }
 

compiler/rustc_borrowck/src/polonius/constraints.rs

@@ -2,15 +2,14 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_index::IndexVec;
 use rustc_middle::mir::{Body, Location};
 use rustc_middle::ty::RegionVid;
-use rustc_mir_dataflow::points::PointIndex;
+use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
 
 use crate::BorrowSet;
 use crate::constraints::OutlivesConstraint;
 use crate::dataflow::BorrowIndex;
-use crate::polonius::{ConstraintDirection, LiveRegionVariances};
-use crate::region_infer::values::LivenessValues;
+use crate::polonius::ConstraintDirection;
+use crate::polonius::liveness::RegionLiveness;
 use crate::type_check::Locations;
-use crate::universal_regions::UniversalRegions;
 
 /// A localized outlives constraint reifies the CFG location where the outlives constraint holds,
 /// within the origins themselves as if they were different from point to point: from `a: b`
@@ -49,11 +48,17 @@ pub(super) struct LocalizedConstraintGraph {
     logical_edges: IndexVec<RegionVid, FxIndexSet<RegionVid>>,
 }
 
+/// The source of liveness information for a given region.
+pub(super) trait LivenessSource<'loc> {
+    fn liveness_for_region(&mut self, region: RegionVid) -> RegionLiveness<'_>;
+    fn location_map(&self) -> &'loc DenseLocationMap;
+}
+
 /// The visitor interface when traversing a `LocalizedConstraintGraph`.
 pub(super) trait LocalizedConstraintGraphVisitor {
     /// Callback called when traversing a given `loan` encounters a localized `node` it hasn't
     /// visited before.
-    fn on_node_traversed(&mut self, _loan: BorrowIndex, _node: LocalizedNode) {}
+    fn on_node_traversed(&mut self, _loan: BorrowIndex, _node: LocalizedNode, _is_live: bool) {}
 
     /// Callback called when discovering a new `successor` node for the `current_node`.
     fn on_successor_discovered(&mut self, _current_node: LocalizedNode, _successor: LocalizedNode) {
@@ -63,7 +68,7 @@ pub(super) trait LocalizedConstraintGraphVisitor {
 impl LocalizedConstraintGraph {
     /// Traverses the constraints and returns the indexed graph of edges per node.
     pub(super) fn new<'tcx>(
-        liveness: &LivenessValues,
+        location_map: &DenseLocationMap,
         outlives_constraints: impl Iterator<Item = OutlivesConstraint<'tcx>>,
     ) -> Self {
         let mut edges: FxHashMap<_, FxIndexSet<_>> = FxHashMap::default();
@@ -80,7 +85,7 @@ impl LocalizedConstraintGraph {
                 Locations::Single(location) => {
                     let node = LocalizedNode {
                         region: outlives_constraint.sup,
-                        point: liveness.point_from_location(location),
+                        point: location_map.point_from_location(location),
                     };
                     edges.entry(node).or_default().insert(outlives_constraint.sub);
                 }
@@ -92,20 +97,18 @@ impl LocalizedConstraintGraph {
 
     /// Traverses the localized constraint graph per-loan, and notifies the `visitor` of discovered
     /// nodes and successors.
-    pub(super) fn traverse<'tcx>(
+    pub(super) fn traverse<'tcx, 'loc>(
         &self,
         body: &Body<'tcx>,
-        liveness: &LivenessValues,
-        live_region_variances: &LiveRegionVariances,
-        universal_regions: &UniversalRegions<'tcx>,
         borrow_set: &BorrowSet<'tcx>,
+        liveness_source: &mut impl LivenessSource<'loc>,
         visitor: &mut impl LocalizedConstraintGraphVisitor,
     ) {
-        let live_regions = liveness.points();
-
         let mut visited = FxHashSet::default();
         let mut stack = Vec::new();
 
+        let location_map = liveness_source.location_map();
+
         // Compute reachability per loan by traversing each loan's subgraph starting from where it
         // is introduced.
         for (loan_idx, loan) in borrow_set.iter_enumerated() {
@@ -114,15 +117,16 @@ impl LocalizedConstraintGraph {
 
             let start_node = LocalizedNode {
                 region: loan.region,
-                point: liveness.point_from_location(loan.reserve_location),
+                point: location_map.point_from_location(loan.reserve_location),
             };
             visited.insert(start_node);
             stack.push(start_node);
 
             while let Some(node) = stack.pop() {
+                let liveness = liveness_source.liveness_for_region(node.region);
                 // We've reached a node we haven't visited before.
-                let location = liveness.location_from_point(node.point);
-                visitor.on_node_traversed(loan_idx, node);
+                let location = location_map.to_location(node.point);
+                visitor.on_node_traversed(loan_idx, node, liveness.is_live_at(node.point));
 
                 // When we find a _new_ successor, we'd like to
                 // - visit it eventually,
@@ -140,26 +144,6 @@ impl LocalizedConstraintGraph {
                 // - the materialized logical edges that exist virtually at all points for this
                 //   node's region, localized at this point.
 
-                // Universal regions propagate loans along the CFG, i.e. forwards only.
-                let is_universal_region = universal_regions.is_universal_region(node.region);
-
-                // Note: there currently are cases related to promoted and const generics, where we don't yet
-                // have variance information (possibly about temporary regions created when typeck sanitizes the
-                // promoteds). Until that is done, we conservatively fallback to maximizing reachability by
-                // adding a bidirectional edge here. This will not limit traversal whatsoever, and thus
-                // propagate liveness when needed.
-                //
-                // FIXME: add the missing variance information and remove this fallback bidirectional edge.
-                let liveness_direction = if is_universal_region {
-                    ConstraintDirection::Forward
-                } else {
-                    live_region_variances
-                        .get(node.region)
-                        .copied()
-                        .flatten()
-                        .unwrap_or(ConstraintDirection::Bidirectional)
-                };
-
                 // The physical edges present at this node are:
                 //
                 // 1. the typeck edges that flow from region to region *at this point*.
@@ -178,14 +162,14 @@ impl LocalizedConstraintGraph {
                 //
                 // We still need to check liveness for each next point though.
                 if matches!(
-                    liveness_direction,
+                    liveness.direction,
                     ConstraintDirection::Forward | ConstraintDirection::Bidirectional
                 ) {
                     if body[location.block].statements.get(location.statement_index).is_some() {
                         // Intra-block edges, straight line constraints from each point to its successor
                         // within the same block.
                         let next_point = node.point + 1;
-                        if live_regions.contains(node.region, next_point) {
+                        if liveness.is_live_at(next_point) {
                             successor_found(LocalizedNode {
                                 region: node.region,
                                 point: next_point,
@@ -197,8 +181,8 @@ impl LocalizedConstraintGraph {
                         for successor_block in body[location.block].terminator().successors() {
                             let next_location =
                                 Location { block: successor_block, statement_index: 0 };
-                            let next_point = liveness.point_from_location(next_location);
-                            if live_regions.contains(node.region, next_point) {
+                            let next_point = location_map.point_from_location(next_location);
+                            if liveness.is_live_at(next_point) {
                                 successor_found(LocalizedNode {
                                     region: node.region,
                                     point: next_point,
@@ -219,9 +203,9 @@ impl LocalizedConstraintGraph {
                 // Liveness flows into the regions live at the next point. So, in a backwards view, we'll link
                 // the region from the current point, if it's live there, to the previous point.
                 if matches!(
-                    liveness_direction,
+                    liveness.direction,
                     ConstraintDirection::Backward | ConstraintDirection::Bidirectional
-                ) && live_regions.contains(node.region, node.point)
+                ) && liveness.is_live_at(node.point)
                 {
                     if location.statement_index > 0 {
                         // Backward edges to the predecessor point in the same block.
@@ -239,7 +223,8 @@ impl LocalizedConstraintGraph {
                                 block: pred_block,
                                 statement_index: body[pred_block].statements.len(),
                             };
-                            let previous_point = liveness.point_from_location(previous_location);
+                            let previous_point =
+                                location_map.point_from_location(previous_location);
                             successor_found(LocalizedNode {
                                 region: node.region,
                                 point: previous_point,

compiler/rustc_borrowck/src/polonius/dump.rs

@@ -5,29 +5,55 @@ use rustc_index::IndexVec;
 use rustc_middle::mir::pretty::{MirDumper, PassWhere, PrettyPrintMirOptions};
 use rustc_middle::mir::{Body, Location};
 use rustc_middle::ty::{RegionVid, TyCtxt};
-use rustc_mir_dataflow::points::PointIndex;
+use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
 use rustc_session::config::MirIncludeSpans;
 
 use crate::borrow_set::BorrowSet;
 use crate::constraints::OutlivesConstraint;
 use crate::dataflow::BorrowIndex;
-use crate::polonius::{LocalizedConstraintGraphVisitor, LocalizedNode, PoloniusContext};
+use crate::polonius::liveness::RegionLiveness;
+use crate::polonius::{
+    LiveRegionVariances, LivenessSource, LocalizedConstraintGraphVisitor, LocalizedNode,
+    PoloniusContext,
+};
 use crate::region_infer::values::LivenessValues;
 use crate::type_check::Locations;
+use crate::universal_regions::UniversalRegions;
 use crate::{BorrowckInferCtxt, ClosureRegionRequirements, RegionInferenceContext};
 
 /// The polonius MIR dump template: a regular HTML file for easy editing, with special dummy
 /// sections to be replaced by real contents.
 const TEMPLATE: &str = include_str!("./dump/polonius-mir-dump.template.html");
 
+/// A `LivenessSource` for already-existing liveness and variance data.
+struct CachedLivenessSource<'a, 'tcx> {
+    live_region_variances: &'a LiveRegionVariances,
+    universal_regions: &'a UniversalRegions<'tcx>,
+    liveness: &'a LivenessValues,
+}
+
+impl<'a, 'tcx> LivenessSource<'a> for CachedLivenessSource<'a, 'tcx> {
+    fn liveness_for_region(&mut self, region: RegionVid) -> RegionLiveness<'_> {
+        RegionLiveness::new(
+            region,
+            self.live_region_variances,
+            self.universal_regions,
+            self.liveness.points(),
+        )
+    }
+    fn location_map(&self) -> &'a DenseLocationMap {
+        self.liveness.location_map()
+    }
+}
+
 /// `-Zdump-mir=polonius` dumps MIR annotated with NLL and polonius specific information.
 pub(crate) fn dump_polonius_mir<'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
     borrow_set: &BorrowSet<'tcx>,
-    polonius_context: Option<&PoloniusContext>,
+    polonius_context: Option<&PoloniusContext<'tcx>>,
 ) {
     let tcx = infcx.tcx;
     if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
@@ -41,16 +67,14 @@ pub(crate) fn dump_polonius_mir<'tcx>(
 
     // If we have a polonius graph to dump along the rest of the MIR and NLL info, we extract its
     // constraints here.
+    let mut liveness_source = CachedLivenessSource {
+        live_region_variances: &polonius_context.live_region_variances,
+        universal_regions: regioncx.universal_regions(),
+        liveness: regioncx.liveness_constraints(),
+    };
     let mut collector = MirDumpCollector::default();
     if let Some(graph) = &polonius_context.graph {
-        graph.traverse(
-            body,
-            regioncx.liveness_constraints(),
-            &polonius_context.live_region_variances,
-            regioncx.universal_regions(),
-            borrow_set,
-            &mut collector,
-        );
+        graph.traverse(body, borrow_set, &mut liveness_source, &mut collector);
     }
 
     let extra_data = &|pass_where, out: &mut dyn io::Write| {
@@ -98,7 +122,7 @@ struct MirDumpCollector {
 }
 
 impl LocalizedConstraintGraphVisitor for MirDumpCollector {
-    fn on_node_traversed(&mut self, loan: BorrowIndex, node: LocalizedNode) {
+    fn on_node_traversed(&mut self, loan: BorrowIndex, node: LocalizedNode, _is_live: bool) {
         self.reachability.entry(loan).or_default().push(node);
     }