Avoid recomputing the constraint graph

Author: amandasystems

compiler/rustc_borrowck/src/handle_placeholders.rs

@@ -10,6 +10,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{RegionVid, UniverseIndex};
 use tracing::{debug, trace};
 
+use crate::constraints::graph::NormalConstraintGraph;
 use crate::constraints::{ConstraintSccIndex, OutlivesConstraintSet};
 use crate::consumers::OutlivesConstraint;
 use crate::region_infer::values::LivenessValues;
@@ -26,6 +27,7 @@ pub(crate) struct LoweredConstraints<'tcx> {
     pub(crate) constraint_sccs: Sccs<RegionVid, ConstraintSccIndex>,
     pub(crate) definitions: Frozen<IndexVec<RegionVid, RegionDefinition<'tcx>>>,
     pub(crate) scc_annotations: IndexVec<ConstraintSccIndex, RegionTracker>,
+    pub(crate) constraint_graph: NormalConstraintGraph,
 }
 
 pub(crate) type RegionDefinitions<'tcx> = IndexVec<RegionVid, RegionDefinition<'tcx>>;
@@ -243,17 +245,19 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
         region_definitions(infcx, universal_regions, liveness_constraints);
 
     let fr_static = universal_regions.fr_static;
-    let compute_sccs =
-        |constraints: &OutlivesConstraintSet<'tcx>,
-         annotations: &mut SccAnnotations<'_, 'tcx, RegionTracker>| {
-            ConstraintSccs::new_with_annotation(
-                &constraints.graph(definitions.len()).region_graph(constraints, fr_static),
-                annotations,
-            )
-        };
+    let constraint_graph = outlives_constraints.graph(definitions.len());
+    let compute_sccs = |constraints: &OutlivesConstraintSet<'tcx>,
+                        annotations: &mut SccAnnotations<'_, 'tcx, RegionTracker>,
+                        constraint_graph: &NormalConstraintGraph| {
+        ConstraintSccs::new_with_annotation(
+            &constraint_graph.region_graph(constraints, fr_static),
+            annotations,
+        )
+    };
 
     let mut scc_annotations = SccAnnotations::init(&definitions);
-    let constraint_sccs = compute_sccs(&outlives_constraints, &mut scc_annotations);
+    let constraint_sccs =
+        compute_sccs(&outlives_constraints, &mut scc_annotations, &constraint_graph);
 
     // This code structure is a bit convoluted because it allows for a planned
     // future change where the early return here has a different type of annotation
@@ -265,6 +269,7 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
             constraint_sccs,
             scc_annotations: scc_annotations.scc_to_annotation,
             definitions,
+            constraint_graph,
         };
     }
     debug!("Placeholders present; activating placeholder handling logic!");
@@ -276,21 +281,26 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
         outlives_constraints,
     );
 
-    let (constraint_sccs, scc_annotations) = if added_constraints {
+    let (constraint_sccs, scc_annotations, constraint_graph) = if added_constraints {
         let mut annotations = SccAnnotations::init(&definitions);
+        let constraint_graph = outlives_constraints.graph(definitions.len());
 
         // We changed the constraint set and so must recompute SCCs.
         // Optimisation opportunity: if we can add them incrementally (and that's
         // possible because edges to 'static always only merge SCCs into 'static),
         // we would potentially save a lot of work here.
-        (compute_sccs(&outlives_constraints, &mut annotations), annotations.scc_to_annotation)
+        (
+            compute_sccs(&outlives_constraints, &mut annotations, &constraint_graph),
+            annotations.scc_to_annotation,
+            constraint_graph,
+        )
     } else {
         // If we didn't add any back-edges; no more work needs doing
         debug!("No constraints rewritten!");
-        (constraint_sccs, scc_annotations.scc_to_annotation)
+        (constraint_sccs, scc_annotations.scc_to_annotation, constraint_graph)
     };
 
-    LoweredConstraints { constraint_sccs, definitions, scc_annotations }
+    LoweredConstraints { constraint_sccs, definitions, scc_annotations, constraint_graph }
 }
 
 pub(crate) fn rewrite_placeholder_outlives<'tcx>(

compiler/rustc_borrowck/src/lib.rs

@@ -440,6 +440,7 @@ fn borrowck_check_region_constraints<'tcx>(
         outlives_constraints,
         universe_causes,
         live_loans,
+        outlives_constraint_graph,
     } = nll::compute_regions(
         root_cx,
         &infcx,
@@ -528,7 +529,7 @@ fn borrowck_check_region_constraints<'tcx>(
             definitions: &definitions,
             universal_region_relations: &universal_region_relations,
             outlives_constraints: &outlives_constraints,
-            constraint_graph: outlives_constraints.graph(definitions.len()),
+            constraint_graph: &outlives_constraint_graph,
             liveness_constraints: &liveness_constraints,
             universe_causes: &universe_causes,
         };
@@ -573,7 +574,7 @@ fn borrowck_check_region_constraints<'tcx>(
         definitions: &definitions,
         universal_region_relations: &universal_region_relations,
         outlives_constraints: &outlives_constraints,
-        constraint_graph: outlives_constraints.graph(definitions.len()),
+        constraint_graph: &outlives_constraint_graph,
         liveness_constraints: &liveness_constraints,
         universe_causes: &universe_causes,
     };
@@ -841,7 +842,7 @@ pub(crate) struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     definitions: &'a IndexVec<RegionVid, RegionDefinition<'tcx>>,
 
     universal_region_relations: &'a Frozen<UniversalRegionRelations<'tcx>>,
-    constraint_graph: NormalConstraintGraph,
+    constraint_graph: &'a NormalConstraintGraph,
     outlives_constraints: &'a OutlivesConstraintSet<'tcx>,
     liveness_constraints: &'a LivenessValues,
 

compiler/rustc_borrowck/src/nll.rs

@@ -21,6 +21,7 @@ use tracing::{debug, instrument};
 
 use crate::borrow_set::BorrowSet;
 use crate::constraints::OutlivesConstraintSet;
+use crate::constraints::graph::NormalConstraintGraph;
 use crate::consumers::RustcFacts;
 use crate::diagnostics::{RegionErrors, UniverseInfo};
 use crate::handle_placeholders::{
@@ -53,6 +54,7 @@ pub(crate) struct NllOutput<'tcx> {
     pub(crate) liveness_constraints: LivenessValues,
     pub(crate) outlives_constraints: Frozen<OutlivesConstraintSet<'tcx>>,
     pub(crate) universe_causes: FxIndexMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
+    pub(crate) outlives_constraint_graph: NormalConstraintGraph,
 
     /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics, e.g.
     /// localized typeck and liveness constraints.
@@ -100,7 +102,7 @@ pub(crate) fn compute_closure_requirements_modulo_opaques<'tcx>(
     universal_region_relations: Rc<Frozen<UniversalRegionRelations<'tcx>>>,
     constraints: &mut MirTypeckRegionConstraints<'tcx>,
 ) -> Option<ClosureRegionRequirements<'tcx>> {
-    let LoweredConstraints { constraint_sccs, definitions, scc_annotations } =
+    let LoweredConstraints { constraint_sccs, definitions, scc_annotations, constraint_graph } =
         compute_sccs_applying_placeholder_outlives_constraints(
             &mut constraints.liveness_constraints,
             &mut constraints.outlives_constraints,
@@ -122,6 +124,7 @@ pub(crate) fn compute_closure_requirements_modulo_opaques<'tcx>(
             None,
             location_map,
             constraints.placeholder_indices.clone(),
+            &constraint_graph,
         );
     closure_region_requirements
 }
@@ -175,7 +178,12 @@ pub(crate) fn compute_regions<'tcx>(
         &outlives_constraints,
     );
 
-    let LoweredConstraints { constraint_sccs, definitions, scc_annotations } = lowered_constraints;
+    let LoweredConstraints {
+        constraint_sccs,
+        definitions,
+        scc_annotations,
+        constraint_graph: outlives_constraint_graph,
+    } = lowered_constraints;
 
     // If requested for `-Zpolonius=next`, convert NLL constraints to localized outlives constraints
     // and use them to compute loan liveness.
@@ -225,6 +233,7 @@ pub(crate) fn compute_regions<'tcx>(
             polonius_output.clone(),
             location_map,
             placeholder_indices,
+            &outlives_constraint_graph,
         );
 
     NllOutput {
@@ -239,6 +248,7 @@ pub(crate) fn compute_regions<'tcx>(
         outlives_constraints,
         universe_causes,
         live_loans,
+        outlives_constraint_graph,
     }
 }
 

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -15,6 +15,7 @@ use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_span::Span;
 use tracing::{Level, debug, enabled, instrument};
 
+use crate::constraints::graph::NormalConstraintGraph;
 use crate::constraints::{ConstraintSccIndex, OutlivesConstraintSet};
 use crate::diagnostics::{RegionErrorKind, RegionErrors};
 use crate::handle_placeholders::{RegionDefinitions, RegionTracker};
@@ -777,6 +778,7 @@ impl<'a, 'tcx> RegionInferenceContext<'a, 'tcx> {
         polonius_output: Option<Box<PoloniusOutput>>,
         location_map: Rc<DenseLocationMap>,
         placeholder_indices: PlaceholderIndices<'tcx>,
+        outlives_constraint_graph: &'a NormalConstraintGraph,
     ) -> (Option<ClosureRegionRequirements<'tcx>>, RegionErrors<'tcx>, InferredRegions<'tcx>) {
         let num_external_vids =
             universal_region_relations.universal_regions.num_global_and_external_regions();
@@ -826,6 +828,7 @@ impl<'a, 'tcx> RegionInferenceContext<'a, 'tcx> {
             outlives_constraints,
             &scc_values,
             regioncx.liveness_constraints,
+            outlives_constraint_graph,
         )
         .check(polonius_output, propagated_outlives_requirements.as_mut());
 

compiler/rustc_borrowck/src/region_infer/universal_regions.rs

@@ -32,7 +32,7 @@ pub(crate) struct UniversalRegionChecker<'a, 'tcx> {
     constraints: &'a OutlivesConstraintSet<'tcx>,
     fr_static: RegionVid,
     values: &'a InferredRegions<'tcx>,
-    constraint_graph: NormalConstraintGraph,
+    constraint_graph: &'a NormalConstraintGraph,
     liveness_constraints: &'a LivenessValues,
 }
 
@@ -61,13 +61,14 @@ impl<'a, 'tcx> UniversalRegionChecker<'a, 'tcx> {
         constraints: &'a OutlivesConstraintSet<'tcx>,
         values: &'a InferredRegions<'tcx>,
         liveness_constraints: &'a LivenessValues,
+        constraint_graph: &'a NormalConstraintGraph,
     ) -> Self {
         Self {
             errors_buffer,
             region_definitions,
             constraints,
             fr_static: values.universal_region_relations.universal_regions.fr_static,
-            constraint_graph: constraints.graph(region_definitions.len()),
+            constraint_graph,
             values,
             liveness_constraints,
         }