Better debug logs for borrowck constraint graph

compiler/rustc_borrowck/src/constraints/mod.rs

@@ -17,7 +17,7 @@ pub(crate) mod graph;
 /// constraints of the form `R1: R2`. Each constraint is identified by
 /// a unique `OutlivesConstraintIndex` and you can index into the set
 /// (`constraint_set[i]`) to access the constraint details.
-#[derive(Clone, Default)]
+#[derive(Clone, Debug, Default)]
 pub(crate) struct OutlivesConstraintSet<'tcx> {
     outlives: IndexVec<OutlivesConstraintIndex, OutlivesConstraint<'tcx>>,
 }

compiler/rustc_borrowck/src/lib.rs

@@ -25,7 +25,9 @@ use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::bit_set::ChunkedBitSet;
 use rustc_index::vec::IndexVec;
-use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{
+    DefiningAnchor, InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt,
+};
 use rustc_middle::mir::{
     traversal, Body, ClearCrossCrate, Local, Location, Mutability, NonDivergingIntrinsic, Operand,
     Place, PlaceElem, PlaceRef, VarDebugInfoContents,
@@ -43,6 +45,7 @@ use smallvec::SmallVec;
 use std::cell::OnceCell;
 use std::cell::RefCell;
 use std::collections::BTreeMap;
+use std::ops::Deref;
 use std::rc::Rc;
 
 use rustc_mir_dataflow::impls::{
@@ -94,6 +97,7 @@ use nll::{PoloniusOutput, ToRegionVid};
 use place_ext::PlaceExt;
 use places_conflict::{places_conflict, PlaceConflictBias};
 use region_infer::RegionInferenceContext;
+use renumber::RegionCtxt;
 
 // FIXME(eddyb) perhaps move this somewhere more centrally.
 #[derive(Debug)]
@@ -167,10 +171,10 @@ fn do_mir_borrowck<'tcx>(
     return_body_with_facts: bool,
 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
     let def = input_body.source.with_opt_param().as_local().unwrap();
-
     debug!(?def);
 
     let tcx = infcx.tcx;
+    let infcx = BorrowckInferCtxt::new(infcx);
     let param_env = tcx.param_env(def.did);
 
     let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
@@ -218,7 +222,7 @@ fn do_mir_borrowck<'tcx>(
     let mut body_owned = input_body.clone();
     let mut promoted = input_promoted.clone();
     let free_regions =
-        nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
+        nll::replace_regions_in_mir(&infcx, param_env, &mut body_owned, &mut promoted);
     let body = &body_owned; // no further changes
 
     let location_table_owned = LocationTable::new(body);
@@ -256,7 +260,7 @@ fn do_mir_borrowck<'tcx>(
         opt_closure_req,
         nll_errors,
     } = nll::compute_regions(
-        infcx,
+        &infcx,
         free_regions,
         body,
         &promoted,
@@ -271,12 +275,12 @@ fn do_mir_borrowck<'tcx>(
 
     // Dump MIR results into a file, if that is enabled. This let us
     // write unit-tests, as well as helping with debugging.
-    nll::dump_mir_results(infcx, &body, &regioncx, &opt_closure_req);
+    nll::dump_mir_results(&infcx, &body, &regioncx, &opt_closure_req);
 
     // We also have a `#[rustc_regions]` annotation that causes us to dump
     // information.
     nll::dump_annotation(
-        infcx,
+        &infcx,
         &body,
         &regioncx,
         &opt_closure_req,
@@ -320,7 +324,7 @@ fn do_mir_borrowck<'tcx>(
 
         if let Err((move_data, move_errors)) = move_data_results {
             let mut promoted_mbcx = MirBorrowckCtxt {
-                infcx,
+                infcx: &infcx,
                 param_env,
                 body: promoted_body,
                 move_data: &move_data,
@@ -349,7 +353,7 @@ fn do_mir_borrowck<'tcx>(
     }
 
     let mut mbcx = MirBorrowckCtxt {
-        infcx,
+        infcx: &infcx,
         param_env,
         body,
         move_data: &mdpe.move_data,
@@ -481,8 +485,84 @@ pub struct BodyWithBorrowckFacts<'tcx> {
     pub location_table: LocationTable,
 }
 
+pub struct BorrowckInferCtxt<'cx, 'tcx> {
+    pub(crate) infcx: &'cx InferCtxt<'tcx>,
+    pub(crate) reg_var_to_origin: RefCell<FxHashMap<ty::RegionVid, RegionCtxt>>,
+}
+
+impl<'cx, 'tcx> BorrowckInferCtxt<'cx, 'tcx> {
+    pub(crate) fn new(infcx: &'cx InferCtxt<'tcx>) -> Self {
+        BorrowckInferCtxt { infcx, reg_var_to_origin: RefCell::new(Default::default()) }
+    }
+
+    pub(crate) fn next_region_var<F>(
+        &self,
+        origin: RegionVariableOrigin,
+        get_ctxt_fn: F,
+    ) -> ty::Region<'tcx>
+    where
+        F: Fn() -> RegionCtxt,
+    {
+        let next_region = self.infcx.next_region_var(origin);
+        let vid = next_region
+            .try_get_var()
+            .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
+
+        if cfg!(debug_assertions) {
+            debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
+            let ctxt = get_ctxt_fn();
+            let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
+            let prev = var_to_origin.insert(vid, ctxt);
+
+            // This only makes sense if not called in a canonicalization context. If this
+            // ever changes we either want to get rid of `BorrowckInferContext::reg_var_to_origin`
+            // or modify how we track nll region vars for that map.
+            assert!(matches!(prev, None));
+        }
+
+        next_region
+    }
+
+    #[instrument(skip(self, get_ctxt_fn), level = "debug")]
+    pub(crate) fn next_nll_region_var<F>(
+        &self,
+        origin: NllRegionVariableOrigin,
+        get_ctxt_fn: F,
+    ) -> ty::Region<'tcx>
+    where
+        F: Fn() -> RegionCtxt,
+    {
+        let next_region = self.infcx.next_nll_region_var(origin.clone());
+        let vid = next_region
+            .try_get_var()
+            .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
+
+        if cfg!(debug_assertions) {
+            debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
+            let ctxt = get_ctxt_fn();
+            let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
+            let prev = var_to_origin.insert(vid, ctxt);
+
+            // This only makes sense if not called in a canonicalization context. If this
+            // ever changes we either want to get rid of `BorrowckInferContext::reg_var_to_origin`
+            // or modify how we track nll region vars for that map.
+            assert!(matches!(prev, None));
+        }
+
+        next_region
+    }
+}
+
+impl<'cx, 'tcx> Deref for BorrowckInferCtxt<'cx, 'tcx> {
+    type Target = InferCtxt<'tcx>;
+
+    fn deref(&self) -> &'cx Self::Target {
+        self.infcx
+    }
+}
+
 struct MirBorrowckCtxt<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'tcx>,
+    infcx: &'cx BorrowckInferCtxt<'cx, 'tcx>,
     param_env: ParamEnv<'tcx>,
     body: &'cx Body<'tcx>,
     move_data: &'cx MoveData<'tcx>,

compiler/rustc_borrowck/src/nll.rs

@@ -5,7 +5,6 @@
 use rustc_data_structures::vec_map::VecMap;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::vec::IndexVec;
-use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::{create_dump_file, dump_enabled, dump_mir, PassWhere};
 use rustc_middle::mir::{
     BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
@@ -37,7 +36,7 @@ use crate::{
     renumber,
     type_check::{self, MirTypeckRegionConstraints, MirTypeckResults},
     universal_regions::UniversalRegions,
-    Upvar,
+    BorrowckInferCtxt, Upvar,
 };
 
 pub type PoloniusOutput = Output<RustcFacts>;
@@ -58,7 +57,7 @@ pub(crate) struct NllOutput<'tcx> {
 /// `compute_regions`.
 #[instrument(skip(infcx, param_env, body, promoted), level = "debug")]
 pub(crate) fn replace_regions_in_mir<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    infcx: &BorrowckInferCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     body: &mut Body<'tcx>,
     promoted: &mut IndexVec<Promoted, Body<'tcx>>,
@@ -157,7 +156,7 @@ fn populate_polonius_move_facts(
 ///
 /// This may result in errors being reported.
 pub(crate) fn compute_regions<'cx, 'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    infcx: &BorrowckInferCtxt<'_, 'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexVec<Promoted, Body<'tcx>>,
@@ -259,6 +258,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     );
 
     let mut regioncx = RegionInferenceContext::new(
+        infcx,
         var_origins,
         universal_regions,
         placeholder_indices,
@@ -322,7 +322,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
 }
 
 pub(super) fn dump_mir_results<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    infcx: &BorrowckInferCtxt<'_, 'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
@@ -372,7 +372,7 @@ pub(super) fn dump_mir_results<'tcx>(
 #[allow(rustc::diagnostic_outside_of_impl)]
 #[allow(rustc::untranslatable_diagnostic)]
 pub(super) fn dump_annotation<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    infcx: &BorrowckInferCtxt<'_, 'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -34,6 +34,7 @@ use crate::{
     },
     type_check::{free_region_relations::UniversalRegionRelations, Locations},
     universal_regions::UniversalRegions,
+    BorrowckInferCtxt,
 };
 
 mod dump_mir;
@@ -243,6 +244,70 @@ pub enum ExtraConstraintInfo {
     PlaceholderFromPredicate(Span),
 }
 
+#[instrument(skip(infcx, sccs), level = "debug")]
+fn sccs_info<'cx, 'tcx>(
+    infcx: &'cx BorrowckInferCtxt<'cx, 'tcx>,
+    sccs: Rc<Sccs<RegionVid, ConstraintSccIndex>>,
+) {
+    use crate::renumber::RegionCtxt;
+
+    let var_to_origin = infcx.reg_var_to_origin.borrow();
+
+    let mut var_to_origin_sorted = var_to_origin.clone().into_iter().collect::<Vec<_>>();
+    var_to_origin_sorted.sort_by(|a, b| a.0.cmp(&b.0));
+    let mut debug_str = "region variables to origins:\n".to_string();
+    for (reg_var, origin) in var_to_origin_sorted.into_iter() {
+        debug_str.push_str(&format!("{:?}: {:?}\n", reg_var, origin));
+    }
+    debug!(debug_str);
+
+    let num_components = sccs.scc_data.ranges.len();
+    let mut components = vec![FxHashSet::default(); num_components];
+
+    for (reg_var_idx, scc_idx) in sccs.scc_indices.iter().enumerate() {
+        let reg_var = ty::RegionVid::from_usize(reg_var_idx);
+        let origin = var_to_origin.get(&reg_var).unwrap_or_else(|| &RegionCtxt::Unknown);
+        components[scc_idx.as_usize()].insert((reg_var, *origin));
+    }
+
+    let mut components_str = "strongly connected components:".to_string();
+    for (scc_idx, reg_vars_origins) in components.iter().enumerate() {
+        let regions_info = reg_vars_origins.clone().into_iter().collect::<Vec<_>>();
+        components_str.push_str(&format!(
+            "{:?}: {:?})",
+            ConstraintSccIndex::from_usize(scc_idx),
+            regions_info,
+        ))
+    }
+    debug!(components_str);
+
+    // calculate the best representative for each component
+    let components_representatives = components
+        .into_iter()
+        .enumerate()
+        .map(|(scc_idx, region_ctxts)| {
+            let repr = region_ctxts
+                .into_iter()
+                .map(|reg_var_origin| reg_var_origin.1)
+                .max_by(|x, y| x.preference_value().cmp(&y.preference_value()))
+                .unwrap();
+
+            (ConstraintSccIndex::from_usize(scc_idx), repr)
+        })
+        .collect::<FxHashMap<_, _>>();
+
+    let mut scc_node_to_edges = FxHashMap::default();
+    for (scc_idx, repr) in components_representatives.iter() {
+        let edges_range = sccs.scc_data.ranges[*scc_idx].clone();
+        let edges = &sccs.scc_data.all_successors[edges_range];
+        let edge_representatives =
+            edges.iter().map(|scc_idx| components_representatives[scc_idx]).collect::<Vec<_>>();
+        scc_node_to_edges.insert((scc_idx, repr), edge_representatives);
+    }
+
+    debug!("SCC edges {:#?}", scc_node_to_edges);
+}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Creates a new region inference context with a total of
     /// `num_region_variables` valid inference variables; the first N
@@ -251,7 +316,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// The `outlives_constraints` and `type_tests` are an initial set
     /// of constraints produced by the MIR type check.
-    pub(crate) fn new(
+    pub(crate) fn new<'cx>(
+        _infcx: &BorrowckInferCtxt<'cx, 'tcx>,
         var_infos: VarInfos,
         universal_regions: Rc<UniversalRegions<'tcx>>,
         placeholder_indices: Rc<PlaceholderIndices>,
@@ -263,6 +329,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         liveness_constraints: LivenessValues<RegionVid>,
         elements: &Rc<RegionValueElements>,
     ) -> Self {
+        debug!("universal_regions: {:#?}", universal_regions);
+        debug!("outlives constraints: {:#?}", outlives_constraints);
+        debug!("placeholder_indices: {:#?}", placeholder_indices);
+        debug!("type tests: {:#?}", type_tests);
+
         // Create a RegionDefinition for each inference variable.
         let definitions: IndexVec<_, _> = var_infos
             .iter()
@@ -274,6 +345,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let fr_static = universal_regions.fr_static;
         let constraint_sccs = Rc::new(constraints.compute_sccs(&constraint_graph, fr_static));
 
+        if cfg!(debug_assertions) {
+            sccs_info(_infcx, constraint_sccs.clone());
+        }
+
         let mut scc_values =
             RegionValues::new(elements, universal_regions.len(), &placeholder_indices);
 

compiler/rustc_borrowck/src/region_infer/values.rs

@@ -181,7 +181,7 @@ impl<N: Idx> LivenessValues<N> {
 /// Maps from `ty::PlaceholderRegion` values that are used in the rest of
 /// rustc to the internal `PlaceholderIndex` values that are used in
 /// NLL.
-#[derive(Default)]
+#[derive(Debug, Default)]
 pub(crate) struct PlaceholderIndices {
     indices: FxIndexSet<ty::PlaceholderRegion>,
 }