Rollup merge of #104239 - b-naber:sccs-info, r=jackh726

Better debug logs for borrowck constraint graph

It's really cumbersome to work with `RegionVar`s when trying to debug borrowck code or when trying to understand how the borrowchecker works. This PR collects some region information (behind `cfg(debug_assertions)`) for created `RegionVar`s (NLL region vars, this PR doesn't touch canonicalization) and prints the nodes and edges of the strongly connected constraints graph using representatives that use that region information (either lifetime names, locations in MIR or spans).

Author: matthiaskrgr

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
+            .as_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
+            .as_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>,
 }