Foundations of location-sensitive polonius

compiler/rustc_borrowck/src/lib.rs

@@ -202,6 +202,7 @@ fn do_mir_borrowck<'tcx>(
         polonius_output,
         opt_closure_req,
         nll_errors,
+        localized_outlives_constraints,
     } = nll::compute_regions(
         &infcx,
         free_regions,
@@ -315,6 +316,16 @@ fn do_mir_borrowck<'tcx>(
 
     mbcx.report_move_errors();
 
+    // If requested, dump polonius MIR.
+    polonius::dump_polonius_mir(
+        &infcx,
+        body,
+        &regioncx,
+        &borrow_set,
+        localized_outlives_constraints,
+        &opt_closure_req,
+    );
+
     // For each non-user used mutable variable, check if it's been assigned from
     // a user-declared local. If so, then put that local into the used_mut set.
     // Note that this set is expected to be small - only upvars from closures

compiler/rustc_borrowck/src/nll.rs

@@ -29,6 +29,7 @@ use crate::consumers::ConsumerOptions;
 use crate::diagnostics::RegionErrors;
 use crate::facts::{AllFacts, AllFactsExt, RustcFacts};
 use crate::location::LocationTable;
+use crate::polonius::LocalizedOutlivesConstraintSet;
 use crate::region_infer::RegionInferenceContext;
 use crate::type_check::{self, MirTypeckResults};
 use crate::universal_regions::UniversalRegions;
@@ -45,6 +46,9 @@ pub(crate) struct NllOutput<'tcx> {
     pub polonius_output: Option<Box<PoloniusOutput>>,
     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
     pub nll_errors: RegionErrors<'tcx>,
+
+    /// When using `-Zpolonius=next`: the localized typeck and liveness constraints.
+    pub localized_outlives_constraints: Option<LocalizedOutlivesConstraintSet>,
 }
 
 /// Rewrites the regions in the MIR to use NLL variables, also scraping out the set of universal
@@ -135,6 +139,15 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         elements,
     );
 
+    // If requested for `-Zpolonius=next`, convert NLL constraints to localized outlives
+    // constraints.
+    let localized_outlives_constraints =
+        if infcx.tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
+            Some(polonius::create_localized_constraints(&mut regioncx, body))
+        } else {
+            None
+        };
+
     // If requested: dump NLL facts, and run legacy polonius analysis.
     let polonius_output = all_facts.as_ref().and_then(|all_facts| {
         if infcx.tcx.sess.opts.unstable_opts.nll_facts {
@@ -175,6 +188,7 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         polonius_output,
         opt_closure_req: closure_region_requirements,
         nll_errors,
+        localized_outlives_constraints,
     }
 }
 
@@ -215,40 +229,7 @@ pub(super) fn dump_nll_mir<'tcx>(
         &0,
         body,
         |pass_where, out| {
-            match pass_where {
-                // Before the CFG, dump out the values for each region variable.
-                PassWhere::BeforeCFG => {
-                    regioncx.dump_mir(tcx, out)?;
-                    writeln!(out, "|")?;
-
-                    if let Some(closure_region_requirements) = closure_region_requirements {
-                        writeln!(out, "| Free Region Constraints")?;
-                        for_each_region_constraint(tcx, closure_region_requirements, &mut |msg| {
-                            writeln!(out, "| {msg}")
-                        })?;
-                        writeln!(out, "|")?;
-                    }
-
-                    if borrow_set.len() > 0 {
-                        writeln!(out, "| Borrows")?;
-                        for (borrow_idx, borrow_data) in borrow_set.iter_enumerated() {
-                            writeln!(
-                                out,
-                                "| {:?}: issued at {:?} in {:?}",
-                                borrow_idx, borrow_data.reserve_location, borrow_data.region
-                            )?;
-                        }
-                        writeln!(out, "|")?;
-                    }
-                }
-
-                PassWhere::BeforeLocation(_) => {}
-
-                PassWhere::AfterTerminator(_) => {}
-
-                PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
-            }
-            Ok(())
+            emit_nll_mir(tcx, regioncx, closure_region_requirements, borrow_set, pass_where, out)
         },
         options,
     );
@@ -266,6 +247,51 @@ pub(super) fn dump_nll_mir<'tcx>(
     };
 }
 
+/// Produces the actual NLL MIR sections to emit during the dumping process.
+pub(crate) fn emit_nll_mir<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    regioncx: &RegionInferenceContext<'tcx>,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
+    borrow_set: &BorrowSet<'tcx>,
+    pass_where: PassWhere,
+    out: &mut dyn io::Write,
+) -> io::Result<()> {
+    match pass_where {
+        // Before the CFG, dump out the values for each region variable.
+        PassWhere::BeforeCFG => {
+            regioncx.dump_mir(tcx, out)?;
+            writeln!(out, "|")?;
+
+            if let Some(closure_region_requirements) = closure_region_requirements {
+                writeln!(out, "| Free Region Constraints")?;
+                for_each_region_constraint(tcx, closure_region_requirements, &mut |msg| {
+                    writeln!(out, "| {msg}")
+                })?;
+                writeln!(out, "|")?;
+            }
+
+            if borrow_set.len() > 0 {
+                writeln!(out, "| Borrows")?;
+                for (borrow_idx, borrow_data) in borrow_set.iter_enumerated() {
+                    writeln!(
+                        out,
+                        "| {:?}: issued at {:?} in {:?}",
+                        borrow_idx, borrow_data.reserve_location, borrow_data.region
+                    )?;
+                }
+                writeln!(out, "|")?;
+            }
+        }
+
+        PassWhere::BeforeLocation(_) => {}
+
+        PassWhere::AfterTerminator(_) => {}
+
+        PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
+    }
+    Ok(())
+}
+
 #[allow(rustc::diagnostic_outside_of_impl)]
 #[allow(rustc::untranslatable_diagnostic)]
 pub(super) fn dump_annotation<'tcx, 'infcx>(

compiler/rustc_borrowck/src/polonius/constraints.rs

@@ -0,0 +1,45 @@
+use rustc_middle::ty::RegionVid;
+use rustc_mir_dataflow::points::PointIndex;
+
+/// 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`
+/// outlives constraints to `a@p: b@p`, where `p` is the point in the CFG.
+///
+/// This models two sources of constraints:
+/// - constraints that traverse the subsets between regions at a given point, `a@p: b@p`. These
+///   depend on typeck constraints generated via assignments, calls, etc. (In practice there are
+///   subtleties where a statement's effect only starts being visible at the successor point, via
+///   the "result" of that statement).
+/// - constraints that traverse the CFG via the same region, `a@p: a@q`, where `p` is a predecessor
+///   of `q`. These depend on the liveness of the regions at these points, as well as their
+///   variance.
+///
+/// The `source` origin at `from` flows into the `target` origin at `to`.
+///
+/// This dual of NLL's [crate::constraints::OutlivesConstraint] therefore encodes the
+/// position-dependent outlives constraints used by Polonius, to model the flow-sensitive loan
+/// propagation via reachability within a graph of localized constraints.
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
+pub(crate) struct LocalizedOutlivesConstraint {
+    pub source: RegionVid,
+    pub from: PointIndex,
+    pub target: RegionVid,
+    pub to: PointIndex,
+}
+
+/// A container of [LocalizedOutlivesConstraint]s that can be turned into a traversable
+/// `rustc_data_structures` graph.
+#[derive(Clone, Default, Debug)]
+pub(crate) struct LocalizedOutlivesConstraintSet {
+    pub outlives: Vec<LocalizedOutlivesConstraint>,
+}
+
+impl LocalizedOutlivesConstraintSet {
+    pub(crate) fn push(&mut self, constraint: LocalizedOutlivesConstraint) {
+        if constraint.source == constraint.target && constraint.from == constraint.to {
+            // 'a@p: 'a@p is pretty uninteresting
+            return;
+        }
+        self.outlives.push(constraint);
+    }
+}

compiler/rustc_borrowck/src/polonius/dump.rs

@@ -0,0 +1,104 @@
+use std::io;
+
+use rustc_middle::mir::pretty::{PrettyPrintMirOptions, dump_mir_with_options};
+use rustc_middle::mir::{Body, ClosureRegionRequirements, PassWhere};
+use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MirIncludeSpans;
+
+use crate::borrow_set::BorrowSet;
+use crate::polonius::{LocalizedOutlivesConstraint, LocalizedOutlivesConstraintSet};
+use crate::{BorrowckInferCtxt, RegionInferenceContext};
+
+/// `-Zdump-mir=polonius` dumps MIR annotated with NLL and polonius specific information.
+// Note: this currently duplicates most of NLL MIR, with some additions for the localized outlives
+// constraints. This is ok for now as this dump will change in the near future to an HTML file to
+// become more useful.
+pub(crate) fn dump_polonius_mir<'tcx>(
+    infcx: &BorrowckInferCtxt<'tcx>,
+    body: &Body<'tcx>,
+    regioncx: &RegionInferenceContext<'tcx>,
+    borrow_set: &BorrowSet<'tcx>,
+    localized_outlives_constraints: Option<LocalizedOutlivesConstraintSet>,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
+) {
+    let tcx = infcx.tcx;
+    if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
+        return;
+    }
+
+    let localized_outlives_constraints = localized_outlives_constraints
+        .expect("missing localized constraints with `-Zpolonius=next`");
+
+    // We want the NLL extra comments printed by default in NLL MIR dumps (they were removed in
+    // #112346). Specifying `-Z mir-include-spans` on the CLI still has priority: for example,
+    // they're always disabled in mir-opt tests to make working with blessed dumps easier.
+    let options = PrettyPrintMirOptions {
+        include_extra_comments: matches!(
+            tcx.sess.opts.unstable_opts.mir_include_spans,
+            MirIncludeSpans::On | MirIncludeSpans::Nll
+        ),
+    };
+
+    dump_mir_with_options(
+        tcx,
+        false,
+        "polonius",
+        &0,
+        body,
+        |pass_where, out| {
+            emit_polonius_mir(
+                tcx,
+                regioncx,
+                closure_region_requirements,
+                borrow_set,
+                &localized_outlives_constraints,
+                pass_where,
+                out,
+            )
+        },
+        options,
+    );
+}
+
+/// Produces the actual NLL + Polonius MIR sections to emit during the dumping process.
+fn emit_polonius_mir<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    regioncx: &RegionInferenceContext<'tcx>,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
+    borrow_set: &BorrowSet<'tcx>,
+    localized_outlives_constraints: &LocalizedOutlivesConstraintSet,
+    pass_where: PassWhere,
+    out: &mut dyn io::Write,
+) -> io::Result<()> {
+    // Emit the regular NLL front-matter
+    crate::nll::emit_nll_mir(
+        tcx,
+        regioncx,
+        closure_region_requirements,
+        borrow_set,
+        pass_where.clone(),
+        out,
+    )?;
+
+    let liveness = regioncx.liveness_constraints();
+
+    // Add localized outlives constraints
+    match pass_where {
+        PassWhere::BeforeCFG => {
+            if localized_outlives_constraints.outlives.len() > 0 {
+                writeln!(out, "| Localized constraints")?;
+
+                for constraint in &localized_outlives_constraints.outlives {
+                    let LocalizedOutlivesConstraint { source, from, target, to } = constraint;
+                    let from = liveness.location_from_point(*from);
+                    let to = liveness.location_from_point(*to);
+                    writeln!(out, "| {source:?} at {from:?} -> {target:?} at {to:?}")?;
+                }
+                writeln!(out, "|")?;
+            }
+        }
+        _ => {}
+    }
+
+    Ok(())
+}