introduce beginnings of polonius MIR dump

This is mostly for test purposes to show the localized constraints until
the MIR debugger is set up.

Author: lqd

compiler/rustc_borrowck/src/lib.rs

@@ -319,6 +319,16 @@ 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/polonius/dump.rs

@@ -0,0 +1,101 @@
+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: &LocalizedOutlivesConstraintSet,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
+) {
+    let tcx = infcx.tcx;
+    if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
+        return;
+    }
+
+    // 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(())
+}

compiler/rustc_borrowck/src/polonius/mod.rs

@@ -35,6 +35,8 @@
 
 mod constraints;
 pub(crate) use constraints::*;
+mod dump;
+pub(crate) use dump::dump_polonius_mir;
 pub(crate) mod legacy;
 
 use rustc_middle::mir::{Body, Location};

compiler/rustc_borrowck/src/region_infer/values.rs

@@ -199,6 +199,11 @@ impl LivenessValues {
         self.elements.point_from_location(location)
     }
 
+    #[inline]
+    pub(crate) fn location_from_point(&self, point: PointIndex) -> Location {
+        self.elements.to_location(point)
+    }
+
     /// When using `-Zpolonius=next`, returns whether the `loan_idx` is live at the given `point`.
     pub(crate) fn is_loan_live_at(&self, loan_idx: BorrowIndex, point: PointIndex) -> bool {
         self.loans