Rollup merge of rust-lang#125652 - amandasystems:you-dropped-something, r=oli-obk

Revert propagation of drop-live information from Polonius

rust-lang#64749 introduced a flow of drop-use data from Polonius to `LivenessResults::add_extra_drop_facts()`, which makes `LivenessResults` agree with Polonius on liveness in the presence of free regions that may be dropped. Later changes accidentally removed this flow. This PR restores it.

Author: jieyouxu

compiler/rustc_borrowck/src/type_check/liveness/mod.rs

@@ -14,7 +14,6 @@ use std::rc::Rc;
 use crate::{
     constraints::OutlivesConstraintSet,
     facts::{AllFacts, AllFactsExt},
-    location::LocationTable,
     region_infer::values::LivenessValues,
     universal_regions::UniversalRegions,
 };
@@ -39,7 +38,6 @@ pub(super) fn generate<'mir, 'tcx>(
     elements: &Rc<DenseLocationMap>,
     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
-    location_table: &LocationTable,
     use_polonius: bool,
 ) {
     debug!("liveness::generate");
@@ -53,11 +51,9 @@ pub(super) fn generate<'mir, 'tcx>(
         compute_relevant_live_locals(typeck.tcx(), &free_regions, body);
     let facts_enabled = use_polonius || AllFacts::enabled(typeck.tcx());
 
-    let polonius_drop_used = facts_enabled.then(|| {
-        let mut drop_used = Vec::new();
-        polonius::populate_access_facts(typeck, body, location_table, move_data, &mut drop_used);
-        drop_used
-    });
+    if facts_enabled {
+        polonius::populate_access_facts(typeck, body, move_data);
+    };
 
     trace::trace(
         typeck,
@@ -67,7 +63,6 @@ pub(super) fn generate<'mir, 'tcx>(
         move_data,
         relevant_live_locals,
         boring_locals,
-        polonius_drop_used,
     );
 
     // Mark regions that should be live where they appear within rvalues or within a call: like

compiler/rustc_borrowck/src/type_check/liveness/polonius.rs

@@ -85,13 +85,10 @@ impl<'a, 'tcx> Visitor<'tcx> for UseFactsExtractor<'a, 'tcx> {
 pub(super) fn populate_access_facts<'a, 'tcx>(
     typeck: &mut TypeChecker<'a, 'tcx>,
     body: &Body<'tcx>,
-    location_table: &LocationTable,
     move_data: &MoveData<'tcx>,
-    //FIXME: this is not mutated, but expected to be modified as
-    // out param, bug?
-    dropped_at: &mut Vec<(Local, Location)>,
 ) {
     debug!("populate_access_facts()");
+    let location_table = typeck.borrowck_context.location_table;
 
     if let Some(facts) = typeck.borrowck_context.all_facts.as_mut() {
         let mut extractor = UseFactsExtractor {
@@ -104,10 +101,6 @@ pub(super) fn populate_access_facts<'a, 'tcx>(
         };
         extractor.visit_body(body);
 
-        facts.var_dropped_at.extend(
-            dropped_at.iter().map(|&(local, location)| (local, location_table.mid_index(location))),
-        );
-
         for (local, local_decl) in body.local_decls.iter_enumerated() {
             debug!(
                 "add use_of_var_derefs_origin facts - local={:?}, type={:?}",

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -16,6 +16,7 @@ use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::{HasMoveData, MoveData, MovePathIndex};
 use rustc_mir_dataflow::ResultsCursor;
 
+use crate::location::RichLocation;
 use crate::{
     region_infer::values::{self, LiveLoans},
     type_check::liveness::local_use_map::LocalUseMap,
@@ -46,7 +47,6 @@ pub(super) fn trace<'mir, 'tcx>(
     move_data: &MoveData<'tcx>,
     relevant_live_locals: Vec<Local>,
     boring_locals: Vec<Local>,
-    polonius_drop_used: Option<Vec<(Local, Location)>>,
 ) {
     let local_use_map = &LocalUseMap::build(&relevant_live_locals, elements, body);
 
@@ -93,9 +93,7 @@ pub(super) fn trace<'mir, 'tcx>(
 
     let mut results = LivenessResults::new(cx);
 
-    if let Some(drop_used) = polonius_drop_used {
-        results.add_extra_drop_facts(drop_used, relevant_live_locals.iter().copied().collect())
-    }
+    results.add_extra_drop_facts(&relevant_live_locals);
 
     results.compute_for_all_locals(relevant_live_locals);
 
@@ -218,21 +216,38 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
     ///
     /// Add facts for all locals with free regions, since regions may outlive
     /// the function body only at certain nodes in the CFG.
-    fn add_extra_drop_facts(
-        &mut self,
-        drop_used: Vec<(Local, Location)>,
-        relevant_live_locals: FxIndexSet<Local>,
-    ) {
+    fn add_extra_drop_facts(&mut self, relevant_live_locals: &[Local]) -> Option<()> {
+        let drop_used = self
+            .cx
+            .typeck
+            .borrowck_context
+            .all_facts
+            .as_ref()
+            .map(|facts| facts.var_dropped_at.clone())?;
+
+        let relevant_live_locals: FxIndexSet<_> = relevant_live_locals.iter().copied().collect();
+
         let locations = IntervalSet::new(self.cx.elements.num_points());
 
-        for (local, location) in drop_used {
+        for (local, location_index) in drop_used {
             if !relevant_live_locals.contains(&local) {
                 let local_ty = self.cx.body.local_decls[local].ty;
                 if local_ty.has_free_regions() {
+                    let location = match self
+                        .cx
+                        .typeck
+                        .borrowck_context
+                        .location_table
+                        .to_location(location_index)
+                    {
+                        RichLocation::Start(l) => l,
+                        RichLocation::Mid(l) => l,
+                    };
                     self.cx.add_drop_live_facts_for(local, local_ty, &[location], &locations);
                 }
             }
         }
+        Some(())
     }
 
     /// Clear the value of fields that are "per local variable".

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -188,15 +188,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
     checker.equate_inputs_and_outputs(body, universal_regions, &normalized_inputs_and_output);
     checker.check_signature_annotation(body);
 
-    liveness::generate(
-        &mut checker,
-        body,
-        elements,
-        flow_inits,
-        move_data,
-        location_table,
-        use_polonius,
-    );
+    liveness::generate(&mut checker, body, elements, flow_inits, move_data, use_polonius);
 
     translate_outlives_facts(&mut checker);
     let opaque_type_values = infcx.take_opaque_types();