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

   1 use crate::def_use::{self, DefUse};
   2 use crate::location::{LocationIndex, LocationTable};
   3 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   4 use rustc_middle::mir::{Body, Local, Location, Place};
   5 use rustc_middle::ty::subst::GenericArg;
   6 use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex};
   7
   8 use super::TypeChecker;
   9
  10 type VarPointRelation = Vec<(Local, LocationIndex)>;
  11 type PathPointRelation = Vec<(MovePathIndex, LocationIndex)>;
  12
  13 struct UseFactsExtractor<'me> {
  14     var_defined_at: &'me mut VarPointRelation,
  15     var_used_at: &'me mut VarPointRelation,
  16     location_table: &'me LocationTable,
  17     var_dropped_at: &'me mut VarPointRelation,
  18     move_data: &'me MoveData<'me>,
  19     path_accessed_at_base: &'me mut PathPointRelation,
  20 }
  21
  22 // A Visitor to walk through the MIR and extract point-wise facts
  23 impl UseFactsExtractor<'_> {
  24     fn location_to_index(&self, location: Location) -> LocationIndex {
  25         self.location_table.mid_index(location)
  26     }
  27
  28     fn insert_def(&mut self, local: Local, location: Location) {
  29         debug!("UseFactsExtractor::insert_def()");
  30         self.var_defined_at.push((local, self.location_to_index(location)));
  31     }
  32
  33     fn insert_use(&mut self, local: Local, location: Location) {
  34         debug!("UseFactsExtractor::insert_use()");
  35         self.var_used_at.push((local, self.location_to_index(location)));
  36     }
  37
  38     fn insert_drop_use(&mut self, local: Local, location: Location) {
  39         debug!("UseFactsExtractor::insert_drop_use()");
  40         self.var_dropped_at.push((local, self.location_to_index(location)));
  41     }
  42
  43     fn insert_path_access(&mut self, path: MovePathIndex, location: Location) {
  44         debug!("UseFactsExtractor::insert_path_access({:?}, {:?})", path, location);
  45         self.path_accessed_at_base.push((path, self.location_to_index(location)));
  46     }
  47
  48     fn place_to_mpi(&self, place: &Place<'_>) -> Option<MovePathIndex> {
  49         match self.move_data.rev_lookup.find(place.as_ref()) {
  50             LookupResult::Exact(mpi) => Some(mpi),
  51             LookupResult::Parent(mmpi) => mmpi,
  52         }
  53     }
  54 }
  55
  56 impl Visitor<'_> for UseFactsExtractor<'_> {
  57     fn visit_local(&mut self, &local: &Local, context: PlaceContext, location: Location) {
  58         match def_use::categorize(context) {
  59             Some(DefUse::Def) => self.insert_def(local, location),
  60             Some(DefUse::Use) => self.insert_use(local, location),
  61             Some(DefUse::Drop) => self.insert_drop_use(local, location),
  62             _ => (),
  63         }
  64     }
  65
  66     fn visit_place(&mut self, place: &Place<'_>, context: PlaceContext, location: Location) {
  67         self.super_place(place, context, location);
  68         match context {
  69             PlaceContext::NonMutatingUse(_) => {
  70                 if let Some(mpi) = self.place_to_mpi(place) {
  71                     self.insert_path_access(mpi, location);
  72                 }
  73             }
  74
  75             PlaceContext::MutatingUse(MutatingUseContext::Borrow) => {
  76                 if let Some(mpi) = self.place_to_mpi(place) {
  77                     self.insert_path_access(mpi, location);
  78                 }
  79             }
  80             _ => (),
  81         }
  82     }
  83 }
  84
  85 pub(super) fn populate_access_facts<'tcx>(
  86     typeck: &mut TypeChecker<'_, 'tcx>,
  87     body: &Body<'tcx>,
  88     location_table: &LocationTable,
  89     move_data: &MoveData<'_>,
  90     dropped_at: &mut Vec<(Local, Location)>,
  91 ) {
  92     debug!("populate_access_facts()");
  93
  94     if let Some(facts) = typeck.borrowck_context.all_facts.as_mut() {
  95         let mut extractor = UseFactsExtractor {
  96             var_defined_at: &mut facts.var_defined_at,
  97             var_used_at: &mut facts.var_used_at,
  98             var_dropped_at: &mut facts.var_dropped_at,
  99             path_accessed_at_base: &mut facts.path_accessed_at_base,
 100             location_table,
 101             move_data,
 102         };
 103         extractor.visit_body(&body);
 104
 105         facts.var_dropped_at.extend(
 106             dropped_at.iter().map(|&(local, location)| (local, location_table.mid_index(location))),
 107         );
 108
 109         for (local, local_decl) in body.local_decls.iter_enumerated() {
 110             debug!(
 111                 "add use_of_var_derefs_origin facts - local={:?}, type={:?}",
 112                 local, local_decl.ty
 113             );
 114             let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
 115             let universal_regions = &typeck.borrowck_context.universal_regions;
 116             typeck.infcx.tcx.for_each_free_region(&local_decl.ty, |region| {
 117                 let region_vid = universal_regions.to_region_vid(region);
 118                 facts.use_of_var_derefs_origin.push((local, region_vid));
 119             });
 120         }
 121     }
 122 }
 123
 124 // For every potentially drop()-touched region `region` in `local`'s type
 125 // (`kind`), emit a Polonius `use_of_var_derefs_origin(local, origin)` fact.
 126 pub(super) fn add_drop_of_var_derefs_origin<'tcx>(
 127     typeck: &mut TypeChecker<'_, 'tcx>,
 128     local: Local,
 129     kind: &GenericArg<'tcx>,
 130 ) {
 131     debug!("add_drop_of_var_derefs_origin(local={:?}, kind={:?}", local, kind);
 132     if let Some(facts) = typeck.borrowck_context.all_facts.as_mut() {
 133         let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
 134         let universal_regions = &typeck.borrowck_context.universal_regions;
 135         typeck.infcx.tcx.for_each_free_region(kind, |drop_live_region| {
 136             let region_vid = universal_regions.to_region_vid(drop_live_region);
 137             facts.drop_of_var_derefs_origin.push((local, region_vid));
 138         });
 139     }
 140 }