compiler/rustc_mir/src/borrow_check/nll.rs

   1 //! The entry point of the NLL borrow checker.
   2
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_errors::Diagnostic;
   5 use rustc_hir::def_id::DefId;
   6 use rustc_index::vec::IndexVec;
   7 use rustc_infer::infer::InferCtxt;
   8 use rustc_middle::mir::{
   9     BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
  10     Promoted,
  11 };
  12 use rustc_middle::ty::{self, RegionKind, RegionVid};
  13 use rustc_span::symbol::sym;
  14 use std::env;
  15 use std::fmt::Debug;
  16 use std::io;
  17 use std::path::PathBuf;
  18 use std::rc::Rc;
  19 use std::str::FromStr;
  20
  21 use self::mir_util::PassWhere;
  22 use polonius_engine::{Algorithm, Output};
  23
  24 use crate::dataflow::impls::MaybeInitializedPlaces;
  25 use crate::dataflow::move_paths::{InitKind, InitLocation, MoveData};
  26 use crate::dataflow::ResultsCursor;
  27 use crate::util as mir_util;
  28 use crate::util::pretty;
  29
  30 use crate::borrow_check::{
  31     borrow_set::BorrowSet,
  32     constraint_generation,
  33     diagnostics::RegionErrors,
  34     facts::{AllFacts, AllFactsExt, RustcFacts},
  35     invalidation,
  36     location::LocationTable,
  37     region_infer::{values::RegionValueElements, RegionInferenceContext},
  38     renumber,
  39     type_check::{self, MirTypeckRegionConstraints, MirTypeckResults},
  40     universal_regions::UniversalRegions,
  41     Upvar,
  42 };
  43
  44 crate type PoloniusOutput = Output<RustcFacts>;
  45
  46 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
  47 /// closure requirements to propagate, and any generated errors.
  48 crate struct NllOutput<'tcx> {
  49     pub regioncx: RegionInferenceContext<'tcx>,
  50     pub opaque_type_values: FxHashMap<DefId, ty::ResolvedOpaqueTy<'tcx>>,
  51     pub polonius_output: Option<Rc<PoloniusOutput>>,
  52     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
  53     pub nll_errors: RegionErrors<'tcx>,
  54 }
  55
  56 /// Rewrites the regions in the MIR to use NLL variables, also scraping out the set of universal
  57 /// regions (e.g., region parameters) declared on the function. That set will need to be given to
  58 /// `compute_regions`.
  59 pub(in crate::borrow_check) fn replace_regions_in_mir<'cx, 'tcx>(
  60     infcx: &InferCtxt<'cx, 'tcx>,
  61     param_env: ty::ParamEnv<'tcx>,
  62     body: &mut Body<'tcx>,
  63     promoted: &mut IndexVec<Promoted, Body<'tcx>>,
  64 ) -> UniversalRegions<'tcx> {
  65     let def = body.source.with_opt_param().as_local().unwrap();
  66
  67     debug!("replace_regions_in_mir(def={:?})", def);
  68
  69     // Compute named region information. This also renumbers the inputs/outputs.
  70     let universal_regions = UniversalRegions::new(infcx, def, param_env);
  71
  72     // Replace all remaining regions with fresh inference variables.
  73     renumber::renumber_mir(infcx, body, promoted);
  74
  75     mir_util::dump_mir(infcx.tcx, None, "renumber", &0, body, |_, _| Ok(()));
  76
  77     universal_regions
  78 }
  79
  80 // This function populates an AllFacts instance with base facts related to
  81 // MovePaths and needed for the move analysis.
  82 fn populate_polonius_move_facts(
  83     all_facts: &mut AllFacts,
  84     move_data: &MoveData<'_>,
  85     location_table: &LocationTable,
  86     body: &Body<'_>,
  87 ) {
  88     all_facts
  89         .path_is_var
  90         .extend(move_data.rev_lookup.iter_locals_enumerated().map(|(v, &m)| (m, v)));
  91
  92     for (child, move_path) in move_data.move_paths.iter_enumerated() {
  93         if let Some(parent) = move_path.parent {
  94             all_facts.child_path.push((child, parent));
  95         }
  96     }
  97
  98     let fn_entry_start = location_table
  99         .start_index(Location { block: BasicBlock::from_u32(0u32), statement_index: 0 });
 100
 101     // initialized_at
 102     for init in move_data.inits.iter() {
 103         match init.location {
 104             InitLocation::Statement(location) => {
 105                 let block_data = &body[location.block];
 106                 let is_terminator = location.statement_index == block_data.statements.len();
 107
 108                 if is_terminator && init.kind == InitKind::NonPanicPathOnly {
 109                     // We are at the terminator of an init that has a panic path,
 110                     // and where the init should not happen on panic
 111
 112                     for &successor in block_data.terminator().successors() {
 113                         if body[successor].is_cleanup {
 114                             continue;
 115                         }
 116
 117                         // The initialization happened in (or rather, when arriving at)
 118                         // the successors, but not in the unwind block.
 119                         let first_statement = Location { block: successor, statement_index: 0 };
 120                         all_facts
 121                             .path_assigned_at_base
 122                             .push((init.path, location_table.start_index(first_statement)));
 123                     }
 124                 } else {
 125                     // In all other cases, the initialization just happens at the
 126                     // midpoint, like any other effect.
 127                     all_facts
 128                         .path_assigned_at_base
 129                         .push((init.path, location_table.mid_index(location)));
 130                 }
 131             }
 132             // Arguments are initialized on function entry
 133             InitLocation::Argument(local) => {
 134                 assert!(body.local_kind(local) == LocalKind::Arg);
 135                 all_facts.path_assigned_at_base.push((init.path, fn_entry_start));
 136             }
 137         }
 138     }
 139
 140     for (local, &path) in move_data.rev_lookup.iter_locals_enumerated() {
 141         if body.local_kind(local) != LocalKind::Arg {
 142             // Non-arguments start out deinitialised; we simulate this with an
 143             // initial move:
 144             all_facts.path_moved_at_base.push((path, fn_entry_start));
 145         }
 146     }
 147
 148     // moved_out_at
 149     // deinitialisation is assumed to always happen!
 150     all_facts
 151         .path_moved_at_base
 152         .extend(move_data.moves.iter().map(|mo| (mo.path, location_table.mid_index(mo.source))));
 153 }
 154
 155 /// Computes the (non-lexical) regions from the input MIR.
 156 ///
 157 /// This may result in errors being reported.
 158 pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
 159     infcx: &InferCtxt<'cx, 'tcx>,
 160     universal_regions: UniversalRegions<'tcx>,
 161     body: &Body<'tcx>,
 162     promoted: &IndexVec<Promoted, Body<'tcx>>,
 163     location_table: &LocationTable,
 164     param_env: ty::ParamEnv<'tcx>,
 165     flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
 166     move_data: &MoveData<'tcx>,
 167     borrow_set: &BorrowSet<'tcx>,
 168     upvars: &[Upvar],
 169 ) -> NllOutput<'tcx> {
 170     let mut all_facts = AllFacts::enabled(infcx.tcx).then_some(AllFacts::default());
 171
 172     let universal_regions = Rc::new(universal_regions);
 173
 174     let elements = &Rc::new(RegionValueElements::new(&body));
 175
 176     // Run the MIR type-checker.
 177     let MirTypeckResults { constraints, universal_region_relations, opaque_type_values } =
 178         type_check::type_check(
 179             infcx,
 180             param_env,
 181             body,
 182             promoted,
 183             &universal_regions,
 184             location_table,
 185             borrow_set,
 186             &mut all_facts,
 187             flow_inits,
 188             move_data,
 189             elements,
 190             upvars,
 191         );
 192
 193     if let Some(all_facts) = &mut all_facts {
 194         let _prof_timer = infcx.tcx.prof.generic_activity("polonius_fact_generation");
 195         all_facts.universal_region.extend(universal_regions.universal_regions());
 196         populate_polonius_move_facts(all_facts, move_data, location_table, &body);
 197
 198         // Emit universal regions facts, and their relations, for Polonius.
 199         //
 200         // 1: universal regions are modeled in Polonius as a pair:
 201         // - the universal region vid itself.
 202         // - a "placeholder loan" associated to this universal region. Since they don't exist in
 203         //   the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
 204         //   added to the existing number of loans, as if they succeeded them in the set.
 205         //
 206         let borrow_count = borrow_set.len();
 207         debug!(
 208             "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
 209             universal_regions.len(),
 210             borrow_count
 211         );
 212
 213         for universal_region in universal_regions.universal_regions() {
 214             let universal_region_idx = universal_region.index();
 215             let placeholder_loan_idx = borrow_count + universal_region_idx;
 216             all_facts.placeholder.push((universal_region, placeholder_loan_idx.into()));
 217         }
 218
 219         // 2: the universal region relations `outlives` constraints are emitted as
 220         //  `known_subset` facts.
 221         for (fr1, fr2) in universal_region_relations.known_outlives() {
 222             if fr1 != fr2 {
 223                 debug!(
 224                     "compute_regions: emitting polonius `known_subset` fr1={:?}, fr2={:?}",
 225                     fr1, fr2
 226                 );
 227                 all_facts.known_subset.push((*fr1, *fr2));
 228             }
 229         }
 230     }
 231
 232     // Create the region inference context, taking ownership of the
 233     // region inference data that was contained in `infcx`, and the
 234     // base constraints generated by the type-check.
 235     let var_origins = infcx.take_region_var_origins();
 236     let MirTypeckRegionConstraints {
 237         placeholder_indices,
 238         placeholder_index_to_region: _,
 239         mut liveness_constraints,
 240         outlives_constraints,
 241         member_constraints,
 242         closure_bounds_mapping,
 243         type_tests,
 244     } = constraints;
 245     let placeholder_indices = Rc::new(placeholder_indices);
 246
 247     constraint_generation::generate_constraints(
 248         infcx,
 249         &mut liveness_constraints,
 250         &mut all_facts,
 251         location_table,
 252         &body,
 253         borrow_set,
 254     );
 255
 256     let mut regioncx = RegionInferenceContext::new(
 257         var_origins,
 258         universal_regions,
 259         placeholder_indices,
 260         universal_region_relations,
 261         outlives_constraints,
 262         member_constraints,
 263         closure_bounds_mapping,
 264         type_tests,
 265         liveness_constraints,
 266         elements,
 267     );
 268
 269     // Generate various additional constraints.
 270     invalidation::generate_invalidates(infcx.tcx, &mut all_facts, location_table, body, borrow_set);
 271
 272     let def_id = body.source.def_id();
 273
 274     // Dump facts if requested.
 275     let polonius_output = all_facts.and_then(|all_facts| {
 276         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
 277             let def_path = infcx.tcx.def_path(def_id);
 278             let dir_path = PathBuf::from(&infcx.tcx.sess.opts.debugging_opts.nll_facts_dir)
 279                 .join(def_path.to_filename_friendly_no_crate());
 280             all_facts.write_to_dir(dir_path, location_table).unwrap();
 281         }
 282
 283         if infcx.tcx.sess.opts.debugging_opts.polonius {
 284             let algorithm =
 285                 env::var("POLONIUS_ALGORITHM").unwrap_or_else(|_| String::from("Naive"));
 286             let algorithm = Algorithm::from_str(&algorithm).unwrap();
 287             debug!("compute_regions: using polonius algorithm {:?}", algorithm);
 288             let _prof_timer = infcx.tcx.prof.generic_activity("polonius_analysis");
 289             Some(Rc::new(Output::compute(&all_facts, algorithm, false)))
 290         } else {
 291             None
 292         }
 293     });
 294
 295     // Solve the region constraints.
 296     let (closure_region_requirements, nll_errors) =
 297         regioncx.solve(infcx, &body, polonius_output.clone());
 298
 299     if !nll_errors.is_empty() {
 300         // Suppress unhelpful extra errors in `infer_opaque_types`.
 301         infcx.set_tainted_by_errors();
 302     }
 303
 304     let remapped_opaque_tys = regioncx.infer_opaque_types(&infcx, opaque_type_values, body.span);
 305
 306     NllOutput {
 307         regioncx,
 308         opaque_type_values: remapped_opaque_tys,
 309         polonius_output,
 310         opt_closure_req: closure_region_requirements,
 311         nll_errors,
 312     }
 313 }
 314
 315 pub(super) fn dump_mir_results<'a, 'tcx>(
 316     infcx: &InferCtxt<'a, 'tcx>,
 317     body: &Body<'tcx>,
 318     regioncx: &RegionInferenceContext<'tcx>,
 319     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
 320 ) {
 321     if !mir_util::dump_enabled(infcx.tcx, "nll", body.source.def_id()) {
 322         return;
 323     }
 324
 325     mir_util::dump_mir(infcx.tcx, None, "nll", &0, body, |pass_where, out| {
 326         match pass_where {
 327             // Before the CFG, dump out the values for each region variable.
 328             PassWhere::BeforeCFG => {
 329                 regioncx.dump_mir(infcx.tcx, out)?;
 330                 writeln!(out, "|")?;
 331
 332                 if let Some(closure_region_requirements) = closure_region_requirements {
 333                     writeln!(out, "| Free Region Constraints")?;
 334                     for_each_region_constraint(closure_region_requirements, &mut |msg| {
 335                         writeln!(out, "| {}", msg)
 336                     })?;
 337                     writeln!(out, "|")?;
 338                 }
 339             }
 340
 341             PassWhere::BeforeLocation(_) => {}
 342
 343             PassWhere::AfterTerminator(_) => {}
 344
 345             PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
 346         }
 347         Ok(())
 348     });
 349
 350     // Also dump the inference graph constraints as a graphviz file.
 351     let _: io::Result<()> = try {
 352         let mut file =
 353             pretty::create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, body.source)?;
 354         regioncx.dump_graphviz_raw_constraints(&mut file)?;
 355     };
 356
 357     // Also dump the inference graph constraints as a graphviz file.
 358     let _: io::Result<()> = try {
 359         let mut file =
 360             pretty::create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, body.source)?;
 361         regioncx.dump_graphviz_scc_constraints(&mut file)?;
 362     };
 363 }
 364
 365 pub(super) fn dump_annotation<'a, 'tcx>(
 366     infcx: &InferCtxt<'a, 'tcx>,
 367     body: &Body<'tcx>,
 368     regioncx: &RegionInferenceContext<'tcx>,
 369     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
 370     opaque_type_values: &FxHashMap<DefId, ty::ResolvedOpaqueTy<'tcx>>,
 371     errors_buffer: &mut Vec<Diagnostic>,
 372 ) {
 373     let tcx = infcx.tcx;
 374     let base_def_id = tcx.closure_base_def_id(body.source.def_id());
 375     if !tcx.has_attr(base_def_id, sym::rustc_regions) {
 376         return;
 377     }
 378
 379     // When the enclosing function is tagged with `#[rustc_regions]`,
 380     // we dump out various bits of state as warnings. This is useful
 381     // for verifying that the compiler is behaving as expected.  These
 382     // warnings focus on the closure region requirements -- for
 383     // viewing the intraprocedural state, the -Zdump-mir output is
 384     // better.
 385
 386     let mut err = if let Some(closure_region_requirements) = closure_region_requirements {
 387         let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "external requirements");
 388
 389         regioncx.annotate(tcx, &mut err);
 390
 391         err.note(&format!(
 392             "number of external vids: {}",
 393             closure_region_requirements.num_external_vids
 394         ));
 395
 396         // Dump the region constraints we are imposing *between* those
 397         // newly created variables.
 398         for_each_region_constraint(closure_region_requirements, &mut |msg| {
 399             err.note(msg);
 400             Ok(())
 401         })
 402         .unwrap();
 403
 404         err
 405     } else {
 406         let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "no external requirements");
 407         regioncx.annotate(tcx, &mut err);
 408
 409         err
 410     };
 411
 412     if !opaque_type_values.is_empty() {
 413         err.note(&format!("Inferred opaque type values:\n{:#?}", opaque_type_values));
 414     }
 415
 416     err.buffer(errors_buffer);
 417 }
 418
 419 fn for_each_region_constraint(
 420     closure_region_requirements: &ClosureRegionRequirements<'_>,
 421     with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
 422 ) -> io::Result<()> {
 423     for req in &closure_region_requirements.outlives_requirements {
 424         let subject: &dyn Debug = match &req.subject {
 425             ClosureOutlivesSubject::Region(subject) => subject,
 426             ClosureOutlivesSubject::Ty(ty) => ty,
 427         };
 428         with_msg(&format!("where {:?}: {:?}", subject, req.outlived_free_region,))?;
 429     }
 430     Ok(())
 431 }
 432
 433 /// Right now, we piggy back on the `ReVar` to store our NLL inference
 434 /// regions. These are indexed with `RegionVid`. This method will
 435 /// assert that the region is a `ReVar` and extract its internal index.
 436 /// This is reasonable because in our MIR we replace all universal regions
 437 /// with inference variables.
 438 pub trait ToRegionVid {
 439     fn to_region_vid(self) -> RegionVid;
 440 }
 441
 442 impl<'tcx> ToRegionVid for &'tcx RegionKind {
 443     fn to_region_vid(self) -> RegionVid {
 444         if let ty::ReVar(vid) = self { *vid } else { bug!("region is not an ReVar: {:?}", self) }
 445     }
 446 }
 447
 448 impl ToRegionVid for RegionVid {
 449     fn to_region_vid(self) -> RegionVid {
 450         self
 451     }
 452 }
 453
 454 crate trait ConstraintDescription {
 455     fn description(&self) -> &'static str;
 456 }