compiler/rustc_borrowck/src/nll.rs

   1 //! The entry point of the NLL borrow checker.
   2
   3 use rustc_data_structures::vec_map::VecMap;
   4 use rustc_hir::def_id::DefId;
   5 use rustc_index::vec::IndexVec;
   6 use rustc_infer::infer::InferCtxt;
   7 use rustc_middle::mir::{create_dump_file, dump_enabled, dump_mir, PassWhere};
   8 use rustc_middle::mir::{
   9     BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
  10     Promoted,
  11 };
  12 use rustc_middle::ty::{self, OpaqueHiddenType, Region, 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 polonius_engine::{Algorithm, Output};
  22
  23 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
  24 use rustc_mir_dataflow::move_paths::{InitKind, InitLocation, MoveData};
  25 use rustc_mir_dataflow::ResultsCursor;
  26
  27 use crate::{
  28     borrow_set::BorrowSet,
  29     constraint_generation,
  30     diagnostics::RegionErrors,
  31     facts::{AllFacts, AllFactsExt, RustcFacts},
  32     invalidation,
  33     location::LocationTable,
  34     region_infer::{values::RegionValueElements, RegionInferenceContext},
  35     renumber,
  36     type_check::{self, MirTypeckRegionConstraints, MirTypeckResults},
  37     universal_regions::UniversalRegions,
  38     Upvar,
  39 };
  40
  41 pub type PoloniusOutput = Output<RustcFacts>;
  42
  43 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
  44 /// closure requirements to propagate, and any generated errors.
  45 crate struct NllOutput<'tcx> {
  46     pub regioncx: RegionInferenceContext<'tcx>,
  47     pub opaque_type_values: VecMap<DefId, OpaqueHiddenType<'tcx>>,
  48     pub polonius_input: Option<Box<AllFacts>>,
  49     pub polonius_output: Option<Rc<PoloniusOutput>>,
  50     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
  51     pub nll_errors: RegionErrors<'tcx>,
  52 }
  53
  54 /// Rewrites the regions in the MIR to use NLL variables, also scraping out the set of universal
  55 /// regions (e.g., region parameters) declared on the function. That set will need to be given to
  56 /// `compute_regions`.
  57 #[instrument(skip(infcx, param_env, body, promoted), level = "debug")]
  58 pub(crate) fn replace_regions_in_mir<'cx, 'tcx>(
  59     infcx: &InferCtxt<'cx, 'tcx>,
  60     param_env: ty::ParamEnv<'tcx>,
  61     body: &mut Body<'tcx>,
  62     promoted: &mut IndexVec<Promoted, Body<'tcx>>,
  63 ) -> UniversalRegions<'tcx> {
  64     let def = body.source.with_opt_param().as_local().unwrap();
  65
  66     debug!(?def);
  67
  68     // Compute named region information. This also renumbers the inputs/outputs.
  69     let universal_regions = UniversalRegions::new(infcx, def, param_env);
  70
  71     // Replace all remaining regions with fresh inference variables.
  72     renumber::renumber_mir(infcx, body, promoted);
  73
  74     dump_mir(infcx.tcx, None, "renumber", &0, body, |_, _| Ok(()));
  75
  76     universal_regions
  77 }
  78
  79 // This function populates an AllFacts instance with base facts related to
  80 // MovePaths and needed for the move analysis.
  81 fn populate_polonius_move_facts(
  82     all_facts: &mut AllFacts,
  83     move_data: &MoveData<'_>,
  84     location_table: &LocationTable,
  85     body: &Body<'_>,
  86 ) {
  87     all_facts
  88         .path_is_var
  89         .extend(move_data.rev_lookup.iter_locals_enumerated().map(|(l, r)| (r, l)));
  90
  91     for (child, move_path) in move_data.move_paths.iter_enumerated() {
  92         if let Some(parent) = move_path.parent {
  93             all_facts.child_path.push((child, parent));
  94         }
  95     }
  96
  97     let fn_entry_start = location_table
  98         .start_index(Location { block: BasicBlock::from_u32(0u32), statement_index: 0 });
  99
 100     // initialized_at
 101     for init in move_data.inits.iter() {
 102         match init.location {
 103             InitLocation::Statement(location) => {
 104                 let block_data = &body[location.block];
 105                 let is_terminator = location.statement_index == block_data.statements.len();
 106
 107                 if is_terminator && init.kind == InitKind::NonPanicPathOnly {
 108                     // We are at the terminator of an init that has a panic path,
 109                     // and where the init should not happen on panic
 110
 111                     for &successor in block_data.terminator().successors() {
 112                         if body[successor].is_cleanup {
 113                             continue;
 114                         }
 115
 116                         // The initialization happened in (or rather, when arriving at)
 117                         // the successors, but not in the unwind block.
 118                         let first_statement = Location { block: successor, statement_index: 0 };
 119                         all_facts
 120                             .path_assigned_at_base
 121                             .push((init.path, location_table.start_index(first_statement)));
 122                     }
 123                 } else {
 124                     // In all other cases, the initialization just happens at the
 125                     // midpoint, like any other effect.
 126                     all_facts
 127                         .path_assigned_at_base
 128                         .push((init.path, location_table.mid_index(location)));
 129                 }
 130             }
 131             // Arguments are initialized on function entry
 132             InitLocation::Argument(local) => {
 133                 assert!(body.local_kind(local) == LocalKind::Arg);
 134                 all_facts.path_assigned_at_base.push((init.path, fn_entry_start));
 135             }
 136         }
 137     }
 138
 139     for (local, path) in move_data.rev_lookup.iter_locals_enumerated() {
 140         if body.local_kind(local) != LocalKind::Arg {
 141             // Non-arguments start out deinitialised; we simulate this with an
 142             // initial move:
 143             all_facts.path_moved_at_base.push((path, fn_entry_start));
 144         }
 145     }
 146
 147     // moved_out_at
 148     // deinitialisation is assumed to always happen!
 149     all_facts
 150         .path_moved_at_base
 151         .extend(move_data.moves.iter().map(|mo| (mo.path, location_table.mid_index(mo.source))));
 152 }
 153
 154 /// Computes the (non-lexical) regions from the input MIR.
 155 ///
 156 /// This may result in errors being reported.
 157 pub(crate) fn compute_regions<'cx, 'tcx>(
 158     infcx: &InferCtxt<'cx, 'tcx>,
 159     universal_regions: UniversalRegions<'tcx>,
 160     body: &Body<'tcx>,
 161     promoted: &IndexVec<Promoted, Body<'tcx>>,
 162     location_table: &LocationTable,
 163     param_env: ty::ParamEnv<'tcx>,
 164     flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
 165     move_data: &MoveData<'tcx>,
 166     borrow_set: &BorrowSet<'tcx>,
 167     upvars: &[Upvar<'tcx>],
 168     use_polonius: bool,
 169 ) -> NllOutput<'tcx> {
 170     let mut all_facts =
 171         (use_polonius || AllFacts::enabled(infcx.tcx)).then_some(AllFacts::default());
 172
 173     let universal_regions = Rc::new(universal_regions);
 174
 175     let elements = &Rc::new(RegionValueElements::new(&body));
 176
 177     // Run the MIR type-checker.
 178     let MirTypeckResults { constraints, universal_region_relations, opaque_type_values } =
 179         type_check::type_check(
 180             infcx,
 181             param_env,
 182             body,
 183             promoted,
 184             &universal_regions,
 185             location_table,
 186             borrow_set,
 187             &mut all_facts,
 188             flow_inits,
 189             move_data,
 190             elements,
 191             upvars,
 192             use_polonius,
 193         );
 194
 195     if let Some(all_facts) = &mut all_facts {
 196         let _prof_timer = infcx.tcx.prof.generic_activity("polonius_fact_generation");
 197         all_facts.universal_region.extend(universal_regions.universal_regions());
 198         populate_polonius_move_facts(all_facts, move_data, location_table, &body);
 199
 200         // Emit universal regions facts, and their relations, for Polonius.
 201         //
 202         // 1: universal regions are modeled in Polonius as a pair:
 203         // - the universal region vid itself.
 204         // - a "placeholder loan" associated to this universal region. Since they don't exist in
 205         //   the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
 206         //   added to the existing number of loans, as if they succeeded them in the set.
 207         //
 208         let borrow_count = borrow_set.len();
 209         debug!(
 210             "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
 211             universal_regions.len(),
 212             borrow_count
 213         );
 214
 215         for universal_region in universal_regions.universal_regions() {
 216             let universal_region_idx = universal_region.index();
 217             let placeholder_loan_idx = borrow_count + universal_region_idx;
 218             all_facts.placeholder.push((universal_region, placeholder_loan_idx.into()));
 219         }
 220
 221         // 2: the universal region relations `outlives` constraints are emitted as
 222         //  `known_placeholder_subset` facts.
 223         for (fr1, fr2) in universal_region_relations.known_outlives() {
 224             if fr1 != fr2 {
 225                 debug!(
 226                     "compute_regions: emitting polonius `known_placeholder_subset` \
 227                      fr1={:?}, fr2={:?}",
 228                     fr1, fr2
 229                 );
 230                 all_facts.known_placeholder_subset.push((fr1, fr2));
 231             }
 232         }
 233     }
 234
 235     // Create the region inference context, taking ownership of the
 236     // region inference data that was contained in `infcx`, and the
 237     // base constraints generated by the type-check.
 238     let var_origins = infcx.take_region_var_origins();
 239     let MirTypeckRegionConstraints {
 240         placeholder_indices,
 241         placeholder_index_to_region: _,
 242         mut liveness_constraints,
 243         outlives_constraints,
 244         member_constraints,
 245         closure_bounds_mapping,
 246         universe_causes,
 247         type_tests,
 248     } = constraints;
 249     let placeholder_indices = Rc::new(placeholder_indices);
 250
 251     constraint_generation::generate_constraints(
 252         infcx,
 253         &mut liveness_constraints,
 254         &mut all_facts,
 255         location_table,
 256         &body,
 257         borrow_set,
 258     );
 259
 260     let mut regioncx = RegionInferenceContext::new(
 261         var_origins,
 262         universal_regions,
 263         placeholder_indices,
 264         universal_region_relations,
 265         outlives_constraints,
 266         member_constraints,
 267         closure_bounds_mapping,
 268         universe_causes,
 269         type_tests,
 270         liveness_constraints,
 271         elements,
 272     );
 273
 274     // Generate various additional constraints.
 275     invalidation::generate_invalidates(infcx.tcx, &mut all_facts, location_table, body, borrow_set);
 276
 277     let def_id = body.source.def_id();
 278
 279     // Dump facts if requested.
 280     let polonius_output = all_facts.as_ref().and_then(|all_facts| {
 281         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
 282             let def_path = infcx.tcx.def_path(def_id);
 283             let dir_path = PathBuf::from(&infcx.tcx.sess.opts.debugging_opts.nll_facts_dir)
 284                 .join(def_path.to_filename_friendly_no_crate());
 285             all_facts.write_to_dir(dir_path, location_table).unwrap();
 286         }
 287
 288         if use_polonius {
 289             let algorithm =
 290                 env::var("POLONIUS_ALGORITHM").unwrap_or_else(|_| String::from("Hybrid"));
 291             let algorithm = Algorithm::from_str(&algorithm).unwrap();
 292             debug!("compute_regions: using polonius algorithm {:?}", algorithm);
 293             let _prof_timer = infcx.tcx.prof.generic_activity("polonius_analysis");
 294             Some(Rc::new(Output::compute(&all_facts, algorithm, false)))
 295         } else {
 296             None
 297         }
 298     });
 299
 300     // Solve the region constraints.
 301     let (closure_region_requirements, nll_errors) =
 302         regioncx.solve(infcx, &body, polonius_output.clone());
 303
 304     if !nll_errors.is_empty() {
 305         // Suppress unhelpful extra errors in `infer_opaque_types`.
 306         infcx.set_tainted_by_errors();
 307     }
 308
 309     let remapped_opaque_tys = regioncx.infer_opaque_types(&infcx, opaque_type_values);
 310
 311     NllOutput {
 312         regioncx,
 313         opaque_type_values: remapped_opaque_tys,
 314         polonius_input: all_facts.map(Box::new),
 315         polonius_output,
 316         opt_closure_req: closure_region_requirements,
 317         nll_errors,
 318     }
 319 }
 320
 321 pub(super) fn dump_mir_results<'a, 'tcx>(
 322     infcx: &InferCtxt<'a, 'tcx>,
 323     body: &Body<'tcx>,
 324     regioncx: &RegionInferenceContext<'tcx>,
 325     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
 326 ) {
 327     if !dump_enabled(infcx.tcx, "nll", body.source.def_id()) {
 328         return;
 329     }
 330
 331     dump_mir(infcx.tcx, None, "nll", &0, body, |pass_where, out| {
 332         match pass_where {
 333             // Before the CFG, dump out the values for each region variable.
 334             PassWhere::BeforeCFG => {
 335                 regioncx.dump_mir(infcx.tcx, out)?;
 336                 writeln!(out, "|")?;
 337
 338                 if let Some(closure_region_requirements) = closure_region_requirements {
 339                     writeln!(out, "| Free Region Constraints")?;
 340                     for_each_region_constraint(closure_region_requirements, &mut |msg| {
 341                         writeln!(out, "| {}", msg)
 342                     })?;
 343                     writeln!(out, "|")?;
 344                 }
 345             }
 346
 347             PassWhere::BeforeLocation(_) => {}
 348
 349             PassWhere::AfterTerminator(_) => {}
 350
 351             PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
 352         }
 353         Ok(())
 354     });
 355
 356     // Also dump the inference graph constraints as a graphviz file.
 357     let _: io::Result<()> = try {
 358         let mut file =
 359             create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, body.source)?;
 360         regioncx.dump_graphviz_raw_constraints(&mut file)?;
 361     };
 362
 363     // Also dump the inference graph constraints as a graphviz file.
 364     let _: io::Result<()> = try {
 365         let mut file =
 366             create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, body.source)?;
 367         regioncx.dump_graphviz_scc_constraints(&mut file)?;
 368     };
 369 }
 370
 371 pub(super) fn dump_annotation<'a, 'tcx>(
 372     infcx: &InferCtxt<'a, 'tcx>,
 373     body: &Body<'tcx>,
 374     regioncx: &RegionInferenceContext<'tcx>,
 375     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
 376     opaque_type_values: &VecMap<DefId, OpaqueHiddenType<'tcx>>,
 377     errors: &mut crate::error::BorrowckErrors<'tcx>,
 378 ) {
 379     let tcx = infcx.tcx;
 380     let base_def_id = tcx.typeck_root_def_id(body.source.def_id());
 381     if !tcx.has_attr(base_def_id, sym::rustc_regions) {
 382         return;
 383     }
 384
 385     // When the enclosing function is tagged with `#[rustc_regions]`,
 386     // we dump out various bits of state as warnings. This is useful
 387     // for verifying that the compiler is behaving as expected.  These
 388     // warnings focus on the closure region requirements -- for
 389     // viewing the intraprocedural state, the -Zdump-mir output is
 390     // better.
 391
 392     let mut err = if let Some(closure_region_requirements) = closure_region_requirements {
 393         let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "external requirements");
 394
 395         regioncx.annotate(tcx, &mut err);
 396
 397         err.note(&format!(
 398             "number of external vids: {}",
 399             closure_region_requirements.num_external_vids
 400         ));
 401
 402         // Dump the region constraints we are imposing *between* those
 403         // newly created variables.
 404         for_each_region_constraint(closure_region_requirements, &mut |msg| {
 405             err.note(msg);
 406             Ok(())
 407         })
 408         .unwrap();
 409
 410         err
 411     } else {
 412         let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "no external requirements");
 413         regioncx.annotate(tcx, &mut err);
 414
 415         err
 416     };
 417
 418     if !opaque_type_values.is_empty() {
 419         err.note(&format!("Inferred opaque type values:\n{:#?}", opaque_type_values));
 420     }
 421
 422     errors.buffer_non_error_diag(err);
 423 }
 424
 425 fn for_each_region_constraint(
 426     closure_region_requirements: &ClosureRegionRequirements<'_>,
 427     with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
 428 ) -> io::Result<()> {
 429     for req in &closure_region_requirements.outlives_requirements {
 430         let subject: &dyn Debug = match &req.subject {
 431             ClosureOutlivesSubject::Region(subject) => subject,
 432             ClosureOutlivesSubject::Ty(ty) => ty,
 433         };
 434         with_msg(&format!("where {:?}: {:?}", subject, req.outlived_free_region,))?;
 435     }
 436     Ok(())
 437 }
 438
 439 /// Right now, we piggy back on the `ReVar` to store our NLL inference
 440 /// regions. These are indexed with `RegionVid`. This method will
 441 /// assert that the region is a `ReVar` and extract its internal index.
 442 /// This is reasonable because in our MIR we replace all universal regions
 443 /// with inference variables.
 444 pub trait ToRegionVid {
 445     fn to_region_vid(self) -> RegionVid;
 446 }
 447
 448 impl<'tcx> ToRegionVid for Region<'tcx> {
 449     fn to_region_vid(self) -> RegionVid {
 450         if let ty::ReVar(vid) = *self { vid } else { bug!("region is not an ReVar: {:?}", self) }
 451     }
 452 }
 453
 454 impl ToRegionVid for RegionVid {
 455     fn to_region_vid(self) -> RegionVid {
 456         self
 457     }
 458 }
 459
 460 crate trait ConstraintDescription {
 461     fn description(&self) -> &'static str;
 462 }