src/librustc_mir/borrow_check/nll/mod.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use borrow_check::borrow_set::BorrowSet;
  12 use borrow_check::location::{LocationIndex, LocationTable};
  13 use borrow_check::nll::facts::AllFactsExt;
  14 use borrow_check::nll::type_check::MirTypeckRegionConstraints;
  15 use dataflow::indexes::BorrowIndex;
  16 use dataflow::move_paths::MoveData;
  17 use dataflow::FlowAtLocation;
  18 use dataflow::MaybeInitializedPlaces;
  19 use rustc::hir::def_id::DefId;
  20 use rustc::infer::InferCtxt;
  21 use rustc::mir::{ClosureOutlivesSubject, ClosureRegionRequirements, Mir};
  22 use rustc::ty::{self, RegionKind, RegionVid};
  23 use rustc::util::nodemap::FxHashMap;
  24 use std::collections::BTreeSet;
  25 use std::fmt::Debug;
  26 use std::env;
  27 use std::io;
  28 use std::path::PathBuf;
  29 use std::rc::Rc;
  30 use std::str::FromStr;
  31 use transform::MirSource;
  32 use util::liveness::{LivenessResults, LocalSet};
  33
  34 use self::mir_util::PassWhere;
  35 use polonius_engine::{Algorithm, Output};
  36 use util as mir_util;
  37 use util::pretty::{self, ALIGN};
  38
  39 mod constraint_generation;
  40 pub mod explain_borrow;
  41 mod facts;
  42 mod invalidation;
  43 crate mod region_infer;
  44 mod renumber;
  45 crate mod type_check;
  46 mod universal_regions;
  47
  48 use self::facts::AllFacts;
  49 use self::region_infer::RegionInferenceContext;
  50 use self::universal_regions::UniversalRegions;
  51
  52 /// Rewrites the regions in the MIR to use NLL variables, also
  53 /// scraping out the set of universal regions (e.g., region parameters)
  54 /// declared on the function. That set will need to be given to
  55 /// `compute_regions`.
  56 pub(in borrow_check) fn replace_regions_in_mir<'cx, 'gcx, 'tcx>(
  57     infcx: &InferCtxt<'cx, 'gcx, 'tcx>,
  58     def_id: DefId,
  59     param_env: ty::ParamEnv<'tcx>,
  60     mir: &mut Mir<'tcx>,
  61 ) -> UniversalRegions<'tcx> {
  62     debug!("replace_regions_in_mir(def_id={:?})", def_id);
  63
  64     // Compute named region information. This also renumbers the inputs/outputs.
  65     let universal_regions = UniversalRegions::new(infcx, def_id, param_env);
  66
  67     // Replace all remaining regions with fresh inference variables.
  68     renumber::renumber_mir(infcx, mir);
  69
  70     let source = MirSource::item(def_id);
  71     mir_util::dump_mir(infcx.tcx, None, "renumber", &0, source, mir, |_, _| Ok(()));
  72
  73     universal_regions
  74 }
  75
  76 /// Computes the (non-lexical) regions from the input MIR.
  77 ///
  78 /// This may result in errors being reported.
  79 pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
  80     infcx: &InferCtxt<'cx, 'gcx, 'tcx>,
  81     def_id: DefId,
  82     universal_regions: UniversalRegions<'tcx>,
  83     mir: &Mir<'tcx>,
  84     location_table: &LocationTable,
  85     param_env: ty::ParamEnv<'gcx>,
  86     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'cx, 'gcx, 'tcx>>,
  87     move_data: &MoveData<'tcx>,
  88     borrow_set: &BorrowSet<'tcx>,
  89 ) -> (
  90     RegionInferenceContext<'tcx>,
  91     Option<Rc<Output<RegionVid, BorrowIndex, LocationIndex>>>,
  92     Option<ClosureRegionRequirements<'gcx>>,
  93 ) {
  94     let mut all_facts = if infcx.tcx.sess.opts.debugging_opts.nll_facts
  95         || infcx.tcx.sess.opts.debugging_opts.polonius
  96     {
  97         Some(AllFacts::default())
  98     } else {
  99         None
 100     };
 101
 102     // Run the MIR type-checker.
 103     let liveness = &LivenessResults::compute(mir);
 104     let constraint_sets = type_check::type_check(
 105         infcx,
 106         param_env,
 107         mir,
 108         def_id,
 109         &universal_regions,
 110         location_table,
 111         &liveness,
 112         &mut all_facts,
 113         flow_inits,
 114         move_data,
 115     );
 116
 117     if let Some(all_facts) = &mut all_facts {
 118         all_facts
 119             .universal_region
 120             .extend(universal_regions.universal_regions());
 121     }
 122
 123     // Create the region inference context, taking ownership of the
 124     // region inference data that was contained in `infcx`, and the
 125     // base constraints generated by the type-check.
 126     let var_origins = infcx.take_region_var_origins();
 127     let MirTypeckRegionConstraints {
 128         liveness_set,
 129         outlives_constraints,
 130         type_tests,
 131     } = constraint_sets;
 132     let mut regioncx = RegionInferenceContext::new(
 133         var_origins,
 134         universal_regions,
 135         mir,
 136         outlives_constraints,
 137         type_tests,
 138     );
 139
 140     // Generate various additional constraints.
 141     constraint_generation::generate_constraints(
 142         infcx,
 143         &mut regioncx,
 144         &mut all_facts,
 145         location_table,
 146         &mir,
 147         borrow_set,
 148         &liveness_set,
 149     );
 150     invalidation::generate_invalidates(
 151         infcx,
 152         &mut all_facts,
 153         location_table,
 154         &mir,
 155         def_id,
 156         borrow_set,
 157     );
 158
 159     // Dump facts if requested.
 160     let polonius_output = all_facts.and_then(|all_facts| {
 161         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
 162             let def_path = infcx.tcx.hir.def_path(def_id);
 163             let dir_path =
 164                 PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
 165             all_facts.write_to_dir(dir_path, location_table).unwrap();
 166         }
 167
 168         if infcx.tcx.sess.opts.debugging_opts.polonius {
 169             let algorithm = env::var("POLONIUS_ALGORITHM")
 170                 .unwrap_or(String::from("DatafrogOpt"));
 171             let algorithm = Algorithm::from_str(&algorithm).unwrap();
 172             debug!("compute_regions: using polonius algorithm {:?}", algorithm);
 173             Some(Rc::new(Output::compute(
 174                 &all_facts,
 175                 algorithm,
 176                 false,
 177             )))
 178         } else {
 179             None
 180         }
 181     });
 182
 183     // Solve the region constraints.
 184     let closure_region_requirements = regioncx.solve(infcx, &mir, def_id);
 185
 186     // Dump MIR results into a file, if that is enabled. This let us
 187     // write unit-tests, as well as helping with debugging.
 188     dump_mir_results(
 189         infcx,
 190         liveness,
 191         MirSource::item(def_id),
 192         &mir,
 193         &regioncx,
 194         &closure_region_requirements,
 195     );
 196
 197     // We also have a `#[rustc_nll]` annotation that causes us to dump
 198     // information
 199     dump_annotation(infcx, &mir, def_id, &regioncx, &closure_region_requirements);
 200
 201     (regioncx, polonius_output, closure_region_requirements)
 202 }
 203
 204 fn dump_mir_results<'a, 'gcx, 'tcx>(
 205     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 206     liveness: &LivenessResults,
 207     source: MirSource,
 208     mir: &Mir<'tcx>,
 209     regioncx: &RegionInferenceContext,
 210     closure_region_requirements: &Option<ClosureRegionRequirements>,
 211 ) {
 212     if !mir_util::dump_enabled(infcx.tcx, "nll", source) {
 213         return;
 214     }
 215
 216     let regular_liveness_per_location: FxHashMap<_, _> = mir
 217         .basic_blocks()
 218         .indices()
 219         .flat_map(|bb| {
 220             let mut results = vec![];
 221             liveness
 222                 .regular
 223                 .simulate_block(&mir, bb, |location, local_set| {
 224                     results.push((location, local_set.clone()));
 225                 });
 226             results
 227         })
 228         .collect();
 229
 230     let drop_liveness_per_location: FxHashMap<_, _> = mir
 231         .basic_blocks()
 232         .indices()
 233         .flat_map(|bb| {
 234             let mut results = vec![];
 235             liveness
 236                 .drop
 237                 .simulate_block(&mir, bb, |location, local_set| {
 238                     results.push((location, local_set.clone()));
 239                 });
 240             results
 241         })
 242         .collect();
 243
 244     mir_util::dump_mir(
 245         infcx.tcx,
 246         None,
 247         "nll",
 248         &0,
 249         source,
 250         mir,
 251         |pass_where, out| {
 252             match pass_where {
 253                 // Before the CFG, dump out the values for each region variable.
 254                 PassWhere::BeforeCFG => {
 255                     regioncx.dump_mir(out)?;
 256
 257                     if let Some(closure_region_requirements) = closure_region_requirements {
 258                         writeln!(out, "|")?;
 259                         writeln!(out, "| Free Region Constraints")?;
 260                         for_each_region_constraint(closure_region_requirements, &mut |msg| {
 261                             writeln!(out, "| {}", msg)
 262                         })?;
 263                     }
 264                 }
 265
 266                 // Before each basic block, dump out the values
 267                 // that are live on entry to the basic block.
 268                 PassWhere::BeforeBlock(bb) => {
 269                     let s = live_variable_set(&liveness.regular.ins[bb], &liveness.drop.ins[bb]);
 270                     writeln!(out, "    | Live variables on entry to {:?}: {}", bb, s)?;
 271                 }
 272
 273                 PassWhere::BeforeLocation(location) => {
 274                     let s = live_variable_set(
 275                         &regular_liveness_per_location[&location],
 276                         &drop_liveness_per_location[&location],
 277                     );
 278                     writeln!(
 279                         out,
 280                         "{:ALIGN$} | Live variables on entry to {:?}: {}",
 281                         "",
 282                         location,
 283                         s,
 284                         ALIGN = ALIGN
 285                     )?;
 286                 }
 287
 288                 PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
 289             }
 290             Ok(())
 291         },
 292     );
 293
 294     // Also dump the inference graph constraints as a graphviz file.
 295     let _: io::Result<()> = do catch {
 296         let mut file =
 297             pretty::create_dump_file(infcx.tcx, "regioncx.dot", None, "nll", &0, source)?;
 298         regioncx.dump_graphviz(&mut file)?;
 299     };
 300 }
 301
 302 fn dump_annotation<'a, 'gcx, 'tcx>(
 303     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 304     mir: &Mir<'tcx>,
 305     mir_def_id: DefId,
 306     regioncx: &RegionInferenceContext,
 307     closure_region_requirements: &Option<ClosureRegionRequirements>,
 308 ) {
 309     let tcx = infcx.tcx;
 310     let base_def_id = tcx.closure_base_def_id(mir_def_id);
 311     if !tcx.has_attr(base_def_id, "rustc_regions") {
 312         return;
 313     }
 314
 315     // When the enclosing function is tagged with `#[rustc_regions]`,
 316     // we dump out various bits of state as warnings. This is useful
 317     // for verifying that the compiler is behaving as expected.  These
 318     // warnings focus on the closure region requirements -- for
 319     // viewing the intraprocedural state, the -Zdump-mir output is
 320     // better.
 321
 322     if let Some(closure_region_requirements) = closure_region_requirements {
 323         let mut err = tcx
 324             .sess
 325             .diagnostic()
 326             .span_note_diag(mir.span, "External requirements");
 327
 328         regioncx.annotate(&mut err);
 329
 330         err.note(&format!(
 331             "number of external vids: {}",
 332             closure_region_requirements.num_external_vids
 333         ));
 334
 335         // Dump the region constraints we are imposing *between* those
 336         // newly created variables.
 337         for_each_region_constraint(closure_region_requirements, &mut |msg| {
 338             err.note(msg);
 339             Ok(())
 340         }).unwrap();
 341
 342         err.emit();
 343     } else {
 344         let mut err = tcx
 345             .sess
 346             .diagnostic()
 347             .span_note_diag(mir.span, "No external requirements");
 348         regioncx.annotate(&mut err);
 349         err.emit();
 350     }
 351 }
 352
 353 fn for_each_region_constraint(
 354     closure_region_requirements: &ClosureRegionRequirements,
 355     with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
 356 ) -> io::Result<()> {
 357     for req in &closure_region_requirements.outlives_requirements {
 358         let subject: &dyn Debug = match &req.subject {
 359             ClosureOutlivesSubject::Region(subject) => subject,
 360             ClosureOutlivesSubject::Ty(ty) => ty,
 361         };
 362         with_msg(&format!(
 363             "where {:?}: {:?}",
 364             subject, req.outlived_free_region,
 365         ))?;
 366     }
 367     Ok(())
 368 }
 369
 370 /// Right now, we piggy back on the `ReVar` to store our NLL inference
 371 /// regions. These are indexed with `RegionVid`. This method will
 372 /// assert that the region is a `ReVar` and extract its internal index.
 373 /// This is reasonable because in our MIR we replace all universal regions
 374 /// with inference variables.
 375 pub trait ToRegionVid {
 376     fn to_region_vid(self) -> RegionVid;
 377 }
 378
 379 impl<'tcx> ToRegionVid for &'tcx RegionKind {
 380     fn to_region_vid(self) -> RegionVid {
 381         if let ty::ReVar(vid) = self {
 382             *vid
 383         } else {
 384             bug!("region is not an ReVar: {:?}", self)
 385         }
 386     }
 387 }
 388
 389 impl ToRegionVid for RegionVid {
 390     fn to_region_vid(self) -> RegionVid {
 391         self
 392     }
 393 }
 394
 395 fn live_variable_set(regular: &LocalSet, drops: &LocalSet) -> String {
 396     // sort and deduplicate:
 397     let all_locals: BTreeSet<_> = regular.iter().chain(drops.iter()).collect();
 398
 399     // construct a string with each local, including `(drop)` if it is
 400     // only dropped, versus a regular use.
 401     let mut string = String::new();
 402     for local in all_locals {
 403         string.push_str(&format!("{:?}", local));
 404
 405         if !regular.contains(&local) {
 406             assert!(drops.contains(&local));
 407             string.push_str(" (drop)");
 408         }
 409
 410         string.push_str(", ");
 411     }
 412
 413     let len = if string.is_empty() {
 414         0
 415     } else {
 416         string.len() - 2
 417     };
 418
 419     format!("[{}]", &string[..len])
 420 }