1 //! The entry point of the NLL borrow checker.
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,
12 use rustc_middle::ty::{self, OpaqueHiddenType, Region, RegionVid};
13 use rustc_span::symbol::sym;
17 use std::path::PathBuf;
19 use std::str::FromStr;
21 use polonius_engine::{Algorithm, Output};
23 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
24 use rustc_mir_dataflow::move_paths::{InitKind, InitLocation, MoveData};
25 use rustc_mir_dataflow::ResultsCursor;
28 borrow_set::BorrowSet,
29 constraint_generation,
30 diagnostics::RegionErrors,
31 facts::{AllFacts, AllFactsExt, RustcFacts},
33 location::LocationTable,
34 region_infer::{values::RegionValueElements, RegionInferenceContext},
36 type_check::{self, MirTypeckRegionConstraints, MirTypeckResults},
37 universal_regions::UniversalRegions,
41 pub type PoloniusOutput = Output<RustcFacts>;
43 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
44 /// closure requirements to propagate, and any generated errors.
45 pub(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>,
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();
68 // Compute named region information. This also renumbers the inputs/outputs.
69 let universal_regions = UniversalRegions::new(infcx, def, param_env);
71 // Replace all remaining regions with fresh inference variables.
72 renumber::renumber_mir(infcx, body, promoted);
74 dump_mir(infcx.tcx, None, "renumber", &0, body, |_, _| Ok(()));
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,
89 .extend(move_data.rev_lookup.iter_locals_enumerated().map(|(l, r)| (r, l)));
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));
97 let fn_entry_start = location_table
98 .start_index(Location { block: BasicBlock::from_u32(0u32), statement_index: 0 });
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();
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
111 for successor in block_data.terminator().successors() {
112 if body[successor].is_cleanup {
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 };
120 .path_assigned_at_base
121 .push((init.path, location_table.start_index(first_statement)));
124 // In all other cases, the initialization just happens at the
125 // midpoint, like any other effect.
127 .path_assigned_at_base
128 .push((init.path, location_table.mid_index(location)));
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));
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
143 all_facts.path_moved_at_base.push((path, fn_entry_start));
148 // deinitialisation is assumed to always happen!
151 .extend(move_data.moves.iter().map(|mo| (mo.path, location_table.mid_index(mo.source))));
154 /// Computes the (non-lexical) regions from the input MIR.
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>,
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>],
169 ) -> NllOutput<'tcx> {
171 (use_polonius || AllFacts::enabled(infcx.tcx)).then_some(AllFacts::default());
173 let universal_regions = Rc::new(universal_regions);
175 let elements = &Rc::new(RegionValueElements::new(&body));
177 // Run the MIR type-checker.
178 let MirTypeckResults { constraints, universal_region_relations, opaque_type_values } =
179 type_check::type_check(
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);
200 // Emit universal regions facts, and their relations, for Polonius.
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.
208 let borrow_count = borrow_set.len();
210 "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
211 universal_regions.len(),
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()));
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() {
226 "compute_regions: emitting polonius `known_placeholder_subset` \
230 all_facts.known_placeholder_subset.push((fr1, fr2));
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 {
241 placeholder_index_to_region: _,
242 mut liveness_constraints,
243 outlives_constraints,
245 closure_bounds_mapping,
249 let placeholder_indices = Rc::new(placeholder_indices);
251 constraint_generation::generate_constraints(
253 &mut liveness_constraints,
260 let mut regioncx = RegionInferenceContext::new(
264 universal_region_relations,
265 outlives_constraints,
267 closure_bounds_mapping,
270 liveness_constraints,
274 // Generate various additional constraints.
275 invalidation::generate_invalidates(infcx.tcx, &mut all_facts, location_table, body, borrow_set);
277 let def_id = body.source.def_id();
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();
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)))
300 // Solve the region constraints.
301 let (closure_region_requirements, nll_errors) =
302 regioncx.solve(infcx, param_env, &body, polonius_output.clone());
304 if !nll_errors.is_empty() {
305 // Suppress unhelpful extra errors in `infer_opaque_types`.
306 infcx.set_tainted_by_errors();
309 let remapped_opaque_tys = regioncx.infer_opaque_types(&infcx, opaque_type_values);
313 opaque_type_values: remapped_opaque_tys,
314 polonius_input: all_facts.map(Box::new),
316 opt_closure_req: closure_region_requirements,
321 pub(super) fn dump_mir_results<'a, 'tcx>(
322 infcx: &InferCtxt<'a, 'tcx>,
324 regioncx: &RegionInferenceContext<'tcx>,
325 closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
327 if !dump_enabled(infcx.tcx, "nll", body.source.def_id()) {
331 dump_mir(infcx.tcx, None, "nll", &0, body, |pass_where, out| {
333 // Before the CFG, dump out the values for each region variable.
334 PassWhere::BeforeCFG => {
335 regioncx.dump_mir(infcx.tcx, out)?;
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)
347 PassWhere::BeforeLocation(_) => {}
349 PassWhere::AfterTerminator(_) => {}
351 PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
356 // Also dump the inference graph constraints as a graphviz file.
357 let _: io::Result<()> = try {
359 create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, body.source)?;
360 regioncx.dump_graphviz_raw_constraints(&mut file)?;
363 // Also dump the inference graph constraints as a graphviz file.
364 let _: io::Result<()> = try {
366 create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, body.source)?;
367 regioncx.dump_graphviz_scc_constraints(&mut file)?;
371 pub(super) fn dump_annotation<'a, 'tcx>(
372 infcx: &InferCtxt<'a, '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>,
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) {
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
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");
395 regioncx.annotate(tcx, &mut err);
398 "number of external vids: {}",
399 closure_region_requirements.num_external_vids
402 // Dump the region constraints we are imposing *between* those
403 // newly created variables.
404 for_each_region_constraint(closure_region_requirements, &mut |msg| {
412 let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "no external requirements");
413 regioncx.annotate(tcx, &mut err);
418 if !opaque_type_values.is_empty() {
419 err.note(&format!("Inferred opaque type values:\n{:#?}", opaque_type_values));
422 errors.buffer_non_error_diag(err);
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,
434 with_msg(&format!("where {:?}: {:?}", subject, req.outlived_free_region,))?;
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;
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) }
454 impl ToRegionVid for RegionVid {
455 fn to_region_vid(self) -> RegionVid {
460 pub(crate) trait ConstraintDescription {
461 fn description(&self) -> &'static str;