1 //! The entry point of the NLL borrow checker.
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,
12 use rustc_middle::ty::{self, RegionKind, RegionVid};
13 use rustc_span::symbol::sym;
17 use std::path::PathBuf;
19 use std::str::FromStr;
21 use self::mir_util::PassWhere;
22 use polonius_engine::{Algorithm, Output};
24 use crate::dataflow::move_paths::{InitKind, InitLocation, MoveData};
25 use crate::dataflow::MaybeInitializedPlaces;
26 use crate::dataflow::ResultsCursor;
27 use crate::transform::MirSource;
28 use crate::util as mir_util;
29 use crate::util::pretty;
31 use crate::borrow_check::{
32 borrow_set::BorrowSet,
33 constraint_generation,
34 diagnostics::RegionErrors,
35 facts::{AllFacts, AllFactsExt, RustcFacts},
37 location::LocationTable,
38 region_infer::{values::RegionValueElements, RegionInferenceContext},
40 type_check::{self, MirTypeckRegionConstraints, MirTypeckResults},
41 universal_regions::UniversalRegions,
44 crate type PoloniusOutput = Output<RustcFacts>;
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>,
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>,
62 param_env: ty::ParamEnv<'tcx>,
63 body: &mut Body<'tcx>,
64 promoted: &mut IndexVec<Promoted, Body<'tcx>>,
65 ) -> UniversalRegions<'tcx> {
66 debug!("replace_regions_in_mir(def_id={:?})", def_id);
68 // Compute named region information. This also renumbers the inputs/outputs.
69 let universal_regions = UniversalRegions::new(infcx, def_id, param_env);
71 // Replace all remaining regions with fresh inference variables.
72 renumber::renumber_mir(infcx, body, promoted);
74 let source = MirSource::item(def_id);
75 mir_util::dump_mir(infcx.tcx, None, "renumber", &0, source, body, |_, _| Ok(()));
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,
90 .extend(move_data.rev_lookup.iter_locals_enumerated().map(|(v, &m)| (m, v)));
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));
98 let fn_entry_start = location_table
99 .start_index(Location { block: BasicBlock::from_u32(0u32), statement_index: 0 });
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();
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
112 for &successor in block_data.terminator().successors() {
113 if body[successor].is_cleanup {
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 };
121 .path_assigned_at_base
122 .push((init.path, location_table.start_index(first_statement)));
125 // In all other cases, the initialization just happens at the
126 // midpoint, like any other effect.
128 .path_assigned_at_base
129 .push((init.path, location_table.mid_index(location)));
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));
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
144 all_facts.path_moved_at_base.push((path, fn_entry_start));
149 // deinitialisation is assumed to always happen!
152 .extend(move_data.moves.iter().map(|mo| (mo.path, location_table.mid_index(mo.source))));
155 /// Computes the (non-lexical) regions from the input MIR.
157 /// This may result in errors being reported.
158 pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
159 infcx: &InferCtxt<'cx, 'tcx>,
161 universal_regions: UniversalRegions<'tcx>,
163 promoted: &IndexVec<Promoted, Body<'tcx>>,
164 location_table: &LocationTable,
165 param_env: ty::ParamEnv<'tcx>,
166 flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
167 move_data: &MoveData<'tcx>,
168 borrow_set: &BorrowSet<'tcx>,
169 ) -> NllOutput<'tcx> {
170 let mut all_facts = AllFacts::enabled(infcx.tcx).then_some(AllFacts::default());
172 let universal_regions = Rc::new(universal_regions);
174 let elements = &Rc::new(RegionValueElements::new(&body));
176 // Run the MIR type-checker.
177 let MirTypeckResults { constraints, universal_region_relations, opaque_type_values } =
178 type_check::type_check(
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);
198 // Emit universal regions facts, and their relations, for Polonius.
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.
206 let borrow_count = borrow_set.borrows.len();
208 "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
209 universal_regions.len(),
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()));
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() {
224 "compute_regions: emitting polonius `known_subset` fr1={:?}, fr2={:?}",
227 all_facts.known_subset.push((*fr1, *fr2));
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 {
238 placeholder_index_to_region: _,
239 mut liveness_constraints,
240 outlives_constraints,
242 closure_bounds_mapping,
245 let placeholder_indices = Rc::new(placeholder_indices);
247 constraint_generation::generate_constraints(
249 &mut liveness_constraints,
256 let mut regioncx = RegionInferenceContext::new(
260 universal_region_relations,
261 outlives_constraints,
263 closure_bounds_mapping,
265 liveness_constraints,
269 // Generate various additional constraints.
270 invalidation::generate_invalidates(infcx.tcx, &mut all_facts, location_table, body, borrow_set);
272 // Dump facts if requested.
273 let polonius_output = all_facts.and_then(|all_facts| {
274 if infcx.tcx.sess.opts.debugging_opts.nll_facts {
275 let def_path = infcx.tcx.def_path(def_id);
277 PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
278 all_facts.write_to_dir(dir_path, location_table).unwrap();
281 if infcx.tcx.sess.opts.debugging_opts.polonius {
283 env::var("POLONIUS_ALGORITHM").unwrap_or_else(|_| String::from("Naive"));
284 let algorithm = Algorithm::from_str(&algorithm).unwrap();
285 debug!("compute_regions: using polonius algorithm {:?}", algorithm);
286 let _prof_timer = infcx.tcx.prof.generic_activity("polonius_analysis");
287 Some(Rc::new(Output::compute(&all_facts, algorithm, false)))
293 // Solve the region constraints.
294 let (closure_region_requirements, nll_errors) =
295 regioncx.solve(infcx, &body, def_id, polonius_output.clone());
297 if !nll_errors.is_empty() {
298 // Suppress unhelpful extra errors in `infer_opaque_types`.
299 infcx.set_tainted_by_errors();
302 let remapped_opaque_tys = regioncx.infer_opaque_types(&infcx, opaque_type_values, body.span);
306 opaque_type_values: remapped_opaque_tys,
308 opt_closure_req: closure_region_requirements,
313 pub(super) fn dump_mir_results<'a, 'tcx>(
314 infcx: &InferCtxt<'a, 'tcx>,
315 source: MirSource<'tcx>,
317 regioncx: &RegionInferenceContext<'_>,
318 closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
320 if !mir_util::dump_enabled(infcx.tcx, "nll", source.def_id()) {
324 mir_util::dump_mir(infcx.tcx, None, "nll", &0, source, body, |pass_where, out| {
326 // Before the CFG, dump out the values for each region variable.
327 PassWhere::BeforeCFG => {
328 regioncx.dump_mir(out)?;
331 if let Some(closure_region_requirements) = closure_region_requirements {
332 writeln!(out, "| Free Region Constraints")?;
333 for_each_region_constraint(closure_region_requirements, &mut |msg| {
334 writeln!(out, "| {}", msg)
340 PassWhere::BeforeLocation(_) => {}
342 PassWhere::AfterTerminator(_) => {}
344 PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
349 // Also dump the inference graph constraints as a graphviz file.
350 let _: io::Result<()> = try {
352 pretty::create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, source)?;
353 regioncx.dump_graphviz_raw_constraints(&mut file)?;
356 // Also dump the inference graph constraints as a graphviz file.
357 let _: io::Result<()> = try {
359 pretty::create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, source)?;
360 regioncx.dump_graphviz_scc_constraints(&mut file)?;
364 pub(super) fn dump_annotation<'a, 'tcx>(
365 infcx: &InferCtxt<'a, '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>,
374 let base_def_id = tcx.closure_base_def_id(mir_def_id);
375 if !tcx.has_attr(base_def_id, sym::rustc_regions) {
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
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");
389 regioncx.annotate(tcx, &mut err);
392 "number of external vids: {}",
393 closure_region_requirements.num_external_vids
396 // Dump the region constraints we are imposing *between* those
397 // newly created variables.
398 for_each_region_constraint(closure_region_requirements, &mut |msg| {
406 let mut err = tcx.sess.diagnostic().span_note_diag(body.span, "no external requirements");
407 regioncx.annotate(tcx, &mut err);
412 if !opaque_type_values.is_empty() {
413 err.note(&format!("Inferred opaque type values:\n{:#?}", opaque_type_values));
416 err.buffer(errors_buffer);
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,
428 with_msg(&format!("where {:?}: {:?}", subject, req.outlived_free_region,))?;
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;
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) }
448 impl ToRegionVid for RegionVid {
449 fn to_region_vid(self) -> RegionVid {
454 crate trait ConstraintDescription {
455 fn description(&self) -> &'static str;