src/librustc_mir/borrow_check/nll/mod.rs - third_party/rust - Git at Google

 use crate::borrow_check::borrow_set::BorrowSet;
 use crate::borrow_check::location::LocationTable;
 use crate::borrow_check::nll::facts::AllFactsExt;
 use crate::borrow_check::nll::type_check::{MirTypeckResults, MirTypeckRegionConstraints};
 use crate::borrow_check::nll::region_infer::values::RegionValueElements;
 use crate::dataflow::move_paths::{InitLocation, MoveData, InitKind};
 use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MaybeInitializedPlaces;
 use crate::transform::MirSource;
 use crate::borrow_check::Upvar;
 use rustc::hir::def_id::DefId;
 use rustc::infer::InferCtxt;
 use rustc::mir::{ClosureOutlivesSubject, ClosureRegionRequirements,
                  Local, Location, Body, BodyAndCache, LocalKind, BasicBlock,
                  Promoted, ReadOnlyBodyAndCache};
 use rustc::ty::{self, RegionKind, RegionVid};
 use rustc_index::vec::IndexVec;
 use rustc_errors::Diagnostic;
 use syntax_pos::symbol::Symbol;
 use std::fmt::Debug;
 use std::env;
 use std::io;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::str::FromStr;
 use syntax::symbol::sym;

 use self::mir_util::PassWhere;
 use polonius_engine::{Algorithm, Output};
 use crate::util as mir_util;
 use crate::util::pretty;

 mod constraint_generation;
 mod facts;
 mod invalidation;
 mod renumber;

 mod member_constraints;

 crate mod constraints;
 crate mod universal_regions;
 crate mod type_check;
 crate mod region_infer;

 use self::facts::{AllFacts, RustcFacts};
 use self::region_infer::RegionInferenceContext;
 use self::universal_regions::UniversalRegions;

 crate type PoloniusOutput = Output<RustcFacts>;

 /// Rewrites the regions in the MIR to use NLL variables, also
 /// scraping out the set of universal regions (e.g., region parameters)
 /// declared on the function. That set will need to be given to
 /// `compute_regions`.
 pub(in crate::borrow_check) fn replace_regions_in_mir<'cx, 'tcx>(
     infcx: &InferCtxt<'cx, 'tcx>,
     def_id: DefId,
     param_env: ty::ParamEnv<'tcx>,
     body: &mut BodyAndCache<'tcx>,
     promoted: &mut IndexVec<Promoted, BodyAndCache<'tcx>>,
 ) -> UniversalRegions<'tcx> {
     debug!("replace_regions_in_mir(def_id={:?})", def_id);

     // Compute named region information. This also renumbers the inputs/outputs.
     let universal_regions = UniversalRegions::new(infcx, def_id, param_env);

     // Replace all remaining regions with fresh inference variables.
     renumber::renumber_mir(infcx, body, promoted);

     let source = MirSource::item(def_id);
     mir_util::dump_mir(infcx.tcx, None, "renumber", &0, source, body, |_, _| Ok(()));

     universal_regions
 }


 // This function populates an AllFacts instance with base facts related to
 // MovePaths and needed for the move analysis.
 fn populate_polonius_move_facts(
     all_facts: &mut AllFacts,
     move_data: &MoveData<'_>,
     location_table: &LocationTable,
     body: &Body<'_>) {
     all_facts
         .path_belongs_to_var
         .extend(
             move_data
                 .rev_lookup
                 .iter_locals_enumerated()
                 .map(|(v, &m)| (m, v)));

     for (child, move_path) in move_data.move_paths.iter_enumerated() {
         all_facts
             .child
             .extend(
                 move_path
                     .parents(&move_data.move_paths)
                     .iter()
                     .map(|&parent| (child, parent)));
     }

     // initialized_at
     for init in move_data.inits.iter() {

         match init.location {
             InitLocation::Statement(location) => {
                 let block_data = &body[location.block];
                 let is_terminator = location.statement_index == block_data.statements.len();

                 if is_terminator && init.kind == InitKind::NonPanicPathOnly {
                     // We are at the terminator of an init that has a panic path,
                     // and where the init should not happen on panic

                     for &successor in block_data.terminator().successors() {
                         if body[successor].is_cleanup {
                             continue;
                         }

                         // The initialization happened in (or rather, when arriving at)
                         // the successors, but not in the unwind block.
                         let first_statement = Location { block: successor, statement_index: 0};
                         all_facts
                             .initialized_at
                             .push((init.path, location_table.start_index(first_statement)));
                     }

                 } else {
                     // In all other cases, the initialization just happens at the
                     // midpoint, like any other effect.
                     all_facts.initialized_at.push((init.path, location_table.mid_index(location)));
                 }
             },
             // Arguments are initialized on function entry
             InitLocation::Argument(local) => {
                 assert!(body.local_kind(local) == LocalKind::Arg);
                 let fn_entry = Location {block: BasicBlock::from_u32(0u32), statement_index: 0 };
                 all_facts.initialized_at.push((init.path, location_table.start_index(fn_entry)));

             }
         }
     }


     // moved_out_at
     // deinitialisation is assumed to always happen!
     all_facts
         .moved_out_at
         .extend(
             move_data
                 .moves
                 .iter()
                 .map(|mo| (mo.path, location_table.mid_index(mo.source))));
 }

 /// Computes the (non-lexical) regions from the input MIR.
 ///
 /// This may result in errors being reported.
 pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     infcx: &InferCtxt<'cx, 'tcx>,
     def_id: DefId,
     universal_regions: UniversalRegions<'tcx>,
     body: ReadOnlyBodyAndCache<'_, 'tcx>,
     promoted: &IndexVec<Promoted, ReadOnlyBodyAndCache<'_, 'tcx>>,
     local_names: &IndexVec<Local, Option<Symbol>>,
     upvars: &[Upvar],
     location_table: &LocationTable,
     param_env: ty::ParamEnv<'tcx>,
     flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     errors_buffer: &mut Vec<Diagnostic>,
 ) -> (
     RegionInferenceContext<'tcx>,
     Option<Rc<PoloniusOutput>>,
     Option<ClosureRegionRequirements<'tcx>>,
 ) {
     let mut all_facts = AllFacts::enabled(infcx.tcx).then_some(AllFacts::default());

     let universal_regions = Rc::new(universal_regions);

     let elements
         = &Rc::new(RegionValueElements::new(&body));

     // Run the MIR type-checker.
     let MirTypeckResults {
         constraints,
         universal_region_relations,
     } = type_check::type_check(
         infcx,
         param_env,
         body,
         promoted,
         def_id,
         &universal_regions,
         location_table,
         borrow_set,
         &mut all_facts,
         flow_inits,
         move_data,
         elements,
     );

     if let Some(all_facts) = &mut all_facts {
         all_facts
             .universal_region
             .extend(universal_regions.universal_regions());
         populate_polonius_move_facts(all_facts, move_data, location_table, &body);

         // Emit universal regions facts, and their relations, for Polonius.
         //
         // 1: universal regions are modeled in Polonius as a pair:
         // - the universal region vid itself.
         // - a "placeholder loan" associated to this universal region. Since they don't exist in
         //   the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
         //   added to the existing number of loans, as if they succeeded them in the set.
         //
         let borrow_count = borrow_set.borrows.len();
         debug!(
             "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
             universal_regions.len(),
             borrow_count
         );

         for universal_region in universal_regions.universal_regions() {
             let universal_region_idx = universal_region.index();
             let placeholder_loan_idx = borrow_count + universal_region_idx;
             all_facts.placeholder.push((universal_region, placeholder_loan_idx.into()));
         }

         // 2: the universal region relations `outlives` constraints are emitted as
         //  `known_subset` facts.
         for (fr1, fr2) in universal_region_relations.known_outlives() {
             if fr1 != fr2 {
                 debug!(
                     "compute_regions: emitting polonius `known_subset` fr1={:?}, fr2={:?}",
                     fr1, fr2
                 );
                 all_facts.known_subset.push((*fr1, *fr2));
             }
         }
     }

     // Create the region inference context, taking ownership of the
     // region inference data that was contained in `infcx`, and the
     // base constraints generated by the type-check.
     let var_origins = infcx.take_region_var_origins();
     let MirTypeckRegionConstraints {
         placeholder_indices,
         placeholder_index_to_region: _,
         mut liveness_constraints,
         outlives_constraints,
         member_constraints,
         closure_bounds_mapping,
         type_tests,
     } = constraints;
     let placeholder_indices = Rc::new(placeholder_indices);

     constraint_generation::generate_constraints(
         infcx,
         param_env,
         &mut liveness_constraints,
         &mut all_facts,
         location_table,
         &body,
         borrow_set,
     );

     let mut regioncx = RegionInferenceContext::new(
         var_origins,
         universal_regions,
         placeholder_indices,
         universal_region_relations,
         outlives_constraints,
         member_constraints,
         closure_bounds_mapping,
         type_tests,
         liveness_constraints,
         elements,
     );

     // Generate various additional constraints.
     invalidation::generate_invalidates(
         infcx.tcx,
         param_env,
         &mut all_facts,
         location_table,
         body,
         borrow_set,
     );

     // Dump facts if requested.
     let polonius_output = all_facts.and_then(|all_facts| {
         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
             let def_path = infcx.tcx.hir().def_path(def_id);
             let dir_path =
                 PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
             all_facts.write_to_dir(dir_path, location_table).unwrap();
         }

         if infcx.tcx.sess.opts.debugging_opts.polonius {
             let algorithm = env::var("POLONIUS_ALGORITHM")
                 .unwrap_or_else(|_| String::from("Naive"));
             let algorithm = Algorithm::from_str(&algorithm).unwrap();
             debug!("compute_regions: using polonius algorithm {:?}", algorithm);
             Some(Rc::new(Output::compute(
                 &all_facts,
                 algorithm,
                 false,
             )))
         } else {
             None
         }
     });

     // Solve the region constraints.
     let closure_region_requirements = regioncx.solve(
         infcx,
         &body,
         local_names,
         upvars,
         def_id,
         errors_buffer,
         polonius_output.clone(),
     );

     // Dump MIR results into a file, if that is enabled. This let us
     // write unit-tests, as well as helping with debugging.
     dump_mir_results(
         infcx,
         MirSource::item(def_id),
         &body,
         &regioncx,
         &closure_region_requirements,
     );

     // We also have a `#[rustc_nll]` annotation that causes us to dump
     // information
     dump_annotation(
         infcx,
         &body,
         def_id,
         &regioncx,
         &closure_region_requirements,
         errors_buffer);

     (regioncx, polonius_output, closure_region_requirements)
 }

 fn dump_mir_results<'a, 'tcx>(
     infcx: &InferCtxt<'a, 'tcx>,
     source: MirSource<'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'_>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
 ) {
     if !mir_util::dump_enabled(infcx.tcx, "nll", source) {
         return;
     }

     mir_util::dump_mir(
         infcx.tcx,
         None,
         "nll",
         &0,
         source,
         body,
         |pass_where, out| {
             match pass_where {
                 // Before the CFG, dump out the values for each region variable.
                 PassWhere::BeforeCFG => {
                     regioncx.dump_mir(out)?;
                     writeln!(out, "|")?;

                     if let Some(closure_region_requirements) = closure_region_requirements {
                         writeln!(out, "| Free Region Constraints")?;
                         for_each_region_constraint(closure_region_requirements, &mut |msg| {
                             writeln!(out, "| {}", msg)
                         })?;
                         writeln!(out, "|")?;
                     }
                 }

                 PassWhere::BeforeLocation(_) => {
                 }

                 PassWhere::AfterTerminator(_) => {
                 }

                 PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
             }
             Ok(())
         },
     );

     // Also dump the inference graph constraints as a graphviz file.
     let _: io::Result<()> = try {
         let mut file =
             pretty::create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, source)?;
         regioncx.dump_graphviz_raw_constraints(&mut file)?;
     };

     // Also dump the inference graph constraints as a graphviz file.
     let _: io::Result<()> = try {
         let mut file =
             pretty::create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, source)?;
         regioncx.dump_graphviz_scc_constraints(&mut file)?;
     };
 }

 fn dump_annotation<'a, 'tcx>(
     infcx: &InferCtxt<'a, 'tcx>,
     body: &Body<'tcx>,
     mir_def_id: DefId,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
     errors_buffer: &mut Vec<Diagnostic>,
 ) {
     let tcx = infcx.tcx;
     let base_def_id = tcx.closure_base_def_id(mir_def_id);
     if !tcx.has_attr(base_def_id, sym::rustc_regions) {
         return;
     }

     // When the enclosing function is tagged with `#[rustc_regions]`,
     // we dump out various bits of state as warnings. This is useful
     // for verifying that the compiler is behaving as expected.  These
     // warnings focus on the closure region requirements -- for
     // viewing the intraprocedural state, the -Zdump-mir output is
     // better.

     if let Some(closure_region_requirements) = closure_region_requirements {
         let mut err = tcx
             .sess
             .diagnostic()
             .span_note_diag(body.span, "External requirements");

         regioncx.annotate(tcx, &mut err);

         err.note(&format!(
             "number of external vids: {}",
             closure_region_requirements.num_external_vids
         ));

         // Dump the region constraints we are imposing *between* those
         // newly created variables.
         for_each_region_constraint(closure_region_requirements, &mut |msg| {
             err.note(msg);
             Ok(())
         }).unwrap();

         err.buffer(errors_buffer);
     } else {
         let mut err = tcx
             .sess
             .diagnostic()
             .span_note_diag(body.span, "No external requirements");
         regioncx.annotate(tcx, &mut err);

         err.buffer(errors_buffer);
     }
 }

 fn for_each_region_constraint(
     closure_region_requirements: &ClosureRegionRequirements<'_>,
     with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
 ) -> io::Result<()> {
     for req in &closure_region_requirements.outlives_requirements {
         let subject: &dyn Debug = match &req.subject {
             ClosureOutlivesSubject::Region(subject) => subject,
             ClosureOutlivesSubject::Ty(ty) => ty,
         };
         with_msg(&format!(
             "where {:?}: {:?}",
             subject, req.outlived_free_region,
         ))?;
     }
     Ok(())
 }

 /// Right now, we piggy back on the `ReVar` to store our NLL inference
 /// regions. These are indexed with `RegionVid`. This method will
 /// assert that the region is a `ReVar` and extract its internal index.
 /// This is reasonable because in our MIR we replace all universal regions
 /// with inference variables.
 pub trait ToRegionVid {
     fn to_region_vid(self) -> RegionVid;
 }

 impl<'tcx> ToRegionVid for &'tcx RegionKind {
     fn to_region_vid(self) -> RegionVid {
         if let ty::ReVar(vid) = self {
             *vid
         } else {
             bug!("region is not an ReVar: {:?}", self)
         }
     }
 }

 impl ToRegionVid for RegionVid {
     fn to_region_vid(self) -> RegionVid {
         self
     }
 }

 crate trait ConstraintDescription {
     fn description(&self) -> &'static str;
 }
	use crate::borrow_check::borrow_set::BorrowSet;
	use crate::borrow_check::location::LocationTable;
	use crate::borrow_check::nll::facts::AllFactsExt;
	use crate::borrow_check::nll::type_check::{MirTypeckResults, MirTypeckRegionConstraints};
	use crate::borrow_check::nll::region_infer::values::RegionValueElements;
	use crate::dataflow::move_paths::{InitLocation, MoveData, InitKind};
	use crate::dataflow::FlowAtLocation;
	use crate::dataflow::MaybeInitializedPlaces;
	use crate::transform::MirSource;
	use crate::borrow_check::Upvar;
	use rustc::hir::def_id::DefId;
	use rustc::infer::InferCtxt;
	use rustc::mir::{ClosureOutlivesSubject, ClosureRegionRequirements,
	Local, Location, Body, BodyAndCache, LocalKind, BasicBlock,
	Promoted, ReadOnlyBodyAndCache};
	use rustc::ty::{self, RegionKind, RegionVid};
	use rustc_index::vec::IndexVec;
	use rustc_errors::Diagnostic;
	use syntax_pos::symbol::Symbol;
	use std::fmt::Debug;
	use std::env;
	use std::io;
	use std::path::PathBuf;
	use std::rc::Rc;
	use std::str::FromStr;
	use syntax::symbol::sym;

	use self::mir_util::PassWhere;
	use polonius_engine::{Algorithm, Output};
	use crate::util as mir_util;
	use crate::util::pretty;

	mod constraint_generation;
	mod facts;
	mod invalidation;
	mod renumber;

	mod member_constraints;

	crate mod constraints;
	crate mod universal_regions;
	crate mod type_check;
	crate mod region_infer;

	use self::facts::{AllFacts, RustcFacts};
	use self::region_infer::RegionInferenceContext;
	use self::universal_regions::UniversalRegions;

	crate type PoloniusOutput = Output<RustcFacts>;

	/// Rewrites the regions in the MIR to use NLL variables, also
	/// scraping out the set of universal regions (e.g., region parameters)
	/// declared on the function. That set will need to be given to
	/// `compute_regions`.
	pub(in crate::borrow_check) fn replace_regions_in_mir<'cx, 'tcx>(
	infcx: &InferCtxt<'cx, 'tcx>,
	def_id: DefId,
	param_env: ty::ParamEnv<'tcx>,
	body: &mut BodyAndCache<'tcx>,
	promoted: &mut IndexVec<Promoted, BodyAndCache<'tcx>>,
	) -> UniversalRegions<'tcx> {
	debug!("replace_regions_in_mir(def_id={:?})", def_id);

	// Compute named region information. This also renumbers the inputs/outputs.
	let universal_regions = UniversalRegions::new(infcx, def_id, param_env);

	// Replace all remaining regions with fresh inference variables.
	renumber::renumber_mir(infcx, body, promoted);

	let source = MirSource::item(def_id);
	mir_util::dump_mir(infcx.tcx, None, "renumber", &0, source, body, \|_, _\| Ok(()));

	universal_regions
	}


	// This function populates an AllFacts instance with base facts related to
	// MovePaths and needed for the move analysis.
	fn populate_polonius_move_facts(
	all_facts: &mut AllFacts,
	move_data: &MoveData<'_>,
	location_table: &LocationTable,
	body: &Body<'_>) {
	all_facts
	.path_belongs_to_var
	.extend(
	move_data
	.rev_lookup
	.iter_locals_enumerated()
	.map(\|(v, &m)\| (m, v)));

	for (child, move_path) in move_data.move_paths.iter_enumerated() {
	all_facts
	.child
	.extend(
	move_path
	.parents(&move_data.move_paths)
	.iter()
	.map(\|&parent\| (child, parent)));
	}

	// initialized_at
	for init in move_data.inits.iter() {

	match init.location {
	InitLocation::Statement(location) => {
	let block_data = &body[location.block];
	let is_terminator = location.statement_index == block_data.statements.len();

	if is_terminator && init.kind == InitKind::NonPanicPathOnly {
	// We are at the terminator of an init that has a panic path,
	// and where the init should not happen on panic

	for &successor in block_data.terminator().successors() {
	if body[successor].is_cleanup {
	continue;
	}

	// The initialization happened in (or rather, when arriving at)
	// the successors, but not in the unwind block.
	let first_statement = Location { block: successor, statement_index: 0};
	all_facts
	.initialized_at
	.push((init.path, location_table.start_index(first_statement)));
	}

	} else {
	// In all other cases, the initialization just happens at the
	// midpoint, like any other effect.
	all_facts.initialized_at.push((init.path, location_table.mid_index(location)));
	}
	},
	// Arguments are initialized on function entry
	InitLocation::Argument(local) => {
	assert!(body.local_kind(local) == LocalKind::Arg);
	let fn_entry = Location {block: BasicBlock::from_u32(0u32), statement_index: 0 };
	all_facts.initialized_at.push((init.path, location_table.start_index(fn_entry)));

	}
	}
	}


	// moved_out_at
	// deinitialisation is assumed to always happen!
	all_facts
	.moved_out_at
	.extend(
	move_data
	.moves
	.iter()
	.map(\|mo\| (mo.path, location_table.mid_index(mo.source))));
	}

	/// Computes the (non-lexical) regions from the input MIR.
	///
	/// This may result in errors being reported.
	pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
	infcx: &InferCtxt<'cx, 'tcx>,
	def_id: DefId,
	universal_regions: UniversalRegions<'tcx>,
	body: ReadOnlyBodyAndCache<'_, 'tcx>,
	promoted: &IndexVec<Promoted, ReadOnlyBodyAndCache<'_, 'tcx>>,
	local_names: &IndexVec<Local, Option<Symbol>>,
	upvars: &[Upvar],
	location_table: &LocationTable,
	param_env: ty::ParamEnv<'tcx>,
	flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
	move_data: &MoveData<'tcx>,
	borrow_set: &BorrowSet<'tcx>,
	errors_buffer: &mut Vec<Diagnostic>,
	) -> (
	RegionInferenceContext<'tcx>,
	Option<Rc<PoloniusOutput>>,
	Option<ClosureRegionRequirements<'tcx>>,
	) {
	let mut all_facts = AllFacts::enabled(infcx.tcx).then_some(AllFacts::default());

	let universal_regions = Rc::new(universal_regions);

	let elements
	= &Rc::new(RegionValueElements::new(&body));

	// Run the MIR type-checker.
	let MirTypeckResults {
	constraints,
	universal_region_relations,
	} = type_check::type_check(
	infcx,
	param_env,
	body,
	promoted,
	def_id,
	&universal_regions,
	location_table,
	borrow_set,
	&mut all_facts,
	flow_inits,
	move_data,
	elements,
	);

	if let Some(all_facts) = &mut all_facts {
	all_facts
	.universal_region
	.extend(universal_regions.universal_regions());
	populate_polonius_move_facts(all_facts, move_data, location_table, &body);

	// Emit universal regions facts, and their relations, for Polonius.
	//
	// 1: universal regions are modeled in Polonius as a pair:
	// - the universal region vid itself.
	// - a "placeholder loan" associated to this universal region. Since they don't exist in
	// the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
	// added to the existing number of loans, as if they succeeded them in the set.
	//
	let borrow_count = borrow_set.borrows.len();
	debug!(
	"compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
	universal_regions.len(),
	borrow_count
	);

	for universal_region in universal_regions.universal_regions() {
	let universal_region_idx = universal_region.index();
	let placeholder_loan_idx = borrow_count + universal_region_idx;
	all_facts.placeholder.push((universal_region, placeholder_loan_idx.into()));
	}

	// 2: the universal region relations `outlives` constraints are emitted as
	// `known_subset` facts.
	for (fr1, fr2) in universal_region_relations.known_outlives() {
	if fr1 != fr2 {
	debug!(
	"compute_regions: emitting polonius `known_subset` fr1={:?}, fr2={:?}",
	fr1, fr2
	);
	all_facts.known_subset.push((fr1, fr2));
	}
	}
	}

	// Create the region inference context, taking ownership of the
	// region inference data that was contained in `infcx`, and the
	// base constraints generated by the type-check.
	let var_origins = infcx.take_region_var_origins();
	let MirTypeckRegionConstraints {
	placeholder_indices,
	placeholder_index_to_region: _,
	mut liveness_constraints,
	outlives_constraints,
	member_constraints,
	closure_bounds_mapping,
	type_tests,
	} = constraints;
	let placeholder_indices = Rc::new(placeholder_indices);

	constraint_generation::generate_constraints(
	infcx,
	param_env,
	&mut liveness_constraints,
	&mut all_facts,
	location_table,
	&body,
	borrow_set,
	);

	let mut regioncx = RegionInferenceContext::new(
	var_origins,
	universal_regions,
	placeholder_indices,
	universal_region_relations,
	outlives_constraints,
	member_constraints,
	closure_bounds_mapping,
	type_tests,
	liveness_constraints,
	elements,
	);

	// Generate various additional constraints.
	invalidation::generate_invalidates(
	infcx.tcx,
	param_env,
	&mut all_facts,
	location_table,
	body,
	borrow_set,
	);

	// Dump facts if requested.
	let polonius_output = all_facts.and_then(\|all_facts\| {
	if infcx.tcx.sess.opts.debugging_opts.nll_facts {
	let def_path = infcx.tcx.hir().def_path(def_id);
	let dir_path =
	PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
	all_facts.write_to_dir(dir_path, location_table).unwrap();
	}

	if infcx.tcx.sess.opts.debugging_opts.polonius {
	let algorithm = env::var("POLONIUS_ALGORITHM")
	.unwrap_or_else(\|_\| String::from("Naive"));
	let algorithm = Algorithm::from_str(&algorithm).unwrap();
	debug!("compute_regions: using polonius algorithm {:?}", algorithm);
	Some(Rc::new(Output::compute(
	&all_facts,
	algorithm,
	false,
	)))
	} else {
	None
	}
	});

	// Solve the region constraints.
	let closure_region_requirements = regioncx.solve(
	infcx,
	&body,
	local_names,
	upvars,
	def_id,
	errors_buffer,
	polonius_output.clone(),
	);

	// Dump MIR results into a file, if that is enabled. This let us
	// write unit-tests, as well as helping with debugging.
	dump_mir_results(
	infcx,
	MirSource::item(def_id),
	&body,
	&regioncx,
	&closure_region_requirements,
	);

	// We also have a `#[rustc_nll]` annotation that causes us to dump
	// information
	dump_annotation(
	infcx,
	&body,
	def_id,
	&regioncx,
	&closure_region_requirements,
	errors_buffer);

	(regioncx, polonius_output, closure_region_requirements)
	}

	fn dump_mir_results<'a, 'tcx>(
	infcx: &InferCtxt<'a, 'tcx>,
	source: MirSource<'tcx>,
	body: &Body<'tcx>,
	regioncx: &RegionInferenceContext<'_>,
	closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
	) {
	if !mir_util::dump_enabled(infcx.tcx, "nll", source) {
	return;
	}

	mir_util::dump_mir(
	infcx.tcx,
	None,
	"nll",
	&0,
	source,
	body,
	\|pass_where, out\| {
	match pass_where {
	// Before the CFG, dump out the values for each region variable.
	PassWhere::BeforeCFG => {
	regioncx.dump_mir(out)?;
	writeln!(out, "\|")?;

	if let Some(closure_region_requirements) = closure_region_requirements {
	writeln!(out, "\| Free Region Constraints")?;
	for_each_region_constraint(closure_region_requirements, &mut \|msg\| {
	writeln!(out, "\| {}", msg)
	})?;
	writeln!(out, "\|")?;
	}
	}

	PassWhere::BeforeLocation(_) => {
	}

	PassWhere::AfterTerminator(_) => {
	}

	PassWhere::BeforeBlock(_) \| PassWhere::AfterLocation(_) \| PassWhere::AfterCFG => {}
	}
	Ok(())
	},
	);

	// Also dump the inference graph constraints as a graphviz file.
	let _: io::Result<()> = try {
	let mut file =
	pretty::create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, source)?;
	regioncx.dump_graphviz_raw_constraints(&mut file)?;
	};

	// Also dump the inference graph constraints as a graphviz file.
	let _: io::Result<()> = try {
	let mut file =
	pretty::create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, source)?;
	regioncx.dump_graphviz_scc_constraints(&mut file)?;
	};
	}

	fn dump_annotation<'a, 'tcx>(
	infcx: &InferCtxt<'a, 'tcx>,
	body: &Body<'tcx>,
	mir_def_id: DefId,
	regioncx: &RegionInferenceContext<'tcx>,
	closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
	errors_buffer: &mut Vec<Diagnostic>,
	) {
	let tcx = infcx.tcx;
	let base_def_id = tcx.closure_base_def_id(mir_def_id);
	if !tcx.has_attr(base_def_id, sym::rustc_regions) {
	return;
	}

	// When the enclosing function is tagged with `#[rustc_regions]`,
	// we dump out various bits of state as warnings. This is useful
	// for verifying that the compiler is behaving as expected. These
	// warnings focus on the closure region requirements -- for
	// viewing the intraprocedural state, the -Zdump-mir output is
	// better.

	if let Some(closure_region_requirements) = closure_region_requirements {
	let mut err = tcx
	.sess
	.diagnostic()
	.span_note_diag(body.span, "External requirements");

	regioncx.annotate(tcx, &mut err);

	err.note(&format!(
	"number of external vids: {}",
	closure_region_requirements.num_external_vids
	));

	// Dump the region constraints we are imposing between those
	// newly created variables.
	for_each_region_constraint(closure_region_requirements, &mut \|msg\| {
	err.note(msg);
	Ok(())
	}).unwrap();

	err.buffer(errors_buffer);
	} else {
	let mut err = tcx
	.sess
	.diagnostic()
	.span_note_diag(body.span, "No external requirements");
	regioncx.annotate(tcx, &mut err);

	err.buffer(errors_buffer);
	}
	}

	fn for_each_region_constraint(
	closure_region_requirements: &ClosureRegionRequirements<'_>,
	with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
	) -> io::Result<()> {
	for req in &closure_region_requirements.outlives_requirements {
	let subject: &dyn Debug = match &req.subject {
	ClosureOutlivesSubject::Region(subject) => subject,
	ClosureOutlivesSubject::Ty(ty) => ty,
	};
	with_msg(&format!(
	"where {:?}: {:?}",
	subject, req.outlived_free_region,
	))?;
	}
	Ok(())
	}

	/// Right now, we piggy back on the `ReVar` to store our NLL inference
	/// regions. These are indexed with `RegionVid`. This method will
	/// assert that the region is a `ReVar` and extract its internal index.
	/// This is reasonable because in our MIR we replace all universal regions
	/// with inference variables.
	pub trait ToRegionVid {
	fn to_region_vid(self) -> RegionVid;
	}

	impl<'tcx> ToRegionVid for &'tcx RegionKind {
	fn to_region_vid(self) -> RegionVid {
	if let ty::ReVar(vid) = self {
	*vid
	} else {
	bug!("region is not an ReVar: {:?}", self)
	}
	}
	}

	impl ToRegionVid for RegionVid {
	fn to_region_vid(self) -> RegionVid {
	self
	}
	}

	crate trait ConstraintDescription {
	fn description(&self) -> &'static str;
	}