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.
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.
11 use borrow_check::nll::type_check::AtLocation;
12 use dataflow::move_paths::{HasMoveData, MoveData};
13 use dataflow::MaybeInitializedPlaces;
14 use dataflow::{FlowAtLocation, FlowsAtLocation};
15 use rustc::infer::canonical::QueryRegionConstraint;
16 use rustc::mir::Local;
17 use rustc::mir::{BasicBlock, Location, Mir};
18 use rustc::traits::query::dropck_outlives::DropckOutlivesResult;
19 use rustc::traits::query::type_op::outlives::DropckOutlives;
20 use rustc::traits::query::type_op::TypeOp;
21 use rustc::ty::{Ty, TypeFoldable};
22 use rustc_data_structures::fx::FxHashMap;
24 use util::liveness::LivenessResults;
26 use super::TypeChecker;
28 /// Combines liveness analysis with initialization analysis to
29 /// determine which variables are live at which points, both due to
30 /// ordinary uses and drops. Returns a set of (ty, location) pairs
31 /// that indicate which types must be live at which point in the CFG.
32 /// This vector is consumed by `constraint_generation`.
34 /// NB. This computation requires normalization; therefore, it must be
36 pub(super) fn generate<'gcx, 'tcx>(
37 cx: &mut TypeChecker<'_, 'gcx, 'tcx>,
39 liveness: &LivenessResults,
40 flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
41 move_data: &MoveData<'tcx>,
43 let mut generator = TypeLivenessGenerator {
49 drop_data: FxHashMap(),
52 for bb in mir.basic_blocks().indices() {
53 generator.add_liveness_constraints(bb);
57 struct TypeLivenessGenerator<'gen, 'typeck, 'flow, 'gcx, 'tcx>
61 'tcx: 'typeck + 'flow,
64 cx: &'gen mut TypeChecker<'typeck, 'gcx, 'tcx>,
66 liveness: &'gen LivenessResults,
67 flow_inits: &'gen mut FlowAtLocation<MaybeInitializedPlaces<'flow, 'gcx, 'tcx>>,
68 move_data: &'gen MoveData<'tcx>,
69 drop_data: FxHashMap<Ty<'tcx>, DropData<'tcx>>,
72 struct DropData<'tcx> {
73 dropck_result: DropckOutlivesResult<'tcx>,
74 region_constraint_data: Option<Rc<Vec<QueryRegionConstraint<'tcx>>>>,
77 impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flow, 'gcx, 'tcx> {
78 /// Liveness constraints:
80 /// > If a variable V is live at point P, then all regions R in the type of V
81 /// > must include the point P.
82 fn add_liveness_constraints(&mut self, bb: BasicBlock) {
83 debug!("add_liveness_constraints(bb={:?})", bb);
87 .simulate_block(self.mir, bb, |location, live_locals| {
88 for live_local in live_locals.iter() {
89 let live_local_ty = self.mir.local_decls[live_local].ty;
90 Self::push_type_live_constraint(&mut self.cx, live_local_ty, location);
94 let mut all_live_locals: Vec<(Location, Vec<Local>)> = vec![];
97 .simulate_block(self.mir, bb, |location, live_locals| {
98 all_live_locals.push((location, live_locals.iter().collect()));
101 "add_liveness_constraints: all_live_locals={:#?}",
105 let terminator_index = self.mir.basic_blocks()[bb].statements.len();
106 self.flow_inits.reset_to_entry_of(bb);
107 while let Some((location, live_locals)) = all_live_locals.pop() {
108 for live_local in live_locals {
110 "add_liveness_constraints: location={:?} live_local={:?}",
114 if log_enabled!(::log::Level::Debug) {
115 self.flow_inits.each_state_bit(|mpi_init| {
117 "add_liveness_constraints: location={:?} initialized={:?}",
119 &self.flow_inits.operator().move_data().move_paths[mpi_init]
124 let mpi = self.move_data.rev_lookup.find_local(live_local);
125 if let Some(initialized_child) = self.flow_inits.has_any_child_of(mpi) {
127 "add_liveness_constraints: mpi={:?} has initialized child {:?}",
128 self.move_data.move_paths[mpi],
129 self.move_data.move_paths[initialized_child]
132 let live_local_ty = self.mir.local_decls[live_local].ty;
133 self.add_drop_live_constraint(live_local, live_local_ty, location);
137 if location.statement_index == terminator_index {
139 "add_liveness_constraints: reconstruct_terminator_effect from {:#?}",
142 self.flow_inits.reconstruct_terminator_effect(location);
145 "add_liveness_constraints: reconstruct_statement_effect from {:#?}",
148 self.flow_inits.reconstruct_statement_effect(location);
150 self.flow_inits.apply_local_effect(location);
154 /// Some variable with type `live_ty` is "regular live" at
155 /// `location` -- i.e., it may be used later. This means that all
156 /// regions appearing in the type `live_ty` must be live at
158 fn push_type_live_constraint<T>(
159 cx: &mut TypeChecker<'_, 'gcx, 'tcx>,
163 T: TypeFoldable<'tcx>,
166 "push_type_live_constraint(live_ty={:?}, location={:?})",
170 cx.tcx().for_each_free_region(&value, |live_region| {
171 if let Some(ref mut borrowck_context) = cx.borrowck_context {
172 let region_vid = borrowck_context.universal_regions.to_region_vid(live_region);
173 borrowck_context.constraints.liveness_constraints.add_element(region_vid, location);
175 if let Some(all_facts) = borrowck_context.all_facts {
176 let start_index = borrowck_context.location_table.start_index(location);
177 all_facts.region_live_at.push((region_vid, start_index));
179 let mid_index = borrowck_context.location_table.mid_index(location);
180 all_facts.region_live_at.push((region_vid, mid_index));
186 /// Some variable with type `live_ty` is "drop live" at `location`
187 /// -- i.e., it may be dropped later. This means that *some* of
188 /// the regions in its type must be live at `location`. The
189 /// precise set will depend on the dropck constraints, and in
190 /// particular this takes `#[may_dangle]` into account.
191 fn add_drop_live_constraint(
193 dropped_local: Local,
194 dropped_ty: Ty<'tcx>,
198 "add_drop_live_constraint(dropped_local={:?}, dropped_ty={:?}, location={:?})",
199 dropped_local, dropped_ty, location
202 let drop_data = self.drop_data.entry(dropped_ty).or_insert_with({
203 let cx = &mut self.cx;
204 move || Self::compute_drop_data(cx, dropped_ty)
207 if let Some(data) = &drop_data.region_constraint_data {
208 self.cx.push_region_constraints(location.boring(), data);
211 drop_data.dropck_result.report_overflows(
213 self.mir.source_info(location).span,
217 // All things in the `outlives` array may be touched by
218 // the destructor and must be live at this point.
219 for &kind in &drop_data.dropck_result.kinds {
220 Self::push_type_live_constraint(&mut self.cx, kind, location);
224 fn compute_drop_data(
225 cx: &mut TypeChecker<'_, 'gcx, 'tcx>,
226 dropped_ty: Ty<'tcx>,
227 ) -> DropData<'tcx> {
228 debug!("compute_drop_data(dropped_ty={:?})", dropped_ty,);
230 let param_env = cx.param_env;
231 let (dropck_result, region_constraint_data) = param_env
232 .and(DropckOutlives::new(dropped_ty))
233 .fully_perform(cx.infcx)
238 region_constraint_data,