Auto merge of #52115 - Dylan-DPC:feature/nll-liveness-regions, r=nikomatsakis

only compute liveness for variables whose types include regions

Closes #52034

r? @nikomatsakis

Author: bors

src/librustc_mir/borrow_check/nll/liveness_map.rs

@@ -0,0 +1,77 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! For the NLL computation, we need to compute liveness, but only for those
+//! local variables whose types contain regions. The others are not of interest
+//! to us. This file defines a new index type (LocalWithRegion) that indexes into
+//! a list of "variables whose type contain regions". It also defines a map from
+//! Local to LocalWithRegion and vice versa -- this map can be given to the
+//! liveness code so that it only operates over variables with regions in their
+//! types, instead of all variables.
+
+use rustc::ty::TypeFoldable;
+use rustc_data_structures::indexed_vec::IndexVec;
+use rustc::mir::{Mir, Local};
+use util::liveness::LiveVariableMap;
+
+use rustc_data_structures::indexed_vec::Idx;
+
+/// Map between Local and LocalWithRegion indices: this map is supplied to the
+/// liveness code so that it will only analyze those variables whose types
+/// contain regions.
+crate struct NllLivenessMap {
+    /// For each local variable, contains either None (if the type has no regions)
+    /// or Some(i) with a suitable index.
+    pub from_local: IndexVec<Local, Option<LocalWithRegion>>,
+    /// For each LocalWithRegion, maps back to the original Local index.
+    pub to_local: IndexVec<LocalWithRegion, Local>,
+
+}
+
+impl LiveVariableMap for NllLivenessMap {
+
+    fn from_local(&self, local: Local) -> Option<Self::LiveVar> {
+        self.from_local[local]
+    }
+
+    type LiveVar = LocalWithRegion;
+
+    fn from_live_var(&self, local: Self::LiveVar) -> Local {
+        self.to_local[local]
+    }
+
+    fn num_variables(&self) -> usize {
+        self.to_local.len()
+    }
+}
+
+impl NllLivenessMap {
+    /// Iterates over the variables in Mir and assigns each Local whose type contains
+    /// regions a LocalWithRegion index. Returns a map for converting back and forth.
+    pub fn compute(mir: &Mir) -> Self {
+        let mut to_local = IndexVec::default();
+        let from_local: IndexVec<Local,Option<_>> = mir
+            .local_decls
+            .iter_enumerated()
+            .map(|(local, local_decl)| {
+                if local_decl.ty.has_free_regions() {
+                    Some(to_local.push(local))
+                }
+                    else {
+                        None
+                    }
+            }).collect();
+
+        Self { from_local, to_local }
+    }
+}
+
+/// Index given to each local variable whose type contains a region.
+newtype_index!(LocalWithRegion);

src/librustc_mir/borrow_check/nll/mod.rs

@@ -13,6 +13,7 @@ use borrow_check::location::{LocationIndex, LocationTable};
 use borrow_check::nll::facts::AllFactsExt;
 use borrow_check::nll::type_check::MirTypeckRegionConstraints;
 use borrow_check::nll::region_infer::values::RegionValueElements;
+use borrow_check::nll::liveness_map::{NllLivenessMap, LocalWithRegion};
 use dataflow::indexes::BorrowIndex;
 use dataflow::move_paths::MoveData;
 use dataflow::FlowAtLocation;
@@ -30,7 +31,7 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::str::FromStr;
 use transform::MirSource;
-use util::liveness::{LivenessResults, LocalSet};
+use util::liveness::{LivenessResults, LiveVarSet};
 
 use self::mir_util::PassWhere;
 use polonius_engine::{Algorithm, Output};
@@ -45,6 +46,7 @@ crate mod region_infer;
 mod renumber;
 crate mod type_check;
 mod universal_regions;
+crate mod liveness_map;
 
 mod constraints;
 
@@ -103,7 +105,8 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
     let elements = &Rc::new(RegionValueElements::new(mir, universal_regions.len()));
 
     // Run the MIR type-checker.
-    let liveness = &LivenessResults::compute(mir);
+    let liveness_map = NllLivenessMap::compute(&mir);
+    let liveness = LivenessResults::compute(mir, &liveness_map);
     let constraint_sets = type_check::type_check(
         infcx,
         param_env,
@@ -193,7 +196,7 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
     // write unit-tests, as well as helping with debugging.
     dump_mir_results(
         infcx,
-        liveness,
+        &liveness,
         MirSource::item(def_id),
         &mir,
         &regioncx,
@@ -209,7 +212,7 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
 
 fn dump_mir_results<'a, 'gcx, 'tcx>(
     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
-    liveness: &LivenessResults,
+    liveness: &LivenessResults<LocalWithRegion>,
     source: MirSource,
     mir: &Mir<'tcx>,
     regioncx: &RegionInferenceContext,
@@ -219,14 +222,16 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
         return;
     }
 
+    let map = &NllLivenessMap::compute(mir);
+
     let regular_liveness_per_location: FxHashMap<_, _> = mir
         .basic_blocks()
         .indices()
         .flat_map(|bb| {
             let mut results = vec![];
             liveness
                 .regular
-                .simulate_block(&mir, bb, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results
@@ -240,7 +245,7 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
             let mut results = vec![];
             liveness
                 .drop
-                .simulate_block(&mir, bb, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results
@@ -405,7 +410,10 @@ impl ToRegionVid for RegionVid {
     }
 }
 
-fn live_variable_set(regular: &LocalSet, drops: &LocalSet) -> String {
+fn live_variable_set(
+    regular: &LiveVarSet<LocalWithRegion>,
+    drops: &LiveVarSet<LocalWithRegion>
+) -> String {
     // sort and deduplicate:
     let all_locals: BTreeSet<_> = regular.iter().chain(drops.iter()).collect();
 

src/librustc_mir/borrow_check/nll/type_check/liveness.rs

@@ -8,20 +8,20 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use borrow_check::nll::{NllLivenessMap, LocalWithRegion};
 use borrow_check::nll::type_check::AtLocation;
 use dataflow::move_paths::{HasMoveData, MoveData};
 use dataflow::MaybeInitializedPlaces;
 use dataflow::{FlowAtLocation, FlowsAtLocation};
 use rustc::infer::canonical::QueryRegionConstraint;
-use rustc::mir::Local;
 use rustc::mir::{BasicBlock, Location, Mir};
 use rustc::traits::query::dropck_outlives::DropckOutlivesResult;
 use rustc::traits::query::type_op::outlives::DropckOutlives;
 use rustc::traits::query::type_op::TypeOp;
 use rustc::ty::{Ty, TypeFoldable};
 use rustc_data_structures::fx::FxHashMap;
 use std::rc::Rc;
-use util::liveness::LivenessResults;
+use util::liveness::{LivenessResults, LiveVariableMap };
 
 use super::TypeChecker;
 
@@ -36,7 +36,7 @@ use super::TypeChecker;
 pub(super) fn generate<'gcx, 'tcx>(
     cx: &mut TypeChecker<'_, 'gcx, 'tcx>,
     mir: &Mir<'tcx>,
-    liveness: &LivenessResults,
+    liveness: &LivenessResults<LocalWithRegion>,
     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
     move_data: &MoveData<'tcx>,
 ) {
@@ -47,6 +47,7 @@ pub(super) fn generate<'gcx, 'tcx>(
         flow_inits,
         move_data,
         drop_data: FxHashMap(),
+        map: &NllLivenessMap::compute(mir),
     };
 
     for bb in mir.basic_blocks().indices() {
@@ -63,10 +64,11 @@ where
 {
     cx: &'gen mut TypeChecker<'typeck, 'gcx, 'tcx>,
     mir: &'gen Mir<'tcx>,
-    liveness: &'gen LivenessResults,
+    liveness: &'gen LivenessResults<LocalWithRegion>,
     flow_inits: &'gen mut FlowAtLocation<MaybeInitializedPlaces<'flow, 'gcx, 'tcx>>,
     move_data: &'gen MoveData<'tcx>,
     drop_data: FxHashMap<Ty<'tcx>, DropData<'tcx>>,
+    map: &'gen NllLivenessMap,
 }
 
 struct DropData<'tcx> {
@@ -84,17 +86,18 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
 
         self.liveness
             .regular
-            .simulate_block(self.mir, bb, |location, live_locals| {
+            .simulate_block(self.mir, bb, self.map, |location, live_locals| {
                 for live_local in live_locals.iter() {
-                    let live_local_ty = self.mir.local_decls[live_local].ty;
+                    let local = self.map.from_live_var(live_local);
+                    let live_local_ty = self.mir.local_decls[local].ty;
                     Self::push_type_live_constraint(&mut self.cx, live_local_ty, location);
                 }
             });
 
-        let mut all_live_locals: Vec<(Location, Vec<Local>)> = vec![];
+        let mut all_live_locals: Vec<(Location, Vec<LocalWithRegion>)> = vec![];
         self.liveness
             .drop
-            .simulate_block(self.mir, bb, |location, live_locals| {
+            .simulate_block(self.mir, bb, self.map, |location, live_locals| {
                 all_live_locals.push((location, live_locals.iter().collect()));
             });
         debug!(
@@ -121,15 +124,17 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
                     });
                 }
 
-                let mpi = self.move_data.rev_lookup.find_local(live_local);
+                let local = self.map.from_live_var(live_local);
+                let mpi = self.move_data.rev_lookup.find_local(local);
                 if let Some(initialized_child) = self.flow_inits.has_any_child_of(mpi) {
                     debug!(
                         "add_liveness_constraints: mpi={:?} has initialized child {:?}",
                         self.move_data.move_paths[mpi],
                         self.move_data.move_paths[initialized_child]
                     );
 
-                    let live_local_ty = self.mir.local_decls[live_local].ty;
+                    let local = self.map.from_live_var(live_local);
+                    let live_local_ty = self.mir.local_decls[local].ty;
                     self.add_drop_live_constraint(live_local, live_local_ty, location);
                 }
             }
@@ -190,7 +195,7 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
     /// particular this takes `#[may_dangle]` into account.
     fn add_drop_live_constraint(
         &mut self,
-        dropped_local: Local,
+        dropped_local: LocalWithRegion,
         dropped_ty: Ty<'tcx>,
         location: Location,
     ) {

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -19,6 +19,7 @@ use borrow_check::nll::region_infer::{ClosureRegionRequirementsExt, TypeTest};
 use borrow_check::nll::region_infer::values::{RegionValues, RegionValueElements};
 use borrow_check::nll::universal_regions::UniversalRegions;
 use borrow_check::nll::ToRegionVid;
+use borrow_check::nll::LocalWithRegion;
 use dataflow::move_paths::MoveData;
 use dataflow::FlowAtLocation;
 use dataflow::MaybeInitializedPlaces;
@@ -109,7 +110,7 @@ pub(crate) fn type_check<'gcx, 'tcx>(
     universal_regions: &UniversalRegions<'tcx>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
-    liveness: &LivenessResults,
+    liveness: &LivenessResults<LocalWithRegion>,
     all_facts: &mut Option<AllFacts>,
     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
     move_data: &MoveData<'tcx>,

src/librustc_mir/transform/generator.rs

@@ -66,7 +66,7 @@ use rustc::mir::visit::{PlaceContext, Visitor, MutVisitor};
 use rustc::ty::{self, TyCtxt, AdtDef, Ty};
 use rustc::ty::subst::Substs;
 use util::dump_mir;
-use util::liveness::{self, LivenessMode};
+use util::liveness::{self, IdentityMap, LivenessMode};
 use rustc_data_structures::indexed_vec::Idx;
 use rustc_data_structures::indexed_set::IdxSetBuf;
 use std::collections::HashMap;
@@ -130,7 +130,7 @@ struct SuspensionPoint {
     state: u32,
     resume: BasicBlock,
     drop: Option<BasicBlock>,
-    storage_liveness: liveness::LocalSet,
+    storage_liveness: liveness::LiveVarSet<Local>,
 }
 
 struct TransformVisitor<'a, 'tcx: 'a> {
@@ -145,7 +145,7 @@ struct TransformVisitor<'a, 'tcx: 'a> {
     remap: HashMap<Local, (Ty<'tcx>, usize)>,
 
     // A map from a suspension point in a block to the locals which have live storage at that point
-    storage_liveness: HashMap<BasicBlock, liveness::LocalSet>,
+    storage_liveness: HashMap<BasicBlock, liveness::LiveVarSet<Local>>,
 
     // A list of suspension points, generated during the transform
     suspension_points: Vec<SuspensionPoint>,
@@ -317,7 +317,7 @@ fn replace_result_variable<'tcx>(ret_ty: Ty<'tcx>,
     new_ret_local
 }
 
-struct StorageIgnored(liveness::LocalSet);
+struct StorageIgnored(liveness::LiveVarSet<Local>);
 
 impl<'tcx> Visitor<'tcx> for StorageIgnored {
     fn visit_statement(&mut self,
@@ -332,7 +332,7 @@ impl<'tcx> Visitor<'tcx> for StorageIgnored {
     }
 }
 
-struct BorrowedLocals(liveness::LocalSet);
+struct BorrowedLocals(liveness::LiveVarSet<Local>);
 
 fn mark_as_borrowed<'tcx>(place: &Place<'tcx>, locals: &mut BorrowedLocals) {
     match *place {
@@ -361,12 +361,12 @@ impl<'tcx> Visitor<'tcx> for BorrowedLocals {
     }
 }
 
-fn locals_live_across_suspend_points<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+fn locals_live_across_suspend_points<'a, 'tcx,>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                mir: &Mir<'tcx>,
                                                source: MirSource,
                                                movable: bool) ->
-                                               (liveness::LocalSet,
-                                                HashMap<BasicBlock, liveness::LocalSet>) {
+                                               (liveness::LiveVarSet<Local>,
+                                                HashMap<BasicBlock, liveness::LiveVarSet<Local>>) {
     let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
     let node_id = tcx.hir.as_local_node_id(source.def_id).unwrap();
 
@@ -396,12 +396,23 @@ fn locals_live_across_suspend_points<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     };
 
     // Calculate the liveness of MIR locals ignoring borrows.
-    let mut set = liveness::LocalSet::new_empty(mir.local_decls.len());
-    let mut liveness = liveness::liveness_of_locals(mir, LivenessMode {
-        include_regular_use: true,
-        include_drops: true,
-    });
-    liveness::dump_mir(tcx, "generator_liveness", source, mir, &liveness);
+    let mut set = liveness::LiveVarSet::new_empty(mir.local_decls.len());
+    let mut liveness = liveness::liveness_of_locals(
+        mir,
+        LivenessMode {
+            include_regular_use: true,
+            include_drops: true,
+        },
+        &IdentityMap::new(mir),
+    );
+    liveness::dump_mir(
+        tcx,
+        "generator_liveness",
+        source,
+        mir,
+        &IdentityMap::new(mir),
+        &liveness,
+    );
 
     let mut storage_liveness_map = HashMap::new();
 
@@ -468,7 +479,7 @@ fn compute_layout<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             mir: &mut Mir<'tcx>)
     -> (HashMap<Local, (Ty<'tcx>, usize)>,
         GeneratorLayout<'tcx>,
-        HashMap<BasicBlock, liveness::LocalSet>)
+        HashMap<BasicBlock, liveness::LiveVarSet<Local>>)
 {
     // Use a liveness analysis to compute locals which are live across a suspension point
     let (live_locals, storage_liveness) = locals_live_across_suspend_points(tcx,