Auto merge of #53314 - nikomatsakis:nll-invert-liveness, r=pnkfelix

NLL: experiment with inverting liveness

I got inspired to see what would happen here.

Fixes #52460

r? @pnkfelix

src/librustc/mir/mod.rs

@@ -194,12 +194,12 @@ impl<'tcx> Mir<'tcx> {
     }
 
     #[inline]
-    pub fn predecessors(&self) -> ReadGuard<IndexVec<BasicBlock, Vec<BasicBlock>>> {
+    pub fn predecessors(&self) -> ReadGuard<'_, IndexVec<BasicBlock, Vec<BasicBlock>>> {
         self.cache.predecessors(self)
     }
 
     #[inline]
-    pub fn predecessors_for(&self, bb: BasicBlock) -> ReadGuard<Vec<BasicBlock>> {
+    pub fn predecessors_for(&self, bb: BasicBlock) -> ReadGuard<'_, Vec<BasicBlock>> {
         ReadGuard::map(self.predecessors(), |p| &p[bb])
     }
 
@@ -328,6 +328,14 @@ impl<'tcx> Mir<'tcx> {
     pub fn return_ty(&self) -> Ty<'tcx> {
         self.local_decls[RETURN_PLACE].ty
     }
+
+    /// Get the location of the terminator for the given block
+    pub fn terminator_loc(&self, bb: BasicBlock) -> Location {
+        Location {
+            block: bb,
+            statement_index: self[bb].statements.len(),
+        }
+    }
 }
 
 #[derive(Copy, Clone, Debug, RustcEncodable, RustcDecodable)]

src/librustc_data_structures/graph/dominators/mod.rs

@@ -38,13 +38,13 @@ pub fn dominators_given_rpo<G: ControlFlowGraph>(
 
     // compute the post order index (rank) for each node
     let mut post_order_rank: IndexVec<G::Node, usize> =
-        IndexVec::from_elem_n(usize::default(), graph.num_nodes());
+        (0..graph.num_nodes()).map(|_| 0).collect();
     for (index, node) in rpo.iter().rev().cloned().enumerate() {
         post_order_rank[node] = index;
     }
 
     let mut immediate_dominators: IndexVec<G::Node, Option<G::Node>> =
-        IndexVec::from_elem_n(Option::default(), graph.num_nodes());
+        (0..graph.num_nodes()).map(|_| None).collect();
     immediate_dominators[start_node] = Some(start_node);
 
     let mut changed = true;

src/librustc_data_structures/lib.rs

@@ -20,6 +20,8 @@
       html_favicon_url = "https://www.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
+#![feature(in_band_lifetimes)]
+#![feature(impl_header_lifetime_elision)]
 #![feature(unboxed_closures)]
 #![feature(fn_traits)]
 #![feature(unsize)]
@@ -86,6 +88,7 @@ pub mod thin_vec;
 pub mod transitive_relation;
 pub mod tuple_slice;
 pub use ena::unify;
+pub mod vec_linked_list;
 pub mod work_queue;
 pub mod fingerprint;
 

src/librustc_data_structures/vec_linked_list.rs

@@ -0,0 +1,83 @@
+// Copyright 2014 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.
+
+use indexed_vec::{Idx, IndexVec};
+
+pub fn iter<Ls>(
+    first: Option<Ls::LinkIndex>,
+    links: &'a Ls,
+) -> impl Iterator<Item = Ls::LinkIndex> + 'a
+where
+    Ls: Links,
+{
+    VecLinkedListIterator {
+        links: links,
+        current: first,
+    }
+}
+
+pub struct VecLinkedListIterator<Ls>
+where
+    Ls: Links,
+{
+    links: Ls,
+    current: Option<Ls::LinkIndex>,
+}
+
+impl<Ls> Iterator for VecLinkedListIterator<Ls>
+where
+    Ls: Links,
+{
+    type Item = Ls::LinkIndex;
+
+    fn next(&mut self) -> Option<Ls::LinkIndex> {
+        if let Some(c) = self.current {
+            self.current = <Ls as Links>::next(&self.links, c);
+            Some(c)
+        } else {
+            None
+        }
+    }
+}
+
+pub trait Links {
+    type LinkIndex: Copy;
+
+    fn next(links: &Self, index: Self::LinkIndex) -> Option<Self::LinkIndex>;
+}
+
+impl<Ls> Links for &Ls
+where
+    Ls: Links,
+{
+    type LinkIndex = Ls::LinkIndex;
+
+    fn next(links: &Self, index: Ls::LinkIndex) -> Option<Ls::LinkIndex> {
+        <Ls as Links>::next(links, index)
+    }
+}
+
+pub trait LinkElem {
+    type LinkIndex: Copy;
+
+    fn next(elem: &Self) -> Option<Self::LinkIndex>;
+}
+
+impl<L, E> Links for IndexVec<L, E>
+where
+    E: LinkElem<LinkIndex = L>,
+    L: Idx,
+{
+    type LinkIndex = L;
+
+    fn next(links: &Self, index: L) -> Option<L> {
+        <E as LinkElem>::next(&links[index])
+    }
+}

src/librustc_mir/borrow_check/flows.rs

@@ -89,6 +89,10 @@ impl<'b, 'gcx, 'tcx> FlowsAtLocation for Flows<'b, 'gcx, 'tcx> {
         each_flow!(self, reset_to_entry_of(bb));
     }
 
+    fn reset_to_exit_of(&mut self, bb: BasicBlock) {
+        each_flow!(self, reset_to_exit_of(bb));
+    }
+
     fn reconstruct_statement_effect(&mut self, location: Location) {
         each_flow!(self, reconstruct_statement_effect(location));
     }

src/librustc_mir/borrow_check/nll/explain_borrow/find_use.rs

@@ -17,7 +17,7 @@ use rustc::mir::visit::{MirVisitable, PlaceContext, Visitor};
 use rustc::mir::{Local, Location, Mir};
 use rustc::ty::{RegionVid, TyCtxt};
 use rustc_data_structures::fx::FxHashSet;
-use util::liveness::{self, DefUse, LivenessMode};
+use util::liveness::{self, DefUse};
 
 crate fn find<'tcx>(
     mir: &Mir<'tcx>,
@@ -32,10 +32,6 @@ crate fn find<'tcx>(
         tcx,
         region_vid,
         start_point,
-        liveness_mode: LivenessMode {
-            include_regular_use: true,
-            include_drops: true,
-        },
     };
 
     uf.find()
@@ -47,7 +43,6 @@ struct UseFinder<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
     region_vid: RegionVid,
     start_point: Location,
-    liveness_mode: LivenessMode,
 }
 
 impl<'cx, 'gcx, 'tcx> UseFinder<'cx, 'gcx, 'tcx> {
@@ -108,7 +103,6 @@ impl<'cx, 'gcx, 'tcx> UseFinder<'cx, 'gcx, 'tcx> {
             mir: self.mir,
             tcx: self.tcx,
             region_vid: self.region_vid,
-            liveness_mode: self.liveness_mode,
             def_use_result: None,
         };
 
@@ -122,7 +116,6 @@ struct DefUseVisitor<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
     mir: &'cx Mir<'tcx>,
     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
     region_vid: RegionVid,
-    liveness_mode: LivenessMode,
     def_use_result: Option<DefUseResult>,
 }
 
@@ -146,23 +139,12 @@ impl<'cx, 'gcx, 'tcx> Visitor<'tcx> for DefUseVisitor<'cx, 'gcx, 'tcx> {
         });
 
         if found_it {
-            match liveness::categorize(context, self.liveness_mode) {
-                Some(DefUse::Def) => {
-                    self.def_use_result = Some(DefUseResult::Def);
-                }
-
-                Some(DefUse::Use) => {
-                    self.def_use_result = if context.is_drop() {
-                        Some(DefUseResult::UseDrop { local })
-                    } else {
-                        Some(DefUseResult::UseLive { local })
-                    };
-                }
-
-                None => {
-                    self.def_use_result = None;
-                }
-            }
+            self.def_use_result = match liveness::categorize(context) {
+                Some(DefUse::Def) => Some(DefUseResult::Def),
+                Some(DefUse::Use) => Some(DefUseResult::UseLive { local }),
+                Some(DefUse::Drop) => Some(DefUseResult::UseDrop { local }),
+                None => None,
+            };
         }
     }
 }

src/librustc_mir/borrow_check/nll/mod.rs

@@ -12,7 +12,7 @@ use borrow_check::borrow_set::BorrowSet;
 use borrow_check::location::{LocationIndex, LocationTable};
 use borrow_check::nll::facts::AllFactsExt;
 use borrow_check::nll::type_check::{MirTypeckResults, MirTypeckRegionConstraints};
-use borrow_check::nll::type_check::liveness::liveness_map::{NllLivenessMap, LocalWithRegion};
+use borrow_check::nll::type_check::liveness::liveness_map::NllLivenessMap;
 use borrow_check::nll::region_infer::values::RegionValueElements;
 use dataflow::indexes::BorrowIndex;
 use dataflow::move_paths::MoveData;
@@ -22,22 +22,19 @@ use rustc::hir::def_id::DefId;
 use rustc::infer::InferCtxt;
 use rustc::mir::{ClosureOutlivesSubject, ClosureRegionRequirements, Mir};
 use rustc::ty::{self, RegionKind, RegionVid};
-use rustc::util::nodemap::FxHashMap;
 use rustc_errors::Diagnostic;
-use std::collections::BTreeSet;
 use std::fmt::Debug;
 use std::env;
 use std::io;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::str::FromStr;
 use transform::MirSource;
-use util::liveness::{LivenessResults, LiveVarSet};
 
 use self::mir_util::PassWhere;
 use polonius_engine::{Algorithm, Output};
 use util as mir_util;
-use util::pretty::{self, ALIGN};
+use util::pretty;
 
 mod constraint_generation;
 pub mod explain_borrow;
@@ -111,8 +108,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
     let MirTypeckResults {
         constraints,
         universal_region_relations,
-        liveness,
-        liveness_map,
     } = type_check::type_check(
         infcx,
         param_env,
@@ -205,8 +200,6 @@ 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_map,
         MirSource::item(def_id),
         &mir,
         &regioncx,
@@ -222,8 +215,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
 
 fn dump_mir_results<'a, 'gcx, 'tcx>(
     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
-    liveness: &LivenessResults<LocalWithRegion>,
-    liveness_map: &NllLivenessMap,
     source: MirSource,
     mir: &Mir<'tcx>,
     regioncx: &RegionInferenceContext,
@@ -233,34 +224,6 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
         return;
     }
 
-    let regular_liveness_per_location: FxHashMap<_, _> = mir
-        .basic_blocks()
-        .indices()
-        .flat_map(|bb| {
-            let mut results = vec![];
-            liveness
-                .regular
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
-                    results.push((location, local_set.clone()));
-                });
-            results
-        })
-        .collect();
-
-    let drop_liveness_per_location: FxHashMap<_, _> = mir
-        .basic_blocks()
-        .indices()
-        .flat_map(|bb| {
-            let mut results = vec![];
-            liveness
-                .drop
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
-                    results.push((location, local_set.clone()));
-                });
-            results
-        })
-        .collect();
-
     mir_util::dump_mir(
         infcx.tcx,
         None,
@@ -283,26 +246,10 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
                     }
                 }
 
-                PassWhere::BeforeLocation(location) => {
-                    let s = live_variable_set(
-                        &regular_liveness_per_location[&location],
-                        &drop_liveness_per_location[&location],
-                    );
-                    writeln!(
-                        out,
-                        "{:ALIGN$} | Live variables on entry to {:?}: {}",
-                        "",
-                        location,
-                        s,
-                        ALIGN = ALIGN
-                    )?;
+                PassWhere::BeforeLocation(_) => {
                 }
 
-                // After each basic block, dump out the values
-                // that are live on exit from the basic block.
-                PassWhere::AfterTerminator(bb) => {
-                    let s = live_variable_set(&liveness.regular.outs[bb], &liveness.drop.outs[bb]);
-                    writeln!(out, "    | Live variables on exit from {:?}: {}", bb, s)?;
+                PassWhere::AfterTerminator(_) => {
                 }
 
                 PassWhere::BeforeBlock(_) | PassWhere::AfterLocation(_) | PassWhere::AfterCFG => {}
@@ -420,33 +367,3 @@ impl ToRegionVid for RegionVid {
         self
     }
 }
-
-fn live_variable_set(
-    regular: &LiveVarSet<LocalWithRegion>,
-    drops: &LiveVarSet<LocalWithRegion>
-) -> String {
-    // sort and deduplicate:
-    let all_locals: BTreeSet<_> = regular.iter().chain(drops.iter()).collect();
-
-    // construct a string with each local, including `(drop)` if it is
-    // only dropped, versus a regular use.
-    let mut string = String::new();
-    for local in all_locals {
-        string.push_str(&format!("{:?}", local));
-
-        if !regular.contains(&local) {
-            assert!(drops.contains(&local));
-            string.push_str(" (drop)");
-        }
-
-        string.push_str(", ");
-    }
-
-    let len = if string.is_empty() {
-        0
-    } else {
-        string.len() - 2
-    };
-
-    format!("[{}]", &string[..len])
-}