Auto merge of #48770 - bobtwinkles:two_phase_borrows_rewrite, r=pnkfelix

Two phase borrows rewrite

This definitely needs a careful review. Both @pnkfelix and @nikomatsakis  were involved with the design of this so they're natural choices here. I'm r?'ing @pnkfelix since they wrote the original two-phase borrow implementation. Also ping @KiChjang who expressed interest in working on this. I'm going to leave a few comments below pointing out some of the more dangerous changes I made (i.e. what I would like reviewers to pay special attention too.)

r? @pnkfelix

src/libgraphviz/lib.rs

@@ -711,6 +711,12 @@ impl<'a> IntoCow<'a, str> for &'a str {
     }
 }
 
+impl<'a> IntoCow<'a, str> for Cow<'a, str> {
+    fn into_cow(self) -> Cow<'a, str> {
+        self
+    }
+}
+
 impl<'a, T: Clone> IntoCow<'a, [T]> for Vec<T> {
     fn into_cow(self) -> Cow<'a, [T]> {
         Cow::Owned(self)

src/librustc_mir/borrow_check/error_reporting.rs

@@ -18,7 +18,7 @@ use rustc_data_structures::sync::Lrc;
 
 use super::{Context, MirBorrowckCtxt};
 use super::{InitializationRequiringAction, PrefixSet};
-use dataflow::{ActiveBorrows, BorrowData, FlowAtLocation, MovingOutStatements};
+use dataflow::{Borrows, BorrowData, FlowAtLocation, MovingOutStatements};
 use dataflow::move_paths::MovePathIndex;
 use util::borrowck_errors::{BorrowckErrors, Origin};
 
@@ -250,7 +250,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
 
         let new_closure_span = self.find_closure_span(span, context.loc);
         let span = new_closure_span.map(|(args, _)| args).unwrap_or(span);
-        let old_closure_span = self.find_closure_span(issued_span, issued_borrow.location);
+        let old_closure_span = self.find_closure_span(issued_span, issued_borrow.reserve_location);
         let issued_span = old_closure_span
             .map(|(args, _)| args)
             .unwrap_or(issued_span);
@@ -372,15 +372,15 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         context: Context,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
-        borrows: &ActiveBorrows<'cx, 'gcx, 'tcx>,
+        borrows: &Borrows<'cx, 'gcx, 'tcx>
     ) {
         let end_span = borrows.opt_region_end_span(&borrow.region);
-        let scope_tree = borrows.0.scope_tree();
+        let scope_tree = borrows.scope_tree();
         let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
             .last()
             .unwrap();
 
-        let borrow_span = self.mir.source_info(borrow.location).span;
+        let borrow_span = self.mir.source_info(borrow.reserve_location).span;
         let proper_span = match *root_place {
             Place::Local(local) => self.mir.local_decls[local].source_info.span,
             _ => drop_span,
@@ -817,7 +817,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
 
     // Retrieve span of given borrow from the current MIR representation
     pub fn retrieve_borrow_span(&self, borrow: &BorrowData) -> Span {
-        self.mir.source_info(borrow.location).span
+        self.mir.source_info(borrow.reserve_location).span
     }
 
     // Retrieve type of a place for the current MIR representation

src/librustc_mir/borrow_check/flows.rs

@@ -17,13 +17,14 @@ use rustc::mir::{BasicBlock, Location};
 
 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
 use dataflow::{EverInitializedPlaces, MovingOutStatements};
-use dataflow::{ActiveBorrows, FlowAtLocation, FlowsAtLocation};
+use dataflow::{Borrows};
+use dataflow::{FlowAtLocation, FlowsAtLocation};
 use dataflow::move_paths::HasMoveData;
 use std::fmt;
 
 // (forced to be `pub` due to its use as an associated type below.)
 pub(crate) struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
-    pub borrows: FlowAtLocation<ActiveBorrows<'b, 'gcx, 'tcx>>,
+    pub borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
     pub inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
     pub uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
     pub move_outs: FlowAtLocation<MovingOutStatements<'b, 'gcx, 'tcx>>,
@@ -32,7 +33,7 @@ pub(crate) struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
 
 impl<'b, 'gcx, 'tcx> Flows<'b, 'gcx, 'tcx> {
     pub fn new(
-        borrows: FlowAtLocation<ActiveBorrows<'b, 'gcx, 'tcx>>,
+        borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
         inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
         uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
         move_outs: FlowAtLocation<MovingOutStatements<'b, 'gcx, 'tcx>>,

src/librustc_mir/borrow_check/mod.rs

@@ -34,11 +34,10 @@ use syntax_pos::Span;
 use dataflow::{do_dataflow, DebugFormatted};
 use dataflow::FlowAtLocation;
 use dataflow::MoveDataParamEnv;
-use dataflow::{DataflowAnalysis, DataflowResultsConsumer};
+use dataflow::{DataflowResultsConsumer};
 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
 use dataflow::{EverInitializedPlaces, MovingOutStatements};
 use dataflow::{BorrowData, Borrows, ReserveOrActivateIndex};
-use dataflow::{ActiveBorrows, Reservations};
 use dataflow::indexes::BorrowIndex;
 use dataflow::move_paths::{IllegalMoveOriginKind, MoveError};
 use dataflow::move_paths::{HasMoveData, LookupResult, MoveData, MovePathIndex};
@@ -54,8 +53,6 @@ mod error_reporting;
 mod flows;
 mod prefixes;
 
-use std::borrow::Cow;
-
 pub(crate) mod nll;
 
 pub fn provide(providers: &mut Providers) {
@@ -209,6 +206,18 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     };
     let flow_inits = flow_inits; // remove mut
 
+    let flow_borrows = FlowAtLocation::new(do_dataflow(
+        tcx,
+        mir,
+        id,
+        &attributes,
+        &dead_unwinds,
+        Borrows::new(tcx, mir, opt_regioncx.clone(), def_id, body_id),
+        |rs, i| {
+            DebugFormatted::new(&(i.kind(), rs.location(i.borrow_index())))
+        }
+    ));
+
     let movable_generator = !match tcx.hir.get(id) {
         hir::map::Node::NodeExpr(&hir::Expr {
             node: hir::ExprClosure(.., Some(hir::GeneratorMovability::Static)),
@@ -230,44 +239,12 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
         },
         access_place_error_reported: FxHashSet(),
         reservation_error_reported: FxHashSet(),
-        nonlexical_regioncx: opt_regioncx.clone(),
+        nonlexical_regioncx: opt_regioncx,
         nonlexical_cause_info: None,
     };
 
-    let borrows = Borrows::new(tcx, mir, opt_regioncx, def_id, body_id);
-    let flow_reservations = do_dataflow(
-        tcx,
-        mir,
-        id,
-        &attributes,
-        &dead_unwinds,
-        Reservations::new(borrows),
-        |rs, i| {
-            // In principle we could make the dataflow ensure that
-            // only reservation bits show up, and assert so here.
-            //
-            // In practice it is easier to be looser; in particular,
-            // it is okay for the kill-sets to hold activation bits.
-            DebugFormatted::new(&(i.kind(), rs.location(i)))
-        },
-    );
-    let flow_active_borrows = {
-        let reservations_on_entry = flow_reservations.0.sets.entry_set_state();
-        let reservations = flow_reservations.0.operator;
-        let a = DataflowAnalysis::new_with_entry_sets(
-            mir,
-            &dead_unwinds,
-            Cow::Borrowed(reservations_on_entry),
-            ActiveBorrows::new(reservations),
-        );
-        let results = a.run(tcx, id, &attributes, |ab, i| {
-            DebugFormatted::new(&(i.kind(), ab.location(i)))
-        });
-        FlowAtLocation::new(results)
-    };
-
     let mut state = Flows::new(
-        flow_active_borrows,
+        flow_borrows,
         flow_inits,
         flow_uninits,
         flow_move_outs,