351 lines
12 KiB
Rust
351 lines
12 KiB
Rust
use crate::borrow_check::place_ext::PlaceExt;
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use crate::borrow_check::nll::ToRegionVid;
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use crate::borrow_check::path_utils::allow_two_phase_borrow;
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use crate::dataflow::indexes::BorrowIndex;
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use crate::dataflow::move_paths::MoveData;
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use rustc::mir::traversal;
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use rustc::mir::visit::{PlaceContext, Visitor, NonUseContext, MutatingUseContext};
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use rustc::mir::{self, Location, Body, Local};
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use rustc::ty::{RegionVid, TyCtxt};
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use rustc::util::nodemap::{FxHashMap, FxHashSet};
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use rustc_index::vec::IndexVec;
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use rustc_index::bit_set::BitSet;
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use std::fmt;
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use std::ops::Index;
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crate struct BorrowSet<'tcx> {
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/// The fundamental map relating bitvector indexes to the borrows
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/// in the MIR.
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crate borrows: IndexVec<BorrowIndex, BorrowData<'tcx>>,
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/// Each borrow is also uniquely identified in the MIR by the
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/// `Location` of the assignment statement in which it appears on
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/// the right hand side; we map each such location to the
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/// corresponding `BorrowIndex`.
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crate location_map: FxHashMap<Location, BorrowIndex>,
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/// Locations which activate borrows.
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/// NOTE: a given location may activate more than one borrow in the future
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/// when more general two-phase borrow support is introduced, but for now we
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/// only need to store one borrow index.
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crate activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
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/// Map from local to all the borrows on that local.
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crate local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
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crate locals_state_at_exit: LocalsStateAtExit,
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}
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impl<'tcx> Index<BorrowIndex> for BorrowSet<'tcx> {
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type Output = BorrowData<'tcx>;
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fn index(&self, index: BorrowIndex) -> &BorrowData<'tcx> {
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&self.borrows[index]
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}
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}
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/// Location where a two-phase borrow is activated, if a borrow
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/// is in fact a two-phase borrow.
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#[derive(Copy, Clone, PartialEq, Eq, Debug)]
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crate enum TwoPhaseActivation {
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NotTwoPhase,
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NotActivated,
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ActivatedAt(Location),
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}
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#[derive(Debug, Clone)]
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crate struct BorrowData<'tcx> {
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/// Location where the borrow reservation starts.
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/// In many cases, this will be equal to the activation location but not always.
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crate reserve_location: Location,
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/// Location where the borrow is activated.
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crate activation_location: TwoPhaseActivation,
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/// What kind of borrow this is
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crate kind: mir::BorrowKind,
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/// The region for which this borrow is live
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crate region: RegionVid,
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/// Place from which we are borrowing
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crate borrowed_place: mir::Place<'tcx>,
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/// Place to which the borrow was stored
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crate assigned_place: mir::Place<'tcx>,
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}
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impl<'tcx> fmt::Display for BorrowData<'tcx> {
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fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
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let kind = match self.kind {
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mir::BorrowKind::Shared => "",
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mir::BorrowKind::Shallow => "shallow ",
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mir::BorrowKind::Unique => "uniq ",
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mir::BorrowKind::Mut { .. } => "mut ",
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};
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write!(w, "&{:?} {}{:?}", self.region, kind, self.borrowed_place)
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}
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}
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crate enum LocalsStateAtExit {
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AllAreInvalidated,
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SomeAreInvalidated { has_storage_dead_or_moved: BitSet<Local> }
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}
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impl LocalsStateAtExit {
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fn build(
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locals_are_invalidated_at_exit: bool,
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body: &Body<'tcx>,
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move_data: &MoveData<'tcx>
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) -> Self {
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struct HasStorageDead(BitSet<Local>);
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impl<'tcx> Visitor<'tcx> for HasStorageDead {
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fn visit_local(&mut self, local: &Local, ctx: PlaceContext, _: Location) {
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if ctx == PlaceContext::NonUse(NonUseContext::StorageDead) {
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self.0.insert(*local);
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}
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}
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}
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if locals_are_invalidated_at_exit {
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LocalsStateAtExit::AllAreInvalidated
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} else {
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let mut has_storage_dead = HasStorageDead(BitSet::new_empty(body.local_decls.len()));
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has_storage_dead.visit_body(body);
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let mut has_storage_dead_or_moved = has_storage_dead.0;
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for move_out in &move_data.moves {
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if let Some(index) = move_data.base_local(move_out.path) {
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has_storage_dead_or_moved.insert(index);
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}
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}
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LocalsStateAtExit::SomeAreInvalidated{ has_storage_dead_or_moved }
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}
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}
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}
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impl<'tcx> BorrowSet<'tcx> {
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pub fn build(
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tcx: TyCtxt<'tcx>,
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body: &Body<'tcx>,
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locals_are_invalidated_at_exit: bool,
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move_data: &MoveData<'tcx>,
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) -> Self {
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let mut visitor = GatherBorrows {
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tcx,
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body,
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idx_vec: IndexVec::new(),
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location_map: Default::default(),
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activation_map: Default::default(),
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local_map: Default::default(),
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pending_activations: Default::default(),
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locals_state_at_exit:
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LocalsStateAtExit::build(locals_are_invalidated_at_exit, body, move_data),
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};
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for (block, block_data) in traversal::preorder(body) {
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visitor.visit_basic_block_data(block, block_data);
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}
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BorrowSet {
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borrows: visitor.idx_vec,
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location_map: visitor.location_map,
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activation_map: visitor.activation_map,
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local_map: visitor.local_map,
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locals_state_at_exit: visitor.locals_state_at_exit,
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}
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}
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crate fn activations_at_location(&self, location: Location) -> &[BorrowIndex] {
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self.activation_map
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.get(&location)
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.map(|activations| &activations[..])
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.unwrap_or(&[])
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}
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}
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struct GatherBorrows<'a, 'tcx> {
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tcx: TyCtxt<'tcx>,
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body: &'a Body<'tcx>,
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idx_vec: IndexVec<BorrowIndex, BorrowData<'tcx>>,
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location_map: FxHashMap<Location, BorrowIndex>,
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activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
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local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
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/// When we encounter a 2-phase borrow statement, it will always
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/// be assigning into a temporary TEMP:
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///
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/// TEMP = &foo
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///
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/// We add TEMP into this map with `b`, where `b` is the index of
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/// the borrow. When we find a later use of this activation, we
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/// remove from the map (and add to the "tombstone" set below).
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pending_activations: FxHashMap<mir::Local, BorrowIndex>,
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locals_state_at_exit: LocalsStateAtExit,
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}
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impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
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fn visit_assign(
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&mut self,
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assigned_place: &mir::Place<'tcx>,
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rvalue: &mir::Rvalue<'tcx>,
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location: mir::Location,
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) {
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if let mir::Rvalue::Ref(region, kind, ref borrowed_place) = *rvalue {
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if borrowed_place.ignore_borrow(
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self.tcx, self.body, &self.locals_state_at_exit) {
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return;
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}
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let region = region.to_region_vid();
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let borrow = BorrowData {
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kind,
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region,
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reserve_location: location,
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activation_location: TwoPhaseActivation::NotTwoPhase,
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borrowed_place: borrowed_place.clone(),
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assigned_place: assigned_place.clone(),
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};
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let idx = self.idx_vec.push(borrow);
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self.location_map.insert(location, idx);
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self.insert_as_pending_if_two_phase(location, &assigned_place, kind, idx);
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if let mir::PlaceBase::Local(local) = borrowed_place.base {
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self.local_map.entry(local).or_default().insert(idx);
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}
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}
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self.super_assign(assigned_place, rvalue, location)
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}
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fn visit_local(
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&mut self,
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temp: &Local,
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context: PlaceContext,
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location: Location,
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) {
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if !context.is_use() {
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return;
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}
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// We found a use of some temporary TMP
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// check whether we (earlier) saw a 2-phase borrow like
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//
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// TMP = &mut place
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if let Some(&borrow_index) = self.pending_activations.get(temp) {
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let borrow_data = &mut self.idx_vec[borrow_index];
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// Watch out: the use of TMP in the borrow itself
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// doesn't count as an activation. =)
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if borrow_data.reserve_location == location &&
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context == PlaceContext::MutatingUse(MutatingUseContext::Store)
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{
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return;
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}
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if let TwoPhaseActivation::ActivatedAt(other_location) =
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borrow_data.activation_location {
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span_bug!(
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self.body.source_info(location).span,
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"found two uses for 2-phase borrow temporary {:?}: \
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{:?} and {:?}",
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temp,
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location,
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other_location,
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);
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}
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// Otherwise, this is the unique later use that we expect.
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// Double check: This borrow is indeed a two-phase borrow (that is,
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// we are 'transitioning' from `NotActivated` to `ActivatedAt`) and
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// we've not found any other activations (checked above).
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assert_eq!(
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borrow_data.activation_location,
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TwoPhaseActivation::NotActivated,
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"never found an activation for this borrow!",
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);
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self.activation_map
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.entry(location)
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.or_default()
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.push(borrow_index);
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borrow_data.activation_location = TwoPhaseActivation::ActivatedAt(location);
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}
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}
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fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: mir::Location) {
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if let mir::Rvalue::Ref(region, kind, ref place) = *rvalue {
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// double-check that we already registered a BorrowData for this
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let borrow_index = self.location_map[&location];
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let borrow_data = &self.idx_vec[borrow_index];
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assert_eq!(borrow_data.reserve_location, location);
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assert_eq!(borrow_data.kind, kind);
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assert_eq!(borrow_data.region, region.to_region_vid());
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assert_eq!(borrow_data.borrowed_place, *place);
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}
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return self.super_rvalue(rvalue, location);
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}
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}
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impl<'a, 'tcx> GatherBorrows<'a, 'tcx> {
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/// If this is a two-phase borrow, then we will record it
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/// as "pending" until we find the activating use.
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fn insert_as_pending_if_two_phase(
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&mut self,
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start_location: Location,
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assigned_place: &mir::Place<'tcx>,
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kind: mir::BorrowKind,
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borrow_index: BorrowIndex,
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) {
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debug!(
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"Borrows::insert_as_pending_if_two_phase({:?}, {:?}, {:?})",
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start_location, assigned_place, borrow_index,
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);
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if !allow_two_phase_borrow(kind) {
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debug!(" -> {:?}", start_location);
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return;
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}
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// When we encounter a 2-phase borrow statement, it will always
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// be assigning into a temporary TEMP:
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//
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// TEMP = &foo
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//
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// so extract `temp`.
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let temp = if let &mir::Place {
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base: mir::PlaceBase::Local(temp),
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projection: box [],
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} = assigned_place {
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temp
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} else {
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span_bug!(
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self.body.source_info(start_location).span,
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"expected 2-phase borrow to assign to a local, not `{:?}`",
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assigned_place,
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);
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};
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// Consider the borrow not activated to start. When we find an activation, we'll update
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// this field.
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{
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let borrow_data = &mut self.idx_vec[borrow_index];
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borrow_data.activation_location = TwoPhaseActivation::NotActivated;
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}
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// Insert `temp` into the list of pending activations. From
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// now on, we'll be on the lookout for a use of it. Note that
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// we are guaranteed that this use will come after the
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// assignment.
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let old_value = self.pending_activations.insert(temp, borrow_index);
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if let Some(old_index) = old_value {
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span_bug!(self.body.source_info(start_location).span,
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"found already pending activation for temp: {:?} \
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at borrow_index: {:?} with associated data {:?}",
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temp, old_index, self.idx_vec[old_index]);
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}
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}
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}
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