1 use rustc::mir::visit::Visitor;
2 use rustc::mir::{self, Local, Location};
3 use rustc::ty::{self, TyCtxt};
4 use rustc_index::bit_set::BitSet;
5 use rustc_span::DUMMY_SP;
7 use crate::dataflow::{self, GenKillSet};
9 /// Whether a borrow to a `Local` has been created that could allow that `Local` to be mutated
10 /// indirectly. This could either be a mutable reference (`&mut`) or a shared borrow if the type of
11 /// that `Local` allows interior mutability. Operations that can mutate local's indirectly include:
12 /// assignments through a pointer (`*p = 42`), function calls, drop terminators and inline assembly.
14 /// If this returns false for a `Local` at a given statement (or terminator), that `Local` could
15 /// not possibly have been mutated indirectly prior to that statement.
16 #[derive(Copy, Clone)]
17 pub struct IndirectlyMutableLocals<'mir, 'tcx> {
18 body: &'mir mir::Body<'tcx>,
20 param_env: ty::ParamEnv<'tcx>,
23 impl<'mir, 'tcx> IndirectlyMutableLocals<'mir, 'tcx> {
26 body: &'mir mir::Body<'tcx>,
27 param_env: ty::ParamEnv<'tcx>,
29 IndirectlyMutableLocals { body, tcx, param_env }
32 fn transfer_function<'a>(
34 trans: &'a mut GenKillSet<Local>,
35 ) -> TransferFunction<'a, 'mir, 'tcx> {
36 TransferFunction { body: self.body, tcx: self.tcx, param_env: self.param_env, trans }
40 impl<'mir, 'tcx> dataflow::BitDenotation<'tcx> for IndirectlyMutableLocals<'mir, 'tcx> {
43 fn name() -> &'static str {
47 fn bits_per_block(&self) -> usize {
48 self.body.local_decls.len()
51 fn start_block_effect(&self, _entry_set: &mut BitSet<Local>) {
52 // Nothing is borrowed on function entry
55 fn statement_effect(&self, trans: &mut GenKillSet<Local>, loc: Location) {
56 let stmt = &self.body[loc.block].statements[loc.statement_index];
57 self.transfer_function(trans).visit_statement(stmt, loc);
60 fn terminator_effect(&self, trans: &mut GenKillSet<Local>, loc: Location) {
61 let terminator = self.body[loc.block].terminator();
62 self.transfer_function(trans).visit_terminator(terminator, loc);
65 fn propagate_call_return(
67 _in_out: &mut BitSet<Local>,
68 _call_bb: mir::BasicBlock,
69 _dest_bb: mir::BasicBlock,
70 _dest_place: &mir::Place<'tcx>,
72 // Nothing to do when a call returns successfully
76 impl<'mir, 'tcx> dataflow::BottomValue for IndirectlyMutableLocals<'mir, 'tcx> {
77 // bottom = unborrowed
78 const BOTTOM_VALUE: bool = false;
81 /// A `Visitor` that defines the transfer function for `IndirectlyMutableLocals`.
82 struct TransferFunction<'a, 'mir, 'tcx> {
83 trans: &'a mut GenKillSet<Local>,
84 body: &'mir mir::Body<'tcx>,
86 param_env: ty::ParamEnv<'tcx>,
89 impl<'tcx> TransferFunction<'_, '_, 'tcx> {
90 /// Returns `true` if this borrow would allow mutation of the `borrowed_place`.
91 fn borrow_allows_mutation(
93 kind: mir::BorrowKind,
94 borrowed_place: &mir::Place<'tcx>,
97 mir::BorrowKind::Mut { .. } => true,
99 mir::BorrowKind::Shared | mir::BorrowKind::Shallow | mir::BorrowKind::Unique => {
100 !borrowed_place.ty(self.body, self.tcx).ty.is_freeze(
110 impl<'tcx> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx> {
111 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
112 if let mir::Rvalue::Ref(_, kind, ref borrowed_place) = *rvalue {
113 if self.borrow_allows_mutation(kind, borrowed_place) {
114 match borrowed_place.base {
115 mir::PlaceBase::Local(borrowed_local) if !borrowed_place.is_indirect() => {
116 self.trans.gen(borrowed_local)
124 self.super_rvalue(rvalue, location);
127 fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
128 // This method purposely does nothing except call `super_terminator`. It exists solely to
129 // document the subtleties around drop terminators.
131 self.super_terminator(terminator, location);
133 if let mir::TerminatorKind::Drop { location: _, .. }
134 | mir::TerminatorKind::DropAndReplace { location: _, .. } = &terminator.kind
136 // Although drop terminators mutably borrow the location being dropped, that borrow
137 // cannot live beyond the drop terminator because the dropped location is invalidated.