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| 1 | +use rustc::mir::visit::Visitor; |
| 2 | +use rustc::mir::{self, Local, Location}; |
| 3 | +use rustc::ty::{self, TyCtxt}; |
| 4 | +use rustc_data_structures::bit_set::BitSet; |
| 5 | +use syntax_pos::DUMMY_SP; |
| 6 | + |
| 7 | +use crate::dataflow::{self, GenKillSet}; |
| 8 | + |
| 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. |
| 13 | +/// |
| 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>, |
| 19 | + tcx: TyCtxt<'tcx>, |
| 20 | + param_env: ty::ParamEnv<'tcx>, |
| 21 | +} |
| 22 | + |
| 23 | +impl<'mir, 'tcx> IndirectlyMutableLocals<'mir, 'tcx> { |
| 24 | + pub fn new( |
| 25 | + tcx: TyCtxt<'tcx>, |
| 26 | + body: &'mir mir::Body<'tcx>, |
| 27 | + param_env: ty::ParamEnv<'tcx>, |
| 28 | + ) -> Self { |
| 29 | + IndirectlyMutableLocals { body, tcx, param_env } |
| 30 | + } |
| 31 | + |
| 32 | + fn transfer_function<'a>( |
| 33 | + &self, |
| 34 | + trans: &'a mut GenKillSet<Local>, |
| 35 | + ) -> TransferFunction<'a, 'mir, 'tcx> { |
| 36 | + TransferFunction { |
| 37 | + body: self.body, |
| 38 | + tcx: self.tcx, |
| 39 | + param_env: self.param_env, |
| 40 | + trans |
| 41 | + } |
| 42 | + } |
| 43 | +} |
| 44 | + |
| 45 | +impl<'mir, 'tcx> dataflow::BitDenotation<'tcx> for IndirectlyMutableLocals<'mir, 'tcx> { |
| 46 | + type Idx = Local; |
| 47 | + |
| 48 | + fn name() -> &'static str { "mut_borrowed_locals" } |
| 49 | + |
| 50 | + fn bits_per_block(&self) -> usize { |
| 51 | + self.body.local_decls.len() |
| 52 | + } |
| 53 | + |
| 54 | + fn start_block_effect(&self, _entry_set: &mut BitSet<Local>) { |
| 55 | + // Nothing is borrowed on function entry |
| 56 | + } |
| 57 | + |
| 58 | + fn statement_effect( |
| 59 | + &self, |
| 60 | + trans: &mut GenKillSet<Local>, |
| 61 | + loc: Location, |
| 62 | + ) { |
| 63 | + let stmt = &self.body[loc.block].statements[loc.statement_index]; |
| 64 | + self.transfer_function(trans).visit_statement(stmt, loc); |
| 65 | + } |
| 66 | + |
| 67 | + fn terminator_effect( |
| 68 | + &self, |
| 69 | + trans: &mut GenKillSet<Local>, |
| 70 | + loc: Location, |
| 71 | + ) { |
| 72 | + let terminator = self.body[loc.block].terminator(); |
| 73 | + self.transfer_function(trans).visit_terminator(terminator, loc); |
| 74 | + } |
| 75 | + |
| 76 | + fn propagate_call_return( |
| 77 | + &self, |
| 78 | + _in_out: &mut BitSet<Local>, |
| 79 | + _call_bb: mir::BasicBlock, |
| 80 | + _dest_bb: mir::BasicBlock, |
| 81 | + _dest_place: &mir::Place<'tcx>, |
| 82 | + ) { |
| 83 | + // Nothing to do when a call returns successfully |
| 84 | + } |
| 85 | +} |
| 86 | + |
| 87 | +impl<'mir, 'tcx> dataflow::BottomValue for IndirectlyMutableLocals<'mir, 'tcx> { |
| 88 | + // bottom = unborrowed |
| 89 | + const BOTTOM_VALUE: bool = false; |
| 90 | +} |
| 91 | + |
| 92 | +/// A `Visitor` that defines the transfer function for `IndirectlyMutableLocals`. |
| 93 | +struct TransferFunction<'a, 'mir, 'tcx> { |
| 94 | + trans: &'a mut GenKillSet<Local>, |
| 95 | + body: &'mir mir::Body<'tcx>, |
| 96 | + tcx: TyCtxt<'tcx>, |
| 97 | + param_env: ty::ParamEnv<'tcx>, |
| 98 | +} |
| 99 | + |
| 100 | +impl<'tcx> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx> { |
| 101 | + fn visit_rvalue( |
| 102 | + &mut self, |
| 103 | + rvalue: &mir::Rvalue<'tcx>, |
| 104 | + location: Location, |
| 105 | + ) { |
| 106 | + if let mir::Rvalue::Ref(_, kind, ref borrowed_place) = *rvalue { |
| 107 | + let is_mut = match kind { |
| 108 | + mir::BorrowKind::Mut { .. } => true, |
| 109 | + |
| 110 | + | mir::BorrowKind::Shared |
| 111 | + | mir::BorrowKind::Shallow |
| 112 | + | mir::BorrowKind::Unique |
| 113 | + => { |
| 114 | + !borrowed_place |
| 115 | + .ty(self.body, self.tcx) |
| 116 | + .ty |
| 117 | + .is_freeze(self.tcx, self.param_env, DUMMY_SP) |
| 118 | + } |
| 119 | + }; |
| 120 | + |
| 121 | + if is_mut { |
| 122 | + match borrowed_place.base { |
| 123 | + mir::PlaceBase::Local(borrowed_local) if !borrowed_place.is_indirect() |
| 124 | + => self.trans.gen(borrowed_local), |
| 125 | + |
| 126 | + _ => (), |
| 127 | + } |
| 128 | + } |
| 129 | + } |
| 130 | + |
| 131 | + self.super_rvalue(rvalue, location); |
| 132 | + } |
| 133 | + |
| 134 | + |
| 135 | + fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) { |
| 136 | + // This method purposely does nothing except call `super_terminator`. It exists solely to |
| 137 | + // document the subtleties around drop terminators. |
| 138 | + |
| 139 | + self.super_terminator(terminator, location); |
| 140 | + |
| 141 | + if let mir::TerminatorKind::Drop { location: _, .. } |
| 142 | + | mir::TerminatorKind::DropAndReplace { location: _, .. } = &terminator.kind |
| 143 | + { |
| 144 | + // Although drop terminators mutably borrow the location being dropped, that borrow |
| 145 | + // cannot live beyond the drop terminator because the dropped location is invalidated. |
| 146 | + } |
| 147 | + } |
| 148 | +} |
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