1 //! Propagate `Qualif`s between locals and query the results.
3 //! This contains the dataflow analysis used to track `Qualif`s on complex control-flow graphs.
5 use rustc_index::bit_set::BitSet;
6 use rustc_middle::mir::visit::Visitor;
7 use rustc_middle::mir::{self, BasicBlock, Local, Location};
9 use std::marker::PhantomData;
11 use super::{qualifs, ConstCx, Qualif};
14 /// A `Visitor` that propagates qualifs between locals. This defines the transfer function of
15 /// `FlowSensitiveAnalysis`.
17 /// This transfer does nothing when encountering an indirect assignment. Consumers should rely on
18 /// the `MaybeMutBorrowedLocals` dataflow pass to see if a `Local` may have become qualified via
19 /// an indirect assignment or function call.
20 struct TransferFunction<'a, 'mir, 'tcx, Q> {
21 ccx: &'a ConstCx<'mir, 'tcx>,
22 qualifs_per_local: &'a mut BitSet<Local>,
24 _qualif: PhantomData<Q>,
27 impl<Q> TransferFunction<'a, 'mir, 'tcx, Q>
31 fn new(ccx: &'a ConstCx<'mir, 'tcx>, qualifs_per_local: &'a mut BitSet<Local>) -> Self {
32 TransferFunction { ccx, qualifs_per_local, _qualif: PhantomData }
35 fn initialize_state(&mut self) {
36 self.qualifs_per_local.clear();
38 for arg in self.ccx.body.args_iter() {
39 let arg_ty = self.ccx.body.local_decls[arg].ty;
40 if Q::in_any_value_of_ty(self.ccx, arg_ty) {
41 self.qualifs_per_local.insert(arg);
46 fn assign_qualif_direct(&mut self, place: &mir::Place<'tcx>, value: bool) {
47 debug_assert!(!place.is_indirect());
49 match (value, place.as_ref()) {
50 (true, mir::PlaceRef { local, .. }) => {
51 self.qualifs_per_local.insert(local);
54 // For now, we do not clear the qualif if a local is overwritten in full by
55 // an unqualified rvalue (e.g. `y = 5`). This is to be consistent
56 // with aggregates where we overwrite all fields with assignments, which would not
58 (false, mir::PlaceRef { local: _, projection: &[] }) => {
59 // self.qualifs_per_local.remove(*local);
66 fn apply_call_return_effect(
69 _func: &mir::Operand<'tcx>,
70 _args: &[mir::Operand<'tcx>],
71 return_place: mir::Place<'tcx>,
73 // We cannot reason about another function's internals, so use conservative type-based
74 // qualification for the result of a function call.
75 let return_ty = return_place.ty(self.ccx.body, self.ccx.tcx).ty;
76 let qualif = Q::in_any_value_of_ty(self.ccx, return_ty);
78 if !return_place.is_indirect() {
79 self.assign_qualif_direct(&return_place, qualif);
84 impl<Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q>
88 fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
89 self.super_operand(operand, location);
91 if !Q::IS_CLEARED_ON_MOVE {
95 // If a local with no projections is moved from (e.g. `x` in `y = x`), record that
96 // it no longer needs to be dropped.
97 if let mir::Operand::Move(place) = operand {
98 if let Some(local) = place.as_local() {
99 self.qualifs_per_local.remove(local);
106 place: &mir::Place<'tcx>,
107 rvalue: &mir::Rvalue<'tcx>,
110 let qualif = qualifs::in_rvalue::<Q, _>(
112 &mut |l| self.qualifs_per_local.contains(l),
115 if !place.is_indirect() {
116 self.assign_qualif_direct(place, qualif);
119 // We need to assign qualifs to the left-hand side before visiting `rvalue` since
120 // qualifs can be cleared on move.
121 self.super_assign(place, rvalue, location);
124 fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
125 // The effect of assignment to the return place in `TerminatorKind::Call` is not applied
126 // here; that occurs in `apply_call_return_effect`.
128 if let mir::TerminatorKind::DropAndReplace { value, place, .. } = &terminator.kind {
129 let qualif = qualifs::in_operand::<Q, _>(
131 &mut |l| self.qualifs_per_local.contains(l),
135 if !place.is_indirect() {
136 self.assign_qualif_direct(place, qualif);
140 // We need to assign qualifs to the dropped location before visiting the operand that
141 // replaces it since qualifs can be cleared on move.
142 self.super_terminator(terminator, location);
146 /// The dataflow analysis used to propagate qualifs on arbitrary CFGs.
147 pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> {
148 ccx: &'a ConstCx<'mir, 'tcx>,
149 _qualif: PhantomData<Q>,
152 impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>
156 pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
157 FlowSensitiveAnalysis { ccx, _qualif: PhantomData }
160 fn transfer_function(
162 state: &'a mut BitSet<Local>,
163 ) -> TransferFunction<'a, 'mir, 'tcx, Q> {
164 TransferFunction::<Q>::new(self.ccx, state)
168 impl<Q> dataflow::AnalysisDomain<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q>
172 type Domain = BitSet<Local>;
174 const NAME: &'static str = Q::ANALYSIS_NAME;
176 fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
177 BitSet::new_empty(body.local_decls.len())
180 fn initialize_start_block(&self, _body: &mir::Body<'tcx>, state: &mut Self::Domain) {
181 self.transfer_function(state).initialize_state();
185 impl<Q> dataflow::Analysis<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q>
189 fn apply_statement_effect(
191 state: &mut Self::Domain,
192 statement: &mir::Statement<'tcx>,
195 self.transfer_function(state).visit_statement(statement, location);
198 fn apply_terminator_effect(
200 state: &mut Self::Domain,
201 terminator: &mir::Terminator<'tcx>,
204 self.transfer_function(state).visit_terminator(terminator, location);
207 fn apply_call_return_effect(
209 state: &mut Self::Domain,
211 func: &mir::Operand<'tcx>,
212 args: &[mir::Operand<'tcx>],
213 return_place: mir::Place<'tcx>,
215 self.transfer_function(state).apply_call_return_effect(block, func, args, return_place)