1 use crate::MirPass;
2 use rustc_index::IndexVec;
3 use rustc_middle::mir::patch::MirPatch;
4 use rustc_middle::mir::visit::NonUseContext::VarDebugInfo;
5 use rustc_middle::mir::visit::{MutVisitor, PlaceContext};
6 use rustc_middle::mir::*;
7 use rustc_middle::ty::TyCtxt;
8
9 pub struct Derefer;
10
11 pub struct DerefChecker<'a, 'tcx> {
12 tcx: TyCtxt<'tcx>,
13 patcher: MirPatch<'tcx>,
14 local_decls: &'a IndexVec<Local, LocalDecl<'tcx>>,
15 }
16
17 impl<'a, 'tcx> MutVisitor<'tcx> for DerefChecker<'a, 'tcx> {
tcx(&self) -> TyCtxt<'tcx>18 fn tcx(&self) -> TyCtxt<'tcx> {
19 self.tcx
20 }
21
visit_place(&mut self, place: &mut Place<'tcx>, cntxt: PlaceContext, loc: Location)22 fn visit_place(&mut self, place: &mut Place<'tcx>, cntxt: PlaceContext, loc: Location) {
23 if !place.projection.is_empty()
24 && cntxt != PlaceContext::NonUse(VarDebugInfo)
25 && place.projection[1..].contains(&ProjectionElem::Deref)
26 {
27 let mut place_local = place.local;
28 let mut last_len = 0;
29 let mut last_deref_idx = 0;
30
31 for (idx, elem) in place.projection[0..].iter().enumerate() {
32 if *elem == ProjectionElem::Deref {
33 last_deref_idx = idx;
34 }
35 }
36
37 for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
38 if !p_ref.projection.is_empty() && p_elem == ProjectionElem::Deref {
39 let ty = p_ref.ty(self.local_decls, self.tcx).ty;
40 let temp = self.patcher.new_internal_with_info(
41 ty,
42 self.local_decls[p_ref.local].source_info.span,
43 LocalInfo::DerefTemp,
44 );
45
46 // We are adding current p_ref's projections to our
47 // temp value, excluding projections we already covered.
48 let deref_place = Place::from(place_local)
49 .project_deeper(&p_ref.projection[last_len..], self.tcx);
50
51 self.patcher.add_assign(
52 loc,
53 Place::from(temp),
54 Rvalue::CopyForDeref(deref_place),
55 );
56 place_local = temp;
57 last_len = p_ref.projection.len();
58
59 // Change `Place` only if we are actually at the Place's last deref
60 if idx == last_deref_idx {
61 let temp_place =
62 Place::from(temp).project_deeper(&place.projection[idx..], self.tcx);
63 *place = temp_place;
64 }
65 }
66 }
67 }
68 }
69 }
70
deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)71 pub fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
72 let patch = MirPatch::new(body);
73 let mut checker = DerefChecker { tcx, patcher: patch, local_decls: &body.local_decls };
74
75 for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
76 checker.visit_basic_block_data(bb, data);
77 }
78
79 checker.patcher.apply(body);
80 }
81
82 impl<'tcx> MirPass<'tcx> for Derefer {
run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)83 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
84 deref_finder(tcx, body);
85 }
86 }
87