rustc_mir_transform/
deref_separator.rs

1use rustc_middle::mir::visit::NonUseContext::VarDebugInfo;
2use rustc_middle::mir::visit::{MutVisitor, PlaceContext};
3use rustc_middle::mir::*;
4use rustc_middle::ty::TyCtxt;
5
6use crate::patch::MirPatch;
7
8pub(super) struct Derefer;
9
10struct DerefChecker<'a, 'tcx> {
11    tcx: TyCtxt<'tcx>,
12    patcher: MirPatch<'tcx>,
13    local_decls: &'a LocalDecls<'tcx>,
14}
15
16impl<'a, 'tcx> MutVisitor<'tcx> for DerefChecker<'a, 'tcx> {
17    fn tcx(&self) -> TyCtxt<'tcx> {
18        self.tcx
19    }
20
21    fn visit_place(&mut self, place: &mut Place<'tcx>, cntxt: PlaceContext, loc: Location) {
22        if !place.projection.is_empty()
23            && cntxt != PlaceContext::NonUse(VarDebugInfo)
24            && place.projection[1..].contains(&ProjectionElem::Deref)
25        {
26            let mut place_local = place.local;
27            let mut last_len = 0;
28            let mut last_deref_idx = 0;
29
30            for (idx, elem) in place.projection[0..].iter().enumerate() {
31                if *elem == ProjectionElem::Deref {
32                    last_deref_idx = idx;
33                }
34            }
35
36            for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
37                if !p_ref.projection.is_empty() && p_elem == ProjectionElem::Deref {
38                    let ty = p_ref.ty(self.local_decls, self.tcx).ty;
39                    let temp = self.patcher.new_local_with_info(
40                        ty,
41                        self.local_decls[p_ref.local].source_info.span,
42                        LocalInfo::DerefTemp,
43                    );
44
45                    // We are adding current p_ref's projections to our
46                    // temp value, excluding projections we already covered.
47                    let deref_place = Place::from(place_local)
48                        .project_deeper(&p_ref.projection[last_len..], self.tcx);
49
50                    self.patcher.add_assign(
51                        loc,
52                        Place::from(temp),
53                        Rvalue::CopyForDeref(deref_place),
54                    );
55                    place_local = temp;
56                    last_len = p_ref.projection.len();
57
58                    // Change `Place` only if we are actually at the Place's last deref
59                    if idx == last_deref_idx {
60                        let temp_place =
61                            Place::from(temp).project_deeper(&place.projection[idx..], self.tcx);
62                        *place = temp_place;
63                    }
64                }
65            }
66        }
67    }
68}
69
70pub(super) fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
71    let patch = MirPatch::new(body);
72    let mut checker = DerefChecker { tcx, patcher: patch, local_decls: &body.local_decls };
73
74    for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
75        checker.visit_basic_block_data(bb, data);
76    }
77
78    checker.patcher.apply(body);
79}
80
81impl<'tcx> crate::MirPass<'tcx> for Derefer {
82    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
83        deref_finder(tcx, body);
84    }
85
86    fn is_required(&self) -> bool {
87        true
88    }
89}
rustc_mir_transform/deref_separator.rs

rustc_mir_transform/
deref_separator.rs
