compiler/rustc_mir_transform/src/deref_separator.rs

   1 use crate::MirPass;
   2 use rustc_index::vec::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<'tcx> {
  12     tcx: TyCtxt<'tcx>,
  13     patcher: MirPatch<'tcx>,
  14     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
  15 }
  16
  17 impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
  18     fn tcx(&self) -> TyCtxt<'tcx> {
  19         self.tcx
  20     }
  21
  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                         Some(Box::new(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
  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.clone() };
  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 {
  83     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  84         deref_finder(tcx, body);
  85     }
  86 }