src/librustc_mir/util/alignment.rs

   1 use rustc::ty::{self, TyCtxt};
   2 use rustc::mir::*;
   3
   4 /// Returns `true` if this place is allowed to be less aligned
   5 /// than its containing struct (because it is within a packed
   6 /// struct).
   7 pub fn is_disaligned<'a, 'tcx, L>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
   8                                   local_decls: &L,
   9                                   param_env: ty::ParamEnv<'tcx>,
  10                                   place: &Place<'tcx>)
  11                                   -> bool
  12     where L: HasLocalDecls<'tcx>
  13 {
  14     debug!("is_disaligned({:?})", place);
  15     if !is_within_packed(tcx, local_decls, place) {
  16         debug!("is_disaligned({:?}) - not within packed", place);
  17         return false
  18     }
  19
  20     let ty = place.ty(local_decls, tcx).to_ty(tcx);
  21     match tcx.layout_raw(param_env.and(ty)) {
  22         Ok(layout) if layout.align.abi.bytes() == 1 => {
  23             // if the alignment is 1, the type can't be further
  24             // disaligned.
  25             debug!("is_disaligned({:?}) - align = 1", place);
  26             false
  27         }
  28         _ => {
  29             debug!("is_disaligned({:?}) - true", place);
  30             true
  31         }
  32     }
  33 }
  34
  35 fn is_within_packed<'a, 'tcx, L>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  36                                  local_decls: &L,
  37                                  place: &Place<'tcx>)
  38                                  -> bool
  39     where L: HasLocalDecls<'tcx>
  40 {
  41     let mut place = place;
  42     while let &Place::Projection(box Projection {
  43         ref base, ref elem
  44     }) = place {
  45         match *elem {
  46             // encountered a Deref, which is ABI-aligned
  47             ProjectionElem::Deref => break,
  48             ProjectionElem::Field(..) => {
  49                 let ty = base.ty(local_decls, tcx).to_ty(tcx);
  50                 match ty.sty {
  51                     ty::Adt(def, _) if def.repr.packed() => {
  52                         return true
  53                     }
  54                     _ => {}
  55                 }
  56             }
  57             _ => {}
  58         }
  59         place = base;
  60     }
  61
  62     false
  63 }