compiler/rustc_mir_build/src/build/matches/util.rs

   1 use crate::build::expr::as_place::PlaceBase;
   2 use crate::build::expr::as_place::PlaceBuilder;
   3 use crate::build::matches::MatchPair;
   4 use crate::build::Builder;
   5 use rustc_middle::mir::*;
   6 use rustc_middle::thir::*;
   7 use rustc_middle::ty;
   8 use rustc_middle::ty::TypeVisitable;
   9 use smallvec::SmallVec;
  10 use std::convert::TryInto;
  11
  12 impl<'a, 'tcx> Builder<'a, 'tcx> {
  13     pub(crate) fn field_match_pairs<'pat>(
  14         &mut self,
  15         place: PlaceBuilder<'tcx>,
  16         subpatterns: &'pat [FieldPat<'tcx>],
  17     ) -> Vec<MatchPair<'pat, 'tcx>> {
  18         subpatterns
  19             .iter()
  20             .map(|fieldpat| {
  21                 let place =
  22                     place.clone_project(PlaceElem::Field(fieldpat.field, fieldpat.pattern.ty));
  23                 MatchPair::new(place, &fieldpat.pattern, self)
  24             })
  25             .collect()
  26     }
  27
  28     pub(crate) fn prefix_slice_suffix<'pat>(
  29         &mut self,
  30         match_pairs: &mut SmallVec<[MatchPair<'pat, 'tcx>; 1]>,
  31         place: &PlaceBuilder<'tcx>,
  32         prefix: &'pat [Box<Pat<'tcx>>],
  33         opt_slice: &'pat Option<Box<Pat<'tcx>>>,
  34         suffix: &'pat [Box<Pat<'tcx>>],
  35     ) {
  36         let tcx = self.tcx;
  37         let (min_length, exact_size) = if let Some(place_resolved) = place.try_to_place(self) {
  38             match place_resolved.ty(&self.local_decls, tcx).ty.kind() {
  39                 ty::Array(_, length) => (length.eval_usize(tcx, self.param_env), true),
  40                 _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
  41             }
  42         } else {
  43             ((prefix.len() + suffix.len()).try_into().unwrap(), false)
  44         };
  45
  46         match_pairs.extend(prefix.iter().enumerate().map(|(idx, subpattern)| {
  47             let elem =
  48                 ProjectionElem::ConstantIndex { offset: idx as u64, min_length, from_end: false };
  49             MatchPair::new(place.clone_project(elem), subpattern, self)
  50         }));
  51
  52         if let Some(subslice_pat) = opt_slice {
  53             let suffix_len = suffix.len() as u64;
  54             let subslice = place.clone_project(PlaceElem::Subslice {
  55                 from: prefix.len() as u64,
  56                 to: if exact_size { min_length - suffix_len } else { suffix_len },
  57                 from_end: !exact_size,
  58             });
  59             match_pairs.push(MatchPair::new(subslice, subslice_pat, self));
  60         }
  61
  62         match_pairs.extend(suffix.iter().rev().enumerate().map(|(idx, subpattern)| {
  63             let end_offset = (idx + 1) as u64;
  64             let elem = ProjectionElem::ConstantIndex {
  65                 offset: if exact_size { min_length - end_offset } else { end_offset },
  66                 min_length,
  67                 from_end: !exact_size,
  68             };
  69             let place = place.clone_project(elem);
  70             MatchPair::new(place, subpattern, self)
  71         }));
  72     }
  73
  74     /// Creates a false edge to `imaginary_target` and a real edge to
  75     /// real_target. If `imaginary_target` is none, or is the same as the real
  76     /// target, a Goto is generated instead to simplify the generated MIR.
  77     pub(crate) fn false_edges(
  78         &mut self,
  79         from_block: BasicBlock,
  80         real_target: BasicBlock,
  81         imaginary_target: Option<BasicBlock>,
  82         source_info: SourceInfo,
  83     ) {
  84         match imaginary_target {
  85             Some(target) if target != real_target => {
  86                 self.cfg.terminate(
  87                     from_block,
  88                     source_info,
  89                     TerminatorKind::FalseEdge { real_target, imaginary_target: target },
  90                 );
  91             }
  92             _ => self.cfg.goto(from_block, source_info, real_target),
  93         }
  94     }
  95 }
  96
  97 impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
  98     pub(in crate::build) fn new(
  99         mut place: PlaceBuilder<'tcx>,
 100         pattern: &'pat Pat<'tcx>,
 101         cx: &Builder<'_, 'tcx>,
 102     ) -> MatchPair<'pat, 'tcx> {
 103         // Force the place type to the pattern's type.
 104         // FIXME(oli-obk): can we use this to simplify slice/array pattern hacks?
 105         if let Some(resolved) = place.resolve_upvar(cx) {
 106             place = resolved;
 107         }
 108
 109         // Only add the OpaqueCast projection if the given place is an opaque type and the
 110         // expected type from the pattern is not.
 111         let may_need_cast = match place.base() {
 112             PlaceBase::Local(local) => {
 113                 let ty = Place::ty_from(local, place.projection(), &cx.local_decls, cx.tcx).ty;
 114                 ty != pattern.ty && ty.has_opaque_types()
 115             }
 116             _ => true,
 117         };
 118         if may_need_cast {
 119             place = place.project(ProjectionElem::OpaqueCast(pattern.ty));
 120         }
 121         MatchPair { place, pattern }
 122     }
 123 }