src/librustc_mir/transform/erase_regions.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! This pass erases all early-bound regions from the types occuring in the MIR.
  12 //! We want to do this once just before trans, so trans does not have to take
  13 //! care erasing regions all over the place.
  14
  15 use rustc::ty::subst::Substs;
  16 use rustc::ty::{Ty, TyCtxt, ClosureSubsts};
  17 use rustc::mir::*;
  18 use rustc::mir::visit::MutVisitor;
  19 use rustc::mir::transform::{MirPass, MirSource};
  20
  21 struct EraseRegionsVisitor<'a, 'tcx: 'a> {
  22     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  23 }
  24
  25 impl<'a, 'tcx> EraseRegionsVisitor<'a, 'tcx> {
  26     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
  27         EraseRegionsVisitor {
  28             tcx: tcx
  29         }
  30     }
  31 }
  32
  33 impl<'a, 'tcx> MutVisitor<'tcx> for EraseRegionsVisitor<'a, 'tcx> {
  34     fn visit_ty(&mut self, ty: &mut Ty<'tcx>) {
  35         let old_ty = *ty;
  36         *ty = self.tcx.erase_regions(&old_ty);
  37     }
  38
  39     fn visit_substs(&mut self, substs: &mut &'tcx Substs<'tcx>) {
  40         *substs = self.tcx.erase_regions(&{*substs});
  41     }
  42
  43     fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
  44         match *rvalue {
  45             Rvalue::Ref(ref mut r, _, _) => {
  46                 *r = self.tcx.types.re_erased;
  47             }
  48             Rvalue::Use(..) |
  49             Rvalue::Repeat(..) |
  50             Rvalue::Len(..) |
  51             Rvalue::Cast(..) |
  52             Rvalue::BinaryOp(..) |
  53             Rvalue::CheckedBinaryOp(..) |
  54             Rvalue::UnaryOp(..) |
  55             Rvalue::Discriminant(..) |
  56             Rvalue::NullaryOp(..) |
  57             Rvalue::Aggregate(..) => {
  58                 // These variants don't contain regions.
  59             }
  60         }
  61         self.super_rvalue(rvalue, location);
  62     }
  63
  64     fn visit_closure_substs(&mut self,
  65                             substs: &mut ClosureSubsts<'tcx>) {
  66         *substs = self.tcx.erase_regions(substs);
  67     }
  68
  69     fn visit_statement(&mut self,
  70                        block: BasicBlock,
  71                        statement: &mut Statement<'tcx>,
  72                        location: Location) {
  73         if let StatementKind::EndRegion(_) = statement.kind {
  74             statement.kind = StatementKind::Nop;
  75         }
  76         self.super_statement(block, statement, location);
  77     }
  78 }
  79
  80 pub struct EraseRegions;
  81
  82 impl MirPass for EraseRegions {
  83     fn run_pass<'a, 'tcx>(&self,
  84                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
  85                           _: MirSource,
  86                           mir: &mut Mir<'tcx>) {
  87         EraseRegionsVisitor::new(tcx).visit_mir(mir);
  88     }
  89 }