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 occurring in the MIR.
  12 //! We want to do this once just before codegen, so codegen does not have to take
  13 //! care erasing regions all over the place.
  14 //! NOTE:  We do NOT erase regions of statements that are relevant for
  15 //! "types-as-contracts"-validation, namely, AcquireValid, ReleaseValid, and EndRegion.
  16
  17 use rustc::ty::subst::Substs;
  18 use rustc::ty::{self, Ty, TyCtxt};
  19 use rustc::mir::*;
  20 use rustc::mir::visit::{MutVisitor, TyContext};
  21 use transform::{MirPass, MirSource};
  22
  23 struct EraseRegionsVisitor<'a, 'tcx: 'a> {
  24     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  25     in_validation_statement: bool,
  26 }
  27
  28 impl<'a, 'tcx> EraseRegionsVisitor<'a, 'tcx> {
  29     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
  30         EraseRegionsVisitor {
  31             tcx,
  32             in_validation_statement: false,
  33         }
  34     }
  35 }
  36
  37 impl<'a, 'tcx> MutVisitor<'tcx> for EraseRegionsVisitor<'a, 'tcx> {
  38     fn visit_ty(&mut self, ty: &mut Ty<'tcx>, _: TyContext) {
  39         if !self.in_validation_statement {
  40             *ty = self.tcx.erase_regions(ty);
  41         }
  42         self.super_ty(ty);
  43     }
  44
  45     fn visit_region(&mut self, region: &mut ty::Region<'tcx>, _: Location) {
  46         *region = self.tcx.types.re_erased;
  47     }
  48
  49     fn visit_const(&mut self, constant: &mut &'tcx ty::Const<'tcx>, _: Location) {
  50         *constant = self.tcx.erase_regions(constant);
  51     }
  52
  53     fn visit_substs(&mut self, substs: &mut &'tcx Substs<'tcx>, _: Location) {
  54         *substs = self.tcx.erase_regions(substs);
  55     }
  56
  57     fn visit_statement(&mut self,
  58                        block: BasicBlock,
  59                        statement: &mut Statement<'tcx>,
  60                        location: Location) {
  61         // Do NOT delete EndRegion if validation statements are emitted.
  62         // Validation needs EndRegion.
  63         if self.tcx.sess.opts.debugging_opts.mir_emit_validate == 0 {
  64             if let StatementKind::EndRegion(_) = statement.kind {
  65                 statement.kind = StatementKind::Nop;
  66             }
  67         }
  68
  69         self.in_validation_statement = match statement.kind {
  70             StatementKind::Validate(..) => true,
  71             _ => false,
  72         };
  73         self.super_statement(block, statement, location);
  74         self.in_validation_statement = false;
  75     }
  76 }
  77
  78 pub struct EraseRegions;
  79
  80 impl MirPass for EraseRegions {
  81     fn run_pass<'a, 'tcx>(&self,
  82                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
  83                           _: MirSource,
  84                           mir: &mut Mir<'tcx>) {
  85         EraseRegionsVisitor::new(tcx).visit_mir(mir);
  86     }
  87 }