src/librustc_mir/build/expr/as_place.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 //! See docs in build/expr/mod.rs
  12
  13 use build::expr::category::Category;
  14 use build::ForGuard::{OutsideGuard, RefWithinGuard};
  15 use build::{BlockAnd, BlockAndExtension, Builder};
  16 use hair::*;
  17 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
  18 use rustc::mir::*;
  19 use rustc::ty::Variance;
  20
  21 use rustc_data_structures::indexed_vec::Idx;
  22
  23 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  24     /// Compile `expr`, yielding a place that we can move from etc.
  25     pub fn as_place<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Place<'tcx>>
  26     where
  27         M: Mirror<'tcx, Output = Expr<'tcx>>,
  28     {
  29         let expr = self.hir.mirror(expr);
  30         self.expr_as_place(block, expr, Mutability::Mut)
  31     }
  32
  33     /// Compile `expr`, yielding a place that we can move from etc.
  34     /// Mutability note: The caller of this method promises only to read from the resulting
  35     /// place. The place itself may or may not be mutable:
  36     /// * If this expr is a place expr like a.b, then we will return that place.
  37     /// * Otherwise, a temporary is created: in that event, it will be an immutable temporary.
  38     pub fn as_read_only_place<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Place<'tcx>>
  39     where
  40         M: Mirror<'tcx, Output = Expr<'tcx>>,
  41     {
  42         let expr = self.hir.mirror(expr);
  43         self.expr_as_place(block, expr, Mutability::Not)
  44     }
  45
  46     fn expr_as_place(
  47         &mut self,
  48         mut block: BasicBlock,
  49         expr: Expr<'tcx>,
  50         mutability: Mutability,
  51     ) -> BlockAnd<Place<'tcx>> {
  52         debug!(
  53             "expr_as_place(block={:?}, expr={:?}, mutability={:?})",
  54             block, expr, mutability
  55         );
  56
  57         let this = self;
  58         let expr_span = expr.span;
  59         let source_info = this.source_info(expr_span);
  60         match expr.kind {
  61             ExprKind::Scope {
  62                 region_scope,
  63                 lint_level,
  64                 value,
  65             } => this.in_scope((region_scope, source_info), lint_level, block, |this| {
  66                 if mutability == Mutability::Not {
  67                     this.as_read_only_place(block, value)
  68                 } else {
  69                     this.as_place(block, value)
  70                 }
  71             }),
  72             ExprKind::Field { lhs, name } => {
  73                 let place = unpack!(block = this.as_place(block, lhs));
  74                 let place = place.field(name, expr.ty);
  75                 block.and(place)
  76             }
  77             ExprKind::Deref { arg } => {
  78                 let place = unpack!(block = this.as_place(block, arg));
  79                 let place = place.deref();
  80                 block.and(place)
  81             }
  82             ExprKind::Index { lhs, index } => {
  83                 let (usize_ty, bool_ty) = (this.hir.usize_ty(), this.hir.bool_ty());
  84
  85                 let slice = unpack!(block = this.as_place(block, lhs));
  86                 // region_scope=None so place indexes live forever. They are scalars so they
  87                 // do not need storage annotations, and they are often copied between
  88                 // places.
  89                 // Making this a *fresh* temporary also means we do not have to worry about
  90                 // the index changing later: Nothing will ever change this temporary.
  91                 // The "retagging" transformation (for Stacked Borrows) relies on this.
  92                 let idx = unpack!(block = this.as_temp(block, None, index, Mutability::Mut));
  93
  94                 // bounds check:
  95                 let (len, lt) = (
  96                     this.temp(usize_ty.clone(), expr_span),
  97                     this.temp(bool_ty, expr_span),
  98                 );
  99                 this.cfg.push_assign(
 100                     block,
 101                     source_info, // len = len(slice)
 102                     &len,
 103                     Rvalue::Len(slice.clone()),
 104                 );
 105                 this.cfg.push_assign(
 106                     block,
 107                     source_info, // lt = idx < len
 108                     &lt,
 109                     Rvalue::BinaryOp(
 110                         BinOp::Lt,
 111                         Operand::Copy(Place::Local(idx)),
 112                         Operand::Copy(len.clone()),
 113                     ),
 114                 );
 115
 116                 let msg = BoundsCheck {
 117                     len: Operand::Move(len),
 118                     index: Operand::Copy(Place::Local(idx)),
 119                 };
 120                 let success = this.assert(block, Operand::Move(lt), true, msg, expr_span);
 121                 success.and(slice.index(idx))
 122             }
 123             ExprKind::SelfRef => block.and(Place::Local(Local::new(1))),
 124             ExprKind::VarRef { id } => {
 125                 let place = if this.is_bound_var_in_guard(id) && this
 126                     .hir
 127                     .tcx()
 128                     .all_pat_vars_are_implicit_refs_within_guards()
 129                 {
 130                     let index = this.var_local_id(id, RefWithinGuard);
 131                     Place::Local(index).deref()
 132                 } else {
 133                     let index = this.var_local_id(id, OutsideGuard);
 134                     Place::Local(index)
 135                 };
 136                 block.and(place)
 137             }
 138             ExprKind::StaticRef { id } => block.and(Place::Static(Box::new(Static {
 139                 def_id: id,
 140                 ty: expr.ty,
 141             }))),
 142
 143             ExprKind::PlaceTypeAscription { source, user_ty } => {
 144                 let place = unpack!(block = this.as_place(block, source));
 145                 if let Some(user_ty) = user_ty {
 146                     this.cfg.push(
 147                         block,
 148                         Statement {
 149                             source_info,
 150                             kind: StatementKind::AscribeUserType(
 151                                 place.clone(),
 152                                 Variance::Invariant,
 153                                 box UserTypeProjection { base: user_ty, projs: vec![], },
 154                             ),
 155                         },
 156                     );
 157                 }
 158                 block.and(place)
 159             }
 160             ExprKind::ValueTypeAscription { source, user_ty } => {
 161                 let source = this.hir.mirror(source);
 162                 let temp = unpack!(
 163                     block = this.as_temp(block, source.temp_lifetime, source, mutability)
 164                 );
 165                 if let Some(user_ty) = user_ty {
 166                     this.cfg.push(
 167                         block,
 168                         Statement {
 169                             source_info,
 170                             kind: StatementKind::AscribeUserType(
 171                                 Place::Local(temp.clone()),
 172                                 Variance::Invariant,
 173                                 box UserTypeProjection { base: user_ty, projs: vec![], },
 174                             ),
 175                         },
 176                     );
 177                 }
 178                 block.and(Place::Local(temp))
 179             }
 180
 181             ExprKind::Array { .. }
 182             | ExprKind::Tuple { .. }
 183             | ExprKind::Adt { .. }
 184             | ExprKind::Closure { .. }
 185             | ExprKind::Unary { .. }
 186             | ExprKind::Binary { .. }
 187             | ExprKind::LogicalOp { .. }
 188             | ExprKind::Box { .. }
 189             | ExprKind::Cast { .. }
 190             | ExprKind::Use { .. }
 191             | ExprKind::NeverToAny { .. }
 192             | ExprKind::ReifyFnPointer { .. }
 193             | ExprKind::ClosureFnPointer { .. }
 194             | ExprKind::UnsafeFnPointer { .. }
 195             | ExprKind::Unsize { .. }
 196             | ExprKind::Repeat { .. }
 197             | ExprKind::Borrow { .. }
 198             | ExprKind::If { .. }
 199             | ExprKind::Match { .. }
 200             | ExprKind::Loop { .. }
 201             | ExprKind::Block { .. }
 202             | ExprKind::Assign { .. }
 203             | ExprKind::AssignOp { .. }
 204             | ExprKind::Break { .. }
 205             | ExprKind::Continue { .. }
 206             | ExprKind::Return { .. }
 207             | ExprKind::Literal { .. }
 208             | ExprKind::InlineAsm { .. }
 209             | ExprKind::Yield { .. }
 210             | ExprKind::Call { .. } => {
 211                 // these are not places, so we need to make a temporary.
 212                 debug_assert!(match Category::of(&expr.kind) {
 213                     Some(Category::Place) => false,
 214                     _ => true,
 215                 });
 216                 let temp =
 217                     unpack!(block = this.as_temp(block, expr.temp_lifetime, expr, mutability));
 218                 block.and(Place::Local(temp))
 219             }
 220         }
 221     }
 222 }