src/librustc_mir/build/expr/as_place.rs

   1 //! See docs in build/expr/mod.rs
   2
   3 use build::expr::category::Category;
   4 use build::ForGuard::{OutsideGuard, RefWithinGuard};
   5 use build::{BlockAnd, BlockAndExtension, Builder};
   6 use hair::*;
   7 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
   8 use rustc::mir::*;
   9 use rustc::ty::Variance;
  10
  11 use rustc_data_structures::indexed_vec::Idx;
  12
  13 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  14     /// Compile `expr`, yielding a place that we can move from etc.
  15     pub fn as_place<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Place<'tcx>>
  16     where
  17         M: Mirror<'tcx, Output = Expr<'tcx>>,
  18     {
  19         let expr = self.hir.mirror(expr);
  20         self.expr_as_place(block, expr, Mutability::Mut)
  21     }
  22
  23     /// Compile `expr`, yielding a place that we can move from etc.
  24     /// Mutability note: The caller of this method promises only to read from the resulting
  25     /// place. The place itself may or may not be mutable:
  26     /// * If this expr is a place expr like a.b, then we will return that place.
  27     /// * Otherwise, a temporary is created: in that event, it will be an immutable temporary.
  28     pub fn as_read_only_place<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Place<'tcx>>
  29     where
  30         M: Mirror<'tcx, Output = Expr<'tcx>>,
  31     {
  32         let expr = self.hir.mirror(expr);
  33         self.expr_as_place(block, expr, Mutability::Not)
  34     }
  35
  36     fn expr_as_place(
  37         &mut self,
  38         mut block: BasicBlock,
  39         expr: Expr<'tcx>,
  40         mutability: Mutability,
  41     ) -> BlockAnd<Place<'tcx>> {
  42         debug!(
  43             "expr_as_place(block={:?}, expr={:?}, mutability={:?})",
  44             block, expr, mutability
  45         );
  46
  47         let this = self;
  48         let expr_span = expr.span;
  49         let source_info = this.source_info(expr_span);
  50         match expr.kind {
  51             ExprKind::Scope {
  52                 region_scope,
  53                 lint_level,
  54                 value,
  55             } => this.in_scope((region_scope, source_info), lint_level, block, |this| {
  56                 if mutability == Mutability::Not {
  57                     this.as_read_only_place(block, value)
  58                 } else {
  59                     this.as_place(block, value)
  60                 }
  61             }),
  62             ExprKind::Field { lhs, name } => {
  63                 let place = unpack!(block = this.as_place(block, lhs));
  64                 let place = place.field(name, expr.ty);
  65                 block.and(place)
  66             }
  67             ExprKind::Deref { arg } => {
  68                 let place = unpack!(block = this.as_place(block, arg));
  69                 let place = place.deref();
  70                 block.and(place)
  71             }
  72             ExprKind::Index { lhs, index } => {
  73                 let (usize_ty, bool_ty) = (this.hir.usize_ty(), this.hir.bool_ty());
  74
  75                 let slice = unpack!(block = this.as_place(block, lhs));
  76                 // region_scope=None so place indexes live forever. They are scalars so they
  77                 // do not need storage annotations, and they are often copied between
  78                 // places.
  79                 // Making this a *fresh* temporary also means we do not have to worry about
  80                 // the index changing later: Nothing will ever change this temporary.
  81                 // The "retagging" transformation (for Stacked Borrows) relies on this.
  82                 let idx = unpack!(block = this.as_temp(block, None, index, Mutability::Mut));
  83
  84                 // bounds check:
  85                 let (len, lt) = (
  86                     this.temp(usize_ty.clone(), expr_span),
  87                     this.temp(bool_ty, expr_span),
  88                 );
  89                 this.cfg.push_assign(
  90                     block,
  91                     source_info, // len = len(slice)
  92                     &len,
  93                     Rvalue::Len(slice.clone()),
  94                 );
  95                 this.cfg.push_assign(
  96                     block,
  97                     source_info, // lt = idx < len
  98                     &lt,
  99                     Rvalue::BinaryOp(
 100                         BinOp::Lt,
 101                         Operand::Copy(Place::Local(idx)),
 102                         Operand::Copy(len.clone()),
 103                     ),
 104                 );
 105
 106                 let msg = BoundsCheck {
 107                     len: Operand::Move(len),
 108                     index: Operand::Copy(Place::Local(idx)),
 109                 };
 110                 let success = this.assert(block, Operand::Move(lt), true, msg, expr_span);
 111                 success.and(slice.index(idx))
 112             }
 113             ExprKind::SelfRef => block.and(Place::Local(Local::new(1))),
 114             ExprKind::VarRef { id } => {
 115                 let place = if this.is_bound_var_in_guard(id) && this
 116                     .hir
 117                     .tcx()
 118                     .all_pat_vars_are_implicit_refs_within_guards()
 119                 {
 120                     let index = this.var_local_id(id, RefWithinGuard);
 121                     Place::Local(index).deref()
 122                 } else {
 123                     let index = this.var_local_id(id, OutsideGuard);
 124                     Place::Local(index)
 125                 };
 126                 block.and(place)
 127             }
 128             ExprKind::StaticRef { id } => block.and(Place::Static(Box::new(Static {
 129                 def_id: id,
 130                 ty: expr.ty,
 131             }))),
 132
 133             ExprKind::PlaceTypeAscription { source, user_ty } => {
 134                 let place = unpack!(block = this.as_place(block, source));
 135                 if let Some(user_ty) = user_ty {
 136                     this.cfg.push(
 137                         block,
 138                         Statement {
 139                             source_info,
 140                             kind: StatementKind::AscribeUserType(
 141                                 place.clone(),
 142                                 Variance::Invariant,
 143                                 box UserTypeProjection { base: user_ty, projs: vec![], },
 144                             ),
 145                         },
 146                     );
 147                 }
 148                 block.and(place)
 149             }
 150             ExprKind::ValueTypeAscription { source, user_ty } => {
 151                 let source = this.hir.mirror(source);
 152                 let temp = unpack!(
 153                     block = this.as_temp(block, source.temp_lifetime, source, mutability)
 154                 );
 155                 if let Some(user_ty) = user_ty {
 156                     this.cfg.push(
 157                         block,
 158                         Statement {
 159                             source_info,
 160                             kind: StatementKind::AscribeUserType(
 161                                 Place::Local(temp.clone()),
 162                                 Variance::Invariant,
 163                                 box UserTypeProjection { base: user_ty, projs: vec![], },
 164                             ),
 165                         },
 166                     );
 167                 }
 168                 block.and(Place::Local(temp))
 169             }
 170
 171             ExprKind::Array { .. }
 172             | ExprKind::Tuple { .. }
 173             | ExprKind::Adt { .. }
 174             | ExprKind::Closure { .. }
 175             | ExprKind::Unary { .. }
 176             | ExprKind::Binary { .. }
 177             | ExprKind::LogicalOp { .. }
 178             | ExprKind::Box { .. }
 179             | ExprKind::Cast { .. }
 180             | ExprKind::Use { .. }
 181             | ExprKind::NeverToAny { .. }
 182             | ExprKind::ReifyFnPointer { .. }
 183             | ExprKind::ClosureFnPointer { .. }
 184             | ExprKind::UnsafeFnPointer { .. }
 185             | ExprKind::Unsize { .. }
 186             | ExprKind::Repeat { .. }
 187             | ExprKind::Borrow { .. }
 188             | ExprKind::If { .. }
 189             | ExprKind::Match { .. }
 190             | ExprKind::Loop { .. }
 191             | ExprKind::Block { .. }
 192             | ExprKind::Assign { .. }
 193             | ExprKind::AssignOp { .. }
 194             | ExprKind::Break { .. }
 195             | ExprKind::Continue { .. }
 196             | ExprKind::Return { .. }
 197             | ExprKind::Literal { .. }
 198             | ExprKind::InlineAsm { .. }
 199             | ExprKind::Yield { .. }
 200             | ExprKind::Call { .. } => {
 201                 // these are not places, so we need to make a temporary.
 202                 debug_assert!(match Category::of(&expr.kind) {
 203                     Some(Category::Place) => false,
 204                     _ => true,
 205                 });
 206                 let temp =
 207                     unpack!(block = this.as_temp(block, expr.temp_lifetime, expr, mutability));
 208                 block.and(Place::Local(temp))
 209             }
 210         }
 211     }
 212 }