src/librustc_mir/build/expr/as_rvalue.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 rustc_data_structures::fnv::FnvHashMap;
  14
  15 use build::{BlockAnd, BlockAndExtension, Builder};
  16 use build::expr::category::{Category, RvalueFunc};
  17 use hair::*;
  18 use rustc::mir::repr::*;
  19
  20 impl<'a,'tcx> Builder<'a,'tcx> {
  21     /// Compile `expr`, yielding an rvalue.
  22     pub fn as_rvalue<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Rvalue<'tcx>>
  23         where M: Mirror<'tcx, Output = Expr<'tcx>>
  24     {
  25         let expr = self.hir.mirror(expr);
  26         self.expr_as_rvalue(block, expr)
  27     }
  28
  29     fn expr_as_rvalue(&mut self,
  30                       mut block: BasicBlock,
  31                       expr: Expr<'tcx>)
  32                       -> BlockAnd<Rvalue<'tcx>> {
  33         debug!("expr_as_rvalue(block={:?}, expr={:?})", block, expr);
  34
  35         let this = self;
  36         let expr_span = expr.span;
  37
  38         match expr.kind {
  39             ExprKind::Scope { extent, value } => {
  40                 this.in_scope(extent, block, |this| this.as_rvalue(block, value))
  41             }
  42             ExprKind::InlineAsm { asm } => {
  43                 block.and(Rvalue::InlineAsm(asm.clone()))
  44             }
  45             ExprKind::Repeat { value, count } => {
  46                 let value_operand = unpack!(block = this.as_operand(block, value));
  47                 let count = this.as_constant(count);
  48                 block.and(Rvalue::Repeat(value_operand, count))
  49             }
  50             ExprKind::Borrow { region, borrow_kind, arg } => {
  51                 let arg_lvalue = unpack!(block = this.as_lvalue(block, arg));
  52                 block.and(Rvalue::Ref(region, borrow_kind, arg_lvalue))
  53             }
  54             ExprKind::Binary { op, lhs, rhs } => {
  55                 let lhs = unpack!(block = this.as_operand(block, lhs));
  56                 let rhs = unpack!(block = this.as_operand(block, rhs));
  57                 block.and(Rvalue::BinaryOp(op, lhs, rhs))
  58             }
  59             ExprKind::Unary { op, arg } => {
  60                 let arg = unpack!(block = this.as_operand(block, arg));
  61                 block.and(Rvalue::UnaryOp(op, arg))
  62             }
  63             ExprKind::Box { value } => {
  64                 let value = this.hir.mirror(value);
  65                 let value_ty = value.ty.clone();
  66                 let result = this.temp(value_ty.clone());
  67
  68                 // to start, malloc some memory of suitable type (thus far, uninitialized):
  69                 let rvalue = Rvalue::Box(value.ty.clone());
  70                 this.cfg.push_assign(block, expr_span, &result, rvalue);
  71
  72                 // schedule a shallow free of that memory, lest we unwind:
  73                 let extent = this.extent_of_innermost_scope();
  74                 this.schedule_drop(expr_span, extent, DropKind::Free, &result, value_ty);
  75
  76                 // initialize the box contents:
  77                 let contents = result.clone().deref();
  78                 unpack!(block = this.into(&contents, block, value));
  79
  80                 // now that the result is fully initialized, cancel the drop
  81                 // by "using" the result (which is linear):
  82                 block.and(Rvalue::Use(Operand::Consume(result)))
  83             }
  84             ExprKind::Cast { source } => {
  85                 let source = unpack!(block = this.as_operand(block, source));
  86                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
  87             }
  88             ExprKind::ReifyFnPointer { source } => {
  89                 let source = unpack!(block = this.as_operand(block, source));
  90                 block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
  91             }
  92             ExprKind::UnsafeFnPointer { source } => {
  93                 let source = unpack!(block = this.as_operand(block, source));
  94                 block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
  95             }
  96             ExprKind::Unsize { source } => {
  97                 let source = unpack!(block = this.as_operand(block, source));
  98                 block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
  99             }
 100             ExprKind::Vec { fields } => {
 101                 // (*) We would (maybe) be closer to trans if we
 102                 // handled this and other aggregate cases via
 103                 // `into()`, not `as_rvalue` -- in that case, instead
 104                 // of generating
 105                 //
 106                 //     let tmp1 = ...1;
 107                 //     let tmp2 = ...2;
 108                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 109                 //
 110                 // we could just generate
 111                 //
 112                 //     dest.f = ...1;
 113                 //     dest.g = ...2;
 114                 //
 115                 // The problem is that then we would need to:
 116                 //
 117                 // (a) have a more complex mechanism for handling
 118                 //     partial cleanup;
 119                 // (b) distinguish the case where the type `Foo` has a
 120                 //     destructor, in which case creating an instance
 121                 //     as a whole "arms" the destructor, and you can't
 122                 //     write individual fields; and,
 123                 // (c) handle the case where the type Foo has no
 124                 //     fields. We don't want `let x: ();` to compile
 125                 //     to the same MIR as `let x = ();`.
 126
 127                 // first process the set of fields
 128                 let fields: Vec<_> =
 129                     fields.into_iter()
 130                           .map(|f| unpack!(block = this.as_operand(block, f)))
 131                           .collect();
 132
 133                 block.and(Rvalue::Aggregate(AggregateKind::Vec, fields))
 134             }
 135             ExprKind::Tuple { fields } => { // see (*) above
 136                 // first process the set of fields
 137                 let fields: Vec<_> =
 138                     fields.into_iter()
 139                           .map(|f| unpack!(block = this.as_operand(block, f)))
 140                           .collect();
 141
 142                 block.and(Rvalue::Aggregate(AggregateKind::Tuple, fields))
 143             }
 144             ExprKind::Closure { closure_id, substs, upvars } => { // see (*) above
 145                 let upvars =
 146                     upvars.into_iter()
 147                           .map(|upvar| unpack!(block = this.as_operand(block, upvar)))
 148                           .collect();
 149                 block.and(Rvalue::Aggregate(AggregateKind::Closure(closure_id, substs), upvars))
 150             }
 151             ExprKind::Adt { adt_def, variant_index, substs, fields, base } => { // see (*) above
 152                 // first process the set of fields that were provided
 153                 // (evaluating them in order given by user)
 154                 let fields_map: FnvHashMap<_, _> =
 155                     fields.into_iter()
 156                           .map(|f| (f.name, unpack!(block = this.as_operand(block, f.expr))))
 157                           .collect();
 158
 159                 // if base expression is given, evaluate it now
 160                 let base = base.map(|base| unpack!(block = this.as_lvalue(block, base)));
 161
 162                 // get list of all fields that we will need
 163                 let field_names = this.hir.all_fields(adt_def, variant_index);
 164
 165                 // for the actual values we use, take either the
 166                 // expr the user specified or, if they didn't
 167                 // specify something for this field name, create a
 168                 // path relative to the base (which must have been
 169                 // supplied, or the IR is internally
 170                 // inconsistent).
 171                 let fields: Vec<_> =
 172                     field_names.into_iter()
 173                                .map(|n| match fields_map.get(&n) {
 174                                    Some(v) => v.clone(),
 175                                    None => Operand::Consume(base.clone().unwrap().field(n)),
 176                                })
 177                                .collect();
 178
 179                 block.and(Rvalue::Aggregate(AggregateKind::Adt(adt_def, variant_index, substs),
 180                                             fields))
 181             }
 182             ExprKind::Literal { .. } |
 183             ExprKind::Block { .. } |
 184             ExprKind::Match { .. } |
 185             ExprKind::If { .. } |
 186             ExprKind::Loop { .. } |
 187             ExprKind::LogicalOp { .. } |
 188             ExprKind::Call { .. } |
 189             ExprKind::Field { .. } |
 190             ExprKind::Deref { .. } |
 191             ExprKind::Index { .. } |
 192             ExprKind::VarRef { .. } |
 193             ExprKind::SelfRef |
 194             ExprKind::Assign { .. } |
 195             ExprKind::AssignOp { .. } |
 196             ExprKind::Break { .. } |
 197             ExprKind::Continue { .. } |
 198             ExprKind::Return { .. } |
 199             ExprKind::StaticRef { .. } => {
 200                 // these do not have corresponding `Rvalue` variants,
 201                 // so make an operand and then return that
 202                 debug_assert!(match Category::of(&expr.kind) {
 203                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 204                     _ => true,
 205                 });
 206                 let operand = unpack!(block = this.as_operand(block, expr));
 207                 block.and(Rvalue::Use(operand))
 208             }
 209         }
 210     }
 211 }