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