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, outputs, inputs } => {
  43                 let outputs = outputs.into_iter().map(|output| {
  44                     unpack!(block = this.as_lvalue(block, output))
  45                 }).collect();
  46
  47                 let inputs = inputs.into_iter().map(|input| {
  48                     unpack!(block = this.as_operand(block, input))
  49                 }).collect();
  50
  51                 block.and(Rvalue::InlineAsm {
  52                     asm: asm.clone(),
  53                     outputs: outputs,
  54                     inputs: inputs
  55                 })
  56             }
  57             ExprKind::Repeat { value, count } => {
  58                 let value_operand = unpack!(block = this.as_operand(block, value));
  59                 block.and(Rvalue::Repeat(value_operand, count))
  60             }
  61             ExprKind::Borrow { region, borrow_kind, arg } => {
  62                 let arg_lvalue = unpack!(block = this.as_lvalue(block, arg));
  63                 block.and(Rvalue::Ref(region, borrow_kind, arg_lvalue))
  64             }
  65             ExprKind::Binary { op, lhs, rhs } => {
  66                 let lhs = unpack!(block = this.as_operand(block, lhs));
  67                 let rhs = unpack!(block = this.as_operand(block, rhs));
  68                 block.and(Rvalue::BinaryOp(op, lhs, rhs))
  69             }
  70             ExprKind::Unary { op, arg } => {
  71                 let arg = unpack!(block = this.as_operand(block, arg));
  72                 block.and(Rvalue::UnaryOp(op, arg))
  73             }
  74             ExprKind::Box { value, value_extents } => {
  75                 let value = this.hir.mirror(value);
  76                 let result = this.temp(expr.ty);
  77                 // to start, malloc some memory of suitable type (thus far, uninitialized):
  78                 this.cfg.push_assign(block, expr_span, &result, Rvalue::Box(value.ty));
  79                 this.in_scope(value_extents, block, |this| {
  80                     // schedule a shallow free of that memory, lest we unwind:
  81                     this.schedule_box_free(expr_span, value_extents, &result, value.ty);
  82                     // initialize the box contents:
  83                     unpack!(block = this.into(&result.clone().deref(), block, value));
  84                     block.and(Rvalue::Use(Operand::Consume(result)))
  85                 })
  86             }
  87             ExprKind::Cast { source } => {
  88                 let source = this.hir.mirror(source);
  89                 if source.ty == expr.ty {
  90                     this.expr_as_rvalue(block, source)
  91                 } else {
  92                     let source = unpack!(block = this.as_operand(block, source));
  93                     block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
  94                 }
  95             }
  96             ExprKind::ReifyFnPointer { source } => {
  97                 let source = unpack!(block = this.as_operand(block, source));
  98                 block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
  99             }
 100             ExprKind::UnsafeFnPointer { source } => {
 101                 let source = unpack!(block = this.as_operand(block, source));
 102                 block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
 103             }
 104             ExprKind::Unsize { source } => {
 105                 let source = unpack!(block = this.as_operand(block, source));
 106                 block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
 107             }
 108             ExprKind::Vec { fields } => {
 109                 // (*) We would (maybe) be closer to trans if we
 110                 // handled this and other aggregate cases via
 111                 // `into()`, not `as_rvalue` -- in that case, instead
 112                 // of generating
 113                 //
 114                 //     let tmp1 = ...1;
 115                 //     let tmp2 = ...2;
 116                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 117                 //
 118                 // we could just generate
 119                 //
 120                 //     dest.f = ...1;
 121                 //     dest.g = ...2;
 122                 //
 123                 // The problem is that then we would need to:
 124                 //
 125                 // (a) have a more complex mechanism for handling
 126                 //     partial cleanup;
 127                 // (b) distinguish the case where the type `Foo` has a
 128                 //     destructor, in which case creating an instance
 129                 //     as a whole "arms" the destructor, and you can't
 130                 //     write individual fields; and,
 131                 // (c) handle the case where the type Foo has no
 132                 //     fields. We don't want `let x: ();` to compile
 133                 //     to the same MIR as `let x = ();`.
 134
 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::Vec, fields))
 142             }
 143             ExprKind::Tuple { fields } => { // see (*) above
 144                 // first process the set of fields
 145                 let fields: Vec<_> =
 146                     fields.into_iter()
 147                           .map(|f| unpack!(block = this.as_operand(block, f)))
 148                           .collect();
 149
 150                 block.and(Rvalue::Aggregate(AggregateKind::Tuple, fields))
 151             }
 152             ExprKind::Closure { closure_id, substs, upvars } => { // see (*) above
 153                 let upvars =
 154                     upvars.into_iter()
 155                           .map(|upvar| unpack!(block = this.as_operand(block, upvar)))
 156                           .collect();
 157                 block.and(Rvalue::Aggregate(AggregateKind::Closure(closure_id, substs), upvars))
 158             }
 159             ExprKind::Adt {
 160                 adt_def, variant_index, substs, fields, base
 161             } => { // see (*) above
 162                 // first process the set of fields that were provided
 163                 // (evaluating them in order given by user)
 164                 let fields_map: FnvHashMap<_, _> =
 165                     fields.into_iter()
 166                           .map(|f| (f.name, unpack!(block = this.as_operand(block, f.expr))))
 167                           .collect();
 168
 169                 let field_names = this.hir.all_fields(adt_def, variant_index);
 170
 171                 let fields = if let Some(FruInfo { base, field_types }) = base {
 172                     let base = unpack!(block = this.as_lvalue(block, base));
 173
 174                     // MIR does not natively support FRU, so for each
 175                     // base-supplied field, generate an operand that
 176                     // reads it from the base.
 177                     field_names.into_iter()
 178                         .zip(field_types.into_iter())
 179                         .map(|(n, ty)| match fields_map.get(&n) {
 180                             Some(v) => v.clone(),
 181                             None => Operand::Consume(base.clone().field(n, ty))
 182                         })
 183                         .collect()
 184                 } else {
 185                     field_names.iter().map(|n| fields_map[n].clone()).collect()
 186                 };
 187
 188                 block.and(Rvalue::Aggregate(AggregateKind::Adt(adt_def, variant_index, substs),
 189                                             fields))
 190             }
 191             ExprKind::Literal { .. } |
 192             ExprKind::Block { .. } |
 193             ExprKind::Match { .. } |
 194             ExprKind::If { .. } |
 195             ExprKind::Loop { .. } |
 196             ExprKind::LogicalOp { .. } |
 197             ExprKind::Call { .. } |
 198             ExprKind::Field { .. } |
 199             ExprKind::Deref { .. } |
 200             ExprKind::Index { .. } |
 201             ExprKind::VarRef { .. } |
 202             ExprKind::SelfRef |
 203             ExprKind::Assign { .. } |
 204             ExprKind::AssignOp { .. } |
 205             ExprKind::Break { .. } |
 206             ExprKind::Continue { .. } |
 207             ExprKind::Return { .. } |
 208             ExprKind::StaticRef { .. } => {
 209                 // these do not have corresponding `Rvalue` variants,
 210                 // so make an operand and then return that
 211                 debug_assert!(match Category::of(&expr.kind) {
 212                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 213                     _ => true,
 214                 });
 215                 let operand = unpack!(block = this.as_operand(block, expr));
 216                 block.and(Rvalue::Use(operand))
 217             }
 218         }
 219     }
 220 }