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::fx::FxHashMap;
  14 use rustc_data_structures::indexed_vec::Idx;
  15
  16 use build::{BlockAnd, BlockAndExtension, Builder};
  17 use build::expr::category::{Category, RvalueFunc};
  18 use hair::*;
  19 use rustc::middle::region;
  20 use rustc::ty::{self, Ty, UpvarSubsts};
  21 use rustc::mir::*;
  22 use rustc::mir::interpret::EvalErrorKind;
  23 use syntax_pos::Span;
  24
  25 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  26     /// See comment on `as_local_operand`
  27     pub fn as_local_rvalue<M>(&mut self, block: BasicBlock, expr: M)
  28                              -> BlockAnd<Rvalue<'tcx>>
  29         where M: Mirror<'tcx, Output = Expr<'tcx>>
  30     {
  31         let local_scope = self.local_scope();
  32         self.as_rvalue(block, local_scope, expr)
  33     }
  34
  35     /// Compile `expr`, yielding an rvalue.
  36     pub fn as_rvalue<M>(&mut self, block: BasicBlock, scope: Option<region::Scope>, expr: M)
  37                         -> BlockAnd<Rvalue<'tcx>>
  38         where M: Mirror<'tcx, Output = Expr<'tcx>>
  39     {
  40         let expr = self.hir.mirror(expr);
  41         self.expr_as_rvalue(block, scope, expr)
  42     }
  43
  44     fn expr_as_rvalue(&mut self,
  45                       mut block: BasicBlock,
  46                       scope: Option<region::Scope>,
  47                       expr: Expr<'tcx>)
  48                       -> BlockAnd<Rvalue<'tcx>> {
  49         debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
  50
  51         let this = self;
  52         let expr_span = expr.span;
  53         let source_info = this.source_info(expr_span);
  54
  55         match expr.kind {
  56             ExprKind::Scope { region_scope, lint_level, value } => {
  57                 let region_scope = (region_scope, source_info);
  58                 this.in_scope(region_scope, lint_level, block,
  59                               |this| this.as_rvalue(block, scope, value))
  60             }
  61             ExprKind::Repeat { value, count } => {
  62                 let value_operand = unpack!(block = this.as_operand(block, scope, value));
  63                 block.and(Rvalue::Repeat(value_operand, count))
  64             }
  65             ExprKind::Borrow { region, borrow_kind, arg } => {
  66                 let arg_place = unpack!(block = this.as_place(block, arg));
  67                 block.and(Rvalue::Ref(region, borrow_kind, arg_place))
  68             }
  69             ExprKind::Binary { op, lhs, rhs } => {
  70                 let lhs = unpack!(block = this.as_operand(block, scope, lhs));
  71                 let rhs = unpack!(block = this.as_operand(block, scope, rhs));
  72                 this.build_binary_op(block, op, expr_span, expr.ty,
  73                                      lhs, rhs)
  74             }
  75             ExprKind::Unary { op, arg } => {
  76                 let arg = unpack!(block = this.as_operand(block, scope, arg));
  77                 // Check for -MIN on signed integers
  78                 if this.hir.check_overflow() && op == UnOp::Neg && expr.ty.is_signed() {
  79                     let bool_ty = this.hir.bool_ty();
  80
  81                     let minval = this.minval_literal(expr_span, expr.ty);
  82                     let is_min = this.temp(bool_ty, expr_span);
  83
  84                     this.cfg.push_assign(block, source_info, &is_min,
  85                                          Rvalue::BinaryOp(BinOp::Eq, arg.to_copy(), minval));
  86
  87                     block = this.assert(block, Operand::Move(is_min), false,
  88                                         EvalErrorKind::OverflowNeg, expr_span);
  89                 }
  90                 block.and(Rvalue::UnaryOp(op, arg))
  91             }
  92             ExprKind::Box { value } => {
  93                 let value = this.hir.mirror(value);
  94                 // The `Box<T>` temporary created here is not a part of the HIR,
  95                 // and therefore is not considered during generator OIBIT
  96                 // determination. See the comment about `box` at `yield_in_scope`.
  97                 let result = this.local_decls.push(
  98                     LocalDecl::new_internal(expr.ty, expr_span));
  99                 this.cfg.push(block, Statement {
 100                     source_info,
 101                     kind: StatementKind::StorageLive(result)
 102                 });
 103                 if let Some(scope) = scope {
 104                     // schedule a shallow free of that memory, lest we unwind:
 105                     this.schedule_drop_storage_and_value(
 106                         expr_span, scope, &Place::Local(result), value.ty,
 107                     );
 108                 }
 109
 110                 // malloc some memory of suitable type (thus far, uninitialized):
 111                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
 112                 this.cfg.push_assign(block, source_info, &Place::Local(result), box_);
 113
 114                 // initialize the box contents:
 115                 unpack!(block = this.into(&Place::Local(result).deref(), block, value));
 116                 block.and(Rvalue::Use(Operand::Move(Place::Local(result))))
 117             }
 118             ExprKind::Cast { source } => {
 119                 let source = this.hir.mirror(source);
 120
 121                 let source = unpack!(block = this.as_operand(block, scope, source));
 122                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 123             }
 124             ExprKind::Use { source } => {
 125                 let source = unpack!(block = this.as_operand(block, scope, source));
 126                 block.and(Rvalue::Use(source))
 127             }
 128             ExprKind::ReifyFnPointer { source } => {
 129                 let source = unpack!(block = this.as_operand(block, scope, source));
 130                 block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
 131             }
 132             ExprKind::UnsafeFnPointer { source } => {
 133                 let source = unpack!(block = this.as_operand(block, scope, source));
 134                 block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
 135             }
 136             ExprKind::ClosureFnPointer { source } => {
 137                 let source = unpack!(block = this.as_operand(block, scope, source));
 138                 block.and(Rvalue::Cast(CastKind::ClosureFnPointer, source, expr.ty))
 139             }
 140             ExprKind::Unsize { source } => {
 141                 let source = unpack!(block = this.as_operand(block, scope, source));
 142                 block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
 143             }
 144             ExprKind::Array { fields } => {
 145                 // (*) We would (maybe) be closer to codegen if we
 146                 // handled this and other aggregate cases via
 147                 // `into()`, not `as_rvalue` -- in that case, instead
 148                 // of generating
 149                 //
 150                 //     let tmp1 = ...1;
 151                 //     let tmp2 = ...2;
 152                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 153                 //
 154                 // we could just generate
 155                 //
 156                 //     dest.f = ...1;
 157                 //     dest.g = ...2;
 158                 //
 159                 // The problem is that then we would need to:
 160                 //
 161                 // (a) have a more complex mechanism for handling
 162                 //     partial cleanup;
 163                 // (b) distinguish the case where the type `Foo` has a
 164                 //     destructor, in which case creating an instance
 165                 //     as a whole "arms" the destructor, and you can't
 166                 //     write individual fields; and,
 167                 // (c) handle the case where the type Foo has no
 168                 //     fields. We don't want `let x: ();` to compile
 169                 //     to the same MIR as `let x = ();`.
 170
 171                 // first process the set of fields
 172                 let el_ty = expr.ty.sequence_element_type(this.hir.tcx());
 173                 let fields: Vec<_> =
 174                     fields.into_iter()
 175                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 176                           .collect();
 177
 178                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 179             }
 180             ExprKind::Tuple { fields } => { // see (*) above
 181                 // first process the set of fields
 182                 let fields: Vec<_> =
 183                     fields.into_iter()
 184                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 185                           .collect();
 186
 187                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 188             }
 189             ExprKind::Closure { closure_id, substs, upvars, movability } => {
 190                 // see (*) above
 191                 let mut operands: Vec<_> = upvars
 192                     .into_iter()
 193                     .map(|upvar| {
 194                         let upvar = this.hir.mirror(upvar);
 195                         match Category::of(&upvar.kind) {
 196                             // Use as_place to avoid creating a temporary when
 197                             // moving a variable into a closure, so that
 198                             // borrowck knows which variables to mark as being
 199                             // used as mut. This is OK here because the upvar
 200                             // expressions have no side effects and act on
 201                             // disjoint places.
 202                             // This occurs when capturing by copy/move, while
 203                             // by reference captures use as_operand
 204                             Some(Category::Place) => {
 205                                 let place = unpack!(block = this.as_place(block, upvar));
 206                                 this.consume_by_copy_or_move(place)
 207                             }
 208                             _ => {
 209                                 unpack!(block = this.as_operand(block, scope, upvar))
 210                             }
 211                         }
 212                     })
 213                     .collect();
 214                 let result = match substs {
 215                     UpvarSubsts::Generator(substs) => {
 216                         let movability = movability.unwrap();
 217                         // Add the state operand since it follows the upvars in the generator
 218                         // struct. See librustc_mir/transform/generator.rs for more details.
 219                         operands.push(Operand::Constant(box Constant {
 220                             span: expr_span,
 221                             ty: this.hir.tcx().types.u32,
 222                             literal: Literal::Value {
 223                                 value: ty::Const::from_bits(
 224                                     this.hir.tcx(),
 225                                     0,
 226                                     ty::ParamEnv::empty().and(this.hir.tcx().types.u32)),
 227                             },
 228                         }));
 229                         box AggregateKind::Generator(closure_id, substs, movability)
 230                     }
 231                     UpvarSubsts::Closure(substs) => {
 232                         box AggregateKind::Closure(closure_id, substs)
 233                     }
 234                 };
 235                 block.and(Rvalue::Aggregate(result, operands))
 236             }
 237             ExprKind::Adt {
 238                 adt_def, variant_index, substs, fields, base
 239             } => { // see (*) above
 240                 let is_union = adt_def.is_union();
 241                 let active_field_index = if is_union { Some(fields[0].name.index()) } else { None };
 242
 243                 // first process the set of fields that were provided
 244                 // (evaluating them in order given by user)
 245                 let fields_map: FxHashMap<_, _> = fields.into_iter()
 246                     .map(|f| (f.name, unpack!(block = this.as_operand(block, scope, f.expr))))
 247                     .collect();
 248
 249                 let field_names = this.hir.all_fields(adt_def, variant_index);
 250
 251                 let fields = if let Some(FruInfo { base, field_types }) = base {
 252                     let base = unpack!(block = this.as_place(block, base));
 253
 254                     // MIR does not natively support FRU, so for each
 255                     // base-supplied field, generate an operand that
 256                     // reads it from the base.
 257                     field_names.into_iter()
 258                         .zip(field_types.into_iter())
 259                         .map(|(n, ty)| match fields_map.get(&n) {
 260                             Some(v) => v.clone(),
 261                             None => this.consume_by_copy_or_move(base.clone().field(n, ty))
 262                         })
 263                         .collect()
 264                 } else {
 265                     field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
 266                 };
 267
 268                 let adt =
 269                     box AggregateKind::Adt(adt_def, variant_index, substs, active_field_index);
 270                 block.and(Rvalue::Aggregate(adt, fields))
 271             }
 272             ExprKind::Assign { .. } |
 273             ExprKind::AssignOp { .. } => {
 274                 block = unpack!(this.stmt_expr(block, expr));
 275                 block.and(this.unit_rvalue())
 276             }
 277             ExprKind::Yield { value } => {
 278                 let value = unpack!(block = this.as_operand(block, scope, value));
 279                 let resume = this.cfg.start_new_block();
 280                 let cleanup = this.generator_drop_cleanup();
 281                 this.cfg.terminate(block, source_info, TerminatorKind::Yield {
 282                     value: value,
 283                     resume: resume,
 284                     drop: cleanup,
 285                 });
 286                 resume.and(this.unit_rvalue())
 287             }
 288             ExprKind::Literal { .. } |
 289             ExprKind::Block { .. } |
 290             ExprKind::Match { .. } |
 291             ExprKind::If { .. } |
 292             ExprKind::NeverToAny { .. } |
 293             ExprKind::Loop { .. } |
 294             ExprKind::LogicalOp { .. } |
 295             ExprKind::Call { .. } |
 296             ExprKind::Field { .. } |
 297             ExprKind::Deref { .. } |
 298             ExprKind::Index { .. } |
 299             ExprKind::VarRef { .. } |
 300             ExprKind::SelfRef |
 301             ExprKind::Break { .. } |
 302             ExprKind::Continue { .. } |
 303             ExprKind::Return { .. } |
 304             ExprKind::InlineAsm { .. } |
 305             ExprKind::StaticRef { .. } => {
 306                 // these do not have corresponding `Rvalue` variants,
 307                 // so make an operand and then return that
 308                 debug_assert!(match Category::of(&expr.kind) {
 309                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 310                     _ => true,
 311                 });
 312                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 313                 block.and(Rvalue::Use(operand))
 314             }
 315         }
 316     }
 317
 318     pub fn build_binary_op(&mut self, mut block: BasicBlock,
 319                            op: BinOp, span: Span, ty: Ty<'tcx>,
 320                            lhs: Operand<'tcx>, rhs: Operand<'tcx>) -> BlockAnd<Rvalue<'tcx>> {
 321         let source_info = self.source_info(span);
 322         let bool_ty = self.hir.bool_ty();
 323         if self.hir.check_overflow() && op.is_checkable() && ty.is_integral() {
 324             let result_tup = self.hir.tcx().intern_tup(&[ty, bool_ty]);
 325             let result_value = self.temp(result_tup, span);
 326
 327             self.cfg.push_assign(block, source_info,
 328                                  &result_value, Rvalue::CheckedBinaryOp(op,
 329                                                                         lhs,
 330                                                                         rhs));
 331             let val_fld = Field::new(0);
 332             let of_fld = Field::new(1);
 333
 334             let val = result_value.clone().field(val_fld, ty);
 335             let of = result_value.field(of_fld, bool_ty);
 336
 337             let err = EvalErrorKind::Overflow(op);
 338
 339             block = self.assert(block, Operand::Move(of), false,
 340                                 err, span);
 341
 342             block.and(Rvalue::Use(Operand::Move(val)))
 343         } else {
 344             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 345                 // Checking division and remainder is more complex, since we 1. always check
 346                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 347
 348                 let (zero_err, overflow_err) = if op == BinOp::Div {
 349                     (EvalErrorKind::DivisionByZero,
 350                      EvalErrorKind::Overflow(op))
 351                 } else {
 352                     (EvalErrorKind::RemainderByZero,
 353                      EvalErrorKind::Overflow(op))
 354                 };
 355
 356                 // Check for / 0
 357                 let is_zero = self.temp(bool_ty, span);
 358                 let zero = self.zero_literal(span, ty);
 359                 self.cfg.push_assign(block, source_info, &is_zero,
 360                                      Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), zero));
 361
 362                 block = self.assert(block, Operand::Move(is_zero), false,
 363                                     zero_err, span);
 364
 365                 // We only need to check for the overflow in one case:
 366                 // MIN / -1, and only for signed values.
 367                 if ty.is_signed() {
 368                     let neg_1 = self.neg_1_literal(span, ty);
 369                     let min = self.minval_literal(span, ty);
 370
 371                     let is_neg_1 = self.temp(bool_ty, span);
 372                     let is_min   = self.temp(bool_ty, span);
 373                     let of       = self.temp(bool_ty, span);
 374
 375                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 376
 377                     self.cfg.push_assign(block, source_info, &is_neg_1,
 378                                          Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), neg_1));
 379                     self.cfg.push_assign(block, source_info, &is_min,
 380                                          Rvalue::BinaryOp(BinOp::Eq, lhs.to_copy(), min));
 381
 382                     let is_neg_1 = Operand::Move(is_neg_1);
 383                     let is_min = Operand::Move(is_min);
 384                     self.cfg.push_assign(block, source_info, &of,
 385                                          Rvalue::BinaryOp(BinOp::BitAnd, is_neg_1, is_min));
 386
 387                     block = self.assert(block, Operand::Move(of), false,
 388                                         overflow_err, span);
 389                 }
 390             }
 391
 392             block.and(Rvalue::BinaryOp(op, lhs, rhs))
 393         }
 394     }
 395
 396     // Helper to get a `-1` value of the appropriate type
 397     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 398         let param_ty = ty::ParamEnv::empty().and(self.hir.tcx().lift_to_global(&ty).unwrap());
 399         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 400         let n = (!0u128) >> (128 - bits);
 401         let literal = Literal::Value {
 402             value: ty::Const::from_bits(self.hir.tcx(), n, param_ty)
 403         };
 404
 405         self.literal_operand(span, ty, literal)
 406     }
 407
 408     // Helper to get the minimum value of the appropriate type
 409     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 410         assert!(ty.is_signed());
 411         let param_ty = ty::ParamEnv::empty().and(self.hir.tcx().lift_to_global(&ty).unwrap());
 412         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 413         let n = 1 << (bits - 1);
 414         let literal = Literal::Value {
 415             value: ty::Const::from_bits(self.hir.tcx(), n, param_ty)
 416         };
 417
 418         self.literal_operand(span, ty, literal)
 419     }
 420 }