src/librustc_mir/build/expr/as_rvalue.rs

   1 //! See docs in `build/expr/mod.rs`.
   2
   3 use rustc_index::vec::Idx;
   4
   5 use crate::build::expr::category::{Category, RvalueFunc};
   6 use crate::build::{BlockAnd, BlockAndExtension, Builder};
   7 use crate::hair::*;
   8 use rustc::middle::region;
   9 use rustc::mir::interpret::PanicInfo;
  10 use rustc::mir::*;
  11 use rustc::ty::{self, Ty, UpvarSubsts};
  12 use rustc_span::Span;
  13
  14 impl<'a, 'tcx> Builder<'a, 'tcx> {
  15     /// Returns an rvalue suitable for use until the end of the current
  16     /// scope expression.
  17     ///
  18     /// The operand returned from this function will *not be valid* after
  19     /// an ExprKind::Scope is passed, so please do *not* return it from
  20     /// functions to avoid bad miscompiles.
  21     pub fn as_local_rvalue<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Rvalue<'tcx>>
  22     where
  23         M: Mirror<'tcx, Output = Expr<'tcx>>,
  24     {
  25         let local_scope = self.local_scope();
  26         self.as_rvalue(block, local_scope, expr)
  27     }
  28
  29     /// Compile `expr`, yielding an rvalue.
  30     fn as_rvalue<M>(
  31         &mut self,
  32         block: BasicBlock,
  33         scope: Option<region::Scope>,
  34         expr: M,
  35     ) -> BlockAnd<Rvalue<'tcx>>
  36     where
  37         M: Mirror<'tcx, Output = Expr<'tcx>>,
  38     {
  39         let expr = self.hir.mirror(expr);
  40         self.expr_as_rvalue(block, scope, expr)
  41     }
  42
  43     fn expr_as_rvalue(
  44         &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, |this| this.as_rvalue(block, scope, value))
  59             }
  60             ExprKind::Repeat { value, count } => {
  61                 let value_operand = unpack!(block = this.as_operand(block, scope, value));
  62                 block.and(Rvalue::Repeat(value_operand, count))
  63             }
  64             ExprKind::Binary { op, lhs, rhs } => {
  65                 let lhs = unpack!(block = this.as_operand(block, scope, lhs));
  66                 let rhs = unpack!(block = this.as_operand(block, scope, rhs));
  67                 this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs)
  68             }
  69             ExprKind::Unary { op, arg } => {
  70                 let arg = unpack!(block = this.as_operand(block, scope, arg));
  71                 // Check for -MIN on signed integers
  72                 if this.hir.check_overflow() && op == UnOp::Neg && expr.ty.is_signed() {
  73                     let bool_ty = this.hir.bool_ty();
  74
  75                     let minval = this.minval_literal(expr_span, expr.ty);
  76                     let is_min = this.temp(bool_ty, expr_span);
  77
  78                     this.cfg.push_assign(
  79                         block,
  80                         source_info,
  81                         &is_min,
  82                         Rvalue::BinaryOp(BinOp::Eq, arg.to_copy(), minval),
  83                     );
  84
  85                     block = this.assert(
  86                         block,
  87                         Operand::Move(is_min),
  88                         false,
  89                         PanicInfo::OverflowNeg,
  90                         expr_span,
  91                     );
  92                 }
  93                 block.and(Rvalue::UnaryOp(op, arg))
  94             }
  95             ExprKind::Box { value } => {
  96                 let value = this.hir.mirror(value);
  97                 // The `Box<T>` temporary created here is not a part of the HIR,
  98                 // and therefore is not considered during generator OIBIT
  99                 // determination. See the comment about `box` at `yield_in_scope`.
 100                 let result = this.local_decls.push(LocalDecl::new_internal(expr.ty, expr_span));
 101                 this.cfg.push(
 102                     block,
 103                     Statement { source_info, kind: StatementKind::StorageLive(result) },
 104                 );
 105                 if let Some(scope) = scope {
 106                     // schedule a shallow free of that memory, lest we unwind:
 107                     this.schedule_drop_storage_and_value(expr_span, scope, result);
 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::from(result), box_);
 113
 114                 // initialize the box contents:
 115                 unpack!(
 116                     block = this.into(
 117                         &this.hir.tcx().mk_place_deref(Place::from(result)),
 118                         block,
 119                         value
 120                     )
 121                 );
 122                 block.and(Rvalue::Use(Operand::Move(Place::from(result))))
 123             }
 124             ExprKind::Cast { source } => {
 125                 let source = unpack!(block = this.as_operand(block, scope, source));
 126                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 127             }
 128             ExprKind::Pointer { cast, source } => {
 129                 let source = unpack!(block = this.as_operand(block, scope, source));
 130                 block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty))
 131             }
 132             ExprKind::Array { fields } => {
 133                 // (*) We would (maybe) be closer to codegen if we
 134                 // handled this and other aggregate cases via
 135                 // `into()`, not `as_rvalue` -- in that case, instead
 136                 // of generating
 137                 //
 138                 //     let tmp1 = ...1;
 139                 //     let tmp2 = ...2;
 140                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 141                 //
 142                 // we could just generate
 143                 //
 144                 //     dest.f = ...1;
 145                 //     dest.g = ...2;
 146                 //
 147                 // The problem is that then we would need to:
 148                 //
 149                 // (a) have a more complex mechanism for handling
 150                 //     partial cleanup;
 151                 // (b) distinguish the case where the type `Foo` has a
 152                 //     destructor, in which case creating an instance
 153                 //     as a whole "arms" the destructor, and you can't
 154                 //     write individual fields; and,
 155                 // (c) handle the case where the type Foo has no
 156                 //     fields. We don't want `let x: ();` to compile
 157                 //     to the same MIR as `let x = ();`.
 158
 159                 // first process the set of fields
 160                 let el_ty = expr.ty.sequence_element_type(this.hir.tcx());
 161                 let fields: Vec<_> = fields
 162                     .into_iter()
 163                     .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 164                     .collect();
 165
 166                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 167             }
 168             ExprKind::Tuple { fields } => {
 169                 // see (*) above
 170                 // first process the set of fields
 171                 let fields: Vec<_> = fields
 172                     .into_iter()
 173                     .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 174                     .collect();
 175
 176                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 177             }
 178             ExprKind::Closure { closure_id, substs, upvars, movability } => {
 179                 // see (*) above
 180                 let operands: Vec<_> = upvars
 181                     .into_iter()
 182                     .map(|upvar| {
 183                         let upvar = this.hir.mirror(upvar);
 184                         match Category::of(&upvar.kind) {
 185                             // Use as_place to avoid creating a temporary when
 186                             // moving a variable into a closure, so that
 187                             // borrowck knows which variables to mark as being
 188                             // used as mut. This is OK here because the upvar
 189                             // expressions have no side effects and act on
 190                             // disjoint places.
 191                             // This occurs when capturing by copy/move, while
 192                             // by reference captures use as_operand
 193                             Some(Category::Place) => {
 194                                 let place = unpack!(block = this.as_place(block, upvar));
 195                                 this.consume_by_copy_or_move(place)
 196                             }
 197                             _ => {
 198                                 // Turn mutable borrow captures into unique
 199                                 // borrow captures when capturing an immutable
 200                                 // variable. This is sound because the mutation
 201                                 // that caused the capture will cause an error.
 202                                 match upvar.kind {
 203                                     ExprKind::Borrow {
 204                                         borrow_kind:
 205                                             BorrowKind::Mut { allow_two_phase_borrow: false },
 206                                         arg,
 207                                     } => unpack!(
 208                                         block = this.limit_capture_mutability(
 209                                             upvar.span, upvar.ty, scope, block, arg,
 210                                         )
 211                                     ),
 212                                     _ => unpack!(block = this.as_operand(block, scope, upvar)),
 213                                 }
 214                             }
 215                         }
 216                     })
 217                     .collect();
 218                 let result = match substs {
 219                     UpvarSubsts::Generator(substs) => {
 220                         // We implicitly set the discriminant to 0. See
 221                         // librustc_mir/transform/deaggregator.rs for details.
 222                         let movability = movability.unwrap();
 223                         box AggregateKind::Generator(closure_id, substs, movability)
 224                     }
 225                     UpvarSubsts::Closure(substs) => box AggregateKind::Closure(closure_id, substs),
 226                 };
 227                 block.and(Rvalue::Aggregate(result, operands))
 228             }
 229             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 230                 block = unpack!(this.stmt_expr(block, expr, None));
 231                 block.and(this.unit_rvalue())
 232             }
 233             ExprKind::Yield { value } => {
 234                 let value = unpack!(block = this.as_operand(block, scope, value));
 235                 let resume = this.cfg.start_new_block();
 236                 let cleanup = this.generator_drop_cleanup();
 237                 this.cfg.terminate(
 238                     block,
 239                     source_info,
 240                     TerminatorKind::Yield { value: value, resume: resume, drop: cleanup },
 241                 );
 242                 resume.and(this.unit_rvalue())
 243             }
 244             ExprKind::Literal { .. }
 245             | ExprKind::StaticRef { .. }
 246             | ExprKind::Block { .. }
 247             | ExprKind::Match { .. }
 248             | ExprKind::NeverToAny { .. }
 249             | ExprKind::Use { .. }
 250             | ExprKind::Borrow { .. }
 251             | ExprKind::AddressOf { .. }
 252             | ExprKind::Adt { .. }
 253             | ExprKind::Loop { .. }
 254             | ExprKind::LogicalOp { .. }
 255             | ExprKind::Call { .. }
 256             | ExprKind::Field { .. }
 257             | ExprKind::Deref { .. }
 258             | ExprKind::Index { .. }
 259             | ExprKind::VarRef { .. }
 260             | ExprKind::SelfRef
 261             | ExprKind::Break { .. }
 262             | ExprKind::Continue { .. }
 263             | ExprKind::Return { .. }
 264             | ExprKind::InlineAsm { .. }
 265             | ExprKind::PlaceTypeAscription { .. }
 266             | ExprKind::ValueTypeAscription { .. } => {
 267                 // these do not have corresponding `Rvalue` variants,
 268                 // so make an operand and then return that
 269                 debug_assert!(match Category::of(&expr.kind) {
 270                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 271                     _ => true,
 272                 });
 273                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 274                 block.and(Rvalue::Use(operand))
 275             }
 276         }
 277     }
 278
 279     pub fn build_binary_op(
 280         &mut self,
 281         mut block: BasicBlock,
 282         op: BinOp,
 283         span: Span,
 284         ty: Ty<'tcx>,
 285         lhs: Operand<'tcx>,
 286         rhs: Operand<'tcx>,
 287     ) -> BlockAnd<Rvalue<'tcx>> {
 288         let source_info = self.source_info(span);
 289         let bool_ty = self.hir.bool_ty();
 290         if self.hir.check_overflow() && op.is_checkable() && ty.is_integral() {
 291             let result_tup = self.hir.tcx().intern_tup(&[ty, bool_ty]);
 292             let result_value = self.temp(result_tup, span);
 293
 294             self.cfg.push_assign(
 295                 block,
 296                 source_info,
 297                 &result_value,
 298                 Rvalue::CheckedBinaryOp(op, lhs, rhs),
 299             );
 300             let val_fld = Field::new(0);
 301             let of_fld = Field::new(1);
 302
 303             let tcx = self.hir.tcx();
 304             let val = tcx.mk_place_field(result_value.clone(), val_fld, ty);
 305             let of = tcx.mk_place_field(result_value, of_fld, bool_ty);
 306
 307             let err = PanicInfo::Overflow(op);
 308
 309             block = self.assert(block, Operand::Move(of), false, err, span);
 310
 311             block.and(Rvalue::Use(Operand::Move(val)))
 312         } else {
 313             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 314                 // Checking division and remainder is more complex, since we 1. always check
 315                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 316
 317                 let zero_err = if op == BinOp::Div {
 318                     PanicInfo::DivisionByZero
 319                 } else {
 320                     PanicInfo::RemainderByZero
 321                 };
 322                 let overflow_err = PanicInfo::Overflow(op);
 323
 324                 // Check for / 0
 325                 let is_zero = self.temp(bool_ty, span);
 326                 let zero = self.zero_literal(span, ty);
 327                 self.cfg.push_assign(
 328                     block,
 329                     source_info,
 330                     &is_zero,
 331                     Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), zero),
 332                 );
 333
 334                 block = self.assert(block, Operand::Move(is_zero), false, zero_err, span);
 335
 336                 // We only need to check for the overflow in one case:
 337                 // MIN / -1, and only for signed values.
 338                 if ty.is_signed() {
 339                     let neg_1 = self.neg_1_literal(span, ty);
 340                     let min = self.minval_literal(span, ty);
 341
 342                     let is_neg_1 = self.temp(bool_ty, span);
 343                     let is_min = self.temp(bool_ty, span);
 344                     let of = self.temp(bool_ty, span);
 345
 346                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 347
 348                     self.cfg.push_assign(
 349                         block,
 350                         source_info,
 351                         &is_neg_1,
 352                         Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), neg_1),
 353                     );
 354                     self.cfg.push_assign(
 355                         block,
 356                         source_info,
 357                         &is_min,
 358                         Rvalue::BinaryOp(BinOp::Eq, lhs.to_copy(), min),
 359                     );
 360
 361                     let is_neg_1 = Operand::Move(is_neg_1);
 362                     let is_min = Operand::Move(is_min);
 363                     self.cfg.push_assign(
 364                         block,
 365                         source_info,
 366                         &of,
 367                         Rvalue::BinaryOp(BinOp::BitAnd, is_neg_1, is_min),
 368                     );
 369
 370                     block = self.assert(block, Operand::Move(of), false, overflow_err, span);
 371                 }
 372             }
 373
 374             block.and(Rvalue::BinaryOp(op, lhs, rhs))
 375         }
 376     }
 377
 378     fn limit_capture_mutability(
 379         &mut self,
 380         upvar_span: Span,
 381         upvar_ty: Ty<'tcx>,
 382         temp_lifetime: Option<region::Scope>,
 383         mut block: BasicBlock,
 384         arg: ExprRef<'tcx>,
 385     ) -> BlockAnd<Operand<'tcx>> {
 386         let this = self;
 387
 388         let source_info = this.source_info(upvar_span);
 389         let temp = this.local_decls.push(LocalDecl::new_temp(upvar_ty, upvar_span));
 390
 391         this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) });
 392
 393         let arg_place = unpack!(block = this.as_place(block, arg));
 394
 395         let mutability = match arg_place.as_ref() {
 396             PlaceRef { base: &PlaceBase::Local(local), projection: &[] } => {
 397                 this.local_decls[local].mutability
 398             }
 399             PlaceRef { base: &PlaceBase::Local(local), projection: &[ProjectionElem::Deref] } => {
 400                 debug_assert!(
 401                     this.local_decls[local].is_ref_for_guard(),
 402                     "Unexpected capture place",
 403                 );
 404                 this.local_decls[local].mutability
 405             }
 406             PlaceRef {
 407                 ref base,
 408                 projection: &[ref proj_base @ .., ProjectionElem::Field(upvar_index, _)],
 409             }
 410             | PlaceRef {
 411                 ref base,
 412                 projection:
 413                     &[ref proj_base @ .., ProjectionElem::Field(upvar_index, _), ProjectionElem::Deref],
 414             } => {
 415                 let place = PlaceRef { base, projection: proj_base };
 416
 417                 // Not projected from the implicit `self` in a closure.
 418                 debug_assert!(
 419                     match place.local_or_deref_local() {
 420                         Some(local) => local == Local::new(1),
 421                         None => false,
 422                     },
 423                     "Unexpected capture place"
 424                 );
 425                 // Not in a closure
 426                 debug_assert!(
 427                     this.upvar_mutbls.len() > upvar_index.index(),
 428                     "Unexpected capture place"
 429                 );
 430                 this.upvar_mutbls[upvar_index.index()]
 431             }
 432             _ => bug!("Unexpected capture place"),
 433         };
 434
 435         let borrow_kind = match mutability {
 436             Mutability::Not => BorrowKind::Unique,
 437             Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
 438         };
 439
 440         this.cfg.push_assign(
 441             block,
 442             source_info,
 443             &Place::from(temp),
 444             Rvalue::Ref(this.hir.tcx().lifetimes.re_erased, borrow_kind, arg_place),
 445         );
 446
 447         // In constants, temp_lifetime is None. We should not need to drop
 448         // anything because no values with a destructor can be created in
 449         // a constant at this time, even if the type may need dropping.
 450         if let Some(temp_lifetime) = temp_lifetime {
 451             this.schedule_drop_storage_and_value(upvar_span, temp_lifetime, temp);
 452         }
 453
 454         block.and(Operand::Move(Place::from(temp)))
 455     }
 456
 457     // Helper to get a `-1` value of the appropriate type
 458     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 459         let param_ty = ty::ParamEnv::empty().and(ty);
 460         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 461         let n = (!0u128) >> (128 - bits);
 462         let literal = ty::Const::from_bits(self.hir.tcx(), n, param_ty);
 463
 464         self.literal_operand(span, literal)
 465     }
 466
 467     // Helper to get the minimum value of the appropriate type
 468     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 469         assert!(ty.is_signed());
 470         let param_ty = ty::ParamEnv::empty().and(ty);
 471         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 472         let n = 1 << (bits - 1);
 473         let literal = ty::Const::from_bits(self.hir.tcx(), n, param_ty);
 474
 475         self.literal_operand(span, literal)
 476     }
 477 }