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 syntax_pos::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!(
  50             "expr_as_rvalue(block={:?}, scope={:?}, expr={:?})",
  51             block, scope, expr
  52         );
  53
  54         let this = self;
  55         let expr_span = expr.span;
  56         let source_info = this.source_info(expr_span);
  57
  58         match expr.kind {
  59             ExprKind::Scope {
  60                 region_scope,
  61                 lint_level,
  62                 value,
  63             } => {
  64                 let region_scope = (region_scope, source_info);
  65                 this.in_scope(region_scope, lint_level, |this| {
  66                     this.as_rvalue(block, scope, value)
  67                 })
  68             }
  69             ExprKind::Repeat { value, count } => {
  70                 let value_operand = unpack!(block = this.as_operand(block, scope, value));
  71                 block.and(Rvalue::Repeat(value_operand, count))
  72             }
  73             ExprKind::Binary { op, lhs, rhs } => {
  74                 let lhs = unpack!(block = this.as_operand(block, scope, lhs));
  75                 let rhs = unpack!(block = this.as_operand(block, scope, rhs));
  76                 this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs)
  77             }
  78             ExprKind::Unary { op, arg } => {
  79                 let arg = unpack!(block = this.as_operand(block, scope, arg));
  80                 // Check for -MIN on signed integers
  81                 if this.hir.check_overflow() && op == UnOp::Neg && expr.ty.is_signed() {
  82                     let bool_ty = this.hir.bool_ty();
  83
  84                     let minval = this.minval_literal(expr_span, expr.ty);
  85                     let is_min = this.temp(bool_ty, expr_span);
  86
  87                     this.cfg.push_assign(
  88                         block,
  89                         source_info,
  90                         &is_min,
  91                         Rvalue::BinaryOp(BinOp::Eq, arg.to_copy(), minval),
  92                     );
  93
  94                     block = this.assert(
  95                         block,
  96                         Operand::Move(is_min),
  97                         false,
  98                         PanicInfo::OverflowNeg,
  99                         expr_span,
 100                     );
 101                 }
 102                 block.and(Rvalue::UnaryOp(op, arg))
 103             }
 104             ExprKind::Box { value } => {
 105                 let value = this.hir.mirror(value);
 106                 // The `Box<T>` temporary created here is not a part of the HIR,
 107                 // and therefore is not considered during generator OIBIT
 108                 // determination. See the comment about `box` at `yield_in_scope`.
 109                 let result = this
 110                     .local_decls
 111                     .push(LocalDecl::new_internal(expr.ty, expr_span));
 112                 this.cfg.push(
 113                     block,
 114                     Statement {
 115                         source_info,
 116                         kind: StatementKind::StorageLive(result),
 117                     },
 118                 );
 119                 if let Some(scope) = scope {
 120                     // schedule a shallow free of that memory, lest we unwind:
 121                     this.schedule_drop_storage_and_value(
 122                         expr_span,
 123                         scope,
 124                         result,
 125                     );
 126                 }
 127
 128                 // malloc some memory of suitable type (thus far, uninitialized):
 129                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
 130                 this.cfg
 131                     .push_assign(block, source_info, &Place::from(result), box_);
 132
 133                 // initialize the box contents:
 134                 unpack!(
 135                     block = this.into(
 136                         &this.hir.tcx().mk_place_deref(Place::from(result)),
 137                         block, value
 138                     )
 139                 );
 140                 block.and(Rvalue::Use(Operand::Move(Place::from(result))))
 141             }
 142             ExprKind::Cast { source } => {
 143                 let source = unpack!(block = this.as_operand(block, scope, source));
 144                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 145             }
 146             ExprKind::Pointer { cast, source } => {
 147                 let source = unpack!(block = this.as_operand(block, scope, source));
 148                 block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty))
 149             }
 150             ExprKind::Array { fields } => {
 151                 // (*) We would (maybe) be closer to codegen if we
 152                 // handled this and other aggregate cases via
 153                 // `into()`, not `as_rvalue` -- in that case, instead
 154                 // of generating
 155                 //
 156                 //     let tmp1 = ...1;
 157                 //     let tmp2 = ...2;
 158                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 159                 //
 160                 // we could just generate
 161                 //
 162                 //     dest.f = ...1;
 163                 //     dest.g = ...2;
 164                 //
 165                 // The problem is that then we would need to:
 166                 //
 167                 // (a) have a more complex mechanism for handling
 168                 //     partial cleanup;
 169                 // (b) distinguish the case where the type `Foo` has a
 170                 //     destructor, in which case creating an instance
 171                 //     as a whole "arms" the destructor, and you can't
 172                 //     write individual fields; and,
 173                 // (c) handle the case where the type Foo has no
 174                 //     fields. We don't want `let x: ();` to compile
 175                 //     to the same MIR as `let x = ();`.
 176
 177                 // first process the set of fields
 178                 let el_ty = expr.ty.sequence_element_type(this.hir.tcx());
 179                 let fields: Vec<_> = fields
 180                     .into_iter()
 181                     .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 182                     .collect();
 183
 184                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 185             }
 186             ExprKind::Tuple { fields } => {
 187                 // see (*) above
 188                 // first process the set of fields
 189                 let fields: Vec<_> = fields
 190                     .into_iter()
 191                     .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 192                     .collect();
 193
 194                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 195             }
 196             ExprKind::Closure {
 197                 closure_id,
 198                 substs,
 199                 upvars,
 200                 movability,
 201             } => {
 202                 // see (*) above
 203                 let operands: Vec<_> = upvars
 204                     .into_iter()
 205                     .map(|upvar| {
 206                         let upvar = this.hir.mirror(upvar);
 207                         match Category::of(&upvar.kind) {
 208                             // Use as_place to avoid creating a temporary when
 209                             // moving a variable into a closure, so that
 210                             // borrowck knows which variables to mark as being
 211                             // used as mut. This is OK here because the upvar
 212                             // expressions have no side effects and act on
 213                             // disjoint places.
 214                             // This occurs when capturing by copy/move, while
 215                             // by reference captures use as_operand
 216                             Some(Category::Place) => {
 217                                 let place = unpack!(block = this.as_place(block, upvar));
 218                                 this.consume_by_copy_or_move(place)
 219                             }
 220                             _ => {
 221                                 // Turn mutable borrow captures into unique
 222                                 // borrow captures when capturing an immutable
 223                                 // variable. This is sound because the mutation
 224                                 // that caused the capture will cause an error.
 225                                 match upvar.kind {
 226                                     ExprKind::Borrow {
 227                                         borrow_kind:
 228                                             BorrowKind::Mut {
 229                                                 allow_two_phase_borrow: false,
 230                                             },
 231                                         arg,
 232                                     } => unpack!(
 233                                         block = this.limit_capture_mutability(
 234                                             upvar.span, upvar.ty, scope, block, arg,
 235                                         )
 236                                     ),
 237                                     _ => unpack!(block = this.as_operand(block, scope, upvar)),
 238                                 }
 239                             }
 240                         }
 241                     }).collect();
 242                 let result = match substs {
 243                     UpvarSubsts::Generator(substs) => {
 244                         // We implicitly set the discriminant to 0. See
 245                         // librustc_mir/transform/deaggregator.rs for details.
 246                         let movability = movability.unwrap();
 247                         box AggregateKind::Generator(closure_id, substs, movability)
 248                     }
 249                     UpvarSubsts::Closure(substs) => box AggregateKind::Closure(closure_id, substs),
 250                 };
 251                 block.and(Rvalue::Aggregate(result, operands))
 252             }
 253             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 254                 block = unpack!(this.stmt_expr(block, expr, None));
 255                 block.and(this.unit_rvalue())
 256             }
 257             ExprKind::Yield { value } => {
 258                 let value = unpack!(block = this.as_operand(block, scope, value));
 259                 let resume = this.cfg.start_new_block();
 260                 let cleanup = this.generator_drop_cleanup();
 261                 this.cfg.terminate(
 262                     block,
 263                     source_info,
 264                     TerminatorKind::Yield {
 265                         value: value,
 266                         resume: resume,
 267                         drop: cleanup,
 268                     },
 269                 );
 270                 resume.and(this.unit_rvalue())
 271             }
 272             ExprKind::Literal { .. }
 273             | ExprKind::StaticRef { .. }
 274             | ExprKind::Block { .. }
 275             | ExprKind::Match { .. }
 276             | ExprKind::NeverToAny { .. }
 277             | ExprKind::Use { .. }
 278             | ExprKind::Borrow { .. }
 279             | ExprKind::Adt { .. }
 280             | ExprKind::Loop { .. }
 281             | ExprKind::LogicalOp { .. }
 282             | ExprKind::Call { .. }
 283             | ExprKind::Field { .. }
 284             | ExprKind::Deref { .. }
 285             | ExprKind::Index { .. }
 286             | ExprKind::VarRef { .. }
 287             | ExprKind::SelfRef
 288             | ExprKind::Break { .. }
 289             | ExprKind::Continue { .. }
 290             | ExprKind::Return { .. }
 291             | ExprKind::InlineAsm { .. }
 292             | ExprKind::PlaceTypeAscription { .. }
 293             | ExprKind::ValueTypeAscription { .. } => {
 294                 // these do not have corresponding `Rvalue` variants,
 295                 // so make an operand and then return that
 296                 debug_assert!(match Category::of(&expr.kind) {
 297                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 298                     _ => true,
 299                 });
 300                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 301                 block.and(Rvalue::Use(operand))
 302             }
 303         }
 304     }
 305
 306     pub fn build_binary_op(
 307         &mut self,
 308         mut block: BasicBlock,
 309         op: BinOp,
 310         span: Span,
 311         ty: Ty<'tcx>,
 312         lhs: Operand<'tcx>,
 313         rhs: Operand<'tcx>,
 314     ) -> BlockAnd<Rvalue<'tcx>> {
 315         let source_info = self.source_info(span);
 316         let bool_ty = self.hir.bool_ty();
 317         if self.hir.check_overflow() && op.is_checkable() && ty.is_integral() {
 318             let result_tup = self.hir.tcx().intern_tup(&[ty, bool_ty]);
 319             let result_value = self.temp(result_tup, span);
 320
 321             self.cfg.push_assign(
 322                 block,
 323                 source_info,
 324                 &result_value,
 325                 Rvalue::CheckedBinaryOp(op, lhs, rhs),
 326             );
 327             let val_fld = Field::new(0);
 328             let of_fld = Field::new(1);
 329
 330             let tcx = self.hir.tcx();
 331             let val = tcx.mk_place_field(result_value.clone(), val_fld, ty);
 332             let of = tcx.mk_place_field(result_value, of_fld, bool_ty);
 333
 334             let err = PanicInfo::Overflow(op);
 335
 336             block = self.assert(block, Operand::Move(of), false, err, span);
 337
 338             block.and(Rvalue::Use(Operand::Move(val)))
 339         } else {
 340             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 341                 // Checking division and remainder is more complex, since we 1. always check
 342                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 343
 344                 let zero_err = if op == BinOp::Div {
 345                     PanicInfo::DivisionByZero
 346                 } else {
 347                     PanicInfo::RemainderByZero
 348                 };
 349                 let overflow_err = PanicInfo::Overflow(op);
 350
 351                 // Check for / 0
 352                 let is_zero = self.temp(bool_ty, span);
 353                 let zero = self.zero_literal(span, ty);
 354                 self.cfg.push_assign(
 355                     block,
 356                     source_info,
 357                     &is_zero,
 358                     Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), zero),
 359                 );
 360
 361                 block = self.assert(block, Operand::Move(is_zero), false, zero_err, span);
 362
 363                 // We only need to check for the overflow in one case:
 364                 // MIN / -1, and only for signed values.
 365                 if ty.is_signed() {
 366                     let neg_1 = self.neg_1_literal(span, ty);
 367                     let min = self.minval_literal(span, ty);
 368
 369                     let is_neg_1 = self.temp(bool_ty, span);
 370                     let is_min = self.temp(bool_ty, span);
 371                     let of = self.temp(bool_ty, span);
 372
 373                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 374
 375                     self.cfg.push_assign(
 376                         block,
 377                         source_info,
 378                         &is_neg_1,
 379                         Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), neg_1),
 380                     );
 381                     self.cfg.push_assign(
 382                         block,
 383                         source_info,
 384                         &is_min,
 385                         Rvalue::BinaryOp(BinOp::Eq, lhs.to_copy(), min),
 386                     );
 387
 388                     let is_neg_1 = Operand::Move(is_neg_1);
 389                     let is_min = Operand::Move(is_min);
 390                     self.cfg.push_assign(
 391                         block,
 392                         source_info,
 393                         &of,
 394                         Rvalue::BinaryOp(BinOp::BitAnd, is_neg_1, is_min),
 395                     );
 396
 397                     block = self.assert(block, Operand::Move(of), false, overflow_err, span);
 398                 }
 399             }
 400
 401             block.and(Rvalue::BinaryOp(op, lhs, rhs))
 402         }
 403     }
 404
 405     fn limit_capture_mutability(
 406         &mut self,
 407         upvar_span: Span,
 408         upvar_ty: Ty<'tcx>,
 409         temp_lifetime: Option<region::Scope>,
 410         mut block: BasicBlock,
 411         arg: ExprRef<'tcx>,
 412     ) -> BlockAnd<Operand<'tcx>> {
 413         let this = self;
 414
 415         let source_info = this.source_info(upvar_span);
 416         let temp = this
 417             .local_decls
 418             .push(LocalDecl::new_temp(upvar_ty, upvar_span));
 419
 420         this.cfg.push(
 421             block,
 422             Statement {
 423                 source_info,
 424                 kind: StatementKind::StorageLive(temp),
 425             },
 426         );
 427
 428         let arg_place = unpack!(block = this.as_place(block, arg));
 429
 430         let mutability = match arg_place.as_ref() {
 431             PlaceRef {
 432                 base: &PlaceBase::Local(local),
 433                 projection: &[],
 434             } => this.local_decls[local].mutability,
 435             PlaceRef {
 436                 base: &PlaceBase::Local(local),
 437                 projection: &[ProjectionElem::Deref],
 438             } => {
 439                 debug_assert!(
 440                     this.local_decls[local].is_ref_for_guard(),
 441                     "Unexpected capture place",
 442                 );
 443                 this.local_decls[local].mutability
 444             }
 445             PlaceRef {
 446                 ref base,
 447                 projection: &[ref proj_base @ .., ProjectionElem::Field(upvar_index, _)],
 448             }
 449             | PlaceRef {
 450                 ref base,
 451                 projection: &[
 452                     ref proj_base @ ..,
 453                     ProjectionElem::Field(upvar_index, _),
 454                     ProjectionElem::Deref
 455                 ],
 456             } => {
 457                 let place = PlaceRef {
 458                     base,
 459                     projection: proj_base,
 460                 };
 461
 462                 // Not projected from the implicit `self` in a closure.
 463                 debug_assert!(
 464                     match place.local_or_deref_local() {
 465                         Some(local) => local == Local::new(1),
 466                         None => false,
 467                     },
 468                     "Unexpected capture place"
 469                 );
 470                 // Not in a closure
 471                 debug_assert!(
 472                     this.upvar_mutbls.len() > upvar_index.index(),
 473                     "Unexpected capture place"
 474                 );
 475                 this.upvar_mutbls[upvar_index.index()]
 476             }
 477             _ => bug!("Unexpected capture place"),
 478         };
 479
 480         let borrow_kind = match mutability {
 481             Mutability::Not => BorrowKind::Unique,
 482             Mutability::Mut => BorrowKind::Mut {
 483                 allow_two_phase_borrow: false,
 484             },
 485         };
 486
 487         this.cfg.push_assign(
 488             block,
 489             source_info,
 490             &Place::from(temp),
 491             Rvalue::Ref(this.hir.tcx().lifetimes.re_erased, borrow_kind, arg_place),
 492         );
 493
 494         // In constants, temp_lifetime is None. We should not need to drop
 495         // anything because no values with a destructor can be created in
 496         // a constant at this time, even if the type may need dropping.
 497         if let Some(temp_lifetime) = temp_lifetime {
 498             this.schedule_drop_storage_and_value(
 499                 upvar_span,
 500                 temp_lifetime,
 501                 temp,
 502             );
 503         }
 504
 505         block.and(Operand::Move(Place::from(temp)))
 506     }
 507
 508     // Helper to get a `-1` value of the appropriate type
 509     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 510         let param_ty = ty::ParamEnv::empty().and(ty);
 511         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 512         let n = (!0u128) >> (128 - bits);
 513         let literal = ty::Const::from_bits(self.hir.tcx(), n, param_ty);
 514
 515         self.literal_operand(span, literal)
 516     }
 517
 518     // Helper to get the minimum value of the appropriate type
 519     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 520         assert!(ty.is_signed());
 521         let param_ty = ty::ParamEnv::empty().and(ty);
 522         let bits = self.hir.tcx().layout_of(param_ty).unwrap().size.bits();
 523         let n = 1 << (bits - 1);
 524         let literal = ty::Const::from_bits(self.hir.tcx(), n, param_ty);
 525
 526         self.literal_operand(span, literal)
 527     }
 528 }