compiler/rustc_mir_build/src/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::as_place::PlaceBase;
   6 use crate::build::expr::category::{Category, RvalueFunc};
   7 use crate::build::{BlockAnd, BlockAndExtension, Builder};
   8 use rustc_hir::lang_items::LangItem;
   9 use rustc_middle::middle::region;
  10 use rustc_middle::mir::AssertKind;
  11 use rustc_middle::mir::Place;
  12 use rustc_middle::mir::*;
  13 use rustc_middle::thir::*;
  14 use rustc_middle::ty::{self, Ty, UpvarSubsts};
  15 use rustc_span::Span;
  16
  17 impl<'a, 'tcx> Builder<'a, 'tcx> {
  18     /// Returns an rvalue suitable for use until the end of the current
  19     /// scope expression.
  20     ///
  21     /// The operand returned from this function will *not be valid* after
  22     /// an ExprKind::Scope is passed, so please do *not* return it from
  23     /// functions to avoid bad miscompiles.
  24     crate fn as_local_rvalue(
  25         &mut self,
  26         block: BasicBlock,
  27         expr: &Expr<'tcx>,
  28     ) -> BlockAnd<Rvalue<'tcx>> {
  29         let local_scope = self.local_scope();
  30         self.as_rvalue(block, Some(local_scope), expr)
  31     }
  32
  33     /// Compile `expr`, yielding an rvalue.
  34     crate fn as_rvalue(
  35         &mut self,
  36         mut block: BasicBlock,
  37         scope: Option<region::Scope>,
  38         expr: &Expr<'tcx>,
  39     ) -> BlockAnd<Rvalue<'tcx>> {
  40         debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
  41
  42         let this = self;
  43         let expr_span = expr.span;
  44         let source_info = this.source_info(expr_span);
  45
  46         match expr.kind {
  47             ExprKind::ThreadLocalRef(did) => block.and(Rvalue::ThreadLocalRef(did)),
  48             ExprKind::Scope { region_scope, lint_level, value } => {
  49                 let region_scope = (region_scope, source_info);
  50                 this.in_scope(region_scope, lint_level, |this| {
  51                     this.as_rvalue(block, scope, &this.thir[value])
  52                 })
  53             }
  54             ExprKind::Repeat { value, count } => {
  55                 let value_operand =
  56                     unpack!(block = this.as_operand(block, scope, &this.thir[value], None));
  57                 block.and(Rvalue::Repeat(value_operand, count))
  58             }
  59             ExprKind::Binary { op, lhs, rhs } => {
  60                 let lhs = unpack!(block = this.as_operand(block, scope, &this.thir[lhs], None));
  61                 let rhs = unpack!(block = this.as_operand(block, scope, &this.thir[rhs], None));
  62                 this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs)
  63             }
  64             ExprKind::Unary { op, arg } => {
  65                 let arg = unpack!(block = this.as_operand(block, scope, &this.thir[arg], None));
  66                 // Check for -MIN on signed integers
  67                 if this.check_overflow && op == UnOp::Neg && expr.ty.is_signed() {
  68                     let bool_ty = this.tcx.types.bool;
  69
  70                     let minval = this.minval_literal(expr_span, expr.ty);
  71                     let is_min = this.temp(bool_ty, expr_span);
  72
  73                     this.cfg.push_assign(
  74                         block,
  75                         source_info,
  76                         is_min,
  77                         Rvalue::BinaryOp(BinOp::Eq, Box::new((arg.to_copy(), minval))),
  78                     );
  79
  80                     block = this.assert(
  81                         block,
  82                         Operand::Move(is_min),
  83                         false,
  84                         AssertKind::OverflowNeg(arg.to_copy()),
  85                         expr_span,
  86                     );
  87                 }
  88                 block.and(Rvalue::UnaryOp(op, arg))
  89             }
  90             ExprKind::Box { value } => {
  91                 let value = &this.thir[value];
  92                 let tcx = this.tcx;
  93
  94                 // `exchange_malloc` is unsafe but box is safe, so need a new scope.
  95                 let synth_scope = this.new_source_scope(
  96                     expr_span,
  97                     LintLevel::Inherited,
  98                     Some(Safety::BuiltinUnsafe),
  99                 );
 100                 let synth_info = SourceInfo { span: expr_span, scope: synth_scope };
 101
 102                 let size = this.temp(tcx.types.usize, expr_span);
 103                 this.cfg.push_assign(
 104                     block,
 105                     synth_info,
 106                     size,
 107                     Rvalue::NullaryOp(NullOp::SizeOf, value.ty),
 108                 );
 109
 110                 let align = this.temp(tcx.types.usize, expr_span);
 111                 this.cfg.push_assign(
 112                     block,
 113                     synth_info,
 114                     align,
 115                     Rvalue::NullaryOp(NullOp::AlignOf, value.ty),
 116                 );
 117
 118                 // malloc some memory of suitable size and align:
 119                 let exchange_malloc = Operand::function_handle(
 120                     tcx,
 121                     tcx.require_lang_item(LangItem::ExchangeMalloc, Some(expr_span)),
 122                     ty::List::empty(),
 123                     expr_span,
 124                 );
 125                 let storage = this.temp(tcx.mk_mut_ptr(tcx.types.u8), expr_span);
 126                 let success = this.cfg.start_new_block();
 127                 this.cfg.terminate(
 128                     block,
 129                     synth_info,
 130                     TerminatorKind::Call {
 131                         func: exchange_malloc,
 132                         args: vec![Operand::Move(size), Operand::Move(align)],
 133                         destination: Some((storage, success)),
 134                         cleanup: None,
 135                         from_hir_call: false,
 136                         fn_span: expr_span,
 137                     },
 138                 );
 139                 this.diverge_from(block);
 140                 block = success;
 141
 142                 // The `Box<T>` temporary created here is not a part of the HIR,
 143                 // and therefore is not considered during generator auto-trait
 144                 // determination. See the comment about `box` at `yield_in_scope`.
 145                 let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span).internal());
 146                 this.cfg.push(
 147                     block,
 148                     Statement { source_info, kind: StatementKind::StorageLive(result) },
 149                 );
 150                 if let Some(scope) = scope {
 151                     // schedule a shallow free of that memory, lest we unwind:
 152                     this.schedule_drop_storage_and_value(expr_span, scope, result);
 153                 }
 154
 155                 // Transmute `*mut u8` to the box (thus far, uninitialized):
 156                 let box_ = Rvalue::ShallowInitBox(Operand::Move(storage), value.ty);
 157                 this.cfg.push_assign(block, source_info, Place::from(result), box_);
 158
 159                 // initialize the box contents:
 160                 unpack!(
 161                     block = this.expr_into_dest(
 162                         this.tcx.mk_place_deref(Place::from(result)),
 163                         block,
 164                         value
 165                     )
 166                 );
 167                 block.and(Rvalue::Use(Operand::Move(Place::from(result))))
 168             }
 169             ExprKind::Cast { source } => {
 170                 let source =
 171                     unpack!(block = this.as_operand(block, scope, &this.thir[source], None));
 172                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 173             }
 174             ExprKind::Pointer { cast, source } => {
 175                 let source =
 176                     unpack!(block = this.as_operand(block, scope, &this.thir[source], None));
 177                 block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty))
 178             }
 179             ExprKind::Array { ref fields } => {
 180                 // (*) We would (maybe) be closer to codegen if we
 181                 // handled this and other aggregate cases via
 182                 // `into()`, not `as_rvalue` -- in that case, instead
 183                 // of generating
 184                 //
 185                 //     let tmp1 = ...1;
 186                 //     let tmp2 = ...2;
 187                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 188                 //
 189                 // we could just generate
 190                 //
 191                 //     dest.f = ...1;
 192                 //     dest.g = ...2;
 193                 //
 194                 // The problem is that then we would need to:
 195                 //
 196                 // (a) have a more complex mechanism for handling
 197                 //     partial cleanup;
 198                 // (b) distinguish the case where the type `Foo` has a
 199                 //     destructor, in which case creating an instance
 200                 //     as a whole "arms" the destructor, and you can't
 201                 //     write individual fields; and,
 202                 // (c) handle the case where the type Foo has no
 203                 //     fields. We don't want `let x: ();` to compile
 204                 //     to the same MIR as `let x = ();`.
 205
 206                 // first process the set of fields
 207                 let el_ty = expr.ty.sequence_element_type(this.tcx);
 208                 let fields: Vec<_> = fields
 209                     .into_iter()
 210                     .copied()
 211                     .map(|f| unpack!(block = this.as_operand(block, scope, &this.thir[f], None)))
 212                     .collect();
 213
 214                 block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(el_ty)), fields))
 215             }
 216             ExprKind::Tuple { ref fields } => {
 217                 // see (*) above
 218                 // first process the set of fields
 219                 let fields: Vec<_> = fields
 220                     .into_iter()
 221                     .copied()
 222                     .map(|f| unpack!(block = this.as_operand(block, scope, &this.thir[f], None)))
 223                     .collect();
 224
 225                 block.and(Rvalue::Aggregate(Box::new(AggregateKind::Tuple), fields))
 226             }
 227             ExprKind::Closure { closure_id, substs, ref upvars, movability, ref fake_reads } => {
 228                 // Convert the closure fake reads, if any, from `ExprRef` to mir `Place`
 229                 // and push the fake reads.
 230                 // This must come before creating the operands. This is required in case
 231                 // there is a fake read and a borrow of the same path, since otherwise the
 232                 // fake read might interfere with the borrow. Consider an example like this
 233                 // one:
 234                 // ```
 235                 // let mut x = 0;
 236                 // let c = || {
 237                 //     &mut x; // mutable borrow of `x`
 238                 //     match x { _ => () } // fake read of `x`
 239                 // };
 240                 // ```
 241                 //
 242                 for (thir_place, cause, hir_id) in fake_reads.into_iter() {
 243                     let place_builder =
 244                         unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
 245
 246                     if let Ok(place_builder_resolved) =
 247                         place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
 248                     {
 249                         let mir_place =
 250                             place_builder_resolved.into_place(this.tcx, this.typeck_results);
 251                         this.cfg.push_fake_read(
 252                             block,
 253                             this.source_info(this.tcx.hir().span(*hir_id)),
 254                             *cause,
 255                             mir_place,
 256                         );
 257                     }
 258                 }
 259
 260                 // see (*) above
 261                 let operands: Vec<_> = upvars
 262                     .into_iter()
 263                     .copied()
 264                     .map(|upvar| {
 265                         let upvar = &this.thir[upvar];
 266                         match Category::of(&upvar.kind) {
 267                             // Use as_place to avoid creating a temporary when
 268                             // moving a variable into a closure, so that
 269                             // borrowck knows which variables to mark as being
 270                             // used as mut. This is OK here because the upvar
 271                             // expressions have no side effects and act on
 272                             // disjoint places.
 273                             // This occurs when capturing by copy/move, while
 274                             // by reference captures use as_operand
 275                             Some(Category::Place) => {
 276                                 let place = unpack!(block = this.as_place(block, upvar));
 277                                 this.consume_by_copy_or_move(place)
 278                             }
 279                             _ => {
 280                                 // Turn mutable borrow captures into unique
 281                                 // borrow captures when capturing an immutable
 282                                 // variable. This is sound because the mutation
 283                                 // that caused the capture will cause an error.
 284                                 match upvar.kind {
 285                                     ExprKind::Borrow {
 286                                         borrow_kind:
 287                                             BorrowKind::Mut { allow_two_phase_borrow: false },
 288                                         arg,
 289                                     } => unpack!(
 290                                         block = this.limit_capture_mutability(
 291                                             upvar.span,
 292                                             upvar.ty,
 293                                             scope,
 294                                             block,
 295                                             &this.thir[arg],
 296                                         )
 297                                     ),
 298                                     _ => {
 299                                         unpack!(block = this.as_operand(block, scope, upvar, None))
 300                                     }
 301                                 }
 302                             }
 303                         }
 304                     })
 305                     .collect();
 306
 307                 let result = match substs {
 308                     UpvarSubsts::Generator(substs) => {
 309                         // We implicitly set the discriminant to 0. See
 310                         // librustc_mir/transform/deaggregator.rs for details.
 311                         let movability = movability.unwrap();
 312                         Box::new(AggregateKind::Generator(closure_id, substs, movability))
 313                     }
 314                     UpvarSubsts::Closure(substs) => {
 315                         Box::new(AggregateKind::Closure(closure_id, substs))
 316                     }
 317                 };
 318                 block.and(Rvalue::Aggregate(result, operands))
 319             }
 320             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 321                 block = unpack!(this.stmt_expr(block, expr, None));
 322                 block.and(Rvalue::Use(Operand::Constant(Box::new(Constant {
 323                     span: expr_span,
 324                     user_ty: None,
 325                     literal: ty::Const::zero_sized(this.tcx, this.tcx.types.unit).into(),
 326                 }))))
 327             }
 328             ExprKind::Yield { .. }
 329             | ExprKind::Literal { .. }
 330             | ExprKind::NamedConst { .. }
 331             | ExprKind::ScalarLiteral { .. }
 332             | ExprKind::ConstParam { .. }
 333             | ExprKind::ConstBlock { .. }
 334             | ExprKind::StaticRef { .. }
 335             | ExprKind::Block { .. }
 336             | ExprKind::Match { .. }
 337             | ExprKind::If { .. }
 338             | ExprKind::NeverToAny { .. }
 339             | ExprKind::Use { .. }
 340             | ExprKind::Borrow { .. }
 341             | ExprKind::AddressOf { .. }
 342             | ExprKind::Adt { .. }
 343             | ExprKind::Loop { .. }
 344             | ExprKind::LogicalOp { .. }
 345             | ExprKind::Call { .. }
 346             | ExprKind::Field { .. }
 347             | ExprKind::Let { .. }
 348             | ExprKind::Deref { .. }
 349             | ExprKind::Index { .. }
 350             | ExprKind::VarRef { .. }
 351             | ExprKind::UpvarRef { .. }
 352             | ExprKind::Break { .. }
 353             | ExprKind::Continue { .. }
 354             | ExprKind::Return { .. }
 355             | ExprKind::InlineAsm { .. }
 356             | ExprKind::PlaceTypeAscription { .. }
 357             | ExprKind::ValueTypeAscription { .. } => {
 358                 // these do not have corresponding `Rvalue` variants,
 359                 // so make an operand and then return that
 360                 debug_assert!(!matches!(
 361                     Category::of(&expr.kind),
 362                     Some(Category::Rvalue(RvalueFunc::AsRvalue))
 363                 ));
 364                 let operand = unpack!(block = this.as_operand(block, scope, expr, None));
 365                 block.and(Rvalue::Use(operand))
 366             }
 367         }
 368     }
 369
 370     crate fn build_binary_op(
 371         &mut self,
 372         mut block: BasicBlock,
 373         op: BinOp,
 374         span: Span,
 375         ty: Ty<'tcx>,
 376         lhs: Operand<'tcx>,
 377         rhs: Operand<'tcx>,
 378     ) -> BlockAnd<Rvalue<'tcx>> {
 379         let source_info = self.source_info(span);
 380         let bool_ty = self.tcx.types.bool;
 381         if self.check_overflow && op.is_checkable() && ty.is_integral() {
 382             let result_tup = self.tcx.intern_tup(&[ty, bool_ty]);
 383             let result_value = self.temp(result_tup, span);
 384
 385             self.cfg.push_assign(
 386                 block,
 387                 source_info,
 388                 result_value,
 389                 Rvalue::CheckedBinaryOp(op, Box::new((lhs.to_copy(), rhs.to_copy()))),
 390             );
 391             let val_fld = Field::new(0);
 392             let of_fld = Field::new(1);
 393
 394             let tcx = self.tcx;
 395             let val = tcx.mk_place_field(result_value, val_fld, ty);
 396             let of = tcx.mk_place_field(result_value, of_fld, bool_ty);
 397
 398             let err = AssertKind::Overflow(op, lhs, rhs);
 399
 400             block = self.assert(block, Operand::Move(of), false, err, span);
 401
 402             block.and(Rvalue::Use(Operand::Move(val)))
 403         } else {
 404             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 405                 // Checking division and remainder is more complex, since we 1. always check
 406                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 407
 408                 let zero_err = if op == BinOp::Div {
 409                     AssertKind::DivisionByZero(lhs.to_copy())
 410                 } else {
 411                     AssertKind::RemainderByZero(lhs.to_copy())
 412                 };
 413                 let overflow_err = AssertKind::Overflow(op, lhs.to_copy(), rhs.to_copy());
 414
 415                 // Check for / 0
 416                 let is_zero = self.temp(bool_ty, span);
 417                 let zero = self.zero_literal(span, ty);
 418                 self.cfg.push_assign(
 419                     block,
 420                     source_info,
 421                     is_zero,
 422                     Rvalue::BinaryOp(BinOp::Eq, Box::new((rhs.to_copy(), zero))),
 423                 );
 424
 425                 block = self.assert(block, Operand::Move(is_zero), false, zero_err, span);
 426
 427                 // We only need to check for the overflow in one case:
 428                 // MIN / -1, and only for signed values.
 429                 if ty.is_signed() {
 430                     let neg_1 = self.neg_1_literal(span, ty);
 431                     let min = self.minval_literal(span, ty);
 432
 433                     let is_neg_1 = self.temp(bool_ty, span);
 434                     let is_min = self.temp(bool_ty, span);
 435                     let of = self.temp(bool_ty, span);
 436
 437                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 438
 439                     self.cfg.push_assign(
 440                         block,
 441                         source_info,
 442                         is_neg_1,
 443                         Rvalue::BinaryOp(BinOp::Eq, Box::new((rhs.to_copy(), neg_1))),
 444                     );
 445                     self.cfg.push_assign(
 446                         block,
 447                         source_info,
 448                         is_min,
 449                         Rvalue::BinaryOp(BinOp::Eq, Box::new((lhs.to_copy(), min))),
 450                     );
 451
 452                     let is_neg_1 = Operand::Move(is_neg_1);
 453                     let is_min = Operand::Move(is_min);
 454                     self.cfg.push_assign(
 455                         block,
 456                         source_info,
 457                         of,
 458                         Rvalue::BinaryOp(BinOp::BitAnd, Box::new((is_neg_1, is_min))),
 459                     );
 460
 461                     block = self.assert(block, Operand::Move(of), false, overflow_err, span);
 462                 }
 463             }
 464
 465             block.and(Rvalue::BinaryOp(op, Box::new((lhs, rhs))))
 466         }
 467     }
 468
 469     fn limit_capture_mutability(
 470         &mut self,
 471         upvar_span: Span,
 472         upvar_ty: Ty<'tcx>,
 473         temp_lifetime: Option<region::Scope>,
 474         mut block: BasicBlock,
 475         arg: &Expr<'tcx>,
 476     ) -> BlockAnd<Operand<'tcx>> {
 477         let this = self;
 478
 479         let source_info = this.source_info(upvar_span);
 480         let temp = this.local_decls.push(LocalDecl::new(upvar_ty, upvar_span));
 481
 482         this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) });
 483
 484         let arg_place_builder = unpack!(block = this.as_place_builder(block, arg));
 485
 486         let mutability = match arg_place_builder.base() {
 487             // We are capturing a path that starts off a local variable in the parent.
 488             // The mutability of the current capture is same as the mutability
 489             // of the local declaration in the parent.
 490             PlaceBase::Local(local) => this.local_decls[local].mutability,
 491             // Parent is a closure and we are capturing a path that is captured
 492             // by the parent itself. The mutability of the current capture
 493             // is same as that of the capture in the parent closure.
 494             PlaceBase::Upvar { .. } => {
 495                 let enclosing_upvars_resolved =
 496                     arg_place_builder.clone().into_place(this.tcx, this.typeck_results);
 497
 498                 match enclosing_upvars_resolved.as_ref() {
 499                     PlaceRef {
 500                         local,
 501                         projection: &[ProjectionElem::Field(upvar_index, _), ..],
 502                     }
 503                     | PlaceRef {
 504                         local,
 505                         projection:
 506                             &[ProjectionElem::Deref, ProjectionElem::Field(upvar_index, _), ..],
 507                     } => {
 508                         // Not in a closure
 509                         debug_assert!(
 510                             local == ty::CAPTURE_STRUCT_LOCAL,
 511                             "Expected local to be Local(1), found {:?}",
 512                             local
 513                         );
 514                         // Not in a closure
 515                         debug_assert!(
 516                             this.upvar_mutbls.len() > upvar_index.index(),
 517                             "Unexpected capture place, upvar_mutbls={:#?}, upvar_index={:?}",
 518                             this.upvar_mutbls,
 519                             upvar_index
 520                         );
 521                         this.upvar_mutbls[upvar_index.index()]
 522                     }
 523                     _ => bug!("Unexpected capture place"),
 524                 }
 525             }
 526         };
 527
 528         let borrow_kind = match mutability {
 529             Mutability::Not => BorrowKind::Unique,
 530             Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
 531         };
 532
 533         let arg_place = arg_place_builder.into_place(this.tcx, this.typeck_results);
 534
 535         this.cfg.push_assign(
 536             block,
 537             source_info,
 538             Place::from(temp),
 539             Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place),
 540         );
 541
 542         // See the comment in `expr_as_temp` and on the `rvalue_scopes` field for why
 543         // this can be `None`.
 544         if let Some(temp_lifetime) = temp_lifetime {
 545             this.schedule_drop_storage_and_value(upvar_span, temp_lifetime, temp);
 546         }
 547
 548         block.and(Operand::Move(Place::from(temp)))
 549     }
 550
 551     // Helper to get a `-1` value of the appropriate type
 552     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 553         let param_ty = ty::ParamEnv::empty().and(ty);
 554         let size = self.tcx.layout_of(param_ty).unwrap().size;
 555         let literal = ty::Const::from_bits(self.tcx, size.unsigned_int_max(), param_ty);
 556
 557         self.literal_operand(span, literal)
 558     }
 559
 560     // Helper to get the minimum value of the appropriate type
 561     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 562         assert!(ty.is_signed());
 563         let param_ty = ty::ParamEnv::empty().and(ty);
 564         let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
 565         let n = 1 << (bits - 1);
 566         let literal = ty::Const::from_bits(self.tcx, n, param_ty);
 567
 568         self.literal_operand(span, literal)
 569     }
 570 }