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_middle::middle::region;
   9 use rustc_middle::mir::AssertKind;
  10 use rustc_middle::mir::Place;
  11 use rustc_middle::mir::*;
  12 use rustc_middle::thir::*;
  13 use rustc_middle::ty::{self, Ty, UpvarSubsts};
  14 use rustc_span::Span;
  15
  16 impl<'a, 'tcx> Builder<'a, 'tcx> {
  17     /// Returns an rvalue suitable for use until the end of the current
  18     /// scope expression.
  19     ///
  20     /// The operand returned from this function will *not be valid* after
  21     /// an ExprKind::Scope is passed, so please do *not* return it from
  22     /// functions to avoid bad miscompiles.
  23     crate fn as_local_rvalue(
  24         &mut self,
  25         block: BasicBlock,
  26         expr: &Expr<'tcx>,
  27     ) -> BlockAnd<Rvalue<'tcx>> {
  28         let local_scope = self.local_scope();
  29         self.as_rvalue(block, Some(local_scope), expr)
  30     }
  31
  32     /// Compile `expr`, yielding an rvalue.
  33     crate fn as_rvalue(
  34         &mut self,
  35         mut block: BasicBlock,
  36         scope: Option<region::Scope>,
  37         expr: &Expr<'tcx>,
  38     ) -> BlockAnd<Rvalue<'tcx>> {
  39         debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
  40
  41         let this = self;
  42         let expr_span = expr.span;
  43         let source_info = this.source_info(expr_span);
  44
  45         match expr.kind {
  46             ExprKind::ThreadLocalRef(did) => block.and(Rvalue::ThreadLocalRef(did)),
  47             ExprKind::Scope { region_scope, lint_level, value } => {
  48                 let region_scope = (region_scope, source_info);
  49                 this.in_scope(region_scope, lint_level, |this| {
  50                     this.as_rvalue(block, scope, &this.thir[value])
  51                 })
  52             }
  53             ExprKind::Repeat { value, count } => {
  54                 let value_operand =
  55                     unpack!(block = this.as_operand(block, scope, &this.thir[value]));
  56                 block.and(Rvalue::Repeat(value_operand, count))
  57             }
  58             ExprKind::Binary { op, lhs, rhs } => {
  59                 let lhs = unpack!(block = this.as_operand(block, scope, &this.thir[lhs]));
  60                 let rhs = unpack!(block = this.as_operand(block, scope, &this.thir[rhs]));
  61                 this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs)
  62             }
  63             ExprKind::Unary { op, arg } => {
  64                 let arg = unpack!(block = this.as_operand(block, scope, &this.thir[arg]));
  65                 // Check for -MIN on signed integers
  66                 if this.check_overflow && op == UnOp::Neg && expr.ty.is_signed() {
  67                     let bool_ty = this.tcx.types.bool;
  68
  69                     let minval = this.minval_literal(expr_span, expr.ty);
  70                     let is_min = this.temp(bool_ty, expr_span);
  71
  72                     this.cfg.push_assign(
  73                         block,
  74                         source_info,
  75                         is_min,
  76                         Rvalue::BinaryOp(BinOp::Eq, box (arg.to_copy(), minval)),
  77                     );
  78
  79                     block = this.assert(
  80                         block,
  81                         Operand::Move(is_min),
  82                         false,
  83                         AssertKind::OverflowNeg(arg.to_copy()),
  84                         expr_span,
  85                     );
  86                 }
  87                 block.and(Rvalue::UnaryOp(op, arg))
  88             }
  89             ExprKind::Box { value } => {
  90                 let value = &this.thir[value];
  91                 // The `Box<T>` temporary created here is not a part of the HIR,
  92                 // and therefore is not considered during generator auto-trait
  93                 // determination. See the comment about `box` at `yield_in_scope`.
  94                 let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span).internal());
  95                 this.cfg.push(
  96                     block,
  97                     Statement { source_info, kind: StatementKind::StorageLive(result) },
  98                 );
  99                 if let Some(scope) = scope {
 100                     // schedule a shallow free of that memory, lest we unwind:
 101                     this.schedule_drop_storage_and_value(expr_span, scope, result);
 102                 }
 103
 104                 // malloc some memory of suitable type (thus far, uninitialized):
 105                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
 106                 this.cfg.push_assign(block, source_info, Place::from(result), box_);
 107
 108                 // initialize the box contents:
 109                 unpack!(
 110                     block = this.expr_into_dest(
 111                         this.tcx.mk_place_deref(Place::from(result)),
 112                         block,
 113                         value
 114                     )
 115                 );
 116                 block.and(Rvalue::Use(Operand::Move(Place::from(result))))
 117             }
 118             ExprKind::Cast { source } => {
 119                 let source = unpack!(block = this.as_operand(block, scope, &this.thir[source]));
 120                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 121             }
 122             ExprKind::Pointer { cast, source } => {
 123                 let source = unpack!(block = this.as_operand(block, scope, &this.thir[source]));
 124                 block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty))
 125             }
 126             ExprKind::Array { ref fields } => {
 127                 // (*) We would (maybe) be closer to codegen if we
 128                 // handled this and other aggregate cases via
 129                 // `into()`, not `as_rvalue` -- in that case, instead
 130                 // of generating
 131                 //
 132                 //     let tmp1 = ...1;
 133                 //     let tmp2 = ...2;
 134                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 135                 //
 136                 // we could just generate
 137                 //
 138                 //     dest.f = ...1;
 139                 //     dest.g = ...2;
 140                 //
 141                 // The problem is that then we would need to:
 142                 //
 143                 // (a) have a more complex mechanism for handling
 144                 //     partial cleanup;
 145                 // (b) distinguish the case where the type `Foo` has a
 146                 //     destructor, in which case creating an instance
 147                 //     as a whole "arms" the destructor, and you can't
 148                 //     write individual fields; and,
 149                 // (c) handle the case where the type Foo has no
 150                 //     fields. We don't want `let x: ();` to compile
 151                 //     to the same MIR as `let x = ();`.
 152
 153                 // first process the set of fields
 154                 let el_ty = expr.ty.sequence_element_type(this.tcx);
 155                 let fields: Vec<_> = fields
 156                     .into_iter()
 157                     .copied()
 158                     .map(|f| unpack!(block = this.as_operand(block, scope, &this.thir[f])))
 159                     .collect();
 160
 161                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 162             }
 163             ExprKind::Tuple { ref fields } => {
 164                 // see (*) above
 165                 // first process the set of fields
 166                 let fields: Vec<_> = fields
 167                     .into_iter()
 168                     .copied()
 169                     .map(|f| unpack!(block = this.as_operand(block, scope, &this.thir[f])))
 170                     .collect();
 171
 172                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 173             }
 174             ExprKind::Closure { closure_id, substs, ref upvars, movability, ref fake_reads } => {
 175                 // Convert the closure fake reads, if any, from `ExprRef` to mir `Place`
 176                 // and push the fake reads.
 177                 // This must come before creating the operands. This is required in case
 178                 // there is a fake read and a borrow of the same path, since otherwise the
 179                 // fake read might interfere with the borrow. Consider an example like this
 180                 // one:
 181                 // ```
 182                 // let mut x = 0;
 183                 // let c = || {
 184                 //     &mut x; // mutable borrow of `x`
 185                 //     match x { _ => () } // fake read of `x`
 186                 // };
 187                 // ```
 188                 //
 189                 // FIXME(RFC2229, rust#85435): Remove feature gate once diagnostics are
 190                 // improved and unsafe checking works properly in closure bodies again.
 191                 if this.tcx.features().capture_disjoint_fields {
 192                     for (thir_place, cause, hir_id) in fake_reads.into_iter() {
 193                         let place_builder =
 194                             unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
 195
 196                         if let Ok(place_builder_resolved) =
 197                             place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
 198                         {
 199                             let mir_place =
 200                                 place_builder_resolved.into_place(this.tcx, this.typeck_results);
 201                             this.cfg.push_fake_read(
 202                                 block,
 203                                 this.source_info(this.tcx.hir().span(*hir_id)),
 204                                 *cause,
 205                                 mir_place,
 206                             );
 207                         }
 208                     }
 209                 }
 210
 211                 // see (*) above
 212                 let operands: Vec<_> = upvars
 213                     .into_iter()
 214                     .copied()
 215                     .map(|upvar| {
 216                         let upvar = &this.thir[upvar];
 217                         match Category::of(&upvar.kind) {
 218                             // Use as_place to avoid creating a temporary when
 219                             // moving a variable into a closure, so that
 220                             // borrowck knows which variables to mark as being
 221                             // used as mut. This is OK here because the upvar
 222                             // expressions have no side effects and act on
 223                             // disjoint places.
 224                             // This occurs when capturing by copy/move, while
 225                             // by reference captures use as_operand
 226                             Some(Category::Place) => {
 227                                 let place = unpack!(block = this.as_place(block, upvar));
 228                                 this.consume_by_copy_or_move(place)
 229                             }
 230                             _ => {
 231                                 // Turn mutable borrow captures into unique
 232                                 // borrow captures when capturing an immutable
 233                                 // variable. This is sound because the mutation
 234                                 // that caused the capture will cause an error.
 235                                 match upvar.kind {
 236                                     ExprKind::Borrow {
 237                                         borrow_kind:
 238                                             BorrowKind::Mut { allow_two_phase_borrow: false },
 239                                         arg,
 240                                     } => unpack!(
 241                                         block = this.limit_capture_mutability(
 242                                             upvar.span,
 243                                             upvar.ty,
 244                                             scope,
 245                                             block,
 246                                             &this.thir[arg],
 247                                         )
 248                                     ),
 249                                     _ => unpack!(block = this.as_operand(block, scope, upvar)),
 250                                 }
 251                             }
 252                         }
 253                     })
 254                     .collect();
 255
 256                 let result = match substs {
 257                     UpvarSubsts::Generator(substs) => {
 258                         // We implicitly set the discriminant to 0. See
 259                         // librustc_mir/transform/deaggregator.rs for details.
 260                         let movability = movability.unwrap();
 261                         box AggregateKind::Generator(closure_id, substs, movability)
 262                     }
 263                     UpvarSubsts::Closure(substs) => box AggregateKind::Closure(closure_id, substs),
 264                 };
 265                 block.and(Rvalue::Aggregate(result, operands))
 266             }
 267             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 268                 block = unpack!(this.stmt_expr(block, expr, None));
 269                 block.and(Rvalue::Use(Operand::Constant(box Constant {
 270                     span: expr_span,
 271                     user_ty: None,
 272                     literal: ty::Const::zero_sized(this.tcx, this.tcx.types.unit).into(),
 273                 })))
 274             }
 275             ExprKind::Yield { .. }
 276             | ExprKind::Literal { .. }
 277             | ExprKind::ConstBlock { .. }
 278             | ExprKind::StaticRef { .. }
 279             | ExprKind::Block { .. }
 280             | ExprKind::Match { .. }
 281             | ExprKind::If { .. }
 282             | ExprKind::NeverToAny { .. }
 283             | ExprKind::Use { .. }
 284             | ExprKind::Borrow { .. }
 285             | ExprKind::AddressOf { .. }
 286             | ExprKind::Adt { .. }
 287             | ExprKind::Loop { .. }
 288             | ExprKind::LogicalOp { .. }
 289             | ExprKind::Call { .. }
 290             | ExprKind::Field { .. }
 291             | ExprKind::Deref { .. }
 292             | ExprKind::Index { .. }
 293             | ExprKind::VarRef { .. }
 294             | ExprKind::UpvarRef { .. }
 295             | ExprKind::Break { .. }
 296             | ExprKind::Continue { .. }
 297             | ExprKind::Return { .. }
 298             | ExprKind::InlineAsm { .. }
 299             | ExprKind::LlvmInlineAsm { .. }
 300             | ExprKind::PlaceTypeAscription { .. }
 301             | ExprKind::ValueTypeAscription { .. } => {
 302                 // these do not have corresponding `Rvalue` variants,
 303                 // so make an operand and then return that
 304                 debug_assert!(!matches!(
 305                     Category::of(&expr.kind),
 306                     Some(Category::Rvalue(RvalueFunc::AsRvalue))
 307                 ));
 308                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 309                 block.and(Rvalue::Use(operand))
 310             }
 311         }
 312     }
 313
 314     crate fn build_binary_op(
 315         &mut self,
 316         mut block: BasicBlock,
 317         op: BinOp,
 318         span: Span,
 319         ty: Ty<'tcx>,
 320         lhs: Operand<'tcx>,
 321         rhs: Operand<'tcx>,
 322     ) -> BlockAnd<Rvalue<'tcx>> {
 323         let source_info = self.source_info(span);
 324         let bool_ty = self.tcx.types.bool;
 325         if self.check_overflow && op.is_checkable() && ty.is_integral() {
 326             let result_tup = self.tcx.intern_tup(&[ty, bool_ty]);
 327             let result_value = self.temp(result_tup, span);
 328
 329             self.cfg.push_assign(
 330                 block,
 331                 source_info,
 332                 result_value,
 333                 Rvalue::CheckedBinaryOp(op, box (lhs.to_copy(), rhs.to_copy())),
 334             );
 335             let val_fld = Field::new(0);
 336             let of_fld = Field::new(1);
 337
 338             let tcx = self.tcx;
 339             let val = tcx.mk_place_field(result_value, val_fld, ty);
 340             let of = tcx.mk_place_field(result_value, of_fld, bool_ty);
 341
 342             let err = AssertKind::Overflow(op, lhs, rhs);
 343
 344             block = self.assert(block, Operand::Move(of), false, err, span);
 345
 346             block.and(Rvalue::Use(Operand::Move(val)))
 347         } else {
 348             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 349                 // Checking division and remainder is more complex, since we 1. always check
 350                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 351
 352                 let zero_err = if op == BinOp::Div {
 353                     AssertKind::DivisionByZero(lhs.to_copy())
 354                 } else {
 355                     AssertKind::RemainderByZero(lhs.to_copy())
 356                 };
 357                 let overflow_err = AssertKind::Overflow(op, lhs.to_copy(), rhs.to_copy());
 358
 359                 // Check for / 0
 360                 let is_zero = self.temp(bool_ty, span);
 361                 let zero = self.zero_literal(span, ty);
 362                 self.cfg.push_assign(
 363                     block,
 364                     source_info,
 365                     is_zero,
 366                     Rvalue::BinaryOp(BinOp::Eq, box (rhs.to_copy(), zero)),
 367                 );
 368
 369                 block = self.assert(block, Operand::Move(is_zero), false, zero_err, span);
 370
 371                 // We only need to check for the overflow in one case:
 372                 // MIN / -1, and only for signed values.
 373                 if ty.is_signed() {
 374                     let neg_1 = self.neg_1_literal(span, ty);
 375                     let min = self.minval_literal(span, ty);
 376
 377                     let is_neg_1 = self.temp(bool_ty, span);
 378                     let is_min = self.temp(bool_ty, span);
 379                     let of = self.temp(bool_ty, span);
 380
 381                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 382
 383                     self.cfg.push_assign(
 384                         block,
 385                         source_info,
 386                         is_neg_1,
 387                         Rvalue::BinaryOp(BinOp::Eq, box (rhs.to_copy(), neg_1)),
 388                     );
 389                     self.cfg.push_assign(
 390                         block,
 391                         source_info,
 392                         is_min,
 393                         Rvalue::BinaryOp(BinOp::Eq, box (lhs.to_copy(), min)),
 394                     );
 395
 396                     let is_neg_1 = Operand::Move(is_neg_1);
 397                     let is_min = Operand::Move(is_min);
 398                     self.cfg.push_assign(
 399                         block,
 400                         source_info,
 401                         of,
 402                         Rvalue::BinaryOp(BinOp::BitAnd, box (is_neg_1, is_min)),
 403                     );
 404
 405                     block = self.assert(block, Operand::Move(of), false, overflow_err, span);
 406                 }
 407             }
 408
 409             block.and(Rvalue::BinaryOp(op, box (lhs, rhs)))
 410         }
 411     }
 412
 413     fn limit_capture_mutability(
 414         &mut self,
 415         upvar_span: Span,
 416         upvar_ty: Ty<'tcx>,
 417         temp_lifetime: Option<region::Scope>,
 418         mut block: BasicBlock,
 419         arg: &Expr<'tcx>,
 420     ) -> BlockAnd<Operand<'tcx>> {
 421         let this = self;
 422
 423         let source_info = this.source_info(upvar_span);
 424         let temp = this.local_decls.push(LocalDecl::new(upvar_ty, upvar_span));
 425
 426         this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) });
 427
 428         let arg_place_builder = unpack!(block = this.as_place_builder(block, arg));
 429
 430         let mutability = match arg_place_builder.base() {
 431             // We are capturing a path that starts off a local variable in the parent.
 432             // The mutability of the current capture is same as the mutability
 433             // of the local declaration in the parent.
 434             PlaceBase::Local(local) => this.local_decls[local].mutability,
 435             // Parent is a closure and we are capturing a path that is captured
 436             // by the parent itself. The mutability of the current capture
 437             // is same as that of the capture in the parent closure.
 438             PlaceBase::Upvar { .. } => {
 439                 let enclosing_upvars_resolved =
 440                     arg_place_builder.clone().into_place(this.tcx, this.typeck_results);
 441
 442                 match enclosing_upvars_resolved.as_ref() {
 443                     PlaceRef {
 444                         local,
 445                         projection: &[ProjectionElem::Field(upvar_index, _), ..],
 446                     }
 447                     | PlaceRef {
 448                         local,
 449                         projection:
 450                             &[ProjectionElem::Deref, ProjectionElem::Field(upvar_index, _), ..],
 451                     } => {
 452                         // Not in a closure
 453                         debug_assert!(
 454                             local == ty::CAPTURE_STRUCT_LOCAL,
 455                             "Expected local to be Local(1), found {:?}",
 456                             local
 457                         );
 458                         // Not in a closure
 459                         debug_assert!(
 460                             this.upvar_mutbls.len() > upvar_index.index(),
 461                             "Unexpected capture place, upvar_mutbls={:#?}, upvar_index={:?}",
 462                             this.upvar_mutbls,
 463                             upvar_index
 464                         );
 465                         this.upvar_mutbls[upvar_index.index()]
 466                     }
 467                     _ => bug!("Unexpected capture place"),
 468                 }
 469             }
 470         };
 471
 472         let borrow_kind = match mutability {
 473             Mutability::Not => BorrowKind::Unique,
 474             Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
 475         };
 476
 477         let arg_place = arg_place_builder.into_place(this.tcx, this.typeck_results);
 478
 479         this.cfg.push_assign(
 480             block,
 481             source_info,
 482             Place::from(temp),
 483             Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place),
 484         );
 485
 486         // See the comment in `expr_as_temp` and on the `rvalue_scopes` field for why
 487         // this can be `None`.
 488         if let Some(temp_lifetime) = temp_lifetime {
 489             this.schedule_drop_storage_and_value(upvar_span, temp_lifetime, temp);
 490         }
 491
 492         block.and(Operand::Move(Place::from(temp)))
 493     }
 494
 495     // Helper to get a `-1` value of the appropriate type
 496     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 497         let param_ty = ty::ParamEnv::empty().and(ty);
 498         let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
 499         let n = (!0u128) >> (128 - bits);
 500         let literal = ty::Const::from_bits(self.tcx, n, param_ty);
 501
 502         self.literal_operand(span, literal)
 503     }
 504
 505     // Helper to get the minimum value of the appropriate type
 506     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 507         assert!(ty.is_signed());
 508         let param_ty = ty::ParamEnv::empty().and(ty);
 509         let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
 510         let n = 1 << (bits - 1);
 511         let literal = ty::Const::from_bits(self.tcx, n, param_ty);
 512
 513         self.literal_operand(span, literal)
 514     }
 515 }