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