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