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