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