compiler/rustc_mir_build/src/build/expr/into.rs

   1 //! See docs in build/expr/mod.rs
   2
   3 use crate::build::expr::category::{Category, RvalueFunc};
   4 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder, NeedsTemporary};
   5 use rustc_ast::InlineAsmOptions;
   6 use rustc_data_structures::fx::FxHashMap;
   7 use rustc_data_structures::stack::ensure_sufficient_stack;
   8 use rustc_hir as hir;
   9 use rustc_index::vec::Idx;
  10 use rustc_middle::mir::*;
  11 use rustc_middle::thir::*;
  12 use rustc_middle::ty::CanonicalUserTypeAnnotation;
  13 use std::iter;
  14
  15 impl<'a, 'tcx> Builder<'a, 'tcx> {
  16     /// Compile `expr`, storing the result into `destination`, which
  17     /// is assumed to be uninitialized.
  18     pub(crate) fn expr_into_dest(
  19         &mut self,
  20         destination: Place<'tcx>,
  21         mut block: BasicBlock,
  22         expr: &Expr<'tcx>,
  23     ) -> BlockAnd<()> {
  24         debug!("expr_into_dest(destination={:?}, block={:?}, expr={:?})", destination, block, expr);
  25
  26         // since we frequently have to reference `self` from within a
  27         // closure, where `self` would be shadowed, it's easier to
  28         // just use the name `this` uniformly
  29         let this = self;
  30         let expr_span = expr.span;
  31         let source_info = this.source_info(expr_span);
  32
  33         let expr_is_block_or_scope =
  34             matches!(expr.kind, ExprKind::Block { .. } | ExprKind::Scope { .. });
  35
  36         if !expr_is_block_or_scope {
  37             this.block_context.push(BlockFrame::SubExpr);
  38         }
  39
  40         let block_and = match expr.kind {
  41             ExprKind::Scope { region_scope, lint_level, value } => {
  42                 let region_scope = (region_scope, source_info);
  43                 ensure_sufficient_stack(|| {
  44                     this.in_scope(region_scope, lint_level, |this| {
  45                         this.expr_into_dest(destination, block, &this.thir[value])
  46                     })
  47                 })
  48             }
  49             ExprKind::Block { body: ref ast_block } => {
  50                 this.ast_block(destination, block, ast_block, source_info)
  51             }
  52             ExprKind::Match { scrutinee, ref arms } => {
  53                 this.match_expr(destination, expr_span, block, &this.thir[scrutinee], arms)
  54             }
  55             ExprKind::If { cond, then, else_opt, if_then_scope } => {
  56                 let then_blk;
  57                 let then_expr = &this.thir[then];
  58                 let then_source_info = this.source_info(then_expr.span);
  59                 let condition_scope = this.local_scope();
  60
  61                 let mut else_blk = unpack!(
  62                     then_blk = this.in_scope(
  63                         (if_then_scope, then_source_info),
  64                         LintLevel::Inherited,
  65                         |this| {
  66                             let (then_block, else_block) =
  67                                 this.in_if_then_scope(condition_scope, |this| {
  68                                     let then_blk = unpack!(this.then_else_break(
  69                                         block,
  70                                         &this.thir[cond],
  71                                         Some(condition_scope),
  72                                         condition_scope,
  73                                         then_expr.span
  74                                     ));
  75
  76                                     this.expr_into_dest(destination, then_blk, then_expr)
  77                                 });
  78                             then_block.and(else_block)
  79                         },
  80                     )
  81                 );
  82
  83                 else_blk = if let Some(else_opt) = else_opt {
  84                     unpack!(this.expr_into_dest(destination, else_blk, &this.thir[else_opt]))
  85                 } else {
  86                     // Body of the `if` expression without an `else` clause must return `()`, thus
  87                     // we implicitly generate an `else {}` if it is not specified.
  88                     let correct_si = this.source_info(expr_span.shrink_to_hi());
  89                     this.cfg.push_assign_unit(else_blk, correct_si, destination, this.tcx);
  90                     else_blk
  91                 };
  92
  93                 let join_block = this.cfg.start_new_block();
  94                 this.cfg.goto(then_blk, source_info, join_block);
  95                 this.cfg.goto(else_blk, source_info, join_block);
  96                 join_block.unit()
  97             }
  98             ExprKind::Let { expr, ref pat } => {
  99                 let scope = this.local_scope();
 100                 let (true_block, false_block) = this.in_if_then_scope(scope, |this| {
 101                     this.lower_let_expr(block, &this.thir[expr], pat, scope, None, expr_span)
 102                 });
 103
 104                 this.cfg.push_assign_constant(
 105                     true_block,
 106                     source_info,
 107                     destination,
 108                     Constant {
 109                         span: expr_span,
 110                         user_ty: None,
 111                         literal: ConstantKind::from_bool(this.tcx, true),
 112                     },
 113                 );
 114
 115                 this.cfg.push_assign_constant(
 116                     false_block,
 117                     source_info,
 118                     destination,
 119                     Constant {
 120                         span: expr_span,
 121                         user_ty: None,
 122                         literal: ConstantKind::from_bool(this.tcx, false),
 123                     },
 124                 );
 125
 126                 let join_block = this.cfg.start_new_block();
 127                 this.cfg.goto(true_block, source_info, join_block);
 128                 this.cfg.goto(false_block, source_info, join_block);
 129                 join_block.unit()
 130             }
 131             ExprKind::NeverToAny { source } => {
 132                 let source = &this.thir[source];
 133                 let is_call =
 134                     matches!(source.kind, ExprKind::Call { .. } | ExprKind::InlineAsm { .. });
 135
 136                 // (#66975) Source could be a const of type `!`, so has to
 137                 // exist in the generated MIR.
 138                 unpack!(
 139                     block = this.as_temp(block, Some(this.local_scope()), source, Mutability::Mut,)
 140                 );
 141
 142                 // This is an optimization. If the expression was a call then we already have an
 143                 // unreachable block. Don't bother to terminate it and create a new one.
 144                 if is_call {
 145                     block.unit()
 146                 } else {
 147                     this.cfg.terminate(block, source_info, TerminatorKind::Unreachable);
 148                     let end_block = this.cfg.start_new_block();
 149                     end_block.unit()
 150                 }
 151             }
 152             ExprKind::LogicalOp { op, lhs, rhs } => {
 153                 // And:
 154                 //
 155                 // [block: If(lhs)] -true-> [else_block: dest = (rhs)]
 156                 //        | (false)
 157                 //  [shortcurcuit_block: dest = false]
 158                 //
 159                 // Or:
 160                 //
 161                 // [block: If(lhs)] -false-> [else_block: dest = (rhs)]
 162                 //        | (true)
 163                 //  [shortcurcuit_block: dest = true]
 164
 165                 let (shortcircuit_block, mut else_block, join_block) = (
 166                     this.cfg.start_new_block(),
 167                     this.cfg.start_new_block(),
 168                     this.cfg.start_new_block(),
 169                 );
 170
 171                 let lhs = unpack!(block = this.as_local_operand(block, &this.thir[lhs]));
 172                 let blocks = match op {
 173                     LogicalOp::And => (else_block, shortcircuit_block),
 174                     LogicalOp::Or => (shortcircuit_block, else_block),
 175                 };
 176                 let term = TerminatorKind::if_(this.tcx, lhs, blocks.0, blocks.1);
 177                 this.cfg.terminate(block, source_info, term);
 178
 179                 this.cfg.push_assign_constant(
 180                     shortcircuit_block,
 181                     source_info,
 182                     destination,
 183                     Constant {
 184                         span: expr_span,
 185                         user_ty: None,
 186                         literal: match op {
 187                             LogicalOp::And => ConstantKind::from_bool(this.tcx, false),
 188                             LogicalOp::Or => ConstantKind::from_bool(this.tcx, true),
 189                         },
 190                     },
 191                 );
 192                 this.cfg.goto(shortcircuit_block, source_info, join_block);
 193
 194                 let rhs = unpack!(else_block = this.as_local_operand(else_block, &this.thir[rhs]));
 195                 this.cfg.push_assign(else_block, source_info, destination, Rvalue::Use(rhs));
 196                 this.cfg.goto(else_block, source_info, join_block);
 197
 198                 join_block.unit()
 199             }
 200             ExprKind::Loop { body } => {
 201                 // [block]
 202                 //    |
 203                 //   [loop_block] -> [body_block] -/eval. body/-> [body_block_end]
 204                 //    |        ^                                         |
 205                 // false link  |                                         |
 206                 //    |        +-----------------------------------------+
 207                 //    +-> [diverge_cleanup]
 208                 // The false link is required to make sure borrowck considers unwinds through the
 209                 // body, even when the exact code in the body cannot unwind
 210
 211                 let loop_block = this.cfg.start_new_block();
 212
 213                 // Start the loop.
 214                 this.cfg.goto(block, source_info, loop_block);
 215
 216                 this.in_breakable_scope(Some(loop_block), destination, expr_span, move |this| {
 217                     // conduct the test, if necessary
 218                     let body_block = this.cfg.start_new_block();
 219                     this.cfg.terminate(
 220                         loop_block,
 221                         source_info,
 222                         TerminatorKind::FalseUnwind { real_target: body_block, unwind: None },
 223                     );
 224                     this.diverge_from(loop_block);
 225
 226                     // The “return” value of the loop body must always be a unit. We therefore
 227                     // introduce a unit temporary as the destination for the loop body.
 228                     let tmp = this.get_unit_temp();
 229                     // Execute the body, branching back to the test.
 230                     let body_block_end =
 231                         unpack!(this.expr_into_dest(tmp, body_block, &this.thir[body]));
 232                     this.cfg.goto(body_block_end, source_info, loop_block);
 233
 234                     // Loops are only exited by `break` expressions.
 235                     None
 236                 })
 237             }
 238             ExprKind::Call { ty: _, fun, ref args, from_hir_call, fn_span } => {
 239                 let fun = unpack!(block = this.as_local_operand(block, &this.thir[fun]));
 240                 let args: Vec<_> = args
 241                     .into_iter()
 242                     .copied()
 243                     .map(|arg| unpack!(block = this.as_local_call_operand(block, &this.thir[arg])))
 244                     .collect();
 245
 246                 let success = this.cfg.start_new_block();
 247
 248                 this.record_operands_moved(&args);
 249
 250                 debug!("expr_into_dest: fn_span={:?}", fn_span);
 251
 252                 this.cfg.terminate(
 253                     block,
 254                     source_info,
 255                     TerminatorKind::Call {
 256                         func: fun,
 257                         args,
 258                         cleanup: None,
 259                         destination,
 260                         // The presence or absence of a return edge affects control-flow sensitive
 261                         // MIR checks and ultimately whether code is accepted or not. We can only
 262                         // omit the return edge if a return type is visibly uninhabited to a module
 263                         // that makes the call.
 264                         target: if this.tcx.is_ty_uninhabited_from(
 265                             this.parent_module,
 266                             expr.ty,
 267                             this.param_env,
 268                         ) {
 269                             None
 270                         } else {
 271                             Some(success)
 272                         },
 273                         from_hir_call,
 274                         fn_span,
 275                     },
 276                 );
 277                 this.diverge_from(block);
 278                 success.unit()
 279             }
 280             ExprKind::Use { source } => this.expr_into_dest(destination, block, &this.thir[source]),
 281             ExprKind::Borrow { arg, borrow_kind } => {
 282                 let arg = &this.thir[arg];
 283                 // We don't do this in `as_rvalue` because we use `as_place`
 284                 // for borrow expressions, so we cannot create an `RValue` that
 285                 // remains valid across user code. `as_rvalue` is usually called
 286                 // by this method anyway, so this shouldn't cause too many
 287                 // unnecessary temporaries.
 288                 let arg_place = match borrow_kind {
 289                     BorrowKind::Shared => unpack!(block = this.as_read_only_place(block, arg)),
 290                     _ => unpack!(block = this.as_place(block, arg)),
 291                 };
 292                 let borrow = Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place);
 293                 this.cfg.push_assign(block, source_info, destination, borrow);
 294                 block.unit()
 295             }
 296             ExprKind::AddressOf { mutability, arg } => {
 297                 let arg = &this.thir[arg];
 298                 let place = match mutability {
 299                     hir::Mutability::Not => this.as_read_only_place(block, arg),
 300                     hir::Mutability::Mut => this.as_place(block, arg),
 301                 };
 302                 let address_of = Rvalue::AddressOf(mutability, unpack!(block = place));
 303                 this.cfg.push_assign(block, source_info, destination, address_of);
 304                 block.unit()
 305             }
 306             ExprKind::Adt(box Adt {
 307                 adt_def,
 308                 variant_index,
 309                 substs,
 310                 user_ty,
 311                 ref fields,
 312                 ref base,
 313             }) => {
 314                 // See the notes for `ExprKind::Array` in `as_rvalue` and for
 315                 // `ExprKind::Borrow` above.
 316                 let is_union = adt_def.is_union();
 317                 let active_field_index = if is_union { Some(fields[0].name.index()) } else { None };
 318
 319                 let scope = this.local_scope();
 320
 321                 // first process the set of fields that were provided
 322                 // (evaluating them in order given by user)
 323                 let fields_map: FxHashMap<_, _> = fields
 324                     .into_iter()
 325                     .map(|f| {
 326                         let local_info = Box::new(LocalInfo::AggregateTemp);
 327                         (
 328                             f.name,
 329                             unpack!(
 330                                 block = this.as_operand(
 331                                     block,
 332                                     Some(scope),
 333                                     &this.thir[f.expr],
 334                                     Some(local_info),
 335                                     NeedsTemporary::Maybe,
 336                                 )
 337                             ),
 338                         )
 339                     })
 340                     .collect();
 341
 342                 let field_names: Vec<_> =
 343                     (0..adt_def.variant(variant_index).fields.len()).map(Field::new).collect();
 344
 345                 let fields: Vec<_> = if let Some(FruInfo { base, field_types }) = base {
 346                     let place_builder =
 347                         unpack!(block = this.as_place_builder(block, &this.thir[*base]));
 348
 349                     // MIR does not natively support FRU, so for each
 350                     // base-supplied field, generate an operand that
 351                     // reads it from the base.
 352                     iter::zip(field_names, &**field_types)
 353                         .map(|(n, ty)| match fields_map.get(&n) {
 354                             Some(v) => v.clone(),
 355                             None => {
 356                                 let place_builder = place_builder.clone();
 357                                 this.consume_by_copy_or_move(
 358                                     place_builder
 359                                         .field(n, *ty)
 360                                         .into_place(this.tcx, this.typeck_results),
 361                                 )
 362                             }
 363                         })
 364                         .collect()
 365                 } else {
 366                     field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
 367                 };
 368
 369                 let inferred_ty = expr.ty;
 370                 let user_ty = user_ty.map(|ty| {
 371                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
 372                         span: source_info.span,
 373                         user_ty: ty,
 374                         inferred_ty,
 375                     })
 376                 });
 377                 let adt = Box::new(AggregateKind::Adt(
 378                     adt_def.did(),
 379                     variant_index,
 380                     substs,
 381                     user_ty,
 382                     active_field_index,
 383                 ));
 384                 this.cfg.push_assign(
 385                     block,
 386                     source_info,
 387                     destination,
 388                     Rvalue::Aggregate(adt, fields),
 389                 );
 390                 block.unit()
 391             }
 392             ExprKind::InlineAsm { template, ref operands, options, line_spans } => {
 393                 use rustc_middle::{mir, thir};
 394                 let operands = operands
 395                     .into_iter()
 396                     .map(|op| match *op {
 397                         thir::InlineAsmOperand::In { reg, expr } => mir::InlineAsmOperand::In {
 398                             reg,
 399                             value: unpack!(block = this.as_local_operand(block, &this.thir[expr])),
 400                         },
 401                         thir::InlineAsmOperand::Out { reg, late, expr } => {
 402                             mir::InlineAsmOperand::Out {
 403                                 reg,
 404                                 late,
 405                                 place: expr.map(|expr| {
 406                                     unpack!(block = this.as_place(block, &this.thir[expr]))
 407                                 }),
 408                             }
 409                         }
 410                         thir::InlineAsmOperand::InOut { reg, late, expr } => {
 411                             let place = unpack!(block = this.as_place(block, &this.thir[expr]));
 412                             mir::InlineAsmOperand::InOut {
 413                                 reg,
 414                                 late,
 415                                 // This works because asm operands must be Copy
 416                                 in_value: Operand::Copy(place),
 417                                 out_place: Some(place),
 418                             }
 419                         }
 420                         thir::InlineAsmOperand::SplitInOut { reg, late, in_expr, out_expr } => {
 421                             mir::InlineAsmOperand::InOut {
 422                                 reg,
 423                                 late,
 424                                 in_value: unpack!(
 425                                     block = this.as_local_operand(block, &this.thir[in_expr])
 426                                 ),
 427                                 out_place: out_expr.map(|out_expr| {
 428                                     unpack!(block = this.as_place(block, &this.thir[out_expr]))
 429                                 }),
 430                             }
 431                         }
 432                         thir::InlineAsmOperand::Const { value, span } => {
 433                             mir::InlineAsmOperand::Const {
 434                                 value: Box::new(Constant { span, user_ty: None, literal: value }),
 435                             }
 436                         }
 437                         thir::InlineAsmOperand::SymFn { value, span } => {
 438                             mir::InlineAsmOperand::SymFn {
 439                                 value: Box::new(Constant { span, user_ty: None, literal: value }),
 440                             }
 441                         }
 442                         thir::InlineAsmOperand::SymStatic { def_id } => {
 443                             mir::InlineAsmOperand::SymStatic { def_id }
 444                         }
 445                     })
 446                     .collect();
 447
 448                 if !options.contains(InlineAsmOptions::NORETURN) {
 449                     this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
 450                 }
 451
 452                 let destination_block = this.cfg.start_new_block();
 453                 this.cfg.terminate(
 454                     block,
 455                     source_info,
 456                     TerminatorKind::InlineAsm {
 457                         template,
 458                         operands,
 459                         options,
 460                         line_spans,
 461                         destination: if options.contains(InlineAsmOptions::NORETURN) {
 462                             None
 463                         } else {
 464                             Some(destination_block)
 465                         },
 466                         cleanup: None,
 467                     },
 468                 );
 469                 if options.contains(InlineAsmOptions::MAY_UNWIND) {
 470                     this.diverge_from(block);
 471                 }
 472                 destination_block.unit()
 473             }
 474
 475             // These cases don't actually need a destination
 476             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 477                 unpack!(block = this.stmt_expr(block, expr, None));
 478                 this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
 479                 block.unit()
 480             }
 481
 482             ExprKind::Continue { .. } | ExprKind::Break { .. } | ExprKind::Return { .. } => {
 483                 unpack!(block = this.stmt_expr(block, expr, None));
 484                 // No assign, as these have type `!`.
 485                 block.unit()
 486             }
 487
 488             // Avoid creating a temporary
 489             ExprKind::VarRef { .. }
 490             | ExprKind::UpvarRef { .. }
 491             | ExprKind::PlaceTypeAscription { .. }
 492             | ExprKind::ValueTypeAscription { .. } => {
 493                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 494
 495                 let place = unpack!(block = this.as_place(block, expr));
 496                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 497                 this.cfg.push_assign(block, source_info, destination, rvalue);
 498                 block.unit()
 499             }
 500             ExprKind::Index { .. } | ExprKind::Deref { .. } | ExprKind::Field { .. } => {
 501                 debug_assert_eq!(Category::of(&expr.kind), Some(Category::Place));
 502
 503                 // Create a "fake" temporary variable so that we check that the
 504                 // value is Sized. Usually, this is caught in type checking, but
 505                 // in the case of box expr there is no such check.
 506                 if !destination.projection.is_empty() {
 507                     this.local_decls.push(LocalDecl::new(expr.ty, expr.span));
 508                 }
 509
 510                 let place = unpack!(block = this.as_place(block, expr));
 511                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 512                 this.cfg.push_assign(block, source_info, destination, rvalue);
 513                 block.unit()
 514             }
 515
 516             ExprKind::Yield { value } => {
 517                 let scope = this.local_scope();
 518                 let value = unpack!(
 519                     block = this.as_operand(
 520                         block,
 521                         Some(scope),
 522                         &this.thir[value],
 523                         None,
 524                         NeedsTemporary::No
 525                     )
 526                 );
 527                 let resume = this.cfg.start_new_block();
 528                 this.cfg.terminate(
 529                     block,
 530                     source_info,
 531                     TerminatorKind::Yield { value, resume, resume_arg: destination, drop: None },
 532                 );
 533                 this.generator_drop_cleanup(block);
 534                 resume.unit()
 535             }
 536
 537             // these are the cases that are more naturally handled by some other mode
 538             ExprKind::Unary { .. }
 539             | ExprKind::Binary { .. }
 540             | ExprKind::Box { .. }
 541             | ExprKind::Cast { .. }
 542             | ExprKind::Pointer { .. }
 543             | ExprKind::Repeat { .. }
 544             | ExprKind::Array { .. }
 545             | ExprKind::Tuple { .. }
 546             | ExprKind::Closure { .. }
 547             | ExprKind::ConstBlock { .. }
 548             | ExprKind::Literal { .. }
 549             | ExprKind::NamedConst { .. }
 550             | ExprKind::NonHirLiteral { .. }
 551             | ExprKind::ConstParam { .. }
 552             | ExprKind::ThreadLocalRef(_)
 553             | ExprKind::StaticRef { .. } => {
 554                 debug_assert!(match Category::of(&expr.kind).unwrap() {
 555                     // should be handled above
 556                     Category::Rvalue(RvalueFunc::Into) => false,
 557
 558                     // must be handled above or else we get an
 559                     // infinite loop in the builder; see
 560                     // e.g., `ExprKind::VarRef` above
 561                     Category::Place => false,
 562
 563                     _ => true,
 564                 });
 565
 566                 let rvalue = unpack!(block = this.as_local_rvalue(block, expr));
 567                 this.cfg.push_assign(block, source_info, destination, rvalue);
 568                 block.unit()
 569             }
 570         };
 571
 572         if !expr_is_block_or_scope {
 573             let popped = this.block_context.pop();
 574             assert!(popped.is_some());
 575         }
 576
 577         block_and
 578     }
 579 }