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