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 { block: 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 source_info = if this.is_let(cond) {
  67                                 let variable_scope = this.new_source_scope(
  68                                     then_expr.span,
  69                                     LintLevel::Inherited,
  70                                     None,
  71                                 );
  72                                 this.source_scope = variable_scope;
  73                                 SourceInfo { span: then_expr.span, scope: variable_scope }
  74                             } else {
  75                                 this.source_info(then_expr.span)
  76                             };
  77                             let (then_block, else_block) =
  78                                 this.in_if_then_scope(condition_scope, |this| {
  79                                     let then_blk = unpack!(this.then_else_break(
  80                                         block,
  81                                         &this.thir[cond],
  82                                         Some(condition_scope),
  83                                         condition_scope,
  84                                         source_info
  85                                     ));
  86
  87                                     this.expr_into_dest(destination, then_blk, then_expr)
  88                                 });
  89                             then_block.and(else_block)
  90                         },
  91                     )
  92                 );
  93
  94                 else_blk = if let Some(else_opt) = else_opt {
  95                     unpack!(this.expr_into_dest(destination, else_blk, &this.thir[else_opt]))
  96                 } else {
  97                     // Body of the `if` expression without an `else` clause must return `()`, thus
  98                     // we implicitly generate an `else {}` if it is not specified.
  99                     let correct_si = this.source_info(expr_span.shrink_to_hi());
 100                     this.cfg.push_assign_unit(else_blk, correct_si, destination, this.tcx);
 101                     else_blk
 102                 };
 103
 104                 let join_block = this.cfg.start_new_block();
 105                 this.cfg.goto(then_blk, source_info, join_block);
 106                 this.cfg.goto(else_blk, source_info, join_block);
 107                 join_block.unit()
 108             }
 109             ExprKind::Let { expr, ref pat } => {
 110                 let scope = this.local_scope();
 111                 let (true_block, false_block) = this.in_if_then_scope(scope, |this| {
 112                     this.lower_let_expr(block, &this.thir[expr], pat, scope, None, expr_span)
 113                 });
 114
 115                 this.cfg.push_assign_constant(
 116                     true_block,
 117                     source_info,
 118                     destination,
 119                     Constant {
 120                         span: expr_span,
 121                         user_ty: None,
 122                         literal: ConstantKind::from_bool(this.tcx, true),
 123                     },
 124                 );
 125
 126                 this.cfg.push_assign_constant(
 127                     false_block,
 128                     source_info,
 129                     destination,
 130                     Constant {
 131                         span: expr_span,
 132                         user_ty: None,
 133                         literal: ConstantKind::from_bool(this.tcx, false),
 134                     },
 135                 );
 136
 137                 let join_block = this.cfg.start_new_block();
 138                 this.cfg.goto(true_block, source_info, join_block);
 139                 this.cfg.goto(false_block, source_info, join_block);
 140                 join_block.unit()
 141             }
 142             ExprKind::NeverToAny { source } => {
 143                 let source = &this.thir[source];
 144                 let is_call =
 145                     matches!(source.kind, ExprKind::Call { .. } | ExprKind::InlineAsm { .. });
 146
 147                 // (#66975) Source could be a const of type `!`, so has to
 148                 // exist in the generated MIR.
 149                 unpack!(
 150                     block = this.as_temp(block, Some(this.local_scope()), source, Mutability::Mut,)
 151                 );
 152
 153                 // This is an optimization. If the expression was a call then we already have an
 154                 // unreachable block. Don't bother to terminate it and create a new one.
 155                 if is_call {
 156                     block.unit()
 157                 } else {
 158                     this.cfg.terminate(block, source_info, TerminatorKind::Unreachable);
 159                     let end_block = this.cfg.start_new_block();
 160                     end_block.unit()
 161                 }
 162             }
 163             ExprKind::LogicalOp { op, lhs, rhs } => {
 164                 // And:
 165                 //
 166                 // [block: If(lhs)] -true-> [else_block: dest = (rhs)]
 167                 //        | (false)
 168                 //  [shortcurcuit_block: dest = false]
 169                 //
 170                 // Or:
 171                 //
 172                 // [block: If(lhs)] -false-> [else_block: dest = (rhs)]
 173                 //        | (true)
 174                 //  [shortcurcuit_block: dest = true]
 175
 176                 let (shortcircuit_block, mut else_block, join_block) = (
 177                     this.cfg.start_new_block(),
 178                     this.cfg.start_new_block(),
 179                     this.cfg.start_new_block(),
 180                 );
 181
 182                 let lhs = unpack!(block = this.as_local_operand(block, &this.thir[lhs]));
 183                 let blocks = match op {
 184                     LogicalOp::And => (else_block, shortcircuit_block),
 185                     LogicalOp::Or => (shortcircuit_block, else_block),
 186                 };
 187                 let term = TerminatorKind::if_(this.tcx, lhs, blocks.0, blocks.1);
 188                 this.cfg.terminate(block, source_info, term);
 189
 190                 this.cfg.push_assign_constant(
 191                     shortcircuit_block,
 192                     source_info,
 193                     destination,
 194                     Constant {
 195                         span: expr_span,
 196                         user_ty: None,
 197                         literal: match op {
 198                             LogicalOp::And => ConstantKind::from_bool(this.tcx, false),
 199                             LogicalOp::Or => ConstantKind::from_bool(this.tcx, true),
 200                         },
 201                     },
 202                 );
 203                 this.cfg.goto(shortcircuit_block, source_info, join_block);
 204
 205                 let rhs = unpack!(else_block = this.as_local_operand(else_block, &this.thir[rhs]));
 206                 this.cfg.push_assign(else_block, source_info, destination, Rvalue::Use(rhs));
 207                 this.cfg.goto(else_block, source_info, join_block);
 208
 209                 join_block.unit()
 210             }
 211             ExprKind::Loop { body } => {
 212                 // [block]
 213                 //    |
 214                 //   [loop_block] -> [body_block] -/eval. body/-> [body_block_end]
 215                 //    |        ^                                         |
 216                 // false link  |                                         |
 217                 //    |        +-----------------------------------------+
 218                 //    +-> [diverge_cleanup]
 219                 // The false link is required to make sure borrowck considers unwinds through the
 220                 // body, even when the exact code in the body cannot unwind
 221
 222                 let loop_block = this.cfg.start_new_block();
 223
 224                 // Start the loop.
 225                 this.cfg.goto(block, source_info, loop_block);
 226
 227                 this.in_breakable_scope(Some(loop_block), destination, expr_span, move |this| {
 228                     // conduct the test, if necessary
 229                     let body_block = this.cfg.start_new_block();
 230                     this.cfg.terminate(
 231                         loop_block,
 232                         source_info,
 233                         TerminatorKind::FalseUnwind { real_target: body_block, unwind: None },
 234                     );
 235                     this.diverge_from(loop_block);
 236
 237                     // The “return” value of the loop body must always be a unit. We therefore
 238                     // introduce a unit temporary as the destination for the loop body.
 239                     let tmp = this.get_unit_temp();
 240                     // Execute the body, branching back to the test.
 241                     let body_block_end =
 242                         unpack!(this.expr_into_dest(tmp, body_block, &this.thir[body]));
 243                     this.cfg.goto(body_block_end, source_info, loop_block);
 244
 245                     // Loops are only exited by `break` expressions.
 246                     None
 247                 })
 248             }
 249             ExprKind::Call { ty: _, fun, ref args, from_hir_call, fn_span } => {
 250                 let fun = unpack!(block = this.as_local_operand(block, &this.thir[fun]));
 251                 let args: Vec<_> = args
 252                     .into_iter()
 253                     .copied()
 254                     .map(|arg| unpack!(block = this.as_local_call_operand(block, &this.thir[arg])))
 255                     .collect();
 256
 257                 let success = this.cfg.start_new_block();
 258
 259                 this.record_operands_moved(&args);
 260
 261                 debug!("expr_into_dest: fn_span={:?}", fn_span);
 262
 263                 this.cfg.terminate(
 264                     block,
 265                     source_info,
 266                     TerminatorKind::Call {
 267                         func: fun,
 268                         args,
 269                         cleanup: None,
 270                         destination,
 271                         // The presence or absence of a return edge affects control-flow sensitive
 272                         // MIR checks and ultimately whether code is accepted or not. We can only
 273                         // omit the return edge if a return type is visibly uninhabited to a module
 274                         // that makes the call.
 275                         target: if this.tcx.is_ty_uninhabited_from(
 276                             this.parent_module,
 277                             expr.ty,
 278                             this.param_env,
 279                         ) {
 280                             None
 281                         } else {
 282                             Some(success)
 283                         },
 284                         from_hir_call,
 285                         fn_span,
 286                     },
 287                 );
 288                 this.diverge_from(block);
 289                 success.unit()
 290             }
 291             ExprKind::Use { source } => this.expr_into_dest(destination, block, &this.thir[source]),
 292             ExprKind::Borrow { arg, borrow_kind } => {
 293                 let arg = &this.thir[arg];
 294                 // We don't do this in `as_rvalue` because we use `as_place`
 295                 // for borrow expressions, so we cannot create an `RValue` that
 296                 // remains valid across user code. `as_rvalue` is usually called
 297                 // by this method anyway, so this shouldn't cause too many
 298                 // unnecessary temporaries.
 299                 let arg_place = match borrow_kind {
 300                     BorrowKind::Shared => unpack!(block = this.as_read_only_place(block, arg)),
 301                     _ => unpack!(block = this.as_place(block, arg)),
 302                 };
 303                 let borrow = Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place);
 304                 this.cfg.push_assign(block, source_info, destination, borrow);
 305                 block.unit()
 306             }
 307             ExprKind::AddressOf { mutability, arg } => {
 308                 let arg = &this.thir[arg];
 309                 let place = match mutability {
 310                     hir::Mutability::Not => this.as_read_only_place(block, arg),
 311                     hir::Mutability::Mut => this.as_place(block, arg),
 312                 };
 313                 let address_of = Rvalue::AddressOf(mutability, unpack!(block = place));
 314                 this.cfg.push_assign(block, source_info, destination, address_of);
 315                 block.unit()
 316             }
 317             ExprKind::Adt(box AdtExpr {
 318                 adt_def,
 319                 variant_index,
 320                 substs,
 321                 ref user_ty,
 322                 ref fields,
 323                 ref base,
 324             }) => {
 325                 // See the notes for `ExprKind::Array` in `as_rvalue` and for
 326                 // `ExprKind::Borrow` above.
 327                 let is_union = adt_def.is_union();
 328                 let active_field_index = if is_union { Some(fields[0].name.index()) } else { None };
 329
 330                 let scope = this.local_scope();
 331
 332                 // first process the set of fields that were provided
 333                 // (evaluating them in order given by user)
 334                 let fields_map: FxHashMap<_, _> = fields
 335                     .into_iter()
 336                     .map(|f| {
 337                         let local_info = Box::new(LocalInfo::AggregateTemp);
 338                         (
 339                             f.name,
 340                             unpack!(
 341                                 block = this.as_operand(
 342                                     block,
 343                                     Some(scope),
 344                                     &this.thir[f.expr],
 345                                     Some(local_info),
 346                                     NeedsTemporary::Maybe,
 347                                 )
 348                             ),
 349                         )
 350                     })
 351                     .collect();
 352
 353                 let field_names: Vec<_> =
 354                     (0..adt_def.variant(variant_index).fields.len()).map(Field::new).collect();
 355
 356                 let fields: Vec<_> = if let Some(FruInfo { base, field_types }) = base {
 357                     let place_builder =
 358                         unpack!(block = this.as_place_builder(block, &this.thir[*base]));
 359
 360                     // MIR does not natively support FRU, so for each
 361                     // base-supplied field, generate an operand that
 362                     // reads it from the base.
 363                     iter::zip(field_names, &**field_types)
 364                         .map(|(n, ty)| match fields_map.get(&n) {
 365                             Some(v) => v.clone(),
 366                             None => {
 367                                 let place_builder = place_builder.clone();
 368                                 this.consume_by_copy_or_move(
 369                                     place_builder
 370                                         .field(n, *ty)
 371                                         .into_place(this.tcx, this.typeck_results),
 372                                 )
 373                             }
 374                         })
 375                         .collect()
 376                 } else {
 377                     field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
 378                 };
 379
 380                 let inferred_ty = expr.ty;
 381                 let user_ty = user_ty.as_ref().map(|user_ty| {
 382                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
 383                         span: source_info.span,
 384                         user_ty: user_ty.clone(),
 385                         inferred_ty,
 386                     })
 387                 });
 388                 let adt = Box::new(AggregateKind::Adt(
 389                     adt_def.did(),
 390                     variant_index,
 391                     substs,
 392                     user_ty,
 393                     active_field_index,
 394                 ));
 395                 this.cfg.push_assign(
 396                     block,
 397                     source_info,
 398                     destination,
 399                     Rvalue::Aggregate(adt, fields),
 400                 );
 401                 block.unit()
 402             }
 403             ExprKind::InlineAsm(box InlineAsmExpr {
 404                 template,
 405                 ref operands,
 406                 options,
 407                 line_spans,
 408             }) => {
 409                 use rustc_middle::{mir, thir};
 410                 let operands = operands
 411                     .into_iter()
 412                     .map(|op| match *op {
 413                         thir::InlineAsmOperand::In { reg, expr } => mir::InlineAsmOperand::In {
 414                             reg,
 415                             value: unpack!(block = this.as_local_operand(block, &this.thir[expr])),
 416                         },
 417                         thir::InlineAsmOperand::Out { reg, late, expr } => {
 418                             mir::InlineAsmOperand::Out {
 419                                 reg,
 420                                 late,
 421                                 place: expr.map(|expr| {
 422                                     unpack!(block = this.as_place(block, &this.thir[expr]))
 423                                 }),
 424                             }
 425                         }
 426                         thir::InlineAsmOperand::InOut { reg, late, expr } => {
 427                             let place = unpack!(block = this.as_place(block, &this.thir[expr]));
 428                             mir::InlineAsmOperand::InOut {
 429                                 reg,
 430                                 late,
 431                                 // This works because asm operands must be Copy
 432                                 in_value: Operand::Copy(place),
 433                                 out_place: Some(place),
 434                             }
 435                         }
 436                         thir::InlineAsmOperand::SplitInOut { reg, late, in_expr, out_expr } => {
 437                             mir::InlineAsmOperand::InOut {
 438                                 reg,
 439                                 late,
 440                                 in_value: unpack!(
 441                                     block = this.as_local_operand(block, &this.thir[in_expr])
 442                                 ),
 443                                 out_place: out_expr.map(|out_expr| {
 444                                     unpack!(block = this.as_place(block, &this.thir[out_expr]))
 445                                 }),
 446                             }
 447                         }
 448                         thir::InlineAsmOperand::Const { value, span } => {
 449                             mir::InlineAsmOperand::Const {
 450                                 value: Box::new(Constant { span, user_ty: None, literal: value }),
 451                             }
 452                         }
 453                         thir::InlineAsmOperand::SymFn { value, span } => {
 454                             mir::InlineAsmOperand::SymFn {
 455                                 value: Box::new(Constant { span, user_ty: None, literal: value }),
 456                             }
 457                         }
 458                         thir::InlineAsmOperand::SymStatic { def_id } => {
 459                             mir::InlineAsmOperand::SymStatic { def_id }
 460                         }
 461                     })
 462                     .collect();
 463
 464                 if !options.contains(InlineAsmOptions::NORETURN) {
 465                     this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
 466                 }
 467
 468                 let destination_block = this.cfg.start_new_block();
 469                 this.cfg.terminate(
 470                     block,
 471                     source_info,
 472                     TerminatorKind::InlineAsm {
 473                         template,
 474                         operands,
 475                         options,
 476                         line_spans,
 477                         destination: if options.contains(InlineAsmOptions::NORETURN) {
 478                             None
 479                         } else {
 480                             Some(destination_block)
 481                         },
 482                         cleanup: None,
 483                     },
 484                 );
 485                 if options.contains(InlineAsmOptions::MAY_UNWIND) {
 486                     this.diverge_from(block);
 487                 }
 488                 destination_block.unit()
 489             }
 490
 491             // These cases don't actually need a destination
 492             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
 493                 unpack!(block = this.stmt_expr(block, expr, None));
 494                 this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
 495                 block.unit()
 496             }
 497
 498             ExprKind::Continue { .. } | ExprKind::Break { .. } | ExprKind::Return { .. } => {
 499                 unpack!(block = this.stmt_expr(block, expr, None));
 500                 // No assign, as these have type `!`.
 501                 block.unit()
 502             }
 503
 504             // Avoid creating a temporary
 505             ExprKind::VarRef { .. }
 506             | ExprKind::UpvarRef { .. }
 507             | ExprKind::PlaceTypeAscription { .. }
 508             | ExprKind::ValueTypeAscription { .. } => {
 509                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 510
 511                 let place = unpack!(block = this.as_place(block, expr));
 512                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 513                 this.cfg.push_assign(block, source_info, destination, rvalue);
 514                 block.unit()
 515             }
 516             ExprKind::Index { .. } | ExprKind::Deref { .. } | ExprKind::Field { .. } => {
 517                 debug_assert_eq!(Category::of(&expr.kind), Some(Category::Place));
 518
 519                 // Create a "fake" temporary variable so that we check that the
 520                 // value is Sized. Usually, this is caught in type checking, but
 521                 // in the case of box expr there is no such check.
 522                 if !destination.projection.is_empty() {
 523                     this.local_decls.push(LocalDecl::new(expr.ty, expr.span));
 524                 }
 525
 526                 let place = unpack!(block = this.as_place(block, expr));
 527                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 528                 this.cfg.push_assign(block, source_info, destination, rvalue);
 529                 block.unit()
 530             }
 531
 532             ExprKind::Yield { value } => {
 533                 let scope = this.local_scope();
 534                 let value = unpack!(
 535                     block = this.as_operand(
 536                         block,
 537                         Some(scope),
 538                         &this.thir[value],
 539                         None,
 540                         NeedsTemporary::No
 541                     )
 542                 );
 543                 let resume = this.cfg.start_new_block();
 544                 this.cfg.terminate(
 545                     block,
 546                     source_info,
 547                     TerminatorKind::Yield { value, resume, resume_arg: destination, drop: None },
 548                 );
 549                 this.generator_drop_cleanup(block);
 550                 resume.unit()
 551             }
 552
 553             // these are the cases that are more naturally handled by some other mode
 554             ExprKind::Unary { .. }
 555             | ExprKind::Binary { .. }
 556             | ExprKind::Box { .. }
 557             | ExprKind::Cast { .. }
 558             | ExprKind::Pointer { .. }
 559             | ExprKind::Repeat { .. }
 560             | ExprKind::Array { .. }
 561             | ExprKind::Tuple { .. }
 562             | ExprKind::Closure { .. }
 563             | ExprKind::ConstBlock { .. }
 564             | ExprKind::Literal { .. }
 565             | ExprKind::NamedConst { .. }
 566             | ExprKind::NonHirLiteral { .. }
 567             | ExprKind::ZstLiteral { .. }
 568             | ExprKind::ConstParam { .. }
 569             | ExprKind::ThreadLocalRef(_)
 570             | ExprKind::StaticRef { .. } => {
 571                 debug_assert!(match Category::of(&expr.kind).unwrap() {
 572                     // should be handled above
 573                     Category::Rvalue(RvalueFunc::Into) => false,
 574
 575                     // must be handled above or else we get an
 576                     // infinite loop in the builder; see
 577                     // e.g., `ExprKind::VarRef` above
 578                     Category::Place => false,
 579
 580                     _ => true,
 581                 });
 582
 583                 let rvalue = unpack!(block = this.as_local_rvalue(block, expr));
 584                 this.cfg.push_assign(block, source_info, destination, rvalue);
 585                 block.unit()
 586             }
 587         };
 588
 589         if !expr_is_block_or_scope {
 590             let popped = this.block_context.pop();
 591             assert!(popped.is_some());
 592         }
 593
 594         block_and
 595     }
 596
 597     fn is_let(&self, expr: ExprId) -> bool {
 598         match self.thir[expr].kind {
 599             ExprKind::Let { .. } => true,
 600             ExprKind::Scope { value, .. } => self.is_let(value),
 601             _ => false,
 602         }
 603     }
 604 }