compiler/rustc_mir_transform/src/lib.rs

   1 #![allow(rustc::potential_query_instability)]
   2 #![feature(box_patterns)]
   3 #![feature(box_syntax)]
   4 #![feature(crate_visibility_modifier)]
   5 #![feature(let_chains)]
   6 #![feature(let_else)]
   7 #![feature(map_try_insert)]
   8 #![feature(min_specialization)]
   9 #![feature(never_type)]
  10 #![feature(once_cell)]
  11 #![feature(option_get_or_insert_default)]
  12 #![feature(trusted_step)]
  13 #![feature(try_blocks)]
  14 #![recursion_limit = "256"]
  15
  16 #[macro_use]
  17 extern crate tracing;
  18 #[macro_use]
  19 extern crate rustc_middle;
  20
  21 use required_consts::RequiredConstsVisitor;
  22 use rustc_const_eval::util;
  23 use rustc_data_structures::fx::FxIndexSet;
  24 use rustc_data_structures::steal::Steal;
  25 use rustc_hir as hir;
  26 use rustc_hir::def_id::{DefId, LocalDefId};
  27 use rustc_hir::intravisit::{self, Visitor};
  28 use rustc_index::vec::IndexVec;
  29 use rustc_middle::mir::visit::Visitor as _;
  30 use rustc_middle::mir::{traversal, Body, ConstQualifs, MirPass, MirPhase, Promoted};
  31 use rustc_middle::ty::query::Providers;
  32 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
  33 use rustc_span::{Span, Symbol};
  34
  35 #[macro_use]
  36 mod pass_manager;
  37
  38 use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};
  39
  40 mod abort_unwinding_calls;
  41 mod add_call_guards;
  42 mod add_moves_for_packed_drops;
  43 mod add_retag;
  44 mod check_const_item_mutation;
  45 mod check_packed_ref;
  46 pub mod check_unsafety;
  47 // This pass is public to allow external drivers to perform MIR cleanup
  48 pub mod cleanup_post_borrowck;
  49 mod const_debuginfo;
  50 mod const_goto;
  51 mod const_prop;
  52 mod coverage;
  53 mod deaggregator;
  54 mod deduplicate_blocks;
  55 mod dest_prop;
  56 pub mod dump_mir;
  57 mod early_otherwise_branch;
  58 mod elaborate_drops;
  59 mod function_item_references;
  60 mod generator;
  61 mod inline;
  62 mod instcombine;
  63 mod lower_intrinsics;
  64 mod lower_slice_len;
  65 mod marker;
  66 mod match_branches;
  67 mod multiple_return_terminators;
  68 mod normalize_array_len;
  69 mod nrvo;
  70 // This pass is public to allow external drivers to perform MIR cleanup
  71 pub mod remove_false_edges;
  72 mod remove_noop_landing_pads;
  73 mod remove_storage_markers;
  74 mod remove_uninit_drops;
  75 mod remove_unneeded_drops;
  76 mod remove_zsts;
  77 mod required_consts;
  78 mod reveal_all;
  79 mod separate_const_switch;
  80 mod shim;
  81 // This pass is public to allow external drivers to perform MIR cleanup
  82 pub mod simplify;
  83 mod simplify_branches;
  84 mod simplify_comparison_integral;
  85 mod simplify_try;
  86 mod uninhabited_enum_branching;
  87 mod unreachable_prop;
  88
  89 use rustc_const_eval::transform::check_consts::{self, ConstCx};
  90 use rustc_const_eval::transform::promote_consts;
  91 use rustc_const_eval::transform::validate;
  92 use rustc_mir_dataflow::rustc_peek;
  93
  94 pub fn provide(providers: &mut Providers) {
  95     check_unsafety::provide(providers);
  96     check_packed_ref::provide(providers);
  97     coverage::query::provide(providers);
  98     shim::provide(providers);
  99     *providers = Providers {
 100         mir_keys,
 101         mir_const,
 102         mir_const_qualif: |tcx, def_id| {
 103             let def_id = def_id.expect_local();
 104             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 105                 tcx.mir_const_qualif_const_arg(def)
 106             } else {
 107                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
 108             }
 109         },
 110         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 111             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 112         },
 113         mir_promoted,
 114         mir_drops_elaborated_and_const_checked,
 115         mir_for_ctfe,
 116         mir_for_ctfe_of_const_arg,
 117         optimized_mir,
 118         is_mir_available,
 119         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 120         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 121         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 122         promoted_mir: |tcx, def_id| {
 123             let def_id = def_id.expect_local();
 124             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 125                 tcx.promoted_mir_of_const_arg(def)
 126             } else {
 127                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 128             }
 129         },
 130         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 131             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 132         },
 133         ..*providers
 134     };
 135 }
 136
 137 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 138     let def_id = def_id.expect_local();
 139     tcx.mir_keys(()).contains(&def_id)
 140 }
 141
 142 /// Finds the full set of `DefId`s within the current crate that have
 143 /// MIR associated with them.
 144 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 145     let mut set = FxIndexSet::default();
 146
 147     // All body-owners have MIR associated with them.
 148     set.extend(tcx.hir().body_owners());
 149
 150     // Additionally, tuple struct/variant constructors have MIR, but
 151     // they don't have a BodyId, so we need to build them separately.
 152     struct GatherCtors<'a, 'tcx> {
 153         tcx: TyCtxt<'tcx>,
 154         set: &'a mut FxIndexSet<LocalDefId>,
 155     }
 156     impl<'tcx> Visitor<'tcx> for GatherCtors<'_, 'tcx> {
 157         fn visit_variant_data(
 158             &mut self,
 159             v: &'tcx hir::VariantData<'tcx>,
 160             _: Symbol,
 161             _: &'tcx hir::Generics<'tcx>,
 162             _: hir::HirId,
 163             _: Span,
 164         ) {
 165             if let hir::VariantData::Tuple(_, hir_id) = *v {
 166                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 167             }
 168             intravisit::walk_struct_def(self, v)
 169         }
 170     }
 171     tcx.hir().visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 172
 173     set
 174 }
 175
 176 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 177     let const_kind = tcx.hir().body_const_context(def.did);
 178
 179     // No need to const-check a non-const `fn`.
 180     if const_kind.is_none() {
 181         return Default::default();
 182     }
 183
 184     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 185     // cannot yet be stolen), because `mir_promoted()`, which steals
 186     // from `mir_const(), forces this query to execute before
 187     // performing the steal.
 188     let body = &tcx.mir_const(def).borrow();
 189
 190     if body.return_ty().references_error() {
 191         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 192         return Default::default();
 193     }
 194
 195     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 196
 197     let mut validator = check_consts::check::Checker::new(&ccx);
 198     validator.check_body();
 199
 200     // We return the qualifs in the return place for every MIR body, even though it is only used
 201     // when deciding to promote a reference to a `const` for now.
 202     validator.qualifs_in_return_place()
 203 }
 204
 205 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 206 fn mir_const<'tcx>(
 207     tcx: TyCtxt<'tcx>,
 208     def: ty::WithOptConstParam<LocalDefId>,
 209 ) -> &'tcx Steal<Body<'tcx>> {
 210     if let Some(def) = def.try_upgrade(tcx) {
 211         return tcx.mir_const(def);
 212     }
 213
 214     // Unsafety check uses the raw mir, so make sure it is run.
 215     if !tcx.sess.opts.debugging_opts.thir_unsafeck {
 216         if let Some(param_did) = def.const_param_did {
 217             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 218         } else {
 219             tcx.ensure().unsafety_check_result(def.did);
 220         }
 221     }
 222
 223     let mut body = tcx.mir_built(def).steal();
 224
 225     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 226
 227     pm::run_passes(
 228         tcx,
 229         &mut body,
 230         &[
 231             // MIR-level lints.
 232             &Lint(check_packed_ref::CheckPackedRef),
 233             &Lint(check_const_item_mutation::CheckConstItemMutation),
 234             &Lint(function_item_references::FunctionItemReferences),
 235             // What we need to do constant evaluation.
 236             &simplify::SimplifyCfg::new("initial"),
 237             &rustc_peek::SanityCheck, // Just a lint
 238             &marker::PhaseChange(MirPhase::Const),
 239         ],
 240     );
 241     tcx.alloc_steal_mir(body)
 242 }
 243
 244 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 245 fn mir_promoted<'tcx>(
 246     tcx: TyCtxt<'tcx>,
 247     def: ty::WithOptConstParam<LocalDefId>,
 248 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 249     if let Some(def) = def.try_upgrade(tcx) {
 250         return tcx.mir_promoted(def);
 251     }
 252
 253     // Ensure that we compute the `mir_const_qualif` for constants at
 254     // this point, before we steal the mir-const result.
 255     // Also this means promotion can rely on all const checks having been done.
 256     let const_qualifs = tcx.mir_const_qualif_opt_const_arg(def);
 257     let mut body = tcx.mir_const(def).steal();
 258     if let Some(error_reported) = const_qualifs.tainted_by_errors {
 259         body.tainted_by_errors = Some(error_reported);
 260     }
 261
 262     let mut required_consts = Vec::new();
 263     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 264     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 265         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 266     }
 267     body.required_consts = required_consts;
 268
 269     // What we need to run borrowck etc.
 270     let promote_pass = promote_consts::PromoteTemps::default();
 271     pm::run_passes(
 272         tcx,
 273         &mut body,
 274         &[
 275             &promote_pass,
 276             &simplify::SimplifyCfg::new("promote-consts"),
 277             &coverage::InstrumentCoverage,
 278         ],
 279     );
 280
 281     let promoted = promote_pass.promoted_fragments.into_inner();
 282     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 283 }
 284
 285 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 286 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 287     let did = def_id.expect_local();
 288     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 289         tcx.mir_for_ctfe_of_const_arg(def)
 290     } else {
 291         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 292     }
 293 }
 294
 295 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 296 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 297 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 298 /// the const parameter while type checking the main body, which in turn would try
 299 /// to type check the main body again.
 300 fn mir_for_ctfe_of_const_arg<'tcx>(
 301     tcx: TyCtxt<'tcx>,
 302     (did, param_did): (LocalDefId, DefId),
 303 ) -> &'tcx Body<'tcx> {
 304     tcx.arena.alloc(inner_mir_for_ctfe(
 305         tcx,
 306         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 307     ))
 308 }
 309
 310 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 311     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 312     if tcx.is_constructor(def.did.to_def_id()) {
 313         // There's no reason to run all of the MIR passes on constructors when
 314         // we can just output the MIR we want directly. This also saves const
 315         // qualification and borrow checking the trouble of special casing
 316         // constructors.
 317         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 318     }
 319
 320     let context = tcx
 321         .hir()
 322         .body_const_context(def.did)
 323         .expect("mir_for_ctfe should not be used for runtime functions");
 324
 325     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 326
 327     match context {
 328         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 329         // so we run const prop on them, or they don't, in which case we const evaluate some control
 330         // flow paths of the function and any errors in those paths will get emitted as const eval
 331         // errors.
 332         hir::ConstContext::ConstFn => {}
 333         // Static items always get evaluated, so we can just let const eval see if any erroneous
 334         // control flow paths get executed.
 335         hir::ConstContext::Static(_) => {}
 336         // Associated constants get const prop run so we detect common failure situations in the
 337         // crate that defined the constant.
 338         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 339         // conveniently detect that at this point without looking at the HIR.
 340         hir::ConstContext::Const => {
 341             pm::run_passes(
 342                 tcx,
 343                 &mut body,
 344                 &[&const_prop::ConstProp, &marker::PhaseChange(MirPhase::Optimization)],
 345             );
 346         }
 347     }
 348
 349     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 350
 351     body
 352 }
 353
 354 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 355 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 356 /// end up missing the source MIR due to stealing happening.
 357 fn mir_drops_elaborated_and_const_checked<'tcx>(
 358     tcx: TyCtxt<'tcx>,
 359     def: ty::WithOptConstParam<LocalDefId>,
 360 ) -> &'tcx Steal<Body<'tcx>> {
 361     if let Some(def) = def.try_upgrade(tcx) {
 362         return tcx.mir_drops_elaborated_and_const_checked(def);
 363     }
 364
 365     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 366
 367     let is_fn_like = tcx.hir().get_by_def_id(def.did).fn_kind().is_some();
 368     if is_fn_like {
 369         let did = def.did.to_def_id();
 370         let def = ty::WithOptConstParam::unknown(did);
 371
 372         // Do not compute the mir call graph without said call graph actually being used.
 373         if inline::Inline.is_enabled(&tcx.sess) {
 374             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 375         }
 376     }
 377
 378     let (body, _) = tcx.mir_promoted(def);
 379     let mut body = body.steal();
 380     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 381         body.tainted_by_errors = Some(error_reported);
 382     }
 383
 384     // IMPORTANT
 385     pm::run_passes(tcx, &mut body, &[&remove_false_edges::RemoveFalseEdges]);
 386
 387     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 388     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 389         pm::run_passes(
 390             tcx,
 391             &mut body,
 392             &[
 393                 &simplify::SimplifyCfg::new("remove-false-edges"),
 394                 &remove_uninit_drops::RemoveUninitDrops,
 395             ],
 396         );
 397         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 398     }
 399
 400     run_post_borrowck_cleanup_passes(tcx, &mut body);
 401     assert!(body.phase == MirPhase::DropLowering);
 402     tcx.alloc_steal_mir(body)
 403 }
 404
 405 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 406 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 407     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 408
 409     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 410         // Remove all things only needed by analysis
 411         &simplify_branches::SimplifyConstCondition::new("initial"),
 412         &remove_noop_landing_pads::RemoveNoopLandingPads,
 413         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 414         &simplify::SimplifyCfg::new("early-opt"),
 415         // These next passes must be executed together
 416         &add_call_guards::CriticalCallEdges,
 417         &elaborate_drops::ElaborateDrops,
 418         // This will remove extraneous landing pads which are no longer
 419         // necessary as well as well as forcing any call in a non-unwinding
 420         // function calling a possibly-unwinding function to abort the process.
 421         &abort_unwinding_calls::AbortUnwindingCalls,
 422         // AddMovesForPackedDrops needs to run after drop
 423         // elaboration.
 424         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 425         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 426         // but before optimizations begin.
 427         &add_retag::AddRetag,
 428         &lower_intrinsics::LowerIntrinsics,
 429         &simplify::SimplifyCfg::new("elaborate-drops"),
 430         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 431         // and it can help optimizations.
 432         &deaggregator::Deaggregator,
 433     ];
 434
 435     pm::run_passes(tcx, body, post_borrowck_cleanup);
 436 }
 437
 438 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 439     fn o1<T>(x: T) -> WithMinOptLevel<T> {
 440         WithMinOptLevel(1, x)
 441     }
 442
 443     // Lowering generator control-flow and variables has to happen before we do anything else
 444     // to them. We run some optimizations before that, because they may be harder to do on the state
 445     // machine than on MIR with async primitives.
 446     pm::run_passes(
 447         tcx,
 448         body,
 449         &[
 450             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 451             &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
 452             &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 453             &unreachable_prop::UnreachablePropagation,
 454             &uninhabited_enum_branching::UninhabitedEnumBranching,
 455             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
 456             &inline::Inline,
 457             &generator::StateTransform,
 458         ],
 459     );
 460
 461     assert!(body.phase == MirPhase::GeneratorLowering);
 462
 463     // The main optimizations that we do on MIR.
 464     pm::run_passes(
 465         tcx,
 466         body,
 467         &[
 468             &remove_storage_markers::RemoveStorageMarkers,
 469             &remove_zsts::RemoveZsts,
 470             &const_goto::ConstGoto,
 471             &remove_unneeded_drops::RemoveUnneededDrops,
 472             &match_branches::MatchBranchSimplification,
 473             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 474             &multiple_return_terminators::MultipleReturnTerminators,
 475             &instcombine::InstCombine,
 476             &separate_const_switch::SeparateConstSwitch,
 477             //
 478             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 479             &const_prop::ConstProp,
 480             //
 481             // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
 482             &o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
 483             &early_otherwise_branch::EarlyOtherwiseBranch,
 484             &simplify_comparison_integral::SimplifyComparisonIntegral,
 485             &simplify_try::SimplifyArmIdentity,
 486             &simplify_try::SimplifyBranchSame,
 487             &dest_prop::DestinationPropagation,
 488             &o1(simplify_branches::SimplifyConstCondition::new("final")),
 489             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
 490             &o1(simplify::SimplifyCfg::new("final")),
 491             &nrvo::RenameReturnPlace,
 492             &const_debuginfo::ConstDebugInfo,
 493             &simplify::SimplifyLocals,
 494             &multiple_return_terminators::MultipleReturnTerminators,
 495             &deduplicate_blocks::DeduplicateBlocks,
 496             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 497             &add_call_guards::CriticalCallEdges,
 498             &marker::PhaseChange(MirPhase::Optimization),
 499             // Dump the end result for testing and debugging purposes.
 500             &dump_mir::Marker("PreCodegen"),
 501         ],
 502     );
 503 }
 504
 505 /// Optimize the MIR and prepare it for codegen.
 506 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 507     let did = did.expect_local();
 508     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 509     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 510 }
 511
 512 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 513     if tcx.is_constructor(did.to_def_id()) {
 514         // There's no reason to run all of the MIR passes on constructors when
 515         // we can just output the MIR we want directly. This also saves const
 516         // qualification and borrow checking the trouble of special casing
 517         // constructors.
 518         return shim::build_adt_ctor(tcx, did.to_def_id());
 519     }
 520
 521     match tcx.hir().body_const_context(did) {
 522         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 523         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 524         // computes and caches its result.
 525         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 526         None => {}
 527         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 528     }
 529     let mut body =
 530         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 531     run_optimization_passes(tcx, &mut body);
 532
 533     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 534
 535     body
 536 }
 537
 538 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 539 /// constant evaluation once all substitutions become known.
 540 fn promoted_mir<'tcx>(
 541     tcx: TyCtxt<'tcx>,
 542     def: ty::WithOptConstParam<LocalDefId>,
 543 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 544     if tcx.is_constructor(def.did.to_def_id()) {
 545         return tcx.arena.alloc(IndexVec::new());
 546     }
 547
 548     let tainted_by_errors = tcx.mir_borrowck_opt_const_arg(def).tainted_by_errors;
 549     let mut promoted = tcx.mir_promoted(def).1.steal();
 550
 551     for body in &mut promoted {
 552         if let Some(error_reported) = tainted_by_errors {
 553             body.tainted_by_errors = Some(error_reported);
 554         }
 555         run_post_borrowck_cleanup_passes(tcx, body);
 556     }
 557
 558     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 559
 560     tcx.arena.alloc(promoted)
 561 }