compiler/rustc_mir_transform/src/lib.rs

   1 #![feature(box_patterns)]
   2 #![feature(box_syntax)]
   3 #![feature(crate_visibility_modifier)]
   4 #![cfg_attr(bootstrap, feature(const_panic))]
   5 #![feature(in_band_lifetimes)]
   6 #![feature(iter_zip)]
   7 #![feature(map_try_insert)]
   8 #![feature(min_specialization)]
   9 #![feature(option_get_or_insert_default)]
  10 #![feature(once_cell)]
  11 #![feature(never_type)]
  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::FxHashSet;
  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, NestedVisitorMap, Visitor};
  28 use rustc_index::vec::IndexVec;
  29 use rustc_middle::mir::visit::Visitor as _;
  30 use rustc_middle::mir::{traversal, Body, ConstQualifs, 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 mod abort_unwinding_calls;
  36 mod add_call_guards;
  37 mod add_moves_for_packed_drops;
  38 mod add_retag;
  39 mod check_const_item_mutation;
  40 mod check_packed_ref;
  41 pub mod check_unsafety;
  42 mod cleanup_post_borrowck;
  43 mod const_debuginfo;
  44 mod const_goto;
  45 mod const_prop;
  46 mod coverage;
  47 mod deaggregator;
  48 mod deduplicate_blocks;
  49 mod dest_prop;
  50 pub mod dump_mir;
  51 mod early_otherwise_branch;
  52 mod elaborate_drops;
  53 mod function_item_references;
  54 mod generator;
  55 mod inline;
  56 mod instcombine;
  57 mod lower_intrinsics;
  58 mod lower_slice_len;
  59 mod match_branches;
  60 mod multiple_return_terminators;
  61 mod nrvo;
  62 mod remove_noop_landing_pads;
  63 mod remove_storage_markers;
  64 mod remove_unneeded_drops;
  65 mod remove_zsts;
  66 mod required_consts;
  67 mod separate_const_switch;
  68 mod shim;
  69 mod simplify;
  70 mod simplify_branches;
  71 mod simplify_comparison_integral;
  72 mod simplify_try;
  73 mod uninhabited_enum_branching;
  74 mod unreachable_prop;
  75
  76 use rustc_const_eval::transform::check_consts;
  77 use rustc_const_eval::transform::promote_consts;
  78 use rustc_const_eval::transform::validate;
  79 pub use rustc_const_eval::transform::MirPass;
  80 use rustc_mir_dataflow::rustc_peek;
  81
  82 pub fn provide(providers: &mut Providers) {
  83     check_unsafety::provide(providers);
  84     check_packed_ref::provide(providers);
  85     coverage::query::provide(providers);
  86     shim::provide(providers);
  87     *providers = Providers {
  88         mir_keys,
  89         mir_const,
  90         mir_const_qualif: |tcx, def_id| {
  91             let def_id = def_id.expect_local();
  92             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  93                 tcx.mir_const_qualif_const_arg(def)
  94             } else {
  95                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  96             }
  97         },
  98         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
  99             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 100         },
 101         mir_promoted,
 102         mir_drops_elaborated_and_const_checked,
 103         mir_for_ctfe,
 104         mir_for_ctfe_of_const_arg,
 105         optimized_mir,
 106         is_mir_available,
 107         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 108         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 109         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 110         promoted_mir: |tcx, def_id| {
 111             let def_id = def_id.expect_local();
 112             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 113                 tcx.promoted_mir_of_const_arg(def)
 114             } else {
 115                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 116             }
 117         },
 118         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 119             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 120         },
 121         ..*providers
 122     };
 123 }
 124
 125 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 126     let def_id = def_id.expect_local();
 127     tcx.mir_keys(()).contains(&def_id)
 128 }
 129
 130 /// Finds the full set of `DefId`s within the current crate that have
 131 /// MIR associated with them.
 132 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxHashSet<LocalDefId> {
 133     let mut set = FxHashSet::default();
 134
 135     // All body-owners have MIR associated with them.
 136     set.extend(tcx.hir().body_owners());
 137
 138     // Additionally, tuple struct/variant constructors have MIR, but
 139     // they don't have a BodyId, so we need to build them separately.
 140     struct GatherCtors<'a, 'tcx> {
 141         tcx: TyCtxt<'tcx>,
 142         set: &'a mut FxHashSet<LocalDefId>,
 143     }
 144     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 145         fn visit_variant_data(
 146             &mut self,
 147             v: &'tcx hir::VariantData<'tcx>,
 148             _: Symbol,
 149             _: &'tcx hir::Generics<'tcx>,
 150             _: hir::HirId,
 151             _: Span,
 152         ) {
 153             if let hir::VariantData::Tuple(_, hir_id) = *v {
 154                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 155             }
 156             intravisit::walk_struct_def(self, v)
 157         }
 158         type Map = intravisit::ErasedMap<'tcx>;
 159         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 160             NestedVisitorMap::None
 161         }
 162     }
 163     tcx.hir().visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 164
 165     set
 166 }
 167
 168 fn run_passes(
 169     tcx: TyCtxt<'tcx>,
 170     body: &mut Body<'tcx>,
 171     mir_phase: MirPhase,
 172     passes: &[&[&dyn MirPass<'tcx>]],
 173 ) {
 174     let phase_index = mir_phase.phase_index();
 175     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 176
 177     if body.phase >= mir_phase {
 178         return;
 179     }
 180
 181     if validate {
 182         validate::Validator { when: format!("input to phase {:?}", mir_phase), mir_phase }
 183             .run_pass(tcx, body);
 184     }
 185
 186     let mut index = 0;
 187     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 188         let run_hooks = |body: &_, index, is_after| {
 189             dump_mir::on_mir_pass(
 190                 tcx,
 191                 &format_args!("{:03}-{:03}", phase_index, index),
 192                 &pass.name(),
 193                 body,
 194                 is_after,
 195             );
 196         };
 197         run_hooks(body, index, false);
 198         pass.run_pass(tcx, body);
 199         run_hooks(body, index, true);
 200
 201         if validate {
 202             validate::Validator {
 203                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 204                 mir_phase,
 205             }
 206             .run_pass(tcx, body);
 207         }
 208
 209         index += 1;
 210     };
 211
 212     for pass_group in passes {
 213         for pass in *pass_group {
 214             run_pass(*pass);
 215         }
 216     }
 217
 218     body.phase = mir_phase;
 219
 220     if mir_phase == MirPhase::Optimization {
 221         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 222             .run_pass(tcx, body);
 223     }
 224 }
 225
 226 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 227     let const_kind = tcx.hir().body_const_context(def.did);
 228
 229     // No need to const-check a non-const `fn`.
 230     if const_kind.is_none() {
 231         return Default::default();
 232     }
 233
 234     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 235     // cannot yet be stolen), because `mir_promoted()`, which steals
 236     // from `mir_const(), forces this query to execute before
 237     // performing the steal.
 238     let body = &tcx.mir_const(def).borrow();
 239
 240     if body.return_ty().references_error() {
 241         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 242         return Default::default();
 243     }
 244
 245     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 246
 247     let mut validator = check_consts::check::Checker::new(&ccx);
 248     validator.check_body();
 249
 250     // We return the qualifs in the return place for every MIR body, even though it is only used
 251     // when deciding to promote a reference to a `const` for now.
 252     validator.qualifs_in_return_place()
 253 }
 254
 255 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 256 fn mir_const<'tcx>(
 257     tcx: TyCtxt<'tcx>,
 258     def: ty::WithOptConstParam<LocalDefId>,
 259 ) -> &'tcx Steal<Body<'tcx>> {
 260     if let Some(def) = def.try_upgrade(tcx) {
 261         return tcx.mir_const(def);
 262     }
 263
 264     // Unsafety check uses the raw mir, so make sure it is run.
 265     if !tcx.sess.opts.debugging_opts.thir_unsafeck {
 266         if let Some(param_did) = def.const_param_did {
 267             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 268         } else {
 269             tcx.ensure().unsafety_check_result(def.did);
 270         }
 271     }
 272
 273     let mut body = tcx.mir_built(def).steal();
 274
 275     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 276
 277     run_passes(
 278         tcx,
 279         &mut body,
 280         MirPhase::Const,
 281         &[&[
 282             // MIR-level lints.
 283             &check_packed_ref::CheckPackedRef,
 284             &check_const_item_mutation::CheckConstItemMutation,
 285             &function_item_references::FunctionItemReferences,
 286             // What we need to do constant evaluation.
 287             &simplify::SimplifyCfg::new("initial"),
 288             &rustc_peek::SanityCheck,
 289         ]],
 290     );
 291     tcx.alloc_steal_mir(body)
 292 }
 293
 294 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 295 fn mir_promoted(
 296     tcx: TyCtxt<'tcx>,
 297     def: ty::WithOptConstParam<LocalDefId>,
 298 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 299     if let Some(def) = def.try_upgrade(tcx) {
 300         return tcx.mir_promoted(def);
 301     }
 302
 303     // Ensure that we compute the `mir_const_qualif` for constants at
 304     // this point, before we steal the mir-const result.
 305     // Also this means promotion can rely on all const checks having been done.
 306     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 307     let mut body = tcx.mir_const(def).steal();
 308
 309     let mut required_consts = Vec::new();
 310     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 311     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 312         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 313     }
 314     body.required_consts = required_consts;
 315
 316     let promote_pass = promote_consts::PromoteTemps::default();
 317     let promote: &[&dyn MirPass<'tcx>] = &[
 318         // What we need to run borrowck etc.
 319         &promote_pass,
 320         &simplify::SimplifyCfg::new("promote-consts"),
 321     ];
 322
 323     let opt_coverage: &[&dyn MirPass<'tcx>] =
 324         if tcx.sess.instrument_coverage() { &[&coverage::InstrumentCoverage] } else { &[] };
 325
 326     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 327
 328     let promoted = promote_pass.promoted_fragments.into_inner();
 329     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 330 }
 331
 332 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 333 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 334     let did = def_id.expect_local();
 335     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 336         tcx.mir_for_ctfe_of_const_arg(def)
 337     } else {
 338         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 339     }
 340 }
 341
 342 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 343 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 344 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 345 /// the const parameter while type checking the main body, which in turn would try
 346 /// to type check the main body again.
 347 fn mir_for_ctfe_of_const_arg<'tcx>(
 348     tcx: TyCtxt<'tcx>,
 349     (did, param_did): (LocalDefId, DefId),
 350 ) -> &'tcx Body<'tcx> {
 351     tcx.arena.alloc(inner_mir_for_ctfe(
 352         tcx,
 353         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 354     ))
 355 }
 356
 357 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 358     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 359     if tcx.is_constructor(def.did.to_def_id()) {
 360         // There's no reason to run all of the MIR passes on constructors when
 361         // we can just output the MIR we want directly. This also saves const
 362         // qualification and borrow checking the trouble of special casing
 363         // constructors.
 364         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 365     }
 366
 367     let context = tcx
 368         .hir()
 369         .body_const_context(def.did)
 370         .expect("mir_for_ctfe should not be used for runtime functions");
 371
 372     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 373
 374     match context {
 375         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 376         // so we run const prop on them, or they don't, in which case we const evaluate some control
 377         // flow paths of the function and any errors in those paths will get emitted as const eval
 378         // errors.
 379         hir::ConstContext::ConstFn => {}
 380         // Static items always get evaluated, so we can just let const eval see if any erroneous
 381         // control flow paths get executed.
 382         hir::ConstContext::Static(_) => {}
 383         // Associated constants get const prop run so we detect common failure situations in the
 384         // crate that defined the constant.
 385         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 386         // conveniently detect that at this point without looking at the HIR.
 387         hir::ConstContext::Const => {
 388             #[rustfmt::skip]
 389             let optimizations: &[&dyn MirPass<'_>] = &[
 390                 &const_prop::ConstProp,
 391             ];
 392
 393             #[rustfmt::skip]
 394             run_passes(
 395                 tcx,
 396                 &mut body,
 397                 MirPhase::Optimization,
 398                 &[
 399                     optimizations,
 400                 ],
 401             );
 402         }
 403     }
 404
 405     debug_assert!(!body.has_free_regions(tcx), "Free regions in MIR for CTFE");
 406
 407     body
 408 }
 409
 410 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 411 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 412 /// end up missing the source MIR due to stealing happening.
 413 fn mir_drops_elaborated_and_const_checked<'tcx>(
 414     tcx: TyCtxt<'tcx>,
 415     def: ty::WithOptConstParam<LocalDefId>,
 416 ) -> &'tcx Steal<Body<'tcx>> {
 417     if let Some(def) = def.try_upgrade(tcx) {
 418         return tcx.mir_drops_elaborated_and_const_checked(def);
 419     }
 420
 421     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 422     // execute before we can steal.
 423     if let Some(param_did) = def.const_param_did {
 424         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 425     } else {
 426         tcx.ensure().mir_borrowck(def.did);
 427     }
 428
 429     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 430     use rustc_middle::hir::map::blocks::FnLikeNode;
 431     let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
 432     if is_fn_like {
 433         let did = def.did.to_def_id();
 434         let def = ty::WithOptConstParam::unknown(did);
 435
 436         // Do not compute the mir call graph without said call graph actually being used.
 437         if inline::is_enabled(tcx) {
 438             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 439         }
 440     }
 441
 442     let (body, _) = tcx.mir_promoted(def);
 443     let mut body = body.steal();
 444
 445     run_post_borrowck_cleanup_passes(tcx, &mut body);
 446     check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
 447     tcx.alloc_steal_mir(body)
 448 }
 449
 450 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 451 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 452     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 453
 454     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 455         // Remove all things only needed by analysis
 456         &simplify_branches::SimplifyBranches::new("initial"),
 457         &remove_noop_landing_pads::RemoveNoopLandingPads,
 458         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 459         &simplify::SimplifyCfg::new("early-opt"),
 460         // These next passes must be executed together
 461         &add_call_guards::CriticalCallEdges,
 462         &elaborate_drops::ElaborateDrops,
 463         // This will remove extraneous landing pads which are no longer
 464         // necessary as well as well as forcing any call in a non-unwinding
 465         // function calling a possibly-unwinding function to abort the process.
 466         &abort_unwinding_calls::AbortUnwindingCalls,
 467         // AddMovesForPackedDrops needs to run after drop
 468         // elaboration.
 469         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 470         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 471         // but before optimizations begin.
 472         &add_retag::AddRetag,
 473         &lower_intrinsics::LowerIntrinsics,
 474         &simplify::SimplifyCfg::new("elaborate-drops"),
 475         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 476         // and it can help optimizations.
 477         &deaggregator::Deaggregator,
 478     ];
 479
 480     run_passes(tcx, body, MirPhase::DropLowering, &[post_borrowck_cleanup]);
 481 }
 482
 483 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 484     let mir_opt_level = tcx.sess.mir_opt_level();
 485
 486     // Lowering generator control-flow and variables has to happen before we do anything else
 487     // to them. We run some optimizations before that, because they may be harder to do on the state
 488     // machine than on MIR with async primitives.
 489     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 490         &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
 491         &unreachable_prop::UnreachablePropagation,
 492         &uninhabited_enum_branching::UninhabitedEnumBranching,
 493         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 494         &inline::Inline,
 495         &generator::StateTransform,
 496     ];
 497
 498     // Even if we don't do optimizations, we still have to lower generators for codegen.
 499     let no_optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[&generator::StateTransform];
 500
 501     // The main optimizations that we do on MIR.
 502     let optimizations: &[&dyn MirPass<'tcx>] = &[
 503         &remove_storage_markers::RemoveStorageMarkers,
 504         &remove_zsts::RemoveZsts,
 505         &const_goto::ConstGoto,
 506         &remove_unneeded_drops::RemoveUnneededDrops,
 507         &match_branches::MatchBranchSimplification,
 508         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 509         &multiple_return_terminators::MultipleReturnTerminators,
 510         &instcombine::InstCombine,
 511         &separate_const_switch::SeparateConstSwitch,
 512         &const_prop::ConstProp,
 513         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 514         &early_otherwise_branch::EarlyOtherwiseBranch,
 515         &simplify_comparison_integral::SimplifyComparisonIntegral,
 516         &simplify_try::SimplifyArmIdentity,
 517         &simplify_try::SimplifyBranchSame,
 518         &dest_prop::DestinationPropagation,
 519         &simplify_branches::SimplifyBranches::new("final"),
 520         &remove_noop_landing_pads::RemoveNoopLandingPads,
 521         &simplify::SimplifyCfg::new("final"),
 522         &nrvo::RenameReturnPlace,
 523         &const_debuginfo::ConstDebugInfo,
 524         &simplify::SimplifyLocals,
 525         &multiple_return_terminators::MultipleReturnTerminators,
 526         &deduplicate_blocks::DeduplicateBlocks,
 527     ];
 528
 529     // Optimizations to run even if mir optimizations have been disabled.
 530     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 531         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 532         &const_prop::ConstProp,
 533     ];
 534
 535     // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 536     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 537         &add_call_guards::CriticalCallEdges,
 538         // Dump the end result for testing and debugging purposes.
 539         &dump_mir::Marker("PreCodegen"),
 540     ];
 541
 542     // End of pass declarations, now actually run the passes.
 543     // Generator Lowering
 544     #[rustfmt::skip]
 545     run_passes(
 546         tcx,
 547         body,
 548         MirPhase::GeneratorLowering,
 549         &[
 550             if mir_opt_level > 0 {
 551                 optimizations_with_generators
 552             } else {
 553                 no_optimizations_with_generators
 554             }
 555         ],
 556     );
 557
 558     // Main optimization passes
 559     #[rustfmt::skip]
 560     run_passes(
 561         tcx,
 562         body,
 563         MirPhase::Optimization,
 564         &[
 565             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 566             pre_codegen_cleanup,
 567         ],
 568     );
 569 }
 570
 571 /// Optimize the MIR and prepare it for codegen.
 572 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 573     let did = did.expect_local();
 574     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 575     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 576 }
 577
 578 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 579     if tcx.is_constructor(did.to_def_id()) {
 580         // There's no reason to run all of the MIR passes on constructors when
 581         // we can just output the MIR we want directly. This also saves const
 582         // qualification and borrow checking the trouble of special casing
 583         // constructors.
 584         return shim::build_adt_ctor(tcx, did.to_def_id());
 585     }
 586
 587     match tcx.hir().body_const_context(did) {
 588         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 589         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 590         // computes and caches its result.
 591         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 592         None => {}
 593         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 594     }
 595     let mut body =
 596         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 597     run_optimization_passes(tcx, &mut body);
 598
 599     debug_assert!(!body.has_free_regions(tcx), "Free regions in optimized MIR");
 600
 601     body
 602 }
 603
 604 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 605 /// constant evaluation once all substitutions become known.
 606 fn promoted_mir<'tcx>(
 607     tcx: TyCtxt<'tcx>,
 608     def: ty::WithOptConstParam<LocalDefId>,
 609 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 610     if tcx.is_constructor(def.did.to_def_id()) {
 611         return tcx.arena.alloc(IndexVec::new());
 612     }
 613
 614     if let Some(param_did) = def.const_param_did {
 615         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 616     } else {
 617         tcx.ensure().mir_borrowck(def.did);
 618     }
 619     let (_, promoted) = tcx.mir_promoted(def);
 620     let mut promoted = promoted.steal();
 621
 622     for body in &mut promoted {
 623         run_post_borrowck_cleanup_passes(tcx, body);
 624     }
 625
 626     debug_assert!(!promoted.has_free_regions(tcx), "Free regions in promoted MIR");
 627
 628     tcx.arena.alloc(promoted)
 629 }