compiler/rustc_mir/src/transform/mod.rs

   1 use crate::{shim, util};
   2 use required_consts::RequiredConstsVisitor;
   3 use rustc_data_structures::fx::FxHashSet;
   4 use rustc_data_structures::steal::Steal;
   5 use rustc_hir as hir;
   6 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
   7 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
   8 use rustc_index::vec::IndexVec;
   9 use rustc_middle::mir::visit::Visitor as _;
  10 use rustc_middle::mir::{traversal, Body, ConstQualifs, MirPhase, Promoted};
  11 use rustc_middle::ty::query::Providers;
  12 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
  13 use rustc_span::{Span, Symbol};
  14 use std::borrow::Cow;
  15
  16 pub mod add_call_guards;
  17 pub mod add_moves_for_packed_drops;
  18 pub mod add_retag;
  19 pub mod check_const_item_mutation;
  20 pub mod check_consts;
  21 pub mod check_packed_ref;
  22 pub mod check_unsafety;
  23 pub mod cleanup_post_borrowck;
  24 pub mod const_debuginfo;
  25 pub mod const_goto;
  26 pub mod const_prop;
  27 pub mod coverage;
  28 pub mod deaggregator;
  29 pub mod deduplicate_blocks;
  30 pub mod dest_prop;
  31 pub mod dump_mir;
  32 pub mod early_otherwise_branch;
  33 pub mod elaborate_drops;
  34 pub mod function_item_references;
  35 pub mod generator;
  36 pub mod inline;
  37 pub mod instcombine;
  38 pub mod lower_intrinsics;
  39 pub mod match_branches;
  40 pub mod multiple_return_terminators;
  41 pub mod no_landing_pads;
  42 pub mod nrvo;
  43 pub mod promote_consts;
  44 pub mod remove_noop_landing_pads;
  45 pub mod remove_storage_markers;
  46 pub mod remove_unneeded_drops;
  47 pub mod required_consts;
  48 pub mod rustc_peek;
  49 pub mod simplify;
  50 pub mod simplify_branches;
  51 pub mod simplify_comparison_integral;
  52 pub mod simplify_try;
  53 pub mod uninhabited_enum_branching;
  54 pub mod unreachable_prop;
  55 pub mod validate;
  56
  57 pub use rustc_middle::mir::MirSource;
  58
  59 pub(crate) fn provide(providers: &mut Providers) {
  60     self::check_unsafety::provide(providers);
  61     *providers = Providers {
  62         mir_keys,
  63         mir_const,
  64         mir_const_qualif: |tcx, def_id| {
  65             let def_id = def_id.expect_local();
  66             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  67                 tcx.mir_const_qualif_const_arg(def)
  68             } else {
  69                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  70             }
  71         },
  72         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
  73             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  74         },
  75         mir_promoted,
  76         mir_drops_elaborated_and_const_checked,
  77         mir_for_ctfe,
  78         mir_for_ctfe_of_const_arg,
  79         optimized_mir,
  80         is_mir_available,
  81         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
  82         promoted_mir: |tcx, def_id| {
  83             let def_id = def_id.expect_local();
  84             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  85                 tcx.promoted_mir_of_const_arg(def)
  86             } else {
  87                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
  88             }
  89         },
  90         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
  91             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  92         },
  93         ..*providers
  94     };
  95     coverage::query::provide(providers);
  96 }
  97
  98 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
  99     tcx.mir_keys(def_id.krate).contains(&def_id.expect_local())
 100 }
 101
 102 /// Finds the full set of `DefId`s within the current crate that have
 103 /// MIR associated with them.
 104 fn mir_keys(tcx: TyCtxt<'_>, krate: CrateNum) -> FxHashSet<LocalDefId> {
 105     assert_eq!(krate, LOCAL_CRATE);
 106
 107     let mut set = FxHashSet::default();
 108
 109     // All body-owners have MIR associated with them.
 110     set.extend(tcx.body_owners());
 111
 112     // Additionally, tuple struct/variant constructors have MIR, but
 113     // they don't have a BodyId, so we need to build them separately.
 114     struct GatherCtors<'a, 'tcx> {
 115         tcx: TyCtxt<'tcx>,
 116         set: &'a mut FxHashSet<LocalDefId>,
 117     }
 118     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 119         fn visit_variant_data(
 120             &mut self,
 121             v: &'tcx hir::VariantData<'tcx>,
 122             _: Symbol,
 123             _: &'tcx hir::Generics<'tcx>,
 124             _: hir::HirId,
 125             _: Span,
 126         ) {
 127             if let hir::VariantData::Tuple(_, hir_id) = *v {
 128                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 129             }
 130             intravisit::walk_struct_def(self, v)
 131         }
 132         type Map = intravisit::ErasedMap<'tcx>;
 133         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 134             NestedVisitorMap::None
 135         }
 136     }
 137     tcx.hir()
 138         .krate()
 139         .visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 140
 141     set
 142 }
 143
 144 /// Generates a default name for the pass based on the name of the
 145 /// type `T`.
 146 pub fn default_name<T: ?Sized>() -> Cow<'static, str> {
 147     let name = std::any::type_name::<T>();
 148     if let Some(tail) = name.rfind(':') { Cow::from(&name[tail + 1..]) } else { Cow::from(name) }
 149 }
 150
 151 /// A streamlined trait that you can implement to create a pass; the
 152 /// pass will be named after the type, and it will consist of a main
 153 /// loop that goes over each available MIR and applies `run_pass`.
 154 pub trait MirPass<'tcx> {
 155     fn name(&self) -> Cow<'_, str> {
 156         default_name::<Self>()
 157     }
 158
 159     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>);
 160 }
 161
 162 pub fn run_passes(
 163     tcx: TyCtxt<'tcx>,
 164     body: &mut Body<'tcx>,
 165     mir_phase: MirPhase,
 166     passes: &[&[&dyn MirPass<'tcx>]],
 167 ) {
 168     let phase_index = mir_phase.phase_index();
 169     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 170
 171     if body.phase >= mir_phase {
 172         return;
 173     }
 174
 175     if validate {
 176         validate::Validator { when: format!("input to phase {:?}", mir_phase), mir_phase }
 177             .run_pass(tcx, body);
 178     }
 179
 180     let mut index = 0;
 181     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 182         let run_hooks = |body: &_, index, is_after| {
 183             dump_mir::on_mir_pass(
 184                 tcx,
 185                 &format_args!("{:03}-{:03}", phase_index, index),
 186                 &pass.name(),
 187                 body,
 188                 is_after,
 189             );
 190         };
 191         run_hooks(body, index, false);
 192         pass.run_pass(tcx, body);
 193         run_hooks(body, index, true);
 194
 195         if validate {
 196             validate::Validator {
 197                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 198                 mir_phase,
 199             }
 200             .run_pass(tcx, body);
 201         }
 202
 203         index += 1;
 204     };
 205
 206     for pass_group in passes {
 207         for pass in *pass_group {
 208             run_pass(*pass);
 209         }
 210     }
 211
 212     body.phase = mir_phase;
 213
 214     if mir_phase == MirPhase::Optimization {
 215         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 216             .run_pass(tcx, body);
 217     }
 218 }
 219
 220 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 221     let const_kind = tcx.hir().body_const_context(def.did);
 222
 223     // No need to const-check a non-const `fn`.
 224     if const_kind.is_none() {
 225         return Default::default();
 226     }
 227
 228     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 229     // cannot yet be stolen), because `mir_promoted()`, which steals
 230     // from `mir_const(), forces this query to execute before
 231     // performing the steal.
 232     let body = &tcx.mir_const(def).borrow();
 233
 234     if body.return_ty().references_error() {
 235         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 236         return Default::default();
 237     }
 238
 239     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 240
 241     let mut validator = check_consts::validation::Validator::new(&ccx);
 242     validator.check_body();
 243
 244     // We return the qualifs in the return place for every MIR body, even though it is only used
 245     // when deciding to promote a reference to a `const` for now.
 246     validator.qualifs_in_return_place()
 247 }
 248
 249 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 250 fn mir_const<'tcx>(
 251     tcx: TyCtxt<'tcx>,
 252     def: ty::WithOptConstParam<LocalDefId>,
 253 ) -> &'tcx Steal<Body<'tcx>> {
 254     if let Some(def) = def.try_upgrade(tcx) {
 255         return tcx.mir_const(def);
 256     }
 257
 258     // Unsafety check uses the raw mir, so make sure it is run.
 259     if let Some(param_did) = def.const_param_did {
 260         tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 261     } else {
 262         tcx.ensure().unsafety_check_result(def.did);
 263     }
 264
 265     let mut body = tcx.mir_built(def).steal();
 266
 267     util::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 268
 269     run_passes(
 270         tcx,
 271         &mut body,
 272         MirPhase::Const,
 273         &[&[
 274             // MIR-level lints.
 275             &check_packed_ref::CheckPackedRef,
 276             &check_const_item_mutation::CheckConstItemMutation,
 277             &function_item_references::FunctionItemReferences,
 278             // What we need to do constant evaluation.
 279             &simplify::SimplifyCfg::new("initial"),
 280             &rustc_peek::SanityCheck,
 281         ]],
 282     );
 283     tcx.alloc_steal_mir(body)
 284 }
 285
 286 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 287 fn mir_promoted(
 288     tcx: TyCtxt<'tcx>,
 289     def: ty::WithOptConstParam<LocalDefId>,
 290 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 291     if let Some(def) = def.try_upgrade(tcx) {
 292         return tcx.mir_promoted(def);
 293     }
 294
 295     // Ensure that we compute the `mir_const_qualif` for constants at
 296     // this point, before we steal the mir-const result.
 297     // Also this means promotion can rely on all const checks having been done.
 298     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 299     let _ = tcx.mir_abstract_const_opt_const_arg(def.to_global());
 300     let mut body = tcx.mir_const(def).steal();
 301
 302     let mut required_consts = Vec::new();
 303     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 304     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 305         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 306     }
 307     body.required_consts = required_consts;
 308
 309     let promote_pass = promote_consts::PromoteTemps::default();
 310     let promote: &[&dyn MirPass<'tcx>] = &[
 311         // What we need to run borrowck etc.
 312         &promote_pass,
 313         &simplify::SimplifyCfg::new("promote-consts"),
 314     ];
 315
 316     let opt_coverage: &[&dyn MirPass<'tcx>] = if tcx.sess.opts.debugging_opts.instrument_coverage {
 317         &[&coverage::InstrumentCoverage]
 318     } else {
 319         &[]
 320     };
 321
 322     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 323
 324     let promoted = promote_pass.promoted_fragments.into_inner();
 325     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 326 }
 327
 328 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 329 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 330     let did = def_id.expect_local();
 331     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 332         tcx.mir_for_ctfe_of_const_arg(def)
 333     } else {
 334         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 335     }
 336 }
 337
 338 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 339 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 340 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 341 /// the const parameter while type checking the main body, which in turn would try
 342 /// to type check the main body again.
 343 fn mir_for_ctfe_of_const_arg<'tcx>(
 344     tcx: TyCtxt<'tcx>,
 345     (did, param_did): (LocalDefId, DefId),
 346 ) -> &'tcx Body<'tcx> {
 347     tcx.arena.alloc(inner_mir_for_ctfe(
 348         tcx,
 349         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 350     ))
 351 }
 352
 353 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 354     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 355     if tcx.is_constructor(def.did.to_def_id()) {
 356         // There's no reason to run all of the MIR passes on constructors when
 357         // we can just output the MIR we want directly. This also saves const
 358         // qualification and borrow checking the trouble of special casing
 359         // constructors.
 360         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 361     }
 362
 363     let context = tcx
 364         .hir()
 365         .body_const_context(def.did)
 366         .expect("mir_for_ctfe should not be used for runtime functions");
 367
 368     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 369
 370     match context {
 371         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 372         // so we run const prop on them, or they don't, in which case we const evaluate some control
 373         // flow paths of the function and any errors in those paths will get emitted as const eval
 374         // errors.
 375         hir::ConstContext::ConstFn => {}
 376         // Static items always get evaluated, so we can just let const eval see if any erroneous
 377         // control flow paths get executed.
 378         hir::ConstContext::Static(_) => {}
 379         // Associated constants get const prop run so we detect common failure situations in the
 380         // crate that defined the constant.
 381         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 382         // conveniently detect that at this point without looking at the HIR.
 383         hir::ConstContext::Const => {
 384             #[rustfmt::skip]
 385             let optimizations: &[&dyn MirPass<'_>] = &[
 386                 &const_prop::ConstProp,
 387             ];
 388
 389             #[rustfmt::skip]
 390             run_passes(
 391                 tcx,
 392                 &mut body,
 393                 MirPhase::Optimization,
 394                 &[
 395                     optimizations,
 396                 ],
 397             );
 398         }
 399     }
 400
 401     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 402
 403     body
 404 }
 405
 406 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 407 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 408 /// end up missing the source MIR due to stealing happening.
 409 fn mir_drops_elaborated_and_const_checked<'tcx>(
 410     tcx: TyCtxt<'tcx>,
 411     def: ty::WithOptConstParam<LocalDefId>,
 412 ) -> &'tcx Steal<Body<'tcx>> {
 413     if let Some(def) = def.try_upgrade(tcx) {
 414         return tcx.mir_drops_elaborated_and_const_checked(def);
 415     }
 416
 417     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 418     // execute before we can steal.
 419     if let Some(param_did) = def.const_param_did {
 420         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 421     } else {
 422         tcx.ensure().mir_borrowck(def.did);
 423     }
 424
 425     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 426     use rustc_middle::hir::map::blocks::FnLikeNode;
 427     let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
 428     if is_fn_like {
 429         let did = def.did.to_def_id();
 430         let def = ty::WithOptConstParam::unknown(did);
 431
 432         // Do not compute the mir call graph without said call graph actually being used.
 433         if inline::is_enabled(tcx) {
 434             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 435         }
 436     }
 437
 438     let (body, _) = tcx.mir_promoted(def);
 439     let mut body = body.steal();
 440
 441     run_post_borrowck_cleanup_passes(tcx, &mut body);
 442     check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
 443     tcx.alloc_steal_mir(body)
 444 }
 445
 446 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 447 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 448     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 449
 450     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 451         // Remove all things only needed by analysis
 452         &no_landing_pads::NoLandingPads,
 453         &simplify_branches::SimplifyBranches::new("initial"),
 454         &remove_noop_landing_pads::RemoveNoopLandingPads,
 455         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 456         &simplify::SimplifyCfg::new("early-opt"),
 457         // These next passes must be executed together
 458         &add_call_guards::CriticalCallEdges,
 459         &elaborate_drops::ElaborateDrops,
 460         &no_landing_pads::NoLandingPads,
 461         // AddMovesForPackedDrops needs to run after drop
 462         // elaboration.
 463         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 464         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 465         // but before optimizations begin.
 466         &add_retag::AddRetag,
 467         &lower_intrinsics::LowerIntrinsics,
 468         &simplify::SimplifyCfg::new("elaborate-drops"),
 469         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 470         // and it can help optimizations.
 471         &deaggregator::Deaggregator,
 472     ];
 473
 474     run_passes(tcx, body, MirPhase::DropLowering, &[post_borrowck_cleanup]);
 475 }
 476
 477 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 478     let mir_opt_level = tcx.sess.mir_opt_level();
 479
 480     // Lowering generator control-flow and variables has to happen before we do anything else
 481     // to them. We run some optimizations before that, because they may be harder to do on the state
 482     // machine than on MIR with async primitives.
 483     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 484         &unreachable_prop::UnreachablePropagation,
 485         &uninhabited_enum_branching::UninhabitedEnumBranching,
 486         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 487         &inline::Inline,
 488         &generator::StateTransform,
 489     ];
 490
 491     // Even if we don't do optimizations, we still have to lower generators for codegen.
 492     let no_optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[&generator::StateTransform];
 493
 494     // The main optimizations that we do on MIR.
 495     let optimizations: &[&dyn MirPass<'tcx>] = &[
 496         &remove_storage_markers::RemoveStorageMarkers,
 497         &const_goto::ConstGoto,
 498         &remove_unneeded_drops::RemoveUnneededDrops,
 499         &match_branches::MatchBranchSimplification,
 500         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 501         &multiple_return_terminators::MultipleReturnTerminators,
 502         &instcombine::InstCombine,
 503         &const_prop::ConstProp,
 504         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 505         &early_otherwise_branch::EarlyOtherwiseBranch,
 506         &simplify_comparison_integral::SimplifyComparisonIntegral,
 507         &simplify_try::SimplifyArmIdentity,
 508         &simplify_try::SimplifyBranchSame,
 509         &dest_prop::DestinationPropagation,
 510         &simplify_branches::SimplifyBranches::new("final"),
 511         &remove_noop_landing_pads::RemoveNoopLandingPads,
 512         &simplify::SimplifyCfg::new("final"),
 513         &nrvo::RenameReturnPlace,
 514         &const_debuginfo::ConstDebugInfo,
 515         &simplify::SimplifyLocals,
 516         &multiple_return_terminators::MultipleReturnTerminators,
 517         &deduplicate_blocks::DeduplicateBlocks,
 518     ];
 519
 520     // Optimizations to run even if mir optimizations have been disabled.
 521     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 522         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 523         &const_prop::ConstProp,
 524     ];
 525
 526     // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 527     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 528         &add_call_guards::CriticalCallEdges,
 529         // Dump the end result for testing and debugging purposes.
 530         &dump_mir::Marker("PreCodegen"),
 531     ];
 532
 533     // End of pass declarations, now actually run the passes.
 534     // Generator Lowering
 535     #[rustfmt::skip]
 536     run_passes(
 537         tcx,
 538         body,
 539         MirPhase::GeneratorLowering,
 540         &[
 541             if mir_opt_level > 0 {
 542                 optimizations_with_generators
 543             } else {
 544                 no_optimizations_with_generators
 545             }
 546         ],
 547     );
 548
 549     // Main optimization passes
 550     #[rustfmt::skip]
 551     run_passes(
 552         tcx,
 553         body,
 554         MirPhase::Optimization,
 555         &[
 556             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 557             pre_codegen_cleanup,
 558         ],
 559     );
 560 }
 561
 562 /// Optimize the MIR and prepare it for codegen.
 563 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 564     let did = did.expect_local();
 565     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 566     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 567 }
 568
 569 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 570     if tcx.is_constructor(did.to_def_id()) {
 571         // There's no reason to run all of the MIR passes on constructors when
 572         // we can just output the MIR we want directly. This also saves const
 573         // qualification and borrow checking the trouble of special casing
 574         // constructors.
 575         return shim::build_adt_ctor(tcx, did.to_def_id());
 576     }
 577
 578     match tcx.hir().body_const_context(did) {
 579         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 580         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 581         // computes and caches its result.
 582         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 583         None => {}
 584         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 585     }
 586     let mut body =
 587         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 588     run_optimization_passes(tcx, &mut body);
 589
 590     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 591
 592     body
 593 }
 594
 595 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 596 /// constant evaluation once all substitutions become known.
 597 fn promoted_mir<'tcx>(
 598     tcx: TyCtxt<'tcx>,
 599     def: ty::WithOptConstParam<LocalDefId>,
 600 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 601     if tcx.is_constructor(def.did.to_def_id()) {
 602         return tcx.arena.alloc(IndexVec::new());
 603     }
 604
 605     if let Some(param_did) = def.const_param_did {
 606         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 607     } else {
 608         tcx.ensure().mir_borrowck(def.did);
 609     }
 610     let (_, promoted) = tcx.mir_promoted(def);
 611     let mut promoted = promoted.steal();
 612
 613     for body in &mut promoted {
 614         run_post_borrowck_cleanup_passes(tcx, body);
 615     }
 616
 617     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 618
 619     tcx.arena.alloc(promoted)
 620 }