compiler/rustc_mir_transform/src/lib.rs

   1 #![feature(box_patterns)]
   2 #![feature(box_syntax)]
   3 #![feature(crate_visibility_modifier)]
   4 #![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 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.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()
 164         .krate()
 165         .visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 166
 167     set
 168 }
 169
 170 fn run_passes(
 171     tcx: TyCtxt<'tcx>,
 172     body: &mut Body<'tcx>,
 173     mir_phase: MirPhase,
 174     passes: &[&[&dyn MirPass<'tcx>]],
 175 ) {
 176     let phase_index = mir_phase.phase_index();
 177     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 178
 179     if body.phase >= mir_phase {
 180         return;
 181     }
 182
 183     if validate {
 184         validate::Validator { when: format!("input to phase {:?}", mir_phase), mir_phase }
 185             .run_pass(tcx, body);
 186     }
 187
 188     let mut index = 0;
 189     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 190         let run_hooks = |body: &_, index, is_after| {
 191             dump_mir::on_mir_pass(
 192                 tcx,
 193                 &format_args!("{:03}-{:03}", phase_index, index),
 194                 &pass.name(),
 195                 body,
 196                 is_after,
 197             );
 198         };
 199         run_hooks(body, index, false);
 200         pass.run_pass(tcx, body);
 201         run_hooks(body, index, true);
 202
 203         if validate {
 204             validate::Validator {
 205                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 206                 mir_phase,
 207             }
 208             .run_pass(tcx, body);
 209         }
 210
 211         index += 1;
 212     };
 213
 214     for pass_group in passes {
 215         for pass in *pass_group {
 216             run_pass(*pass);
 217         }
 218     }
 219
 220     body.phase = mir_phase;
 221
 222     if mir_phase == MirPhase::Optimization {
 223         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 224             .run_pass(tcx, body);
 225     }
 226 }
 227
 228 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 229     let const_kind = tcx.hir().body_const_context(def.did);
 230
 231     // No need to const-check a non-const `fn`.
 232     if const_kind.is_none() {
 233         return Default::default();
 234     }
 235
 236     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 237     // cannot yet be stolen), because `mir_promoted()`, which steals
 238     // from `mir_const(), forces this query to execute before
 239     // performing the steal.
 240     let body = &tcx.mir_const(def).borrow();
 241
 242     if body.return_ty().references_error() {
 243         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 244         return Default::default();
 245     }
 246
 247     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 248
 249     let mut validator = check_consts::check::Checker::new(&ccx);
 250     validator.check_body();
 251
 252     // We return the qualifs in the return place for every MIR body, even though it is only used
 253     // when deciding to promote a reference to a `const` for now.
 254     validator.qualifs_in_return_place()
 255 }
 256
 257 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 258 fn mir_const<'tcx>(
 259     tcx: TyCtxt<'tcx>,
 260     def: ty::WithOptConstParam<LocalDefId>,
 261 ) -> &'tcx Steal<Body<'tcx>> {
 262     if let Some(def) = def.try_upgrade(tcx) {
 263         return tcx.mir_const(def);
 264     }
 265
 266     // Unsafety check uses the raw mir, so make sure it is run.
 267     if !tcx.sess.opts.debugging_opts.thir_unsafeck {
 268         if let Some(param_did) = def.const_param_did {
 269             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 270         } else {
 271             tcx.ensure().unsafety_check_result(def.did);
 272         }
 273     }
 274
 275     let mut body = tcx.mir_built(def).steal();
 276
 277     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 278
 279     run_passes(
 280         tcx,
 281         &mut body,
 282         MirPhase::Const,
 283         &[&[
 284             // MIR-level lints.
 285             &check_packed_ref::CheckPackedRef,
 286             &check_const_item_mutation::CheckConstItemMutation,
 287             &function_item_references::FunctionItemReferences,
 288             // What we need to do constant evaluation.
 289             &simplify::SimplifyCfg::new("initial"),
 290             &rustc_peek::SanityCheck,
 291         ]],
 292     );
 293     tcx.alloc_steal_mir(body)
 294 }
 295
 296 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 297 fn mir_promoted(
 298     tcx: TyCtxt<'tcx>,
 299     def: ty::WithOptConstParam<LocalDefId>,
 300 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 301     if let Some(def) = def.try_upgrade(tcx) {
 302         return tcx.mir_promoted(def);
 303     }
 304
 305     // Ensure that we compute the `mir_const_qualif` for constants at
 306     // this point, before we steal the mir-const result.
 307     // Also this means promotion can rely on all const checks having been done.
 308     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 309     let mut body = tcx.mir_const(def).steal();
 310
 311     let mut required_consts = Vec::new();
 312     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 313     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 314         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 315     }
 316     body.required_consts = required_consts;
 317
 318     let promote_pass = promote_consts::PromoteTemps::default();
 319     let promote: &[&dyn MirPass<'tcx>] = &[
 320         // What we need to run borrowck etc.
 321         &promote_pass,
 322         &simplify::SimplifyCfg::new("promote-consts"),
 323     ];
 324
 325     let opt_coverage: &[&dyn MirPass<'tcx>] =
 326         if tcx.sess.instrument_coverage() { &[&coverage::InstrumentCoverage] } else { &[] };
 327
 328     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 329
 330     let promoted = promote_pass.promoted_fragments.into_inner();
 331     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 332 }
 333
 334 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 335 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 336     let did = def_id.expect_local();
 337     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 338         tcx.mir_for_ctfe_of_const_arg(def)
 339     } else {
 340         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 341     }
 342 }
 343
 344 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 345 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 346 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 347 /// the const parameter while type checking the main body, which in turn would try
 348 /// to type check the main body again.
 349 fn mir_for_ctfe_of_const_arg<'tcx>(
 350     tcx: TyCtxt<'tcx>,
 351     (did, param_did): (LocalDefId, DefId),
 352 ) -> &'tcx Body<'tcx> {
 353     tcx.arena.alloc(inner_mir_for_ctfe(
 354         tcx,
 355         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 356     ))
 357 }
 358
 359 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 360     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 361     if tcx.is_constructor(def.did.to_def_id()) {
 362         // There's no reason to run all of the MIR passes on constructors when
 363         // we can just output the MIR we want directly. This also saves const
 364         // qualification and borrow checking the trouble of special casing
 365         // constructors.
 366         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 367     }
 368
 369     let context = tcx
 370         .hir()
 371         .body_const_context(def.did)
 372         .expect("mir_for_ctfe should not be used for runtime functions");
 373
 374     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 375
 376     match context {
 377         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 378         // so we run const prop on them, or they don't, in which case we const evaluate some control
 379         // flow paths of the function and any errors in those paths will get emitted as const eval
 380         // errors.
 381         hir::ConstContext::ConstFn => {}
 382         // Static items always get evaluated, so we can just let const eval see if any erroneous
 383         // control flow paths get executed.
 384         hir::ConstContext::Static(_) => {}
 385         // Associated constants get const prop run so we detect common failure situations in the
 386         // crate that defined the constant.
 387         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 388         // conveniently detect that at this point without looking at the HIR.
 389         hir::ConstContext::Const => {
 390             #[rustfmt::skip]
 391             let optimizations: &[&dyn MirPass<'_>] = &[
 392                 &const_prop::ConstProp,
 393             ];
 394
 395             #[rustfmt::skip]
 396             run_passes(
 397                 tcx,
 398                 &mut body,
 399                 MirPhase::Optimization,
 400                 &[
 401                     optimizations,
 402                 ],
 403             );
 404         }
 405     }
 406
 407     debug_assert!(!body.has_free_regions(tcx), "Free regions in MIR for CTFE");
 408
 409     body
 410 }
 411
 412 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 413 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 414 /// end up missing the source MIR due to stealing happening.
 415 fn mir_drops_elaborated_and_const_checked<'tcx>(
 416     tcx: TyCtxt<'tcx>,
 417     def: ty::WithOptConstParam<LocalDefId>,
 418 ) -> &'tcx Steal<Body<'tcx>> {
 419     if let Some(def) = def.try_upgrade(tcx) {
 420         return tcx.mir_drops_elaborated_and_const_checked(def);
 421     }
 422
 423     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 424     // execute before we can steal.
 425     if let Some(param_did) = def.const_param_did {
 426         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 427     } else {
 428         tcx.ensure().mir_borrowck(def.did);
 429     }
 430
 431     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 432     use rustc_middle::hir::map::blocks::FnLikeNode;
 433     let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
 434     if is_fn_like {
 435         let did = def.did.to_def_id();
 436         let def = ty::WithOptConstParam::unknown(did);
 437
 438         // Do not compute the mir call graph without said call graph actually being used.
 439         if inline::is_enabled(tcx) {
 440             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 441         }
 442     }
 443
 444     let (body, _) = tcx.mir_promoted(def);
 445     let mut body = body.steal();
 446
 447     run_post_borrowck_cleanup_passes(tcx, &mut body);
 448     check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
 449     tcx.alloc_steal_mir(body)
 450 }
 451
 452 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 453 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 454     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 455
 456     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 457         // Remove all things only needed by analysis
 458         &simplify_branches::SimplifyBranches::new("initial"),
 459         &remove_noop_landing_pads::RemoveNoopLandingPads,
 460         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 461         &simplify::SimplifyCfg::new("early-opt"),
 462         // These next passes must be executed together
 463         &add_call_guards::CriticalCallEdges,
 464         &elaborate_drops::ElaborateDrops,
 465         // This will remove extraneous landing pads which are no longer
 466         // necessary as well as well as forcing any call in a non-unwinding
 467         // function calling a possibly-unwinding function to abort the process.
 468         &abort_unwinding_calls::AbortUnwindingCalls,
 469         // AddMovesForPackedDrops needs to run after drop
 470         // elaboration.
 471         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 472         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 473         // but before optimizations begin.
 474         &add_retag::AddRetag,
 475         &lower_intrinsics::LowerIntrinsics,
 476         &simplify::SimplifyCfg::new("elaborate-drops"),
 477         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 478         // and it can help optimizations.
 479         &deaggregator::Deaggregator,
 480     ];
 481
 482     run_passes(tcx, body, MirPhase::DropLowering, &[post_borrowck_cleanup]);
 483 }
 484
 485 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 486     let mir_opt_level = tcx.sess.mir_opt_level();
 487
 488     // Lowering generator control-flow and variables has to happen before we do anything else
 489     // to them. We run some optimizations before that, because they may be harder to do on the state
 490     // machine than on MIR with async primitives.
 491     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 492         &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
 493         &unreachable_prop::UnreachablePropagation,
 494         &uninhabited_enum_branching::UninhabitedEnumBranching,
 495         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 496         &inline::Inline,
 497         &generator::StateTransform,
 498     ];
 499
 500     // Even if we don't do optimizations, we still have to lower generators for codegen.
 501     let no_optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[&generator::StateTransform];
 502
 503     // The main optimizations that we do on MIR.
 504     let optimizations: &[&dyn MirPass<'tcx>] = &[
 505         &remove_storage_markers::RemoveStorageMarkers,
 506         &remove_zsts::RemoveZsts,
 507         &const_goto::ConstGoto,
 508         &remove_unneeded_drops::RemoveUnneededDrops,
 509         &match_branches::MatchBranchSimplification,
 510         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 511         &multiple_return_terminators::MultipleReturnTerminators,
 512         &instcombine::InstCombine,
 513         &separate_const_switch::SeparateConstSwitch,
 514         &const_prop::ConstProp,
 515         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 516         &early_otherwise_branch::EarlyOtherwiseBranch,
 517         &simplify_comparison_integral::SimplifyComparisonIntegral,
 518         &simplify_try::SimplifyArmIdentity,
 519         &simplify_try::SimplifyBranchSame,
 520         &dest_prop::DestinationPropagation,
 521         &simplify_branches::SimplifyBranches::new("final"),
 522         &remove_noop_landing_pads::RemoveNoopLandingPads,
 523         &simplify::SimplifyCfg::new("final"),
 524         &nrvo::RenameReturnPlace,
 525         &const_debuginfo::ConstDebugInfo,
 526         &simplify::SimplifyLocals,
 527         &multiple_return_terminators::MultipleReturnTerminators,
 528         &deduplicate_blocks::DeduplicateBlocks,
 529     ];
 530
 531     // Optimizations to run even if mir optimizations have been disabled.
 532     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 533         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 534         &const_prop::ConstProp,
 535     ];
 536
 537     // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 538     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 539         &add_call_guards::CriticalCallEdges,
 540         // Dump the end result for testing and debugging purposes.
 541         &dump_mir::Marker("PreCodegen"),
 542     ];
 543
 544     // End of pass declarations, now actually run the passes.
 545     // Generator Lowering
 546     #[rustfmt::skip]
 547     run_passes(
 548         tcx,
 549         body,
 550         MirPhase::GeneratorLowering,
 551         &[
 552             if mir_opt_level > 0 {
 553                 optimizations_with_generators
 554             } else {
 555                 no_optimizations_with_generators
 556             }
 557         ],
 558     );
 559
 560     // Main optimization passes
 561     #[rustfmt::skip]
 562     run_passes(
 563         tcx,
 564         body,
 565         MirPhase::Optimization,
 566         &[
 567             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 568             pre_codegen_cleanup,
 569         ],
 570     );
 571 }
 572
 573 /// Optimize the MIR and prepare it for codegen.
 574 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 575     let did = did.expect_local();
 576     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 577     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 578 }
 579
 580 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 581     if tcx.is_constructor(did.to_def_id()) {
 582         // There's no reason to run all of the MIR passes on constructors when
 583         // we can just output the MIR we want directly. This also saves const
 584         // qualification and borrow checking the trouble of special casing
 585         // constructors.
 586         return shim::build_adt_ctor(tcx, did.to_def_id());
 587     }
 588
 589     match tcx.hir().body_const_context(did) {
 590         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 591         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 592         // computes and caches its result.
 593         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 594         None => {}
 595         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 596     }
 597     let mut body =
 598         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 599     run_optimization_passes(tcx, &mut body);
 600
 601     debug_assert!(!body.has_free_regions(tcx), "Free regions in optimized MIR");
 602
 603     body
 604 }
 605
 606 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 607 /// constant evaluation once all substitutions become known.
 608 fn promoted_mir<'tcx>(
 609     tcx: TyCtxt<'tcx>,
 610     def: ty::WithOptConstParam<LocalDefId>,
 611 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 612     if tcx.is_constructor(def.did.to_def_id()) {
 613         return tcx.arena.alloc(IndexVec::new());
 614     }
 615
 616     if let Some(param_did) = def.const_param_did {
 617         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 618     } else {
 619         tcx.ensure().mir_borrowck(def.did);
 620     }
 621     let (_, promoted) = tcx.mir_promoted(def);
 622     let mut promoted = promoted.steal();
 623
 624     for body in &mut promoted {
 625         run_post_borrowck_cleanup_passes(tcx, body);
 626     }
 627
 628     debug_assert!(!promoted.has_free_regions(tcx), "Free regions in promoted MIR");
 629
 630     tcx.arena.alloc(promoted)
 631 }