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 normalize_array_len;
  62 mod nrvo;
  63 mod remove_noop_landing_pads;
  64 mod remove_storage_markers;
  65 mod remove_unneeded_drops;
  66 mod remove_zsts;
  67 mod required_consts;
  68 mod separate_const_switch;
  69 mod shim;
  70 mod simplify;
  71 mod simplify_branches;
  72 mod simplify_comparison_integral;
  73 mod simplify_try;
  74 mod uninhabited_enum_branching;
  75 mod unreachable_prop;
  76
  77 use rustc_const_eval::transform::check_consts;
  78 use rustc_const_eval::transform::promote_consts;
  79 use rustc_const_eval::transform::validate;
  80 pub use rustc_const_eval::transform::MirPass;
  81 use rustc_mir_dataflow::rustc_peek;
  82
  83 pub fn provide(providers: &mut Providers) {
  84     check_unsafety::provide(providers);
  85     check_packed_ref::provide(providers);
  86     coverage::query::provide(providers);
  87     shim::provide(providers);
  88     *providers = Providers {
  89         mir_keys,
  90         mir_const,
  91         mir_const_qualif: |tcx, def_id| {
  92             let def_id = def_id.expect_local();
  93             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  94                 tcx.mir_const_qualif_const_arg(def)
  95             } else {
  96                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  97             }
  98         },
  99         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 100             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 101         },
 102         mir_promoted,
 103         mir_drops_elaborated_and_const_checked,
 104         mir_for_ctfe,
 105         mir_for_ctfe_of_const_arg,
 106         optimized_mir,
 107         is_mir_available,
 108         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 109         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 110         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 111         promoted_mir: |tcx, def_id| {
 112             let def_id = def_id.expect_local();
 113             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 114                 tcx.promoted_mir_of_const_arg(def)
 115             } else {
 116                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 117             }
 118         },
 119         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 120             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 121         },
 122         ..*providers
 123     };
 124 }
 125
 126 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 127     let def_id = def_id.expect_local();
 128     tcx.mir_keys(()).contains(&def_id)
 129 }
 130
 131 /// Finds the full set of `DefId`s within the current crate that have
 132 /// MIR associated with them.
 133 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxHashSet<LocalDefId> {
 134     let mut set = FxHashSet::default();
 135
 136     // All body-owners have MIR associated with them.
 137     set.extend(tcx.hir().body_owners());
 138
 139     // Additionally, tuple struct/variant constructors have MIR, but
 140     // they don't have a BodyId, so we need to build them separately.
 141     struct GatherCtors<'a, 'tcx> {
 142         tcx: TyCtxt<'tcx>,
 143         set: &'a mut FxHashSet<LocalDefId>,
 144     }
 145     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 146         fn visit_variant_data(
 147             &mut self,
 148             v: &'tcx hir::VariantData<'tcx>,
 149             _: Symbol,
 150             _: &'tcx hir::Generics<'tcx>,
 151             _: hir::HirId,
 152             _: Span,
 153         ) {
 154             if let hir::VariantData::Tuple(_, hir_id) = *v {
 155                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 156             }
 157             intravisit::walk_struct_def(self, v)
 158         }
 159         type Map = intravisit::ErasedMap<'tcx>;
 160         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 161             NestedVisitorMap::None
 162         }
 163     }
 164     tcx.hir().visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 165
 166     set
 167 }
 168
 169 fn run_passes(
 170     tcx: TyCtxt<'tcx>,
 171     body: &mut Body<'tcx>,
 172     mir_phase: MirPhase,
 173     passes: &[&[&dyn MirPass<'tcx>]],
 174 ) {
 175     let phase_index = mir_phase.phase_index();
 176     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 177
 178     if body.phase >= mir_phase {
 179         return;
 180     }
 181
 182     if validate {
 183         validate::Validator { when: format!("input to phase {:?}", mir_phase), mir_phase }
 184             .run_pass(tcx, body);
 185     }
 186
 187     let mut index = 0;
 188     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 189         let run_hooks = |body: &_, index, is_after| {
 190             dump_mir::on_mir_pass(
 191                 tcx,
 192                 &format_args!("{:03}-{:03}", phase_index, index),
 193                 &pass.name(),
 194                 body,
 195                 is_after,
 196             );
 197         };
 198         run_hooks(body, index, false);
 199         pass.run_pass(tcx, body);
 200         run_hooks(body, index, true);
 201
 202         if validate {
 203             validate::Validator {
 204                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 205                 mir_phase,
 206             }
 207             .run_pass(tcx, body);
 208         }
 209
 210         index += 1;
 211     };
 212
 213     for pass_group in passes {
 214         for pass in *pass_group {
 215             run_pass(*pass);
 216         }
 217     }
 218
 219     body.phase = mir_phase;
 220
 221     if mir_phase == MirPhase::Optimization {
 222         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 223             .run_pass(tcx, body);
 224     }
 225 }
 226
 227 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 228     let const_kind = tcx.hir().body_const_context(def.did);
 229
 230     // No need to const-check a non-const `fn`.
 231     if const_kind.is_none() {
 232         return Default::default();
 233     }
 234
 235     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 236     // cannot yet be stolen), because `mir_promoted()`, which steals
 237     // from `mir_const(), forces this query to execute before
 238     // performing the steal.
 239     let body = &tcx.mir_const(def).borrow();
 240
 241     if body.return_ty().references_error() {
 242         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 243         return Default::default();
 244     }
 245
 246     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 247
 248     let mut validator = check_consts::check::Checker::new(&ccx);
 249     validator.check_body();
 250
 251     // We return the qualifs in the return place for every MIR body, even though it is only used
 252     // when deciding to promote a reference to a `const` for now.
 253     validator.qualifs_in_return_place()
 254 }
 255
 256 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 257 fn mir_const<'tcx>(
 258     tcx: TyCtxt<'tcx>,
 259     def: ty::WithOptConstParam<LocalDefId>,
 260 ) -> &'tcx Steal<Body<'tcx>> {
 261     if let Some(def) = def.try_upgrade(tcx) {
 262         return tcx.mir_const(def);
 263     }
 264
 265     // Unsafety check uses the raw mir, so make sure it is run.
 266     if !tcx.sess.opts.debugging_opts.thir_unsafeck {
 267         if let Some(param_did) = def.const_param_did {
 268             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 269         } else {
 270             tcx.ensure().unsafety_check_result(def.did);
 271         }
 272     }
 273
 274     let mut body = tcx.mir_built(def).steal();
 275
 276     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 277
 278     run_passes(
 279         tcx,
 280         &mut body,
 281         MirPhase::Const,
 282         &[&[
 283             // MIR-level lints.
 284             &check_packed_ref::CheckPackedRef,
 285             &check_const_item_mutation::CheckConstItemMutation,
 286             &function_item_references::FunctionItemReferences,
 287             // What we need to do constant evaluation.
 288             &simplify::SimplifyCfg::new("initial"),
 289             &rustc_peek::SanityCheck,
 290         ]],
 291     );
 292     tcx.alloc_steal_mir(body)
 293 }
 294
 295 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 296 fn mir_promoted(
 297     tcx: TyCtxt<'tcx>,
 298     def: ty::WithOptConstParam<LocalDefId>,
 299 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 300     if let Some(def) = def.try_upgrade(tcx) {
 301         return tcx.mir_promoted(def);
 302     }
 303
 304     // Ensure that we compute the `mir_const_qualif` for constants at
 305     // this point, before we steal the mir-const result.
 306     // Also this means promotion can rely on all const checks having been done.
 307     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 308     let mut body = tcx.mir_const(def).steal();
 309
 310     let mut required_consts = Vec::new();
 311     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 312     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 313         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 314     }
 315     body.required_consts = required_consts;
 316
 317     let promote_pass = promote_consts::PromoteTemps::default();
 318     let promote: &[&dyn MirPass<'tcx>] = &[
 319         // What we need to run borrowck etc.
 320         &promote_pass,
 321         &simplify::SimplifyCfg::new("promote-consts"),
 322     ];
 323
 324     let opt_coverage: &[&dyn MirPass<'tcx>] =
 325         if tcx.sess.instrument_coverage() { &[&coverage::InstrumentCoverage] } else { &[] };
 326
 327     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 328
 329     let promoted = promote_pass.promoted_fragments.into_inner();
 330     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 331 }
 332
 333 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 334 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 335     let did = def_id.expect_local();
 336     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 337         tcx.mir_for_ctfe_of_const_arg(def)
 338     } else {
 339         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 340     }
 341 }
 342
 343 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 344 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 345 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 346 /// the const parameter while type checking the main body, which in turn would try
 347 /// to type check the main body again.
 348 fn mir_for_ctfe_of_const_arg<'tcx>(
 349     tcx: TyCtxt<'tcx>,
 350     (did, param_did): (LocalDefId, DefId),
 351 ) -> &'tcx Body<'tcx> {
 352     tcx.arena.alloc(inner_mir_for_ctfe(
 353         tcx,
 354         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 355     ))
 356 }
 357
 358 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 359     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 360     if tcx.is_constructor(def.did.to_def_id()) {
 361         // There's no reason to run all of the MIR passes on constructors when
 362         // we can just output the MIR we want directly. This also saves const
 363         // qualification and borrow checking the trouble of special casing
 364         // constructors.
 365         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 366     }
 367
 368     let context = tcx
 369         .hir()
 370         .body_const_context(def.did)
 371         .expect("mir_for_ctfe should not be used for runtime functions");
 372
 373     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 374
 375     match context {
 376         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 377         // so we run const prop on them, or they don't, in which case we const evaluate some control
 378         // flow paths of the function and any errors in those paths will get emitted as const eval
 379         // errors.
 380         hir::ConstContext::ConstFn => {}
 381         // Static items always get evaluated, so we can just let const eval see if any erroneous
 382         // control flow paths get executed.
 383         hir::ConstContext::Static(_) => {}
 384         // Associated constants get const prop run so we detect common failure situations in the
 385         // crate that defined the constant.
 386         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 387         // conveniently detect that at this point without looking at the HIR.
 388         hir::ConstContext::Const => {
 389             #[rustfmt::skip]
 390             let optimizations: &[&dyn MirPass<'_>] = &[
 391                 &const_prop::ConstProp,
 392             ];
 393
 394             #[rustfmt::skip]
 395             run_passes(
 396                 tcx,
 397                 &mut body,
 398                 MirPhase::Optimization,
 399                 &[
 400                     optimizations,
 401                 ],
 402             );
 403         }
 404     }
 405
 406     debug_assert!(!body.has_free_regions(tcx), "Free regions in MIR for CTFE");
 407
 408     body
 409 }
 410
 411 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 412 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 413 /// end up missing the source MIR due to stealing happening.
 414 fn mir_drops_elaborated_and_const_checked<'tcx>(
 415     tcx: TyCtxt<'tcx>,
 416     def: ty::WithOptConstParam<LocalDefId>,
 417 ) -> &'tcx Steal<Body<'tcx>> {
 418     if let Some(def) = def.try_upgrade(tcx) {
 419         return tcx.mir_drops_elaborated_and_const_checked(def);
 420     }
 421
 422     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 423     // execute before we can steal.
 424     if let Some(param_did) = def.const_param_did {
 425         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 426     } else {
 427         tcx.ensure().mir_borrowck(def.did);
 428     }
 429
 430     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 431     use rustc_middle::hir::map::blocks::FnLikeNode;
 432     let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
 433     if is_fn_like {
 434         let did = def.did.to_def_id();
 435         let def = ty::WithOptConstParam::unknown(did);
 436
 437         // Do not compute the mir call graph without said call graph actually being used.
 438         if inline::is_enabled(tcx) {
 439             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 440         }
 441     }
 442
 443     let (body, _) = tcx.mir_promoted(def);
 444     let mut body = body.steal();
 445
 446     run_post_borrowck_cleanup_passes(tcx, &mut body);
 447     check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
 448     tcx.alloc_steal_mir(body)
 449 }
 450
 451 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 452 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 453     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 454
 455     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 456         // Remove all things only needed by analysis
 457         &simplify_branches::SimplifyBranches::new("initial"),
 458         &remove_noop_landing_pads::RemoveNoopLandingPads,
 459         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 460         &simplify::SimplifyCfg::new("early-opt"),
 461         // These next passes must be executed together
 462         &add_call_guards::CriticalCallEdges,
 463         &elaborate_drops::ElaborateDrops,
 464         // This will remove extraneous landing pads which are no longer
 465         // necessary as well as well as forcing any call in a non-unwinding
 466         // function calling a possibly-unwinding function to abort the process.
 467         &abort_unwinding_calls::AbortUnwindingCalls,
 468         // AddMovesForPackedDrops needs to run after drop
 469         // elaboration.
 470         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 471         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 472         // but before optimizations begin.
 473         &add_retag::AddRetag,
 474         &lower_intrinsics::LowerIntrinsics,
 475         &simplify::SimplifyCfg::new("elaborate-drops"),
 476         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 477         // and it can help optimizations.
 478         &deaggregator::Deaggregator,
 479     ];
 480
 481     run_passes(tcx, body, MirPhase::DropLowering, &[post_borrowck_cleanup]);
 482 }
 483
 484 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 485     let mir_opt_level = tcx.sess.mir_opt_level();
 486
 487     // Lowering generator control-flow and variables has to happen before we do anything else
 488     // to them. We run some optimizations before that, because they may be harder to do on the state
 489     // machine than on MIR with async primitives.
 490     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 491         &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
 492         &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 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 }