compiler/rustc_mir_transform/src/lib.rs

   1 #![feature(box_patterns)]
   2 #![feature(box_syntax)]
   3 #![feature(crate_visibility_modifier)]
   4 #![feature(in_band_lifetimes)]
   5 #![feature(iter_zip)]
   6 #![feature(let_else)]
   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::{dump_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 reveal_all;
  69 mod separate_const_switch;
  70 mod shim;
  71 mod simplify;
  72 mod simplify_branches;
  73 mod simplify_comparison_integral;
  74 mod simplify_try;
  75 mod uninhabited_enum_branching;
  76 mod unreachable_prop;
  77
  78 use rustc_const_eval::transform::check_consts;
  79 use rustc_const_eval::transform::promote_consts;
  80 use rustc_const_eval::transform::validate;
  81 pub use rustc_const_eval::transform::MirPass;
  82 use rustc_mir_dataflow::rustc_peek;
  83
  84 pub fn provide(providers: &mut Providers) {
  85     check_unsafety::provide(providers);
  86     check_packed_ref::provide(providers);
  87     coverage::query::provide(providers);
  88     shim::provide(providers);
  89     *providers = Providers {
  90         mir_keys,
  91         mir_const,
  92         mir_const_qualif: |tcx, def_id| {
  93             let def_id = def_id.expect_local();
  94             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  95                 tcx.mir_const_qualif_const_arg(def)
  96             } else {
  97                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  98             }
  99         },
 100         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 101             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 102         },
 103         mir_promoted,
 104         mir_drops_elaborated_and_const_checked,
 105         mir_for_ctfe,
 106         mir_for_ctfe_of_const_arg,
 107         optimized_mir,
 108         is_mir_available,
 109         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 110         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 111         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 112         promoted_mir: |tcx, def_id| {
 113             let def_id = def_id.expect_local();
 114             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 115                 tcx.promoted_mir_of_const_arg(def)
 116             } else {
 117                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 118             }
 119         },
 120         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 121             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 122         },
 123         ..*providers
 124     };
 125 }
 126
 127 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 128     let def_id = def_id.expect_local();
 129     tcx.mir_keys(()).contains(&def_id)
 130 }
 131
 132 /// Finds the full set of `DefId`s within the current crate that have
 133 /// MIR associated with them.
 134 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxHashSet<LocalDefId> {
 135     let mut set = FxHashSet::default();
 136
 137     // All body-owners have MIR associated with them.
 138     set.extend(tcx.hir().body_owners());
 139
 140     // Additionally, tuple struct/variant constructors have MIR, but
 141     // they don't have a BodyId, so we need to build them separately.
 142     struct GatherCtors<'a, 'tcx> {
 143         tcx: TyCtxt<'tcx>,
 144         set: &'a mut FxHashSet<LocalDefId>,
 145     }
 146     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 147         fn visit_variant_data(
 148             &mut self,
 149             v: &'tcx hir::VariantData<'tcx>,
 150             _: Symbol,
 151             _: &'tcx hir::Generics<'tcx>,
 152             _: hir::HirId,
 153             _: Span,
 154         ) {
 155             if let hir::VariantData::Tuple(_, hir_id) = *v {
 156                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 157             }
 158             intravisit::walk_struct_def(self, v)
 159         }
 160         type Map = intravisit::ErasedMap<'tcx>;
 161         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 162             NestedVisitorMap::None
 163         }
 164     }
 165     tcx.hir().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             let disambiguator = if is_after { "after" } else { "before" };
 192             dump_mir(
 193                 tcx,
 194                 Some(&format_args!("{:03}-{:03}", phase_index, index)),
 195                 &pass.name(),
 196                 &disambiguator,
 197                 body,
 198                 |_, _| Ok(()),
 199             );
 200         };
 201         run_hooks(body, index, false);
 202         pass.run_pass(tcx, body);
 203         run_hooks(body, index, true);
 204
 205         if validate {
 206             validate::Validator {
 207                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 208                 mir_phase,
 209             }
 210             .run_pass(tcx, body);
 211         }
 212
 213         index += 1;
 214     };
 215
 216     for pass_group in passes {
 217         for pass in *pass_group {
 218             run_pass(*pass);
 219         }
 220     }
 221
 222     body.phase = mir_phase;
 223
 224     if mir_phase == MirPhase::Optimization {
 225         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 226             .run_pass(tcx, body);
 227     }
 228 }
 229
 230 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 231     let const_kind = tcx.hir().body_const_context(def.did);
 232
 233     // No need to const-check a non-const `fn`.
 234     if const_kind.is_none() {
 235         return Default::default();
 236     }
 237
 238     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 239     // cannot yet be stolen), because `mir_promoted()`, which steals
 240     // from `mir_const(), forces this query to execute before
 241     // performing the steal.
 242     let body = &tcx.mir_const(def).borrow();
 243
 244     if body.return_ty().references_error() {
 245         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 246         return Default::default();
 247     }
 248
 249     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 250
 251     let mut validator = check_consts::check::Checker::new(&ccx);
 252     validator.check_body();
 253
 254     // We return the qualifs in the return place for every MIR body, even though it is only used
 255     // when deciding to promote a reference to a `const` for now.
 256     validator.qualifs_in_return_place()
 257 }
 258
 259 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 260 fn mir_const<'tcx>(
 261     tcx: TyCtxt<'tcx>,
 262     def: ty::WithOptConstParam<LocalDefId>,
 263 ) -> &'tcx Steal<Body<'tcx>> {
 264     if let Some(def) = def.try_upgrade(tcx) {
 265         return tcx.mir_const(def);
 266     }
 267
 268     // Unsafety check uses the raw mir, so make sure it is run.
 269     if !tcx.sess.opts.debugging_opts.thir_unsafeck {
 270         if let Some(param_did) = def.const_param_did {
 271             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 272         } else {
 273             tcx.ensure().unsafety_check_result(def.did);
 274         }
 275     }
 276
 277     let mut body = tcx.mir_built(def).steal();
 278
 279     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 280
 281     run_passes(
 282         tcx,
 283         &mut body,
 284         MirPhase::Const,
 285         &[&[
 286             // MIR-level lints.
 287             &check_packed_ref::CheckPackedRef,
 288             &check_const_item_mutation::CheckConstItemMutation,
 289             &function_item_references::FunctionItemReferences,
 290             // What we need to do constant evaluation.
 291             &simplify::SimplifyCfg::new("initial"),
 292             &rustc_peek::SanityCheck,
 293         ]],
 294     );
 295     tcx.alloc_steal_mir(body)
 296 }
 297
 298 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 299 fn mir_promoted(
 300     tcx: TyCtxt<'tcx>,
 301     def: ty::WithOptConstParam<LocalDefId>,
 302 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 303     if let Some(def) = def.try_upgrade(tcx) {
 304         return tcx.mir_promoted(def);
 305     }
 306
 307     // Ensure that we compute the `mir_const_qualif` for constants at
 308     // this point, before we steal the mir-const result.
 309     // Also this means promotion can rely on all const checks having been done.
 310     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 311     let mut body = tcx.mir_const(def).steal();
 312
 313     let mut required_consts = Vec::new();
 314     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 315     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 316         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 317     }
 318     body.required_consts = required_consts;
 319
 320     let promote_pass = promote_consts::PromoteTemps::default();
 321     let promote: &[&dyn MirPass<'tcx>] = &[
 322         // What we need to run borrowck etc.
 323         &promote_pass,
 324         &simplify::SimplifyCfg::new("promote-consts"),
 325     ];
 326
 327     let opt_coverage: &[&dyn MirPass<'tcx>] =
 328         if tcx.sess.instrument_coverage() { &[&coverage::InstrumentCoverage] } else { &[] };
 329
 330     run_passes(tcx, &mut body, MirPhase::ConstPromotion, &[promote, opt_coverage]);
 331
 332     let promoted = promote_pass.promoted_fragments.into_inner();
 333     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 334 }
 335
 336 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 337 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 338     let did = def_id.expect_local();
 339     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 340         tcx.mir_for_ctfe_of_const_arg(def)
 341     } else {
 342         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 343     }
 344 }
 345
 346 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 347 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 348 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 349 /// the const parameter while type checking the main body, which in turn would try
 350 /// to type check the main body again.
 351 fn mir_for_ctfe_of_const_arg<'tcx>(
 352     tcx: TyCtxt<'tcx>,
 353     (did, param_did): (LocalDefId, DefId),
 354 ) -> &'tcx Body<'tcx> {
 355     tcx.arena.alloc(inner_mir_for_ctfe(
 356         tcx,
 357         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 358     ))
 359 }
 360
 361 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 362     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 363     if tcx.is_constructor(def.did.to_def_id()) {
 364         // There's no reason to run all of the MIR passes on constructors when
 365         // we can just output the MIR we want directly. This also saves const
 366         // qualification and borrow checking the trouble of special casing
 367         // constructors.
 368         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 369     }
 370
 371     let context = tcx
 372         .hir()
 373         .body_const_context(def.did)
 374         .expect("mir_for_ctfe should not be used for runtime functions");
 375
 376     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 377
 378     match context {
 379         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 380         // so we run const prop on them, or they don't, in which case we const evaluate some control
 381         // flow paths of the function and any errors in those paths will get emitted as const eval
 382         // errors.
 383         hir::ConstContext::ConstFn => {}
 384         // Static items always get evaluated, so we can just let const eval see if any erroneous
 385         // control flow paths get executed.
 386         hir::ConstContext::Static(_) => {}
 387         // Associated constants get const prop run so we detect common failure situations in the
 388         // crate that defined the constant.
 389         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 390         // conveniently detect that at this point without looking at the HIR.
 391         hir::ConstContext::Const => {
 392             #[rustfmt::skip]
 393             let optimizations: &[&dyn MirPass<'_>] = &[
 394                 &const_prop::ConstProp,
 395             ];
 396
 397             #[rustfmt::skip]
 398             run_passes(
 399                 tcx,
 400                 &mut body,
 401                 MirPhase::Optimization,
 402                 &[
 403                     optimizations,
 404                 ],
 405             );
 406         }
 407     }
 408
 409     debug_assert!(!body.has_free_regions(tcx), "Free regions in MIR for CTFE");
 410
 411     body
 412 }
 413
 414 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 415 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 416 /// end up missing the source MIR due to stealing happening.
 417 fn mir_drops_elaborated_and_const_checked<'tcx>(
 418     tcx: TyCtxt<'tcx>,
 419     def: ty::WithOptConstParam<LocalDefId>,
 420 ) -> &'tcx Steal<Body<'tcx>> {
 421     if let Some(def) = def.try_upgrade(tcx) {
 422         return tcx.mir_drops_elaborated_and_const_checked(def);
 423     }
 424
 425     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 426     // execute before we can steal.
 427     if let Some(param_did) = def.const_param_did {
 428         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 429     } else {
 430         tcx.ensure().mir_borrowck(def.did);
 431     }
 432
 433     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 434     let is_fn_like = tcx.hir().get(hir_id).fn_kind().is_some();
 435     if is_fn_like {
 436         let did = def.did.to_def_id();
 437         let def = ty::WithOptConstParam::unknown(did);
 438
 439         // Do not compute the mir call graph without said call graph actually being used.
 440         if inline::is_enabled(tcx) {
 441             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 442         }
 443     }
 444
 445     let (body, _) = tcx.mir_promoted(def);
 446     let mut body = body.steal();
 447
 448     run_post_borrowck_cleanup_passes(tcx, &mut body);
 449     check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
 450     tcx.alloc_steal_mir(body)
 451 }
 452
 453 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 454 fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 455     debug!("post_borrowck_cleanup({:?})", body.source.def_id());
 456
 457     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 458         // Remove all things only needed by analysis
 459         &simplify_branches::SimplifyBranches::new("initial"),
 460         &remove_noop_landing_pads::RemoveNoopLandingPads,
 461         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 462         &simplify::SimplifyCfg::new("early-opt"),
 463         // These next passes must be executed together
 464         &add_call_guards::CriticalCallEdges,
 465         &elaborate_drops::ElaborateDrops,
 466         // This will remove extraneous landing pads which are no longer
 467         // necessary as well as well as forcing any call in a non-unwinding
 468         // function calling a possibly-unwinding function to abort the process.
 469         &abort_unwinding_calls::AbortUnwindingCalls,
 470         // AddMovesForPackedDrops needs to run after drop
 471         // elaboration.
 472         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 473         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 474         // but before optimizations begin.
 475         &add_retag::AddRetag,
 476         &lower_intrinsics::LowerIntrinsics,
 477         &simplify::SimplifyCfg::new("elaborate-drops"),
 478         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 479         // and it can help optimizations.
 480         &deaggregator::Deaggregator,
 481     ];
 482
 483     run_passes(tcx, body, MirPhase::DropLowering, &[post_borrowck_cleanup]);
 484 }
 485
 486 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 487     let mir_opt_level = tcx.sess.mir_opt_level();
 488
 489     // Lowering generator control-flow and variables has to happen before we do anything else
 490     // to them. We run some optimizations before that, because they may be harder to do on the state
 491     // machine than on MIR with async primitives.
 492     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 493         &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 494         &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
 495         &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 496         &unreachable_prop::UnreachablePropagation,
 497         &uninhabited_enum_branching::UninhabitedEnumBranching,
 498         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 499         &inline::Inline,
 500         &generator::StateTransform,
 501     ];
 502
 503     // Even if we don't do optimizations, we still have to lower generators for codegen.
 504     let no_optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[&generator::StateTransform];
 505
 506     // The main optimizations that we do on MIR.
 507     let optimizations: &[&dyn MirPass<'tcx>] = &[
 508         &remove_storage_markers::RemoveStorageMarkers,
 509         &remove_zsts::RemoveZsts,
 510         &const_goto::ConstGoto,
 511         &remove_unneeded_drops::RemoveUnneededDrops,
 512         &match_branches::MatchBranchSimplification,
 513         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 514         &multiple_return_terminators::MultipleReturnTerminators,
 515         &instcombine::InstCombine,
 516         &separate_const_switch::SeparateConstSwitch,
 517         &const_prop::ConstProp,
 518         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 519         &early_otherwise_branch::EarlyOtherwiseBranch,
 520         &simplify_comparison_integral::SimplifyComparisonIntegral,
 521         &simplify_try::SimplifyArmIdentity,
 522         &simplify_try::SimplifyBranchSame,
 523         &dest_prop::DestinationPropagation,
 524         &simplify_branches::SimplifyBranches::new("final"),
 525         &remove_noop_landing_pads::RemoveNoopLandingPads,
 526         &simplify::SimplifyCfg::new("final"),
 527         &nrvo::RenameReturnPlace,
 528         &const_debuginfo::ConstDebugInfo,
 529         &simplify::SimplifyLocals,
 530         &multiple_return_terminators::MultipleReturnTerminators,
 531         &deduplicate_blocks::DeduplicateBlocks,
 532     ];
 533
 534     // Optimizations to run even if mir optimizations have been disabled.
 535     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 536         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 537         &const_prop::ConstProp,
 538     ];
 539
 540     // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 541     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 542         &add_call_guards::CriticalCallEdges,
 543         // Dump the end result for testing and debugging purposes.
 544         &dump_mir::Marker("PreCodegen"),
 545     ];
 546
 547     // End of pass declarations, now actually run the passes.
 548     // Generator Lowering
 549     #[rustfmt::skip]
 550     run_passes(
 551         tcx,
 552         body,
 553         MirPhase::GeneratorLowering,
 554         &[
 555             if mir_opt_level > 0 {
 556                 optimizations_with_generators
 557             } else {
 558                 no_optimizations_with_generators
 559             }
 560         ],
 561     );
 562
 563     // Main optimization passes
 564     #[rustfmt::skip]
 565     run_passes(
 566         tcx,
 567         body,
 568         MirPhase::Optimization,
 569         &[
 570             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 571             pre_codegen_cleanup,
 572         ],
 573     );
 574 }
 575
 576 /// Optimize the MIR and prepare it for codegen.
 577 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 578     let did = did.expect_local();
 579     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 580     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 581 }
 582
 583 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 584     if tcx.is_constructor(did.to_def_id()) {
 585         // There's no reason to run all of the MIR passes on constructors when
 586         // we can just output the MIR we want directly. This also saves const
 587         // qualification and borrow checking the trouble of special casing
 588         // constructors.
 589         return shim::build_adt_ctor(tcx, did.to_def_id());
 590     }
 591
 592     match tcx.hir().body_const_context(did) {
 593         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 594         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 595         // computes and caches its result.
 596         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 597         None => {}
 598         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 599     }
 600     let mut body =
 601         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 602     run_optimization_passes(tcx, &mut body);
 603
 604     debug_assert!(!body.has_free_regions(tcx), "Free regions in optimized MIR");
 605
 606     body
 607 }
 608
 609 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 610 /// constant evaluation once all substitutions become known.
 611 fn promoted_mir<'tcx>(
 612     tcx: TyCtxt<'tcx>,
 613     def: ty::WithOptConstParam<LocalDefId>,
 614 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 615     if tcx.is_constructor(def.did.to_def_id()) {
 616         return tcx.arena.alloc(IndexVec::new());
 617     }
 618
 619     if let Some(param_did) = def.const_param_did {
 620         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 621     } else {
 622         tcx.ensure().mir_borrowck(def.did);
 623     }
 624     let (_, promoted) = tcx.mir_promoted(def);
 625     let mut promoted = promoted.steal();
 626
 627     for body in &mut promoted {
 628         run_post_borrowck_cleanup_passes(tcx, body);
 629     }
 630
 631     debug_assert!(!promoted.has_free_regions(tcx), "Free regions in promoted MIR");
 632
 633     tcx.arena.alloc(promoted)
 634 }