compiler/rustc_mir_transform/src/lib.rs

   1 #![allow(rustc::potential_query_instability)]
   2 #![feature(box_patterns)]
   3 #![feature(let_chains)]
   4 #![feature(let_else)]
   5 #![feature(map_try_insert)]
   6 #![feature(min_specialization)]
   7 #![feature(never_type)]
   8 #![feature(once_cell)]
   9 #![feature(option_get_or_insert_default)]
  10 #![feature(trusted_step)]
  11 #![feature(try_blocks)]
  12 #![feature(yeet_expr)]
  13 #![recursion_limit = "256"]
  14
  15 #[macro_use]
  16 extern crate tracing;
  17 #[macro_use]
  18 extern crate rustc_middle;
  19
  20 use required_consts::RequiredConstsVisitor;
  21 use rustc_const_eval::util;
  22 use rustc_data_structures::fx::FxIndexSet;
  23 use rustc_data_structures::steal::Steal;
  24 use rustc_hir as hir;
  25 use rustc_hir::def_id::{DefId, LocalDefId};
  26 use rustc_hir::intravisit::{self, Visitor};
  27 use rustc_index::vec::IndexVec;
  28 use rustc_middle::mir::visit::Visitor as _;
  29 use rustc_middle::mir::{
  30     traversal, AnalysisPhase, Body, ConstQualifs, MirPass, MirPhase, Promoted, RuntimePhase,
  31 };
  32 use rustc_middle::ty::query::Providers;
  33 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
  34
  35 #[macro_use]
  36 mod pass_manager;
  37
  38 use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};
  39
  40 mod abort_unwinding_calls;
  41 mod add_call_guards;
  42 mod add_moves_for_packed_drops;
  43 mod add_retag;
  44 mod check_const_item_mutation;
  45 mod check_packed_ref;
  46 pub mod check_unsafety;
  47 // This pass is public to allow external drivers to perform MIR cleanup
  48 pub mod cleanup_post_borrowck;
  49 mod const_debuginfo;
  50 mod const_goto;
  51 mod const_prop;
  52 mod const_prop_lint;
  53 mod coverage;
  54 mod dead_store_elimination;
  55 mod deaggregator;
  56 mod deduplicate_blocks;
  57 mod deref_separator;
  58 mod dest_prop;
  59 pub mod dump_mir;
  60 mod early_otherwise_branch;
  61 mod elaborate_box_derefs;
  62 mod elaborate_drops;
  63 mod ffi_unwind_calls;
  64 mod function_item_references;
  65 mod generator;
  66 mod inline;
  67 mod instcombine;
  68 mod lower_intrinsics;
  69 mod lower_slice_len;
  70 mod marker;
  71 mod match_branches;
  72 mod multiple_return_terminators;
  73 mod normalize_array_len;
  74 mod nrvo;
  75 // This pass is public to allow external drivers to perform MIR cleanup
  76 pub mod remove_false_edges;
  77 mod remove_noop_landing_pads;
  78 mod remove_storage_markers;
  79 mod remove_uninit_drops;
  80 mod remove_unneeded_drops;
  81 mod remove_zsts;
  82 mod required_consts;
  83 mod reveal_all;
  84 mod separate_const_switch;
  85 mod shim;
  86 // This pass is public to allow external drivers to perform MIR cleanup
  87 pub mod simplify;
  88 mod simplify_branches;
  89 mod simplify_comparison_integral;
  90 mod simplify_try;
  91 mod uninhabited_enum_branching;
  92 mod unreachable_prop;
  93
  94 use rustc_const_eval::transform::check_consts::{self, ConstCx};
  95 use rustc_const_eval::transform::promote_consts;
  96 use rustc_const_eval::transform::validate;
  97 use rustc_mir_dataflow::rustc_peek;
  98
  99 pub fn provide(providers: &mut Providers) {
 100     check_unsafety::provide(providers);
 101     check_packed_ref::provide(providers);
 102     coverage::query::provide(providers);
 103     ffi_unwind_calls::provide(providers);
 104     shim::provide(providers);
 105     *providers = Providers {
 106         mir_keys,
 107         mir_const,
 108         mir_const_qualif: |tcx, def_id| {
 109             let def_id = def_id.expect_local();
 110             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 111                 tcx.mir_const_qualif_const_arg(def)
 112             } else {
 113                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
 114             }
 115         },
 116         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 117             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 118         },
 119         mir_promoted,
 120         mir_drops_elaborated_and_const_checked,
 121         mir_for_ctfe,
 122         mir_for_ctfe_of_const_arg,
 123         optimized_mir,
 124         is_mir_available,
 125         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 126         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 127         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 128         promoted_mir: |tcx, def_id| {
 129             let def_id = def_id.expect_local();
 130             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 131                 tcx.promoted_mir_of_const_arg(def)
 132             } else {
 133                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 134             }
 135         },
 136         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 137             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 138         },
 139         ..*providers
 140     };
 141 }
 142
 143 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 144     let def_id = def_id.expect_local();
 145     tcx.mir_keys(()).contains(&def_id)
 146 }
 147
 148 /// Finds the full set of `DefId`s within the current crate that have
 149 /// MIR associated with them.
 150 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 151     let mut set = FxIndexSet::default();
 152
 153     // All body-owners have MIR associated with them.
 154     set.extend(tcx.hir().body_owners());
 155
 156     // Additionally, tuple struct/variant constructors have MIR, but
 157     // they don't have a BodyId, so we need to build them separately.
 158     struct GatherCtors<'a, 'tcx> {
 159         tcx: TyCtxt<'tcx>,
 160         set: &'a mut FxIndexSet<LocalDefId>,
 161     }
 162     impl<'tcx> Visitor<'tcx> for GatherCtors<'_, 'tcx> {
 163         fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
 164             if let hir::VariantData::Tuple(_, hir_id) = *v {
 165                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 166             }
 167             intravisit::walk_struct_def(self, v)
 168         }
 169     }
 170     tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { tcx, set: &mut set });
 171
 172     set
 173 }
 174
 175 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 176     let const_kind = tcx.hir().body_const_context(def.did);
 177
 178     // No need to const-check a non-const `fn`.
 179     if const_kind.is_none() {
 180         return Default::default();
 181     }
 182
 183     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 184     // cannot yet be stolen), because `mir_promoted()`, which steals
 185     // from `mir_const(), forces this query to execute before
 186     // performing the steal.
 187     let body = &tcx.mir_const(def).borrow();
 188
 189     if body.return_ty().references_error() {
 190         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 191         return Default::default();
 192     }
 193
 194     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 195
 196     let mut validator = check_consts::check::Checker::new(&ccx);
 197     validator.check_body();
 198
 199     // We return the qualifs in the return place for every MIR body, even though it is only used
 200     // when deciding to promote a reference to a `const` for now.
 201     validator.qualifs_in_return_place()
 202 }
 203
 204 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 205 /// FIXME(oli-obk): it's unclear whether we still need this phase (and its corresponding query).
 206 /// We used to have this for pre-miri MIR based const eval.
 207 fn mir_const<'tcx>(
 208     tcx: TyCtxt<'tcx>,
 209     def: ty::WithOptConstParam<LocalDefId>,
 210 ) -> &'tcx Steal<Body<'tcx>> {
 211     if let Some(def) = def.try_upgrade(tcx) {
 212         return tcx.mir_const(def);
 213     }
 214
 215     // Unsafety check uses the raw mir, so make sure it is run.
 216     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 217         if let Some(param_did) = def.const_param_did {
 218             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 219         } else {
 220             tcx.ensure().unsafety_check_result(def.did);
 221         }
 222     }
 223
 224     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
 225     tcx.ensure().has_ffi_unwind_calls(def.did);
 226
 227     let mut body = tcx.mir_built(def).steal();
 228
 229     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 230
 231     pm::run_passes(
 232         tcx,
 233         &mut body,
 234         &[
 235             // MIR-level lints.
 236             &Lint(check_packed_ref::CheckPackedRef),
 237             &Lint(check_const_item_mutation::CheckConstItemMutation),
 238             &Lint(function_item_references::FunctionItemReferences),
 239             // What we need to do constant evaluation.
 240             &simplify::SimplifyCfg::new("initial"),
 241             &rustc_peek::SanityCheck, // Just a lint
 242         ],
 243     );
 244     tcx.alloc_steal_mir(body)
 245 }
 246
 247 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 248 fn mir_promoted<'tcx>(
 249     tcx: TyCtxt<'tcx>,
 250     def: ty::WithOptConstParam<LocalDefId>,
 251 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 252     if let Some(def) = def.try_upgrade(tcx) {
 253         return tcx.mir_promoted(def);
 254     }
 255
 256     // Ensure that we compute the `mir_const_qualif` for constants at
 257     // this point, before we steal the mir-const result.
 258     // Also this means promotion can rely on all const checks having been done.
 259     let const_qualifs = tcx.mir_const_qualif_opt_const_arg(def);
 260     let mut body = tcx.mir_const(def).steal();
 261     if let Some(error_reported) = const_qualifs.tainted_by_errors {
 262         body.tainted_by_errors = Some(error_reported);
 263     }
 264
 265     let mut required_consts = Vec::new();
 266     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 267     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 268         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 269     }
 270     body.required_consts = required_consts;
 271
 272     // What we need to run borrowck etc.
 273     let promote_pass = promote_consts::PromoteTemps::default();
 274     pm::run_passes(
 275         tcx,
 276         &mut body,
 277         &[
 278             &promote_pass,
 279             &simplify::SimplifyCfg::new("promote-consts"),
 280             &coverage::InstrumentCoverage,
 281         ],
 282     );
 283
 284     let promoted = promote_pass.promoted_fragments.into_inner();
 285     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 286 }
 287
 288 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 289 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 290     let did = def_id.expect_local();
 291     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 292         tcx.mir_for_ctfe_of_const_arg(def)
 293     } else {
 294         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 295     }
 296 }
 297
 298 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 299 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 300 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 301 /// the const parameter while type checking the main body, which in turn would try
 302 /// to type check the main body again.
 303 fn mir_for_ctfe_of_const_arg<'tcx>(
 304     tcx: TyCtxt<'tcx>,
 305     (did, param_did): (LocalDefId, DefId),
 306 ) -> &'tcx Body<'tcx> {
 307     tcx.arena.alloc(inner_mir_for_ctfe(
 308         tcx,
 309         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 310     ))
 311 }
 312
 313 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 314     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 315     if tcx.is_constructor(def.did.to_def_id()) {
 316         // There's no reason to run all of the MIR passes on constructors when
 317         // we can just output the MIR we want directly. This also saves const
 318         // qualification and borrow checking the trouble of special casing
 319         // constructors.
 320         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 321     }
 322
 323     let context = tcx
 324         .hir()
 325         .body_const_context(def.did)
 326         .expect("mir_for_ctfe should not be used for runtime functions");
 327
 328     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 329
 330     match context {
 331         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 332         // so we run const prop on them, or they don't, in which case we const evaluate some control
 333         // flow paths of the function and any errors in those paths will get emitted as const eval
 334         // errors.
 335         hir::ConstContext::ConstFn => {}
 336         // Static items always get evaluated, so we can just let const eval see if any erroneous
 337         // control flow paths get executed.
 338         hir::ConstContext::Static(_) => {}
 339         // Associated constants get const prop run so we detect common failure situations in the
 340         // crate that defined the constant.
 341         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 342         // conveniently detect that at this point without looking at the HIR.
 343         hir::ConstContext::Const => {
 344             pm::run_passes(
 345                 tcx,
 346                 &mut body,
 347                 &[
 348                     &const_prop::ConstProp,
 349                     &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 350                 ],
 351             );
 352         }
 353     }
 354
 355     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 356
 357     body
 358 }
 359
 360 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 361 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 362 /// end up missing the source MIR due to stealing happening.
 363 fn mir_drops_elaborated_and_const_checked<'tcx>(
 364     tcx: TyCtxt<'tcx>,
 365     def: ty::WithOptConstParam<LocalDefId>,
 366 ) -> &'tcx Steal<Body<'tcx>> {
 367     if let Some(def) = def.try_upgrade(tcx) {
 368         return tcx.mir_drops_elaborated_and_const_checked(def);
 369     }
 370
 371     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 372
 373     let is_fn_like = tcx.def_kind(def.did).is_fn_like();
 374     if is_fn_like {
 375         let did = def.did.to_def_id();
 376         let def = ty::WithOptConstParam::unknown(did);
 377
 378         // Do not compute the mir call graph without said call graph actually being used.
 379         if inline::Inline.is_enabled(&tcx.sess) {
 380             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 381         }
 382     }
 383
 384     let (body, _) = tcx.mir_promoted(def);
 385     let mut body = body.steal();
 386     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 387         body.tainted_by_errors = Some(error_reported);
 388     }
 389
 390     run_analysis_to_runtime_passes(tcx, &mut body);
 391
 392     tcx.alloc_steal_mir(body)
 393 }
 394
 395 fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 396     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
 397     let did = body.source.def_id();
 398
 399     debug!("analysis_mir_cleanup({:?})", did);
 400     run_analysis_cleanup_passes(tcx, body);
 401     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));
 402
 403     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 404     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 405         pm::run_passes(
 406             tcx,
 407             body,
 408             &[
 409                 &remove_uninit_drops::RemoveUninitDrops,
 410                 &simplify::SimplifyCfg::new("remove-false-edges"),
 411             ],
 412         );
 413         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 414     }
 415
 416     debug!("runtime_mir_lowering({:?})", did);
 417     run_runtime_lowering_passes(tcx, body);
 418     assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));
 419
 420     debug!("runtime_mir_cleanup({:?})", did);
 421     run_runtime_cleanup_passes(tcx, body);
 422     assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
 423 }
 424
 425 // FIXME(JakobDegen): Can we make these lists of passes consts?
 426
 427 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 428 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 429     let passes: &[&dyn MirPass<'tcx>] = &[
 430         &remove_false_edges::RemoveFalseEdges,
 431         &simplify_branches::SimplifyConstCondition::new("initial"),
 432         &remove_noop_landing_pads::RemoveNoopLandingPads,
 433         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 434         &simplify::SimplifyCfg::new("early-opt"),
 435         &deref_separator::Derefer,
 436         &marker::PhaseChange(MirPhase::Analysis(AnalysisPhase::PostCleanup)),
 437     ];
 438
 439     pm::run_passes(tcx, body, passes);
 440 }
 441
 442 /// Returns the sequence of passes that lowers analysis to runtime MIR.
 443 fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 444     let passes: &[&dyn MirPass<'tcx>] = &[
 445         // These next passes must be executed together
 446         &add_call_guards::CriticalCallEdges,
 447         &elaborate_drops::ElaborateDrops,
 448         // This will remove extraneous landing pads which are no longer
 449         // necessary as well as well as forcing any call in a non-unwinding
 450         // function calling a possibly-unwinding function to abort the process.
 451         &abort_unwinding_calls::AbortUnwindingCalls,
 452         // AddMovesForPackedDrops needs to run after drop
 453         // elaboration.
 454         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 455         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 456         // but before optimizations begin.
 457         &elaborate_box_derefs::ElaborateBoxDerefs,
 458         &generator::StateTransform,
 459         &add_retag::AddRetag,
 460         // Deaggregator is necessary for const prop. We may want to consider implementing
 461         // CTFE support for aggregates.
 462         &deaggregator::Deaggregator,
 463         &Lint(const_prop_lint::ConstProp),
 464         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Initial)),
 465     ];
 466     pm::run_passes_no_validate(tcx, body, passes);
 467 }
 468
 469 /// Returns the sequence of passes that do the initial cleanup of runtime MIR.
 470 fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 471     let passes: &[&dyn MirPass<'tcx>] = &[
 472         &elaborate_box_derefs::ElaborateBoxDerefs,
 473         &lower_intrinsics::LowerIntrinsics,
 474         &simplify::SimplifyCfg::new("elaborate-drops"),
 475         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::PostCleanup)),
 476     ];
 477
 478     pm::run_passes(tcx, body, passes);
 479 }
 480
 481 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 482     fn o1<T>(x: T) -> WithMinOptLevel<T> {
 483         WithMinOptLevel(1, x)
 484     }
 485
 486     // The main optimizations that we do on MIR.
 487     pm::run_passes(
 488         tcx,
 489         body,
 490         &[
 491             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 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             &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 494             &unreachable_prop::UnreachablePropagation,
 495             &uninhabited_enum_branching::UninhabitedEnumBranching,
 496             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
 497             &inline::Inline,
 498             &remove_storage_markers::RemoveStorageMarkers,
 499             &remove_zsts::RemoveZsts,
 500             &const_goto::ConstGoto,
 501             &remove_unneeded_drops::RemoveUnneededDrops,
 502             &match_branches::MatchBranchSimplification,
 503             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 504             &multiple_return_terminators::MultipleReturnTerminators,
 505             &instcombine::InstCombine,
 506             &separate_const_switch::SeparateConstSwitch,
 507             //
 508             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 509             &const_prop::ConstProp,
 510             //
 511             // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
 512             &const_debuginfo::ConstDebugInfo,
 513             &o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
 514             &early_otherwise_branch::EarlyOtherwiseBranch,
 515             &simplify_comparison_integral::SimplifyComparisonIntegral,
 516             &simplify_try::SimplifyArmIdentity,
 517             &simplify_try::SimplifyBranchSame,
 518             &dead_store_elimination::DeadStoreElimination,
 519             &dest_prop::DestinationPropagation,
 520             &o1(simplify_branches::SimplifyConstCondition::new("final")),
 521             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
 522             &o1(simplify::SimplifyCfg::new("final")),
 523             &nrvo::RenameReturnPlace,
 524             &simplify::SimplifyLocals,
 525             &multiple_return_terminators::MultipleReturnTerminators,
 526             &deduplicate_blocks::DeduplicateBlocks,
 527             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 528             &add_call_guards::CriticalCallEdges,
 529             &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 530             // Dump the end result for testing and debugging purposes.
 531             &dump_mir::Marker("PreCodegen"),
 532         ],
 533     );
 534 }
 535
 536 /// Optimize the MIR and prepare it for codegen.
 537 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 538     let did = did.expect_local();
 539     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 540     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 541 }
 542
 543 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 544     if tcx.is_constructor(did.to_def_id()) {
 545         // There's no reason to run all of the MIR passes on constructors when
 546         // we can just output the MIR we want directly. This also saves const
 547         // qualification and borrow checking the trouble of special casing
 548         // constructors.
 549         return shim::build_adt_ctor(tcx, did.to_def_id());
 550     }
 551
 552     match tcx.hir().body_const_context(did) {
 553         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 554         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 555         // computes and caches its result.
 556         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 557         None => {}
 558         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 559     }
 560     debug!("about to call mir_drops_elaborated...");
 561     let mut body =
 562         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 563     debug!("body: {:#?}", body);
 564     run_optimization_passes(tcx, &mut body);
 565
 566     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 567
 568     body
 569 }
 570
 571 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 572 /// constant evaluation once all substitutions become known.
 573 fn promoted_mir<'tcx>(
 574     tcx: TyCtxt<'tcx>,
 575     def: ty::WithOptConstParam<LocalDefId>,
 576 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 577     if tcx.is_constructor(def.did.to_def_id()) {
 578         return tcx.arena.alloc(IndexVec::new());
 579     }
 580
 581     let tainted_by_errors = tcx.mir_borrowck_opt_const_arg(def).tainted_by_errors;
 582     let mut promoted = tcx.mir_promoted(def).1.steal();
 583
 584     for body in &mut promoted {
 585         if let Some(error_reported) = tainted_by_errors {
 586             body.tainted_by_errors = Some(error_reported);
 587         }
 588         run_analysis_to_runtime_passes(tcx, body);
 589     }
 590
 591     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 592
 593     tcx.arena.alloc(promoted)
 594 }