compiler/rustc_mir_transform/src/lib.rs

   1 #![allow(rustc::potential_query_instability)]
   2 #![feature(box_patterns)]
   3 #![feature(drain_filter)]
   4 #![feature(let_chains)]
   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 #![feature(if_let_guard)]
  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::FxIndexSet;
  24 use rustc_data_structures::steal::Steal;
  25 use rustc_hir as hir;
  26 use rustc_hir::def::DefKind;
  27 use rustc_hir::def_id::{DefId, LocalDefId};
  28 use rustc_hir::intravisit::{self, Visitor};
  29 use rustc_index::vec::IndexVec;
  30 use rustc_middle::mir::visit::Visitor as _;
  31 use rustc_middle::mir::{
  32     traversal, AnalysisPhase, Body, ConstQualifs, Constant, LocalDecl, MirPass, MirPhase, Operand,
  33     Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo, Statement, StatementKind,
  34     TerminatorKind,
  35 };
  36 use rustc_middle::ty::query::Providers;
  37 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
  38 use rustc_span::sym;
  39
  40 #[macro_use]
  41 mod pass_manager;
  42
  43 use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};
  44
  45 mod abort_unwinding_calls;
  46 mod add_call_guards;
  47 mod add_moves_for_packed_drops;
  48 mod add_retag;
  49 mod check_const_item_mutation;
  50 mod check_packed_ref;
  51 pub mod check_unsafety;
  52 // This pass is public to allow external drivers to perform MIR cleanup
  53 pub mod cleanup_post_borrowck;
  54 mod const_debuginfo;
  55 mod const_goto;
  56 mod const_prop;
  57 mod const_prop_lint;
  58 mod copy_prop;
  59 mod coverage;
  60 mod ctfe_limit;
  61 mod dataflow_const_prop;
  62 mod dead_store_elimination;
  63 mod deaggregator;
  64 mod deduce_param_attrs;
  65 mod deduplicate_blocks;
  66 mod deref_separator;
  67 mod dest_prop;
  68 pub mod dump_mir;
  69 mod early_otherwise_branch;
  70 mod elaborate_box_derefs;
  71 mod elaborate_drops;
  72 mod ffi_unwind_calls;
  73 mod function_item_references;
  74 mod generator;
  75 mod inline;
  76 mod instcombine;
  77 mod lower_intrinsics;
  78 mod lower_slice_len;
  79 mod match_branches;
  80 mod multiple_return_terminators;
  81 mod normalize_array_len;
  82 mod nrvo;
  83 mod remove_noop_landing_pads;
  84 mod remove_storage_markers;
  85 mod remove_uninit_drops;
  86 mod remove_unneeded_drops;
  87 mod remove_zsts;
  88 mod required_consts;
  89 mod reveal_all;
  90 mod separate_const_switch;
  91 mod shim;
  92 mod ssa;
  93 // This pass is public to allow external drivers to perform MIR cleanup
  94 pub mod simplify;
  95 mod simplify_branches;
  96 mod simplify_comparison_integral;
  97 mod sroa;
  98 mod uninhabited_enum_branching;
  99 mod unreachable_prop;
 100
 101 use rustc_const_eval::transform::check_consts::{self, ConstCx};
 102 use rustc_const_eval::transform::promote_consts;
 103 use rustc_const_eval::transform::validate;
 104 use rustc_mir_dataflow::rustc_peek;
 105
 106 pub fn provide(providers: &mut Providers) {
 107     check_unsafety::provide(providers);
 108     coverage::query::provide(providers);
 109     ffi_unwind_calls::provide(providers);
 110     shim::provide(providers);
 111     *providers = Providers {
 112         mir_keys,
 113         mir_const,
 114         mir_const_qualif: |tcx, def_id| {
 115             let def_id = def_id.expect_local();
 116             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 117                 tcx.mir_const_qualif_const_arg(def)
 118             } else {
 119                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
 120             }
 121         },
 122         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 123             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 124         },
 125         mir_promoted,
 126         mir_drops_elaborated_and_const_checked,
 127         mir_for_ctfe,
 128         mir_for_ctfe_of_const_arg,
 129         mir_generator_witnesses: generator::mir_generator_witnesses,
 130         optimized_mir,
 131         is_mir_available,
 132         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 133         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 134         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 135         promoted_mir: |tcx, def_id| {
 136             let def_id = def_id.expect_local();
 137             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 138                 tcx.promoted_mir_of_const_arg(def)
 139             } else {
 140                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 141             }
 142         },
 143         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 144             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 145         },
 146         deduced_param_attrs: deduce_param_attrs::deduced_param_attrs,
 147         ..*providers
 148     };
 149 }
 150
 151 fn remap_mir_for_const_eval_select<'tcx>(
 152     tcx: TyCtxt<'tcx>,
 153     mut body: Body<'tcx>,
 154     context: hir::Constness,
 155 ) -> Body<'tcx> {
 156     for bb in body.basic_blocks.as_mut().iter_mut() {
 157         let terminator = bb.terminator.as_mut().expect("invalid terminator");
 158         match terminator.kind {
 159             TerminatorKind::Call {
 160                 func: Operand::Constant(box Constant { ref literal, .. }),
 161                 ref mut args,
 162                 destination,
 163                 target,
 164                 cleanup,
 165                 fn_span,
 166                 ..
 167             } if let ty::FnDef(def_id, _) = *literal.ty().kind()
 168                 && tcx.item_name(def_id) == sym::const_eval_select
 169                 && tcx.is_intrinsic(def_id) =>
 170             {
 171                 let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
 172                 let ty = tupled_args.ty(&body.local_decls, tcx);
 173                 let fields = ty.tuple_fields();
 174                 let num_args = fields.len();
 175                 let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
 176                 let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
 177                     Operand::Constant(_) => {
 178                         // there is no good way of extracting a tuple arg from a constant (const generic stuff)
 179                         // so we just create a temporary and deconstruct that.
 180                         let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
 181                         bb.statements.push(Statement {
 182                             source_info: SourceInfo::outermost(fn_span),
 183                             kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
 184                         });
 185                         (Operand::Move, local.into())
 186                     }
 187                     Operand::Move(place) => (Operand::Move, place),
 188                     Operand::Copy(place) => (Operand::Copy, place),
 189                 };
 190                 let place_elems = place.projection;
 191                 let arguments = (0..num_args).map(|x| {
 192                     let mut place_elems = place_elems.to_vec();
 193                     place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
 194                     let projection = tcx.intern_place_elems(&place_elems);
 195                     let place = Place {
 196                         local: place.local,
 197                         projection,
 198                     };
 199                     method(place)
 200                 }).collect();
 201                 terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, cleanup, from_hir_call: false, fn_span };
 202             }
 203             _ => {}
 204         }
 205     }
 206     body
 207 }
 208
 209 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 210     let def_id = def_id.expect_local();
 211     tcx.mir_keys(()).contains(&def_id)
 212 }
 213
 214 /// Finds the full set of `DefId`s within the current crate that have
 215 /// MIR associated with them.
 216 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 217     let mut set = FxIndexSet::default();
 218
 219     // All body-owners have MIR associated with them.
 220     set.extend(tcx.hir().body_owners());
 221
 222     // Additionally, tuple struct/variant constructors have MIR, but
 223     // they don't have a BodyId, so we need to build them separately.
 224     struct GatherCtors<'a> {
 225         set: &'a mut FxIndexSet<LocalDefId>,
 226     }
 227     impl<'tcx> Visitor<'tcx> for GatherCtors<'_> {
 228         fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
 229             if let hir::VariantData::Tuple(_, _, def_id) = *v {
 230                 self.set.insert(def_id);
 231             }
 232             intravisit::walk_struct_def(self, v)
 233         }
 234     }
 235     tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { set: &mut set });
 236
 237     set
 238 }
 239
 240 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 241     let const_kind = tcx.hir().body_const_context(def.did);
 242
 243     // No need to const-check a non-const `fn`.
 244     if const_kind.is_none() {
 245         return Default::default();
 246     }
 247
 248     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 249     // cannot yet be stolen), because `mir_promoted()`, which steals
 250     // from `mir_const(), forces this query to execute before
 251     // performing the steal.
 252     let body = &tcx.mir_const(def).borrow();
 253
 254     if body.return_ty().references_error() {
 255         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 256         return Default::default();
 257     }
 258
 259     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 260
 261     let mut validator = check_consts::check::Checker::new(&ccx);
 262     validator.check_body();
 263
 264     // We return the qualifs in the return place for every MIR body, even though it is only used
 265     // when deciding to promote a reference to a `const` for now.
 266     validator.qualifs_in_return_place()
 267 }
 268
 269 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 270 /// FIXME(oli-obk): it's unclear whether we still need this phase (and its corresponding query).
 271 /// We used to have this for pre-miri MIR based const eval.
 272 fn mir_const(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &Steal<Body<'_>> {
 273     if let Some(def) = def.try_upgrade(tcx) {
 274         return tcx.mir_const(def);
 275     }
 276
 277     // Unsafety check uses the raw mir, so make sure it is run.
 278     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 279         if let Some(param_did) = def.const_param_did {
 280             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 281         } else {
 282             tcx.ensure().unsafety_check_result(def.did);
 283         }
 284     }
 285
 286     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
 287     tcx.ensure().has_ffi_unwind_calls(def.did);
 288
 289     let mut body = tcx.mir_built(def).steal();
 290
 291     pass_manager::dump_mir_for_phase_change(tcx, &body);
 292
 293     pm::run_passes(
 294         tcx,
 295         &mut body,
 296         &[
 297             // MIR-level lints.
 298             &Lint(check_packed_ref::CheckPackedRef),
 299             &Lint(check_const_item_mutation::CheckConstItemMutation),
 300             &Lint(function_item_references::FunctionItemReferences),
 301             // What we need to do constant evaluation.
 302             &simplify::SimplifyCfg::new("initial"),
 303             &rustc_peek::SanityCheck, // Just a lint
 304         ],
 305         None,
 306     );
 307     tcx.alloc_steal_mir(body)
 308 }
 309
 310 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 311 fn mir_promoted(
 312     tcx: TyCtxt<'_>,
 313     def: ty::WithOptConstParam<LocalDefId>,
 314 ) -> (&Steal<Body<'_>>, &Steal<IndexVec<Promoted, Body<'_>>>) {
 315     if let Some(def) = def.try_upgrade(tcx) {
 316         return tcx.mir_promoted(def);
 317     }
 318
 319     // Ensure that we compute the `mir_const_qualif` for constants at
 320     // this point, before we steal the mir-const result.
 321     // Also this means promotion can rely on all const checks having been done.
 322     let const_qualifs = tcx.mir_const_qualif_opt_const_arg(def);
 323     let mut body = tcx.mir_const(def).steal();
 324     if let Some(error_reported) = const_qualifs.tainted_by_errors {
 325         body.tainted_by_errors = Some(error_reported);
 326     }
 327
 328     let mut required_consts = Vec::new();
 329     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 330     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 331         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 332     }
 333     body.required_consts = required_consts;
 334
 335     // What we need to run borrowck etc.
 336     let promote_pass = promote_consts::PromoteTemps::default();
 337     pm::run_passes(
 338         tcx,
 339         &mut body,
 340         &[
 341             &promote_pass,
 342             &simplify::SimplifyCfg::new("promote-consts"),
 343             &coverage::InstrumentCoverage,
 344         ],
 345         Some(MirPhase::Analysis(AnalysisPhase::Initial)),
 346     );
 347
 348     let promoted = promote_pass.promoted_fragments.into_inner();
 349     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 350 }
 351
 352 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 353 fn mir_for_ctfe(tcx: TyCtxt<'_>, def_id: DefId) -> &Body<'_> {
 354     let did = def_id.expect_local();
 355     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 356         tcx.mir_for_ctfe_of_const_arg(def)
 357     } else {
 358         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 359     }
 360 }
 361
 362 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 363 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 364 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 365 /// the const parameter while type checking the main body, which in turn would try
 366 /// to type check the main body again.
 367 fn mir_for_ctfe_of_const_arg(tcx: TyCtxt<'_>, (did, param_did): (LocalDefId, DefId)) -> &Body<'_> {
 368     tcx.arena.alloc(inner_mir_for_ctfe(
 369         tcx,
 370         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 371     ))
 372 }
 373
 374 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 375     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 376     if tcx.is_constructor(def.did.to_def_id()) {
 377         // There's no reason to run all of the MIR passes on constructors when
 378         // we can just output the MIR we want directly. This also saves const
 379         // qualification and borrow checking the trouble of special casing
 380         // constructors.
 381         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 382     }
 383
 384     let context = tcx
 385         .hir()
 386         .body_const_context(def.did)
 387         .expect("mir_for_ctfe should not be used for runtime functions");
 388
 389     let body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 390
 391     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::Const);
 392
 393     match context {
 394         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 395         // so we run const prop on them, or they don't, in which case we const evaluate some control
 396         // flow paths of the function and any errors in those paths will get emitted as const eval
 397         // errors.
 398         hir::ConstContext::ConstFn => {}
 399         // Static items always get evaluated, so we can just let const eval see if any erroneous
 400         // control flow paths get executed.
 401         hir::ConstContext::Static(_) => {}
 402         // Associated constants get const prop run so we detect common failure situations in the
 403         // crate that defined the constant.
 404         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 405         // conveniently detect that at this point without looking at the HIR.
 406         hir::ConstContext::Const => {
 407             pm::run_passes(
 408                 tcx,
 409                 &mut body,
 410                 &[&const_prop::ConstProp],
 411                 Some(MirPhase::Runtime(RuntimePhase::Optimized)),
 412             );
 413         }
 414     }
 415
 416     pm::run_passes(tcx, &mut body, &[&ctfe_limit::CtfeLimit], None);
 417
 418     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 419
 420     body
 421 }
 422
 423 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 424 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 425 /// end up missing the source MIR due to stealing happening.
 426 fn mir_drops_elaborated_and_const_checked(
 427     tcx: TyCtxt<'_>,
 428     def: ty::WithOptConstParam<LocalDefId>,
 429 ) -> &Steal<Body<'_>> {
 430     if let Some(def) = def.try_upgrade(tcx) {
 431         return tcx.mir_drops_elaborated_and_const_checked(def);
 432     }
 433
 434     if tcx.sess.opts.unstable_opts.drop_tracking_mir
 435         && let DefKind::Generator = tcx.def_kind(def.did)
 436     {
 437         tcx.ensure().mir_generator_witnesses(def.did);
 438     }
 439     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 440
 441     let is_fn_like = tcx.def_kind(def.did).is_fn_like();
 442     if is_fn_like {
 443         let did = def.did.to_def_id();
 444         let def = ty::WithOptConstParam::unknown(did);
 445
 446         // Do not compute the mir call graph without said call graph actually being used.
 447         if inline::Inline.is_enabled(&tcx.sess) {
 448             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 449         }
 450     }
 451
 452     let (body, _) = tcx.mir_promoted(def);
 453     let mut body = body.steal();
 454     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 455         body.tainted_by_errors = Some(error_reported);
 456     }
 457
 458     run_analysis_to_runtime_passes(tcx, &mut body);
 459
 460     tcx.alloc_steal_mir(body)
 461 }
 462
 463 fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 464     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
 465     let did = body.source.def_id();
 466
 467     debug!("analysis_mir_cleanup({:?})", did);
 468     run_analysis_cleanup_passes(tcx, body);
 469     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));
 470
 471     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 472     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 473         pm::run_passes(
 474             tcx,
 475             body,
 476             &[
 477                 &remove_uninit_drops::RemoveUninitDrops,
 478                 &simplify::SimplifyCfg::new("remove-false-edges"),
 479             ],
 480             None,
 481         );
 482         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 483     }
 484
 485     debug!("runtime_mir_lowering({:?})", did);
 486     run_runtime_lowering_passes(tcx, body);
 487     assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));
 488
 489     debug!("runtime_mir_cleanup({:?})", did);
 490     run_runtime_cleanup_passes(tcx, body);
 491     assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
 492 }
 493
 494 // FIXME(JakobDegen): Can we make these lists of passes consts?
 495
 496 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 497 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 498     let passes: &[&dyn MirPass<'tcx>] = &[
 499         &cleanup_post_borrowck::CleanupPostBorrowck,
 500         &remove_noop_landing_pads::RemoveNoopLandingPads,
 501         &simplify::SimplifyCfg::new("early-opt"),
 502         &deref_separator::Derefer,
 503     ];
 504
 505     pm::run_passes(tcx, body, passes, Some(MirPhase::Analysis(AnalysisPhase::PostCleanup)));
 506 }
 507
 508 /// Returns the sequence of passes that lowers analysis to runtime MIR.
 509 fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 510     let passes: &[&dyn MirPass<'tcx>] = &[
 511         // These next passes must be executed together
 512         &add_call_guards::CriticalCallEdges,
 513         &elaborate_drops::ElaborateDrops,
 514         // This will remove extraneous landing pads which are no longer
 515         // necessary as well as well as forcing any call in a non-unwinding
 516         // function calling a possibly-unwinding function to abort the process.
 517         &abort_unwinding_calls::AbortUnwindingCalls,
 518         // AddMovesForPackedDrops needs to run after drop
 519         // elaboration.
 520         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 521         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 522         // but before optimizations begin.
 523         &elaborate_box_derefs::ElaborateBoxDerefs,
 524         &generator::StateTransform,
 525         &add_retag::AddRetag,
 526         // Deaggregator is necessary for const prop. We may want to consider implementing
 527         // CTFE support for aggregates.
 528         &deaggregator::Deaggregator,
 529         &Lint(const_prop_lint::ConstProp),
 530     ];
 531     pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));
 532 }
 533
 534 /// Returns the sequence of passes that do the initial cleanup of runtime MIR.
 535 fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 536     let passes: &[&dyn MirPass<'tcx>] =
 537         &[&lower_intrinsics::LowerIntrinsics, &simplify::SimplifyCfg::new("elaborate-drops")];
 538
 539     pm::run_passes(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::PostCleanup)));
 540 }
 541
 542 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 543     fn o1<T>(x: T) -> WithMinOptLevel<T> {
 544         WithMinOptLevel(1, x)
 545     }
 546
 547     // The main optimizations that we do on MIR.
 548     pm::run_passes(
 549         tcx,
 550         body,
 551         &[
 552             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 553             &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
 554             &unreachable_prop::UnreachablePropagation,
 555             &uninhabited_enum_branching::UninhabitedEnumBranching,
 556             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
 557             &inline::Inline,
 558             &remove_storage_markers::RemoveStorageMarkers,
 559             &remove_zsts::RemoveZsts,
 560             &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 561             &const_goto::ConstGoto,
 562             &remove_unneeded_drops::RemoveUnneededDrops,
 563             &sroa::ScalarReplacementOfAggregates,
 564             &match_branches::MatchBranchSimplification,
 565             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 566             &multiple_return_terminators::MultipleReturnTerminators,
 567             &instcombine::InstCombine,
 568             &separate_const_switch::SeparateConstSwitch,
 569             &simplify::SimplifyLocals::new("before-const-prop"),
 570             &copy_prop::CopyProp,
 571             //
 572             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 573             &const_prop::ConstProp,
 574             &dataflow_const_prop::DataflowConstProp,
 575             //
 576             // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
 577             &const_debuginfo::ConstDebugInfo,
 578             &o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
 579             &early_otherwise_branch::EarlyOtherwiseBranch,
 580             &simplify_comparison_integral::SimplifyComparisonIntegral,
 581             &dead_store_elimination::DeadStoreElimination,
 582             &dest_prop::DestinationPropagation,
 583             &o1(simplify_branches::SimplifyConstCondition::new("final")),
 584             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
 585             &o1(simplify::SimplifyCfg::new("final")),
 586             &nrvo::RenameReturnPlace,
 587             &simplify::SimplifyLocals::new("final"),
 588             &multiple_return_terminators::MultipleReturnTerminators,
 589             &deduplicate_blocks::DeduplicateBlocks,
 590             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 591             &add_call_guards::CriticalCallEdges,
 592             // Dump the end result for testing and debugging purposes.
 593             &dump_mir::Marker("PreCodegen"),
 594         ],
 595         Some(MirPhase::Runtime(RuntimePhase::Optimized)),
 596     );
 597 }
 598
 599 /// Optimize the MIR and prepare it for codegen.
 600 fn optimized_mir(tcx: TyCtxt<'_>, did: DefId) -> &Body<'_> {
 601     let did = did.expect_local();
 602     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 603     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 604 }
 605
 606 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 607     if tcx.is_constructor(did.to_def_id()) {
 608         // There's no reason to run all of the MIR passes on constructors when
 609         // we can just output the MIR we want directly. This also saves const
 610         // qualification and borrow checking the trouble of special casing
 611         // constructors.
 612         return shim::build_adt_ctor(tcx, did.to_def_id());
 613     }
 614
 615     match tcx.hir().body_const_context(did) {
 616         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 617         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 618         // computes and caches its result.
 619         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 620         None => {}
 621         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 622     }
 623     debug!("about to call mir_drops_elaborated...");
 624     let body =
 625         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 626     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::NotConst);
 627     debug!("body: {:#?}", body);
 628     run_optimization_passes(tcx, &mut body);
 629
 630     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 631
 632     body
 633 }
 634
 635 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 636 /// constant evaluation once all substitutions become known.
 637 fn promoted_mir(
 638     tcx: TyCtxt<'_>,
 639     def: ty::WithOptConstParam<LocalDefId>,
 640 ) -> &IndexVec<Promoted, Body<'_>> {
 641     if tcx.is_constructor(def.did.to_def_id()) {
 642         return tcx.arena.alloc(IndexVec::new());
 643     }
 644
 645     let tainted_by_errors = tcx.mir_borrowck_opt_const_arg(def).tainted_by_errors;
 646     let mut promoted = tcx.mir_promoted(def).1.steal();
 647
 648     for body in &mut promoted {
 649         if let Some(error_reported) = tainted_by_errors {
 650             body.tainted_by_errors = Some(error_reported);
 651         }
 652         run_analysis_to_runtime_passes(tcx, body);
 653     }
 654
 655     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 656
 657     tcx.arena.alloc(promoted)
 658 }