compiler/rustc_mir_transform/src/lib.rs

   1 #![allow(rustc::potential_query_instability)]
   2 #![feature(box_patterns)]
   3 #![feature(let_chains)]
   4 #![feature(map_try_insert)]
   5 #![feature(min_specialization)]
   6 #![feature(never_type)]
   7 #![feature(once_cell)]
   8 #![feature(option_get_or_insert_default)]
   9 #![feature(trusted_step)]
  10 #![feature(try_blocks)]
  11 #![feature(yeet_expr)]
  12 #![feature(if_let_guard)]
  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, Constant, LocalDecl, MirPass, MirPhase, Operand,
  31     Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo, Statement, StatementKind,
  32     TerminatorKind,
  33 };
  34 use rustc_middle::ty::query::Providers;
  35 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
  36 use rustc_span::sym;
  37
  38 #[macro_use]
  39 mod pass_manager;
  40
  41 use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};
  42
  43 mod abort_unwinding_calls;
  44 mod add_call_guards;
  45 mod add_moves_for_packed_drops;
  46 mod add_retag;
  47 mod check_const_item_mutation;
  48 mod check_packed_ref;
  49 pub mod check_unsafety;
  50 // This pass is public to allow external drivers to perform MIR cleanup
  51 pub mod cleanup_post_borrowck;
  52 mod const_debuginfo;
  53 mod const_goto;
  54 mod const_prop;
  55 mod const_prop_lint;
  56 mod coverage;
  57 mod dead_store_elimination;
  58 mod deaggregator;
  59 mod deduce_param_attrs;
  60 mod deduplicate_blocks;
  61 mod deref_separator;
  62 mod dest_prop;
  63 pub mod dump_mir;
  64 mod early_otherwise_branch;
  65 mod elaborate_box_derefs;
  66 mod elaborate_drops;
  67 mod ffi_unwind_calls;
  68 mod function_item_references;
  69 mod generator;
  70 mod inline;
  71 mod instcombine;
  72 mod lower_intrinsics;
  73 mod lower_slice_len;
  74 mod marker;
  75 mod match_branches;
  76 mod multiple_return_terminators;
  77 mod normalize_array_len;
  78 mod nrvo;
  79 // This pass is public to allow external drivers to perform MIR cleanup
  80 pub mod remove_false_edges;
  81 mod remove_noop_landing_pads;
  82 mod remove_storage_markers;
  83 mod remove_uninit_drops;
  84 mod remove_unneeded_drops;
  85 mod remove_zsts;
  86 mod required_consts;
  87 mod reveal_all;
  88 mod separate_const_switch;
  89 mod shim;
  90 // This pass is public to allow external drivers to perform MIR cleanup
  91 pub mod simplify;
  92 mod simplify_branches;
  93 mod simplify_comparison_integral;
  94 mod simplify_try;
  95 mod uninhabited_enum_branching;
  96 mod unreachable_prop;
  97
  98 use rustc_const_eval::transform::check_consts::{self, ConstCx};
  99 use rustc_const_eval::transform::promote_consts;
 100 use rustc_const_eval::transform::validate;
 101 use rustc_mir_dataflow::rustc_peek;
 102
 103 pub fn provide(providers: &mut Providers) {
 104     check_unsafety::provide(providers);
 105     check_packed_ref::provide(providers);
 106     coverage::query::provide(providers);
 107     ffi_unwind_calls::provide(providers);
 108     shim::provide(providers);
 109     *providers = Providers {
 110         mir_keys,
 111         mir_const,
 112         mir_const_qualif: |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.mir_const_qualif_const_arg(def)
 116             } else {
 117                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
 118             }
 119         },
 120         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
 121             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 122         },
 123         mir_promoted,
 124         mir_drops_elaborated_and_const_checked,
 125         mir_for_ctfe,
 126         mir_for_ctfe_of_const_arg,
 127         optimized_mir,
 128         is_mir_available,
 129         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 130         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 131         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 132         promoted_mir: |tcx, def_id| {
 133             let def_id = def_id.expect_local();
 134             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 135                 tcx.promoted_mir_of_const_arg(def)
 136             } else {
 137                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 138             }
 139         },
 140         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 141             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 142         },
 143         deduced_param_attrs: deduce_param_attrs::deduced_param_attrs,
 144         ..*providers
 145     };
 146 }
 147
 148 fn remap_mir_for_const_eval_select<'tcx>(
 149     tcx: TyCtxt<'tcx>,
 150     mut body: Body<'tcx>,
 151     context: hir::Constness,
 152 ) -> Body<'tcx> {
 153     for bb in body.basic_blocks.as_mut().iter_mut() {
 154         let terminator = bb.terminator.as_mut().expect("invalid terminator");
 155         match terminator.kind {
 156             TerminatorKind::Call {
 157                 func: Operand::Constant(box Constant { ref literal, .. }),
 158                 ref mut args,
 159                 destination,
 160                 target,
 161                 cleanup,
 162                 fn_span,
 163                 ..
 164             } if let ty::FnDef(def_id, _) = *literal.ty().kind()
 165                 && tcx.item_name(def_id) == sym::const_eval_select
 166                 && tcx.is_intrinsic(def_id) =>
 167             {
 168                 let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
 169                 let ty = tupled_args.ty(&body.local_decls, tcx);
 170                 let fields = ty.tuple_fields();
 171                 let num_args = fields.len();
 172                 let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
 173                 let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
 174                     Operand::Constant(_) => {
 175                         // there is no good way of extracting a tuple arg from a constant (const generic stuff)
 176                         // so we just create a temporary and deconstruct that.
 177                         let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
 178                         bb.statements.push(Statement {
 179                             source_info: SourceInfo::outermost(fn_span),
 180                             kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
 181                         });
 182                         (Operand::Move, local.into())
 183                     }
 184                     Operand::Move(place) => (Operand::Move, place),
 185                     Operand::Copy(place) => (Operand::Copy, place),
 186                 };
 187                 let place_elems = place.projection;
 188                 let arguments = (0..num_args).map(|x| {
 189                     let mut place_elems = place_elems.to_vec();
 190                     place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
 191                     let projection = tcx.intern_place_elems(&place_elems);
 192                     let place = Place {
 193                         local: place.local,
 194                         projection,
 195                     };
 196                     method(place)
 197                 }).collect();
 198                 terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, cleanup, from_hir_call: false, fn_span };
 199             }
 200             _ => {}
 201         }
 202     }
 203     body
 204 }
 205
 206 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 207     let def_id = def_id.expect_local();
 208     tcx.mir_keys(()).contains(&def_id)
 209 }
 210
 211 /// Finds the full set of `DefId`s within the current crate that have
 212 /// MIR associated with them.
 213 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 214     let mut set = FxIndexSet::default();
 215
 216     // All body-owners have MIR associated with them.
 217     set.extend(tcx.hir().body_owners());
 218
 219     // Additionally, tuple struct/variant constructors have MIR, but
 220     // they don't have a BodyId, so we need to build them separately.
 221     struct GatherCtors<'a, 'tcx> {
 222         tcx: TyCtxt<'tcx>,
 223         set: &'a mut FxIndexSet<LocalDefId>,
 224     }
 225     impl<'tcx> Visitor<'tcx> for GatherCtors<'_, 'tcx> {
 226         fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
 227             if let hir::VariantData::Tuple(_, hir_id) = *v {
 228                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 229             }
 230             intravisit::walk_struct_def(self, v)
 231         }
 232     }
 233     tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { tcx, set: &mut set });
 234
 235     set
 236 }
 237
 238 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 239     let const_kind = tcx.hir().body_const_context(def.did);
 240
 241     // No need to const-check a non-const `fn`.
 242     if const_kind.is_none() {
 243         return Default::default();
 244     }
 245
 246     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 247     // cannot yet be stolen), because `mir_promoted()`, which steals
 248     // from `mir_const(), forces this query to execute before
 249     // performing the steal.
 250     let body = &tcx.mir_const(def).borrow();
 251
 252     if body.return_ty().references_error() {
 253         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 254         return Default::default();
 255     }
 256
 257     let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def.did) };
 258
 259     let mut validator = check_consts::check::Checker::new(&ccx);
 260     validator.check_body();
 261
 262     // We return the qualifs in the return place for every MIR body, even though it is only used
 263     // when deciding to promote a reference to a `const` for now.
 264     validator.qualifs_in_return_place()
 265 }
 266
 267 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 268 /// FIXME(oli-obk): it's unclear whether we still need this phase (and its corresponding query).
 269 /// We used to have this for pre-miri MIR based const eval.
 270 fn mir_const<'tcx>(
 271     tcx: TyCtxt<'tcx>,
 272     def: ty::WithOptConstParam<LocalDefId>,
 273 ) -> &'tcx Steal<Body<'tcx>> {
 274     if let Some(def) = def.try_upgrade(tcx) {
 275         return tcx.mir_const(def);
 276     }
 277
 278     // Unsafety check uses the raw mir, so make sure it is run.
 279     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 280         if let Some(param_did) = def.const_param_did {
 281             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 282         } else {
 283             tcx.ensure().unsafety_check_result(def.did);
 284         }
 285     }
 286
 287     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
 288     tcx.ensure().has_ffi_unwind_calls(def.did);
 289
 290     let mut body = tcx.mir_built(def).steal();
 291
 292     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 293
 294     pm::run_passes(
 295         tcx,
 296         &mut body,
 297         &[
 298             // MIR-level lints.
 299             &Lint(check_packed_ref::CheckPackedRef),
 300             &Lint(check_const_item_mutation::CheckConstItemMutation),
 301             &Lint(function_item_references::FunctionItemReferences),
 302             // What we need to do constant evaluation.
 303             &simplify::SimplifyCfg::new("initial"),
 304             &rustc_peek::SanityCheck, // Just a lint
 305         ],
 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<'tcx>(
 312     tcx: TyCtxt<'tcx>,
 313     def: ty::WithOptConstParam<LocalDefId>,
 314 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 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     );
 346
 347     let promoted = promote_pass.promoted_fragments.into_inner();
 348     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 349 }
 350
 351 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 352 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 353     let did = def_id.expect_local();
 354     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 355         tcx.mir_for_ctfe_of_const_arg(def)
 356     } else {
 357         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 358     }
 359 }
 360
 361 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 362 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 363 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 364 /// the const parameter while type checking the main body, which in turn would try
 365 /// to type check the main body again.
 366 fn mir_for_ctfe_of_const_arg<'tcx>(
 367     tcx: TyCtxt<'tcx>,
 368     (did, param_did): (LocalDefId, DefId),
 369 ) -> &'tcx Body<'tcx> {
 370     tcx.arena.alloc(inner_mir_for_ctfe(
 371         tcx,
 372         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 373     ))
 374 }
 375
 376 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 377     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 378     if tcx.is_constructor(def.did.to_def_id()) {
 379         // There's no reason to run all of the MIR passes on constructors when
 380         // we can just output the MIR we want directly. This also saves const
 381         // qualification and borrow checking the trouble of special casing
 382         // constructors.
 383         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 384     }
 385
 386     let context = tcx
 387         .hir()
 388         .body_const_context(def.did)
 389         .expect("mir_for_ctfe should not be used for runtime functions");
 390
 391     let body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 392
 393     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::Const);
 394
 395     match context {
 396         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 397         // so we run const prop on them, or they don't, in which case we const evaluate some control
 398         // flow paths of the function and any errors in those paths will get emitted as const eval
 399         // errors.
 400         hir::ConstContext::ConstFn => {}
 401         // Static items always get evaluated, so we can just let const eval see if any erroneous
 402         // control flow paths get executed.
 403         hir::ConstContext::Static(_) => {}
 404         // Associated constants get const prop run so we detect common failure situations in the
 405         // crate that defined the constant.
 406         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 407         // conveniently detect that at this point without looking at the HIR.
 408         hir::ConstContext::Const => {
 409             pm::run_passes(
 410                 tcx,
 411                 &mut body,
 412                 &[
 413                     &const_prop::ConstProp,
 414                     &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 415                 ],
 416             );
 417         }
 418     }
 419
 420     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 421
 422     body
 423 }
 424
 425 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 426 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 427 /// end up missing the source MIR due to stealing happening.
 428 fn mir_drops_elaborated_and_const_checked<'tcx>(
 429     tcx: TyCtxt<'tcx>,
 430     def: ty::WithOptConstParam<LocalDefId>,
 431 ) -> &'tcx Steal<Body<'tcx>> {
 432     if let Some(def) = def.try_upgrade(tcx) {
 433         return tcx.mir_drops_elaborated_and_const_checked(def);
 434     }
 435
 436     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 437
 438     let is_fn_like = tcx.def_kind(def.did).is_fn_like();
 439     if is_fn_like {
 440         let did = def.did.to_def_id();
 441         let def = ty::WithOptConstParam::unknown(did);
 442
 443         // Do not compute the mir call graph without said call graph actually being used.
 444         if inline::Inline.is_enabled(&tcx.sess) {
 445             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 446         }
 447     }
 448
 449     let (body, _) = tcx.mir_promoted(def);
 450     let mut body = body.steal();
 451     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 452         body.tainted_by_errors = Some(error_reported);
 453     }
 454
 455     run_analysis_to_runtime_passes(tcx, &mut body);
 456
 457     tcx.alloc_steal_mir(body)
 458 }
 459
 460 fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 461     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
 462     let did = body.source.def_id();
 463
 464     debug!("analysis_mir_cleanup({:?})", did);
 465     run_analysis_cleanup_passes(tcx, body);
 466     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));
 467
 468     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 469     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 470         pm::run_passes(
 471             tcx,
 472             body,
 473             &[
 474                 &remove_uninit_drops::RemoveUninitDrops,
 475                 &simplify::SimplifyCfg::new("remove-false-edges"),
 476             ],
 477         );
 478         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 479     }
 480
 481     debug!("runtime_mir_lowering({:?})", did);
 482     run_runtime_lowering_passes(tcx, body);
 483     assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));
 484
 485     debug!("runtime_mir_cleanup({:?})", did);
 486     run_runtime_cleanup_passes(tcx, body);
 487     assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
 488 }
 489
 490 // FIXME(JakobDegen): Can we make these lists of passes consts?
 491
 492 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 493 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 494     let passes: &[&dyn MirPass<'tcx>] = &[
 495         &remove_false_edges::RemoveFalseEdges,
 496         &simplify_branches::SimplifyConstCondition::new("initial"),
 497         &remove_noop_landing_pads::RemoveNoopLandingPads,
 498         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 499         &simplify::SimplifyCfg::new("early-opt"),
 500         &deref_separator::Derefer,
 501         &marker::PhaseChange(MirPhase::Analysis(AnalysisPhase::PostCleanup)),
 502     ];
 503
 504     pm::run_passes(tcx, body, passes);
 505 }
 506
 507 /// Returns the sequence of passes that lowers analysis to runtime MIR.
 508 fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 509     let passes: &[&dyn MirPass<'tcx>] = &[
 510         // These next passes must be executed together
 511         &add_call_guards::CriticalCallEdges,
 512         &elaborate_drops::ElaborateDrops,
 513         // This will remove extraneous landing pads which are no longer
 514         // necessary as well as well as forcing any call in a non-unwinding
 515         // function calling a possibly-unwinding function to abort the process.
 516         &abort_unwinding_calls::AbortUnwindingCalls,
 517         // AddMovesForPackedDrops needs to run after drop
 518         // elaboration.
 519         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 520         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 521         // but before optimizations begin.
 522         &elaborate_box_derefs::ElaborateBoxDerefs,
 523         &generator::StateTransform,
 524         &add_retag::AddRetag,
 525         // Deaggregator is necessary for const prop. We may want to consider implementing
 526         // CTFE support for aggregates.
 527         &deaggregator::Deaggregator,
 528         &Lint(const_prop_lint::ConstProp),
 529         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Initial)),
 530     ];
 531     pm::run_passes_no_validate(tcx, body, passes);
 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         &elaborate_box_derefs::ElaborateBoxDerefs,
 538         &lower_intrinsics::LowerIntrinsics,
 539         &simplify::SimplifyCfg::new("elaborate-drops"),
 540         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::PostCleanup)),
 541     ];
 542
 543     pm::run_passes(tcx, body, passes);
 544 }
 545
 546 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 547     fn o1<T>(x: T) -> WithMinOptLevel<T> {
 548         WithMinOptLevel(1, x)
 549     }
 550
 551     // The main optimizations that we do on MIR.
 552     pm::run_passes(
 553         tcx,
 554         body,
 555         &[
 556             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 557             &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
 558             &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 559             &unreachable_prop::UnreachablePropagation,
 560             &uninhabited_enum_branching::UninhabitedEnumBranching,
 561             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
 562             &inline::Inline,
 563             &remove_storage_markers::RemoveStorageMarkers,
 564             &remove_zsts::RemoveZsts,
 565             &const_goto::ConstGoto,
 566             &remove_unneeded_drops::RemoveUnneededDrops,
 567             &match_branches::MatchBranchSimplification,
 568             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 569             &multiple_return_terminators::MultipleReturnTerminators,
 570             &instcombine::InstCombine,
 571             &separate_const_switch::SeparateConstSwitch,
 572             //
 573             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 574             &const_prop::ConstProp,
 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             &simplify_try::SimplifyArmIdentity,
 582             &simplify_try::SimplifyBranchSame,
 583             &dead_store_elimination::DeadStoreElimination,
 584             &dest_prop::DestinationPropagation,
 585             &o1(simplify_branches::SimplifyConstCondition::new("final")),
 586             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
 587             &o1(simplify::SimplifyCfg::new("final")),
 588             &nrvo::RenameReturnPlace,
 589             &simplify::SimplifyLocals,
 590             &multiple_return_terminators::MultipleReturnTerminators,
 591             &deduplicate_blocks::DeduplicateBlocks,
 592             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 593             &add_call_guards::CriticalCallEdges,
 594             &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 595             // Dump the end result for testing and debugging purposes.
 596             &dump_mir::Marker("PreCodegen"),
 597         ],
 598     );
 599 }
 600
 601 /// Optimize the MIR and prepare it for codegen.
 602 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 603     let did = did.expect_local();
 604     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 605     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 606 }
 607
 608 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 609     if tcx.is_constructor(did.to_def_id()) {
 610         // There's no reason to run all of the MIR passes on constructors when
 611         // we can just output the MIR we want directly. This also saves const
 612         // qualification and borrow checking the trouble of special casing
 613         // constructors.
 614         return shim::build_adt_ctor(tcx, did.to_def_id());
 615     }
 616
 617     match tcx.hir().body_const_context(did) {
 618         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 619         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 620         // computes and caches its result.
 621         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 622         None => {}
 623         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 624     }
 625     debug!("about to call mir_drops_elaborated...");
 626     let body =
 627         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 628     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::NotConst);
 629     debug!("body: {:#?}", body);
 630     run_optimization_passes(tcx, &mut body);
 631
 632     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 633
 634     body
 635 }
 636
 637 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 638 /// constant evaluation once all substitutions become known.
 639 fn promoted_mir<'tcx>(
 640     tcx: TyCtxt<'tcx>,
 641     def: ty::WithOptConstParam<LocalDefId>,
 642 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 643     if tcx.is_constructor(def.did.to_def_id()) {
 644         return tcx.arena.alloc(IndexVec::new());
 645     }
 646
 647     let tainted_by_errors = tcx.mir_borrowck_opt_const_arg(def).tainted_by_errors;
 648     let mut promoted = tcx.mir_promoted(def).1.steal();
 649
 650     for body in &mut promoted {
 651         if let Some(error_reported) = tainted_by_errors {
 652             body.tainted_by_errors = Some(error_reported);
 653         }
 654         run_analysis_to_runtime_passes(tcx, body);
 655     }
 656
 657     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 658
 659     tcx.arena.alloc(promoted)
 660 }