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_id::{DefId, LocalDefId};
  27 use rustc_hir::intravisit::{self, Visitor};
  28 use rustc_index::vec::IndexVec;
  29 use rustc_middle::mir::visit::Visitor as _;
  30 use rustc_middle::mir::{
  31     traversal, AnalysisPhase, Body, ConstQualifs, Constant, LocalDecl, MirPass, MirPhase, Operand,
  32     Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo, Statement, StatementKind,
  33     TerminatorKind,
  34 };
  35 use rustc_middle::ty::query::Providers;
  36 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
  37 use rustc_span::sym;
  38
  39 #[macro_use]
  40 mod pass_manager;
  41
  42 use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};
  43
  44 mod abort_unwinding_calls;
  45 mod add_call_guards;
  46 mod add_moves_for_packed_drops;
  47 mod add_retag;
  48 mod check_const_item_mutation;
  49 mod check_packed_ref;
  50 pub mod check_unsafety;
  51 // This pass is public to allow external drivers to perform MIR cleanup
  52 pub mod cleanup_post_borrowck;
  53 mod const_debuginfo;
  54 mod const_goto;
  55 mod const_prop;
  56 mod const_prop_lint;
  57 mod coverage;
  58 mod dataflow_const_prop;
  59 mod dead_store_elimination;
  60 mod deaggregator;
  61 mod deduce_param_attrs;
  62 mod deduplicate_blocks;
  63 mod deref_separator;
  64 mod dest_prop;
  65 pub mod dump_mir;
  66 mod early_otherwise_branch;
  67 mod elaborate_box_derefs;
  68 mod elaborate_drops;
  69 mod ffi_unwind_calls;
  70 mod function_item_references;
  71 mod generator;
  72 mod inline;
  73 mod instcombine;
  74 mod lower_intrinsics;
  75 mod lower_slice_len;
  76 mod match_branches;
  77 mod multiple_return_terminators;
  78 mod normalize_array_len;
  79 mod nrvo;
  80 // This pass is public to allow external drivers to perform MIR cleanup
  81 pub mod remove_false_edges;
  82 mod remove_noop_landing_pads;
  83 mod remove_storage_markers;
  84 mod remove_uninit_drops;
  85 mod remove_unneeded_drops;
  86 mod remove_zsts;
  87 mod required_consts;
  88 mod reveal_all;
  89 mod separate_const_switch;
  90 mod shim;
  91 // This pass is public to allow external drivers to perform MIR cleanup
  92 pub mod simplify;
  93 mod simplify_branches;
  94 mod simplify_comparison_integral;
  95 mod simplify_try;
  96 mod sroa;
  97 mod uninhabited_enum_branching;
  98 mod unreachable_prop;
  99
 100 use rustc_const_eval::transform::check_consts::{self, ConstCx};
 101 use rustc_const_eval::transform::promote_consts;
 102 use rustc_const_eval::transform::validate;
 103 use rustc_mir_dataflow::rustc_peek;
 104
 105 pub fn provide(providers: &mut Providers) {
 106     check_unsafety::provide(providers);
 107     check_packed_ref::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         optimized_mir,
 130         is_mir_available,
 131         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
 132         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
 133         mir_inliner_callees: inline::cycle::mir_inliner_callees,
 134         promoted_mir: |tcx, def_id| {
 135             let def_id = def_id.expect_local();
 136             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 137                 tcx.promoted_mir_of_const_arg(def)
 138             } else {
 139                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
 140             }
 141         },
 142         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
 143             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 144         },
 145         deduced_param_attrs: deduce_param_attrs::deduced_param_attrs,
 146         ..*providers
 147     };
 148 }
 149
 150 fn remap_mir_for_const_eval_select<'tcx>(
 151     tcx: TyCtxt<'tcx>,
 152     mut body: Body<'tcx>,
 153     context: hir::Constness,
 154 ) -> Body<'tcx> {
 155     for bb in body.basic_blocks.as_mut().iter_mut() {
 156         let terminator = bb.terminator.as_mut().expect("invalid terminator");
 157         match terminator.kind {
 158             TerminatorKind::Call {
 159                 func: Operand::Constant(box Constant { ref literal, .. }),
 160                 ref mut args,
 161                 destination,
 162                 target,
 163                 cleanup,
 164                 fn_span,
 165                 ..
 166             } if let ty::FnDef(def_id, _) = *literal.ty().kind()
 167                 && tcx.item_name(def_id) == sym::const_eval_select
 168                 && tcx.is_intrinsic(def_id) =>
 169             {
 170                 let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
 171                 let ty = tupled_args.ty(&body.local_decls, tcx);
 172                 let fields = ty.tuple_fields();
 173                 let num_args = fields.len();
 174                 let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
 175                 let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
 176                     Operand::Constant(_) => {
 177                         // there is no good way of extracting a tuple arg from a constant (const generic stuff)
 178                         // so we just create a temporary and deconstruct that.
 179                         let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
 180                         bb.statements.push(Statement {
 181                             source_info: SourceInfo::outermost(fn_span),
 182                             kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
 183                         });
 184                         (Operand::Move, local.into())
 185                     }
 186                     Operand::Move(place) => (Operand::Move, place),
 187                     Operand::Copy(place) => (Operand::Copy, place),
 188                 };
 189                 let place_elems = place.projection;
 190                 let arguments = (0..num_args).map(|x| {
 191                     let mut place_elems = place_elems.to_vec();
 192                     place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
 193                     let projection = tcx.intern_place_elems(&place_elems);
 194                     let place = Place {
 195                         local: place.local,
 196                         projection,
 197                     };
 198                     method(place)
 199                 }).collect();
 200                 terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, cleanup, from_hir_call: false, fn_span };
 201             }
 202             _ => {}
 203         }
 204     }
 205     body
 206 }
 207
 208 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 209     let def_id = def_id.expect_local();
 210     tcx.mir_keys(()).contains(&def_id)
 211 }
 212
 213 /// Finds the full set of `DefId`s within the current crate that have
 214 /// MIR associated with them.
 215 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 216     let mut set = FxIndexSet::default();
 217
 218     // All body-owners have MIR associated with them.
 219     set.extend(tcx.hir().body_owners());
 220
 221     // Additionally, tuple struct/variant constructors have MIR, but
 222     // they don't have a BodyId, so we need to build them separately.
 223     struct GatherCtors<'a, 'tcx> {
 224         tcx: TyCtxt<'tcx>,
 225         set: &'a mut FxIndexSet<LocalDefId>,
 226     }
 227     impl<'tcx> Visitor<'tcx> for GatherCtors<'_, 'tcx> {
 228         fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
 229             if let hir::VariantData::Tuple(_, hir_id) = *v {
 230                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 231             }
 232             intravisit::walk_struct_def(self, v)
 233         }
 234     }
 235     tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { tcx, 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>(
 273     tcx: TyCtxt<'tcx>,
 274     def: ty::WithOptConstParam<LocalDefId>,
 275 ) -> &'tcx Steal<Body<'tcx>> {
 276     if let Some(def) = def.try_upgrade(tcx) {
 277         return tcx.mir_const(def);
 278     }
 279
 280     // Unsafety check uses the raw mir, so make sure it is run.
 281     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 282         if let Some(param_did) = def.const_param_did {
 283             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 284         } else {
 285             tcx.ensure().unsafety_check_result(def.did);
 286         }
 287     }
 288
 289     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
 290     tcx.ensure().has_ffi_unwind_calls(def.did);
 291
 292     let mut body = tcx.mir_built(def).steal();
 293
 294     pass_manager::dump_mir_for_phase_change(tcx, &body);
 295
 296     pm::run_passes(
 297         tcx,
 298         &mut body,
 299         &[
 300             // MIR-level lints.
 301             &Lint(check_packed_ref::CheckPackedRef),
 302             &Lint(check_const_item_mutation::CheckConstItemMutation),
 303             &Lint(function_item_references::FunctionItemReferences),
 304             // What we need to do constant evaluation.
 305             &simplify::SimplifyCfg::new("initial"),
 306             &rustc_peek::SanityCheck, // Just a lint
 307         ],
 308         None,
 309     );
 310     tcx.alloc_steal_mir(body)
 311 }
 312
 313 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 314 fn mir_promoted<'tcx>(
 315     tcx: TyCtxt<'tcx>,
 316     def: ty::WithOptConstParam<LocalDefId>,
 317 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 318     if let Some(def) = def.try_upgrade(tcx) {
 319         return tcx.mir_promoted(def);
 320     }
 321
 322     // Ensure that we compute the `mir_const_qualif` for constants at
 323     // this point, before we steal the mir-const result.
 324     // Also this means promotion can rely on all const checks having been done.
 325     let const_qualifs = tcx.mir_const_qualif_opt_const_arg(def);
 326     let mut body = tcx.mir_const(def).steal();
 327     if let Some(error_reported) = const_qualifs.tainted_by_errors {
 328         body.tainted_by_errors = Some(error_reported);
 329     }
 330
 331     let mut required_consts = Vec::new();
 332     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 333     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 334         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 335     }
 336     body.required_consts = required_consts;
 337
 338     // What we need to run borrowck etc.
 339     let promote_pass = promote_consts::PromoteTemps::default();
 340     pm::run_passes(
 341         tcx,
 342         &mut body,
 343         &[
 344             &promote_pass,
 345             &simplify::SimplifyCfg::new("promote-consts"),
 346             &coverage::InstrumentCoverage,
 347         ],
 348         Some(MirPhase::Analysis(AnalysisPhase::Initial)),
 349     );
 350
 351     let promoted = promote_pass.promoted_fragments.into_inner();
 352     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 353 }
 354
 355 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 356 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 357     let did = def_id.expect_local();
 358     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 359         tcx.mir_for_ctfe_of_const_arg(def)
 360     } else {
 361         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 362     }
 363 }
 364
 365 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 366 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 367 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 368 /// the const parameter while type checking the main body, which in turn would try
 369 /// to type check the main body again.
 370 fn mir_for_ctfe_of_const_arg<'tcx>(
 371     tcx: TyCtxt<'tcx>,
 372     (did, param_did): (LocalDefId, DefId),
 373 ) -> &'tcx Body<'tcx> {
 374     tcx.arena.alloc(inner_mir_for_ctfe(
 375         tcx,
 376         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 377     ))
 378 }
 379
 380 fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 381     // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
 382     if tcx.is_constructor(def.did.to_def_id()) {
 383         // There's no reason to run all of the MIR passes on constructors when
 384         // we can just output the MIR we want directly. This also saves const
 385         // qualification and borrow checking the trouble of special casing
 386         // constructors.
 387         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 388     }
 389
 390     let context = tcx
 391         .hir()
 392         .body_const_context(def.did)
 393         .expect("mir_for_ctfe should not be used for runtime functions");
 394
 395     let body = tcx.mir_drops_elaborated_and_const_checked(def).borrow().clone();
 396
 397     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::Const);
 398
 399     match context {
 400         // Do not const prop functions, either they get executed at runtime or exported to metadata,
 401         // so we run const prop on them, or they don't, in which case we const evaluate some control
 402         // flow paths of the function and any errors in those paths will get emitted as const eval
 403         // errors.
 404         hir::ConstContext::ConstFn => {}
 405         // Static items always get evaluated, so we can just let const eval see if any erroneous
 406         // control flow paths get executed.
 407         hir::ConstContext::Static(_) => {}
 408         // Associated constants get const prop run so we detect common failure situations in the
 409         // crate that defined the constant.
 410         // Technically we want to not run on regular const items, but oli-obk doesn't know how to
 411         // conveniently detect that at this point without looking at the HIR.
 412         hir::ConstContext::Const => {
 413             pm::run_passes(
 414                 tcx,
 415                 &mut body,
 416                 &[&const_prop::ConstProp],
 417                 Some(MirPhase::Runtime(RuntimePhase::Optimized)),
 418             );
 419         }
 420     }
 421
 422     debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
 423
 424     body
 425 }
 426
 427 /// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
 428 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 429 /// end up missing the source MIR due to stealing happening.
 430 fn mir_drops_elaborated_and_const_checked<'tcx>(
 431     tcx: TyCtxt<'tcx>,
 432     def: ty::WithOptConstParam<LocalDefId>,
 433 ) -> &'tcx Steal<Body<'tcx>> {
 434     if let Some(def) = def.try_upgrade(tcx) {
 435         return tcx.mir_drops_elaborated_and_const_checked(def);
 436     }
 437
 438     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 439
 440     let is_fn_like = tcx.def_kind(def.did).is_fn_like();
 441     if is_fn_like {
 442         let did = def.did.to_def_id();
 443         let def = ty::WithOptConstParam::unknown(did);
 444
 445         // Do not compute the mir call graph without said call graph actually being used.
 446         if inline::Inline.is_enabled(&tcx.sess) {
 447             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 448         }
 449     }
 450
 451     let (body, _) = tcx.mir_promoted(def);
 452     let mut body = body.steal();
 453     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 454         body.tainted_by_errors = Some(error_reported);
 455     }
 456
 457     run_analysis_to_runtime_passes(tcx, &mut body);
 458
 459     tcx.alloc_steal_mir(body)
 460 }
 461
 462 fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 463     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
 464     let did = body.source.def_id();
 465
 466     debug!("analysis_mir_cleanup({:?})", did);
 467     run_analysis_cleanup_passes(tcx, body);
 468     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));
 469
 470     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 471     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 472         pm::run_passes(
 473             tcx,
 474             body,
 475             &[
 476                 &remove_uninit_drops::RemoveUninitDrops,
 477                 &simplify::SimplifyCfg::new("remove-false-edges"),
 478             ],
 479             None,
 480         );
 481         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 482     }
 483
 484     debug!("runtime_mir_lowering({:?})", did);
 485     run_runtime_lowering_passes(tcx, body);
 486     assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));
 487
 488     debug!("runtime_mir_cleanup({:?})", did);
 489     run_runtime_cleanup_passes(tcx, body);
 490     assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
 491 }
 492
 493 // FIXME(JakobDegen): Can we make these lists of passes consts?
 494
 495 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 496 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 497     let passes: &[&dyn MirPass<'tcx>] = &[
 498         &remove_false_edges::RemoveFalseEdges,
 499         &simplify_branches::SimplifyConstCondition::new("initial"),
 500         &remove_noop_landing_pads::RemoveNoopLandingPads,
 501         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 502         &simplify::SimplifyCfg::new("early-opt"),
 503         &deref_separator::Derefer,
 504     ];
 505
 506     pm::run_passes(tcx, body, passes, Some(MirPhase::Analysis(AnalysisPhase::PostCleanup)));
 507 }
 508
 509 /// Returns the sequence of passes that lowers analysis to runtime MIR.
 510 fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 511     let passes: &[&dyn MirPass<'tcx>] = &[
 512         // These next passes must be executed together
 513         &add_call_guards::CriticalCallEdges,
 514         &elaborate_drops::ElaborateDrops,
 515         // This will remove extraneous landing pads which are no longer
 516         // necessary as well as well as forcing any call in a non-unwinding
 517         // function calling a possibly-unwinding function to abort the process.
 518         &abort_unwinding_calls::AbortUnwindingCalls,
 519         // AddMovesForPackedDrops needs to run after drop
 520         // elaboration.
 521         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 522         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 523         // but before optimizations begin.
 524         &elaborate_box_derefs::ElaborateBoxDerefs,
 525         &generator::StateTransform,
 526         &add_retag::AddRetag,
 527         // Deaggregator is necessary for const prop. We may want to consider implementing
 528         // CTFE support for aggregates.
 529         &deaggregator::Deaggregator,
 530         &Lint(const_prop_lint::ConstProp),
 531     ];
 532     pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));
 533 }
 534
 535 /// Returns the sequence of passes that do the initial cleanup of runtime MIR.
 536 fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 537     let passes: &[&dyn MirPass<'tcx>] = &[
 538         &elaborate_box_derefs::ElaborateBoxDerefs,
 539         &lower_intrinsics::LowerIntrinsics,
 540         &simplify::SimplifyCfg::new("elaborate-drops"),
 541     ];
 542
 543     pm::run_passes(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::PostCleanup)));
 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             &sroa::ScalarReplacementOfAggregates,
 568             &match_branches::MatchBranchSimplification,
 569             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 570             &multiple_return_terminators::MultipleReturnTerminators,
 571             &instcombine::InstCombine,
 572             &separate_const_switch::SeparateConstSwitch,
 573             //
 574             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 575             &const_prop::ConstProp,
 576             &dataflow_const_prop::DataflowConstProp,
 577             //
 578             // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
 579             &const_debuginfo::ConstDebugInfo,
 580             &o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
 581             &early_otherwise_branch::EarlyOtherwiseBranch,
 582             &simplify_comparison_integral::SimplifyComparisonIntegral,
 583             &simplify_try::SimplifyArmIdentity,
 584             &simplify_try::SimplifyBranchSame,
 585             &dead_store_elimination::DeadStoreElimination,
 586             &dest_prop::DestinationPropagation,
 587             &o1(simplify_branches::SimplifyConstCondition::new("final")),
 588             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
 589             &o1(simplify::SimplifyCfg::new("final")),
 590             &nrvo::RenameReturnPlace,
 591             &simplify::SimplifyLocals,
 592             &multiple_return_terminators::MultipleReturnTerminators,
 593             &deduplicate_blocks::DeduplicateBlocks,
 594             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 595             &add_call_guards::CriticalCallEdges,
 596             // Dump the end result for testing and debugging purposes.
 597             &dump_mir::Marker("PreCodegen"),
 598         ],
 599         Some(MirPhase::Runtime(RuntimePhase::Optimized)),
 600     );
 601 }
 602
 603 /// Optimize the MIR and prepare it for codegen.
 604 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 605     let did = did.expect_local();
 606     assert_eq!(ty::WithOptConstParam::try_lookup(did, tcx), None);
 607     tcx.arena.alloc(inner_optimized_mir(tcx, did))
 608 }
 609
 610 fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
 611     if tcx.is_constructor(did.to_def_id()) {
 612         // There's no reason to run all of the MIR passes on constructors when
 613         // we can just output the MIR we want directly. This also saves const
 614         // qualification and borrow checking the trouble of special casing
 615         // constructors.
 616         return shim::build_adt_ctor(tcx, did.to_def_id());
 617     }
 618
 619     match tcx.hir().body_const_context(did) {
 620         // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
 621         // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
 622         // computes and caches its result.
 623         Some(hir::ConstContext::ConstFn) => tcx.ensure().mir_for_ctfe(did),
 624         None => {}
 625         Some(other) => panic!("do not use `optimized_mir` for constants: {:?}", other),
 626     }
 627     debug!("about to call mir_drops_elaborated...");
 628     let body =
 629         tcx.mir_drops_elaborated_and_const_checked(ty::WithOptConstParam::unknown(did)).steal();
 630     let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::NotConst);
 631     debug!("body: {:#?}", body);
 632     run_optimization_passes(tcx, &mut body);
 633
 634     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 635
 636     body
 637 }
 638
 639 /// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
 640 /// constant evaluation once all substitutions become known.
 641 fn promoted_mir<'tcx>(
 642     tcx: TyCtxt<'tcx>,
 643     def: ty::WithOptConstParam<LocalDefId>,
 644 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 645     if tcx.is_constructor(def.did.to_def_id()) {
 646         return tcx.arena.alloc(IndexVec::new());
 647     }
 648
 649     let tainted_by_errors = tcx.mir_borrowck_opt_const_arg(def).tainted_by_errors;
 650     let mut promoted = tcx.mir_promoted(def).1.steal();
 651
 652     for body in &mut promoted {
 653         if let Some(error_reported) = tainted_by_errors {
 654             body.tainted_by_errors = Some(error_reported);
 655         }
 656         run_analysis_to_runtime_passes(tcx, body);
 657     }
 658
 659     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 660
 661     tcx.arena.alloc(promoted)
 662 }