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