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 deduplicate_blocks;
  60 mod deref_separator;
  61 mod dest_prop;
  62 pub mod dump_mir;
  63 mod early_otherwise_branch;
  64 mod elaborate_box_derefs;
  65 mod elaborate_drops;
  66 mod ffi_unwind_calls;
  67 mod function_item_references;
  68 mod generator;
  69 mod inline;
  70 mod instcombine;
  71 mod lower_intrinsics;
  72 mod lower_slice_len;
  73 mod marker;
  74 mod match_branches;
  75 mod multiple_return_terminators;
  76 mod normalize_array_len;
  77 mod nrvo;
  78 // This pass is public to allow external drivers to perform MIR cleanup
  79 pub mod remove_false_edges;
  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 simplify_try;
  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         ..*providers
 143     };
 144 }
 145
 146 fn remap_mir_for_const_eval_select<'tcx>(
 147     tcx: TyCtxt<'tcx>,
 148     mut body: Body<'tcx>,
 149     context: hir::Constness,
 150 ) -> Body<'tcx> {
 151     for bb in body.basic_blocks.as_mut().iter_mut() {
 152         let terminator = bb.terminator.as_mut().expect("invalid terminator");
 153         match terminator.kind {
 154             TerminatorKind::Call {
 155                 func: Operand::Constant(box Constant { ref literal, .. }),
 156                 ref mut args,
 157                 destination,
 158                 target,
 159                 cleanup,
 160                 fn_span,
 161                 ..
 162             } if let ty::FnDef(def_id, _) = *literal.ty().kind()
 163                 && tcx.item_name(def_id) == sym::const_eval_select
 164                 && tcx.is_intrinsic(def_id) =>
 165             {
 166                 let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
 167                 let ty = tupled_args.ty(&body.local_decls, tcx);
 168                 let fields = ty.tuple_fields();
 169                 let num_args = fields.len();
 170                 let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
 171                 let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
 172                     Operand::Constant(_) => {
 173                         // there is no good way of extracting a tuple arg from a constant (const generic stuff)
 174                         // so we just create a temporary and deconstruct that.
 175                         let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
 176                         bb.statements.push(Statement {
 177                             source_info: SourceInfo::outermost(fn_span),
 178                             kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
 179                         });
 180                         (Operand::Move, local.into())
 181                     }
 182                     Operand::Move(place) => (Operand::Move, place),
 183                     Operand::Copy(place) => (Operand::Copy, place),
 184                 };
 185                 let place_elems = place.projection;
 186                 let arguments = (0..num_args).map(|x| {
 187                     let mut place_elems = place_elems.to_vec();
 188                     place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
 189                     let projection = tcx.intern_place_elems(&place_elems);
 190                     let place = Place {
 191                         local: place.local,
 192                         projection,
 193                     };
 194                     method(place)
 195                 }).collect();
 196                 terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, cleanup, from_hir_call: false, fn_span };
 197             }
 198             _ => {}
 199         }
 200     }
 201     body
 202 }
 203
 204 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 205     let def_id = def_id.expect_local();
 206     tcx.mir_keys(()).contains(&def_id)
 207 }
 208
 209 /// Finds the full set of `DefId`s within the current crate that have
 210 /// MIR associated with them.
 211 fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
 212     let mut set = FxIndexSet::default();
 213
 214     // All body-owners have MIR associated with them.
 215     set.extend(tcx.hir().body_owners());
 216
 217     // Additionally, tuple struct/variant constructors have MIR, but
 218     // they don't have a BodyId, so we need to build them separately.
 219     struct GatherCtors<'a, 'tcx> {
 220         tcx: TyCtxt<'tcx>,
 221         set: &'a mut FxIndexSet<LocalDefId>,
 222     }
 223     impl<'tcx> Visitor<'tcx> for GatherCtors<'_, 'tcx> {
 224         fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
 225             if let hir::VariantData::Tuple(_, hir_id) = *v {
 226                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 227             }
 228             intravisit::walk_struct_def(self, v)
 229         }
 230     }
 231     tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { tcx, 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>(
 269     tcx: TyCtxt<'tcx>,
 270     def: ty::WithOptConstParam<LocalDefId>,
 271 ) -> &'tcx Steal<Body<'tcx>> {
 272     if let Some(def) = def.try_upgrade(tcx) {
 273         return tcx.mir_const(def);
 274     }
 275
 276     // Unsafety check uses the raw mir, so make sure it is run.
 277     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 278         if let Some(param_did) = def.const_param_did {
 279             tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 280         } else {
 281             tcx.ensure().unsafety_check_result(def.did);
 282         }
 283     }
 284
 285     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
 286     tcx.ensure().has_ffi_unwind_calls(def.did);
 287
 288     let mut body = tcx.mir_built(def).steal();
 289
 290     rustc_middle::mir::dump_mir(tcx, None, "mir_map", &0, &body, |_, _| Ok(()));
 291
 292     pm::run_passes(
 293         tcx,
 294         &mut body,
 295         &[
 296             // MIR-level lints.
 297             &Lint(check_packed_ref::CheckPackedRef),
 298             &Lint(check_const_item_mutation::CheckConstItemMutation),
 299             &Lint(function_item_references::FunctionItemReferences),
 300             // What we need to do constant evaluation.
 301             &simplify::SimplifyCfg::new("initial"),
 302             &rustc_peek::SanityCheck, // Just a lint
 303         ],
 304     );
 305     tcx.alloc_steal_mir(body)
 306 }
 307
 308 /// Compute the main MIR body and the list of MIR bodies of the promoteds.
 309 fn mir_promoted<'tcx>(
 310     tcx: TyCtxt<'tcx>,
 311     def: ty::WithOptConstParam<LocalDefId>,
 312 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 313     if let Some(def) = def.try_upgrade(tcx) {
 314         return tcx.mir_promoted(def);
 315     }
 316
 317     // Ensure that we compute the `mir_const_qualif` for constants at
 318     // this point, before we steal the mir-const result.
 319     // Also this means promotion can rely on all const checks having been done.
 320     let const_qualifs = tcx.mir_const_qualif_opt_const_arg(def);
 321     let mut body = tcx.mir_const(def).steal();
 322     if let Some(error_reported) = const_qualifs.tainted_by_errors {
 323         body.tainted_by_errors = Some(error_reported);
 324     }
 325
 326     let mut required_consts = Vec::new();
 327     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 328     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 329         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 330     }
 331     body.required_consts = required_consts;
 332
 333     // What we need to run borrowck etc.
 334     let promote_pass = promote_consts::PromoteTemps::default();
 335     pm::run_passes(
 336         tcx,
 337         &mut body,
 338         &[
 339             &promote_pass,
 340             &simplify::SimplifyCfg::new("promote-consts"),
 341             &coverage::InstrumentCoverage,
 342         ],
 343     );
 344
 345     let promoted = promote_pass.promoted_fragments.into_inner();
 346     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 347 }
 348
 349 /// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
 350 fn mir_for_ctfe<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Body<'tcx> {
 351     let did = def_id.expect_local();
 352     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 353         tcx.mir_for_ctfe_of_const_arg(def)
 354     } else {
 355         tcx.arena.alloc(inner_mir_for_ctfe(tcx, ty::WithOptConstParam::unknown(did)))
 356     }
 357 }
 358
 359 /// Same as `mir_for_ctfe`, but used to get the MIR of a const generic parameter.
 360 /// The docs on `WithOptConstParam` explain this a bit more, but the TLDR is that
 361 /// we'd get cycle errors with `mir_for_ctfe`, because typeck would need to typeck
 362 /// the const parameter while type checking the main body, which in turn would try
 363 /// to type check the main body again.
 364 fn mir_for_ctfe_of_const_arg<'tcx>(
 365     tcx: TyCtxt<'tcx>,
 366     (did, param_did): (LocalDefId, DefId),
 367 ) -> &'tcx Body<'tcx> {
 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                 &[
 411                     &const_prop::ConstProp,
 412                     &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 413                 ],
 414             );
 415         }
 416     }
 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<'tcx>(
 427     tcx: TyCtxt<'tcx>,
 428     def: ty::WithOptConstParam<LocalDefId>,
 429 ) -> &'tcx Steal<Body<'tcx>> {
 430     if let Some(def) = def.try_upgrade(tcx) {
 431         return tcx.mir_drops_elaborated_and_const_checked(def);
 432     }
 433
 434     let mir_borrowck = tcx.mir_borrowck_opt_const_arg(def);
 435
 436     let is_fn_like = tcx.def_kind(def.did).is_fn_like();
 437     if is_fn_like {
 438         let did = def.did.to_def_id();
 439         let def = ty::WithOptConstParam::unknown(did);
 440
 441         // Do not compute the mir call graph without said call graph actually being used.
 442         if inline::Inline.is_enabled(&tcx.sess) {
 443             let _ = tcx.mir_inliner_callees(ty::InstanceDef::Item(def));
 444         }
 445     }
 446
 447     let (body, _) = tcx.mir_promoted(def);
 448     let mut body = body.steal();
 449     if let Some(error_reported) = mir_borrowck.tainted_by_errors {
 450         body.tainted_by_errors = Some(error_reported);
 451     }
 452
 453     run_analysis_to_runtime_passes(tcx, &mut body);
 454
 455     tcx.alloc_steal_mir(body)
 456 }
 457
 458 fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 459     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
 460     let did = body.source.def_id();
 461
 462     debug!("analysis_mir_cleanup({:?})", did);
 463     run_analysis_cleanup_passes(tcx, body);
 464     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));
 465
 466     // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
 467     if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
 468         pm::run_passes(
 469             tcx,
 470             body,
 471             &[
 472                 &remove_uninit_drops::RemoveUninitDrops,
 473                 &simplify::SimplifyCfg::new("remove-false-edges"),
 474             ],
 475         );
 476         check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
 477     }
 478
 479     debug!("runtime_mir_lowering({:?})", did);
 480     run_runtime_lowering_passes(tcx, body);
 481     assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));
 482
 483     debug!("runtime_mir_cleanup({:?})", did);
 484     run_runtime_cleanup_passes(tcx, body);
 485     assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
 486 }
 487
 488 // FIXME(JakobDegen): Can we make these lists of passes consts?
 489
 490 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 491 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 492     let passes: &[&dyn MirPass<'tcx>] = &[
 493         &remove_false_edges::RemoveFalseEdges,
 494         &simplify_branches::SimplifyConstCondition::new("initial"),
 495         &remove_noop_landing_pads::RemoveNoopLandingPads,
 496         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 497         &simplify::SimplifyCfg::new("early-opt"),
 498         &deref_separator::Derefer,
 499         &marker::PhaseChange(MirPhase::Analysis(AnalysisPhase::PostCleanup)),
 500     ];
 501
 502     pm::run_passes(tcx, body, passes);
 503 }
 504
 505 /// Returns the sequence of passes that lowers analysis to runtime MIR.
 506 fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 507     let passes: &[&dyn MirPass<'tcx>] = &[
 508         // These next passes must be executed together
 509         &add_call_guards::CriticalCallEdges,
 510         &elaborate_drops::ElaborateDrops,
 511         // This will remove extraneous landing pads which are no longer
 512         // necessary as well as well as forcing any call in a non-unwinding
 513         // function calling a possibly-unwinding function to abort the process.
 514         &abort_unwinding_calls::AbortUnwindingCalls,
 515         // AddMovesForPackedDrops needs to run after drop
 516         // elaboration.
 517         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 518         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 519         // but before optimizations begin.
 520         &elaborate_box_derefs::ElaborateBoxDerefs,
 521         &generator::StateTransform,
 522         &add_retag::AddRetag,
 523         // Deaggregator is necessary for const prop. We may want to consider implementing
 524         // CTFE support for aggregates.
 525         &deaggregator::Deaggregator,
 526         &Lint(const_prop_lint::ConstProp),
 527         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Initial)),
 528     ];
 529     pm::run_passes_no_validate(tcx, body, passes);
 530 }
 531
 532 /// Returns the sequence of passes that do the initial cleanup of runtime MIR.
 533 fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 534     let passes: &[&dyn MirPass<'tcx>] = &[
 535         &elaborate_box_derefs::ElaborateBoxDerefs,
 536         &lower_intrinsics::LowerIntrinsics,
 537         &simplify::SimplifyCfg::new("elaborate-drops"),
 538         &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::PostCleanup)),
 539     ];
 540
 541     pm::run_passes(tcx, body, passes);
 542 }
 543
 544 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 545     fn o1<T>(x: T) -> WithMinOptLevel<T> {
 546         WithMinOptLevel(1, x)
 547     }
 548
 549     // The main optimizations that we do on MIR.
 550     pm::run_passes(
 551         tcx,
 552         body,
 553         &[
 554             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
 555             &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
 556             &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
 557             &unreachable_prop::UnreachablePropagation,
 558             &uninhabited_enum_branching::UninhabitedEnumBranching,
 559             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
 560             &inline::Inline,
 561             &remove_storage_markers::RemoveStorageMarkers,
 562             &remove_zsts::RemoveZsts,
 563             &const_goto::ConstGoto,
 564             &remove_unneeded_drops::RemoveUnneededDrops,
 565             &match_branches::MatchBranchSimplification,
 566             // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 567             &multiple_return_terminators::MultipleReturnTerminators,
 568             &instcombine::InstCombine,
 569             &separate_const_switch::SeparateConstSwitch,
 570             //
 571             // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 572             &const_prop::ConstProp,
 573             //
 574             // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
 575             &const_debuginfo::ConstDebugInfo,
 576             &o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
 577             &early_otherwise_branch::EarlyOtherwiseBranch,
 578             &simplify_comparison_integral::SimplifyComparisonIntegral,
 579             &simplify_try::SimplifyArmIdentity,
 580             &simplify_try::SimplifyBranchSame,
 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,
 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             &marker::PhaseChange(MirPhase::Runtime(RuntimePhase::Optimized)),
 593             // Dump the end result for testing and debugging purposes.
 594             &dump_mir::Marker("PreCodegen"),
 595         ],
 596     );
 597 }
 598
 599 /// Optimize the MIR and prepare it for codegen.
 600 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 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<'tcx>(
 638     tcx: TyCtxt<'tcx>,
 639     def: ty::WithOptConstParam<LocalDefId>,
 640 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 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 }