compiler/rustc_mir/src/transform/mod.rs

   1 use crate::{shim, util};
   2 use required_consts::RequiredConstsVisitor;
   3 use rustc_data_structures::fx::FxHashSet;
   4 use rustc_hir as hir;
   5 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
   6 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
   7 use rustc_index::vec::IndexVec;
   8 use rustc_middle::mir::visit::Visitor as _;
   9 use rustc_middle::mir::{traversal, Body, ConstQualifs, MirPhase, Promoted};
  10 use rustc_middle::ty::query::Providers;
  11 use rustc_middle::ty::steal::Steal;
  12 use rustc_middle::ty::{self, InstanceDef, TyCtxt, TypeFoldable};
  13 use rustc_span::{Span, Symbol};
  14 use std::borrow::Cow;
  15
  16 pub mod add_call_guards;
  17 pub mod add_moves_for_packed_drops;
  18 pub mod add_retag;
  19 pub mod check_const_item_mutation;
  20 pub mod check_consts;
  21 pub mod check_packed_ref;
  22 pub mod check_unsafety;
  23 pub mod cleanup_post_borrowck;
  24 pub mod const_prop;
  25 pub mod copy_prop;
  26 pub mod deaggregator;
  27 pub mod dest_prop;
  28 pub mod dump_mir;
  29 pub mod early_otherwise_branch;
  30 pub mod elaborate_drops;
  31 pub mod generator;
  32 pub mod inline;
  33 pub mod instcombine;
  34 pub mod instrument_coverage;
  35 pub mod match_branches;
  36 pub mod no_landing_pads;
  37 pub mod nrvo;
  38 pub mod promote_consts;
  39 pub mod qualify_min_const_fn;
  40 pub mod remove_noop_landing_pads;
  41 pub mod remove_unneeded_drops;
  42 pub mod required_consts;
  43 pub mod rustc_peek;
  44 pub mod simplify;
  45 pub mod simplify_branches;
  46 pub mod simplify_comparison_integral;
  47 pub mod simplify_try;
  48 pub mod uninhabited_enum_branching;
  49 pub mod unreachable_prop;
  50 pub mod validate;
  51
  52 pub(crate) fn provide(providers: &mut Providers) {
  53     self::check_unsafety::provide(providers);
  54     *providers = Providers {
  55         mir_keys,
  56         mir_const,
  57         mir_const_qualif: |tcx, def_id| {
  58             let def_id = def_id.expect_local();
  59             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  60                 tcx.mir_const_qualif_const_arg(def)
  61             } else {
  62                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  63             }
  64         },
  65         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
  66             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  67         },
  68         mir_promoted,
  69         mir_drops_elaborated_and_const_checked,
  70         optimized_mir,
  71         optimized_mir_of_const_arg,
  72         is_mir_available,
  73         promoted_mir: |tcx, def_id| {
  74             let def_id = def_id.expect_local();
  75             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
  76                 tcx.promoted_mir_of_const_arg(def)
  77             } else {
  78                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
  79             }
  80         },
  81         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
  82             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  83         },
  84         ..*providers
  85     };
  86     instrument_coverage::provide(providers);
  87 }
  88
  89 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
  90     tcx.mir_keys(def_id.krate).contains(&def_id.expect_local())
  91 }
  92
  93 /// Finds the full set of `DefId`s within the current crate that have
  94 /// MIR associated with them.
  95 fn mir_keys(tcx: TyCtxt<'_>, krate: CrateNum) -> FxHashSet<LocalDefId> {
  96     assert_eq!(krate, LOCAL_CRATE);
  97
  98     let mut set = FxHashSet::default();
  99
 100     // All body-owners have MIR associated with them.
 101     set.extend(tcx.body_owners());
 102
 103     // Additionally, tuple struct/variant constructors have MIR, but
 104     // they don't have a BodyId, so we need to build them separately.
 105     struct GatherCtors<'a, 'tcx> {
 106         tcx: TyCtxt<'tcx>,
 107         set: &'a mut FxHashSet<LocalDefId>,
 108     }
 109     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 110         fn visit_variant_data(
 111             &mut self,
 112             v: &'tcx hir::VariantData<'tcx>,
 113             _: Symbol,
 114             _: &'tcx hir::Generics<'tcx>,
 115             _: hir::HirId,
 116             _: Span,
 117         ) {
 118             if let hir::VariantData::Tuple(_, hir_id) = *v {
 119                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 120             }
 121             intravisit::walk_struct_def(self, v)
 122         }
 123         type Map = intravisit::ErasedMap<'tcx>;
 124         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 125             NestedVisitorMap::None
 126         }
 127     }
 128     tcx.hir()
 129         .krate()
 130         .visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 131
 132     set
 133 }
 134
 135 /// Where a specific `mir::Body` comes from.
 136 #[derive(Debug, Copy, Clone)]
 137 pub struct MirSource<'tcx> {
 138     pub instance: InstanceDef<'tcx>,
 139
 140     /// If `Some`, this is a promoted rvalue within the parent function.
 141     pub promoted: Option<Promoted>,
 142 }
 143
 144 impl<'tcx> MirSource<'tcx> {
 145     pub fn item(def_id: DefId) -> Self {
 146         MirSource {
 147             instance: InstanceDef::Item(ty::WithOptConstParam::unknown(def_id)),
 148             promoted: None,
 149         }
 150     }
 151
 152     pub fn with_opt_param(self) -> ty::WithOptConstParam<DefId> {
 153         self.instance.with_opt_param()
 154     }
 155
 156     #[inline]
 157     pub fn def_id(&self) -> DefId {
 158         self.instance.def_id()
 159     }
 160 }
 161
 162 /// Generates a default name for the pass based on the name of the
 163 /// type `T`.
 164 pub fn default_name<T: ?Sized>() -> Cow<'static, str> {
 165     let name = ::std::any::type_name::<T>();
 166     if let Some(tail) = name.rfind(':') { Cow::from(&name[tail + 1..]) } else { Cow::from(name) }
 167 }
 168
 169 /// A streamlined trait that you can implement to create a pass; the
 170 /// pass will be named after the type, and it will consist of a main
 171 /// loop that goes over each available MIR and applies `run_pass`.
 172 pub trait MirPass<'tcx> {
 173     fn name(&self) -> Cow<'_, str> {
 174         default_name::<Self>()
 175     }
 176
 177     fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>);
 178 }
 179
 180 pub fn run_passes(
 181     tcx: TyCtxt<'tcx>,
 182     body: &mut Body<'tcx>,
 183     instance: InstanceDef<'tcx>,
 184     promoted: Option<Promoted>,
 185     mir_phase: MirPhase,
 186     passes: &[&[&dyn MirPass<'tcx>]],
 187 ) {
 188     let phase_index = mir_phase.phase_index();
 189     let source = MirSource { instance, promoted };
 190     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 191
 192     if body.phase >= mir_phase {
 193         return;
 194     }
 195
 196     if validate {
 197         validate::Validator { when: format!("input to phase {:?}", mir_phase), mir_phase }
 198             .run_pass(tcx, source, body);
 199     }
 200
 201     let mut index = 0;
 202     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 203         let run_hooks = |body: &_, index, is_after| {
 204             dump_mir::on_mir_pass(
 205                 tcx,
 206                 &format_args!("{:03}-{:03}", phase_index, index),
 207                 &pass.name(),
 208                 source,
 209                 body,
 210                 is_after,
 211             );
 212         };
 213         run_hooks(body, index, false);
 214         pass.run_pass(tcx, source, body);
 215         run_hooks(body, index, true);
 216
 217         if validate {
 218             validate::Validator {
 219                 when: format!("after {} in phase {:?}", pass.name(), mir_phase),
 220                 mir_phase,
 221             }
 222             .run_pass(tcx, source, body);
 223         }
 224
 225         index += 1;
 226     };
 227
 228     for pass_group in passes {
 229         for pass in *pass_group {
 230             run_pass(*pass);
 231         }
 232     }
 233
 234     body.phase = mir_phase;
 235
 236     if mir_phase == MirPhase::Optimization {
 237         validate::Validator { when: format!("end of phase {:?}", mir_phase), mir_phase }
 238             .run_pass(tcx, source, body);
 239     }
 240 }
 241
 242 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 243     let const_kind = tcx.hir().body_const_context(def.did);
 244
 245     // No need to const-check a non-const `fn`.
 246     if const_kind.is_none() {
 247         return Default::default();
 248     }
 249
 250     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 251     // cannot yet be stolen), because `mir_promoted()`, which steals
 252     // from `mir_const(), forces this query to execute before
 253     // performing the steal.
 254     let body = &tcx.mir_const(def).borrow();
 255
 256     if body.return_ty().references_error() {
 257         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 258         return Default::default();
 259     }
 260
 261     let ccx = check_consts::ConstCx {
 262         body,
 263         tcx,
 264         def_id: def.did,
 265         const_kind,
 266         param_env: tcx.param_env(def.did),
 267     };
 268
 269     let mut validator = check_consts::validation::Validator::new(&ccx);
 270     validator.check_body();
 271
 272     // We return the qualifs in the return place for every MIR body, even though it is only used
 273     // when deciding to promote a reference to a `const` for now.
 274     validator.qualifs_in_return_place()
 275 }
 276
 277 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 278 fn mir_const<'tcx>(
 279     tcx: TyCtxt<'tcx>,
 280     def: ty::WithOptConstParam<LocalDefId>,
 281 ) -> &'tcx Steal<Body<'tcx>> {
 282     if let Some(def) = def.try_upgrade(tcx) {
 283         return tcx.mir_const(def);
 284     }
 285
 286     // Unsafety check uses the raw mir, so make sure it is run.
 287     if let Some(param_did) = def.const_param_did {
 288         tcx.ensure().unsafety_check_result_for_const_arg((def.did, param_did));
 289     } else {
 290         tcx.ensure().unsafety_check_result(def.did);
 291     }
 292
 293     let mut body = tcx.mir_built(def).steal();
 294
 295     util::dump_mir(
 296         tcx,
 297         None,
 298         "mir_map",
 299         &0,
 300         MirSource { instance: InstanceDef::Item(def.to_global()), promoted: None },
 301         &body,
 302         |_, _| Ok(()),
 303     );
 304
 305     run_passes(
 306         tcx,
 307         &mut body,
 308         InstanceDef::Item(def.to_global()),
 309         None,
 310         MirPhase::Const,
 311         &[&[
 312             // MIR-level lints.
 313             &check_packed_ref::CheckPackedRef,
 314             &check_const_item_mutation::CheckConstItemMutation,
 315             // What we need to do constant evaluation.
 316             &simplify::SimplifyCfg::new("initial"),
 317             &rustc_peek::SanityCheck,
 318         ]],
 319     );
 320     tcx.alloc_steal_mir(body)
 321 }
 322
 323 fn mir_promoted(
 324     tcx: TyCtxt<'tcx>,
 325     def: ty::WithOptConstParam<LocalDefId>,
 326 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 327     if let Some(def) = def.try_upgrade(tcx) {
 328         return tcx.mir_promoted(def);
 329     }
 330
 331     // Ensure that we compute the `mir_const_qualif` for constants at
 332     // this point, before we steal the mir-const result.
 333     // Also this means promotion can rely on all const checks having been done.
 334     let _ = tcx.mir_const_qualif_opt_const_arg(def);
 335     let _ = if let Some(param_did) = def.const_param_did {
 336         tcx.mir_abstract_const_of_const_arg((def.did, param_did))
 337     } else {
 338         tcx.mir_abstract_const(def.did.to_def_id())
 339     };
 340     let mut body = tcx.mir_const(def).steal();
 341
 342     let mut required_consts = Vec::new();
 343     let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
 344     for (bb, bb_data) in traversal::reverse_postorder(&body) {
 345         required_consts_visitor.visit_basic_block_data(bb, bb_data);
 346     }
 347     body.required_consts = required_consts;
 348
 349     let promote_pass = promote_consts::PromoteTemps::default();
 350     let promote: &[&dyn MirPass<'tcx>] = &[
 351         // What we need to run borrowck etc.
 352         &promote_pass,
 353         &simplify::SimplifyCfg::new("promote-consts"),
 354     ];
 355
 356     let opt_coverage: &[&dyn MirPass<'tcx>] = if tcx.sess.opts.debugging_opts.instrument_coverage {
 357         &[&instrument_coverage::InstrumentCoverage]
 358     } else {
 359         &[]
 360     };
 361
 362     run_passes(
 363         tcx,
 364         &mut body,
 365         InstanceDef::Item(def.to_global()),
 366         None,
 367         MirPhase::ConstPromotion,
 368         &[promote, opt_coverage],
 369     );
 370
 371     let promoted = promote_pass.promoted_fragments.into_inner();
 372     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 373 }
 374
 375 fn mir_drops_elaborated_and_const_checked<'tcx>(
 376     tcx: TyCtxt<'tcx>,
 377     def: ty::WithOptConstParam<LocalDefId>,
 378 ) -> &'tcx Steal<Body<'tcx>> {
 379     if let Some(def) = def.try_upgrade(tcx) {
 380         return tcx.mir_drops_elaborated_and_const_checked(def);
 381     }
 382
 383     // (Mir-)Borrowck uses `mir_promoted`, so we have to force it to
 384     // execute before we can steal.
 385     if let Some(param_did) = def.const_param_did {
 386         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 387     } else {
 388         tcx.ensure().mir_borrowck(def.did);
 389     }
 390
 391     let (body, _) = tcx.mir_promoted(def);
 392     let mut body = body.steal();
 393
 394     run_post_borrowck_cleanup_passes(tcx, &mut body, def.did, None);
 395     check_consts::post_drop_elaboration::check_live_drops(tcx, def.did, &body);
 396     tcx.alloc_steal_mir(body)
 397 }
 398
 399 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 400 fn run_post_borrowck_cleanup_passes<'tcx>(
 401     tcx: TyCtxt<'tcx>,
 402     body: &mut Body<'tcx>,
 403     def_id: LocalDefId,
 404     promoted: Option<Promoted>,
 405 ) {
 406     debug!("post_borrowck_cleanup({:?})", def_id);
 407
 408     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 409         // Remove all things only needed by analysis
 410         &no_landing_pads::NoLandingPads::new(tcx),
 411         &simplify_branches::SimplifyBranches::new("initial"),
 412         &remove_noop_landing_pads::RemoveNoopLandingPads,
 413         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 414         &simplify::SimplifyCfg::new("early-opt"),
 415         // These next passes must be executed together
 416         &add_call_guards::CriticalCallEdges,
 417         &elaborate_drops::ElaborateDrops,
 418         &no_landing_pads::NoLandingPads::new(tcx),
 419         // AddMovesForPackedDrops needs to run after drop
 420         // elaboration.
 421         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 422         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 423         // but before optimizations begin.
 424         &add_retag::AddRetag,
 425         &simplify::SimplifyCfg::new("elaborate-drops"),
 426         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
 427         // and it can help optimizations.
 428         &deaggregator::Deaggregator,
 429     ];
 430
 431     run_passes(
 432         tcx,
 433         body,
 434         InstanceDef::Item(ty::WithOptConstParam::unknown(def_id.to_def_id())),
 435         promoted,
 436         MirPhase::DropLowering,
 437         &[post_borrowck_cleanup],
 438     );
 439 }
 440
 441 fn run_optimization_passes<'tcx>(
 442     tcx: TyCtxt<'tcx>,
 443     body: &mut Body<'tcx>,
 444     def_id: LocalDefId,
 445     promoted: Option<Promoted>,
 446 ) {
 447     let mir_opt_level = tcx.sess.opts.debugging_opts.mir_opt_level;
 448
 449     // Lowering generator control-flow and variables has to happen before we do anything else
 450     // to them. We run some optimizations before that, because they may be harder to do on the state
 451     // machine than on MIR with async primitives.
 452     let optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[
 453         &unreachable_prop::UnreachablePropagation,
 454         &uninhabited_enum_branching::UninhabitedEnumBranching,
 455         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 456         &inline::Inline,
 457         &generator::StateTransform,
 458     ];
 459
 460     // Even if we don't do optimizations, we still have to lower generators for codegen.
 461     let no_optimizations_with_generators: &[&dyn MirPass<'tcx>] = &[&generator::StateTransform];
 462
 463     // The main optimizations that we do on MIR.
 464     let optimizations: &[&dyn MirPass<'tcx>] = &[
 465         &remove_unneeded_drops::RemoveUnneededDrops,
 466         &match_branches::MatchBranchSimplification,
 467         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
 468         &instcombine::InstCombine,
 469         &const_prop::ConstProp,
 470         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 471         &early_otherwise_branch::EarlyOtherwiseBranch,
 472         &simplify_comparison_integral::SimplifyComparisonIntegral,
 473         &simplify_try::SimplifyArmIdentity,
 474         &simplify_try::SimplifyBranchSame,
 475         &dest_prop::DestinationPropagation,
 476         &copy_prop::CopyPropagation,
 477         &simplify_branches::SimplifyBranches::new("after-copy-prop"),
 478         &remove_noop_landing_pads::RemoveNoopLandingPads,
 479         &simplify::SimplifyCfg::new("after-remove-noop-landing-pads"),
 480         &simplify::SimplifyCfg::new("final"),
 481         &nrvo::RenameReturnPlace,
 482         &simplify::SimplifyLocals,
 483     ];
 484
 485     // Optimizations to run even if mir optimizations have been disabled.
 486     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 487         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 488         &const_prop::ConstProp,
 489     ];
 490
 491     // Some cleanup necessary at least for LLVM and potentially other codegen backends.
 492     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 493         &add_call_guards::CriticalCallEdges,
 494         // Dump the end result for testing and debugging purposes.
 495         &dump_mir::Marker("PreCodegen"),
 496     ];
 497
 498     // End of pass declarations, now actually run the passes.
 499     // Generator Lowering
 500     #[rustfmt::skip]
 501     run_passes(
 502         tcx,
 503         body,
 504         InstanceDef::Item(ty::WithOptConstParam::unknown(def_id.to_def_id())),
 505         promoted,
 506         MirPhase::GeneratorLowering,
 507         &[
 508             if mir_opt_level > 0 {
 509                 optimizations_with_generators
 510             } else {
 511                 no_optimizations_with_generators
 512             }
 513         ],
 514     );
 515
 516     // Main optimization passes
 517     #[rustfmt::skip]
 518     run_passes(
 519         tcx,
 520         body,
 521         InstanceDef::Item(ty::WithOptConstParam::unknown(def_id.to_def_id())),
 522         promoted,
 523         MirPhase::Optimization,
 524         &[
 525             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 526             pre_codegen_cleanup,
 527         ],
 528     );
 529 }
 530
 531 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 532     let did = did.expect_local();
 533     if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
 534         tcx.optimized_mir_of_const_arg(def)
 535     } else {
 536         tcx.arena.alloc(inner_optimized_mir(tcx, ty::WithOptConstParam::unknown(did)))
 537     }
 538 }
 539
 540 fn optimized_mir_of_const_arg<'tcx>(
 541     tcx: TyCtxt<'tcx>,
 542     (did, param_did): (LocalDefId, DefId),
 543 ) -> &'tcx Body<'tcx> {
 544     tcx.arena.alloc(inner_optimized_mir(
 545         tcx,
 546         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 547     ))
 548 }
 549
 550 fn inner_optimized_mir(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 551     if tcx.is_constructor(def.did.to_def_id()) {
 552         // There's no reason to run all of the MIR passes on constructors when
 553         // we can just output the MIR we want directly. This also saves const
 554         // qualification and borrow checking the trouble of special casing
 555         // constructors.
 556         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 557     }
 558
 559     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).steal();
 560     run_optimization_passes(tcx, &mut body, def.did, None);
 561
 562     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 563
 564     body
 565 }
 566
 567 fn promoted_mir<'tcx>(
 568     tcx: TyCtxt<'tcx>,
 569     def: ty::WithOptConstParam<LocalDefId>,
 570 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 571     if tcx.is_constructor(def.did.to_def_id()) {
 572         return tcx.arena.alloc(IndexVec::new());
 573     }
 574
 575     if let Some(param_did) = def.const_param_did {
 576         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 577     } else {
 578         tcx.ensure().mir_borrowck(def.did);
 579     }
 580     let (_, promoted) = tcx.mir_promoted(def);
 581     let mut promoted = promoted.steal();
 582
 583     for (p, mut body) in promoted.iter_enumerated_mut() {
 584         run_post_borrowck_cleanup_passes(tcx, &mut body, def.did, Some(p));
 585         run_optimization_passes(tcx, &mut body, def.did, Some(p));
 586     }
 587
 588     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 589
 590     tcx.arena.alloc(promoted)
 591 }