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