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