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