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, def_id| {
  52             let def_id = def_id.expect_local();
  53             if let Some(def) = ty::WithOptConstParam::try_fetch(def_id, tcx) {
  54                 tcx.mir_const_qualif_const_arg(def)
  55             } else {
  56                 mir_const_qualif(tcx, ty::WithOptConstParam::unknown(def_id))
  57             }
  58         },
  59         mir_const_qualif_const_arg: |tcx, (did, param_did)| {
  60             mir_const_qualif(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  61         },
  62         mir_validated,
  63         mir_drops_elaborated_and_const_checked,
  64         optimized_mir,
  65         optimized_mir_of_const_arg,
  66         is_mir_available,
  67         promoted_mir: |tcx, def_id| {
  68             let def_id = def_id.expect_local();
  69             if let Some(def) = ty::WithOptConstParam::try_fetch(def_id, tcx) {
  70                 tcx.promoted_mir_of_const_arg(def)
  71             } else {
  72                 promoted_mir(tcx, ty::WithOptConstParam::unknown(def_id))
  73             }
  74         },
  75         promoted_mir_of_const_arg: |tcx, (did, param_did)| {
  76             promoted_mir(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
  77         },
  78         ..*providers
  79     };
  80     instrument_coverage::provide(providers);
  81 }
  82
  83 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
  84     tcx.mir_keys(def_id.krate).contains(&def_id.expect_local())
  85 }
  86
  87 /// Finds the full set of `DefId`s within the current crate that have
  88 /// MIR associated with them.
  89 fn mir_keys(tcx: TyCtxt<'_>, krate: CrateNum) -> FxHashSet<LocalDefId> {
  90     assert_eq!(krate, LOCAL_CRATE);
  91
  92     let mut set = FxHashSet::default();
  93
  94     // All body-owners have MIR associated with them.
  95     set.extend(tcx.body_owners());
  96
  97     // Additionally, tuple struct/variant constructors have MIR, but
  98     // they don't have a BodyId, so we need to build them separately.
  99     struct GatherCtors<'a, 'tcx> {
 100         tcx: TyCtxt<'tcx>,
 101         set: &'a mut FxHashSet<LocalDefId>,
 102     }
 103     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
 104         fn visit_variant_data(
 105             &mut self,
 106             v: &'tcx hir::VariantData<'tcx>,
 107             _: Symbol,
 108             _: &'tcx hir::Generics<'tcx>,
 109             _: hir::HirId,
 110             _: Span,
 111         ) {
 112             if let hir::VariantData::Tuple(_, hir_id) = *v {
 113                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
 114             }
 115             intravisit::walk_struct_def(self, v)
 116         }
 117         type Map = intravisit::ErasedMap<'tcx>;
 118         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 119             NestedVisitorMap::None
 120         }
 121     }
 122     tcx.hir()
 123         .krate()
 124         .visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
 125
 126     set
 127 }
 128
 129 /// Where a specific `mir::Body` comes from.
 130 #[derive(Debug, Copy, Clone)]
 131 pub struct MirSource<'tcx> {
 132     pub instance: InstanceDef<'tcx>,
 133
 134     /// If `Some`, this is a promoted rvalue within the parent function.
 135     pub promoted: Option<Promoted>,
 136 }
 137
 138 impl<'tcx> MirSource<'tcx> {
 139     pub fn item(def_id: DefId) -> Self {
 140         MirSource {
 141             instance: InstanceDef::Item(ty::WithOptConstParam::unknown(def_id)),
 142             promoted: None,
 143         }
 144     }
 145
 146     pub fn with_opt_param(self) -> ty::WithOptConstParam<DefId> {
 147         self.instance.with_opt_param()
 148     }
 149
 150     #[inline]
 151     pub fn def_id(&self) -> DefId {
 152         self.instance.def_id()
 153     }
 154 }
 155
 156 /// Generates a default name for the pass based on the name of the
 157 /// type `T`.
 158 pub fn default_name<T: ?Sized>() -> Cow<'static, str> {
 159     let name = ::std::any::type_name::<T>();
 160     if let Some(tail) = name.rfind(':') { Cow::from(&name[tail + 1..]) } else { Cow::from(name) }
 161 }
 162
 163 /// A streamlined trait that you can implement to create a pass; the
 164 /// pass will be named after the type, and it will consist of a main
 165 /// loop that goes over each available MIR and applies `run_pass`.
 166 pub trait MirPass<'tcx> {
 167     fn name(&self) -> Cow<'_, str> {
 168         default_name::<Self>()
 169     }
 170
 171     fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>);
 172 }
 173
 174 pub fn run_passes(
 175     tcx: TyCtxt<'tcx>,
 176     body: &mut Body<'tcx>,
 177     instance: InstanceDef<'tcx>,
 178     promoted: Option<Promoted>,
 179     mir_phase: MirPhase,
 180     passes: &[&[&dyn MirPass<'tcx>]],
 181 ) {
 182     let phase_index = mir_phase.phase_index();
 183     let source = MirSource { instance, promoted };
 184     let validate = tcx.sess.opts.debugging_opts.validate_mir;
 185
 186     if body.phase >= mir_phase {
 187         return;
 188     }
 189
 190     if validate {
 191         validate::Validator { when: format!("input to phase {:?}", mir_phase) }
 192             .run_pass(tcx, source, body);
 193     }
 194
 195     let mut index = 0;
 196     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 197         let run_hooks = |body: &_, index, is_after| {
 198             dump_mir::on_mir_pass(
 199                 tcx,
 200                 &format_args!("{:03}-{:03}", phase_index, index),
 201                 &pass.name(),
 202                 source,
 203                 body,
 204                 is_after,
 205             );
 206         };
 207         run_hooks(body, index, false);
 208         pass.run_pass(tcx, source, body);
 209         run_hooks(body, index, true);
 210
 211         if validate {
 212             validate::Validator { when: format!("after {} in phase {:?}", pass.name(), mir_phase) }
 213                 .run_pass(tcx, source, body);
 214         }
 215
 216         index += 1;
 217     };
 218
 219     for pass_group in passes {
 220         for pass in *pass_group {
 221             run_pass(*pass);
 222         }
 223     }
 224
 225     body.phase = mir_phase;
 226
 227     if mir_phase == MirPhase::Optimized {
 228         validate::Validator { when: format!("end of phase {:?}", mir_phase) }
 229             .run_pass(tcx, source, body);
 230     }
 231 }
 232
 233 fn mir_const_qualif(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> ConstQualifs {
 234     let const_kind = tcx.hir().body_const_context(def.did);
 235
 236     // No need to const-check a non-const `fn`.
 237     if const_kind.is_none() {
 238         return Default::default();
 239     }
 240
 241     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 242     // cannot yet be stolen), because `mir_validated()`, which steals
 243     // from `mir_const(), forces this query to execute before
 244     // performing the steal.
 245     let body = &tcx.mir_const(def).borrow();
 246
 247     if body.return_ty().references_error() {
 248         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 249         return Default::default();
 250     }
 251
 252     let ccx = check_consts::ConstCx {
 253         body,
 254         tcx,
 255         def_id: def.did,
 256         const_kind,
 257         param_env: tcx.param_env(def.did),
 258     };
 259
 260     let mut validator = check_consts::validation::Validator::new(&ccx);
 261     validator.check_body();
 262
 263     // We return the qualifs in the return place for every MIR body, even though it is only used
 264     // when deciding to promote a reference to a `const` for now.
 265     validator.qualifs_in_return_place()
 266 }
 267
 268 /// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
 269 fn mir_const<'tcx>(
 270     tcx: TyCtxt<'tcx>,
 271     def: ty::WithOptConstParam<LocalDefId>,
 272 ) -> &'tcx Steal<Body<'tcx>> {
 273     if let Some(def) = def.try_upgrade(tcx) {
 274         return tcx.mir_const(def);
 275     }
 276
 277     // Unsafety check uses the raw mir, so make sure it is run.
 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     let mut body = tcx.mir_built(def).steal();
 285
 286     util::dump_mir(
 287         tcx,
 288         None,
 289         "mir_map",
 290         &0,
 291         MirSource { instance: InstanceDef::Item(def.to_global()), promoted: None },
 292         &body,
 293         |_, _| Ok(()),
 294     );
 295
 296     run_passes(
 297         tcx,
 298         &mut body,
 299         InstanceDef::Item(def.to_global()),
 300         None,
 301         MirPhase::Const,
 302         &[&[
 303             // MIR-level lints.
 304             &check_packed_ref::CheckPackedRef,
 305             // What we need to do constant evaluation.
 306             &simplify::SimplifyCfg::new("initial"),
 307             &rustc_peek::SanityCheck,
 308         ]],
 309     );
 310     tcx.alloc_steal_mir(body)
 311 }
 312
 313 fn mir_validated(
 314     tcx: TyCtxt<'tcx>,
 315     def: ty::WithOptConstParam<LocalDefId>,
 316 ) -> (&'tcx Steal<Body<'tcx>>, &'tcx Steal<IndexVec<Promoted, Body<'tcx>>>) {
 317     if let Some(def) = def.try_upgrade(tcx) {
 318         return tcx.mir_validated(def);
 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 let Some(def) = def.try_upgrade(tcx) {
 361         return tcx.mir_drops_elaborated_and_const_checked(def);
 362     }
 363
 364     // (Mir-)Borrowck uses `mir_validated`, so we have to force it to
 365     // execute before we can steal.
 366     if let Some(param_did) = def.const_param_did {
 367         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 368     } else {
 369         tcx.ensure().mir_borrowck(def.did);
 370     }
 371
 372     let (body, _) = tcx.mir_validated(def);
 373     let mut body = body.steal();
 374
 375     run_post_borrowck_cleanup_passes(tcx, &mut body, def.did, None);
 376     check_consts::post_drop_elaboration::check_live_drops(tcx, def.did, &body);
 377     tcx.alloc_steal_mir(body)
 378 }
 379
 380 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 381 fn run_post_borrowck_cleanup_passes<'tcx>(
 382     tcx: TyCtxt<'tcx>,
 383     body: &mut Body<'tcx>,
 384     def_id: LocalDefId,
 385     promoted: Option<Promoted>,
 386 ) {
 387     debug!("post_borrowck_cleanup({:?})", def_id);
 388
 389     let post_borrowck_cleanup: &[&dyn MirPass<'tcx>] = &[
 390         // Remove all things only needed by analysis
 391         &no_landing_pads::NoLandingPads::new(tcx),
 392         &simplify_branches::SimplifyBranches::new("initial"),
 393         &remove_noop_landing_pads::RemoveNoopLandingPads,
 394         &cleanup_post_borrowck::CleanupNonCodegenStatements,
 395         &simplify::SimplifyCfg::new("early-opt"),
 396         // These next passes must be executed together
 397         &add_call_guards::CriticalCallEdges,
 398         &elaborate_drops::ElaborateDrops,
 399         &no_landing_pads::NoLandingPads::new(tcx),
 400         // AddMovesForPackedDrops needs to run after drop
 401         // elaboration.
 402         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 403         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
 404         // but before optimizations begin.
 405         &add_retag::AddRetag,
 406         &simplify::SimplifyCfg::new("elaborate-drops"),
 407     ];
 408
 409     run_passes(
 410         tcx,
 411         body,
 412         InstanceDef::Item(ty::WithOptConstParam::unknown(def_id.to_def_id())),
 413         promoted,
 414         MirPhase::DropElab,
 415         &[post_borrowck_cleanup],
 416     );
 417 }
 418
 419 fn run_optimization_passes<'tcx>(
 420     tcx: TyCtxt<'tcx>,
 421     body: &mut Body<'tcx>,
 422     def_id: LocalDefId,
 423     promoted: Option<Promoted>,
 424 ) {
 425     let optimizations: &[&dyn MirPass<'tcx>] = &[
 426         &unreachable_prop::UnreachablePropagation,
 427         &uninhabited_enum_branching::UninhabitedEnumBranching,
 428         &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 429         &inline::Inline,
 430         // Lowering generator control-flow and variables has to happen before we do anything else
 431         // to them. We do this inside the "optimizations" block so that it can benefit from
 432         // optimizations that run before, that might be harder to do on the state machine than MIR
 433         // with async primitives.
 434         &generator::StateTransform,
 435         &instcombine::InstCombine,
 436         &const_prop::ConstProp,
 437         &simplify_branches::SimplifyBranches::new("after-const-prop"),
 438         // Run deaggregation here because:
 439         //   1. Some codegen backends require it
 440         //   2. It creates additional possibilities for some MIR optimizations to trigger
 441         // FIXME(#70073): Why is this done here and not in `post_borrowck_cleanup`?
 442         &deaggregator::Deaggregator,
 443         &simplify_try::SimplifyArmIdentity,
 444         &simplify_try::SimplifyBranchSame,
 445         &copy_prop::CopyPropagation,
 446         &simplify_branches::SimplifyBranches::new("after-copy-prop"),
 447         &remove_noop_landing_pads::RemoveNoopLandingPads,
 448         &simplify::SimplifyCfg::new("after-remove-noop-landing-pads"),
 449         &simplify::SimplifyCfg::new("final"),
 450         &nrvo::RenameReturnPlace,
 451         &simplify::SimplifyLocals,
 452     ];
 453
 454     let no_optimizations: &[&dyn MirPass<'tcx>] = &[
 455         // Even if we don't do optimizations, we still have to lower generators for codegen.
 456         &generator::StateTransform,
 457         // FIXME(#70073): This pass is responsible for both optimization as well as some lints.
 458         &const_prop::ConstProp,
 459         // Even if we don't do optimizations, still run deaggregation because some backends assume
 460         // that deaggregation always occurs.
 461         &deaggregator::Deaggregator,
 462     ];
 463
 464     let pre_codegen_cleanup: &[&dyn MirPass<'tcx>] = &[
 465         &add_call_guards::CriticalCallEdges,
 466         // Dump the end result for testing and debugging purposes.
 467         &dump_mir::Marker("PreCodegen"),
 468     ];
 469
 470     let mir_opt_level = tcx.sess.opts.debugging_opts.mir_opt_level;
 471
 472     #[rustfmt::skip]
 473     run_passes(
 474         tcx,
 475         body,
 476         InstanceDef::Item(ty::WithOptConstParam::unknown(def_id.to_def_id())),
 477         promoted,
 478         MirPhase::Optimized,
 479         &[
 480             if mir_opt_level > 0 { optimizations } else { no_optimizations },
 481             pre_codegen_cleanup,
 482         ],
 483     );
 484 }
 485
 486 fn optimized_mir<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx Body<'tcx> {
 487     let did = did.expect_local();
 488     if let Some(def) = ty::WithOptConstParam::try_fetch(did, tcx) {
 489         tcx.optimized_mir_of_const_arg(def)
 490     } else {
 491         tcx.arena.alloc(inner_optimized_mir(tcx, ty::WithOptConstParam::unknown(did)))
 492     }
 493 }
 494
 495 fn optimized_mir_of_const_arg<'tcx>(
 496     tcx: TyCtxt<'tcx>,
 497     (did, param_did): (LocalDefId, DefId),
 498 ) -> &'tcx Body<'tcx> {
 499     tcx.arena.alloc(inner_optimized_mir(
 500         tcx,
 501         ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 502     ))
 503 }
 504
 505 fn inner_optimized_mir(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
 506     if tcx.is_constructor(def.did.to_def_id()) {
 507         // There's no reason to run all of the MIR passes on constructors when
 508         // we can just output the MIR we want directly. This also saves const
 509         // qualification and borrow checking the trouble of special casing
 510         // constructors.
 511         return shim::build_adt_ctor(tcx, def.did.to_def_id());
 512     }
 513
 514     let mut body = tcx.mir_drops_elaborated_and_const_checked(def).steal();
 515     run_optimization_passes(tcx, &mut body, def.did, None);
 516
 517     debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
 518
 519     body
 520 }
 521
 522 fn promoted_mir<'tcx>(
 523     tcx: TyCtxt<'tcx>,
 524     def: ty::WithOptConstParam<LocalDefId>,
 525 ) -> &'tcx IndexVec<Promoted, Body<'tcx>> {
 526     if tcx.is_constructor(def.did.to_def_id()) {
 527         return tcx.arena.alloc(IndexVec::new());
 528     }
 529
 530     if let Some(param_did) = def.const_param_did {
 531         tcx.ensure().mir_borrowck_const_arg((def.did, param_did));
 532     } else {
 533         tcx.ensure().mir_borrowck(def.did);
 534     }
 535     let (_, promoted) = tcx.mir_validated(def);
 536     let mut promoted = promoted.steal();
 537
 538     for (p, mut body) in promoted.iter_enumerated_mut() {
 539         run_post_borrowck_cleanup_passes(tcx, &mut body, def.did, Some(p));
 540         run_optimization_passes(tcx, &mut body, def.did, Some(p));
 541     }
 542
 543     debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
 544
 545     tcx.arena.alloc(promoted)
 546 }