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