src/librustc_mir/transform/mod.rs

   1 use crate::{shim, util};
   2 use rustc::hir::map::Map;
   3 use rustc::mir::{BodyAndCache, ConstQualifs, MirPhase, Promoted};
   4 use rustc::ty::query::Providers;
   5 use rustc::ty::steal::Steal;
   6 use rustc::ty::{InstanceDef, TyCtxt, TypeFoldable};
   7 use rustc_hir as hir;
   8 use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, LOCAL_CRATE};
   9 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  10 use rustc_index::vec::IndexVec;
  11 use rustc_span::Span;
  12 use std::borrow::Cow;
  13 use syntax::ast;
  14
  15 pub mod add_call_guards;
  16 pub mod add_moves_for_packed_drops;
  17 pub mod add_retag;
  18 pub mod check_consts;
  19 pub mod check_unsafety;
  20 pub mod cleanup_post_borrowck;
  21 pub mod const_prop;
  22 pub mod copy_prop;
  23 pub mod deaggregator;
  24 pub mod dump_mir;
  25 pub mod elaborate_drops;
  26 pub mod erase_regions;
  27 pub mod generator;
  28 pub mod inline;
  29 pub mod instcombine;
  30 pub mod no_landing_pads;
  31 pub mod promote_consts;
  32 pub mod qualify_min_const_fn;
  33 pub mod remove_noop_landing_pads;
  34 pub mod rustc_peek;
  35 pub mod simplify;
  36 pub mod simplify_branches;
  37 pub mod simplify_try;
  38 pub mod uninhabited_enum_branching;
  39 pub mod unreachable_prop;
  40
  41 pub(crate) fn provide(providers: &mut Providers<'_>) {
  42     self::check_unsafety::provide(providers);
  43     *providers = Providers {
  44         mir_keys,
  45         mir_const,
  46         mir_const_qualif,
  47         mir_validated,
  48         optimized_mir,
  49         is_mir_available,
  50         promoted_mir,
  51         ..*providers
  52     };
  53 }
  54
  55 fn is_mir_available(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
  56     tcx.mir_keys(def_id.krate).contains(&def_id)
  57 }
  58
  59 /// Finds the full set of `DefId`s within the current crate that have
  60 /// MIR associated with them.
  61 fn mir_keys(tcx: TyCtxt<'_>, krate: CrateNum) -> &DefIdSet {
  62     assert_eq!(krate, LOCAL_CRATE);
  63
  64     let mut set = DefIdSet::default();
  65
  66     // All body-owners have MIR associated with them.
  67     set.extend(tcx.body_owners());
  68
  69     // Additionally, tuple struct/variant constructors have MIR, but
  70     // they don't have a BodyId, so we need to build them separately.
  71     struct GatherCtors<'a, 'tcx> {
  72         tcx: TyCtxt<'tcx>,
  73         set: &'a mut DefIdSet,
  74     }
  75     impl<'a, 'tcx> Visitor<'tcx> for GatherCtors<'a, 'tcx> {
  76         fn visit_variant_data(
  77             &mut self,
  78             v: &'tcx hir::VariantData<'tcx>,
  79             _: ast::Name,
  80             _: &'tcx hir::Generics<'tcx>,
  81             _: hir::HirId,
  82             _: Span,
  83         ) {
  84             if let hir::VariantData::Tuple(_, hir_id) = *v {
  85                 self.set.insert(self.tcx.hir().local_def_id(hir_id));
  86             }
  87             intravisit::walk_struct_def(self, v)
  88         }
  89         type Map = Map<'tcx>;
  90         fn nested_visit_map<'b>(&'b mut self) -> NestedVisitorMap<'b, Self::Map> {
  91             NestedVisitorMap::None
  92         }
  93     }
  94     tcx.hir()
  95         .krate()
  96         .visit_all_item_likes(&mut GatherCtors { tcx, set: &mut set }.as_deep_visitor());
  97
  98     tcx.arena.alloc(set)
  99 }
 100
 101 /// Where a specific `mir::Body` comes from.
 102 #[derive(Debug, Copy, Clone)]
 103 pub struct MirSource<'tcx> {
 104     pub instance: InstanceDef<'tcx>,
 105
 106     /// If `Some`, this is a promoted rvalue within the parent function.
 107     pub promoted: Option<Promoted>,
 108 }
 109
 110 impl<'tcx> MirSource<'tcx> {
 111     pub fn item(def_id: DefId) -> Self {
 112         MirSource { instance: InstanceDef::Item(def_id), promoted: None }
 113     }
 114
 115     #[inline]
 116     pub fn def_id(&self) -> DefId {
 117         self.instance.def_id()
 118     }
 119 }
 120
 121 /// Generates a default name for the pass based on the name of the
 122 /// type `T`.
 123 pub fn default_name<T: ?Sized>() -> Cow<'static, str> {
 124     let name = ::std::any::type_name::<T>();
 125     if let Some(tail) = name.rfind(":") { Cow::from(&name[tail + 1..]) } else { Cow::from(name) }
 126 }
 127
 128 /// A streamlined trait that you can implement to create a pass; the
 129 /// pass will be named after the type, and it will consist of a main
 130 /// loop that goes over each available MIR and applies `run_pass`.
 131 pub trait MirPass<'tcx> {
 132     fn name(&self) -> Cow<'_, str> {
 133         default_name::<Self>()
 134     }
 135
 136     fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut BodyAndCache<'tcx>);
 137 }
 138
 139 pub fn run_passes(
 140     tcx: TyCtxt<'tcx>,
 141     body: &mut BodyAndCache<'tcx>,
 142     instance: InstanceDef<'tcx>,
 143     promoted: Option<Promoted>,
 144     mir_phase: MirPhase,
 145     passes: &[&dyn MirPass<'tcx>],
 146 ) {
 147     let phase_index = mir_phase.phase_index();
 148
 149     if body.phase >= mir_phase {
 150         return;
 151     }
 152
 153     let source = MirSource { instance, promoted };
 154     let mut index = 0;
 155     let mut run_pass = |pass: &dyn MirPass<'tcx>| {
 156         let run_hooks = |body: &_, index, is_after| {
 157             dump_mir::on_mir_pass(
 158                 tcx,
 159                 &format_args!("{:03}-{:03}", phase_index, index),
 160                 &pass.name(),
 161                 source,
 162                 body,
 163                 is_after,
 164             );
 165         };
 166         run_hooks(body, index, false);
 167         pass.run_pass(tcx, source, body);
 168         run_hooks(body, index, true);
 169
 170         index += 1;
 171     };
 172
 173     for pass in passes {
 174         run_pass(*pass);
 175     }
 176
 177     body.phase = mir_phase;
 178 }
 179
 180 fn mir_const_qualif(tcx: TyCtxt<'_>, def_id: DefId) -> ConstQualifs {
 181     let const_kind = check_consts::ConstKind::for_item(tcx, def_id);
 182
 183     // No need to const-check a non-const `fn`.
 184     if const_kind.is_none() {
 185         return Default::default();
 186     }
 187
 188     // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
 189     // cannot yet be stolen), because `mir_validated()`, which steals
 190     // from `mir_const(), forces this query to execute before
 191     // performing the steal.
 192     let body = &tcx.mir_const(def_id).borrow();
 193
 194     if body.return_ty().references_error() {
 195         tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
 196         return Default::default();
 197     }
 198
 199     let item = check_consts::Item {
 200         body: body.unwrap_read_only(),
 201         tcx,
 202         def_id,
 203         const_kind,
 204         param_env: tcx.param_env(def_id),
 205     };
 206
 207     let mut validator = check_consts::validation::Validator::new(&item);
 208     validator.check_body();
 209
 210     // We return the qualifs in the return place for every MIR body, even though it is only used
 211     // when deciding to promote a reference to a `const` for now.
 212     validator.qualifs_in_return_place().into()
 213 }
 214
 215 fn mir_const(tcx: TyCtxt<'_>, def_id: DefId) -> &Steal<BodyAndCache<'_>> {
 216     // Unsafety check uses the raw mir, so make sure it is run
 217     let _ = tcx.unsafety_check_result(def_id);
 218
 219     let mut body = tcx.mir_built(def_id).steal();
 220
 221     util::dump_mir(tcx, None, "mir_map", &0, MirSource::item(def_id), &body, |_, _| Ok(()));
 222
 223     run_passes(
 224         tcx,
 225         &mut body,
 226         InstanceDef::Item(def_id),
 227         None,
 228         MirPhase::Const,
 229         &[
 230             // What we need to do constant evaluation.
 231             &simplify::SimplifyCfg::new("initial"),
 232             &rustc_peek::SanityCheck,
 233         ],
 234     );
 235     body.ensure_predecessors();
 236     tcx.alloc_steal_mir(body)
 237 }
 238
 239 fn mir_validated(
 240     tcx: TyCtxt<'tcx>,
 241     def_id: DefId,
 242 ) -> (&'tcx Steal<BodyAndCache<'tcx>>, &'tcx Steal<IndexVec<Promoted, BodyAndCache<'tcx>>>) {
 243     // Ensure that we compute the `mir_const_qualif` for constants at
 244     // this point, before we steal the mir-const result.
 245     let _ = tcx.mir_const_qualif(def_id);
 246
 247     let mut body = tcx.mir_const(def_id).steal();
 248     let promote_pass = promote_consts::PromoteTemps::default();
 249     run_passes(
 250         tcx,
 251         &mut body,
 252         InstanceDef::Item(def_id),
 253         None,
 254         MirPhase::Validated,
 255         &[
 256             // What we need to run borrowck etc.
 257             &promote_pass,
 258             &simplify::SimplifyCfg::new("qualify-consts"),
 259         ],
 260     );
 261
 262     let promoted = promote_pass.promoted_fragments.into_inner();
 263     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 264 }
 265
 266 fn run_optimization_passes<'tcx>(
 267     tcx: TyCtxt<'tcx>,
 268     body: &mut BodyAndCache<'tcx>,
 269     def_id: DefId,
 270     promoted: Option<Promoted>,
 271 ) {
 272     run_passes(
 273         tcx,
 274         body,
 275         InstanceDef::Item(def_id),
 276         promoted,
 277         MirPhase::Optimized,
 278         &[
 279             // Remove all things only needed by analysis
 280             &no_landing_pads::NoLandingPads::new(tcx),
 281             &simplify_branches::SimplifyBranches::new("initial"),
 282             &remove_noop_landing_pads::RemoveNoopLandingPads,
 283             &cleanup_post_borrowck::CleanupNonCodegenStatements,
 284             &simplify::SimplifyCfg::new("early-opt"),
 285             // These next passes must be executed together
 286             &add_call_guards::CriticalCallEdges,
 287             &elaborate_drops::ElaborateDrops,
 288             &no_landing_pads::NoLandingPads::new(tcx),
 289             // AddMovesForPackedDrops needs to run after drop
 290             // elaboration.
 291             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 292             // AddRetag needs to run after ElaborateDrops, and it needs
 293             // an AllCallEdges pass right before it.  Otherwise it should
 294             // run fairly late, but before optimizations begin.
 295             &add_call_guards::AllCallEdges,
 296             &add_retag::AddRetag,
 297             &simplify::SimplifyCfg::new("elaborate-drops"),
 298             // No lifetime analysis based on borrowing can be done from here on out.
 299
 300             // From here on out, regions are gone.
 301             &erase_regions::EraseRegions,
 302             // Optimizations begin.
 303             &unreachable_prop::UnreachablePropagation,
 304             &uninhabited_enum_branching::UninhabitedEnumBranching,
 305             &simplify::SimplifyCfg::new("after-uninhabited-enum-branching"),
 306             &inline::Inline,
 307             // Lowering generator control-flow and variables
 308             // has to happen before we do anything else to them.
 309             &generator::StateTransform,
 310             &instcombine::InstCombine,
 311             &const_prop::ConstProp,
 312             &simplify_branches::SimplifyBranches::new("after-const-prop"),
 313             &deaggregator::Deaggregator,
 314             &copy_prop::CopyPropagation,
 315             &simplify_branches::SimplifyBranches::new("after-copy-prop"),
 316             &remove_noop_landing_pads::RemoveNoopLandingPads,
 317             &simplify::SimplifyCfg::new("after-remove-noop-landing-pads"),
 318             &simplify_try::SimplifyArmIdentity,
 319             &simplify_try::SimplifyBranchSame,
 320             &simplify::SimplifyCfg::new("final"),
 321             &simplify::SimplifyLocals,
 322             &add_call_guards::CriticalCallEdges,
 323             &dump_mir::Marker("PreCodegen"),
 324         ],
 325     );
 326 }
 327
 328 fn optimized_mir(tcx: TyCtxt<'_>, def_id: DefId) -> &BodyAndCache<'_> {
 329     if tcx.is_constructor(def_id) {
 330         // There's no reason to run all of the MIR passes on constructors when
 331         // we can just output the MIR we want directly. This also saves const
 332         // qualification and borrow checking the trouble of special casing
 333         // constructors.
 334         return shim::build_adt_ctor(tcx, def_id);
 335     }
 336
 337     // (Mir-)Borrowck uses `mir_validated`, so we have to force it to
 338     // execute before we can steal.
 339     tcx.ensure().mir_borrowck(def_id);
 340
 341     let (body, _) = tcx.mir_validated(def_id);
 342     let mut body = body.steal();
 343     run_optimization_passes(tcx, &mut body, def_id, None);
 344     body.ensure_predecessors();
 345     tcx.arena.alloc(body)
 346 }
 347
 348 fn promoted_mir(tcx: TyCtxt<'_>, def_id: DefId) -> &IndexVec<Promoted, BodyAndCache<'_>> {
 349     if tcx.is_constructor(def_id) {
 350         return tcx.intern_promoted(IndexVec::new());
 351     }
 352
 353     tcx.ensure().mir_borrowck(def_id);
 354     let (_, promoted) = tcx.mir_validated(def_id);
 355     let mut promoted = promoted.steal();
 356
 357     for (p, mut body) in promoted.iter_enumerated_mut() {
 358         run_optimization_passes(tcx, &mut body, def_id, Some(p));
 359         body.ensure_predecessors();
 360     }
 361
 362     tcx.intern_promoted(promoted)
 363 }