src/librustc_mir/shim.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::hir;
  12 use rustc::hir::def_id::DefId;
  13 use rustc::infer;
  14 use rustc::middle::const_val::ConstVal;
  15 use rustc::mir::*;
  16 use rustc::mir::transform::MirSource;
  17 use rustc::ty::{self, Ty};
  18 use rustc::ty::subst::{Kind, Subst, Substs};
  19 use rustc::ty::maps::Providers;
  20
  21 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  22
  23 use syntax::abi::Abi;
  24 use syntax::ast;
  25 use syntax_pos::Span;
  26
  27 use std::fmt;
  28 use std::iter;
  29
  30 use transform::{add_call_guards, no_landing_pads, simplify};
  31 use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
  32 use util::patch::MirPatch;
  33
  34 pub fn provide(providers: &mut Providers) {
  35     providers.mir_shims = make_shim;
  36 }
  37
  38 fn make_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
  39                        instance: ty::InstanceDef<'tcx>)
  40                        -> &'tcx Mir<'tcx>
  41 {
  42     debug!("make_shim({:?})", instance);
  43
  44     let mut result = match instance {
  45         ty::InstanceDef::Item(..) =>
  46             bug!("item {:?} passed to make_shim", instance),
  47         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  48             let trait_ = tcx.trait_of_item(def_id).unwrap();
  49             let adjustment = match tcx.lang_items.fn_trait_kind(trait_) {
  50                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  51                 Some(ty::ClosureKind::FnMut) |
  52                 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  53                 None => bug!("fn pointer {:?} is not an fn", ty)
  54             };
  55             // HACK: we need the "real" argument types for the MIR,
  56             // but because our substs are (Self, Args), where Args
  57             // is a tuple, we must include the *concrete* argument
  58             // types in the MIR. They will be substituted again with
  59             // the param-substs, but because they are concrete, this
  60             // will not do any harm.
  61             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  62             let arg_tys = sig.inputs();
  63
  64             build_call_shim(
  65                 tcx,
  66                 def_id,
  67                 adjustment,
  68                 CallKind::Indirect,
  69                 Some(arg_tys)
  70             )
  71         }
  72         ty::InstanceDef::Virtual(def_id, _) => {
  73             // We are translating a call back to our def-id, which
  74             // trans::mir knows to turn to an actual virtual call.
  75             build_call_shim(
  76                 tcx,
  77                 def_id,
  78                 Adjustment::Identity,
  79                 CallKind::Direct(def_id),
  80                 None
  81             )
  82         }
  83         ty::InstanceDef::ClosureOnceShim { call_once } => {
  84             let fn_mut = tcx.lang_items.fn_mut_trait().unwrap();
  85             let call_mut = tcx.global_tcx()
  86                 .associated_items(fn_mut)
  87                 .find(|it| it.kind == ty::AssociatedKind::Method)
  88                 .unwrap().def_id;
  89
  90             build_call_shim(
  91                 tcx,
  92                 call_once,
  93                 Adjustment::RefMut,
  94                 CallKind::Direct(call_mut),
  95                 None
  96             )
  97         }
  98         ty::InstanceDef::DropGlue(def_id, ty) => {
  99             build_drop_shim(tcx, def_id, ty)
 100         }
 101         ty::InstanceDef::Intrinsic(_) => {
 102             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 103         }
 104     };
 105         debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 106         no_landing_pads::no_landing_pads(tcx, &mut result);
 107         simplify::simplify_cfg(&mut result);
 108         add_call_guards::add_call_guards(&mut result);
 109     debug!("make_shim({:?}) = {:?}", instance, result);
 110
 111     tcx.alloc_mir(result)
 112 }
 113
 114 #[derive(Copy, Clone, Debug, PartialEq)]
 115 enum Adjustment {
 116     Identity,
 117     Deref,
 118     RefMut,
 119 }
 120
 121 #[derive(Copy, Clone, Debug, PartialEq)]
 122 enum CallKind {
 123     Indirect,
 124     Direct(DefId),
 125 }
 126
 127 fn temp_decl(mutability: Mutability, ty: Ty, span: Span) -> LocalDecl {
 128     LocalDecl {
 129         mutability, ty, name: None,
 130         source_info: SourceInfo { scope: ARGUMENT_VISIBILITY_SCOPE, span },
 131         is_user_variable: false
 132     }
 133 }
 134
 135 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 136     -> IndexVec<Local, LocalDecl<'tcx>>
 137 {
 138     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 139         .chain(sig.inputs().iter().map(
 140             |ity| temp_decl(Mutability::Not, ity, span)))
 141         .collect()
 142 }
 143
 144 fn build_drop_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 145                              def_id: DefId,
 146                              ty: Option<Ty<'tcx>>)
 147                              -> Mir<'tcx>
 148 {
 149     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 150
 151     let substs = if let Some(ty) = ty {
 152         tcx.mk_substs(iter::once(Kind::from(ty)))
 153     } else {
 154         Substs::identity_for_item(tcx, def_id)
 155     };
 156     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 157     let sig = tcx.erase_late_bound_regions(&sig);
 158     let span = tcx.def_span(def_id);
 159
 160     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 161
 162     let return_block = BasicBlock::new(1);
 163     let mut blocks = IndexVec::new();
 164     let block = |blocks: &mut IndexVec<_, _>, kind| {
 165         blocks.push(BasicBlockData {
 166             statements: vec![],
 167             terminator: Some(Terminator { source_info, kind }),
 168             is_cleanup: false
 169         })
 170     };
 171     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 172     block(&mut blocks, TerminatorKind::Return);
 173
 174     let mut mir = Mir::new(
 175         blocks,
 176         IndexVec::from_elem_n(
 177             VisibilityScopeData { span: span, parent_scope: None }, 1
 178         ),
 179         IndexVec::new(),
 180         sig.output(),
 181         local_decls_for_sig(&sig, span),
 182         sig.inputs().len(),
 183         vec![],
 184         span
 185     );
 186
 187     if let Some(..) = ty {
 188         let patch = {
 189             let param_env = tcx.param_env(def_id);
 190             let mut elaborator = DropShimElaborator {
 191                 mir: &mir,
 192                 patch: MirPatch::new(&mir),
 193                 tcx,
 194                 param_env
 195             };
 196             let dropee = Lvalue::Local(Local::new(1+0)).deref();
 197             let resume_block = elaborator.patch.resume_block();
 198             elaborate_drops::elaborate_drop(
 199                 &mut elaborator,
 200                 source_info,
 201                 &dropee,
 202                 (),
 203                 return_block,
 204                 elaborate_drops::Unwind::To(resume_block),
 205                 START_BLOCK
 206             );
 207             elaborator.patch
 208         };
 209         patch.apply(&mut mir);
 210     }
 211
 212     mir
 213 }
 214
 215 pub struct DropShimElaborator<'a, 'tcx: 'a> {
 216     mir: &'a Mir<'tcx>,
 217     patch: MirPatch<'tcx>,
 218     tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 219     param_env: ty::ParamEnv<'tcx>,
 220 }
 221
 222 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 223     fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 224         Ok(())
 225     }
 226 }
 227
 228 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 229     type Path = ();
 230
 231     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 232     fn mir(&self) -> &'a Mir<'tcx> { self.mir }
 233     fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
 234     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 235
 236     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 237         if let DropFlagMode::Shallow = mode {
 238             DropStyle::Static
 239         } else {
 240             DropStyle::Open
 241         }
 242     }
 243
 244     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 245         None
 246     }
 247
 248     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 249     }
 250
 251     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 252         None
 253     }
 254     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 255         None
 256     }
 257     fn downcast_subpath(&self, _path: Self::Path, _variant: usize) -> Option<Self::Path> {
 258         Some(())
 259     }
 260 }
 261
 262 /// Build a "call" shim for `def_id`. The shim calls the
 263 /// function specified by `call_kind`, first adjusting its first
 264 /// argument according to `rcvr_adjustment`.
 265 ///
 266 /// If `untuple_args` is a vec of types, the second argument of the
 267 /// function will be untupled as these types.
 268 fn build_call_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 269                              def_id: DefId,
 270                              rcvr_adjustment: Adjustment,
 271                              call_kind: CallKind,
 272                              untuple_args: Option<&[Ty<'tcx>]>)
 273                              -> Mir<'tcx>
 274 {
 275     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 276             call_kind={:?}, untuple_args={:?})",
 277            def_id, rcvr_adjustment, call_kind, untuple_args);
 278
 279     let sig = tcx.fn_sig(def_id);
 280     let sig = tcx.erase_late_bound_regions(&sig);
 281     let span = tcx.def_span(def_id);
 282
 283     debug!("build_call_shim: sig={:?}", sig);
 284
 285     let mut local_decls = local_decls_for_sig(&sig, span);
 286     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 287
 288     let rcvr_arg = Local::new(1+0);
 289     let rcvr_l = Lvalue::Local(rcvr_arg);
 290     let mut statements = vec![];
 291
 292     let rcvr = match rcvr_adjustment {
 293         Adjustment::Identity => Operand::Consume(rcvr_l),
 294         Adjustment::Deref => Operand::Consume(rcvr_l.deref()),
 295         Adjustment::RefMut => {
 296             // let rcvr = &mut rcvr;
 297             let ref_rcvr = local_decls.push(temp_decl(
 298                 Mutability::Not,
 299                 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 300                     ty: sig.inputs()[0],
 301                     mutbl: hir::Mutability::MutMutable
 302                 }),
 303                 span
 304             ));
 305             statements.push(Statement {
 306                 source_info: source_info,
 307                 kind: StatementKind::Assign(
 308                     Lvalue::Local(ref_rcvr),
 309                     Rvalue::Ref(tcx.types.re_erased, BorrowKind::Mut, rcvr_l)
 310                 )
 311             });
 312             Operand::Consume(Lvalue::Local(ref_rcvr))
 313         }
 314     };
 315
 316     let (callee, mut args) = match call_kind {
 317         CallKind::Indirect => (rcvr, vec![]),
 318         CallKind::Direct(def_id) => (
 319             Operand::Constant(box Constant {
 320                 span: span,
 321                 ty: tcx.type_of(def_id),
 322                 literal: Literal::Value {
 323                     value: ConstVal::Function(def_id,
 324                         Substs::identity_for_item(tcx, def_id)),
 325                 },
 326             }),
 327             vec![rcvr]
 328         )
 329     };
 330
 331     if let Some(untuple_args) = untuple_args {
 332         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 333             let arg_lv = Lvalue::Local(Local::new(1+1));
 334             Operand::Consume(arg_lv.field(Field::new(i), *ity))
 335         }));
 336     } else {
 337         args.extend((1..sig.inputs().len()).map(|i| {
 338             Operand::Consume(Lvalue::Local(Local::new(1+i)))
 339         }));
 340     }
 341
 342     let mut blocks = IndexVec::new();
 343     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 344         blocks.push(BasicBlockData {
 345             statements,
 346             terminator: Some(Terminator { source_info, kind }),
 347             is_cleanup
 348         })
 349     };
 350
 351     // BB #0
 352     block(&mut blocks, statements, TerminatorKind::Call {
 353         func: callee,
 354         args: args,
 355         destination: Some((Lvalue::Local(RETURN_POINTER),
 356                            BasicBlock::new(1))),
 357         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 358             Some(BasicBlock::new(3))
 359         } else {
 360             None
 361         }
 362     }, false);
 363
 364     if let Adjustment::RefMut = rcvr_adjustment {
 365         // BB #1 - drop for Self
 366         block(&mut blocks, vec![], TerminatorKind::Drop {
 367             location: Lvalue::Local(rcvr_arg),
 368             target: BasicBlock::new(2),
 369             unwind: None
 370         }, false);
 371     }
 372     // BB #1/#2 - return
 373     block(&mut blocks, vec![], TerminatorKind::Return, false);
 374     if let Adjustment::RefMut = rcvr_adjustment {
 375         // BB #3 - drop if closure panics
 376         block(&mut blocks, vec![], TerminatorKind::Drop {
 377             location: Lvalue::Local(rcvr_arg),
 378             target: BasicBlock::new(4),
 379             unwind: None
 380         }, true);
 381
 382         // BB #4 - resume
 383         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 384     }
 385
 386     let mut mir = Mir::new(
 387         blocks,
 388         IndexVec::from_elem_n(
 389             VisibilityScopeData { span: span, parent_scope: None }, 1
 390         ),
 391         IndexVec::new(),
 392         sig.output(),
 393         local_decls,
 394         sig.inputs().len(),
 395         vec![],
 396         span
 397     );
 398     if let Abi::RustCall = sig.abi {
 399         mir.spread_arg = Some(Local::new(sig.inputs().len()));
 400     }
 401     mir
 402 }
 403
 404 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 405                                       ctor_id: ast::NodeId,
 406                                       fields: &[hir::StructField],
 407                                       span: Span)
 408                                       -> (Mir<'tcx>, MirSource)
 409 {
 410     let tcx = infcx.tcx;
 411     let def_id = tcx.hir.local_def_id(ctor_id);
 412     let sig = tcx.no_late_bound_regions(&tcx.fn_sig(def_id))
 413         .expect("LBR in ADT constructor signature");
 414     let sig = tcx.erase_regions(&sig);
 415
 416     let (adt_def, substs) = match sig.output().sty {
 417         ty::TyAdt(adt_def, substs) => (adt_def, substs),
 418         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 419     };
 420
 421     debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
 422
 423     let local_decls = local_decls_for_sig(&sig, span);
 424
 425     let source_info = SourceInfo {
 426         span: span,
 427         scope: ARGUMENT_VISIBILITY_SCOPE
 428     };
 429
 430     let variant_no = if adt_def.is_enum() {
 431         adt_def.variant_index_with_id(def_id)
 432     } else {
 433         0
 434     };
 435
 436     // return = ADT(arg0, arg1, ...); return
 437     let start_block = BasicBlockData {
 438         statements: vec![Statement {
 439             source_info: source_info,
 440             kind: StatementKind::Assign(
 441                 Lvalue::Local(RETURN_POINTER),
 442                 Rvalue::Aggregate(
 443                     box AggregateKind::Adt(adt_def, variant_no, substs, None),
 444                     (1..sig.inputs().len()+1).map(|i| {
 445                         Operand::Consume(Lvalue::Local(Local::new(i)))
 446                     }).collect()
 447                 )
 448             )
 449         }],
 450         terminator: Some(Terminator {
 451             source_info: source_info,
 452             kind: TerminatorKind::Return,
 453         }),
 454         is_cleanup: false
 455     };
 456
 457     let mir = Mir::new(
 458         IndexVec::from_elem_n(start_block, 1),
 459         IndexVec::from_elem_n(
 460             VisibilityScopeData { span: span, parent_scope: None }, 1
 461         ),
 462         IndexVec::new(),
 463         sig.output(),
 464         local_decls,
 465         sig.inputs().len(),
 466         vec![],
 467         span
 468     );
 469     (mir, MirSource::Fn(ctor_id))
 470 }