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::region::ROOT_CODE_EXTENT;
  15 use rustc::middle::const_val::ConstVal;
  16 use rustc::mir::*;
  17 use rustc::mir::transform::MirSource;
  18 use rustc::ty::{self, Ty};
  19 use rustc::ty::subst::{Kind, Subst};
  20 use rustc::ty::maps::Providers;
  21
  22 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  23
  24 use syntax::abi::Abi;
  25 use syntax::ast;
  26 use syntax_pos::Span;
  27
  28 use std::cell::RefCell;
  29 use std::fmt;
  30 use std::iter;
  31 use std::mem;
  32
  33 use transform::{add_call_guards, no_landing_pads, simplify};
  34 use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
  35 use util::patch::MirPatch;
  36
  37 pub fn provide(providers: &mut Providers) {
  38     providers.mir_shims = make_shim;
  39 }
  40
  41 fn make_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
  42                        instance: ty::InstanceDef<'tcx>)
  43                        -> &'tcx RefCell<Mir<'tcx>>
  44 {
  45     debug!("make_shim({:?})", instance);
  46     let did = instance.def_id();
  47     let span = tcx.def_span(did);
  48     let param_env =
  49         tcx.construct_parameter_environment(span, did, ROOT_CODE_EXTENT);
  50
  51     let mut result = match instance {
  52         ty::InstanceDef::Item(..) =>
  53             bug!("item {:?} passed to make_shim", instance),
  54         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  55             let trait_ = tcx.trait_of_item(def_id).unwrap();
  56             let adjustment = match tcx.lang_items.fn_trait_kind(trait_) {
  57                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  58                 Some(ty::ClosureKind::FnMut) |
  59                 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  60                 None => bug!("fn pointer {:?} is not an fn", ty)
  61             };
  62             // HACK: we need the "real" argument types for the MIR,
  63             // but because our substs are (Self, Args), where Args
  64             // is a tuple, we must include the *concrete* argument
  65             // types in the MIR. They will be substituted again with
  66             // the param-substs, but because they are concrete, this
  67             // will not do any harm.
  68             let sig = tcx.erase_late_bound_regions(&ty.fn_sig());
  69             let arg_tys = sig.inputs();
  70
  71             build_call_shim(
  72                 tcx,
  73                 &param_env,
  74                 def_id,
  75                 adjustment,
  76                 CallKind::Indirect,
  77                 Some(arg_tys)
  78             )
  79         }
  80         ty::InstanceDef::Virtual(def_id, _) => {
  81             // We are translating a call back to our def-id, which
  82             // trans::mir knows to turn to an actual virtual call.
  83             build_call_shim(
  84                 tcx,
  85                 &param_env,
  86                 def_id,
  87                 Adjustment::Identity,
  88                 CallKind::Direct(def_id),
  89                 None
  90             )
  91         }
  92         ty::InstanceDef::ClosureOnceShim { call_once } => {
  93             let fn_mut = tcx.lang_items.fn_mut_trait().unwrap();
  94             let call_mut = tcx.global_tcx()
  95                 .associated_items(fn_mut)
  96                 .find(|it| it.kind == ty::AssociatedKind::Method)
  97                 .unwrap().def_id;
  98
  99             build_call_shim(
 100                 tcx,
 101                 &param_env,
 102                 call_once,
 103                 Adjustment::RefMut,
 104                 CallKind::Direct(call_mut),
 105                 None
 106             )
 107         }
 108         ty::InstanceDef::DropGlue(def_id, ty) => {
 109             build_drop_shim(tcx, &param_env, def_id, ty)
 110         }
 111         ty::InstanceDef::Intrinsic(_) => {
 112             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 113         }
 114     };
 115         debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 116         no_landing_pads::no_landing_pads(tcx, &mut result);
 117         simplify::simplify_cfg(&mut result);
 118         add_call_guards::add_call_guards(&mut result);
 119     debug!("make_shim({:?}) = {:?}", instance, result);
 120
 121     let result = tcx.alloc_mir(result);
 122     // Perma-borrow MIR from shims to prevent mutation.
 123     mem::forget(result.borrow());
 124     result
 125 }
 126
 127 #[derive(Copy, Clone, Debug, PartialEq)]
 128 enum Adjustment {
 129     Identity,
 130     Deref,
 131     RefMut,
 132 }
 133
 134 #[derive(Copy, Clone, Debug, PartialEq)]
 135 enum CallKind {
 136     Indirect,
 137     Direct(DefId),
 138 }
 139
 140 fn temp_decl(mutability: Mutability, ty: Ty, span: Span) -> LocalDecl {
 141     LocalDecl {
 142         mutability, ty, name: None,
 143         source_info: SourceInfo { scope: ARGUMENT_VISIBILITY_SCOPE, span },
 144         is_user_variable: false
 145     }
 146 }
 147
 148 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 149     -> IndexVec<Local, LocalDecl<'tcx>>
 150 {
 151     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 152         .chain(sig.inputs().iter().map(
 153             |ity| temp_decl(Mutability::Not, ity, span)))
 154         .collect()
 155 }
 156
 157 fn build_drop_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 158                              param_env: &ty::ParameterEnvironment<'tcx>,
 159                              def_id: DefId,
 160                              ty: Option<Ty<'tcx>>)
 161                              -> Mir<'tcx>
 162 {
 163     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 164
 165     let substs = if let Some(ty) = ty {
 166         tcx.mk_substs(iter::once(Kind::from(ty)))
 167     } else {
 168         param_env.free_substs
 169     };
 170     let fn_ty = tcx.item_type(def_id).subst(tcx, substs);
 171     let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
 172     let span = tcx.def_span(def_id);
 173
 174     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 175
 176     let return_block = BasicBlock::new(1);
 177     let mut blocks = IndexVec::new();
 178     let block = |blocks: &mut IndexVec<_, _>, kind| {
 179         blocks.push(BasicBlockData {
 180             statements: vec![],
 181             terminator: Some(Terminator { source_info, kind }),
 182             is_cleanup: false
 183         })
 184     };
 185     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 186     block(&mut blocks, TerminatorKind::Return);
 187
 188     let mut mir = Mir::new(
 189         blocks,
 190         IndexVec::from_elem_n(
 191             VisibilityScopeData { span: span, parent_scope: None }, 1
 192         ),
 193         IndexVec::new(),
 194         sig.output(),
 195         local_decls_for_sig(&sig, span),
 196         sig.inputs().len(),
 197         vec![],
 198         span
 199     );
 200
 201     if let Some(..) = ty {
 202         let patch = {
 203             let mut elaborator = DropShimElaborator {
 204                 mir: &mir,
 205                 patch: MirPatch::new(&mir),
 206                 tcx, param_env
 207             };
 208             let dropee = Lvalue::Local(Local::new(1+0)).deref();
 209             let resume_block = elaborator.patch.resume_block();
 210             elaborate_drops::elaborate_drop(
 211                 &mut elaborator,
 212                 source_info,
 213                 false,
 214                 &dropee,
 215                 (),
 216                 return_block,
 217                 Some(resume_block),
 218                 START_BLOCK
 219             );
 220             elaborator.patch
 221         };
 222         patch.apply(&mut mir);
 223     }
 224
 225     mir
 226 }
 227
 228 pub struct DropShimElaborator<'a, 'tcx: 'a> {
 229     mir: &'a Mir<'tcx>,
 230     patch: MirPatch<'tcx>,
 231     tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 232     param_env: &'a ty::ParameterEnvironment<'tcx>,
 233 }
 234
 235 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 236     fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 237         Ok(())
 238     }
 239 }
 240
 241 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 242     type Path = ();
 243
 244     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 245     fn mir(&self) -> &'a Mir<'tcx> { self.mir }
 246     fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
 247     fn param_env(&self) -> &'a ty::ParameterEnvironment<'tcx> { self.param_env }
 248
 249     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 250         if let DropFlagMode::Shallow = mode {
 251             DropStyle::Static
 252         } else {
 253             DropStyle::Open
 254         }
 255     }
 256
 257     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 258         None
 259     }
 260
 261     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 262     }
 263
 264     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 265         None
 266     }
 267     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 268         None
 269     }
 270     fn downcast_subpath(&self, _path: Self::Path, _variant: usize) -> Option<Self::Path> {
 271         Some(())
 272     }
 273 }
 274
 275 /// Build a "call" shim for `def_id`. The shim calls the
 276 /// function specified by `call_kind`, first adjusting its first
 277 /// argument according to `rcvr_adjustment`.
 278 ///
 279 /// If `untuple_args` is a vec of types, the second argument of the
 280 /// function will be untupled as these types.
 281 fn build_call_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 282                              param_env: &ty::ParameterEnvironment<'tcx>,
 283                              def_id: DefId,
 284                              rcvr_adjustment: Adjustment,
 285                              call_kind: CallKind,
 286                              untuple_args: Option<&[Ty<'tcx>]>)
 287                              -> Mir<'tcx>
 288 {
 289     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 290             call_kind={:?}, untuple_args={:?})",
 291            def_id, rcvr_adjustment, call_kind, untuple_args);
 292
 293     let fn_ty = tcx.item_type(def_id).subst(tcx, param_env.free_substs);
 294     let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
 295     let span = tcx.def_span(def_id);
 296
 297     debug!("build_call_shim: sig={:?}", sig);
 298
 299     let mut local_decls = local_decls_for_sig(&sig, span);
 300     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 301
 302     let rcvr_arg = Local::new(1+0);
 303     let rcvr_l = Lvalue::Local(rcvr_arg);
 304     let mut statements = vec![];
 305
 306     let rcvr = match rcvr_adjustment {
 307         Adjustment::Identity => Operand::Consume(rcvr_l),
 308         Adjustment::Deref => Operand::Consume(rcvr_l.deref()),
 309         Adjustment::RefMut => {
 310             // let rcvr = &mut rcvr;
 311             let ref_rcvr = local_decls.push(temp_decl(
 312                 Mutability::Not,
 313                 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 314                     ty: sig.inputs()[0],
 315                     mutbl: hir::Mutability::MutMutable
 316                 }),
 317                 span
 318             ));
 319             statements.push(Statement {
 320                 source_info: source_info,
 321                 kind: StatementKind::Assign(
 322                     Lvalue::Local(ref_rcvr),
 323                     Rvalue::Ref(tcx.types.re_erased, BorrowKind::Mut, rcvr_l)
 324                 )
 325             });
 326             Operand::Consume(Lvalue::Local(ref_rcvr))
 327         }
 328     };
 329
 330     let (callee, mut args) = match call_kind {
 331         CallKind::Indirect => (rcvr, vec![]),
 332         CallKind::Direct(def_id) => (
 333             Operand::Constant(box Constant {
 334                 span: span,
 335                 ty: tcx.item_type(def_id).subst(tcx, param_env.free_substs),
 336                 literal: Literal::Value {
 337                     value: ConstVal::Function(def_id, param_env.free_substs),
 338                 },
 339             }),
 340             vec![rcvr]
 341         )
 342     };
 343
 344     if let Some(untuple_args) = untuple_args {
 345         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 346             let arg_lv = Lvalue::Local(Local::new(1+1));
 347             Operand::Consume(arg_lv.field(Field::new(i), *ity))
 348         }));
 349     } else {
 350         args.extend((1..sig.inputs().len()).map(|i| {
 351             Operand::Consume(Lvalue::Local(Local::new(1+i)))
 352         }));
 353     }
 354
 355     let mut blocks = IndexVec::new();
 356     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 357         blocks.push(BasicBlockData {
 358             statements,
 359             terminator: Some(Terminator { source_info, kind }),
 360             is_cleanup
 361         })
 362     };
 363
 364     // BB #0
 365     block(&mut blocks, statements, TerminatorKind::Call {
 366         func: callee,
 367         args: args,
 368         destination: Some((Lvalue::Local(RETURN_POINTER),
 369                            BasicBlock::new(1))),
 370         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 371             Some(BasicBlock::new(3))
 372         } else {
 373             None
 374         }
 375     }, false);
 376
 377     if let Adjustment::RefMut = rcvr_adjustment {
 378         // BB #1 - drop for Self
 379         block(&mut blocks, vec![], TerminatorKind::Drop {
 380             location: Lvalue::Local(rcvr_arg),
 381             target: BasicBlock::new(2),
 382             unwind: None
 383         }, false);
 384     }
 385     // BB #1/#2 - return
 386     block(&mut blocks, vec![], TerminatorKind::Return, false);
 387     if let Adjustment::RefMut = rcvr_adjustment {
 388         // BB #3 - drop if closure panics
 389         block(&mut blocks, vec![], TerminatorKind::Drop {
 390             location: Lvalue::Local(rcvr_arg),
 391             target: BasicBlock::new(4),
 392             unwind: None
 393         }, true);
 394
 395         // BB #4 - resume
 396         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 397     }
 398
 399     let mut mir = Mir::new(
 400         blocks,
 401         IndexVec::from_elem_n(
 402             VisibilityScopeData { span: span, parent_scope: None }, 1
 403         ),
 404         IndexVec::new(),
 405         sig.output(),
 406         local_decls,
 407         sig.inputs().len(),
 408         vec![],
 409         span
 410     );
 411     if let Abi::RustCall = sig.abi {
 412         mir.spread_arg = Some(Local::new(sig.inputs().len()));
 413     }
 414     mir
 415 }
 416
 417 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 418                                       ctor_id: ast::NodeId,
 419                                       fields: &[hir::StructField],
 420                                       span: Span)
 421                                       -> (Mir<'tcx>, MirSource)
 422 {
 423     let tcx = infcx.tcx;
 424     let def_id = tcx.hir.local_def_id(ctor_id);
 425     let sig = match tcx.item_type(def_id).sty {
 426         ty::TyFnDef(_, _, fty) => tcx.no_late_bound_regions(&fty)
 427             .expect("LBR in ADT constructor signature"),
 428         _ => bug!("unexpected type for ctor {:?}", def_id)
 429     };
 430     let sig = tcx.erase_regions(&sig);
 431
 432     let (adt_def, substs) = match sig.output().sty {
 433         ty::TyAdt(adt_def, substs) => (adt_def, substs),
 434         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 435     };
 436
 437     debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
 438
 439     let local_decls = local_decls_for_sig(&sig, span);
 440
 441     let source_info = SourceInfo {
 442         span: span,
 443         scope: ARGUMENT_VISIBILITY_SCOPE
 444     };
 445
 446     let variant_no = if adt_def.is_enum() {
 447         adt_def.variant_index_with_id(def_id)
 448     } else {
 449         0
 450     };
 451
 452     // return = ADT(arg0, arg1, ...); return
 453     let start_block = BasicBlockData {
 454         statements: vec![Statement {
 455             source_info: source_info,
 456             kind: StatementKind::Assign(
 457                 Lvalue::Local(RETURN_POINTER),
 458                 Rvalue::Aggregate(
 459                     box AggregateKind::Adt(adt_def, variant_no, substs, None),
 460                     (1..sig.inputs().len()+1).map(|i| {
 461                         Operand::Consume(Lvalue::Local(Local::new(i)))
 462                     }).collect()
 463                 )
 464             )
 465         }],
 466         terminator: Some(Terminator {
 467             source_info: source_info,
 468             kind: TerminatorKind::Return,
 469         }),
 470         is_cleanup: false
 471     };
 472
 473     let mir = Mir::new(
 474         IndexVec::from_elem_n(start_block, 1),
 475         IndexVec::from_elem_n(
 476             VisibilityScopeData { span: span, parent_scope: None }, 1
 477         ),
 478         IndexVec::new(),
 479         sig.output(),
 480         local_decls,
 481         sig.inputs().len(),
 482         vec![],
 483         span
 484     );
 485     (mir, MirSource::Fn(ctor_id))
 486 }