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) -> LocalDecl {
 141     LocalDecl { mutability, ty, name: None, source_info: None }
 142 }
 143
 144 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>)
 145     -> IndexVec<Local, LocalDecl<'tcx>>
 146 {
 147     iter::once(temp_decl(Mutability::Mut, sig.output()))
 148         .chain(sig.inputs().iter().map(
 149             |ity| temp_decl(Mutability::Not, ity)))
 150         .collect()
 151 }
 152
 153 fn build_drop_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 154                              param_env: &ty::ParameterEnvironment<'tcx>,
 155                              def_id: DefId,
 156                              ty: Option<Ty<'tcx>>)
 157                              -> Mir<'tcx>
 158 {
 159     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 160
 161     let substs = if let Some(ty) = ty {
 162         tcx.mk_substs(iter::once(Kind::from(ty)))
 163     } else {
 164         param_env.free_substs
 165     };
 166     let fn_ty = tcx.item_type(def_id).subst(tcx, substs);
 167     let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
 168     let span = tcx.def_span(def_id);
 169
 170     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 171
 172     let return_block = BasicBlock::new(1);
 173     let mut blocks = IndexVec::new();
 174     let block = |blocks: &mut IndexVec<_, _>, kind| {
 175         blocks.push(BasicBlockData {
 176             statements: vec![],
 177             terminator: Some(Terminator { source_info, kind }),
 178             is_cleanup: false
 179         })
 180     };
 181     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 182     block(&mut blocks, TerminatorKind::Return);
 183
 184     let mut mir = Mir::new(
 185         blocks,
 186         IndexVec::from_elem_n(
 187             VisibilityScopeData { span: span, parent_scope: None }, 1
 188         ),
 189         IndexVec::new(),
 190         sig.output(),
 191         local_decls_for_sig(&sig),
 192         sig.inputs().len(),
 193         vec![],
 194         span
 195     );
 196
 197     if let Some(..) = ty {
 198         let patch = {
 199             let mut elaborator = DropShimElaborator {
 200                 mir: &mir,
 201                 patch: MirPatch::new(&mir),
 202                 tcx, param_env
 203             };
 204             let dropee = Lvalue::Projection(
 205                 box Projection {
 206                     base: Lvalue::Local(Local::new(1+0)),
 207                     elem: ProjectionElem::Deref
 208                 }
 209                 );
 210             let resume_block = elaborator.patch.resume_block();
 211             elaborate_drops::elaborate_drop(
 212                 &mut elaborator,
 213                 source_info,
 214                 false,
 215                 &dropee,
 216                 (),
 217                 return_block,
 218                 Some(resume_block),
 219                 START_BLOCK
 220             );
 221             elaborator.patch
 222         };
 223         patch.apply(&mut mir);
 224     }
 225
 226     mir
 227 }
 228
 229 pub struct DropShimElaborator<'a, 'tcx: 'a> {
 230     mir: &'a Mir<'tcx>,
 231     patch: MirPatch<'tcx>,
 232     tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 233     param_env: &'a ty::ParameterEnvironment<'tcx>,
 234 }
 235
 236 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 237     fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 238         Ok(())
 239     }
 240 }
 241
 242 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 243     type Path = ();
 244
 245     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 246     fn mir(&self) -> &'a Mir<'tcx> { self.mir }
 247     fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
 248     fn param_env(&self) -> &'a ty::ParameterEnvironment<'tcx> { self.param_env }
 249
 250     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 251         if let DropFlagMode::Shallow = mode {
 252             DropStyle::Static
 253         } else {
 254             DropStyle::Open
 255         }
 256     }
 257
 258     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 259         None
 260     }
 261
 262     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 263     }
 264
 265     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 266         None
 267     }
 268     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 269         None
 270     }
 271     fn downcast_subpath(&self, _path: Self::Path, _variant: usize) -> Option<Self::Path> {
 272         Some(())
 273     }
 274 }
 275
 276 /// Build a "call" shim for `def_id`. The shim calls the
 277 /// function specified by `call_kind`, first adjusting its first
 278 /// argument according to `rcvr_adjustment`.
 279 ///
 280 /// If `untuple_args` is a vec of types, the second argument of the
 281 /// function will be untupled as these types.
 282 fn build_call_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
 283                              param_env: &ty::ParameterEnvironment<'tcx>,
 284                              def_id: DefId,
 285                              rcvr_adjustment: Adjustment,
 286                              call_kind: CallKind,
 287                              untuple_args: Option<&[Ty<'tcx>]>)
 288                              -> Mir<'tcx>
 289 {
 290     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 291             call_kind={:?}, untuple_args={:?})",
 292            def_id, rcvr_adjustment, call_kind, untuple_args);
 293
 294     let fn_ty = tcx.item_type(def_id).subst(tcx, param_env.free_substs);
 295     let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
 296     let span = tcx.def_span(def_id);
 297
 298     debug!("build_call_shim: sig={:?}", sig);
 299
 300     let mut local_decls = local_decls_for_sig(&sig);
 301     let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
 302
 303     let rcvr_arg = Local::new(1+0);
 304     let rcvr_l = Lvalue::Local(rcvr_arg);
 305     let mut statements = vec![];
 306
 307     let rcvr = match rcvr_adjustment {
 308         Adjustment::Identity => Operand::Consume(rcvr_l),
 309         Adjustment::Deref => Operand::Consume(Lvalue::Projection(
 310             box Projection { base: rcvr_l, elem: ProjectionElem::Deref }
 311         )),
 312         Adjustment::RefMut => {
 313             // let rcvr = &mut rcvr;
 314             let re_erased = tcx.mk_region(ty::ReErased);
 315             let ref_rcvr = local_decls.push(temp_decl(
 316                 Mutability::Not,
 317                 tcx.mk_ref(re_erased, ty::TypeAndMut {
 318                     ty: sig.inputs()[0],
 319                     mutbl: hir::Mutability::MutMutable
 320                 })
 321             ));
 322             statements.push(Statement {
 323                 source_info: source_info,
 324                 kind: StatementKind::Assign(
 325                     Lvalue::Local(ref_rcvr),
 326                     Rvalue::Ref(re_erased, BorrowKind::Mut, rcvr_l)
 327                 )
 328             });
 329             Operand::Consume(Lvalue::Local(ref_rcvr))
 330         }
 331     };
 332
 333     let (callee, mut args) = match call_kind {
 334         CallKind::Indirect => (rcvr, vec![]),
 335         CallKind::Direct(def_id) => (
 336             Operand::Constant(Constant {
 337                 span: span,
 338                 ty: tcx.item_type(def_id).subst(tcx, param_env.free_substs),
 339                 literal: Literal::Value {
 340                     value: ConstVal::Function(def_id, param_env.free_substs),
 341                 },
 342             }),
 343             vec![rcvr]
 344         )
 345     };
 346
 347     if let Some(untuple_args) = untuple_args {
 348         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 349             let arg_lv = Lvalue::Local(Local::new(1+1));
 350             Operand::Consume(Lvalue::Projection(box Projection {
 351                 base: arg_lv,
 352                 elem: ProjectionElem::Field(Field::new(i), *ity)
 353             }))
 354         }));
 355     } else {
 356         args.extend((1..sig.inputs().len()).map(|i| {
 357             Operand::Consume(Lvalue::Local(Local::new(1+i)))
 358         }));
 359     }
 360
 361     let mut blocks = IndexVec::new();
 362     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 363         blocks.push(BasicBlockData {
 364             statements,
 365             terminator: Some(Terminator { source_info, kind }),
 366             is_cleanup
 367         })
 368     };
 369
 370     // BB #0
 371     block(&mut blocks, statements, TerminatorKind::Call {
 372         func: callee,
 373         args: args,
 374         destination: Some((Lvalue::Local(RETURN_POINTER),
 375                            BasicBlock::new(1))),
 376         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 377             Some(BasicBlock::new(3))
 378         } else {
 379             None
 380         }
 381     }, false);
 382
 383     if let Adjustment::RefMut = rcvr_adjustment {
 384         // BB #1 - drop for Self
 385         block(&mut blocks, vec![], TerminatorKind::Drop {
 386             location: Lvalue::Local(rcvr_arg),
 387             target: BasicBlock::new(2),
 388             unwind: None
 389         }, false);
 390     }
 391     // BB #1/#2 - return
 392     block(&mut blocks, vec![], TerminatorKind::Return, false);
 393     if let Adjustment::RefMut = rcvr_adjustment {
 394         // BB #3 - drop if closure panics
 395         block(&mut blocks, vec![], TerminatorKind::Drop {
 396             location: Lvalue::Local(rcvr_arg),
 397             target: BasicBlock::new(4),
 398             unwind: None
 399         }, true);
 400
 401         // BB #4 - resume
 402         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 403     }
 404
 405     let mut mir = Mir::new(
 406         blocks,
 407         IndexVec::from_elem_n(
 408             VisibilityScopeData { span: span, parent_scope: None }, 1
 409         ),
 410         IndexVec::new(),
 411         sig.output(),
 412         local_decls,
 413         sig.inputs().len(),
 414         vec![],
 415         span
 416     );
 417     if let Abi::RustCall = sig.abi {
 418         mir.spread_arg = Some(Local::new(sig.inputs().len()));
 419     }
 420     mir
 421 }
 422
 423 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 424                                       ctor_id: ast::NodeId,
 425                                       fields: &[hir::StructField],
 426                                       span: Span)
 427                                       -> (Mir<'tcx>, MirSource)
 428 {
 429     let tcx = infcx.tcx;
 430     let def_id = tcx.hir.local_def_id(ctor_id);
 431     let sig = match tcx.item_type(def_id).sty {
 432         ty::TyFnDef(_, _, fty) => tcx.no_late_bound_regions(&fty)
 433             .expect("LBR in ADT constructor signature"),
 434         _ => bug!("unexpected type for ctor {:?}", def_id)
 435     };
 436     let sig = tcx.erase_regions(&sig);
 437
 438     let (adt_def, substs) = match sig.output().sty {
 439         ty::TyAdt(adt_def, substs) => (adt_def, substs),
 440         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 441     };
 442
 443     debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
 444
 445     let local_decls = local_decls_for_sig(&sig);
 446
 447     let source_info = SourceInfo {
 448         span: span,
 449         scope: ARGUMENT_VISIBILITY_SCOPE
 450     };
 451
 452     let variant_no = if adt_def.is_enum() {
 453         adt_def.variant_index_with_id(def_id)
 454     } else {
 455         0
 456     };
 457
 458     // return = ADT(arg0, arg1, ...); return
 459     let start_block = BasicBlockData {
 460         statements: vec![Statement {
 461             source_info: source_info,
 462             kind: StatementKind::Assign(
 463                 Lvalue::Local(RETURN_POINTER),
 464                 Rvalue::Aggregate(
 465                     AggregateKind::Adt(adt_def, variant_no, substs, None),
 466                     (1..sig.inputs().len()+1).map(|i| {
 467                         Operand::Consume(Lvalue::Local(Local::new(i)))
 468                     }).collect()
 469                 )
 470             )
 471         }],
 472         terminator: Some(Terminator {
 473             source_info: source_info,
 474             kind: TerminatorKind::Return,
 475         }),
 476         is_cleanup: false
 477     };
 478
 479     let mir = Mir::new(
 480         IndexVec::from_elem_n(start_block, 1),
 481         IndexVec::from_elem_n(
 482             VisibilityScopeData { span: span, parent_scope: None }, 1
 483         ),
 484         IndexVec::new(),
 485         sig.output(),
 486         local_decls,
 487         sig.inputs().len(),
 488         vec![],
 489         span
 490     );
 491     (mir, MirSource::Fn(ctor_id))
 492 }