src/librustc_mir/shim.rs

   1 use rustc::hir;
   2 use rustc::hir::def_id::DefId;
   3 use rustc::mir::*;
   4 use rustc::ty::{self, Ty, TyCtxt};
   5 use rustc::ty::layout::VariantIdx;
   6 use rustc::ty::subst::{Subst, InternalSubsts};
   7 use rustc::ty::query::Providers;
   8
   9 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  10
  11 use rustc_target::spec::abi::Abi;
  12 use syntax_pos::{Span, sym};
  13
  14 use std::fmt;
  15 use std::iter;
  16
  17 use crate::transform::{
  18     add_moves_for_packed_drops, add_call_guards,
  19     remove_noop_landing_pads, no_landing_pads, simplify, run_passes
  20 };
  21 use crate::util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
  22 use crate::util::patch::MirPatch;
  23 use crate::util::expand_aggregate;
  24
  25 pub fn provide(providers: &mut Providers<'_>) {
  26     providers.mir_shims = make_shim;
  27 }
  28
  29 fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> &'tcx Body<'tcx> {
  30     debug!("make_shim({:?})", instance);
  31
  32     let mut result = match instance {
  33         ty::InstanceDef::Item(..) =>
  34             bug!("item {:?} passed to make_shim", instance),
  35         ty::InstanceDef::VtableShim(def_id) => {
  36             build_call_shim(
  37                 tcx,
  38                 def_id,
  39                 Adjustment::DerefMove,
  40                 CallKind::Direct(def_id),
  41                 None,
  42             )
  43         }
  44         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  45             let trait_ = tcx.trait_of_item(def_id).unwrap();
  46             let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
  47                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  48                 Some(ty::ClosureKind::FnMut) |
  49                 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  50                 None => bug!("fn pointer {:?} is not an fn", ty)
  51             };
  52             // HACK: we need the "real" argument types for the MIR,
  53             // but because our substs are (Self, Args), where Args
  54             // is a tuple, we must include the *concrete* argument
  55             // types in the MIR. They will be substituted again with
  56             // the param-substs, but because they are concrete, this
  57             // will not do any harm.
  58             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  59             let arg_tys = sig.inputs();
  60
  61             build_call_shim(
  62                 tcx,
  63                 def_id,
  64                 adjustment,
  65                 CallKind::Indirect,
  66                 Some(arg_tys)
  67             )
  68         }
  69         ty::InstanceDef::Virtual(def_id, _) => {
  70             // We are generating a call back to our def-id, which the
  71             // codegen backend knows to turn to an actual virtual call.
  72             build_call_shim(
  73                 tcx,
  74                 def_id,
  75                 Adjustment::Identity,
  76                 CallKind::Direct(def_id),
  77                 None
  78             )
  79         }
  80         ty::InstanceDef::ClosureOnceShim { call_once } => {
  81             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  82             let call_mut = tcx.global_tcx()
  83                 .associated_items(fn_mut)
  84                 .find(|it| it.kind == ty::AssocKind::Method)
  85                 .unwrap().def_id;
  86
  87             build_call_shim(
  88                 tcx,
  89                 call_once,
  90                 Adjustment::RefMut,
  91                 CallKind::Direct(call_mut),
  92                 None
  93             )
  94         }
  95         ty::InstanceDef::DropGlue(def_id, ty) => {
  96             build_drop_shim(tcx, def_id, ty)
  97         }
  98         ty::InstanceDef::CloneShim(def_id, ty) => {
  99             let name = tcx.item_name(def_id);
 100             if name == sym::clone {
 101                 build_clone_shim(tcx, def_id, ty)
 102             } else if name == sym::clone_from {
 103                 debug!("make_shim({:?}: using default trait implementation", instance);
 104                 return tcx.optimized_mir(def_id);
 105             } else {
 106                 bug!("builtin clone shim {:?} not supported", instance)
 107             }
 108         }
 109         ty::InstanceDef::Intrinsic(_) => {
 110             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 111         }
 112     };
 113     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 114
 115     run_passes(tcx, &mut result, instance, None, MirPhase::Const, &[
 116         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 117         &no_landing_pads::NoLandingPads,
 118         &remove_noop_landing_pads::RemoveNoopLandingPads,
 119         &simplify::SimplifyCfg::new("make_shim"),
 120         &add_call_guards::CriticalCallEdges,
 121     ]);
 122
 123     debug!("make_shim({:?}) = {:?}", instance, result);
 124
 125     tcx.arena.alloc(result)
 126 }
 127
 128 #[derive(Copy, Clone, Debug, PartialEq)]
 129 enum Adjustment {
 130     Identity,
 131     Deref,
 132     DerefMove,
 133     RefMut,
 134 }
 135
 136 #[derive(Copy, Clone, Debug, PartialEq)]
 137 enum CallKind {
 138     Indirect,
 139     Direct(DefId),
 140 }
 141
 142 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 143     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 144     LocalDecl {
 145         mutability,
 146         ty,
 147         user_ty: UserTypeProjections::none(),
 148         name: None,
 149         source_info,
 150         visibility_scope: source_info.scope,
 151         internal: false,
 152         is_user_variable: None,
 153         is_block_tail: None,
 154     }
 155 }
 156
 157 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 158     -> IndexVec<Local, LocalDecl<'tcx>>
 159 {
 160     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 161         .chain(sig.inputs().iter().map(
 162             |ity| temp_decl(Mutability::Not, ity, span)))
 163         .collect()
 164 }
 165
 166 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 167     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 168
 169     // Check if this is a generator, if so, return the drop glue for it
 170     if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 171         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 172         return body.subst(tcx, substs.substs);
 173     }
 174
 175     let substs = if let Some(ty) = ty {
 176         tcx.intern_substs(&[ty.into()])
 177     } else {
 178         InternalSubsts::identity_for_item(tcx, def_id)
 179     };
 180     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 181     let sig = tcx.erase_late_bound_regions(&sig);
 182     let span = tcx.def_span(def_id);
 183
 184     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 185
 186     let return_block = BasicBlock::new(1);
 187     let mut blocks = IndexVec::with_capacity(2);
 188     let block = |blocks: &mut IndexVec<_, _>, kind| {
 189         blocks.push(BasicBlockData {
 190             statements: vec![],
 191             terminator: Some(Terminator { source_info, kind }),
 192             is_cleanup: false
 193         })
 194     };
 195     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 196     block(&mut blocks, TerminatorKind::Return);
 197
 198     let mut body = Body::new(
 199         blocks,
 200         IndexVec::from_elem_n(
 201             SourceScopeData { span: span, parent_scope: None }, 1
 202         ),
 203         ClearCrossCrate::Clear,
 204         None,
 205         local_decls_for_sig(&sig, span),
 206         IndexVec::new(),
 207         sig.inputs().len(),
 208         vec![],
 209         span,
 210         vec![],
 211     );
 212
 213     if let Some(..) = ty {
 214         // The first argument (index 0), but add 1 for the return value.
 215         let dropee_ptr = Place::from(Local::new(1+0));
 216         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 217             // Function arguments should be retagged, and we make this one raw.
 218             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 219                 source_info,
 220                 kind: StatementKind::Retag(RetagKind::Raw, dropee_ptr.clone()),
 221             });
 222         }
 223         let patch = {
 224             let param_env = tcx.param_env(def_id).with_reveal_all();
 225             let mut elaborator = DropShimElaborator {
 226                 body: &body,
 227                 patch: MirPatch::new(&body),
 228                 tcx,
 229                 param_env
 230             };
 231             let dropee = dropee_ptr.deref();
 232             let resume_block = elaborator.patch.resume_block();
 233             elaborate_drops::elaborate_drop(
 234                 &mut elaborator,
 235                 source_info,
 236                 &dropee,
 237                 (),
 238                 return_block,
 239                 elaborate_drops::Unwind::To(resume_block),
 240                 START_BLOCK
 241             );
 242             elaborator.patch
 243         };
 244         patch.apply(&mut body);
 245     }
 246
 247     body
 248 }
 249
 250 pub struct DropShimElaborator<'a, 'tcx> {
 251     pub body: &'a Body<'tcx>,
 252     pub patch: MirPatch<'tcx>,
 253     pub tcx: TyCtxt<'tcx>,
 254     pub param_env: ty::ParamEnv<'tcx>,
 255 }
 256
 257 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 258     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 259         Ok(())
 260     }
 261 }
 262
 263 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 264     type Path = ();
 265
 266     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 267     fn body(&self) -> &'a Body<'tcx> { self.body }
 268     fn tcx(&self) -> TyCtxt<'tcx> {
 269         self.tcx
 270         }
 271     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 272
 273     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 274         if let DropFlagMode::Shallow = mode {
 275             DropStyle::Static
 276         } else {
 277             DropStyle::Open
 278         }
 279     }
 280
 281     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 282         None
 283     }
 284
 285     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 286     }
 287
 288     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 289         None
 290     }
 291     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 292         None
 293     }
 294     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 295         Some(())
 296     }
 297     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 298         None
 299     }
 300 }
 301
 302 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 303 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 304     debug!("build_clone_shim(def_id={:?})", def_id);
 305
 306     let param_env = tcx.param_env(def_id);
 307
 308     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 309     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 310
 311     let dest = Place::RETURN_PLACE;
 312     let src = Place::from(Local::new(1+0)).deref();
 313
 314     match self_ty.sty {
 315         _ if is_copy => builder.copy_shim(),
 316         ty::Array(ty, len) => {
 317             let len = len.eval_usize(tcx, param_env);
 318             builder.array_shim(dest, src, ty, len)
 319         }
 320         ty::Closure(def_id, substs) => {
 321             builder.tuple_like_shim(
 322                 dest, src,
 323                 substs.upvar_tys(def_id, tcx)
 324             )
 325         }
 326         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 327         _ => {
 328             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 329         }
 330     };
 331
 332     builder.into_mir()
 333 }
 334
 335 struct CloneShimBuilder<'tcx> {
 336     tcx: TyCtxt<'tcx>,
 337     def_id: DefId,
 338     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 339     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 340     span: Span,
 341     sig: ty::FnSig<'tcx>,
 342 }
 343
 344 impl CloneShimBuilder<'tcx> {
 345     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 346         // we must subst the self_ty because it's
 347         // otherwise going to be TySelf and we can't index
 348         // or access fields of a Place of type TySelf.
 349         let substs = tcx.mk_substs_trait(self_ty, &[]);
 350         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 351         let sig = tcx.erase_late_bound_regions(&sig);
 352         let span = tcx.def_span(def_id);
 353
 354         CloneShimBuilder {
 355             tcx,
 356             def_id,
 357             local_decls: local_decls_for_sig(&sig, span),
 358             blocks: IndexVec::new(),
 359             span,
 360             sig,
 361         }
 362     }
 363
 364     fn into_mir(self) -> Body<'tcx> {
 365         Body::new(
 366             self.blocks,
 367             IndexVec::from_elem_n(
 368                 SourceScopeData { span: self.span, parent_scope: None }, 1
 369             ),
 370             ClearCrossCrate::Clear,
 371             None,
 372             self.local_decls,
 373             IndexVec::new(),
 374             self.sig.inputs().len(),
 375             vec![],
 376             self.span,
 377             vec![],
 378         )
 379     }
 380
 381     fn source_info(&self) -> SourceInfo {
 382         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 383     }
 384
 385     fn block(
 386         &mut self,
 387         statements: Vec<Statement<'tcx>>,
 388         kind: TerminatorKind<'tcx>,
 389         is_cleanup: bool
 390     ) -> BasicBlock {
 391         let source_info = self.source_info();
 392         self.blocks.push(BasicBlockData {
 393             statements,
 394             terminator: Some(Terminator { source_info, kind }),
 395             is_cleanup,
 396         })
 397     }
 398
 399     /// Gives the index of an upcoming BasicBlock, with an offset.
 400     /// offset=0 will give you the index of the next BasicBlock,
 401     /// offset=1 will give the index of the next-to-next block,
 402     /// offset=-1 will give you the index of the last-created block
 403     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 404         BasicBlock::new(self.blocks.len() + offset)
 405     }
 406
 407     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 408         Statement {
 409             source_info: self.source_info(),
 410             kind,
 411         }
 412     }
 413
 414     fn copy_shim(&mut self) {
 415         let rcvr = Place::from(Local::new(1+0)).deref();
 416         let ret_statement = self.make_statement(
 417             StatementKind::Assign(
 418                 Place::RETURN_PLACE,
 419                 box Rvalue::Use(Operand::Copy(rcvr))
 420             )
 421         );
 422         self.block(vec![ret_statement], TerminatorKind::Return, false);
 423     }
 424
 425     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 426         let span = self.span;
 427         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 428     }
 429
 430     fn make_clone_call(
 431         &mut self,
 432         dest: Place<'tcx>,
 433         src: Place<'tcx>,
 434         ty: Ty<'tcx>,
 435         next: BasicBlock,
 436         cleanup: BasicBlock
 437     ) {
 438         let tcx = self.tcx;
 439
 440         let substs = tcx.mk_substs_trait(ty, &[]);
 441
 442         // `func == Clone::clone(&ty) -> ty`
 443         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 444         let func = Operand::Constant(box Constant {
 445             span: self.span,
 446             user_ty: None,
 447             literal: ty::Const::zero_sized(tcx, func_ty),
 448         });
 449
 450         let ref_loc = self.make_place(
 451             Mutability::Not,
 452             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 453                 ty,
 454                 mutbl: hir::Mutability::MutImmutable,
 455             })
 456         );
 457
 458         // `let ref_loc: &ty = &src;`
 459         let statement = self.make_statement(
 460             StatementKind::Assign(
 461                 ref_loc.clone(),
 462                 box Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 463             )
 464         );
 465
 466         // `let loc = Clone::clone(ref_loc);`
 467         self.block(vec![statement], TerminatorKind::Call {
 468             func,
 469             args: vec![Operand::Move(ref_loc)],
 470             destination: Some((dest, next)),
 471             cleanup: Some(cleanup),
 472             from_hir_call: true,
 473         }, false);
 474     }
 475
 476     fn loop_header(
 477         &mut self,
 478         beg: Place<'tcx>,
 479         end: Place<'tcx>,
 480         loop_body: BasicBlock,
 481         loop_end: BasicBlock,
 482         is_cleanup: bool
 483     ) {
 484         let tcx = self.tcx;
 485
 486         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 487         let compute_cond = self.make_statement(
 488             StatementKind::Assign(
 489                 cond.clone(),
 490                 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 491             )
 492         );
 493
 494         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 495         self.block(
 496             vec![compute_cond],
 497             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 498             is_cleanup
 499         );
 500     }
 501
 502     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 503         box Constant {
 504             span: self.span,
 505             user_ty: None,
 506             literal: ty::Const::from_usize(self.tcx, value),
 507         }
 508     }
 509
 510     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 511         let tcx = self.tcx;
 512         let span = self.span;
 513
 514         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 515         let end = self.make_place(Mutability::Not, tcx.types.usize);
 516
 517         // BB #0
 518         // `let mut beg = 0;`
 519         // `let end = len;`
 520         // `goto #1;`
 521         let inits = vec![
 522             self.make_statement(
 523                 StatementKind::Assign(
 524                     Place::from(beg),
 525                     box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 526                 )
 527             ),
 528             self.make_statement(
 529                 StatementKind::Assign(
 530                     end.clone(),
 531                     box Rvalue::Use(Operand::Constant(self.make_usize(len)))
 532                 )
 533             )
 534         ];
 535         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 536
 537         // BB #1: loop {
 538         //     BB #2;
 539         //     BB #3;
 540         // }
 541         // BB #4;
 542         self.loop_header(Place::from(beg),
 543                          end,
 544                          BasicBlock::new(2),
 545                          BasicBlock::new(4),
 546                          false);
 547
 548         // BB #2
 549         // `dest[i] = Clone::clone(src[beg])`;
 550         // Goto #3 if ok, #5 if unwinding happens.
 551         let dest_field = dest.clone().index(beg);
 552         let src_field = src.index(beg);
 553         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 554                              BasicBlock::new(5));
 555
 556         // BB #3
 557         // `beg = beg + 1;`
 558         // `goto #1`;
 559         let statements = vec![
 560             self.make_statement(
 561                 StatementKind::Assign(
 562                     Place::from(beg),
 563                     box Rvalue::BinaryOp(
 564                         BinOp::Add,
 565                         Operand::Copy(Place::from(beg)),
 566                         Operand::Constant(self.make_usize(1))
 567                     )
 568                 )
 569             )
 570         ];
 571         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 572
 573         // BB #4
 574         // `return dest;`
 575         self.block(vec![], TerminatorKind::Return, false);
 576
 577         // BB #5 (cleanup)
 578         // `let end = beg;`
 579         // `let mut beg = 0;`
 580         // goto #6;
 581         let end = beg;
 582         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 583         let init = self.make_statement(
 584             StatementKind::Assign(
 585                 Place::from(beg),
 586                 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 587             )
 588         );
 589         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 590
 591         // BB #6 (cleanup): loop {
 592         //     BB #7;
 593         //     BB #8;
 594         // }
 595         // BB #9;
 596         self.loop_header(Place::from(beg), Place::from(end),
 597                          BasicBlock::new(7), BasicBlock::new(9), true);
 598
 599         // BB #7 (cleanup)
 600         // `drop(dest[beg])`;
 601         self.block(vec![], TerminatorKind::Drop {
 602             location: dest.index(beg),
 603             target: BasicBlock::new(8),
 604             unwind: None,
 605         }, true);
 606
 607         // BB #8 (cleanup)
 608         // `beg = beg + 1;`
 609         // `goto #6;`
 610         let statement = self.make_statement(
 611             StatementKind::Assign(
 612                 Place::from(beg),
 613                 box Rvalue::BinaryOp(
 614                     BinOp::Add,
 615                     Operand::Copy(Place::from(beg)),
 616                     Operand::Constant(self.make_usize(1))
 617                 )
 618             )
 619         );
 620         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 621
 622         // BB #9 (resume)
 623         self.block(vec![], TerminatorKind::Resume, true);
 624     }
 625
 626     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 627                           src: Place<'tcx>, tys: I)
 628             where I: Iterator<Item = Ty<'tcx>> {
 629         let mut previous_field = None;
 630         for (i, ity) in tys.enumerate() {
 631             let field = Field::new(i);
 632             let src_field = src.clone().field(field, ity);
 633
 634             let dest_field = dest.clone().field(field, ity);
 635
 636             // #(2i + 1) is the cleanup block for the previous clone operation
 637             let cleanup_block = self.block_index_offset(1);
 638             // #(2i + 2) is the next cloning block
 639             // (or the Return terminator if this is the last block)
 640             let next_block = self.block_index_offset(2);
 641
 642             // BB #(2i)
 643             // `dest.i = Clone::clone(&src.i);`
 644             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 645             self.make_clone_call(
 646                 dest_field.clone(),
 647                 src_field,
 648                 ity,
 649                 next_block,
 650                 cleanup_block,
 651             );
 652
 653             // BB #(2i + 1) (cleanup)
 654             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 655                 // Drop previous field and goto previous cleanup block.
 656                 self.block(vec![], TerminatorKind::Drop {
 657                     location: previous_field,
 658                     target: previous_cleanup,
 659                     unwind: None,
 660                 }, true);
 661             } else {
 662                 // Nothing to drop, just resume.
 663                 self.block(vec![], TerminatorKind::Resume, true);
 664             }
 665
 666             previous_field = Some((dest_field, cleanup_block));
 667         }
 668
 669         self.block(vec![], TerminatorKind::Return, false);
 670     }
 671 }
 672
 673 /// Builds a "call" shim for `def_id`. The shim calls the
 674 /// function specified by `call_kind`, first adjusting its first
 675 /// argument according to `rcvr_adjustment`.
 676 ///
 677 /// If `untuple_args` is a vec of types, the second argument of the
 678 /// function will be untupled as these types.
 679 fn build_call_shim<'tcx>(
 680     tcx: TyCtxt<'tcx>,
 681     def_id: DefId,
 682     rcvr_adjustment: Adjustment,
 683     call_kind: CallKind,
 684     untuple_args: Option<&[Ty<'tcx>]>,
 685 ) -> Body<'tcx> {
 686     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 687             call_kind={:?}, untuple_args={:?})",
 688            def_id, rcvr_adjustment, call_kind, untuple_args);
 689
 690     let sig = tcx.fn_sig(def_id);
 691     let sig = tcx.erase_late_bound_regions(&sig);
 692     let span = tcx.def_span(def_id);
 693
 694     debug!("build_call_shim: sig={:?}", sig);
 695
 696     let mut local_decls = local_decls_for_sig(&sig, span);
 697     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 698
 699     let rcvr_arg = Local::new(1+0);
 700     let rcvr_l = Place::from(rcvr_arg);
 701     let mut statements = vec![];
 702
 703     let rcvr = match rcvr_adjustment {
 704         Adjustment::Identity => Operand::Move(rcvr_l),
 705         Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
 706         Adjustment::DerefMove => {
 707             // fn(Self, ...) -> fn(*mut Self, ...)
 708             let arg_ty = local_decls[rcvr_arg].ty;
 709             debug_assert!(tcx.generics_of(def_id).has_self && arg_ty == tcx.types.self_param);
 710             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 711
 712             Operand::Move(rcvr_l.deref())
 713         }
 714         Adjustment::RefMut => {
 715             // let rcvr = &mut rcvr;
 716             let ref_rcvr = local_decls.push(temp_decl(
 717                 Mutability::Not,
 718                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 719                     ty: sig.inputs()[0],
 720                     mutbl: hir::Mutability::MutMutable
 721                 }),
 722                 span
 723             ));
 724             let borrow_kind = BorrowKind::Mut {
 725                 allow_two_phase_borrow: false,
 726             };
 727             statements.push(Statement {
 728                 source_info,
 729                 kind: StatementKind::Assign(
 730                     Place::from(ref_rcvr),
 731                     box Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 732                 )
 733             });
 734             Operand::Move(Place::from(ref_rcvr))
 735         }
 736     };
 737
 738     let (callee, mut args) = match call_kind {
 739         CallKind::Indirect => (rcvr, vec![]),
 740         CallKind::Direct(def_id) => {
 741             let ty = tcx.type_of(def_id);
 742             (Operand::Constant(box Constant {
 743                 span,
 744                 user_ty: None,
 745                 literal: ty::Const::zero_sized(tcx, ty),
 746              }),
 747              vec![rcvr])
 748         }
 749     };
 750
 751     if let Some(untuple_args) = untuple_args {
 752         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 753             let arg_place = Place::from(Local::new(1+1));
 754             Operand::Move(arg_place.field(Field::new(i), *ity))
 755         }));
 756     } else {
 757         args.extend((1..sig.inputs().len()).map(|i| {
 758             Operand::Move(Place::from(Local::new(1+i)))
 759         }));
 760     }
 761
 762     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 763     let mut blocks = IndexVec::with_capacity(n_blocks);
 764     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 765         blocks.push(BasicBlockData {
 766             statements,
 767             terminator: Some(Terminator { source_info, kind }),
 768             is_cleanup
 769         })
 770     };
 771
 772     // BB #0
 773     block(&mut blocks, statements, TerminatorKind::Call {
 774         func: callee,
 775         args,
 776         destination: Some((Place::RETURN_PLACE,
 777                            BasicBlock::new(1))),
 778         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 779             Some(BasicBlock::new(3))
 780         } else {
 781             None
 782         },
 783         from_hir_call: true,
 784     }, false);
 785
 786     if let Adjustment::RefMut = rcvr_adjustment {
 787         // BB #1 - drop for Self
 788         block(&mut blocks, vec![], TerminatorKind::Drop {
 789             location: Place::from(rcvr_arg),
 790             target: BasicBlock::new(2),
 791             unwind: None
 792         }, false);
 793     }
 794     // BB #1/#2 - return
 795     block(&mut blocks, vec![], TerminatorKind::Return, false);
 796     if let Adjustment::RefMut = rcvr_adjustment {
 797         // BB #3 - drop if closure panics
 798         block(&mut blocks, vec![], TerminatorKind::Drop {
 799             location: Place::from(rcvr_arg),
 800             target: BasicBlock::new(4),
 801             unwind: None
 802         }, true);
 803
 804         // BB #4 - resume
 805         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 806     }
 807
 808     let mut body = Body::new(
 809         blocks,
 810         IndexVec::from_elem_n(
 811             SourceScopeData { span: span, parent_scope: None }, 1
 812         ),
 813         ClearCrossCrate::Clear,
 814         None,
 815         local_decls,
 816         IndexVec::new(),
 817         sig.inputs().len(),
 818         vec![],
 819         span,
 820         vec![],
 821     );
 822     if let Abi::RustCall = sig.abi {
 823         body.spread_arg = Some(Local::new(sig.inputs().len()));
 824     }
 825     body
 826 }
 827
 828 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &Body<'_> {
 829     debug_assert!(tcx.is_constructor(ctor_id));
 830
 831     let span = tcx.hir().span_if_local(ctor_id)
 832         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 833
 834     let param_env = tcx.param_env(ctor_id);
 835
 836     // Normalize the sig.
 837     let sig = tcx.fn_sig(ctor_id)
 838         .no_bound_vars()
 839         .expect("LBR in ADT constructor signature");
 840     let sig = tcx.normalize_erasing_regions(param_env, sig);
 841
 842     let (adt_def, substs) = match sig.output().sty {
 843         ty::Adt(adt_def, substs) => (adt_def, substs),
 844         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 845     };
 846
 847     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 848
 849     let local_decls = local_decls_for_sig(&sig, span);
 850
 851     let source_info = SourceInfo {
 852         span,
 853         scope: OUTERMOST_SOURCE_SCOPE
 854     };
 855
 856     let variant_index = if adt_def.is_enum() {
 857         adt_def.variant_index_with_ctor_id(ctor_id)
 858     } else {
 859         VariantIdx::new(0)
 860     };
 861
 862     // Generate the following MIR:
 863     //
 864     // (return as Variant).field0 = arg0;
 865     // (return as Variant).field1 = arg1;
 866     //
 867     // return;
 868     debug!("build_ctor: variant_index={:?}", variant_index);
 869
 870     let statements = expand_aggregate(
 871         Place::RETURN_PLACE,
 872         adt_def
 873             .variants[variant_index]
 874             .fields
 875             .iter()
 876             .enumerate()
 877             .map(|(idx, field_def)| (
 878                 Operand::Move(Place::from(Local::new(idx + 1))),
 879                 field_def.ty(tcx, substs),
 880             )),
 881         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 882         source_info,
 883     ).collect();
 884
 885     let start_block = BasicBlockData {
 886         statements,
 887         terminator: Some(Terminator {
 888             source_info,
 889             kind: TerminatorKind::Return,
 890         }),
 891         is_cleanup: false
 892     };
 893
 894     let body = Body::new(
 895         IndexVec::from_elem_n(start_block, 1),
 896         IndexVec::from_elem_n(
 897             SourceScopeData { span: span, parent_scope: None }, 1
 898         ),
 899         ClearCrossCrate::Clear,
 900         None,
 901         local_decls,
 902         IndexVec::new(),
 903         sig.inputs().len(),
 904         vec![],
 905         span,
 906         vec![],
 907     );
 908
 909     crate::util::dump_mir(
 910         tcx,
 911         None,
 912         "mir_map",
 913         &0,
 914         crate::transform::MirSource::item(ctor_id),
 915         &body,
 916         |_, _| Ok(()),
 917     );
 918
 919     tcx.arena.alloc(body)
 920 }