src/librustc_mir/shim.rs

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