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, '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, 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>(
 167     tcx: TyCtxt<'tcx, 'tcx>,
 168     def_id: DefId,
 169     ty: Option<Ty<'tcx>>,
 170 ) -> Body<'tcx> {
 171     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 172
 173     // Check if this is a generator, if so, return the drop glue for it
 174     if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 175         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 176         return body.subst(tcx, substs.substs);
 177     }
 178
 179     let substs = if let Some(ty) = ty {
 180         tcx.intern_substs(&[ty.into()])
 181     } else {
 182         InternalSubsts::identity_for_item(tcx, def_id)
 183     };
 184     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 185     let sig = tcx.erase_late_bound_regions(&sig);
 186     let span = tcx.def_span(def_id);
 187
 188     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 189
 190     let return_block = BasicBlock::new(1);
 191     let mut blocks = IndexVec::with_capacity(2);
 192     let block = |blocks: &mut IndexVec<_, _>, kind| {
 193         blocks.push(BasicBlockData {
 194             statements: vec![],
 195             terminator: Some(Terminator { source_info, kind }),
 196             is_cleanup: false
 197         })
 198     };
 199     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 200     block(&mut blocks, TerminatorKind::Return);
 201
 202     let mut body = Body::new(
 203         blocks,
 204         IndexVec::from_elem_n(
 205             SourceScopeData { span: span, parent_scope: None }, 1
 206         ),
 207         ClearCrossCrate::Clear,
 208         IndexVec::new(),
 209         None,
 210         local_decls_for_sig(&sig, span),
 211         IndexVec::new(),
 212         sig.inputs().len(),
 213         vec![],
 214         span,
 215         vec![],
 216     );
 217
 218     if let Some(..) = ty {
 219         // The first argument (index 0), but add 1 for the return value.
 220         let dropee_ptr = Place::Base(PlaceBase::Local(Local::new(1+0)));
 221         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 222             // Function arguments should be retagged, and we make this one raw.
 223             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 224                 source_info,
 225                 kind: StatementKind::Retag(RetagKind::Raw, dropee_ptr.clone()),
 226             });
 227         }
 228         let patch = {
 229             let param_env = tcx.param_env(def_id).with_reveal_all();
 230             let mut elaborator = DropShimElaborator {
 231                 body: &body,
 232                 patch: MirPatch::new(&body),
 233                 tcx,
 234                 param_env
 235             };
 236             let dropee = dropee_ptr.deref();
 237             let resume_block = elaborator.patch.resume_block();
 238             elaborate_drops::elaborate_drop(
 239                 &mut elaborator,
 240                 source_info,
 241                 &dropee,
 242                 (),
 243                 return_block,
 244                 elaborate_drops::Unwind::To(resume_block),
 245                 START_BLOCK
 246             );
 247             elaborator.patch
 248         };
 249         patch.apply(&mut body);
 250     }
 251
 252     body
 253 }
 254
 255 pub struct DropShimElaborator<'a, 'tcx: 'a> {
 256     pub body: &'a Body<'tcx>,
 257     pub patch: MirPatch<'tcx>,
 258     pub tcx: TyCtxt<'tcx, 'tcx>,
 259     pub param_env: ty::ParamEnv<'tcx>,
 260 }
 261
 262 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 263     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 264         Ok(())
 265     }
 266 }
 267
 268 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 269     type Path = ();
 270
 271     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 272     fn body(&self) -> &'a Body<'tcx> { self.body }
 273     fn tcx(&self) -> TyCtxt<'tcx, 'tcx> {
 274         self.tcx
 275         }
 276     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 277
 278     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 279         if let DropFlagMode::Shallow = mode {
 280             DropStyle::Static
 281         } else {
 282             DropStyle::Open
 283         }
 284     }
 285
 286     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 287         None
 288     }
 289
 290     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 291     }
 292
 293     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 294         None
 295     }
 296     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 297         None
 298     }
 299     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 300         Some(())
 301     }
 302     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 303         None
 304     }
 305 }
 306
 307 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 308 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 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.is_copy_modulo_regions(tcx, tcx.param_env(def_id), builder.span);
 313
 314     let dest = Place::RETURN_PLACE;
 315     let src = Place::Base(PlaceBase::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().map(|k| k.expect_ty())),
 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<'tcx> {
 339     tcx: TyCtxt<'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 CloneShimBuilder<'tcx> {
 348     fn new(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 349         // we must subst the self_ty because it's
 350         // otherwise going to be TySelf and we can't index
 351         // or access fields of a Place of type TySelf.
 352         let substs = tcx.mk_substs_trait(self_ty, &[]);
 353         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 354         let sig = tcx.erase_late_bound_regions(&sig);
 355         let span = tcx.def_span(def_id);
 356
 357         CloneShimBuilder {
 358             tcx,
 359             def_id,
 360             local_decls: local_decls_for_sig(&sig, span),
 361             blocks: IndexVec::new(),
 362             span,
 363             sig,
 364         }
 365     }
 366
 367     fn into_mir(self) -> Body<'tcx> {
 368         Body::new(
 369             self.blocks,
 370             IndexVec::from_elem_n(
 371                 SourceScopeData { span: self.span, parent_scope: None }, 1
 372             ),
 373             ClearCrossCrate::Clear,
 374             IndexVec::new(),
 375             None,
 376             self.local_decls,
 377             IndexVec::new(),
 378             self.sig.inputs().len(),
 379             vec![],
 380             self.span,
 381             vec![],
 382         )
 383     }
 384
 385     fn source_info(&self) -> SourceInfo {
 386         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 387     }
 388
 389     fn block(
 390         &mut self,
 391         statements: Vec<Statement<'tcx>>,
 392         kind: TerminatorKind<'tcx>,
 393         is_cleanup: bool
 394     ) -> BasicBlock {
 395         let source_info = self.source_info();
 396         self.blocks.push(BasicBlockData {
 397             statements,
 398             terminator: Some(Terminator { source_info, kind }),
 399             is_cleanup,
 400         })
 401     }
 402
 403     /// Gives the index of an upcoming BasicBlock, with an offset.
 404     /// offset=0 will give you the index of the next BasicBlock,
 405     /// offset=1 will give the index of the next-to-next block,
 406     /// offset=-1 will give you the index of the last-created block
 407     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 408         BasicBlock::new(self.blocks.len() + offset)
 409     }
 410
 411     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 412         Statement {
 413             source_info: self.source_info(),
 414             kind,
 415         }
 416     }
 417
 418     fn copy_shim(&mut self) {
 419         let rcvr = Place::Base(PlaceBase::Local(Local::new(1+0))).deref();
 420         let ret_statement = self.make_statement(
 421             StatementKind::Assign(
 422                 Place::RETURN_PLACE,
 423                 box Rvalue::Use(Operand::Copy(rcvr))
 424             )
 425         );
 426         self.block(vec![ret_statement], TerminatorKind::Return, false);
 427     }
 428
 429     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 430         let span = self.span;
 431         Place::Base(PlaceBase::Local(
 432             self.local_decls.push(temp_decl(mutability, ty, span))
 433         ))
 434     }
 435
 436     fn make_clone_call(
 437         &mut self,
 438         dest: Place<'tcx>,
 439         src: Place<'tcx>,
 440         ty: Ty<'tcx>,
 441         next: BasicBlock,
 442         cleanup: BasicBlock
 443     ) {
 444         let tcx = self.tcx;
 445
 446         let substs = tcx.mk_substs_trait(ty, &[]);
 447
 448         // `func == Clone::clone(&ty) -> ty`
 449         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 450         let func = Operand::Constant(box Constant {
 451             span: self.span,
 452             ty: func_ty,
 453             user_ty: None,
 454             literal: ty::Const::zero_sized(tcx, func_ty),
 455         });
 456
 457         let ref_loc = self.make_place(
 458             Mutability::Not,
 459             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 460                 ty,
 461                 mutbl: hir::Mutability::MutImmutable,
 462             })
 463         );
 464
 465         // `let ref_loc: &ty = &src;`
 466         let statement = self.make_statement(
 467             StatementKind::Assign(
 468                 ref_loc.clone(),
 469                 box Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 470             )
 471         );
 472
 473         // `let loc = Clone::clone(ref_loc);`
 474         self.block(vec![statement], TerminatorKind::Call {
 475             func,
 476             args: vec![Operand::Move(ref_loc)],
 477             destination: Some((dest, next)),
 478             cleanup: Some(cleanup),
 479             from_hir_call: true,
 480         }, false);
 481     }
 482
 483     fn loop_header(
 484         &mut self,
 485         beg: Place<'tcx>,
 486         end: Place<'tcx>,
 487         loop_body: BasicBlock,
 488         loop_end: BasicBlock,
 489         is_cleanup: bool
 490     ) {
 491         let tcx = self.tcx;
 492
 493         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 494         let compute_cond = self.make_statement(
 495             StatementKind::Assign(
 496                 cond.clone(),
 497                 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 498             )
 499         );
 500
 501         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 502         self.block(
 503             vec![compute_cond],
 504             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 505             is_cleanup
 506         );
 507     }
 508
 509     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 510         box Constant {
 511             span: self.span,
 512             ty: self.tcx.types.usize,
 513             user_ty: None,
 514             literal: ty::Const::from_usize(self.tcx, value),
 515         }
 516     }
 517
 518     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 519         let tcx = self.tcx;
 520         let span = self.span;
 521
 522         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 523         let end = self.make_place(Mutability::Not, tcx.types.usize);
 524
 525         // BB #0
 526         // `let mut beg = 0;`
 527         // `let end = len;`
 528         // `goto #1;`
 529         let inits = vec![
 530             self.make_statement(
 531                 StatementKind::Assign(
 532                     Place::Base(PlaceBase::Local(beg)),
 533                     box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 534                 )
 535             ),
 536             self.make_statement(
 537                 StatementKind::Assign(
 538                     end.clone(),
 539                     box Rvalue::Use(Operand::Constant(self.make_usize(len)))
 540                 )
 541             )
 542         ];
 543         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 544
 545         // BB #1: loop {
 546         //     BB #2;
 547         //     BB #3;
 548         // }
 549         // BB #4;
 550         self.loop_header(Place::Base(PlaceBase::Local(beg)),
 551                          end,
 552                          BasicBlock::new(2),
 553                          BasicBlock::new(4),
 554                          false);
 555
 556         // BB #2
 557         // `dest[i] = Clone::clone(src[beg])`;
 558         // Goto #3 if ok, #5 if unwinding happens.
 559         let dest_field = dest.clone().index(beg);
 560         let src_field = src.index(beg);
 561         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 562                              BasicBlock::new(5));
 563
 564         // BB #3
 565         // `beg = beg + 1;`
 566         // `goto #1`;
 567         let statements = vec![
 568             self.make_statement(
 569                 StatementKind::Assign(
 570                     Place::Base(PlaceBase::Local(beg)),
 571                     box Rvalue::BinaryOp(
 572                         BinOp::Add,
 573                         Operand::Copy(Place::Base(PlaceBase::Local(beg))),
 574                         Operand::Constant(self.make_usize(1))
 575                     )
 576                 )
 577             )
 578         ];
 579         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 580
 581         // BB #4
 582         // `return dest;`
 583         self.block(vec![], TerminatorKind::Return, false);
 584
 585         // BB #5 (cleanup)
 586         // `let end = beg;`
 587         // `let mut beg = 0;`
 588         // goto #6;
 589         let end = beg;
 590         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 591         let init = self.make_statement(
 592             StatementKind::Assign(
 593                 Place::Base(PlaceBase::Local(beg)),
 594                 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 595             )
 596         );
 597         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 598
 599         // BB #6 (cleanup): loop {
 600         //     BB #7;
 601         //     BB #8;
 602         // }
 603         // BB #9;
 604         self.loop_header(Place::Base(PlaceBase::Local(beg)), Place::Base(PlaceBase::Local(end)),
 605                          BasicBlock::new(7), BasicBlock::new(9), true);
 606
 607         // BB #7 (cleanup)
 608         // `drop(dest[beg])`;
 609         self.block(vec![], TerminatorKind::Drop {
 610             location: dest.index(beg),
 611             target: BasicBlock::new(8),
 612             unwind: None,
 613         }, true);
 614
 615         // BB #8 (cleanup)
 616         // `beg = beg + 1;`
 617         // `goto #6;`
 618         let statement = self.make_statement(
 619             StatementKind::Assign(
 620                 Place::Base(PlaceBase::Local(beg)),
 621                 box Rvalue::BinaryOp(
 622                     BinOp::Add,
 623                     Operand::Copy(Place::Base(PlaceBase::Local(beg))),
 624                     Operand::Constant(self.make_usize(1))
 625                 )
 626             )
 627         );
 628         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 629
 630         // BB #9 (resume)
 631         self.block(vec![], TerminatorKind::Resume, true);
 632     }
 633
 634     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 635                           src: Place<'tcx>, tys: I)
 636             where I: Iterator<Item = Ty<'tcx>> {
 637         let mut previous_field = None;
 638         for (i, ity) in tys.enumerate() {
 639             let field = Field::new(i);
 640             let src_field = src.clone().field(field, ity);
 641
 642             let dest_field = dest.clone().field(field, ity);
 643
 644             // #(2i + 1) is the cleanup block for the previous clone operation
 645             let cleanup_block = self.block_index_offset(1);
 646             // #(2i + 2) is the next cloning block
 647             // (or the Return terminator if this is the last block)
 648             let next_block = self.block_index_offset(2);
 649
 650             // BB #(2i)
 651             // `dest.i = Clone::clone(&src.i);`
 652             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 653             self.make_clone_call(
 654                 dest_field.clone(),
 655                 src_field,
 656                 ity,
 657                 next_block,
 658                 cleanup_block,
 659             );
 660
 661             // BB #(2i + 1) (cleanup)
 662             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 663                 // Drop previous field and goto previous cleanup block.
 664                 self.block(vec![], TerminatorKind::Drop {
 665                     location: previous_field,
 666                     target: previous_cleanup,
 667                     unwind: None,
 668                 }, true);
 669             } else {
 670                 // Nothing to drop, just resume.
 671                 self.block(vec![], TerminatorKind::Resume, true);
 672             }
 673
 674             previous_field = Some((dest_field, cleanup_block));
 675         }
 676
 677         self.block(vec![], TerminatorKind::Return, false);
 678     }
 679 }
 680
 681 /// Builds a "call" shim for `def_id`. The shim calls the
 682 /// function specified by `call_kind`, first adjusting its first
 683 /// argument according to `rcvr_adjustment`.
 684 ///
 685 /// If `untuple_args` is a vec of types, the second argument of the
 686 /// function will be untupled as these types.
 687 fn build_call_shim<'tcx>(
 688     tcx: TyCtxt<'tcx, 'tcx>,
 689     def_id: DefId,
 690     rcvr_adjustment: Adjustment,
 691     call_kind: CallKind,
 692     untuple_args: Option<&[Ty<'tcx>]>,
 693 ) -> Body<'tcx> {
 694     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 695             call_kind={:?}, untuple_args={:?})",
 696            def_id, rcvr_adjustment, call_kind, untuple_args);
 697
 698     let sig = tcx.fn_sig(def_id);
 699     let sig = tcx.erase_late_bound_regions(&sig);
 700     let span = tcx.def_span(def_id);
 701
 702     debug!("build_call_shim: sig={:?}", sig);
 703
 704     let mut local_decls = local_decls_for_sig(&sig, span);
 705     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 706
 707     let rcvr_arg = Local::new(1+0);
 708     let rcvr_l = Place::Base(PlaceBase::Local(rcvr_arg));
 709     let mut statements = vec![];
 710
 711     let rcvr = match rcvr_adjustment {
 712         Adjustment::Identity => Operand::Move(rcvr_l),
 713         Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
 714         Adjustment::DerefMove => {
 715             // fn(Self, ...) -> fn(*mut Self, ...)
 716             let arg_ty = local_decls[rcvr_arg].ty;
 717             assert!(arg_ty.is_self());
 718             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 719
 720             Operand::Move(rcvr_l.deref())
 721         }
 722         Adjustment::RefMut => {
 723             // let rcvr = &mut rcvr;
 724             let ref_rcvr = local_decls.push(temp_decl(
 725                 Mutability::Not,
 726                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 727                     ty: sig.inputs()[0],
 728                     mutbl: hir::Mutability::MutMutable
 729                 }),
 730                 span
 731             ));
 732             let borrow_kind = BorrowKind::Mut {
 733                 allow_two_phase_borrow: false,
 734             };
 735             statements.push(Statement {
 736                 source_info,
 737                 kind: StatementKind::Assign(
 738                     Place::Base(PlaceBase::Local(ref_rcvr)),
 739                     box Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 740                 )
 741             });
 742             Operand::Move(Place::Base(PlaceBase::Local(ref_rcvr)))
 743         }
 744     };
 745
 746     let (callee, mut args) = match call_kind {
 747         CallKind::Indirect => (rcvr, vec![]),
 748         CallKind::Direct(def_id) => {
 749             let ty = tcx.type_of(def_id);
 750             (Operand::Constant(box Constant {
 751                 span,
 752                 ty,
 753                 user_ty: None,
 754                 literal: ty::Const::zero_sized(tcx, ty),
 755              }),
 756              vec![rcvr])
 757         }
 758     };
 759
 760     if let Some(untuple_args) = untuple_args {
 761         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 762             let arg_place = Place::Base(PlaceBase::Local(Local::new(1+1)));
 763             Operand::Move(arg_place.field(Field::new(i), *ity))
 764         }));
 765     } else {
 766         args.extend((1..sig.inputs().len()).map(|i| {
 767             Operand::Move(Place::Base(PlaceBase::Local(Local::new(1+i))))
 768         }));
 769     }
 770
 771     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 772     let mut blocks = IndexVec::with_capacity(n_blocks);
 773     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 774         blocks.push(BasicBlockData {
 775             statements,
 776             terminator: Some(Terminator { source_info, kind }),
 777             is_cleanup
 778         })
 779     };
 780
 781     // BB #0
 782     block(&mut blocks, statements, TerminatorKind::Call {
 783         func: callee,
 784         args,
 785         destination: Some((Place::RETURN_PLACE,
 786                            BasicBlock::new(1))),
 787         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 788             Some(BasicBlock::new(3))
 789         } else {
 790             None
 791         },
 792         from_hir_call: true,
 793     }, false);
 794
 795     if let Adjustment::RefMut = rcvr_adjustment {
 796         // BB #1 - drop for Self
 797         block(&mut blocks, vec![], TerminatorKind::Drop {
 798             location: Place::Base(PlaceBase::Local(rcvr_arg)),
 799             target: BasicBlock::new(2),
 800             unwind: None
 801         }, false);
 802     }
 803     // BB #1/#2 - return
 804     block(&mut blocks, vec![], TerminatorKind::Return, false);
 805     if let Adjustment::RefMut = rcvr_adjustment {
 806         // BB #3 - drop if closure panics
 807         block(&mut blocks, vec![], TerminatorKind::Drop {
 808             location: Place::Base(PlaceBase::Local(rcvr_arg)),
 809             target: BasicBlock::new(4),
 810             unwind: None
 811         }, true);
 812
 813         // BB #4 - resume
 814         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 815     }
 816
 817     let mut body = Body::new(
 818         blocks,
 819         IndexVec::from_elem_n(
 820             SourceScopeData { span: span, parent_scope: None }, 1
 821         ),
 822         ClearCrossCrate::Clear,
 823         IndexVec::new(),
 824         None,
 825         local_decls,
 826         IndexVec::new(),
 827         sig.inputs().len(),
 828         vec![],
 829         span,
 830         vec![],
 831     );
 832     if let Abi::RustCall = sig.abi {
 833         body.spread_arg = Some(Local::new(sig.inputs().len()));
 834     }
 835     body
 836 }
 837
 838 pub fn build_adt_ctor<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, ctor_id: DefId) -> &'tcx Body<'tcx> {
 839     debug_assert!(tcx.is_constructor(ctor_id));
 840
 841     let span = tcx.hir().span_if_local(ctor_id)
 842         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 843
 844     let param_env = tcx.param_env(ctor_id);
 845
 846     // Normalize the sig.
 847     let sig = tcx.fn_sig(ctor_id)
 848         .no_bound_vars()
 849         .expect("LBR in ADT constructor signature");
 850     let sig = tcx.normalize_erasing_regions(param_env, sig);
 851
 852     let (adt_def, substs) = match sig.output().sty {
 853         ty::Adt(adt_def, substs) => (adt_def, substs),
 854         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 855     };
 856
 857     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 858
 859     let local_decls = local_decls_for_sig(&sig, span);
 860
 861     let source_info = SourceInfo {
 862         span,
 863         scope: OUTERMOST_SOURCE_SCOPE
 864     };
 865
 866     let variant_index = if adt_def.is_enum() {
 867         adt_def.variant_index_with_ctor_id(ctor_id)
 868     } else {
 869         VariantIdx::new(0)
 870     };
 871
 872     // Generate the following MIR:
 873     //
 874     // (return as Variant).field0 = arg0;
 875     // (return as Variant).field1 = arg1;
 876     //
 877     // return;
 878     debug!("build_ctor: variant_index={:?}", variant_index);
 879
 880     let statements = expand_aggregate(
 881         Place::RETURN_PLACE,
 882         adt_def
 883             .variants[variant_index]
 884             .fields
 885             .iter()
 886             .enumerate()
 887             .map(|(idx, field_def)| (
 888                 Operand::Move(Place::Base(PlaceBase::Local(Local::new(idx + 1)))),
 889                 field_def.ty(tcx, substs),
 890             )),
 891         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 892         source_info,
 893     ).collect();
 894
 895     let start_block = BasicBlockData {
 896         statements,
 897         terminator: Some(Terminator {
 898             source_info,
 899             kind: TerminatorKind::Return,
 900         }),
 901         is_cleanup: false
 902     };
 903
 904     let body = Body::new(
 905         IndexVec::from_elem_n(start_block, 1),
 906         IndexVec::from_elem_n(
 907             SourceScopeData { span: span, parent_scope: None }, 1
 908         ),
 909         ClearCrossCrate::Clear,
 910         IndexVec::new(),
 911         None,
 912         local_decls,
 913         IndexVec::new(),
 914         sig.inputs().len(),
 915         vec![],
 916         span,
 917         vec![],
 918     );
 919
 920     crate::util::dump_mir(
 921         tcx,
 922         None,
 923         "mir_map",
 924         &0,
 925         crate::transform::MirSource::item(ctor_id),
 926         &body,
 927         |_, _| Ok(()),
 928     );
 929
 930     tcx.arena.alloc(body)
 931 }