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_index::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         // We are generating a call back to our def-id, which the
  70         // codegen backend knows to turn to an actual virtual call.
  71         ty::InstanceDef::Virtual(def_id, _) |
  72         // ...or we are generating a direct call to a function for which indirect calls must be
  73         // codegen'd differently than direct ones (example: #[track_caller])
  74         ty::InstanceDef::ReifyShim(def_id) => {
  75             build_call_shim(
  76                 tcx,
  77                 def_id,
  78                 Adjustment::Identity,
  79                 CallKind::Direct(def_id),
  80                 None
  81             )
  82         }
  83         ty::InstanceDef::ClosureOnceShim { call_once } => {
  84             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  85             let call_mut = tcx
  86                 .associated_items(fn_mut)
  87                 .find(|it| it.kind == ty::AssocKind::Method)
  88                 .unwrap().def_id;
  89
  90             build_call_shim(
  91                 tcx,
  92                 call_once,
  93                 Adjustment::RefMut,
  94                 CallKind::Direct(call_mut),
  95                 None
  96             )
  97         }
  98         ty::InstanceDef::DropGlue(def_id, ty) => {
  99             build_drop_shim(tcx, def_id, ty)
 100         }
 101         ty::InstanceDef::CloneShim(def_id, ty) => {
 102             let name = tcx.item_name(def_id);
 103             if name == sym::clone {
 104                 build_clone_shim(tcx, def_id, ty)
 105             } else if name == sym::clone_from {
 106                 debug!("make_shim({:?}: using default trait implementation", instance);
 107                 return tcx.optimized_mir(def_id);
 108             } else {
 109                 bug!("builtin clone shim {:?} not supported", instance)
 110             }
 111         }
 112         ty::InstanceDef::Intrinsic(_) => {
 113             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 114         }
 115     };
 116     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 117
 118     run_passes(tcx, &mut result, instance, None, MirPhase::Const, &[
 119         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 120         &no_landing_pads::NoLandingPads::new(tcx),
 121         &remove_noop_landing_pads::RemoveNoopLandingPads,
 122         &simplify::SimplifyCfg::new("make_shim"),
 123         &add_call_guards::CriticalCallEdges,
 124     ]);
 125
 126     debug!("make_shim({:?}) = {:?}", instance, result);
 127
 128     tcx.arena.alloc(result)
 129 }
 130
 131 #[derive(Copy, Clone, Debug, PartialEq)]
 132 enum Adjustment {
 133     Identity,
 134     Deref,
 135     DerefMove,
 136     RefMut,
 137 }
 138
 139 #[derive(Copy, Clone, Debug, PartialEq)]
 140 enum CallKind {
 141     Indirect,
 142     Direct(DefId),
 143 }
 144
 145 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 146     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 147     LocalDecl {
 148         mutability,
 149         ty,
 150         user_ty: UserTypeProjections::none(),
 151         source_info,
 152         internal: false,
 153         local_info: LocalInfo::Other,
 154         is_block_tail: None,
 155     }
 156 }
 157
 158 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 159     -> IndexVec<Local, LocalDecl<'tcx>>
 160 {
 161     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 162         .chain(sig.inputs().iter().map(
 163             |ity| temp_decl(Mutability::Not, ity, span)))
 164         .collect()
 165 }
 166
 167 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 168     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 169
 170     // Check if this is a generator, if so, return the drop glue for it
 171     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 172         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 173         return body.subst(tcx, substs);
 174     }
 175
 176     let substs = if let Some(ty) = ty {
 177         tcx.intern_substs(&[ty.into()])
 178     } else {
 179         InternalSubsts::identity_for_item(tcx, def_id)
 180     };
 181     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 182     let sig = tcx.erase_late_bound_regions(&sig);
 183     let span = tcx.def_span(def_id);
 184
 185     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 186
 187     let return_block = BasicBlock::new(1);
 188     let mut blocks = IndexVec::with_capacity(2);
 189     let block = |blocks: &mut IndexVec<_, _>, kind| {
 190         blocks.push(BasicBlockData {
 191             statements: vec![],
 192             terminator: Some(Terminator { source_info, kind }),
 193             is_cleanup: false
 194         })
 195     };
 196     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 197     block(&mut blocks, TerminatorKind::Return);
 198
 199     let mut body = new_body(
 200         blocks,
 201         local_decls_for_sig(&sig, span),
 202         sig.inputs().len(),
 203         span);
 204
 205     if let Some(..) = ty {
 206         // The first argument (index 0), but add 1 for the return value.
 207         let dropee_ptr = Place::from(Local::new(1+0));
 208         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 209             // Function arguments should be retagged, and we make this one raw.
 210             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 211                 source_info,
 212                 kind: StatementKind::Retag(RetagKind::Raw, box(dropee_ptr.clone())),
 213             });
 214         }
 215         let patch = {
 216             let param_env = tcx.param_env(def_id).with_reveal_all();
 217             let mut elaborator = DropShimElaborator {
 218                 body: &body,
 219                 patch: MirPatch::new(&body),
 220                 tcx,
 221                 param_env
 222             };
 223             let dropee = tcx.mk_place_deref(dropee_ptr);
 224             let resume_block = elaborator.patch.resume_block();
 225             elaborate_drops::elaborate_drop(
 226                 &mut elaborator,
 227                 source_info,
 228                 &dropee,
 229                 (),
 230                 return_block,
 231                 elaborate_drops::Unwind::To(resume_block),
 232                 START_BLOCK
 233             );
 234             elaborator.patch
 235         };
 236         patch.apply(&mut body);
 237     }
 238
 239     body
 240 }
 241
 242 fn new_body<'tcx>(
 243     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 244     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 245     arg_count: usize,
 246     span: Span,
 247 ) -> Body<'tcx> {
 248     Body::new(
 249         basic_blocks,
 250         IndexVec::from_elem_n(
 251             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 252             1,
 253         ),
 254         local_decls,
 255         IndexVec::new(),
 256         arg_count,
 257         vec![],
 258         span,
 259         vec![],
 260         None,
 261     )
 262 }
 263
 264 pub struct DropShimElaborator<'a, 'tcx> {
 265     pub body: &'a Body<'tcx>,
 266     pub patch: MirPatch<'tcx>,
 267     pub tcx: TyCtxt<'tcx>,
 268     pub param_env: ty::ParamEnv<'tcx>,
 269 }
 270
 271 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 272     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 273         Ok(())
 274     }
 275 }
 276
 277 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 278     type Path = ();
 279
 280     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 281     fn body(&self) -> &'a Body<'tcx> { self.body }
 282     fn tcx(&self) -> TyCtxt<'tcx> {
 283         self.tcx
 284         }
 285     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 286
 287     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 288         if let DropFlagMode::Shallow = mode {
 289             DropStyle::Static
 290         } else {
 291             DropStyle::Open
 292         }
 293     }
 294
 295     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 296         None
 297     }
 298
 299     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 300     }
 301
 302     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 303         None
 304     }
 305     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 306         None
 307     }
 308     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 309         Some(())
 310     }
 311     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 312         None
 313     }
 314 }
 315
 316 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 317 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 318     debug!("build_clone_shim(def_id={:?})", def_id);
 319
 320     let param_env = tcx.param_env(def_id);
 321
 322     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 323     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 324
 325     let dest = Place::return_place();
 326     let src = tcx.mk_place_deref(Place::from(Local::new(1+0)));
 327
 328     match self_ty.kind {
 329         _ if is_copy => builder.copy_shim(),
 330         ty::Array(ty, len) => {
 331             let len = len.eval_usize(tcx, param_env);
 332             builder.array_shim(dest, src, ty, len)
 333         }
 334         ty::Closure(def_id, substs) => {
 335             builder.tuple_like_shim(
 336                 dest, src,
 337                 substs.as_closure().upvar_tys(def_id, tcx)
 338             )
 339         }
 340         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 341         _ => {
 342             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 343         }
 344     };
 345
 346     builder.into_mir()
 347 }
 348
 349 struct CloneShimBuilder<'tcx> {
 350     tcx: TyCtxt<'tcx>,
 351     def_id: DefId,
 352     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 353     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 354     span: Span,
 355     sig: ty::FnSig<'tcx>,
 356 }
 357
 358 impl CloneShimBuilder<'tcx> {
 359     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 360         // we must subst the self_ty because it's
 361         // otherwise going to be TySelf and we can't index
 362         // or access fields of a Place of type TySelf.
 363         let substs = tcx.mk_substs_trait(self_ty, &[]);
 364         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 365         let sig = tcx.erase_late_bound_regions(&sig);
 366         let span = tcx.def_span(def_id);
 367
 368         CloneShimBuilder {
 369             tcx,
 370             def_id,
 371             local_decls: local_decls_for_sig(&sig, span),
 372             blocks: IndexVec::new(),
 373             span,
 374             sig,
 375         }
 376     }
 377
 378     fn into_mir(self) -> Body<'tcx> {
 379         new_body(
 380             self.blocks,
 381             self.local_decls,
 382             self.sig.inputs().len(),
 383             self.span,
 384         )
 385     }
 386
 387     fn source_info(&self) -> SourceInfo {
 388         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 389     }
 390
 391     fn block(
 392         &mut self,
 393         statements: Vec<Statement<'tcx>>,
 394         kind: TerminatorKind<'tcx>,
 395         is_cleanup: bool
 396     ) -> BasicBlock {
 397         let source_info = self.source_info();
 398         self.blocks.push(BasicBlockData {
 399             statements,
 400             terminator: Some(Terminator { source_info, kind }),
 401             is_cleanup,
 402         })
 403     }
 404
 405     /// Gives the index of an upcoming BasicBlock, with an offset.
 406     /// offset=0 will give you the index of the next BasicBlock,
 407     /// offset=1 will give the index of the next-to-next block,
 408     /// offset=-1 will give you the index of the last-created block
 409     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 410         BasicBlock::new(self.blocks.len() + offset)
 411     }
 412
 413     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 414         Statement {
 415             source_info: self.source_info(),
 416             kind,
 417         }
 418     }
 419
 420     fn copy_shim(&mut self) {
 421         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1+0)));
 422         let ret_statement = self.make_statement(
 423             StatementKind::Assign(
 424                 box(
 425                     Place::return_place(),
 426                     Rvalue::Use(Operand::Copy(rcvr))
 427                 )
 428             )
 429         );
 430         self.block(vec![ret_statement], TerminatorKind::Return, false);
 431     }
 432
 433     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 434         let span = self.span;
 435         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 436     }
 437
 438     fn make_clone_call(
 439         &mut self,
 440         dest: Place<'tcx>,
 441         src: Place<'tcx>,
 442         ty: Ty<'tcx>,
 443         next: BasicBlock,
 444         cleanup: BasicBlock
 445     ) {
 446         let tcx = self.tcx;
 447
 448         let substs = tcx.mk_substs_trait(ty, &[]);
 449
 450         // `func == Clone::clone(&ty) -> ty`
 451         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 452         let func = Operand::Constant(box Constant {
 453             span: self.span,
 454             user_ty: None,
 455             literal: ty::Const::zero_sized(tcx, func_ty),
 456         });
 457
 458         let ref_loc = self.make_place(
 459             Mutability::Not,
 460             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 461                 ty,
 462                 mutbl: hir::Mutability::Immutable,
 463             })
 464         );
 465
 466         // `let ref_loc: &ty = &src;`
 467         let statement = self.make_statement(
 468             StatementKind::Assign(
 469                 box(
 470                     ref_loc.clone(),
 471                     Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 472                 )
 473             )
 474         );
 475
 476         // `let loc = Clone::clone(ref_loc);`
 477         self.block(vec![statement], TerminatorKind::Call {
 478             func,
 479             args: vec![Operand::Move(ref_loc)],
 480             destination: Some((dest, next)),
 481             cleanup: Some(cleanup),
 482             from_hir_call: true,
 483         }, false);
 484     }
 485
 486     fn loop_header(
 487         &mut self,
 488         beg: Place<'tcx>,
 489         end: Place<'tcx>,
 490         loop_body: BasicBlock,
 491         loop_end: BasicBlock,
 492         is_cleanup: bool
 493     ) {
 494         let tcx = self.tcx;
 495
 496         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 497         let compute_cond = self.make_statement(
 498             StatementKind::Assign(
 499                 box(
 500                     cond.clone(),
 501                     Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 502                 )
 503             )
 504         );
 505
 506         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 507         self.block(
 508             vec![compute_cond],
 509             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 510             is_cleanup
 511         );
 512     }
 513
 514     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 515         box Constant {
 516             span: self.span,
 517             user_ty: None,
 518             literal: ty::Const::from_usize(self.tcx, value),
 519         }
 520     }
 521
 522     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 523         let tcx = self.tcx;
 524         let span = self.span;
 525
 526         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 527         let end = self.make_place(Mutability::Not, tcx.types.usize);
 528
 529         // BB #0
 530         // `let mut beg = 0;`
 531         // `let end = len;`
 532         // `goto #1;`
 533         let inits = vec![
 534             self.make_statement(
 535                 StatementKind::Assign(
 536                     box(
 537                         Place::from(beg),
 538                         Rvalue::Use(Operand::Constant(self.make_usize(0)))
 539                     )
 540                 )
 541             ),
 542             self.make_statement(
 543                 StatementKind::Assign(
 544                     box(
 545                         end.clone(),
 546                         Rvalue::Use(Operand::Constant(self.make_usize(len)))
 547                     )
 548                 )
 549             )
 550         ];
 551         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 552
 553         // BB #1: loop {
 554         //     BB #2;
 555         //     BB #3;
 556         // }
 557         // BB #4;
 558         self.loop_header(Place::from(beg),
 559                          end,
 560                          BasicBlock::new(2),
 561                          BasicBlock::new(4),
 562                          false);
 563
 564         // BB #2
 565         // `dest[i] = Clone::clone(src[beg])`;
 566         // Goto #3 if ok, #5 if unwinding happens.
 567         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 568         let src_field = self.tcx.mk_place_index(src, beg);
 569         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 570                              BasicBlock::new(5));
 571
 572         // BB #3
 573         // `beg = beg + 1;`
 574         // `goto #1`;
 575         let statements = vec![
 576             self.make_statement(
 577                 StatementKind::Assign(
 578                     box(
 579                         Place::from(beg),
 580                         Rvalue::BinaryOp(
 581                             BinOp::Add,
 582                             Operand::Copy(Place::from(beg)),
 583                             Operand::Constant(self.make_usize(1))
 584                         )
 585                     )
 586                 )
 587             )
 588         ];
 589         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 590
 591         // BB #4
 592         // `return dest;`
 593         self.block(vec![], TerminatorKind::Return, false);
 594
 595         // BB #5 (cleanup)
 596         // `let end = beg;`
 597         // `let mut beg = 0;`
 598         // goto #6;
 599         let end = beg;
 600         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 601         let init = self.make_statement(
 602             StatementKind::Assign(
 603                 box(
 604                     Place::from(beg),
 605                     Rvalue::Use(Operand::Constant(self.make_usize(0)))
 606                 )
 607             )
 608         );
 609         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 610
 611         // BB #6 (cleanup): loop {
 612         //     BB #7;
 613         //     BB #8;
 614         // }
 615         // BB #9;
 616         self.loop_header(Place::from(beg), Place::from(end),
 617                          BasicBlock::new(7), BasicBlock::new(9), true);
 618
 619         // BB #7 (cleanup)
 620         // `drop(dest[beg])`;
 621         self.block(vec![], TerminatorKind::Drop {
 622             location: self.tcx.mk_place_index(dest, beg),
 623             target: BasicBlock::new(8),
 624             unwind: None,
 625         }, true);
 626
 627         // BB #8 (cleanup)
 628         // `beg = beg + 1;`
 629         // `goto #6;`
 630         let statement = self.make_statement(
 631             StatementKind::Assign(
 632                 box(
 633                     Place::from(beg),
 634                     Rvalue::BinaryOp(
 635                         BinOp::Add,
 636                         Operand::Copy(Place::from(beg)),
 637                         Operand::Constant(self.make_usize(1))
 638                     )
 639                 )
 640             )
 641         );
 642         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 643
 644         // BB #9 (resume)
 645         self.block(vec![], TerminatorKind::Resume, true);
 646     }
 647
 648     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 649                           src: Place<'tcx>, tys: I)
 650             where I: Iterator<Item = Ty<'tcx>> {
 651         let mut previous_field = None;
 652         for (i, ity) in tys.enumerate() {
 653             let field = Field::new(i);
 654             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 655
 656             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 657
 658             // #(2i + 1) is the cleanup block for the previous clone operation
 659             let cleanup_block = self.block_index_offset(1);
 660             // #(2i + 2) is the next cloning block
 661             // (or the Return terminator if this is the last block)
 662             let next_block = self.block_index_offset(2);
 663
 664             // BB #(2i)
 665             // `dest.i = Clone::clone(&src.i);`
 666             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 667             self.make_clone_call(
 668                 dest_field.clone(),
 669                 src_field,
 670                 ity,
 671                 next_block,
 672                 cleanup_block,
 673             );
 674
 675             // BB #(2i + 1) (cleanup)
 676             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 677                 // Drop previous field and goto previous cleanup block.
 678                 self.block(vec![], TerminatorKind::Drop {
 679                     location: previous_field,
 680                     target: previous_cleanup,
 681                     unwind: None,
 682                 }, true);
 683             } else {
 684                 // Nothing to drop, just resume.
 685                 self.block(vec![], TerminatorKind::Resume, true);
 686             }
 687
 688             previous_field = Some((dest_field, cleanup_block));
 689         }
 690
 691         self.block(vec![], TerminatorKind::Return, false);
 692     }
 693 }
 694
 695 /// Builds a "call" shim for `def_id`. The shim calls the
 696 /// function specified by `call_kind`, first adjusting its first
 697 /// argument according to `rcvr_adjustment`.
 698 ///
 699 /// If `untuple_args` is a vec of types, the second argument of the
 700 /// function will be untupled as these types.
 701 fn build_call_shim<'tcx>(
 702     tcx: TyCtxt<'tcx>,
 703     def_id: DefId,
 704     rcvr_adjustment: Adjustment,
 705     call_kind: CallKind,
 706     untuple_args: Option<&[Ty<'tcx>]>,
 707 ) -> Body<'tcx> {
 708     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 709             call_kind={:?}, untuple_args={:?})",
 710            def_id, rcvr_adjustment, call_kind, untuple_args);
 711
 712     let sig = tcx.fn_sig(def_id);
 713     let sig = tcx.erase_late_bound_regions(&sig);
 714     let span = tcx.def_span(def_id);
 715
 716     debug!("build_call_shim: sig={:?}", sig);
 717
 718     let mut local_decls = local_decls_for_sig(&sig, span);
 719     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 720
 721     let rcvr_arg = Local::new(1+0);
 722     let rcvr_l = Place::from(rcvr_arg);
 723     let mut statements = vec![];
 724
 725     let rcvr = match rcvr_adjustment {
 726         Adjustment::Identity => Operand::Move(rcvr_l),
 727         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_l)),
 728         Adjustment::DerefMove => {
 729             // fn(Self, ...) -> fn(*mut Self, ...)
 730             let arg_ty = local_decls[rcvr_arg].ty;
 731             debug_assert!(tcx.generics_of(def_id).has_self && arg_ty == tcx.types.self_param);
 732             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 733
 734             Operand::Move(tcx.mk_place_deref(rcvr_l))
 735         }
 736         Adjustment::RefMut => {
 737             // let rcvr = &mut rcvr;
 738             let ref_rcvr = local_decls.push(temp_decl(
 739                 Mutability::Not,
 740                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 741                     ty: sig.inputs()[0],
 742                     mutbl: hir::Mutability::Mutable
 743                 }),
 744                 span
 745             ));
 746             let borrow_kind = BorrowKind::Mut {
 747                 allow_two_phase_borrow: false,
 748             };
 749             statements.push(Statement {
 750                 source_info,
 751                 kind: StatementKind::Assign(
 752                     box(
 753                         Place::from(ref_rcvr),
 754                         Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 755                     )
 756                 )
 757             });
 758             Operand::Move(Place::from(ref_rcvr))
 759         }
 760     };
 761
 762     let (callee, mut args) = match call_kind {
 763         CallKind::Indirect => (rcvr, vec![]),
 764         CallKind::Direct(def_id) => {
 765             let ty = tcx.type_of(def_id);
 766             (Operand::Constant(box Constant {
 767                 span,
 768                 user_ty: None,
 769                 literal: ty::Const::zero_sized(tcx, ty),
 770              }),
 771              vec![rcvr])
 772         }
 773     };
 774
 775     if let Some(untuple_args) = untuple_args {
 776         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 777             let arg_place = Place::from(Local::new(1+1));
 778             Operand::Move(tcx.mk_place_field(arg_place, Field::new(i), *ity))
 779         }));
 780     } else {
 781         args.extend((1..sig.inputs().len()).map(|i| {
 782             Operand::Move(Place::from(Local::new(1+i)))
 783         }));
 784     }
 785
 786     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 787     let mut blocks = IndexVec::with_capacity(n_blocks);
 788     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 789         blocks.push(BasicBlockData {
 790             statements,
 791             terminator: Some(Terminator { source_info, kind }),
 792             is_cleanup
 793         })
 794     };
 795
 796     // BB #0
 797     block(&mut blocks, statements, TerminatorKind::Call {
 798         func: callee,
 799         args,
 800         destination: Some((Place::return_place(),
 801                            BasicBlock::new(1))),
 802         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 803             Some(BasicBlock::new(3))
 804         } else {
 805             None
 806         },
 807         from_hir_call: true,
 808     }, false);
 809
 810     if let Adjustment::RefMut = rcvr_adjustment {
 811         // BB #1 - drop for Self
 812         block(&mut blocks, vec![], TerminatorKind::Drop {
 813             location: Place::from(rcvr_arg),
 814             target: BasicBlock::new(2),
 815             unwind: None
 816         }, false);
 817     }
 818     // BB #1/#2 - return
 819     block(&mut blocks, vec![], TerminatorKind::Return, false);
 820     if let Adjustment::RefMut = rcvr_adjustment {
 821         // BB #3 - drop if closure panics
 822         block(&mut blocks, vec![], TerminatorKind::Drop {
 823             location: Place::from(rcvr_arg),
 824             target: BasicBlock::new(4),
 825             unwind: None
 826         }, true);
 827
 828         // BB #4 - resume
 829         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 830     }
 831
 832     let mut body = new_body(
 833         blocks,
 834         local_decls,
 835         sig.inputs().len(),
 836         span,
 837     );
 838
 839     if let Abi::RustCall = sig.abi {
 840         body.spread_arg = Some(Local::new(sig.inputs().len()));
 841     }
 842     body
 843 }
 844
 845 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &Body<'_> {
 846     debug_assert!(tcx.is_constructor(ctor_id));
 847
 848     let span = tcx.hir().span_if_local(ctor_id)
 849         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 850
 851     let param_env = tcx.param_env(ctor_id);
 852
 853     // Normalize the sig.
 854     let sig = tcx.fn_sig(ctor_id)
 855         .no_bound_vars()
 856         .expect("LBR in ADT constructor signature");
 857     let sig = tcx.normalize_erasing_regions(param_env, sig);
 858
 859     let (adt_def, substs) = match sig.output().kind {
 860         ty::Adt(adt_def, substs) => (adt_def, substs),
 861         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 862     };
 863
 864     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 865
 866     let local_decls = local_decls_for_sig(&sig, span);
 867
 868     let source_info = SourceInfo {
 869         span,
 870         scope: OUTERMOST_SOURCE_SCOPE
 871     };
 872
 873     let variant_index = if adt_def.is_enum() {
 874         adt_def.variant_index_with_ctor_id(ctor_id)
 875     } else {
 876         VariantIdx::new(0)
 877     };
 878
 879     // Generate the following MIR:
 880     //
 881     // (return as Variant).field0 = arg0;
 882     // (return as Variant).field1 = arg1;
 883     //
 884     // return;
 885     debug!("build_ctor: variant_index={:?}", variant_index);
 886
 887     let statements = expand_aggregate(
 888         Place::return_place(),
 889         adt_def
 890             .variants[variant_index]
 891             .fields
 892             .iter()
 893             .enumerate()
 894             .map(|(idx, field_def)| (
 895                 Operand::Move(Place::from(Local::new(idx + 1))),
 896                 field_def.ty(tcx, substs),
 897             )),
 898         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 899         source_info,
 900         tcx,
 901     ).collect();
 902
 903     let start_block = BasicBlockData {
 904         statements,
 905         terminator: Some(Terminator {
 906             source_info,
 907             kind: TerminatorKind::Return,
 908         }),
 909         is_cleanup: false
 910     };
 911
 912     let body = new_body(
 913         IndexVec::from_elem_n(start_block, 1),
 914         local_decls,
 915         sig.inputs().len(),
 916         span,
 917     );
 918
 919     crate::util::dump_mir(
 920         tcx,
 921         None,
 922         "mir_map",
 923         &0,
 924         crate::transform::MirSource::item(ctor_id),
 925         &body,
 926         |_, _| Ok(()),
 927     );
 928
 929     tcx.arena.alloc(body)
 930 }