src/librustc_mir/shim.rs

   1 use rustc::hir;
   2 use rustc::hir::def_id::DefId;
   3 use rustc::mir::*;
   4 use rustc::ty::{self, Ty, TyCtxt};
   5 use rustc::ty::layout::VariantIdx;
   6 use rustc::ty::subst::{Subst, InternalSubsts};
   7 use rustc::ty::query::Providers;
   8
   9 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  10
  11 use rustc_target::spec::abi::Abi;
  12 use syntax_pos::{Span, sym};
  13
  14 use std::fmt;
  15 use std::iter;
  16
  17 use crate::transform::{
  18     add_moves_for_packed_drops, add_call_guards,
  19     remove_noop_landing_pads, no_landing_pads, simplify, run_passes
  20 };
  21 use crate::util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
  22 use crate::util::patch::MirPatch;
  23 use crate::util::expand_aggregate;
  24
  25 pub fn provide(providers: &mut Providers<'_>) {
  26     providers.mir_shims = make_shim;
  27 }
  28
  29 fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> &'tcx Body<'tcx> {
  30     debug!("make_shim({:?})", instance);
  31
  32     let mut result = match instance {
  33         ty::InstanceDef::Item(..) =>
  34             bug!("item {:?} passed to make_shim", instance),
  35         ty::InstanceDef::VtableShim(def_id) => {
  36             build_call_shim(
  37                 tcx,
  38                 def_id,
  39                 Adjustment::DerefMove,
  40                 CallKind::Direct(def_id),
  41                 None,
  42             )
  43         }
  44         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  45             let trait_ = tcx.trait_of_item(def_id).unwrap();
  46             let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
  47                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  48                 Some(ty::ClosureKind::FnMut) |
  49                 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  50                 None => bug!("fn pointer {:?} is not an fn", ty)
  51             };
  52             // HACK: we need the "real" argument types for the MIR,
  53             // but because our substs are (Self, Args), where Args
  54             // is a tuple, we must include the *concrete* argument
  55             // types in the MIR. They will be substituted again with
  56             // the param-substs, but because they are concrete, this
  57             // will not do any harm.
  58             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  59             let arg_tys = sig.inputs();
  60
  61             build_call_shim(
  62                 tcx,
  63                 def_id,
  64                 adjustment,
  65                 CallKind::Indirect,
  66                 Some(arg_tys)
  67             )
  68         }
  69         ty::InstanceDef::Virtual(def_id, _) => {
  70             // We are generating a call back to our def-id, which the
  71             // codegen backend knows to turn to an actual virtual call.
  72             build_call_shim(
  73                 tcx,
  74                 def_id,
  75                 Adjustment::Identity,
  76                 CallKind::Direct(def_id),
  77                 None
  78             )
  79         }
  80         ty::InstanceDef::ClosureOnceShim { call_once } => {
  81             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  82             let call_mut = tcx.global_tcx()
  83                 .associated_items(fn_mut)
  84                 .find(|it| it.kind == ty::AssocKind::Method)
  85                 .unwrap().def_id;
  86
  87             build_call_shim(
  88                 tcx,
  89                 call_once,
  90                 Adjustment::RefMut,
  91                 CallKind::Direct(call_mut),
  92                 None
  93             )
  94         }
  95         ty::InstanceDef::DropGlue(def_id, ty) => {
  96             build_drop_shim(tcx, def_id, ty)
  97         }
  98         ty::InstanceDef::CloneShim(def_id, ty) => {
  99             let name = tcx.item_name(def_id);
 100             if name == sym::clone {
 101                 build_clone_shim(tcx, def_id, ty)
 102             } else if name == sym::clone_from {
 103                 debug!("make_shim({:?}: using default trait implementation", instance);
 104                 return tcx.optimized_mir(def_id);
 105             } else {
 106                 bug!("builtin clone shim {:?} not supported", instance)
 107             }
 108         }
 109         ty::InstanceDef::Intrinsic(_) => {
 110             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 111         }
 112     };
 113     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 114
 115     run_passes(tcx, &mut result, instance, MirPhase::Const, &[
 116         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 117         &no_landing_pads::NoLandingPads,
 118         &remove_noop_landing_pads::RemoveNoopLandingPads,
 119         &simplify::SimplifyCfg::new("make_shim"),
 120         &add_call_guards::CriticalCallEdges,
 121     ]);
 122
 123     debug!("make_shim({:?}) = {:?}", instance, result);
 124
 125     tcx.arena.alloc(result)
 126 }
 127
 128 #[derive(Copy, Clone, Debug, PartialEq)]
 129 enum Adjustment {
 130     Identity,
 131     Deref,
 132     DerefMove,
 133     RefMut,
 134 }
 135
 136 #[derive(Copy, Clone, Debug, PartialEq)]
 137 enum CallKind {
 138     Indirect,
 139     Direct(DefId),
 140 }
 141
 142 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 143     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 144     LocalDecl {
 145         mutability,
 146         ty,
 147         user_ty: UserTypeProjections::none(),
 148         name: None,
 149         source_info,
 150         visibility_scope: source_info.scope,
 151         internal: false,
 152         is_user_variable: None,
 153         is_block_tail: None,
 154     }
 155 }
 156
 157 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 158     -> IndexVec<Local, LocalDecl<'tcx>>
 159 {
 160     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 161         .chain(sig.inputs().iter().map(
 162             |ity| temp_decl(Mutability::Not, ity, span)))
 163         .collect()
 164 }
 165
 166 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 167     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 168
 169     // Check if this is a generator, if so, return the drop glue for it
 170     if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 171         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 172         return body.subst(tcx, substs.substs);
 173     }
 174
 175     let substs = if let Some(ty) = ty {
 176         tcx.intern_substs(&[ty.into()])
 177     } else {
 178         InternalSubsts::identity_for_item(tcx, def_id)
 179     };
 180     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 181     let sig = tcx.erase_late_bound_regions(&sig);
 182     let span = tcx.def_span(def_id);
 183
 184     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 185
 186     let return_block = BasicBlock::new(1);
 187     let mut blocks = IndexVec::with_capacity(2);
 188     let block = |blocks: &mut IndexVec<_, _>, kind| {
 189         blocks.push(BasicBlockData {
 190             statements: vec![],
 191             terminator: Some(Terminator { source_info, kind }),
 192             is_cleanup: false
 193         })
 194     };
 195     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 196     block(&mut blocks, TerminatorKind::Return);
 197
 198     let mut body = Body::new(
 199         blocks,
 200         IndexVec::from_elem_n(
 201             SourceScopeData { span: span, parent_scope: None }, 1
 202         ),
 203         ClearCrossCrate::Clear,
 204         IndexVec::new(),
 205         None,
 206         local_decls_for_sig(&sig, span),
 207         IndexVec::new(),
 208         sig.inputs().len(),
 209         vec![],
 210         span,
 211         vec![],
 212     );
 213
 214     if let Some(..) = ty {
 215         // The first argument (index 0), but add 1 for the return value.
 216         let dropee_ptr = Place::from(Local::new(1+0));
 217         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 218             // Function arguments should be retagged, and we make this one raw.
 219             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 220                 source_info,
 221                 kind: StatementKind::Retag(RetagKind::Raw, dropee_ptr.clone()),
 222             });
 223         }
 224         let patch = {
 225             let param_env = tcx.param_env(def_id).with_reveal_all();
 226             let mut elaborator = DropShimElaborator {
 227                 body: &body,
 228                 patch: MirPatch::new(&body),
 229                 tcx,
 230                 param_env
 231             };
 232             let dropee = dropee_ptr.deref();
 233             let resume_block = elaborator.patch.resume_block();
 234             elaborate_drops::elaborate_drop(
 235                 &mut elaborator,
 236                 source_info,
 237                 &dropee,
 238                 (),
 239                 return_block,
 240                 elaborate_drops::Unwind::To(resume_block),
 241                 START_BLOCK
 242             );
 243             elaborator.patch
 244         };
 245         patch.apply(&mut body);
 246     }
 247
 248     body
 249 }
 250
 251 pub struct DropShimElaborator<'a, 'tcx> {
 252     pub body: &'a Body<'tcx>,
 253     pub patch: MirPatch<'tcx>,
 254     pub tcx: TyCtxt<'tcx>,
 255     pub param_env: ty::ParamEnv<'tcx>,
 256 }
 257
 258 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 259     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 260         Ok(())
 261     }
 262 }
 263
 264 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 265     type Path = ();
 266
 267     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 268     fn body(&self) -> &'a Body<'tcx> { self.body }
 269     fn tcx(&self) -> TyCtxt<'tcx> {
 270         self.tcx
 271         }
 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 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 304 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 305     debug!("build_clone_shim(def_id={:?})", def_id);
 306
 307     let param_env = tcx.param_env(def_id);
 308
 309     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 310     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 311
 312     let dest = Place::RETURN_PLACE;
 313     let src = Place::from(Local::new(1+0)).deref();
 314
 315     match self_ty.sty {
 316         _ if is_copy => builder.copy_shim(),
 317         ty::Array(ty, len) => {
 318             let len = len.eval_usize(tcx, param_env);
 319             builder.array_shim(dest, src, ty, len)
 320         }
 321         ty::Closure(def_id, substs) => {
 322             builder.tuple_like_shim(
 323                 dest, src,
 324                 substs.upvar_tys(def_id, tcx)
 325             )
 326         }
 327         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 328         _ => {
 329             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 330         }
 331     };
 332
 333     builder.into_mir()
 334 }
 335
 336 struct CloneShimBuilder<'tcx> {
 337     tcx: TyCtxt<'tcx>,
 338     def_id: DefId,
 339     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 340     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 341     span: Span,
 342     sig: ty::FnSig<'tcx>,
 343 }
 344
 345 impl CloneShimBuilder<'tcx> {
 346     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 347         // we must subst the self_ty because it's
 348         // otherwise going to be TySelf and we can't index
 349         // or access fields of a Place of type TySelf.
 350         let substs = tcx.mk_substs_trait(self_ty, &[]);
 351         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 352         let sig = tcx.erase_late_bound_regions(&sig);
 353         let span = tcx.def_span(def_id);
 354
 355         CloneShimBuilder {
 356             tcx,
 357             def_id,
 358             local_decls: local_decls_for_sig(&sig, span),
 359             blocks: IndexVec::new(),
 360             span,
 361             sig,
 362         }
 363     }
 364
 365     fn into_mir(self) -> Body<'tcx> {
 366         Body::new(
 367             self.blocks,
 368             IndexVec::from_elem_n(
 369                 SourceScopeData { span: self.span, parent_scope: None }, 1
 370             ),
 371             ClearCrossCrate::Clear,
 372             IndexVec::new(),
 373             None,
 374             self.local_decls,
 375             IndexVec::new(),
 376             self.sig.inputs().len(),
 377             vec![],
 378             self.span,
 379             vec![],
 380         )
 381     }
 382
 383     fn source_info(&self) -> SourceInfo {
 384         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 385     }
 386
 387     fn block(
 388         &mut self,
 389         statements: Vec<Statement<'tcx>>,
 390         kind: TerminatorKind<'tcx>,
 391         is_cleanup: bool
 392     ) -> BasicBlock {
 393         let source_info = self.source_info();
 394         self.blocks.push(BasicBlockData {
 395             statements,
 396             terminator: Some(Terminator { source_info, kind }),
 397             is_cleanup,
 398         })
 399     }
 400
 401     /// Gives the index of an upcoming BasicBlock, with an offset.
 402     /// offset=0 will give you the index of the next BasicBlock,
 403     /// offset=1 will give the index of the next-to-next block,
 404     /// offset=-1 will give you the index of the last-created block
 405     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 406         BasicBlock::new(self.blocks.len() + offset)
 407     }
 408
 409     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 410         Statement {
 411             source_info: self.source_info(),
 412             kind,
 413         }
 414     }
 415
 416     fn copy_shim(&mut self) {
 417         let rcvr = Place::from(Local::new(1+0)).deref();
 418         let ret_statement = self.make_statement(
 419             StatementKind::Assign(
 420                 Place::RETURN_PLACE,
 421                 box Rvalue::Use(Operand::Copy(rcvr))
 422             )
 423         );
 424         self.block(vec![ret_statement], TerminatorKind::Return, false);
 425     }
 426
 427     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 428         let span = self.span;
 429         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 430     }
 431
 432     fn make_clone_call(
 433         &mut self,
 434         dest: Place<'tcx>,
 435         src: Place<'tcx>,
 436         ty: Ty<'tcx>,
 437         next: BasicBlock,
 438         cleanup: BasicBlock
 439     ) {
 440         let tcx = self.tcx;
 441
 442         let substs = tcx.mk_substs_trait(ty, &[]);
 443
 444         // `func == Clone::clone(&ty) -> ty`
 445         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 446         let func = Operand::Constant(box Constant {
 447             span: self.span,
 448             ty: func_ty,
 449             user_ty: None,
 450             literal: ty::Const::zero_sized(tcx, func_ty),
 451         });
 452
 453         let ref_loc = self.make_place(
 454             Mutability::Not,
 455             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 456                 ty,
 457                 mutbl: hir::Mutability::MutImmutable,
 458             })
 459         );
 460
 461         // `let ref_loc: &ty = &src;`
 462         let statement = self.make_statement(
 463             StatementKind::Assign(
 464                 ref_loc.clone(),
 465                 box Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 466             )
 467         );
 468
 469         // `let loc = Clone::clone(ref_loc);`
 470         self.block(vec![statement], TerminatorKind::Call {
 471             func,
 472             args: vec![Operand::Move(ref_loc)],
 473             destination: Some((dest, next)),
 474             cleanup: Some(cleanup),
 475             from_hir_call: true,
 476         }, false);
 477     }
 478
 479     fn loop_header(
 480         &mut self,
 481         beg: Place<'tcx>,
 482         end: Place<'tcx>,
 483         loop_body: BasicBlock,
 484         loop_end: BasicBlock,
 485         is_cleanup: bool
 486     ) {
 487         let tcx = self.tcx;
 488
 489         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 490         let compute_cond = self.make_statement(
 491             StatementKind::Assign(
 492                 cond.clone(),
 493                 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 494             )
 495         );
 496
 497         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 498         self.block(
 499             vec![compute_cond],
 500             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 501             is_cleanup
 502         );
 503     }
 504
 505     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 506         box Constant {
 507             span: self.span,
 508             ty: self.tcx.types.usize,
 509             user_ty: None,
 510             literal: ty::Const::from_usize(self.tcx, value),
 511         }
 512     }
 513
 514     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 515         let tcx = self.tcx;
 516         let span = self.span;
 517
 518         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 519         let end = self.make_place(Mutability::Not, tcx.types.usize);
 520
 521         // BB #0
 522         // `let mut beg = 0;`
 523         // `let end = len;`
 524         // `goto #1;`
 525         let inits = vec![
 526             self.make_statement(
 527                 StatementKind::Assign(
 528                     Place::from(beg),
 529                     box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 530                 )
 531             ),
 532             self.make_statement(
 533                 StatementKind::Assign(
 534                     end.clone(),
 535                     box Rvalue::Use(Operand::Constant(self.make_usize(len)))
 536                 )
 537             )
 538         ];
 539         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 540
 541         // BB #1: loop {
 542         //     BB #2;
 543         //     BB #3;
 544         // }
 545         // BB #4;
 546         self.loop_header(Place::from(beg),
 547                          end,
 548                          BasicBlock::new(2),
 549                          BasicBlock::new(4),
 550                          false);
 551
 552         // BB #2
 553         // `dest[i] = Clone::clone(src[beg])`;
 554         // Goto #3 if ok, #5 if unwinding happens.
 555         let dest_field = dest.clone().index(beg);
 556         let src_field = src.index(beg);
 557         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 558                              BasicBlock::new(5));
 559
 560         // BB #3
 561         // `beg = beg + 1;`
 562         // `goto #1`;
 563         let statements = vec![
 564             self.make_statement(
 565                 StatementKind::Assign(
 566                     Place::from(beg),
 567                     box Rvalue::BinaryOp(
 568                         BinOp::Add,
 569                         Operand::Copy(Place::from(beg)),
 570                         Operand::Constant(self.make_usize(1))
 571                     )
 572                 )
 573             )
 574         ];
 575         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 576
 577         // BB #4
 578         // `return dest;`
 579         self.block(vec![], TerminatorKind::Return, false);
 580
 581         // BB #5 (cleanup)
 582         // `let end = beg;`
 583         // `let mut beg = 0;`
 584         // goto #6;
 585         let end = beg;
 586         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 587         let init = self.make_statement(
 588             StatementKind::Assign(
 589                 Place::from(beg),
 590                 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 591             )
 592         );
 593         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 594
 595         // BB #6 (cleanup): loop {
 596         //     BB #7;
 597         //     BB #8;
 598         // }
 599         // BB #9;
 600         self.loop_header(Place::from(beg), Place::from(end),
 601                          BasicBlock::new(7), BasicBlock::new(9), true);
 602
 603         // BB #7 (cleanup)
 604         // `drop(dest[beg])`;
 605         self.block(vec![], TerminatorKind::Drop {
 606             location: dest.index(beg),
 607             target: BasicBlock::new(8),
 608             unwind: None,
 609         }, true);
 610
 611         // BB #8 (cleanup)
 612         // `beg = beg + 1;`
 613         // `goto #6;`
 614         let statement = self.make_statement(
 615             StatementKind::Assign(
 616                 Place::from(beg),
 617                 box Rvalue::BinaryOp(
 618                     BinOp::Add,
 619                     Operand::Copy(Place::from(beg)),
 620                     Operand::Constant(self.make_usize(1))
 621                 )
 622             )
 623         );
 624         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 625
 626         // BB #9 (resume)
 627         self.block(vec![], TerminatorKind::Resume, true);
 628     }
 629
 630     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 631                           src: Place<'tcx>, tys: I)
 632             where I: Iterator<Item = Ty<'tcx>> {
 633         let mut previous_field = None;
 634         for (i, ity) in tys.enumerate() {
 635             let field = Field::new(i);
 636             let src_field = src.clone().field(field, ity);
 637
 638             let dest_field = dest.clone().field(field, ity);
 639
 640             // #(2i + 1) is the cleanup block for the previous clone operation
 641             let cleanup_block = self.block_index_offset(1);
 642             // #(2i + 2) is the next cloning block
 643             // (or the Return terminator if this is the last block)
 644             let next_block = self.block_index_offset(2);
 645
 646             // BB #(2i)
 647             // `dest.i = Clone::clone(&src.i);`
 648             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 649             self.make_clone_call(
 650                 dest_field.clone(),
 651                 src_field,
 652                 ity,
 653                 next_block,
 654                 cleanup_block,
 655             );
 656
 657             // BB #(2i + 1) (cleanup)
 658             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 659                 // Drop previous field and goto previous cleanup block.
 660                 self.block(vec![], TerminatorKind::Drop {
 661                     location: previous_field,
 662                     target: previous_cleanup,
 663                     unwind: None,
 664                 }, true);
 665             } else {
 666                 // Nothing to drop, just resume.
 667                 self.block(vec![], TerminatorKind::Resume, true);
 668             }
 669
 670             previous_field = Some((dest_field, cleanup_block));
 671         }
 672
 673         self.block(vec![], TerminatorKind::Return, false);
 674     }
 675 }
 676
 677 /// Builds a "call" shim for `def_id`. The shim calls the
 678 /// function specified by `call_kind`, first adjusting its first
 679 /// argument according to `rcvr_adjustment`.
 680 ///
 681 /// If `untuple_args` is a vec of types, the second argument of the
 682 /// function will be untupled as these types.
 683 fn build_call_shim<'tcx>(
 684     tcx: TyCtxt<'tcx>,
 685     def_id: DefId,
 686     rcvr_adjustment: Adjustment,
 687     call_kind: CallKind,
 688     untuple_args: Option<&[Ty<'tcx>]>,
 689 ) -> Body<'tcx> {
 690     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 691             call_kind={:?}, untuple_args={:?})",
 692            def_id, rcvr_adjustment, call_kind, untuple_args);
 693
 694     let sig = tcx.fn_sig(def_id);
 695     let sig = tcx.erase_late_bound_regions(&sig);
 696     let span = tcx.def_span(def_id);
 697
 698     debug!("build_call_shim: sig={:?}", sig);
 699
 700     let mut local_decls = local_decls_for_sig(&sig, span);
 701     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 702
 703     let rcvr_arg = Local::new(1+0);
 704     let rcvr_l = Place::from(rcvr_arg);
 705     let mut statements = vec![];
 706
 707     let rcvr = match rcvr_adjustment {
 708         Adjustment::Identity => Operand::Move(rcvr_l),
 709         Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
 710         Adjustment::DerefMove => {
 711             // fn(Self, ...) -> fn(*mut Self, ...)
 712             let arg_ty = local_decls[rcvr_arg].ty;
 713             assert!(arg_ty.is_self());
 714             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 715
 716             Operand::Move(rcvr_l.deref())
 717         }
 718         Adjustment::RefMut => {
 719             // let rcvr = &mut rcvr;
 720             let ref_rcvr = local_decls.push(temp_decl(
 721                 Mutability::Not,
 722                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 723                     ty: sig.inputs()[0],
 724                     mutbl: hir::Mutability::MutMutable
 725                 }),
 726                 span
 727             ));
 728             let borrow_kind = BorrowKind::Mut {
 729                 allow_two_phase_borrow: false,
 730             };
 731             statements.push(Statement {
 732                 source_info,
 733                 kind: StatementKind::Assign(
 734                     Place::from(ref_rcvr),
 735                     box Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 736                 )
 737             });
 738             Operand::Move(Place::from(ref_rcvr))
 739         }
 740     };
 741
 742     let (callee, mut args) = match call_kind {
 743         CallKind::Indirect => (rcvr, vec![]),
 744         CallKind::Direct(def_id) => {
 745             let ty = tcx.type_of(def_id);
 746             (Operand::Constant(box Constant {
 747                 span,
 748                 ty,
 749                 user_ty: None,
 750                 literal: ty::Const::zero_sized(tcx, ty),
 751              }),
 752              vec![rcvr])
 753         }
 754     };
 755
 756     if let Some(untuple_args) = untuple_args {
 757         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 758             let arg_place = Place::from(Local::new(1+1));
 759             Operand::Move(arg_place.field(Field::new(i), *ity))
 760         }));
 761     } else {
 762         args.extend((1..sig.inputs().len()).map(|i| {
 763             Operand::Move(Place::from(Local::new(1+i)))
 764         }));
 765     }
 766
 767     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 768     let mut blocks = IndexVec::with_capacity(n_blocks);
 769     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 770         blocks.push(BasicBlockData {
 771             statements,
 772             terminator: Some(Terminator { source_info, kind }),
 773             is_cleanup
 774         })
 775     };
 776
 777     // BB #0
 778     block(&mut blocks, statements, TerminatorKind::Call {
 779         func: callee,
 780         args,
 781         destination: Some((Place::RETURN_PLACE,
 782                            BasicBlock::new(1))),
 783         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 784             Some(BasicBlock::new(3))
 785         } else {
 786             None
 787         },
 788         from_hir_call: true,
 789     }, false);
 790
 791     if let Adjustment::RefMut = rcvr_adjustment {
 792         // BB #1 - drop for Self
 793         block(&mut blocks, vec![], TerminatorKind::Drop {
 794             location: Place::from(rcvr_arg),
 795             target: BasicBlock::new(2),
 796             unwind: None
 797         }, false);
 798     }
 799     // BB #1/#2 - return
 800     block(&mut blocks, vec![], TerminatorKind::Return, false);
 801     if let Adjustment::RefMut = rcvr_adjustment {
 802         // BB #3 - drop if closure panics
 803         block(&mut blocks, vec![], TerminatorKind::Drop {
 804             location: Place::from(rcvr_arg),
 805             target: BasicBlock::new(4),
 806             unwind: None
 807         }, true);
 808
 809         // BB #4 - resume
 810         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 811     }
 812
 813     let mut body = Body::new(
 814         blocks,
 815         IndexVec::from_elem_n(
 816             SourceScopeData { span: span, parent_scope: None }, 1
 817         ),
 818         ClearCrossCrate::Clear,
 819         IndexVec::new(),
 820         None,
 821         local_decls,
 822         IndexVec::new(),
 823         sig.inputs().len(),
 824         vec![],
 825         span,
 826         vec![],
 827     );
 828     if let Abi::RustCall = sig.abi {
 829         body.spread_arg = Some(Local::new(sig.inputs().len()));
 830     }
 831     body
 832 }
 833
 834 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &Body<'_> {
 835     debug_assert!(tcx.is_constructor(ctor_id));
 836
 837     let span = tcx.hir().span_if_local(ctor_id)
 838         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 839
 840     let param_env = tcx.param_env(ctor_id);
 841
 842     // Normalize the sig.
 843     let sig = tcx.fn_sig(ctor_id)
 844         .no_bound_vars()
 845         .expect("LBR in ADT constructor signature");
 846     let sig = tcx.normalize_erasing_regions(param_env, sig);
 847
 848     let (adt_def, substs) = match sig.output().sty {
 849         ty::Adt(adt_def, substs) => (adt_def, substs),
 850         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 851     };
 852
 853     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 854
 855     let local_decls = local_decls_for_sig(&sig, span);
 856
 857     let source_info = SourceInfo {
 858         span,
 859         scope: OUTERMOST_SOURCE_SCOPE
 860     };
 861
 862     let variant_index = if adt_def.is_enum() {
 863         adt_def.variant_index_with_ctor_id(ctor_id)
 864     } else {
 865         VariantIdx::new(0)
 866     };
 867
 868     // Generate the following MIR:
 869     //
 870     // (return as Variant).field0 = arg0;
 871     // (return as Variant).field1 = arg1;
 872     //
 873     // return;
 874     debug!("build_ctor: variant_index={:?}", variant_index);
 875
 876     let statements = expand_aggregate(
 877         Place::RETURN_PLACE,
 878         adt_def
 879             .variants[variant_index]
 880             .fields
 881             .iter()
 882             .enumerate()
 883             .map(|(idx, field_def)| (
 884                 Operand::Move(Place::from(Local::new(idx + 1))),
 885                 field_def.ty(tcx, substs),
 886             )),
 887         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 888         source_info,
 889     ).collect();
 890
 891     let start_block = BasicBlockData {
 892         statements,
 893         terminator: Some(Terminator {
 894             source_info,
 895             kind: TerminatorKind::Return,
 896         }),
 897         is_cleanup: false
 898     };
 899
 900     let body = Body::new(
 901         IndexVec::from_elem_n(start_block, 1),
 902         IndexVec::from_elem_n(
 903             SourceScopeData { span: span, parent_scope: None }, 1
 904         ),
 905         ClearCrossCrate::Clear,
 906         IndexVec::new(),
 907         None,
 908         local_decls,
 909         IndexVec::new(),
 910         sig.inputs().len(),
 911         vec![],
 912         span,
 913         vec![],
 914     );
 915
 916     crate::util::dump_mir(
 917         tcx,
 918         None,
 919         "mir_map",
 920         &0,
 921         crate::transform::MirSource::item(ctor_id),
 922         &body,
 923         |_, _| Ok(()),
 924     );
 925
 926     tcx.arena.alloc(body)
 927 }