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         name: None,
 152         source_info,
 153         visibility_scope: source_info.scope,
 154         internal: false,
 155         local_info: LocalInfo::Other,
 156         is_block_tail: None,
 157     }
 158 }
 159
 160 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 161     -> IndexVec<Local, LocalDecl<'tcx>>
 162 {
 163     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 164         .chain(sig.inputs().iter().map(
 165             |ity| temp_decl(Mutability::Not, ity, span)))
 166         .collect()
 167 }
 168
 169 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 170     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 171
 172     // Check if this is a generator, if so, return the drop glue for it
 173     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 174         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 175         return body.subst(tcx, substs);
 176     }
 177
 178     let substs = if let Some(ty) = ty {
 179         tcx.intern_substs(&[ty.into()])
 180     } else {
 181         InternalSubsts::identity_for_item(tcx, def_id)
 182     };
 183     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 184     let sig = tcx.erase_late_bound_regions(&sig);
 185     let span = tcx.def_span(def_id);
 186
 187     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 188
 189     let return_block = BasicBlock::new(1);
 190     let mut blocks = IndexVec::with_capacity(2);
 191     let block = |blocks: &mut IndexVec<_, _>, kind| {
 192         blocks.push(BasicBlockData {
 193             statements: vec![],
 194             terminator: Some(Terminator { source_info, kind }),
 195             is_cleanup: false
 196         })
 197     };
 198     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 199     block(&mut blocks, TerminatorKind::Return);
 200
 201     let mut body = Body::new(
 202         blocks,
 203         IndexVec::from_elem_n(
 204             SourceScopeData { span: span, parent_scope: None }, 1
 205         ),
 206         ClearCrossCrate::Clear,
 207         None,
 208         local_decls_for_sig(&sig, span),
 209         IndexVec::new(),
 210         sig.inputs().len(),
 211         vec![],
 212         span,
 213         vec![],
 214     );
 215
 216     if let Some(..) = ty {
 217         // The first argument (index 0), but add 1 for the return value.
 218         let dropee_ptr = Place::from(Local::new(1+0));
 219         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 220             // Function arguments should be retagged, and we make this one raw.
 221             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 222                 source_info,
 223                 kind: StatementKind::Retag(RetagKind::Raw, box(dropee_ptr.clone())),
 224             });
 225         }
 226         let patch = {
 227             let param_env = tcx.param_env(def_id).with_reveal_all();
 228             let mut elaborator = DropShimElaborator {
 229                 body: &body,
 230                 patch: MirPatch::new(&body),
 231                 tcx,
 232                 param_env
 233             };
 234             let dropee = tcx.mk_place_deref(dropee_ptr);
 235             let resume_block = elaborator.patch.resume_block();
 236             elaborate_drops::elaborate_drop(
 237                 &mut elaborator,
 238                 source_info,
 239                 &dropee,
 240                 (),
 241                 return_block,
 242                 elaborate_drops::Unwind::To(resume_block),
 243                 START_BLOCK
 244             );
 245             elaborator.patch
 246         };
 247         patch.apply(&mut body);
 248     }
 249
 250     body
 251 }
 252
 253 pub struct DropShimElaborator<'a, 'tcx> {
 254     pub body: &'a Body<'tcx>,
 255     pub patch: MirPatch<'tcx>,
 256     pub tcx: TyCtxt<'tcx>,
 257     pub param_env: ty::ParamEnv<'tcx>,
 258 }
 259
 260 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 261     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 262         Ok(())
 263     }
 264 }
 265
 266 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 267     type Path = ();
 268
 269     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 270     fn body(&self) -> &'a Body<'tcx> { self.body }
 271     fn tcx(&self) -> TyCtxt<'tcx> {
 272         self.tcx
 273         }
 274     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 275
 276     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 277         if let DropFlagMode::Shallow = mode {
 278             DropStyle::Static
 279         } else {
 280             DropStyle::Open
 281         }
 282     }
 283
 284     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 285         None
 286     }
 287
 288     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 289     }
 290
 291     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 292         None
 293     }
 294     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 295         None
 296     }
 297     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 298         Some(())
 299     }
 300     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 301         None
 302     }
 303 }
 304
 305 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 306 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 307     debug!("build_clone_shim(def_id={:?})", def_id);
 308
 309     let param_env = tcx.param_env(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, param_env, builder.span);
 313
 314     let dest = Place::return_place();
 315     let src = tcx.mk_place_deref(Place::from(Local::new(1+0)));
 316
 317     match self_ty.kind {
 318         _ if is_copy => builder.copy_shim(),
 319         ty::Array(ty, len) => {
 320             let len = len.eval_usize(tcx, param_env);
 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.as_closure().upvar_tys(def_id, tcx)
 327             )
 328         }
 329         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 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>,
 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>, 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             None,
 375             self.local_decls,
 376             IndexVec::new(),
 377             self.sig.inputs().len(),
 378             vec![],
 379             self.span,
 380             vec![],
 381         )
 382     }
 383
 384     fn source_info(&self) -> SourceInfo {
 385         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 386     }
 387
 388     fn block(
 389         &mut self,
 390         statements: Vec<Statement<'tcx>>,
 391         kind: TerminatorKind<'tcx>,
 392         is_cleanup: bool
 393     ) -> BasicBlock {
 394         let source_info = self.source_info();
 395         self.blocks.push(BasicBlockData {
 396             statements,
 397             terminator: Some(Terminator { source_info, kind }),
 398             is_cleanup,
 399         })
 400     }
 401
 402     /// Gives the index of an upcoming BasicBlock, with an offset.
 403     /// offset=0 will give you the index of the next BasicBlock,
 404     /// offset=1 will give the index of the next-to-next block,
 405     /// offset=-1 will give you the index of the last-created block
 406     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 407         BasicBlock::new(self.blocks.len() + offset)
 408     }
 409
 410     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 411         Statement {
 412             source_info: self.source_info(),
 413             kind,
 414         }
 415     }
 416
 417     fn copy_shim(&mut self) {
 418         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1+0)));
 419         let ret_statement = self.make_statement(
 420             StatementKind::Assign(
 421                 box(
 422                     Place::return_place(),
 423                     Rvalue::Use(Operand::Copy(rcvr))
 424                 )
 425             )
 426         );
 427         self.block(vec![ret_statement], TerminatorKind::Return, false);
 428     }
 429
 430     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 431         let span = self.span;
 432         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 433     }
 434
 435     fn make_clone_call(
 436         &mut self,
 437         dest: Place<'tcx>,
 438         src: Place<'tcx>,
 439         ty: Ty<'tcx>,
 440         next: BasicBlock,
 441         cleanup: BasicBlock
 442     ) {
 443         let tcx = self.tcx;
 444
 445         let substs = tcx.mk_substs_trait(ty, &[]);
 446
 447         // `func == Clone::clone(&ty) -> ty`
 448         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 449         let func = Operand::Constant(box Constant {
 450             span: self.span,
 451             user_ty: None,
 452             literal: ty::Const::zero_sized(tcx, func_ty),
 453         });
 454
 455         let ref_loc = self.make_place(
 456             Mutability::Not,
 457             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 458                 ty,
 459                 mutbl: hir::Mutability::Immutable,
 460             })
 461         );
 462
 463         // `let ref_loc: &ty = &src;`
 464         let statement = self.make_statement(
 465             StatementKind::Assign(
 466                 box(
 467                     ref_loc.clone(),
 468                     Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 469                 )
 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                 box(
 497                     cond.clone(),
 498                     Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 499                 )
 500             )
 501         );
 502
 503         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 504         self.block(
 505             vec![compute_cond],
 506             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 507             is_cleanup
 508         );
 509     }
 510
 511     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 512         box Constant {
 513             span: self.span,
 514             user_ty: None,
 515             literal: ty::Const::from_usize(self.tcx, value),
 516         }
 517     }
 518
 519     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 520         let tcx = self.tcx;
 521         let span = self.span;
 522
 523         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 524         let end = self.make_place(Mutability::Not, tcx.types.usize);
 525
 526         // BB #0
 527         // `let mut beg = 0;`
 528         // `let end = len;`
 529         // `goto #1;`
 530         let inits = vec![
 531             self.make_statement(
 532                 StatementKind::Assign(
 533                     box(
 534                         Place::from(beg),
 535                         Rvalue::Use(Operand::Constant(self.make_usize(0)))
 536                     )
 537                 )
 538             ),
 539             self.make_statement(
 540                 StatementKind::Assign(
 541                     box(
 542                         end.clone(),
 543                         Rvalue::Use(Operand::Constant(self.make_usize(len)))
 544                     )
 545                 )
 546             )
 547         ];
 548         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 549
 550         // BB #1: loop {
 551         //     BB #2;
 552         //     BB #3;
 553         // }
 554         // BB #4;
 555         self.loop_header(Place::from(beg),
 556                          end,
 557                          BasicBlock::new(2),
 558                          BasicBlock::new(4),
 559                          false);
 560
 561         // BB #2
 562         // `dest[i] = Clone::clone(src[beg])`;
 563         // Goto #3 if ok, #5 if unwinding happens.
 564         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 565         let src_field = self.tcx.mk_place_index(src, beg);
 566         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 567                              BasicBlock::new(5));
 568
 569         // BB #3
 570         // `beg = beg + 1;`
 571         // `goto #1`;
 572         let statements = vec![
 573             self.make_statement(
 574                 StatementKind::Assign(
 575                     box(
 576                         Place::from(beg),
 577                         Rvalue::BinaryOp(
 578                             BinOp::Add,
 579                             Operand::Copy(Place::from(beg)),
 580                             Operand::Constant(self.make_usize(1))
 581                         )
 582                     )
 583                 )
 584             )
 585         ];
 586         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 587
 588         // BB #4
 589         // `return dest;`
 590         self.block(vec![], TerminatorKind::Return, false);
 591
 592         // BB #5 (cleanup)
 593         // `let end = beg;`
 594         // `let mut beg = 0;`
 595         // goto #6;
 596         let end = beg;
 597         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 598         let init = self.make_statement(
 599             StatementKind::Assign(
 600                 box(
 601                     Place::from(beg),
 602                     Rvalue::Use(Operand::Constant(self.make_usize(0)))
 603                 )
 604             )
 605         );
 606         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 607
 608         // BB #6 (cleanup): loop {
 609         //     BB #7;
 610         //     BB #8;
 611         // }
 612         // BB #9;
 613         self.loop_header(Place::from(beg), Place::from(end),
 614                          BasicBlock::new(7), BasicBlock::new(9), true);
 615
 616         // BB #7 (cleanup)
 617         // `drop(dest[beg])`;
 618         self.block(vec![], TerminatorKind::Drop {
 619             location: self.tcx.mk_place_index(dest, beg),
 620             target: BasicBlock::new(8),
 621             unwind: None,
 622         }, true);
 623
 624         // BB #8 (cleanup)
 625         // `beg = beg + 1;`
 626         // `goto #6;`
 627         let statement = self.make_statement(
 628             StatementKind::Assign(
 629                 box(
 630                     Place::from(beg),
 631                     Rvalue::BinaryOp(
 632                         BinOp::Add,
 633                         Operand::Copy(Place::from(beg)),
 634                         Operand::Constant(self.make_usize(1))
 635                     )
 636                 )
 637             )
 638         );
 639         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 640
 641         // BB #9 (resume)
 642         self.block(vec![], TerminatorKind::Resume, true);
 643     }
 644
 645     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 646                           src: Place<'tcx>, tys: I)
 647             where I: Iterator<Item = Ty<'tcx>> {
 648         let mut previous_field = None;
 649         for (i, ity) in tys.enumerate() {
 650             let field = Field::new(i);
 651             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 652
 653             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 654
 655             // #(2i + 1) is the cleanup block for the previous clone operation
 656             let cleanup_block = self.block_index_offset(1);
 657             // #(2i + 2) is the next cloning block
 658             // (or the Return terminator if this is the last block)
 659             let next_block = self.block_index_offset(2);
 660
 661             // BB #(2i)
 662             // `dest.i = Clone::clone(&src.i);`
 663             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 664             self.make_clone_call(
 665                 dest_field.clone(),
 666                 src_field,
 667                 ity,
 668                 next_block,
 669                 cleanup_block,
 670             );
 671
 672             // BB #(2i + 1) (cleanup)
 673             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 674                 // Drop previous field and goto previous cleanup block.
 675                 self.block(vec![], TerminatorKind::Drop {
 676                     location: previous_field,
 677                     target: previous_cleanup,
 678                     unwind: None,
 679                 }, true);
 680             } else {
 681                 // Nothing to drop, just resume.
 682                 self.block(vec![], TerminatorKind::Resume, true);
 683             }
 684
 685             previous_field = Some((dest_field, cleanup_block));
 686         }
 687
 688         self.block(vec![], TerminatorKind::Return, false);
 689     }
 690 }
 691
 692 /// Builds a "call" shim for `def_id`. The shim calls the
 693 /// function specified by `call_kind`, first adjusting its first
 694 /// argument according to `rcvr_adjustment`.
 695 ///
 696 /// If `untuple_args` is a vec of types, the second argument of the
 697 /// function will be untupled as these types.
 698 fn build_call_shim<'tcx>(
 699     tcx: TyCtxt<'tcx>,
 700     def_id: DefId,
 701     rcvr_adjustment: Adjustment,
 702     call_kind: CallKind,
 703     untuple_args: Option<&[Ty<'tcx>]>,
 704 ) -> Body<'tcx> {
 705     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 706             call_kind={:?}, untuple_args={:?})",
 707            def_id, rcvr_adjustment, call_kind, untuple_args);
 708
 709     let sig = tcx.fn_sig(def_id);
 710     let sig = tcx.erase_late_bound_regions(&sig);
 711     let span = tcx.def_span(def_id);
 712
 713     debug!("build_call_shim: sig={:?}", sig);
 714
 715     let mut local_decls = local_decls_for_sig(&sig, span);
 716     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 717
 718     let rcvr_arg = Local::new(1+0);
 719     let rcvr_l = Place::from(rcvr_arg);
 720     let mut statements = vec![];
 721
 722     let rcvr = match rcvr_adjustment {
 723         Adjustment::Identity => Operand::Move(rcvr_l),
 724         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_l)),
 725         Adjustment::DerefMove => {
 726             // fn(Self, ...) -> fn(*mut Self, ...)
 727             let arg_ty = local_decls[rcvr_arg].ty;
 728             debug_assert!(tcx.generics_of(def_id).has_self && arg_ty == tcx.types.self_param);
 729             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 730
 731             Operand::Move(tcx.mk_place_deref(rcvr_l))
 732         }
 733         Adjustment::RefMut => {
 734             // let rcvr = &mut rcvr;
 735             let ref_rcvr = local_decls.push(temp_decl(
 736                 Mutability::Not,
 737                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 738                     ty: sig.inputs()[0],
 739                     mutbl: hir::Mutability::Mutable
 740                 }),
 741                 span
 742             ));
 743             let borrow_kind = BorrowKind::Mut {
 744                 allow_two_phase_borrow: false,
 745             };
 746             statements.push(Statement {
 747                 source_info,
 748                 kind: StatementKind::Assign(
 749                     box(
 750                         Place::from(ref_rcvr),
 751                         Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 752                     )
 753                 )
 754             });
 755             Operand::Move(Place::from(ref_rcvr))
 756         }
 757     };
 758
 759     let (callee, mut args) = match call_kind {
 760         CallKind::Indirect => (rcvr, vec![]),
 761         CallKind::Direct(def_id) => {
 762             let ty = tcx.type_of(def_id);
 763             (Operand::Constant(box Constant {
 764                 span,
 765                 user_ty: None,
 766                 literal: ty::Const::zero_sized(tcx, ty),
 767              }),
 768              vec![rcvr])
 769         }
 770     };
 771
 772     if let Some(untuple_args) = untuple_args {
 773         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 774             let arg_place = Place::from(Local::new(1+1));
 775             Operand::Move(tcx.mk_place_field(arg_place, Field::new(i), *ity))
 776         }));
 777     } else {
 778         args.extend((1..sig.inputs().len()).map(|i| {
 779             Operand::Move(Place::from(Local::new(1+i)))
 780         }));
 781     }
 782
 783     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 784     let mut blocks = IndexVec::with_capacity(n_blocks);
 785     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 786         blocks.push(BasicBlockData {
 787             statements,
 788             terminator: Some(Terminator { source_info, kind }),
 789             is_cleanup
 790         })
 791     };
 792
 793     // BB #0
 794     block(&mut blocks, statements, TerminatorKind::Call {
 795         func: callee,
 796         args,
 797         destination: Some((Place::return_place(),
 798                            BasicBlock::new(1))),
 799         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 800             Some(BasicBlock::new(3))
 801         } else {
 802             None
 803         },
 804         from_hir_call: true,
 805     }, false);
 806
 807     if let Adjustment::RefMut = rcvr_adjustment {
 808         // BB #1 - drop for Self
 809         block(&mut blocks, vec![], TerminatorKind::Drop {
 810             location: Place::from(rcvr_arg),
 811             target: BasicBlock::new(2),
 812             unwind: None
 813         }, false);
 814     }
 815     // BB #1/#2 - return
 816     block(&mut blocks, vec![], TerminatorKind::Return, false);
 817     if let Adjustment::RefMut = rcvr_adjustment {
 818         // BB #3 - drop if closure panics
 819         block(&mut blocks, vec![], TerminatorKind::Drop {
 820             location: Place::from(rcvr_arg),
 821             target: BasicBlock::new(4),
 822             unwind: None
 823         }, true);
 824
 825         // BB #4 - resume
 826         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 827     }
 828
 829     let mut body = Body::new(
 830         blocks,
 831         IndexVec::from_elem_n(
 832             SourceScopeData { span: span, parent_scope: None }, 1
 833         ),
 834         ClearCrossCrate::Clear,
 835         None,
 836         local_decls,
 837         IndexVec::new(),
 838         sig.inputs().len(),
 839         vec![],
 840         span,
 841         vec![],
 842     );
 843     if let Abi::RustCall = sig.abi {
 844         body.spread_arg = Some(Local::new(sig.inputs().len()));
 845     }
 846     body
 847 }
 848
 849 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &Body<'_> {
 850     debug_assert!(tcx.is_constructor(ctor_id));
 851
 852     let span = tcx.hir().span_if_local(ctor_id)
 853         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 854
 855     let param_env = tcx.param_env(ctor_id);
 856
 857     // Normalize the sig.
 858     let sig = tcx.fn_sig(ctor_id)
 859         .no_bound_vars()
 860         .expect("LBR in ADT constructor signature");
 861     let sig = tcx.normalize_erasing_regions(param_env, sig);
 862
 863     let (adt_def, substs) = match sig.output().kind {
 864         ty::Adt(adt_def, substs) => (adt_def, substs),
 865         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 866     };
 867
 868     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 869
 870     let local_decls = local_decls_for_sig(&sig, span);
 871
 872     let source_info = SourceInfo {
 873         span,
 874         scope: OUTERMOST_SOURCE_SCOPE
 875     };
 876
 877     let variant_index = if adt_def.is_enum() {
 878         adt_def.variant_index_with_ctor_id(ctor_id)
 879     } else {
 880         VariantIdx::new(0)
 881     };
 882
 883     // Generate the following MIR:
 884     //
 885     // (return as Variant).field0 = arg0;
 886     // (return as Variant).field1 = arg1;
 887     //
 888     // return;
 889     debug!("build_ctor: variant_index={:?}", variant_index);
 890
 891     let statements = expand_aggregate(
 892         Place::return_place(),
 893         adt_def
 894             .variants[variant_index]
 895             .fields
 896             .iter()
 897             .enumerate()
 898             .map(|(idx, field_def)| (
 899                 Operand::Move(Place::from(Local::new(idx + 1))),
 900                 field_def.ty(tcx, substs),
 901             )),
 902         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 903         source_info,
 904         tcx,
 905     ).collect();
 906
 907     let start_block = BasicBlockData {
 908         statements,
 909         terminator: Some(Terminator {
 910             source_info,
 911             kind: TerminatorKind::Return,
 912         }),
 913         is_cleanup: false
 914     };
 915
 916     let body = Body::new(
 917         IndexVec::from_elem_n(start_block, 1),
 918         IndexVec::from_elem_n(
 919             SourceScopeData { span: span, parent_scope: None }, 1
 920         ),
 921         ClearCrossCrate::Clear,
 922         None,
 923         local_decls,
 924         IndexVec::new(),
 925         sig.inputs().len(),
 926         vec![],
 927         span,
 928         vec![],
 929     );
 930
 931     crate::util::dump_mir(
 932         tcx,
 933         None,
 934         "mir_map",
 935         &0,
 936         crate::transform::MirSource::item(ctor_id),
 937         &body,
 938         |_, _| Ok(()),
 939     );
 940
 941     tcx.arena.alloc(body)
 942 }