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