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 BodyAndCache<'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                 instance,
  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                 instance,
  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 call, be it
  71         // a virtual call, or a direct call to a function for which
  72         // indirect calls must be codegen'd differently than direct ones
  73         // (such as `#[track_caller]`).
  74         ty::InstanceDef::ReifyShim(def_id) => {
  75             build_call_shim(
  76                 tcx,
  77                 instance,
  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                 instance,
  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::Virtual(..) => {
 113             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
 114         }
 115         ty::InstanceDef::Intrinsic(_) => {
 116             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 117         }
 118     };
 119     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 120
 121     run_passes(tcx, &mut result, instance, None, MirPhase::Const, &[
 122         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 123         &no_landing_pads::NoLandingPads::new(tcx),
 124         &remove_noop_landing_pads::RemoveNoopLandingPads,
 125         &simplify::SimplifyCfg::new("make_shim"),
 126         &add_call_guards::CriticalCallEdges,
 127     ]);
 128
 129     debug!("make_shim({:?}) = {:?}", instance, result);
 130
 131     result.ensure_predecessors();
 132     tcx.arena.alloc(result)
 133 }
 134
 135 #[derive(Copy, Clone, Debug, PartialEq)]
 136 enum Adjustment {
 137     Identity,
 138     Deref,
 139     DerefMove,
 140     RefMut,
 141 }
 142
 143 #[derive(Copy, Clone, Debug, PartialEq)]
 144 enum CallKind {
 145     Indirect,
 146     Direct(DefId),
 147 }
 148
 149 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 150     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 151     LocalDecl {
 152         mutability,
 153         ty,
 154         user_ty: UserTypeProjections::none(),
 155         source_info,
 156         internal: false,
 157         local_info: LocalInfo::Other,
 158         is_block_tail: None,
 159     }
 160 }
 161
 162 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 163     -> IndexVec<Local, LocalDecl<'tcx>>
 164 {
 165     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 166         .chain(sig.inputs().iter().map(
 167             |ity| temp_decl(Mutability::Not, ity, span)))
 168         .collect()
 169 }
 170
 171 fn build_drop_shim<'tcx>(
 172     tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>
 173 ) -> BodyAndCache<'tcx> {
 174     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 175
 176     // Check if this is a generator, if so, return the drop glue for it
 177     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 178         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 179         return body.subst(tcx, substs);
 180     }
 181
 182     let substs = if let Some(ty) = ty {
 183         tcx.intern_substs(&[ty.into()])
 184     } else {
 185         InternalSubsts::identity_for_item(tcx, def_id)
 186     };
 187     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 188     let sig = tcx.erase_late_bound_regions(&sig);
 189     let span = tcx.def_span(def_id);
 190
 191     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 192
 193     let return_block = BasicBlock::new(1);
 194     let mut blocks = IndexVec::with_capacity(2);
 195     let block = |blocks: &mut IndexVec<_, _>, kind| {
 196         blocks.push(BasicBlockData {
 197             statements: vec![],
 198             terminator: Some(Terminator { source_info, kind }),
 199             is_cleanup: false
 200         })
 201     };
 202     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 203     block(&mut blocks, TerminatorKind::Return);
 204
 205     let body = new_body(
 206         blocks,
 207         local_decls_for_sig(&sig, span),
 208         sig.inputs().len(),
 209         span);
 210
 211     let mut body = BodyAndCache::new(body);
 212
 213     if let Some(..) = ty {
 214         // The first argument (index 0), but add 1 for the return value.
 215         let dropee_ptr = Place::from(Local::new(1+0));
 216         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 217             // Function arguments should be retagged, and we make this one raw.
 218             body.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 219                 source_info,
 220                 kind: StatementKind::Retag(RetagKind::Raw, box(dropee_ptr.clone())),
 221             });
 222         }
 223         let patch = {
 224             let param_env = tcx.param_env(def_id).with_reveal_all();
 225             let mut elaborator = DropShimElaborator {
 226                 body: &body,
 227                 patch: MirPatch::new(&body),
 228                 tcx,
 229                 param_env
 230             };
 231             let dropee = tcx.mk_place_deref(dropee_ptr);
 232             let resume_block = elaborator.patch.resume_block();
 233             elaborate_drops::elaborate_drop(
 234                 &mut elaborator,
 235                 source_info,
 236                 &dropee,
 237                 (),
 238                 return_block,
 239                 elaborate_drops::Unwind::To(resume_block),
 240                 START_BLOCK
 241             );
 242             elaborator.patch
 243         };
 244         patch.apply(&mut body);
 245     }
 246
 247     body
 248 }
 249
 250 fn new_body<'tcx>(
 251     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 252     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 253     arg_count: usize,
 254     span: Span,
 255 ) -> Body<'tcx> {
 256     Body::new(
 257         basic_blocks,
 258         IndexVec::from_elem_n(
 259             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 260             1,
 261         ),
 262         local_decls,
 263         IndexVec::new(),
 264         arg_count,
 265         vec![],
 266         span,
 267         vec![],
 268         None,
 269     )
 270 }
 271
 272 pub struct DropShimElaborator<'a, 'tcx> {
 273     pub body: &'a Body<'tcx>,
 274     pub patch: MirPatch<'tcx>,
 275     pub tcx: TyCtxt<'tcx>,
 276     pub param_env: ty::ParamEnv<'tcx>,
 277 }
 278
 279 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 280     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 281         Ok(())
 282     }
 283 }
 284
 285 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 286     type Path = ();
 287
 288     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 289     fn body(&self) -> &'a Body<'tcx> { self.body }
 290     fn tcx(&self) -> TyCtxt<'tcx> {
 291         self.tcx
 292         }
 293     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 294
 295     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 296         if let DropFlagMode::Shallow = mode {
 297             DropStyle::Static
 298         } else {
 299             DropStyle::Open
 300         }
 301     }
 302
 303     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 304         None
 305     }
 306
 307     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 308     }
 309
 310     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 311         None
 312     }
 313     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 314         None
 315     }
 316     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 317         Some(())
 318     }
 319     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 320         None
 321     }
 322 }
 323
 324 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 325 fn build_clone_shim<'tcx>(
 326     tcx: TyCtxt<'tcx>,
 327     def_id: DefId,
 328     self_ty: Ty<'tcx>,
 329 ) -> BodyAndCache<'tcx> {
 330     debug!("build_clone_shim(def_id={:?})", def_id);
 331
 332     let param_env = tcx.param_env(def_id);
 333
 334     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 335     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 336
 337     let dest = Place::return_place();
 338     let src = tcx.mk_place_deref(Place::from(Local::new(1+0)));
 339
 340     match self_ty.kind {
 341         _ if is_copy => builder.copy_shim(),
 342         ty::Array(ty, len) => {
 343             let len = len.eval_usize(tcx, param_env);
 344             builder.array_shim(dest, src, ty, len)
 345         }
 346         ty::Closure(def_id, substs) => {
 347             builder.tuple_like_shim(
 348                 dest, src,
 349                 substs.as_closure().upvar_tys(def_id, tcx)
 350             )
 351         }
 352         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 353         _ => {
 354             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 355         }
 356     };
 357
 358     BodyAndCache::new(builder.into_mir())
 359 }
 360
 361 struct CloneShimBuilder<'tcx> {
 362     tcx: TyCtxt<'tcx>,
 363     def_id: DefId,
 364     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 365     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 366     span: Span,
 367     sig: ty::FnSig<'tcx>,
 368 }
 369
 370 impl CloneShimBuilder<'tcx> {
 371     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 372         // we must subst the self_ty because it's
 373         // otherwise going to be TySelf and we can't index
 374         // or access fields of a Place of type TySelf.
 375         let substs = tcx.mk_substs_trait(self_ty, &[]);
 376         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 377         let sig = tcx.erase_late_bound_regions(&sig);
 378         let span = tcx.def_span(def_id);
 379
 380         CloneShimBuilder {
 381             tcx,
 382             def_id,
 383             local_decls: local_decls_for_sig(&sig, span),
 384             blocks: IndexVec::new(),
 385             span,
 386             sig,
 387         }
 388     }
 389
 390     fn into_mir(self) -> Body<'tcx> {
 391         new_body(
 392             self.blocks,
 393             self.local_decls,
 394             self.sig.inputs().len(),
 395             self.span,
 396         )
 397     }
 398
 399     fn source_info(&self) -> SourceInfo {
 400         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 401     }
 402
 403     fn block(
 404         &mut self,
 405         statements: Vec<Statement<'tcx>>,
 406         kind: TerminatorKind<'tcx>,
 407         is_cleanup: bool
 408     ) -> BasicBlock {
 409         let source_info = self.source_info();
 410         self.blocks.push(BasicBlockData {
 411             statements,
 412             terminator: Some(Terminator { source_info, kind }),
 413             is_cleanup,
 414         })
 415     }
 416
 417     /// Gives the index of an upcoming BasicBlock, with an offset.
 418     /// offset=0 will give you the index of the next BasicBlock,
 419     /// offset=1 will give the index of the next-to-next block,
 420     /// offset=-1 will give you the index of the last-created block
 421     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 422         BasicBlock::new(self.blocks.len() + offset)
 423     }
 424
 425     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 426         Statement {
 427             source_info: self.source_info(),
 428             kind,
 429         }
 430     }
 431
 432     fn copy_shim(&mut self) {
 433         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1+0)));
 434         let ret_statement = self.make_statement(
 435             StatementKind::Assign(
 436                 box(
 437                     Place::return_place(),
 438                     Rvalue::Use(Operand::Copy(rcvr))
 439                 )
 440             )
 441         );
 442         self.block(vec![ret_statement], TerminatorKind::Return, false);
 443     }
 444
 445     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 446         let span = self.span;
 447         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 448     }
 449
 450     fn make_clone_call(
 451         &mut self,
 452         dest: Place<'tcx>,
 453         src: Place<'tcx>,
 454         ty: Ty<'tcx>,
 455         next: BasicBlock,
 456         cleanup: BasicBlock
 457     ) {
 458         let tcx = self.tcx;
 459
 460         let substs = tcx.mk_substs_trait(ty, &[]);
 461
 462         // `func == Clone::clone(&ty) -> ty`
 463         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 464         let func = Operand::Constant(box Constant {
 465             span: self.span,
 466             user_ty: None,
 467             literal: ty::Const::zero_sized(tcx, func_ty),
 468         });
 469
 470         let ref_loc = self.make_place(
 471             Mutability::Not,
 472             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 473                 ty,
 474                 mutbl: hir::Mutability::Not,
 475             })
 476         );
 477
 478         // `let ref_loc: &ty = &src;`
 479         let statement = self.make_statement(
 480             StatementKind::Assign(
 481                 box(
 482                     ref_loc.clone(),
 483                     Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 484                 )
 485             )
 486         );
 487
 488         // `let loc = Clone::clone(ref_loc);`
 489         self.block(vec![statement], TerminatorKind::Call {
 490             func,
 491             args: vec![Operand::Move(ref_loc)],
 492             destination: Some((dest, next)),
 493             cleanup: Some(cleanup),
 494             from_hir_call: true,
 495         }, false);
 496     }
 497
 498     fn loop_header(
 499         &mut self,
 500         beg: Place<'tcx>,
 501         end: Place<'tcx>,
 502         loop_body: BasicBlock,
 503         loop_end: BasicBlock,
 504         is_cleanup: bool
 505     ) {
 506         let tcx = self.tcx;
 507
 508         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 509         let compute_cond = self.make_statement(
 510             StatementKind::Assign(
 511                 box(
 512                     cond.clone(),
 513                     Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 514                 )
 515             )
 516         );
 517
 518         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 519         self.block(
 520             vec![compute_cond],
 521             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 522             is_cleanup
 523         );
 524     }
 525
 526     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 527         box Constant {
 528             span: self.span,
 529             user_ty: None,
 530             literal: ty::Const::from_usize(self.tcx, value),
 531         }
 532     }
 533
 534     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 535         let tcx = self.tcx;
 536         let span = self.span;
 537
 538         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 539         let end = self.make_place(Mutability::Not, tcx.types.usize);
 540
 541         // BB #0
 542         // `let mut beg = 0;`
 543         // `let end = len;`
 544         // `goto #1;`
 545         let inits = vec![
 546             self.make_statement(
 547                 StatementKind::Assign(
 548                     box(
 549                         Place::from(beg),
 550                         Rvalue::Use(Operand::Constant(self.make_usize(0)))
 551                     )
 552                 )
 553             ),
 554             self.make_statement(
 555                 StatementKind::Assign(
 556                     box(
 557                         end.clone(),
 558                         Rvalue::Use(Operand::Constant(self.make_usize(len)))
 559                     )
 560                 )
 561             )
 562         ];
 563         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 564
 565         // BB #1: loop {
 566         //     BB #2;
 567         //     BB #3;
 568         // }
 569         // BB #4;
 570         self.loop_header(Place::from(beg),
 571                          end,
 572                          BasicBlock::new(2),
 573                          BasicBlock::new(4),
 574                          false);
 575
 576         // BB #2
 577         // `dest[i] = Clone::clone(src[beg])`;
 578         // Goto #3 if ok, #5 if unwinding happens.
 579         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 580         let src_field = self.tcx.mk_place_index(src, beg);
 581         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 582                              BasicBlock::new(5));
 583
 584         // BB #3
 585         // `beg = beg + 1;`
 586         // `goto #1`;
 587         let statements = vec![
 588             self.make_statement(
 589                 StatementKind::Assign(
 590                     box(
 591                         Place::from(beg),
 592                         Rvalue::BinaryOp(
 593                             BinOp::Add,
 594                             Operand::Copy(Place::from(beg)),
 595                             Operand::Constant(self.make_usize(1))
 596                         )
 597                     )
 598                 )
 599             )
 600         ];
 601         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 602
 603         // BB #4
 604         // `return dest;`
 605         self.block(vec![], TerminatorKind::Return, false);
 606
 607         // BB #5 (cleanup)
 608         // `let end = beg;`
 609         // `let mut beg = 0;`
 610         // goto #6;
 611         let end = beg;
 612         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 613         let init = self.make_statement(
 614             StatementKind::Assign(
 615                 box(
 616                     Place::from(beg),
 617                     Rvalue::Use(Operand::Constant(self.make_usize(0)))
 618                 )
 619             )
 620         );
 621         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 622
 623         // BB #6 (cleanup): loop {
 624         //     BB #7;
 625         //     BB #8;
 626         // }
 627         // BB #9;
 628         self.loop_header(Place::from(beg), Place::from(end),
 629                          BasicBlock::new(7), BasicBlock::new(9), true);
 630
 631         // BB #7 (cleanup)
 632         // `drop(dest[beg])`;
 633         self.block(vec![], TerminatorKind::Drop {
 634             location: self.tcx.mk_place_index(dest, beg),
 635             target: BasicBlock::new(8),
 636             unwind: None,
 637         }, true);
 638
 639         // BB #8 (cleanup)
 640         // `beg = beg + 1;`
 641         // `goto #6;`
 642         let statement = self.make_statement(
 643             StatementKind::Assign(
 644                 box(
 645                     Place::from(beg),
 646                     Rvalue::BinaryOp(
 647                         BinOp::Add,
 648                         Operand::Copy(Place::from(beg)),
 649                         Operand::Constant(self.make_usize(1))
 650                     )
 651                 )
 652             )
 653         );
 654         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 655
 656         // BB #9 (resume)
 657         self.block(vec![], TerminatorKind::Resume, true);
 658     }
 659
 660     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 661                           src: Place<'tcx>, tys: I)
 662             where I: Iterator<Item = Ty<'tcx>> {
 663         let mut previous_field = None;
 664         for (i, ity) in tys.enumerate() {
 665             let field = Field::new(i);
 666             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 667
 668             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 669
 670             // #(2i + 1) is the cleanup block for the previous clone operation
 671             let cleanup_block = self.block_index_offset(1);
 672             // #(2i + 2) is the next cloning block
 673             // (or the Return terminator if this is the last block)
 674             let next_block = self.block_index_offset(2);
 675
 676             // BB #(2i)
 677             // `dest.i = Clone::clone(&src.i);`
 678             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 679             self.make_clone_call(
 680                 dest_field.clone(),
 681                 src_field,
 682                 ity,
 683                 next_block,
 684                 cleanup_block,
 685             );
 686
 687             // BB #(2i + 1) (cleanup)
 688             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 689                 // Drop previous field and goto previous cleanup block.
 690                 self.block(vec![], TerminatorKind::Drop {
 691                     location: previous_field,
 692                     target: previous_cleanup,
 693                     unwind: None,
 694                 }, true);
 695             } else {
 696                 // Nothing to drop, just resume.
 697                 self.block(vec![], TerminatorKind::Resume, true);
 698             }
 699
 700             previous_field = Some((dest_field, cleanup_block));
 701         }
 702
 703         self.block(vec![], TerminatorKind::Return, false);
 704     }
 705 }
 706
 707 /// Builds a "call" shim for `instance`. The shim calls the
 708 /// function specified by `call_kind`, first adjusting its first
 709 /// argument according to `rcvr_adjustment`.
 710 ///
 711 /// If `untuple_args` is a vec of types, the second argument of the
 712 /// function will be untupled as these types.
 713 fn build_call_shim<'tcx>(
 714     tcx: TyCtxt<'tcx>,
 715     instance: ty::InstanceDef<'tcx>,
 716     rcvr_adjustment: Adjustment,
 717     call_kind: CallKind,
 718     untuple_args: Option<&[Ty<'tcx>]>,
 719 ) -> BodyAndCache<'tcx> {
 720     debug!("build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 721             call_kind={:?}, untuple_args={:?})",
 722            instance, rcvr_adjustment, call_kind, untuple_args);
 723
 724     let def_id = instance.def_id();
 725     let sig = tcx.fn_sig(def_id);
 726     let mut sig = tcx.erase_late_bound_regions(&sig);
 727
 728     // FIXME(eddyb) avoid having this snippet both here and in
 729     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 730     if let ty::InstanceDef::VtableShim(..) = instance {
 731         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 732         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 733         let self_arg = &mut inputs_and_output[0];
 734         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 735         *self_arg = tcx.mk_mut_ptr(*self_arg);
 736         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 737     }
 738
 739     let span = tcx.def_span(def_id);
 740
 741     debug!("build_call_shim: sig={:?}", sig);
 742
 743     let mut local_decls = local_decls_for_sig(&sig, span);
 744     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 745
 746     let rcvr_arg = Local::new(1+0);
 747     let rcvr_l = Place::from(rcvr_arg);
 748     let mut statements = vec![];
 749
 750     let rcvr = match rcvr_adjustment {
 751         Adjustment::Identity => Operand::Move(rcvr_l),
 752         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_l)),
 753         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_l)),
 754         Adjustment::RefMut => {
 755             // let rcvr = &mut rcvr;
 756             let ref_rcvr = local_decls.push(temp_decl(
 757                 Mutability::Not,
 758                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 759                     ty: sig.inputs()[0],
 760                     mutbl: hir::Mutability::Mut
 761                 }),
 762                 span
 763             ));
 764             let borrow_kind = BorrowKind::Mut {
 765                 allow_two_phase_borrow: false,
 766             };
 767             statements.push(Statement {
 768                 source_info,
 769                 kind: StatementKind::Assign(
 770                     box(
 771                         Place::from(ref_rcvr),
 772                         Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 773                     )
 774                 )
 775             });
 776             Operand::Move(Place::from(ref_rcvr))
 777         }
 778     };
 779
 780     let (callee, mut args) = match call_kind {
 781         CallKind::Indirect => (rcvr, vec![]),
 782         CallKind::Direct(def_id) => {
 783             let ty = tcx.type_of(def_id);
 784             (Operand::Constant(box Constant {
 785                 span,
 786                 user_ty: None,
 787                 literal: ty::Const::zero_sized(tcx, ty),
 788              }),
 789              vec![rcvr])
 790         }
 791     };
 792
 793     if let Some(untuple_args) = untuple_args {
 794         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 795             let arg_place = Place::from(Local::new(1+1));
 796             Operand::Move(tcx.mk_place_field(arg_place, Field::new(i), *ity))
 797         }));
 798     } else {
 799         args.extend((1..sig.inputs().len()).map(|i| {
 800             Operand::Move(Place::from(Local::new(1+i)))
 801         }));
 802     }
 803
 804     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 805     let mut blocks = IndexVec::with_capacity(n_blocks);
 806     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 807         blocks.push(BasicBlockData {
 808             statements,
 809             terminator: Some(Terminator { source_info, kind }),
 810             is_cleanup
 811         })
 812     };
 813
 814     // BB #0
 815     block(&mut blocks, statements, TerminatorKind::Call {
 816         func: callee,
 817         args,
 818         destination: Some((Place::return_place(),
 819                            BasicBlock::new(1))),
 820         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 821             Some(BasicBlock::new(3))
 822         } else {
 823             None
 824         },
 825         from_hir_call: true,
 826     }, false);
 827
 828     if let Adjustment::RefMut = rcvr_adjustment {
 829         // BB #1 - drop for Self
 830         block(&mut blocks, vec![], TerminatorKind::Drop {
 831             location: Place::from(rcvr_arg),
 832             target: BasicBlock::new(2),
 833             unwind: None
 834         }, false);
 835     }
 836     // BB #1/#2 - return
 837     block(&mut blocks, vec![], TerminatorKind::Return, false);
 838     if let Adjustment::RefMut = rcvr_adjustment {
 839         // BB #3 - drop if closure panics
 840         block(&mut blocks, vec![], TerminatorKind::Drop {
 841             location: Place::from(rcvr_arg),
 842             target: BasicBlock::new(4),
 843             unwind: None
 844         }, true);
 845
 846         // BB #4 - resume
 847         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 848     }
 849
 850     let mut body = new_body(
 851         blocks,
 852         local_decls,
 853         sig.inputs().len(),
 854         span,
 855     );
 856
 857     if let Abi::RustCall = sig.abi {
 858         body.spread_arg = Some(Local::new(sig.inputs().len()));
 859     }
 860     BodyAndCache::new(body)
 861 }
 862
 863 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &BodyAndCache<'_> {
 864     debug_assert!(tcx.is_constructor(ctor_id));
 865
 866     let span = tcx.hir().span_if_local(ctor_id)
 867         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 868
 869     let param_env = tcx.param_env(ctor_id);
 870
 871     // Normalize the sig.
 872     let sig = tcx.fn_sig(ctor_id)
 873         .no_bound_vars()
 874         .expect("LBR in ADT constructor signature");
 875     let sig = tcx.normalize_erasing_regions(param_env, sig);
 876
 877     let (adt_def, substs) = match sig.output().kind {
 878         ty::Adt(adt_def, substs) => (adt_def, substs),
 879         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 880     };
 881
 882     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 883
 884     let local_decls = local_decls_for_sig(&sig, span);
 885
 886     let source_info = SourceInfo {
 887         span,
 888         scope: OUTERMOST_SOURCE_SCOPE
 889     };
 890
 891     let variant_index = if adt_def.is_enum() {
 892         adt_def.variant_index_with_ctor_id(ctor_id)
 893     } else {
 894         VariantIdx::new(0)
 895     };
 896
 897     // Generate the following MIR:
 898     //
 899     // (return as Variant).field0 = arg0;
 900     // (return as Variant).field1 = arg1;
 901     //
 902     // return;
 903     debug!("build_ctor: variant_index={:?}", variant_index);
 904
 905     let statements = expand_aggregate(
 906         Place::return_place(),
 907         adt_def
 908             .variants[variant_index]
 909             .fields
 910             .iter()
 911             .enumerate()
 912             .map(|(idx, field_def)| (
 913                 Operand::Move(Place::from(Local::new(idx + 1))),
 914                 field_def.ty(tcx, substs),
 915             )),
 916         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 917         source_info,
 918         tcx,
 919     ).collect();
 920
 921     let start_block = BasicBlockData {
 922         statements,
 923         terminator: Some(Terminator {
 924             source_info,
 925             kind: TerminatorKind::Return,
 926         }),
 927         is_cleanup: false
 928     };
 929
 930     let body = new_body(
 931         IndexVec::from_elem_n(start_block, 1),
 932         local_decls,
 933         sig.inputs().len(),
 934         span,
 935     );
 936
 937     crate::util::dump_mir(
 938         tcx,
 939         None,
 940         "mir_map",
 941         &0,
 942         crate::transform::MirSource::item(ctor_id),
 943         &body,
 944         |_, _| Ok(()),
 945     );
 946
 947     let mut body = BodyAndCache::new(body);
 948     body.ensure_predecessors();
 949     tcx.arena.alloc(body)
 950 }