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         ty::InstanceDef::Virtual(def_id, _) => {
  70             // We are generating a call back to our def-id, which the
  71             // codegen backend knows to turn to an actual virtual call.
  72             build_call_shim(
  73                 tcx,
  74                 def_id,
  75                 Adjustment::Identity,
  76                 CallKind::Direct(def_id),
  77                 None
  78             )
  79         }
  80         ty::InstanceDef::ClosureOnceShim { call_once } => {
  81             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  82             let call_mut = tcx
  83                 .associated_items(fn_mut)
  84                 .find(|it| it.kind == ty::AssocKind::Method)
  85                 .unwrap().def_id;
  86
  87             build_call_shim(
  88                 tcx,
  89                 call_once,
  90                 Adjustment::RefMut,
  91                 CallKind::Direct(call_mut),
  92                 None
  93             )
  94         }
  95         ty::InstanceDef::DropGlue(def_id, ty) => {
  96             build_drop_shim(tcx, def_id, ty)
  97         }
  98         ty::InstanceDef::CloneShim(def_id, ty) => {
  99             let name = tcx.item_name(def_id);
 100             if name == sym::clone {
 101                 build_clone_shim(tcx, def_id, ty)
 102             } else if name == sym::clone_from {
 103                 debug!("make_shim({:?}: using default trait implementation", instance);
 104                 return tcx.optimized_mir(def_id);
 105             } else {
 106                 bug!("builtin clone shim {:?} not supported", instance)
 107             }
 108         }
 109         ty::InstanceDef::Intrinsic(_) => {
 110             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 111         }
 112     };
 113     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 114
 115     run_passes(tcx, &mut result, instance, None, MirPhase::Const, &[
 116         &add_moves_for_packed_drops::AddMovesForPackedDrops,
 117         &no_landing_pads::NoLandingPads,
 118         &remove_noop_landing_pads::RemoveNoopLandingPads,
 119         &simplify::SimplifyCfg::new("make_shim"),
 120         &add_call_guards::CriticalCallEdges,
 121     ]);
 122
 123     debug!("make_shim({:?}) = {:?}", instance, result);
 124
 125     tcx.arena.alloc(result)
 126 }
 127
 128 #[derive(Copy, Clone, Debug, PartialEq)]
 129 enum Adjustment {
 130     Identity,
 131     Deref,
 132     DerefMove,
 133     RefMut,
 134 }
 135
 136 #[derive(Copy, Clone, Debug, PartialEq)]
 137 enum CallKind {
 138     Indirect,
 139     Direct(DefId),
 140 }
 141
 142 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 143     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 144     LocalDecl {
 145         mutability,
 146         ty,
 147         user_ty: UserTypeProjections::none(),
 148         name: None,
 149         source_info,
 150         visibility_scope: source_info.scope,
 151         internal: false,
 152         is_user_variable: None,
 153         is_block_tail: None,
 154     }
 155 }
 156
 157 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 158     -> IndexVec<Local, LocalDecl<'tcx>>
 159 {
 160     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 161         .chain(sig.inputs().iter().map(
 162             |ity| temp_decl(Mutability::Not, ity, span)))
 163         .collect()
 164 }
 165
 166 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 167     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 168
 169     // Check if this is a generator, if so, return the drop glue for it
 170     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 171         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 172         return body.subst(tcx, substs.substs);
 173     }
 174
 175     let substs = if let Some(ty) = ty {
 176         tcx.intern_substs(&[ty.into()])
 177     } else {
 178         InternalSubsts::identity_for_item(tcx, def_id)
 179     };
 180     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 181     let sig = tcx.erase_late_bound_regions(&sig);
 182     let span = tcx.def_span(def_id);
 183
 184     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 185
 186     let return_block = BasicBlock::new(1);
 187     let mut blocks = IndexVec::with_capacity(2);
 188     let block = |blocks: &mut IndexVec<_, _>, kind| {
 189         blocks.push(BasicBlockData {
 190             statements: vec![],
 191             terminator: Some(Terminator { source_info, kind }),
 192             is_cleanup: false
 193         })
 194     };
 195     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 196     block(&mut blocks, TerminatorKind::Return);
 197
 198     let mut body = Body::new(
 199         blocks,
 200         IndexVec::from_elem_n(
 201             SourceScopeData { span: span, parent_scope: None }, 1
 202         ),
 203         ClearCrossCrate::Clear,
 204         None,
 205         local_decls_for_sig(&sig, span),
 206         IndexVec::new(),
 207         sig.inputs().len(),
 208         vec![],
 209         span,
 210         vec![],
 211     );
 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 = dropee_ptr.deref();
 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 pub struct DropShimElaborator<'a, 'tcx> {
 251     pub body: &'a Body<'tcx>,
 252     pub patch: MirPatch<'tcx>,
 253     pub tcx: TyCtxt<'tcx>,
 254     pub param_env: ty::ParamEnv<'tcx>,
 255 }
 256
 257 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 258     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 259         Ok(())
 260     }
 261 }
 262
 263 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 264     type Path = ();
 265
 266     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 267     fn body(&self) -> &'a Body<'tcx> { self.body }
 268     fn tcx(&self) -> TyCtxt<'tcx> {
 269         self.tcx
 270         }
 271     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 272
 273     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 274         if let DropFlagMode::Shallow = mode {
 275             DropStyle::Static
 276         } else {
 277             DropStyle::Open
 278         }
 279     }
 280
 281     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 282         None
 283     }
 284
 285     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 286     }
 287
 288     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 289         None
 290     }
 291     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 292         None
 293     }
 294     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 295         Some(())
 296     }
 297     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 298         None
 299     }
 300 }
 301
 302 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 303 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 304     debug!("build_clone_shim(def_id={:?})", def_id);
 305
 306     let param_env = tcx.param_env(def_id);
 307
 308     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 309     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 310
 311     let dest = Place::return_place();
 312     let src = Place::from(Local::new(1+0)).deref();
 313
 314     match self_ty.kind {
 315         _ if is_copy => builder.copy_shim(),
 316         ty::Array(ty, len) => {
 317             let len = len.eval_usize(tcx, param_env);
 318             builder.array_shim(dest, src, ty, len)
 319         }
 320         ty::Closure(def_id, substs) => {
 321             builder.tuple_like_shim(
 322                 dest, src,
 323                 substs.upvar_tys(def_id, tcx)
 324             )
 325         }
 326         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 327         _ => {
 328             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 329         }
 330     };
 331
 332     builder.into_mir()
 333 }
 334
 335 struct CloneShimBuilder<'tcx> {
 336     tcx: TyCtxt<'tcx>,
 337     def_id: DefId,
 338     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 339     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 340     span: Span,
 341     sig: ty::FnSig<'tcx>,
 342 }
 343
 344 impl CloneShimBuilder<'tcx> {
 345     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 346         // we must subst the self_ty because it's
 347         // otherwise going to be TySelf and we can't index
 348         // or access fields of a Place of type TySelf.
 349         let substs = tcx.mk_substs_trait(self_ty, &[]);
 350         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 351         let sig = tcx.erase_late_bound_regions(&sig);
 352         let span = tcx.def_span(def_id);
 353
 354         CloneShimBuilder {
 355             tcx,
 356             def_id,
 357             local_decls: local_decls_for_sig(&sig, span),
 358             blocks: IndexVec::new(),
 359             span,
 360             sig,
 361         }
 362     }
 363
 364     fn into_mir(self) -> Body<'tcx> {
 365         Body::new(
 366             self.blocks,
 367             IndexVec::from_elem_n(
 368                 SourceScopeData { span: self.span, parent_scope: None }, 1
 369             ),
 370             ClearCrossCrate::Clear,
 371             None,
 372             self.local_decls,
 373             IndexVec::new(),
 374             self.sig.inputs().len(),
 375             vec![],
 376             self.span,
 377             vec![],
 378         )
 379     }
 380
 381     fn source_info(&self) -> SourceInfo {
 382         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 383     }
 384
 385     fn block(
 386         &mut self,
 387         statements: Vec<Statement<'tcx>>,
 388         kind: TerminatorKind<'tcx>,
 389         is_cleanup: bool
 390     ) -> BasicBlock {
 391         let source_info = self.source_info();
 392         self.blocks.push(BasicBlockData {
 393             statements,
 394             terminator: Some(Terminator { source_info, kind }),
 395             is_cleanup,
 396         })
 397     }
 398
 399     /// Gives the index of an upcoming BasicBlock, with an offset.
 400     /// offset=0 will give you the index of the next BasicBlock,
 401     /// offset=1 will give the index of the next-to-next block,
 402     /// offset=-1 will give you the index of the last-created block
 403     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 404         BasicBlock::new(self.blocks.len() + offset)
 405     }
 406
 407     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 408         Statement {
 409             source_info: self.source_info(),
 410             kind,
 411         }
 412     }
 413
 414     fn copy_shim(&mut self) {
 415         let rcvr = Place::from(Local::new(1+0)).deref();
 416         let ret_statement = self.make_statement(
 417             StatementKind::Assign(
 418                 box(
 419                     Place::return_place(),
 420                     Rvalue::Use(Operand::Copy(rcvr))
 421                 )
 422             )
 423         );
 424         self.block(vec![ret_statement], TerminatorKind::Return, false);
 425     }
 426
 427     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 428         let span = self.span;
 429         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 430     }
 431
 432     fn make_clone_call(
 433         &mut self,
 434         dest: Place<'tcx>,
 435         src: Place<'tcx>,
 436         ty: Ty<'tcx>,
 437         next: BasicBlock,
 438         cleanup: BasicBlock
 439     ) {
 440         let tcx = self.tcx;
 441
 442         let substs = tcx.mk_substs_trait(ty, &[]);
 443
 444         // `func == Clone::clone(&ty) -> ty`
 445         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 446         let func = Operand::Constant(box Constant {
 447             span: self.span,
 448             user_ty: None,
 449             literal: ty::Const::zero_sized(tcx, func_ty),
 450         });
 451
 452         let ref_loc = self.make_place(
 453             Mutability::Not,
 454             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 455                 ty,
 456                 mutbl: hir::Mutability::MutImmutable,
 457             })
 458         );
 459
 460         // `let ref_loc: &ty = &src;`
 461         let statement = self.make_statement(
 462             StatementKind::Assign(
 463                 box(
 464                     ref_loc.clone(),
 465                     Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src)
 466                 )
 467             )
 468         );
 469
 470         // `let loc = Clone::clone(ref_loc);`
 471         self.block(vec![statement], TerminatorKind::Call {
 472             func,
 473             args: vec![Operand::Move(ref_loc)],
 474             destination: Some((dest, next)),
 475             cleanup: Some(cleanup),
 476             from_hir_call: true,
 477         }, false);
 478     }
 479
 480     fn loop_header(
 481         &mut self,
 482         beg: Place<'tcx>,
 483         end: Place<'tcx>,
 484         loop_body: BasicBlock,
 485         loop_end: BasicBlock,
 486         is_cleanup: bool
 487     ) {
 488         let tcx = self.tcx;
 489
 490         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 491         let compute_cond = self.make_statement(
 492             StatementKind::Assign(
 493                 box(
 494                     cond.clone(),
 495                     Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 496                 )
 497             )
 498         );
 499
 500         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 501         self.block(
 502             vec![compute_cond],
 503             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 504             is_cleanup
 505         );
 506     }
 507
 508     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 509         box Constant {
 510             span: self.span,
 511             user_ty: None,
 512             literal: ty::Const::from_usize(self.tcx, value),
 513         }
 514     }
 515
 516     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 517         let tcx = self.tcx;
 518         let span = self.span;
 519
 520         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 521         let end = self.make_place(Mutability::Not, tcx.types.usize);
 522
 523         // BB #0
 524         // `let mut beg = 0;`
 525         // `let end = len;`
 526         // `goto #1;`
 527         let inits = vec![
 528             self.make_statement(
 529                 StatementKind::Assign(
 530                     box(
 531                         Place::from(beg),
 532                         Rvalue::Use(Operand::Constant(self.make_usize(0)))
 533                     )
 534                 )
 535             ),
 536             self.make_statement(
 537                 StatementKind::Assign(
 538                     box(
 539                         end.clone(),
 540                         Rvalue::Use(Operand::Constant(self.make_usize(len)))
 541                     )
 542                 )
 543             )
 544         ];
 545         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 546
 547         // BB #1: loop {
 548         //     BB #2;
 549         //     BB #3;
 550         // }
 551         // BB #4;
 552         self.loop_header(Place::from(beg),
 553                          end,
 554                          BasicBlock::new(2),
 555                          BasicBlock::new(4),
 556                          false);
 557
 558         // BB #2
 559         // `dest[i] = Clone::clone(src[beg])`;
 560         // Goto #3 if ok, #5 if unwinding happens.
 561         let dest_field = dest.clone().index(beg);
 562         let src_field = src.index(beg);
 563         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 564                              BasicBlock::new(5));
 565
 566         // BB #3
 567         // `beg = beg + 1;`
 568         // `goto #1`;
 569         let statements = vec![
 570             self.make_statement(
 571                 StatementKind::Assign(
 572                     box(
 573                         Place::from(beg),
 574                         Rvalue::BinaryOp(
 575                             BinOp::Add,
 576                             Operand::Copy(Place::from(beg)),
 577                             Operand::Constant(self.make_usize(1))
 578                         )
 579                     )
 580                 )
 581             )
 582         ];
 583         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 584
 585         // BB #4
 586         // `return dest;`
 587         self.block(vec![], TerminatorKind::Return, false);
 588
 589         // BB #5 (cleanup)
 590         // `let end = beg;`
 591         // `let mut beg = 0;`
 592         // goto #6;
 593         let end = beg;
 594         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 595         let init = self.make_statement(
 596             StatementKind::Assign(
 597                 box(
 598                     Place::from(beg),
 599                     Rvalue::Use(Operand::Constant(self.make_usize(0)))
 600                 )
 601             )
 602         );
 603         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 604
 605         // BB #6 (cleanup): loop {
 606         //     BB #7;
 607         //     BB #8;
 608         // }
 609         // BB #9;
 610         self.loop_header(Place::from(beg), Place::from(end),
 611                          BasicBlock::new(7), BasicBlock::new(9), true);
 612
 613         // BB #7 (cleanup)
 614         // `drop(dest[beg])`;
 615         self.block(vec![], TerminatorKind::Drop {
 616             location: dest.index(beg),
 617             target: BasicBlock::new(8),
 618             unwind: None,
 619         }, true);
 620
 621         // BB #8 (cleanup)
 622         // `beg = beg + 1;`
 623         // `goto #6;`
 624         let statement = self.make_statement(
 625             StatementKind::Assign(
 626                 box(
 627                     Place::from(beg),
 628                     Rvalue::BinaryOp(
 629                         BinOp::Add,
 630                         Operand::Copy(Place::from(beg)),
 631                         Operand::Constant(self.make_usize(1))
 632                     )
 633                 )
 634             )
 635         );
 636         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 637
 638         // BB #9 (resume)
 639         self.block(vec![], TerminatorKind::Resume, true);
 640     }
 641
 642     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 643                           src: Place<'tcx>, tys: I)
 644             where I: Iterator<Item = Ty<'tcx>> {
 645         let mut previous_field = None;
 646         for (i, ity) in tys.enumerate() {
 647             let field = Field::new(i);
 648             let src_field = src.clone().field(field, ity);
 649
 650             let dest_field = dest.clone().field(field, ity);
 651
 652             // #(2i + 1) is the cleanup block for the previous clone operation
 653             let cleanup_block = self.block_index_offset(1);
 654             // #(2i + 2) is the next cloning block
 655             // (or the Return terminator if this is the last block)
 656             let next_block = self.block_index_offset(2);
 657
 658             // BB #(2i)
 659             // `dest.i = Clone::clone(&src.i);`
 660             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 661             self.make_clone_call(
 662                 dest_field.clone(),
 663                 src_field,
 664                 ity,
 665                 next_block,
 666                 cleanup_block,
 667             );
 668
 669             // BB #(2i + 1) (cleanup)
 670             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 671                 // Drop previous field and goto previous cleanup block.
 672                 self.block(vec![], TerminatorKind::Drop {
 673                     location: previous_field,
 674                     target: previous_cleanup,
 675                     unwind: None,
 676                 }, true);
 677             } else {
 678                 // Nothing to drop, just resume.
 679                 self.block(vec![], TerminatorKind::Resume, true);
 680             }
 681
 682             previous_field = Some((dest_field, cleanup_block));
 683         }
 684
 685         self.block(vec![], TerminatorKind::Return, false);
 686     }
 687 }
 688
 689 /// Builds a "call" shim for `def_id`. The shim calls the
 690 /// function specified by `call_kind`, first adjusting its first
 691 /// argument according to `rcvr_adjustment`.
 692 ///
 693 /// If `untuple_args` is a vec of types, the second argument of the
 694 /// function will be untupled as these types.
 695 fn build_call_shim<'tcx>(
 696     tcx: TyCtxt<'tcx>,
 697     def_id: DefId,
 698     rcvr_adjustment: Adjustment,
 699     call_kind: CallKind,
 700     untuple_args: Option<&[Ty<'tcx>]>,
 701 ) -> Body<'tcx> {
 702     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 703             call_kind={:?}, untuple_args={:?})",
 704            def_id, rcvr_adjustment, call_kind, untuple_args);
 705
 706     let sig = tcx.fn_sig(def_id);
 707     let sig = tcx.erase_late_bound_regions(&sig);
 708     let span = tcx.def_span(def_id);
 709
 710     debug!("build_call_shim: sig={:?}", sig);
 711
 712     let mut local_decls = local_decls_for_sig(&sig, span);
 713     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 714
 715     let rcvr_arg = Local::new(1+0);
 716     let rcvr_l = Place::from(rcvr_arg);
 717     let mut statements = vec![];
 718
 719     let rcvr = match rcvr_adjustment {
 720         Adjustment::Identity => Operand::Move(rcvr_l),
 721         Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
 722         Adjustment::DerefMove => {
 723             // fn(Self, ...) -> fn(*mut Self, ...)
 724             let arg_ty = local_decls[rcvr_arg].ty;
 725             debug_assert!(tcx.generics_of(def_id).has_self && arg_ty == tcx.types.self_param);
 726             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 727
 728             Operand::Move(rcvr_l.deref())
 729         }
 730         Adjustment::RefMut => {
 731             // let rcvr = &mut rcvr;
 732             let ref_rcvr = local_decls.push(temp_decl(
 733                 Mutability::Not,
 734                 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut {
 735                     ty: sig.inputs()[0],
 736                     mutbl: hir::Mutability::MutMutable
 737                 }),
 738                 span
 739             ));
 740             let borrow_kind = BorrowKind::Mut {
 741                 allow_two_phase_borrow: false,
 742             };
 743             statements.push(Statement {
 744                 source_info,
 745                 kind: StatementKind::Assign(
 746                     box(
 747                         Place::from(ref_rcvr),
 748                         Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l)
 749                     )
 750                 )
 751             });
 752             Operand::Move(Place::from(ref_rcvr))
 753         }
 754     };
 755
 756     let (callee, mut args) = match call_kind {
 757         CallKind::Indirect => (rcvr, vec![]),
 758         CallKind::Direct(def_id) => {
 759             let ty = tcx.type_of(def_id);
 760             (Operand::Constant(box Constant {
 761                 span,
 762                 user_ty: None,
 763                 literal: ty::Const::zero_sized(tcx, ty),
 764              }),
 765              vec![rcvr])
 766         }
 767     };
 768
 769     if let Some(untuple_args) = untuple_args {
 770         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 771             let arg_place = Place::from(Local::new(1+1));
 772             Operand::Move(arg_place.field(Field::new(i), *ity))
 773         }));
 774     } else {
 775         args.extend((1..sig.inputs().len()).map(|i| {
 776             Operand::Move(Place::from(Local::new(1+i)))
 777         }));
 778     }
 779
 780     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 781     let mut blocks = IndexVec::with_capacity(n_blocks);
 782     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 783         blocks.push(BasicBlockData {
 784             statements,
 785             terminator: Some(Terminator { source_info, kind }),
 786             is_cleanup
 787         })
 788     };
 789
 790     // BB #0
 791     block(&mut blocks, statements, TerminatorKind::Call {
 792         func: callee,
 793         args,
 794         destination: Some((Place::return_place(),
 795                            BasicBlock::new(1))),
 796         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 797             Some(BasicBlock::new(3))
 798         } else {
 799             None
 800         },
 801         from_hir_call: true,
 802     }, false);
 803
 804     if let Adjustment::RefMut = rcvr_adjustment {
 805         // BB #1 - drop for Self
 806         block(&mut blocks, vec![], TerminatorKind::Drop {
 807             location: Place::from(rcvr_arg),
 808             target: BasicBlock::new(2),
 809             unwind: None
 810         }, false);
 811     }
 812     // BB #1/#2 - return
 813     block(&mut blocks, vec![], TerminatorKind::Return, false);
 814     if let Adjustment::RefMut = rcvr_adjustment {
 815         // BB #3 - drop if closure panics
 816         block(&mut blocks, vec![], TerminatorKind::Drop {
 817             location: Place::from(rcvr_arg),
 818             target: BasicBlock::new(4),
 819             unwind: None
 820         }, true);
 821
 822         // BB #4 - resume
 823         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 824     }
 825
 826     let mut body = Body::new(
 827         blocks,
 828         IndexVec::from_elem_n(
 829             SourceScopeData { span: span, parent_scope: None }, 1
 830         ),
 831         ClearCrossCrate::Clear,
 832         None,
 833         local_decls,
 834         IndexVec::new(),
 835         sig.inputs().len(),
 836         vec![],
 837         span,
 838         vec![],
 839     );
 840     if let Abi::RustCall = sig.abi {
 841         body.spread_arg = Some(Local::new(sig.inputs().len()));
 842     }
 843     body
 844 }
 845
 846 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &Body<'_> {
 847     debug_assert!(tcx.is_constructor(ctor_id));
 848
 849     let span = tcx.hir().span_if_local(ctor_id)
 850         .unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 851
 852     let param_env = tcx.param_env(ctor_id);
 853
 854     // Normalize the sig.
 855     let sig = tcx.fn_sig(ctor_id)
 856         .no_bound_vars()
 857         .expect("LBR in ADT constructor signature");
 858     let sig = tcx.normalize_erasing_regions(param_env, sig);
 859
 860     let (adt_def, substs) = match sig.output().kind {
 861         ty::Adt(adt_def, substs) => (adt_def, substs),
 862         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 863     };
 864
 865     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 866
 867     let local_decls = local_decls_for_sig(&sig, span);
 868
 869     let source_info = SourceInfo {
 870         span,
 871         scope: OUTERMOST_SOURCE_SCOPE
 872     };
 873
 874     let variant_index = if adt_def.is_enum() {
 875         adt_def.variant_index_with_ctor_id(ctor_id)
 876     } else {
 877         VariantIdx::new(0)
 878     };
 879
 880     // Generate the following MIR:
 881     //
 882     // (return as Variant).field0 = arg0;
 883     // (return as Variant).field1 = arg1;
 884     //
 885     // return;
 886     debug!("build_ctor: variant_index={:?}", variant_index);
 887
 888     let statements = expand_aggregate(
 889         Place::return_place(),
 890         adt_def
 891             .variants[variant_index]
 892             .fields
 893             .iter()
 894             .enumerate()
 895             .map(|(idx, field_def)| (
 896                 Operand::Move(Place::from(Local::new(idx + 1))),
 897                 field_def.ty(tcx, substs),
 898             )),
 899         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 900         source_info,
 901     ).collect();
 902
 903     let start_block = BasicBlockData {
 904         statements,
 905         terminator: Some(Terminator {
 906             source_info,
 907             kind: TerminatorKind::Return,
 908         }),
 909         is_cleanup: false
 910     };
 911
 912     let body = Body::new(
 913         IndexVec::from_elem_n(start_block, 1),
 914         IndexVec::from_elem_n(
 915             SourceScopeData { span: span, parent_scope: None }, 1
 916         ),
 917         ClearCrossCrate::Clear,
 918         None,
 919         local_decls,
 920         IndexVec::new(),
 921         sig.inputs().len(),
 922         vec![],
 923         span,
 924         vec![],
 925     );
 926
 927     crate::util::dump_mir(
 928         tcx,
 929         None,
 930         "mir_map",
 931         &0,
 932         crate::transform::MirSource::item(ctor_id),
 933         &body,
 934         |_, _| Ok(()),
 935     );
 936
 937     tcx.arena.alloc(body)
 938 }