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