src/librustc_mir/shim.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::hir;
  12 use rustc::hir::def_id::DefId;
  13 use rustc::infer;
  14 use rustc::mir::*;
  15 use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind};
  16 use rustc::ty::layout::VariantIdx;
  17 use rustc::ty::subst::{Subst, Substs};
  18 use rustc::ty::query::Providers;
  19
  20 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  21
  22 use rustc_target::spec::abi::Abi;
  23 use syntax::ast;
  24 use syntax_pos::Span;
  25
  26 use std::fmt;
  27 use std::iter;
  28
  29 use transform::{add_moves_for_packed_drops, add_call_guards};
  30 use transform::{remove_noop_landing_pads, no_landing_pads, simplify};
  31 use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
  32 use util::patch::MirPatch;
  33
  34 pub fn provide(providers: &mut Providers) {
  35     providers.mir_shims = make_shim;
  36 }
  37
  38 fn make_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  39                        instance: ty::InstanceDef<'tcx>)
  40                        -> &'tcx Mir<'tcx>
  41 {
  42     debug!("make_shim({:?})", instance);
  43
  44     let mut result = match instance {
  45         ty::InstanceDef::Item(..) =>
  46             bug!("item {:?} passed to make_shim", instance),
  47         ty::InstanceDef::VtableShim(def_id) => {
  48             build_call_shim(
  49                 tcx,
  50                 def_id,
  51                 Adjustment::DerefMove,
  52                 CallKind::Direct(def_id),
  53                 None,
  54             )
  55         }
  56         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  57             let trait_ = tcx.trait_of_item(def_id).unwrap();
  58             let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
  59                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  60                 Some(ty::ClosureKind::FnMut) |
  61                 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  62                 None => bug!("fn pointer {:?} is not an fn", ty)
  63             };
  64             // HACK: we need the "real" argument types for the MIR,
  65             // but because our substs are (Self, Args), where Args
  66             // is a tuple, we must include the *concrete* argument
  67             // types in the MIR. They will be substituted again with
  68             // the param-substs, but because they are concrete, this
  69             // will not do any harm.
  70             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  71             let arg_tys = sig.inputs();
  72
  73             build_call_shim(
  74                 tcx,
  75                 def_id,
  76                 adjustment,
  77                 CallKind::Indirect,
  78                 Some(arg_tys)
  79             )
  80         }
  81         ty::InstanceDef::Virtual(def_id, _) => {
  82             // We are generating a call back to our def-id, which the
  83             // codegen backend knows to turn to an actual virtual call.
  84             build_call_shim(
  85                 tcx,
  86                 def_id,
  87                 Adjustment::Identity,
  88                 CallKind::Direct(def_id),
  89                 None
  90             )
  91         }
  92         ty::InstanceDef::ClosureOnceShim { call_once } => {
  93             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  94             let call_mut = tcx.global_tcx()
  95                 .associated_items(fn_mut)
  96                 .find(|it| it.kind == ty::AssociatedKind::Method)
  97                 .unwrap().def_id;
  98
  99             build_call_shim(
 100                 tcx,
 101                 call_once,
 102                 Adjustment::RefMut,
 103                 CallKind::Direct(call_mut),
 104                 None
 105             )
 106         }
 107         ty::InstanceDef::DropGlue(def_id, ty) => {
 108             build_drop_shim(tcx, def_id, ty)
 109         }
 110         ty::InstanceDef::CloneShim(def_id, ty) => {
 111             let name = tcx.item_name(def_id);
 112             if name == "clone" {
 113                 build_clone_shim(tcx, def_id, ty)
 114             } else if name == "clone_from" {
 115                 debug!("make_shim({:?}: using default trait implementation", instance);
 116                 return tcx.optimized_mir(def_id);
 117             } else {
 118                 bug!("builtin clone shim {:?} not supported", instance)
 119             }
 120         }
 121         ty::InstanceDef::Intrinsic(_) => {
 122             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 123         }
 124     };
 125     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 126     add_moves_for_packed_drops::add_moves_for_packed_drops(
 127         tcx, &mut result, instance.def_id());
 128     no_landing_pads::no_landing_pads(tcx, &mut result);
 129     remove_noop_landing_pads::remove_noop_landing_pads(tcx, &mut result);
 130     simplify::simplify_cfg(&mut result);
 131     add_call_guards::CriticalCallEdges.add_call_guards(&mut result);
 132     debug!("make_shim({:?}) = {:?}", instance, result);
 133
 134     tcx.alloc_mir(result)
 135 }
 136
 137 #[derive(Copy, Clone, Debug, PartialEq)]
 138 enum Adjustment {
 139     Identity,
 140     Deref,
 141     DerefMove,
 142     RefMut,
 143 }
 144
 145 #[derive(Copy, Clone, Debug, PartialEq)]
 146 enum CallKind {
 147     Indirect,
 148     Direct(DefId),
 149 }
 150
 151 fn temp_decl(mutability: Mutability, ty: Ty, span: Span) -> LocalDecl {
 152     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 153     LocalDecl {
 154         mutability,
 155         ty,
 156         user_ty: UserTypeProjections::none(),
 157         name: None,
 158         source_info,
 159         visibility_scope: source_info.scope,
 160         internal: false,
 161         is_user_variable: None,
 162         is_block_tail: None,
 163     }
 164 }
 165
 166 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
 167     -> IndexVec<Local, LocalDecl<'tcx>>
 168 {
 169     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 170         .chain(sig.inputs().iter().map(
 171             |ity| temp_decl(Mutability::Not, ity, span)))
 172         .collect()
 173 }
 174
 175 fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 176                              def_id: DefId,
 177                              ty: Option<Ty<'tcx>>)
 178                              -> Mir<'tcx>
 179 {
 180     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 181
 182     // Check if this is a generator, if so, return the drop glue for it
 183     if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 184         let mir = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 185         return mir.subst(tcx, substs.substs);
 186     }
 187
 188     let substs = if let Some(ty) = ty {
 189         tcx.intern_substs(&[ty.into()])
 190     } else {
 191         Substs::identity_for_item(tcx, def_id)
 192     };
 193     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 194     let sig = tcx.erase_late_bound_regions(&sig);
 195     let span = tcx.def_span(def_id);
 196
 197     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 198
 199     let return_block = BasicBlock::new(1);
 200     let mut blocks = IndexVec::with_capacity(2);
 201     let block = |blocks: &mut IndexVec<_, _>, kind| {
 202         blocks.push(BasicBlockData {
 203             statements: vec![],
 204             terminator: Some(Terminator { source_info, kind }),
 205             is_cleanup: false
 206         })
 207     };
 208     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 209     block(&mut blocks, TerminatorKind::Return);
 210
 211     let mut mir = Mir::new(
 212         blocks,
 213         IndexVec::from_elem_n(
 214             SourceScopeData { span: span, parent_scope: None }, 1
 215         ),
 216         ClearCrossCrate::Clear,
 217         IndexVec::new(),
 218         None,
 219         local_decls_for_sig(&sig, span),
 220         sig.inputs().len(),
 221         vec![],
 222         span
 223     );
 224
 225     if let Some(..) = ty {
 226         // The first argument (index 0), but add 1 for the return value.
 227         let dropee_ptr = Place::Local(Local::new(1+0));
 228         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 229             // Function arguments should be retagged
 230             mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
 231                 source_info,
 232                 kind: StatementKind::Retag {
 233                     fn_entry: true,
 234                     two_phase: false,
 235                     place: dropee_ptr.clone(),
 236                 },
 237             });
 238             // We use raw ptr operations, better prepare the alias tracking for that
 239             mir.basic_blocks_mut()[START_BLOCK].statements.insert(1, Statement {
 240                 source_info,
 241                 kind: StatementKind::EscapeToRaw(Operand::Copy(dropee_ptr.clone())),
 242             })
 243         }
 244         let patch = {
 245             let param_env = tcx.param_env(def_id).with_reveal_all();
 246             let mut elaborator = DropShimElaborator {
 247                 mir: &mir,
 248                 patch: MirPatch::new(&mir),
 249                 tcx,
 250                 param_env
 251             };
 252             let dropee = dropee_ptr.deref();
 253             let resume_block = elaborator.patch.resume_block();
 254             elaborate_drops::elaborate_drop(
 255                 &mut elaborator,
 256                 source_info,
 257                 &dropee,
 258                 (),
 259                 return_block,
 260                 elaborate_drops::Unwind::To(resume_block),
 261                 START_BLOCK
 262             );
 263             elaborator.patch
 264         };
 265         patch.apply(&mut mir);
 266     }
 267
 268     mir
 269 }
 270
 271 pub struct DropShimElaborator<'a, 'tcx: 'a> {
 272     pub mir: &'a Mir<'tcx>,
 273     pub patch: MirPatch<'tcx>,
 274     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 275     pub param_env: ty::ParamEnv<'tcx>,
 276 }
 277
 278 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 279     fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 280         Ok(())
 281     }
 282 }
 283
 284 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 285     type Path = ();
 286
 287     fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
 288     fn mir(&self) -> &'a Mir<'tcx> { self.mir }
 289     fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
 290     fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
 291
 292     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 293         if let DropFlagMode::Shallow = mode {
 294             DropStyle::Static
 295         } else {
 296             DropStyle::Open
 297         }
 298     }
 299
 300     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 301         None
 302     }
 303
 304     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
 305     }
 306
 307     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 308         None
 309     }
 310     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 311         None
 312     }
 313     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 314         Some(())
 315     }
 316     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 317         None
 318     }
 319 }
 320
 321 /// Build a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 322 fn build_clone_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 323                               def_id: DefId,
 324                               self_ty: Ty<'tcx>)
 325                               -> Mir<'tcx>
 326 {
 327     debug!("build_clone_shim(def_id={:?})", def_id);
 328
 329     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 330     let is_copy = !self_ty.moves_by_default(tcx, tcx.param_env(def_id), builder.span);
 331
 332     let dest = Place::Local(RETURN_PLACE);
 333     let src = Place::Local(Local::new(1+0)).deref();
 334
 335     match self_ty.sty {
 336         _ if is_copy => builder.copy_shim(),
 337         ty::Array(ty, len) => {
 338             let len = len.unwrap_usize(tcx);
 339             builder.array_shim(dest, src, ty, len)
 340         }
 341         ty::Closure(def_id, substs) => {
 342             builder.tuple_like_shim(
 343                 dest, src,
 344                 substs.upvar_tys(def_id, tcx)
 345             )
 346         }
 347         ty::Tuple(tys) => builder.tuple_like_shim(dest, src, tys.iter().cloned()),
 348         _ => {
 349             bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
 350         }
 351     };
 352
 353     builder.into_mir()
 354 }
 355
 356 struct CloneShimBuilder<'a, 'tcx: 'a> {
 357     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 358     def_id: DefId,
 359     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 360     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 361     span: Span,
 362     sig: ty::FnSig<'tcx>,
 363 }
 364
 365 impl<'a, 'tcx> CloneShimBuilder<'a, 'tcx> {
 366     fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 367            def_id: DefId,
 368            self_ty: Ty<'tcx>) -> Self {
 369         // we must subst the self_ty because it's
 370         // otherwise going to be TySelf and we can't index
 371         // or access fields of a Place of type TySelf.
 372         let substs = tcx.mk_substs_trait(self_ty, &[]);
 373         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 374         let sig = tcx.erase_late_bound_regions(&sig);
 375         let span = tcx.def_span(def_id);
 376
 377         CloneShimBuilder {
 378             tcx,
 379             def_id,
 380             local_decls: local_decls_for_sig(&sig, span),
 381             blocks: IndexVec::new(),
 382             span,
 383             sig,
 384         }
 385     }
 386
 387     fn into_mir(self) -> Mir<'tcx> {
 388         Mir::new(
 389             self.blocks,
 390             IndexVec::from_elem_n(
 391                 SourceScopeData { span: self.span, parent_scope: None }, 1
 392             ),
 393             ClearCrossCrate::Clear,
 394             IndexVec::new(),
 395             None,
 396             self.local_decls,
 397             self.sig.inputs().len(),
 398             vec![],
 399             self.span
 400         )
 401     }
 402
 403     fn source_info(&self) -> SourceInfo {
 404         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 405     }
 406
 407     fn block(
 408         &mut self,
 409         statements: Vec<Statement<'tcx>>,
 410         kind: TerminatorKind<'tcx>,
 411         is_cleanup: bool
 412     ) -> BasicBlock {
 413         let source_info = self.source_info();
 414         self.blocks.push(BasicBlockData {
 415             statements,
 416             terminator: Some(Terminator { source_info, kind }),
 417             is_cleanup,
 418         })
 419     }
 420
 421     /// Gives the index of an upcoming BasicBlock, with an offset.
 422     /// offset=0 will give you the index of the next BasicBlock,
 423     /// offset=1 will give the index of the next-to-next block,
 424     /// offset=-1 will give you the index of the last-created block
 425     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 426         BasicBlock::new(self.blocks.len() + offset)
 427     }
 428
 429     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 430         Statement {
 431             source_info: self.source_info(),
 432             kind,
 433         }
 434     }
 435
 436     fn copy_shim(&mut self) {
 437         let rcvr = Place::Local(Local::new(1+0)).deref();
 438         let ret_statement = self.make_statement(
 439             StatementKind::Assign(
 440                 Place::Local(RETURN_PLACE),
 441                 box Rvalue::Use(Operand::Copy(rcvr))
 442             )
 443         );
 444         self.block(vec![ret_statement], TerminatorKind::Return, false);
 445     }
 446
 447     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 448         let span = self.span;
 449         Place::Local(
 450             self.local_decls.push(temp_decl(mutability, ty, span))
 451         )
 452     }
 453
 454     fn make_clone_call(
 455         &mut self,
 456         dest: Place<'tcx>,
 457         src: Place<'tcx>,
 458         ty: Ty<'tcx>,
 459         next: BasicBlock,
 460         cleanup: BasicBlock
 461     ) {
 462         let tcx = self.tcx;
 463
 464         let substs = Substs::for_item(tcx, self.def_id, |param, _| {
 465             match param.kind {
 466                 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
 467                 GenericParamDefKind::Type {..} => ty.into(),
 468             }
 469         });
 470
 471         // `func == Clone::clone(&ty) -> ty`
 472         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 473         let func = Operand::Constant(box Constant {
 474             span: self.span,
 475             ty: func_ty,
 476             user_ty: None,
 477             literal: ty::Const::zero_sized(self.tcx, func_ty),
 478         });
 479
 480         let ref_loc = self.make_place(
 481             Mutability::Not,
 482             tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 483                 ty,
 484                 mutbl: hir::Mutability::MutImmutable,
 485             })
 486         );
 487
 488         // `let ref_loc: &ty = &src;`
 489         let statement = self.make_statement(
 490             StatementKind::Assign(
 491                 ref_loc.clone(),
 492                 box Rvalue::Ref(tcx.types.re_erased, BorrowKind::Shared, src)
 493             )
 494         );
 495
 496         // `let loc = Clone::clone(ref_loc);`
 497         self.block(vec![statement], TerminatorKind::Call {
 498             func,
 499             args: vec![Operand::Move(ref_loc)],
 500             destination: Some((dest, next)),
 501             cleanup: Some(cleanup),
 502             from_hir_call: true,
 503         }, false);
 504     }
 505
 506     fn loop_header(
 507         &mut self,
 508         beg: Place<'tcx>,
 509         end: Place<'tcx>,
 510         loop_body: BasicBlock,
 511         loop_end: BasicBlock,
 512         is_cleanup: bool
 513     ) {
 514         let tcx = self.tcx;
 515
 516         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 517         let compute_cond = self.make_statement(
 518             StatementKind::Assign(
 519                 cond.clone(),
 520                 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
 521             )
 522         );
 523
 524         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 525         self.block(
 526             vec![compute_cond],
 527             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 528             is_cleanup
 529         );
 530     }
 531
 532     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 533         box Constant {
 534             span: self.span,
 535             ty: self.tcx.types.usize,
 536             user_ty: None,
 537             literal: ty::Const::from_usize(self.tcx, value),
 538         }
 539     }
 540
 541     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 542         let tcx = self.tcx;
 543         let span = self.span;
 544
 545         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 546         let end = self.make_place(Mutability::Not, tcx.types.usize);
 547
 548         // BB #0
 549         // `let mut beg = 0;`
 550         // `let end = len;`
 551         // `goto #1;`
 552         let inits = vec![
 553             self.make_statement(
 554                 StatementKind::Assign(
 555                     Place::Local(beg),
 556                     box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 557                 )
 558             ),
 559             self.make_statement(
 560                 StatementKind::Assign(
 561                     end.clone(),
 562                     box Rvalue::Use(Operand::Constant(self.make_usize(len)))
 563                 )
 564             )
 565         ];
 566         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 567
 568         // BB #1: loop {
 569         //     BB #2;
 570         //     BB #3;
 571         // }
 572         // BB #4;
 573         self.loop_header(Place::Local(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 574
 575         // BB #2
 576         // `dest[i] = Clone::clone(src[beg])`;
 577         // Goto #3 if ok, #5 if unwinding happens.
 578         let dest_field = dest.clone().index(beg);
 579         let src_field = src.index(beg);
 580         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
 581                              BasicBlock::new(5));
 582
 583         // BB #3
 584         // `beg = beg + 1;`
 585         // `goto #1`;
 586         let statements = vec![
 587             self.make_statement(
 588                 StatementKind::Assign(
 589                     Place::Local(beg),
 590                     box Rvalue::BinaryOp(
 591                         BinOp::Add,
 592                         Operand::Copy(Place::Local(beg)),
 593                         Operand::Constant(self.make_usize(1))
 594                     )
 595                 )
 596             )
 597         ];
 598         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 599
 600         // BB #4
 601         // `return dest;`
 602         self.block(vec![], TerminatorKind::Return, false);
 603
 604         // BB #5 (cleanup)
 605         // `let end = beg;`
 606         // `let mut beg = 0;`
 607         // goto #6;
 608         let end = beg;
 609         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 610         let init = self.make_statement(
 611             StatementKind::Assign(
 612                 Place::Local(beg),
 613                 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
 614             )
 615         );
 616         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 617
 618         // BB #6 (cleanup): loop {
 619         //     BB #7;
 620         //     BB #8;
 621         // }
 622         // BB #9;
 623         self.loop_header(Place::Local(beg), Place::Local(end),
 624                          BasicBlock::new(7), BasicBlock::new(9), true);
 625
 626         // BB #7 (cleanup)
 627         // `drop(dest[beg])`;
 628         self.block(vec![], TerminatorKind::Drop {
 629             location: dest.index(beg),
 630             target: BasicBlock::new(8),
 631             unwind: None,
 632         }, true);
 633
 634         // BB #8 (cleanup)
 635         // `beg = beg + 1;`
 636         // `goto #6;`
 637         let statement = self.make_statement(
 638             StatementKind::Assign(
 639                 Place::Local(beg),
 640                 box Rvalue::BinaryOp(
 641                     BinOp::Add,
 642                     Operand::Copy(Place::Local(beg)),
 643                     Operand::Constant(self.make_usize(1))
 644                 )
 645             )
 646         );
 647         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 648
 649         // BB #9 (resume)
 650         self.block(vec![], TerminatorKind::Resume, true);
 651     }
 652
 653     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
 654                           src: Place<'tcx>, tys: I)
 655             where I: Iterator<Item = ty::Ty<'tcx>> {
 656         let mut previous_field = None;
 657         for (i, ity) in tys.enumerate() {
 658             let field = Field::new(i);
 659             let src_field = src.clone().field(field, ity);
 660
 661             let dest_field = dest.clone().field(field, ity);
 662
 663             // #(2i + 1) is the cleanup block for the previous clone operation
 664             let cleanup_block = self.block_index_offset(1);
 665             // #(2i + 2) is the next cloning block
 666             // (or the Return terminator if this is the last block)
 667             let next_block = self.block_index_offset(2);
 668
 669             // BB #(2i)
 670             // `dest.i = Clone::clone(&src.i);`
 671             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 672             self.make_clone_call(
 673                 dest_field.clone(),
 674                 src_field,
 675                 ity,
 676                 next_block,
 677                 cleanup_block,
 678             );
 679
 680             // BB #(2i + 1) (cleanup)
 681             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 682                 // Drop previous field and goto previous cleanup block.
 683                 self.block(vec![], TerminatorKind::Drop {
 684                     location: previous_field,
 685                     target: previous_cleanup,
 686                     unwind: None,
 687                 }, true);
 688             } else {
 689                 // Nothing to drop, just resume.
 690                 self.block(vec![], TerminatorKind::Resume, true);
 691             }
 692
 693             previous_field = Some((dest_field, cleanup_block));
 694         }
 695
 696         self.block(vec![], TerminatorKind::Return, false);
 697     }
 698 }
 699
 700 /// Build a "call" shim for `def_id`. The shim calls the
 701 /// function specified by `call_kind`, first adjusting its first
 702 /// argument according to `rcvr_adjustment`.
 703 ///
 704 /// If `untuple_args` is a vec of types, the second argument of the
 705 /// function will be untupled as these types.
 706 fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 707                              def_id: DefId,
 708                              rcvr_adjustment: Adjustment,
 709                              call_kind: CallKind,
 710                              untuple_args: Option<&[Ty<'tcx>]>)
 711                              -> Mir<'tcx>
 712 {
 713     debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
 714             call_kind={:?}, untuple_args={:?})",
 715            def_id, rcvr_adjustment, call_kind, untuple_args);
 716
 717     let sig = tcx.fn_sig(def_id);
 718     let sig = tcx.erase_late_bound_regions(&sig);
 719     let span = tcx.def_span(def_id);
 720
 721     debug!("build_call_shim: sig={:?}", sig);
 722
 723     let mut local_decls = local_decls_for_sig(&sig, span);
 724     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 725
 726     let rcvr_arg = Local::new(1+0);
 727     let rcvr_l = Place::Local(rcvr_arg);
 728     let mut statements = vec![];
 729
 730     let rcvr = match rcvr_adjustment {
 731         Adjustment::Identity => Operand::Move(rcvr_l),
 732         Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
 733         Adjustment::DerefMove => {
 734             // fn(Self, ...) -> fn(*mut Self, ...)
 735             let arg_ty = local_decls[rcvr_arg].ty;
 736             assert!(arg_ty.is_self());
 737             local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
 738
 739             Operand::Move(rcvr_l.deref())
 740         }
 741         Adjustment::RefMut => {
 742             // let rcvr = &mut rcvr;
 743             let ref_rcvr = local_decls.push(temp_decl(
 744                 Mutability::Not,
 745                 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 746                     ty: sig.inputs()[0],
 747                     mutbl: hir::Mutability::MutMutable
 748                 }),
 749                 span
 750             ));
 751             let borrow_kind = BorrowKind::Mut {
 752                 allow_two_phase_borrow: false,
 753             };
 754             statements.push(Statement {
 755                 source_info,
 756                 kind: StatementKind::Assign(
 757                     Place::Local(ref_rcvr),
 758                     box Rvalue::Ref(tcx.types.re_erased, borrow_kind, rcvr_l)
 759                 )
 760             });
 761             Operand::Move(Place::Local(ref_rcvr))
 762         }
 763     };
 764
 765     let (callee, mut args) = match call_kind {
 766         CallKind::Indirect => (rcvr, vec![]),
 767         CallKind::Direct(def_id) => {
 768             let ty = tcx.type_of(def_id);
 769             (Operand::Constant(box Constant {
 770                 span,
 771                 ty,
 772                 user_ty: None,
 773                 literal: ty::Const::zero_sized(tcx, ty),
 774              }),
 775              vec![rcvr])
 776         }
 777     };
 778
 779     if let Some(untuple_args) = untuple_args {
 780         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 781             let arg_place = Place::Local(Local::new(1+1));
 782             Operand::Move(arg_place.field(Field::new(i), *ity))
 783         }));
 784     } else {
 785         args.extend((1..sig.inputs().len()).map(|i| {
 786             Operand::Move(Place::Local(Local::new(1+i)))
 787         }));
 788     }
 789
 790     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 791     let mut blocks = IndexVec::with_capacity(n_blocks);
 792     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 793         blocks.push(BasicBlockData {
 794             statements,
 795             terminator: Some(Terminator { source_info, kind }),
 796             is_cleanup
 797         })
 798     };
 799
 800     // BB #0
 801     block(&mut blocks, statements, TerminatorKind::Call {
 802         func: callee,
 803         args,
 804         destination: Some((Place::Local(RETURN_PLACE),
 805                            BasicBlock::new(1))),
 806         cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 807             Some(BasicBlock::new(3))
 808         } else {
 809             None
 810         },
 811         from_hir_call: true,
 812     }, false);
 813
 814     if let Adjustment::RefMut = rcvr_adjustment {
 815         // BB #1 - drop for Self
 816         block(&mut blocks, vec![], TerminatorKind::Drop {
 817             location: Place::Local(rcvr_arg),
 818             target: BasicBlock::new(2),
 819             unwind: None
 820         }, false);
 821     }
 822     // BB #1/#2 - return
 823     block(&mut blocks, vec![], TerminatorKind::Return, false);
 824     if let Adjustment::RefMut = rcvr_adjustment {
 825         // BB #3 - drop if closure panics
 826         block(&mut blocks, vec![], TerminatorKind::Drop {
 827             location: Place::Local(rcvr_arg),
 828             target: BasicBlock::new(4),
 829             unwind: None
 830         }, true);
 831
 832         // BB #4 - resume
 833         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 834     }
 835
 836     let mut mir = Mir::new(
 837         blocks,
 838         IndexVec::from_elem_n(
 839             SourceScopeData { span: span, parent_scope: None }, 1
 840         ),
 841         ClearCrossCrate::Clear,
 842         IndexVec::new(),
 843         None,
 844         local_decls,
 845         sig.inputs().len(),
 846         vec![],
 847         span
 848     );
 849     if let Abi::RustCall = sig.abi {
 850         mir.spread_arg = Some(Local::new(sig.inputs().len()));
 851     }
 852     mir
 853 }
 854
 855 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 856                                       ctor_id: ast::NodeId,
 857                                       fields: &[hir::StructField],
 858                                       span: Span)
 859                                       -> Mir<'tcx>
 860 {
 861     let tcx = infcx.tcx;
 862     let gcx = tcx.global_tcx();
 863     let def_id = tcx.hir().local_def_id(ctor_id);
 864     let param_env = gcx.param_env(def_id);
 865
 866     // Normalize the sig.
 867     let sig = gcx.fn_sig(def_id)
 868         .no_bound_vars()
 869         .expect("LBR in ADT constructor signature");
 870     let sig = gcx.normalize_erasing_regions(param_env, sig);
 871
 872     let (adt_def, substs) = match sig.output().sty {
 873         ty::Adt(adt_def, substs) => (adt_def, substs),
 874         _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
 875     };
 876
 877     debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
 878
 879     let local_decls = local_decls_for_sig(&sig, span);
 880
 881     let source_info = SourceInfo {
 882         span,
 883         scope: OUTERMOST_SOURCE_SCOPE
 884     };
 885
 886     let variant_no = if adt_def.is_enum() {
 887         adt_def.variant_index_with_id(def_id)
 888     } else {
 889         VariantIdx::new(0)
 890     };
 891
 892     // return = ADT(arg0, arg1, ...); return
 893     let start_block = BasicBlockData {
 894         statements: vec![Statement {
 895             source_info,
 896             kind: StatementKind::Assign(
 897                 Place::Local(RETURN_PLACE),
 898                 box Rvalue::Aggregate(
 899                     box AggregateKind::Adt(adt_def, variant_no, substs, None, None),
 900                     (1..sig.inputs().len()+1).map(|i| {
 901                         Operand::Move(Place::Local(Local::new(i)))
 902                     }).collect()
 903                 )
 904             )
 905         }],
 906         terminator: Some(Terminator {
 907             source_info,
 908             kind: TerminatorKind::Return,
 909         }),
 910         is_cleanup: false
 911     };
 912
 913     Mir::new(
 914         IndexVec::from_elem_n(start_block, 1),
 915         IndexVec::from_elem_n(
 916             SourceScopeData { span: span, parent_scope: None }, 1
 917         ),
 918         ClearCrossCrate::Clear,
 919         IndexVec::new(),
 920         None,
 921         local_decls,
 922         sig.inputs().len(),
 923         vec![],
 924         span
 925     )
 926 }