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