src/librustc_mir/shim.rs

   1 use rustc::mir::*;
   2 use rustc::ty::layout::VariantIdx;
   3 use rustc::ty::query::Providers;
   4 use rustc::ty::subst::{InternalSubsts, Subst};
   5 use rustc::ty::{self, Ty, TyCtxt};
   6 use rustc_hir as hir;
   7 use rustc_hir::def_id::DefId;
   8
   9 use rustc_index::vec::{Idx, IndexVec};
  10
  11 use rustc_span::{sym, Span};
  12 use rustc_target::spec::abi::Abi;
  13
  14 use std::fmt;
  15 use std::iter;
  16
  17 use crate::transform::{
  18     add_call_guards, add_moves_for_packed_drops, no_landing_pads, remove_noop_landing_pads,
  19     run_passes, simplify,
  20 };
  21 use crate::util::elaborate_drops::{self, DropElaborator, DropFlagMode, DropStyle};
  22 use crate::util::expand_aggregate;
  23 use crate::util::patch::MirPatch;
  24
  25 pub fn provide(providers: &mut Providers<'_>) {
  26     providers.mir_shims = make_shim;
  27 }
  28
  29 fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> &'tcx BodyAndCache<'tcx> {
  30     debug!("make_shim({:?})", instance);
  31
  32     let mut result = match instance {
  33         ty::InstanceDef::Item(..) => bug!("item {:?} passed to make_shim", instance),
  34         ty::InstanceDef::VtableShim(def_id) => {
  35             build_call_shim(tcx, instance, Adjustment::DerefMove, CallKind::Direct(def_id), None)
  36         }
  37         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  38             let trait_ = tcx.trait_of_item(def_id).unwrap();
  39             let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
  40                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  41                 Some(ty::ClosureKind::FnMut) | Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  42                 None => bug!("fn pointer {:?} is not an fn", ty),
  43             };
  44             // HACK: we need the "real" argument types for the MIR,
  45             // but because our substs are (Self, Args), where Args
  46             // is a tuple, we must include the *concrete* argument
  47             // types in the MIR. They will be substituted again with
  48             // the param-substs, but because they are concrete, this
  49             // will not do any harm.
  50             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  51             let arg_tys = sig.inputs();
  52
  53             build_call_shim(tcx, instance, adjustment, CallKind::Indirect, Some(arg_tys))
  54         }
  55         // We are generating a call back to our def-id, which the
  56         // codegen backend knows to turn to an actual call, be it
  57         // a virtual call, or a direct call to a function for which
  58         // indirect calls must be codegen'd differently than direct ones
  59         // (such as `#[track_caller]`).
  60         ty::InstanceDef::ReifyShim(def_id) => {
  61             build_call_shim(tcx, instance, Adjustment::Identity, CallKind::Direct(def_id), None)
  62         }
  63         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
  64             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  65             let call_mut = tcx
  66                 .associated_items(fn_mut)
  67                 .find(|it| it.kind == ty::AssocKind::Method)
  68                 .unwrap()
  69                 .def_id;
  70
  71             build_call_shim(tcx, instance, Adjustment::RefMut, CallKind::Direct(call_mut), None)
  72         }
  73         ty::InstanceDef::DropGlue(def_id, ty) => build_drop_shim(tcx, def_id, ty),
  74         ty::InstanceDef::CloneShim(def_id, ty) => {
  75             let name = tcx.item_name(def_id);
  76             if name == sym::clone {
  77                 build_clone_shim(tcx, def_id, ty)
  78             } else if name == sym::clone_from {
  79                 debug!("make_shim({:?}: using default trait implementation", instance);
  80                 return tcx.optimized_mir(def_id);
  81             } else {
  82                 bug!("builtin clone shim {:?} not supported", instance)
  83             }
  84         }
  85         ty::InstanceDef::Virtual(..) => {
  86             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
  87         }
  88         ty::InstanceDef::Intrinsic(_) => {
  89             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
  90         }
  91     };
  92     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
  93
  94     run_passes(
  95         tcx,
  96         &mut result,
  97         instance,
  98         None,
  99         MirPhase::Const,
 100         &[
 101             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 102             &no_landing_pads::NoLandingPads::new(tcx),
 103             &remove_noop_landing_pads::RemoveNoopLandingPads,
 104             &simplify::SimplifyCfg::new("make_shim"),
 105             &add_call_guards::CriticalCallEdges,
 106         ],
 107     );
 108
 109     debug!("make_shim({:?}) = {:?}", instance, result);
 110
 111     result.ensure_predecessors();
 112     tcx.arena.alloc(result)
 113 }
 114
 115 #[derive(Copy, Clone, Debug, PartialEq)]
 116 enum Adjustment {
 117     Identity,
 118     Deref,
 119     DerefMove,
 120     RefMut,
 121 }
 122
 123 #[derive(Copy, Clone, Debug, PartialEq)]
 124 enum CallKind {
 125     Indirect,
 126     Direct(DefId),
 127 }
 128
 129 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 130     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 131     LocalDecl {
 132         mutability,
 133         ty,
 134         user_ty: UserTypeProjections::none(),
 135         source_info,
 136         internal: false,
 137         local_info: LocalInfo::Other,
 138         is_block_tail: None,
 139     }
 140 }
 141
 142 fn local_decls_for_sig<'tcx>(
 143     sig: &ty::FnSig<'tcx>,
 144     span: Span,
 145 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 146     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 147         .chain(sig.inputs().iter().map(|ity| temp_decl(Mutability::Not, ity, span)))
 148         .collect()
 149 }
 150
 151 fn build_drop_shim<'tcx>(
 152     tcx: TyCtxt<'tcx>,
 153     def_id: DefId,
 154     ty: Option<Ty<'tcx>>,
 155 ) -> BodyAndCache<'tcx> {
 156     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 157
 158     // Check if this is a generator, if so, return the drop glue for it
 159     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 160         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 161         return body.subst(tcx, substs);
 162     }
 163
 164     let substs = if let Some(ty) = ty {
 165         tcx.intern_substs(&[ty.into()])
 166     } else {
 167         InternalSubsts::identity_for_item(tcx, def_id)
 168     };
 169     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 170     let sig = tcx.erase_late_bound_regions(&sig);
 171     let span = tcx.def_span(def_id);
 172
 173     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 174
 175     let return_block = BasicBlock::new(1);
 176     let mut blocks = IndexVec::with_capacity(2);
 177     let block = |blocks: &mut IndexVec<_, _>, kind| {
 178         blocks.push(BasicBlockData {
 179             statements: vec![],
 180             terminator: Some(Terminator { source_info, kind }),
 181             is_cleanup: false,
 182         })
 183     };
 184     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 185     block(&mut blocks, TerminatorKind::Return);
 186
 187     let body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 188
 189     let mut body = BodyAndCache::new(body);
 190
 191     if let Some(..) = ty {
 192         // The first argument (index 0), but add 1 for the return value.
 193         let dropee_ptr = Place::from(Local::new(1 + 0));
 194         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 195             // Function arguments should be retagged, and we make this one raw.
 196             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 197                 0,
 198                 Statement {
 199                     source_info,
 200                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr.clone())),
 201                 },
 202             );
 203         }
 204         let patch = {
 205             let param_env = tcx.param_env(def_id).with_reveal_all();
 206             let mut elaborator =
 207                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 208             let dropee = tcx.mk_place_deref(dropee_ptr);
 209             let resume_block = elaborator.patch.resume_block();
 210             elaborate_drops::elaborate_drop(
 211                 &mut elaborator,
 212                 source_info,
 213                 &dropee,
 214                 (),
 215                 return_block,
 216                 elaborate_drops::Unwind::To(resume_block),
 217                 START_BLOCK,
 218             );
 219             elaborator.patch
 220         };
 221         patch.apply(&mut body);
 222     }
 223
 224     body
 225 }
 226
 227 fn new_body<'tcx>(
 228     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 229     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 230     arg_count: usize,
 231     span: Span,
 232 ) -> Body<'tcx> {
 233     Body::new(
 234         basic_blocks,
 235         IndexVec::from_elem_n(
 236             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 237             1,
 238         ),
 239         local_decls,
 240         IndexVec::new(),
 241         arg_count,
 242         vec![],
 243         span,
 244         vec![],
 245         None,
 246     )
 247 }
 248
 249 pub struct DropShimElaborator<'a, 'tcx> {
 250     pub body: &'a Body<'tcx>,
 251     pub patch: MirPatch<'tcx>,
 252     pub tcx: TyCtxt<'tcx>,
 253     pub param_env: ty::ParamEnv<'tcx>,
 254 }
 255
 256 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 257     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 258         Ok(())
 259     }
 260 }
 261
 262 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 263     type Path = ();
 264
 265     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 266         &mut self.patch
 267     }
 268     fn body(&self) -> &'a Body<'tcx> {
 269         self.body
 270     }
 271     fn tcx(&self) -> TyCtxt<'tcx> {
 272         self.tcx
 273     }
 274     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 275         self.param_env
 276     }
 277
 278     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 279         if let DropFlagMode::Shallow = mode { DropStyle::Static } else { DropStyle::Open }
 280     }
 281
 282     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 283         None
 284     }
 285
 286     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 287
 288     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 289         None
 290     }
 291     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 292         None
 293     }
 294     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 295         Some(())
 296     }
 297     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 298         None
 299     }
 300 }
 301
 302 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 303 fn build_clone_shim<'tcx>(
 304     tcx: TyCtxt<'tcx>,
 305     def_id: DefId,
 306     self_ty: Ty<'tcx>,
 307 ) -> BodyAndCache<'tcx> {
 308     debug!("build_clone_shim(def_id={:?})", def_id);
 309
 310     let param_env = tcx.param_env(def_id);
 311
 312     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 313     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 314
 315     let dest = Place::return_place();
 316     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 317
 318     match self_ty.kind {
 319         _ if is_copy => builder.copy_shim(),
 320         ty::Array(ty, len) => {
 321             let len = len.eval_usize(tcx, param_env);
 322             builder.array_shim(dest, src, ty, len)
 323         }
 324         ty::Closure(def_id, substs) => {
 325             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys(def_id, tcx))
 326         }
 327         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 328         _ => bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty),
 329     };
 330
 331     BodyAndCache::new(builder.into_mir())
 332 }
 333
 334 struct CloneShimBuilder<'tcx> {
 335     tcx: TyCtxt<'tcx>,
 336     def_id: DefId,
 337     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 338     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 339     span: Span,
 340     sig: ty::FnSig<'tcx>,
 341 }
 342
 343 impl CloneShimBuilder<'tcx> {
 344     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 345         // we must subst the self_ty because it's
 346         // otherwise going to be TySelf and we can't index
 347         // or access fields of a Place of type TySelf.
 348         let substs = tcx.mk_substs_trait(self_ty, &[]);
 349         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 350         let sig = tcx.erase_late_bound_regions(&sig);
 351         let span = tcx.def_span(def_id);
 352
 353         CloneShimBuilder {
 354             tcx,
 355             def_id,
 356             local_decls: local_decls_for_sig(&sig, span),
 357             blocks: IndexVec::new(),
 358             span,
 359             sig,
 360         }
 361     }
 362
 363     fn into_mir(self) -> Body<'tcx> {
 364         new_body(self.blocks, self.local_decls, self.sig.inputs().len(), self.span)
 365     }
 366
 367     fn source_info(&self) -> SourceInfo {
 368         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 369     }
 370
 371     fn block(
 372         &mut self,
 373         statements: Vec<Statement<'tcx>>,
 374         kind: TerminatorKind<'tcx>,
 375         is_cleanup: bool,
 376     ) -> BasicBlock {
 377         let source_info = self.source_info();
 378         self.blocks.push(BasicBlockData {
 379             statements,
 380             terminator: Some(Terminator { source_info, kind }),
 381             is_cleanup,
 382         })
 383     }
 384
 385     /// Gives the index of an upcoming BasicBlock, with an offset.
 386     /// offset=0 will give you the index of the next BasicBlock,
 387     /// offset=1 will give the index of the next-to-next block,
 388     /// offset=-1 will give you the index of the last-created block
 389     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 390         BasicBlock::new(self.blocks.len() + offset)
 391     }
 392
 393     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 394         Statement { source_info: self.source_info(), kind }
 395     }
 396
 397     fn copy_shim(&mut self) {
 398         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 399         let ret_statement = self.make_statement(StatementKind::Assign(box (
 400             Place::return_place(),
 401             Rvalue::Use(Operand::Copy(rcvr)),
 402         )));
 403         self.block(vec![ret_statement], TerminatorKind::Return, false);
 404     }
 405
 406     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 407         let span = self.span;
 408         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 409     }
 410
 411     fn make_clone_call(
 412         &mut self,
 413         dest: Place<'tcx>,
 414         src: Place<'tcx>,
 415         ty: Ty<'tcx>,
 416         next: BasicBlock,
 417         cleanup: BasicBlock,
 418     ) {
 419         let tcx = self.tcx;
 420
 421         let substs = tcx.mk_substs_trait(ty, &[]);
 422
 423         // `func == Clone::clone(&ty) -> ty`
 424         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 425         let func = Operand::Constant(box Constant {
 426             span: self.span,
 427             user_ty: None,
 428             literal: ty::Const::zero_sized(tcx, func_ty),
 429         });
 430
 431         let ref_loc = self.make_place(
 432             Mutability::Not,
 433             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 434         );
 435
 436         // `let ref_loc: &ty = &src;`
 437         let statement = self.make_statement(StatementKind::Assign(box (
 438             ref_loc.clone(),
 439             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 440         )));
 441
 442         // `let loc = Clone::clone(ref_loc);`
 443         self.block(
 444             vec![statement],
 445             TerminatorKind::Call {
 446                 func,
 447                 args: vec![Operand::Move(ref_loc)],
 448                 destination: Some((dest, next)),
 449                 cleanup: Some(cleanup),
 450                 from_hir_call: true,
 451             },
 452             false,
 453         );
 454     }
 455
 456     fn loop_header(
 457         &mut self,
 458         beg: Place<'tcx>,
 459         end: Place<'tcx>,
 460         loop_body: BasicBlock,
 461         loop_end: BasicBlock,
 462         is_cleanup: bool,
 463     ) {
 464         let tcx = self.tcx;
 465
 466         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 467         let compute_cond = self.make_statement(StatementKind::Assign(box (
 468             cond.clone(),
 469             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 470         )));
 471
 472         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 473         self.block(
 474             vec![compute_cond],
 475             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 476             is_cleanup,
 477         );
 478     }
 479
 480     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 481         box Constant {
 482             span: self.span,
 483             user_ty: None,
 484             literal: ty::Const::from_usize(self.tcx, value),
 485         }
 486     }
 487
 488     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 489         let tcx = self.tcx;
 490         let span = self.span;
 491
 492         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 493         let end = self.make_place(Mutability::Not, tcx.types.usize);
 494
 495         // BB #0
 496         // `let mut beg = 0;`
 497         // `let end = len;`
 498         // `goto #1;`
 499         let inits = vec![
 500             self.make_statement(StatementKind::Assign(box (
 501                 Place::from(beg),
 502                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 503             ))),
 504             self.make_statement(StatementKind::Assign(box (
 505                 end.clone(),
 506                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 507             ))),
 508         ];
 509         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 510
 511         // BB #1: loop {
 512         //     BB #2;
 513         //     BB #3;
 514         // }
 515         // BB #4;
 516         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 517
 518         // BB #2
 519         // `dest[i] = Clone::clone(src[beg])`;
 520         // Goto #3 if ok, #5 if unwinding happens.
 521         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 522         let src_field = self.tcx.mk_place_index(src, beg);
 523         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 524
 525         // BB #3
 526         // `beg = beg + 1;`
 527         // `goto #1`;
 528         let statements = vec![self.make_statement(StatementKind::Assign(box (
 529             Place::from(beg),
 530             Rvalue::BinaryOp(
 531                 BinOp::Add,
 532                 Operand::Copy(Place::from(beg)),
 533                 Operand::Constant(self.make_usize(1)),
 534             ),
 535         )))];
 536         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 537
 538         // BB #4
 539         // `return dest;`
 540         self.block(vec![], TerminatorKind::Return, false);
 541
 542         // BB #5 (cleanup)
 543         // `let end = beg;`
 544         // `let mut beg = 0;`
 545         // goto #6;
 546         let end = beg;
 547         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 548         let init = self.make_statement(StatementKind::Assign(box (
 549             Place::from(beg),
 550             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 551         )));
 552         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 553
 554         // BB #6 (cleanup): loop {
 555         //     BB #7;
 556         //     BB #8;
 557         // }
 558         // BB #9;
 559         self.loop_header(
 560             Place::from(beg),
 561             Place::from(end),
 562             BasicBlock::new(7),
 563             BasicBlock::new(9),
 564             true,
 565         );
 566
 567         // BB #7 (cleanup)
 568         // `drop(dest[beg])`;
 569         self.block(
 570             vec![],
 571             TerminatorKind::Drop {
 572                 location: self.tcx.mk_place_index(dest, beg),
 573                 target: BasicBlock::new(8),
 574                 unwind: None,
 575             },
 576             true,
 577         );
 578
 579         // BB #8 (cleanup)
 580         // `beg = beg + 1;`
 581         // `goto #6;`
 582         let statement = self.make_statement(StatementKind::Assign(box (
 583             Place::from(beg),
 584             Rvalue::BinaryOp(
 585                 BinOp::Add,
 586                 Operand::Copy(Place::from(beg)),
 587                 Operand::Constant(self.make_usize(1)),
 588             ),
 589         )));
 590         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 591
 592         // BB #9 (resume)
 593         self.block(vec![], TerminatorKind::Resume, true);
 594     }
 595
 596     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 597     where
 598         I: Iterator<Item = Ty<'tcx>>,
 599     {
 600         let mut previous_field = None;
 601         for (i, ity) in tys.enumerate() {
 602             let field = Field::new(i);
 603             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 604
 605             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 606
 607             // #(2i + 1) is the cleanup block for the previous clone operation
 608             let cleanup_block = self.block_index_offset(1);
 609             // #(2i + 2) is the next cloning block
 610             // (or the Return terminator if this is the last block)
 611             let next_block = self.block_index_offset(2);
 612
 613             // BB #(2i)
 614             // `dest.i = Clone::clone(&src.i);`
 615             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 616             self.make_clone_call(dest_field.clone(), src_field, ity, next_block, cleanup_block);
 617
 618             // BB #(2i + 1) (cleanup)
 619             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 620                 // Drop previous field and goto previous cleanup block.
 621                 self.block(
 622                     vec![],
 623                     TerminatorKind::Drop {
 624                         location: previous_field,
 625                         target: previous_cleanup,
 626                         unwind: None,
 627                     },
 628                     true,
 629                 );
 630             } else {
 631                 // Nothing to drop, just resume.
 632                 self.block(vec![], TerminatorKind::Resume, true);
 633             }
 634
 635             previous_field = Some((dest_field, cleanup_block));
 636         }
 637
 638         self.block(vec![], TerminatorKind::Return, false);
 639     }
 640 }
 641
 642 /// Builds a "call" shim for `instance`. The shim calls the
 643 /// function specified by `call_kind`, first adjusting its first
 644 /// argument according to `rcvr_adjustment`.
 645 ///
 646 /// If `untuple_args` is a vec of types, the second argument of the
 647 /// function will be untupled as these types.
 648 fn build_call_shim<'tcx>(
 649     tcx: TyCtxt<'tcx>,
 650     instance: ty::InstanceDef<'tcx>,
 651     rcvr_adjustment: Adjustment,
 652     call_kind: CallKind,
 653     untuple_args: Option<&[Ty<'tcx>]>,
 654 ) -> BodyAndCache<'tcx> {
 655     debug!(
 656         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 657             call_kind={:?}, untuple_args={:?})",
 658         instance, rcvr_adjustment, call_kind, untuple_args
 659     );
 660
 661     let def_id = instance.def_id();
 662     let sig = tcx.fn_sig(def_id);
 663     let mut sig = tcx.erase_late_bound_regions(&sig);
 664
 665     // FIXME(eddyb) avoid having this snippet both here and in
 666     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 667     if let ty::InstanceDef::VtableShim(..) = instance {
 668         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 669         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 670         let self_arg = &mut inputs_and_output[0];
 671         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 672         *self_arg = tcx.mk_mut_ptr(*self_arg);
 673         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 674     }
 675
 676     let span = tcx.def_span(def_id);
 677
 678     debug!("build_call_shim: sig={:?}", sig);
 679
 680     let mut local_decls = local_decls_for_sig(&sig, span);
 681     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 682
 683     let rcvr_arg = Local::new(1 + 0);
 684     let rcvr_l = Place::from(rcvr_arg);
 685     let mut statements = vec![];
 686
 687     let rcvr = match rcvr_adjustment {
 688         Adjustment::Identity => Operand::Move(rcvr_l),
 689         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_l)),
 690         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_l)),
 691         Adjustment::RefMut => {
 692             // let rcvr = &mut rcvr;
 693             let ref_rcvr = local_decls.push(temp_decl(
 694                 Mutability::Not,
 695                 tcx.mk_ref(
 696                     tcx.lifetimes.re_erased,
 697                     ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 698                 ),
 699                 span,
 700             ));
 701             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 702             statements.push(Statement {
 703                 source_info,
 704                 kind: StatementKind::Assign(box (
 705                     Place::from(ref_rcvr),
 706                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_l),
 707                 )),
 708             });
 709             Operand::Move(Place::from(ref_rcvr))
 710         }
 711     };
 712
 713     let (callee, mut args) = match call_kind {
 714         CallKind::Indirect => (rcvr, vec![]),
 715         CallKind::Direct(def_id) => {
 716             let ty = tcx.type_of(def_id);
 717             (
 718                 Operand::Constant(box Constant {
 719                     span,
 720                     user_ty: None,
 721                     literal: ty::Const::zero_sized(tcx, ty),
 722                 }),
 723                 vec![rcvr],
 724             )
 725         }
 726     };
 727
 728     if let Some(untuple_args) = untuple_args {
 729         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 730             let arg_place = Place::from(Local::new(1 + 1));
 731             Operand::Move(tcx.mk_place_field(arg_place, Field::new(i), *ity))
 732         }));
 733     } else {
 734         args.extend((1..sig.inputs().len()).map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 735     }
 736
 737     let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
 738     let mut blocks = IndexVec::with_capacity(n_blocks);
 739     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 740         blocks.push(BasicBlockData {
 741             statements,
 742             terminator: Some(Terminator { source_info, kind }),
 743             is_cleanup,
 744         })
 745     };
 746
 747     // BB #0
 748     block(
 749         &mut blocks,
 750         statements,
 751         TerminatorKind::Call {
 752             func: callee,
 753             args,
 754             destination: Some((Place::return_place(), BasicBlock::new(1))),
 755             cleanup: if let Adjustment::RefMut = rcvr_adjustment {
 756                 Some(BasicBlock::new(3))
 757             } else {
 758                 None
 759             },
 760             from_hir_call: true,
 761         },
 762         false,
 763     );
 764
 765     if let Adjustment::RefMut = rcvr_adjustment {
 766         // BB #1 - drop for Self
 767         block(
 768             &mut blocks,
 769             vec![],
 770             TerminatorKind::Drop {
 771                 location: Place::from(rcvr_arg),
 772                 target: BasicBlock::new(2),
 773                 unwind: None,
 774             },
 775             false,
 776         );
 777     }
 778     // BB #1/#2 - return
 779     block(&mut blocks, vec![], TerminatorKind::Return, false);
 780     if let Adjustment::RefMut = rcvr_adjustment {
 781         // BB #3 - drop if closure panics
 782         block(
 783             &mut blocks,
 784             vec![],
 785             TerminatorKind::Drop {
 786                 location: Place::from(rcvr_arg),
 787                 target: BasicBlock::new(4),
 788                 unwind: None,
 789             },
 790             true,
 791         );
 792
 793         // BB #4 - resume
 794         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 795     }
 796
 797     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 798
 799     if let Abi::RustCall = sig.abi {
 800         body.spread_arg = Some(Local::new(sig.inputs().len()));
 801     }
 802     BodyAndCache::new(body)
 803 }
 804
 805 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &BodyAndCache<'_> {
 806     debug_assert!(tcx.is_constructor(ctor_id));
 807
 808     let span =
 809         tcx.hir().span_if_local(ctor_id).unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 810
 811     let param_env = tcx.param_env(ctor_id);
 812
 813     // Normalize the sig.
 814     let sig = tcx.fn_sig(ctor_id).no_bound_vars().expect("LBR in ADT constructor signature");
 815     let sig = tcx.normalize_erasing_regions(param_env, sig);
 816
 817     let (adt_def, substs) = match sig.output().kind {
 818         ty::Adt(adt_def, substs) => (adt_def, substs),
 819         _ => bug!("unexpected type for ADT ctor {:?}", sig.output()),
 820     };
 821
 822     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 823
 824     let local_decls = local_decls_for_sig(&sig, span);
 825
 826     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 827
 828     let variant_index = if adt_def.is_enum() {
 829         adt_def.variant_index_with_ctor_id(ctor_id)
 830     } else {
 831         VariantIdx::new(0)
 832     };
 833
 834     // Generate the following MIR:
 835     //
 836     // (return as Variant).field0 = arg0;
 837     // (return as Variant).field1 = arg1;
 838     //
 839     // return;
 840     debug!("build_ctor: variant_index={:?}", variant_index);
 841
 842     let statements = expand_aggregate(
 843         Place::return_place(),
 844         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
 845             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
 846         }),
 847         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 848         source_info,
 849         tcx,
 850     )
 851     .collect();
 852
 853     let start_block = BasicBlockData {
 854         statements,
 855         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
 856         is_cleanup: false,
 857     };
 858
 859     let body =
 860         new_body(IndexVec::from_elem_n(start_block, 1), local_decls, sig.inputs().len(), span);
 861
 862     crate::util::dump_mir(
 863         tcx,
 864         None,
 865         "mir_map",
 866         &0,
 867         crate::transform::MirSource::item(ctor_id),
 868         &body,
 869         |_, _| Ok(()),
 870     );
 871
 872     let mut body = BodyAndCache::new(body);
 873     body.ensure_predecessors();
 874     tcx.arena.alloc(body)
 875 }