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) => build_call_shim(
  35             tcx,
  36             instance,
  37             Some(Adjustment::DerefMove),
  38             CallKind::Direct(def_id),
  39             None,
  40         ),
  41         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  42             let trait_ = tcx.trait_of_item(def_id).unwrap();
  43             let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
  44                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  45                 Some(ty::ClosureKind::FnMut) | Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  46                 None => bug!("fn pointer {:?} is not an fn", ty),
  47             };
  48             // HACK: we need the "real" argument types for the MIR,
  49             // but because our substs are (Self, Args), where Args
  50             // is a tuple, we must include the *concrete* argument
  51             // types in the MIR. They will be substituted again with
  52             // the param-substs, but because they are concrete, this
  53             // will not do any harm.
  54             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  55             let arg_tys = sig.inputs();
  56
  57             build_call_shim(tcx, instance, Some(adjustment), CallKind::Indirect, Some(arg_tys))
  58         }
  59         // We are generating a call back to our def-id, which the
  60         // codegen backend knows to turn to an actual call, be it
  61         // a virtual call, or a direct call to a function for which
  62         // indirect calls must be codegen'd differently than direct ones
  63         // (such as `#[track_caller]`).
  64         ty::InstanceDef::ReifyShim(def_id) => {
  65             build_call_shim(tcx, instance, None, CallKind::Direct(def_id), None)
  66         }
  67         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
  68             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  69             let call_mut = tcx
  70                 .associated_items(fn_mut)
  71                 .find(|it| it.kind == ty::AssocKind::Method)
  72                 .unwrap()
  73                 .def_id;
  74
  75             build_call_shim(
  76                 tcx,
  77                 instance,
  78                 Some(Adjustment::RefMut),
  79                 CallKind::Direct(call_mut),
  80                 None,
  81             )
  82         }
  83         ty::InstanceDef::DropGlue(def_id, ty) => build_drop_shim(tcx, def_id, ty),
  84         ty::InstanceDef::CloneShim(def_id, ty) => {
  85             let name = tcx.item_name(def_id);
  86             if name == sym::clone {
  87                 build_clone_shim(tcx, def_id, ty)
  88             } else if name == sym::clone_from {
  89                 debug!("make_shim({:?}: using default trait implementation", instance);
  90                 return tcx.optimized_mir(def_id);
  91             } else {
  92                 bug!("builtin clone shim {:?} not supported", instance)
  93             }
  94         }
  95         ty::InstanceDef::Virtual(..) => {
  96             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
  97         }
  98         ty::InstanceDef::Intrinsic(_) => {
  99             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 100         }
 101     };
 102     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 103
 104     run_passes(
 105         tcx,
 106         &mut result,
 107         instance,
 108         None,
 109         MirPhase::Const,
 110         &[
 111             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 112             &no_landing_pads::NoLandingPads::new(tcx),
 113             &remove_noop_landing_pads::RemoveNoopLandingPads,
 114             &simplify::SimplifyCfg::new("make_shim"),
 115             &add_call_guards::CriticalCallEdges,
 116         ],
 117     );
 118
 119     debug!("make_shim({:?}) = {:?}", instance, result);
 120
 121     result.ensure_predecessors();
 122     tcx.arena.alloc(result)
 123 }
 124
 125 #[derive(Copy, Clone, Debug, PartialEq)]
 126 enum Adjustment {
 127     Identity,
 128     Deref,
 129     DerefMove,
 130     RefMut,
 131 }
 132
 133 #[derive(Copy, Clone, Debug, PartialEq)]
 134 enum CallKind {
 135     Indirect,
 136     Direct(DefId),
 137 }
 138
 139 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 140     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 141     LocalDecl {
 142         mutability,
 143         ty,
 144         user_ty: UserTypeProjections::none(),
 145         source_info,
 146         internal: false,
 147         local_info: LocalInfo::Other,
 148         is_block_tail: None,
 149     }
 150 }
 151
 152 fn local_decls_for_sig<'tcx>(
 153     sig: &ty::FnSig<'tcx>,
 154     span: Span,
 155 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 156     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 157         .chain(sig.inputs().iter().map(|ity| temp_decl(Mutability::Not, ity, span)))
 158         .collect()
 159 }
 160
 161 fn build_drop_shim<'tcx>(
 162     tcx: TyCtxt<'tcx>,
 163     def_id: DefId,
 164     ty: Option<Ty<'tcx>>,
 165 ) -> BodyAndCache<'tcx> {
 166     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 167
 168     // Check if this is a generator, if so, return the drop glue for it
 169     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 170         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 171         return body.subst(tcx, substs);
 172     }
 173
 174     let substs = if let Some(ty) = ty {
 175         tcx.intern_substs(&[ty.into()])
 176     } else {
 177         InternalSubsts::identity_for_item(tcx, def_id)
 178     };
 179     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 180     let sig = tcx.erase_late_bound_regions(&sig);
 181     let span = tcx.def_span(def_id);
 182
 183     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 184
 185     let return_block = BasicBlock::new(1);
 186     let mut blocks = IndexVec::with_capacity(2);
 187     let block = |blocks: &mut IndexVec<_, _>, kind| {
 188         blocks.push(BasicBlockData {
 189             statements: vec![],
 190             terminator: Some(Terminator { source_info, kind }),
 191             is_cleanup: false,
 192         })
 193     };
 194     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 195     block(&mut blocks, TerminatorKind::Return);
 196
 197     let body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 198
 199     let mut body = BodyAndCache::new(body);
 200
 201     if let Some(..) = ty {
 202         // The first argument (index 0), but add 1 for the return value.
 203         let dropee_ptr = Place::from(Local::new(1 + 0));
 204         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 205             // Function arguments should be retagged, and we make this one raw.
 206             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 207                 0,
 208                 Statement {
 209                     source_info,
 210                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr.clone())),
 211                 },
 212             );
 213         }
 214         let patch = {
 215             let param_env = tcx.param_env(def_id).with_reveal_all();
 216             let mut elaborator =
 217                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 218             let dropee = tcx.mk_place_deref(dropee_ptr);
 219             let resume_block = elaborator.patch.resume_block();
 220             elaborate_drops::elaborate_drop(
 221                 &mut elaborator,
 222                 source_info,
 223                 &dropee,
 224                 (),
 225                 return_block,
 226                 elaborate_drops::Unwind::To(resume_block),
 227                 START_BLOCK,
 228             );
 229             elaborator.patch
 230         };
 231         patch.apply(&mut body);
 232     }
 233
 234     body
 235 }
 236
 237 fn new_body<'tcx>(
 238     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 239     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 240     arg_count: usize,
 241     span: Span,
 242 ) -> Body<'tcx> {
 243     Body::new(
 244         basic_blocks,
 245         IndexVec::from_elem_n(
 246             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 247             1,
 248         ),
 249         local_decls,
 250         IndexVec::new(),
 251         arg_count,
 252         vec![],
 253         span,
 254         vec![],
 255         None,
 256     )
 257 }
 258
 259 pub struct DropShimElaborator<'a, 'tcx> {
 260     pub body: &'a Body<'tcx>,
 261     pub patch: MirPatch<'tcx>,
 262     pub tcx: TyCtxt<'tcx>,
 263     pub param_env: ty::ParamEnv<'tcx>,
 264 }
 265
 266 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 267     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 268         Ok(())
 269     }
 270 }
 271
 272 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 273     type Path = ();
 274
 275     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 276         &mut self.patch
 277     }
 278     fn body(&self) -> &'a Body<'tcx> {
 279         self.body
 280     }
 281     fn tcx(&self) -> TyCtxt<'tcx> {
 282         self.tcx
 283     }
 284     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 285         self.param_env
 286     }
 287
 288     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 289         if let DropFlagMode::Shallow = mode { DropStyle::Static } else { DropStyle::Open }
 290     }
 291
 292     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 293         None
 294     }
 295
 296     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 297
 298     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 299         None
 300     }
 301     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 302         None
 303     }
 304     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 305         Some(())
 306     }
 307     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 308         None
 309     }
 310 }
 311
 312 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 313 fn build_clone_shim<'tcx>(
 314     tcx: TyCtxt<'tcx>,
 315     def_id: DefId,
 316     self_ty: Ty<'tcx>,
 317 ) -> BodyAndCache<'tcx> {
 318     debug!("build_clone_shim(def_id={:?})", def_id);
 319
 320     let param_env = tcx.param_env(def_id);
 321
 322     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 323     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 324
 325     let dest = Place::return_place();
 326     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 327
 328     match self_ty.kind {
 329         _ if is_copy => builder.copy_shim(),
 330         ty::Array(ty, len) => {
 331             let len = len.eval_usize(tcx, param_env);
 332             builder.array_shim(dest, src, ty, len)
 333         }
 334         ty::Closure(def_id, substs) => {
 335             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys(def_id, tcx))
 336         }
 337         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 338         _ => bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty),
 339     };
 340
 341     BodyAndCache::new(builder.into_mir())
 342 }
 343
 344 struct CloneShimBuilder<'tcx> {
 345     tcx: TyCtxt<'tcx>,
 346     def_id: DefId,
 347     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 348     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 349     span: Span,
 350     sig: ty::FnSig<'tcx>,
 351 }
 352
 353 impl CloneShimBuilder<'tcx> {
 354     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 355         // we must subst the self_ty because it's
 356         // otherwise going to be TySelf and we can't index
 357         // or access fields of a Place of type TySelf.
 358         let substs = tcx.mk_substs_trait(self_ty, &[]);
 359         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 360         let sig = tcx.erase_late_bound_regions(&sig);
 361         let span = tcx.def_span(def_id);
 362
 363         CloneShimBuilder {
 364             tcx,
 365             def_id,
 366             local_decls: local_decls_for_sig(&sig, span),
 367             blocks: IndexVec::new(),
 368             span,
 369             sig,
 370         }
 371     }
 372
 373     fn into_mir(self) -> Body<'tcx> {
 374         new_body(self.blocks, self.local_decls, self.sig.inputs().len(), self.span)
 375     }
 376
 377     fn source_info(&self) -> SourceInfo {
 378         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 379     }
 380
 381     fn block(
 382         &mut self,
 383         statements: Vec<Statement<'tcx>>,
 384         kind: TerminatorKind<'tcx>,
 385         is_cleanup: bool,
 386     ) -> BasicBlock {
 387         let source_info = self.source_info();
 388         self.blocks.push(BasicBlockData {
 389             statements,
 390             terminator: Some(Terminator { source_info, kind }),
 391             is_cleanup,
 392         })
 393     }
 394
 395     /// Gives the index of an upcoming BasicBlock, with an offset.
 396     /// offset=0 will give you the index of the next BasicBlock,
 397     /// offset=1 will give the index of the next-to-next block,
 398     /// offset=-1 will give you the index of the last-created block
 399     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 400         BasicBlock::new(self.blocks.len() + offset)
 401     }
 402
 403     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 404         Statement { source_info: self.source_info(), kind }
 405     }
 406
 407     fn copy_shim(&mut self) {
 408         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 409         let ret_statement = self.make_statement(StatementKind::Assign(box (
 410             Place::return_place(),
 411             Rvalue::Use(Operand::Copy(rcvr)),
 412         )));
 413         self.block(vec![ret_statement], TerminatorKind::Return, false);
 414     }
 415
 416     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 417         let span = self.span;
 418         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 419     }
 420
 421     fn make_clone_call(
 422         &mut self,
 423         dest: Place<'tcx>,
 424         src: Place<'tcx>,
 425         ty: Ty<'tcx>,
 426         next: BasicBlock,
 427         cleanup: BasicBlock,
 428     ) {
 429         let tcx = self.tcx;
 430
 431         let substs = tcx.mk_substs_trait(ty, &[]);
 432
 433         // `func == Clone::clone(&ty) -> ty`
 434         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 435         let func = Operand::Constant(box Constant {
 436             span: self.span,
 437             user_ty: None,
 438             literal: ty::Const::zero_sized(tcx, func_ty),
 439         });
 440
 441         let ref_loc = self.make_place(
 442             Mutability::Not,
 443             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 444         );
 445
 446         // `let ref_loc: &ty = &src;`
 447         let statement = self.make_statement(StatementKind::Assign(box (
 448             ref_loc.clone(),
 449             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 450         )));
 451
 452         // `let loc = Clone::clone(ref_loc);`
 453         self.block(
 454             vec![statement],
 455             TerminatorKind::Call {
 456                 func,
 457                 args: vec![Operand::Move(ref_loc)],
 458                 destination: Some((dest, next)),
 459                 cleanup: Some(cleanup),
 460                 from_hir_call: true,
 461             },
 462             false,
 463         );
 464     }
 465
 466     fn loop_header(
 467         &mut self,
 468         beg: Place<'tcx>,
 469         end: Place<'tcx>,
 470         loop_body: BasicBlock,
 471         loop_end: BasicBlock,
 472         is_cleanup: bool,
 473     ) {
 474         let tcx = self.tcx;
 475
 476         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 477         let compute_cond = self.make_statement(StatementKind::Assign(box (
 478             cond.clone(),
 479             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 480         )));
 481
 482         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 483         self.block(
 484             vec![compute_cond],
 485             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 486             is_cleanup,
 487         );
 488     }
 489
 490     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 491         box Constant {
 492             span: self.span,
 493             user_ty: None,
 494             literal: ty::Const::from_usize(self.tcx, value),
 495         }
 496     }
 497
 498     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 499         let tcx = self.tcx;
 500         let span = self.span;
 501
 502         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 503         let end = self.make_place(Mutability::Not, tcx.types.usize);
 504
 505         // BB #0
 506         // `let mut beg = 0;`
 507         // `let end = len;`
 508         // `goto #1;`
 509         let inits = vec![
 510             self.make_statement(StatementKind::Assign(box (
 511                 Place::from(beg),
 512                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 513             ))),
 514             self.make_statement(StatementKind::Assign(box (
 515                 end.clone(),
 516                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 517             ))),
 518         ];
 519         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 520
 521         // BB #1: loop {
 522         //     BB #2;
 523         //     BB #3;
 524         // }
 525         // BB #4;
 526         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 527
 528         // BB #2
 529         // `dest[i] = Clone::clone(src[beg])`;
 530         // Goto #3 if ok, #5 if unwinding happens.
 531         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 532         let src_field = self.tcx.mk_place_index(src, beg);
 533         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 534
 535         // BB #3
 536         // `beg = beg + 1;`
 537         // `goto #1`;
 538         let statements = vec![self.make_statement(StatementKind::Assign(box (
 539             Place::from(beg),
 540             Rvalue::BinaryOp(
 541                 BinOp::Add,
 542                 Operand::Copy(Place::from(beg)),
 543                 Operand::Constant(self.make_usize(1)),
 544             ),
 545         )))];
 546         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 547
 548         // BB #4
 549         // `return dest;`
 550         self.block(vec![], TerminatorKind::Return, false);
 551
 552         // BB #5 (cleanup)
 553         // `let end = beg;`
 554         // `let mut beg = 0;`
 555         // goto #6;
 556         let end = beg;
 557         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 558         let init = self.make_statement(StatementKind::Assign(box (
 559             Place::from(beg),
 560             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 561         )));
 562         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 563
 564         // BB #6 (cleanup): loop {
 565         //     BB #7;
 566         //     BB #8;
 567         // }
 568         // BB #9;
 569         self.loop_header(
 570             Place::from(beg),
 571             Place::from(end),
 572             BasicBlock::new(7),
 573             BasicBlock::new(9),
 574             true,
 575         );
 576
 577         // BB #7 (cleanup)
 578         // `drop(dest[beg])`;
 579         self.block(
 580             vec![],
 581             TerminatorKind::Drop {
 582                 location: self.tcx.mk_place_index(dest, beg),
 583                 target: BasicBlock::new(8),
 584                 unwind: None,
 585             },
 586             true,
 587         );
 588
 589         // BB #8 (cleanup)
 590         // `beg = beg + 1;`
 591         // `goto #6;`
 592         let statement = self.make_statement(StatementKind::Assign(box (
 593             Place::from(beg),
 594             Rvalue::BinaryOp(
 595                 BinOp::Add,
 596                 Operand::Copy(Place::from(beg)),
 597                 Operand::Constant(self.make_usize(1)),
 598             ),
 599         )));
 600         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 601
 602         // BB #9 (resume)
 603         self.block(vec![], TerminatorKind::Resume, true);
 604     }
 605
 606     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 607     where
 608         I: Iterator<Item = Ty<'tcx>>,
 609     {
 610         let mut previous_field = None;
 611         for (i, ity) in tys.enumerate() {
 612             let field = Field::new(i);
 613             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 614
 615             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 616
 617             // #(2i + 1) is the cleanup block for the previous clone operation
 618             let cleanup_block = self.block_index_offset(1);
 619             // #(2i + 2) is the next cloning block
 620             // (or the Return terminator if this is the last block)
 621             let next_block = self.block_index_offset(2);
 622
 623             // BB #(2i)
 624             // `dest.i = Clone::clone(&src.i);`
 625             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 626             self.make_clone_call(dest_field.clone(), src_field, ity, next_block, cleanup_block);
 627
 628             // BB #(2i + 1) (cleanup)
 629             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 630                 // Drop previous field and goto previous cleanup block.
 631                 self.block(
 632                     vec![],
 633                     TerminatorKind::Drop {
 634                         location: previous_field,
 635                         target: previous_cleanup,
 636                         unwind: None,
 637                     },
 638                     true,
 639                 );
 640             } else {
 641                 // Nothing to drop, just resume.
 642                 self.block(vec![], TerminatorKind::Resume, true);
 643             }
 644
 645             previous_field = Some((dest_field, cleanup_block));
 646         }
 647
 648         self.block(vec![], TerminatorKind::Return, false);
 649     }
 650 }
 651
 652 /// Builds a "call" shim for `instance`. The shim calls the
 653 /// function specified by `call_kind`, first adjusting its first
 654 /// argument according to `rcvr_adjustment`.
 655 ///
 656 /// If `untuple_args` is a vec of types, the second argument of the
 657 /// function will be untupled as these types.
 658 fn build_call_shim<'tcx>(
 659     tcx: TyCtxt<'tcx>,
 660     instance: ty::InstanceDef<'tcx>,
 661     rcvr_adjustment: Option<Adjustment>,
 662     call_kind: CallKind,
 663     untuple_args: Option<&[Ty<'tcx>]>,
 664 ) -> BodyAndCache<'tcx> {
 665     debug!(
 666         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 667             call_kind={:?}, untuple_args={:?})",
 668         instance, rcvr_adjustment, call_kind, untuple_args
 669     );
 670
 671     let def_id = instance.def_id();
 672     let sig = tcx.fn_sig(def_id);
 673     let mut sig = tcx.erase_late_bound_regions(&sig);
 674
 675     // FIXME(eddyb) avoid having this snippet both here and in
 676     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 677     if let ty::InstanceDef::VtableShim(..) = instance {
 678         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 679         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 680         let self_arg = &mut inputs_and_output[0];
 681         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 682         *self_arg = tcx.mk_mut_ptr(*self_arg);
 683         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 684     }
 685
 686     let span = tcx.def_span(def_id);
 687
 688     debug!("build_call_shim: sig={:?}", sig);
 689
 690     let mut local_decls = local_decls_for_sig(&sig, span);
 691     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 692
 693     let rcvr_place = || {
 694         assert!(rcvr_adjustment.is_some());
 695         Place::from(Local::new(1 + 0))
 696     };
 697     let mut statements = vec![];
 698
 699     let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
 700         Adjustment::Identity => Operand::Move(rcvr_place()),
 701         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_place())),
 702         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_place())),
 703         Adjustment::RefMut => {
 704             // let rcvr = &mut rcvr;
 705             let ref_rcvr = local_decls.push(temp_decl(
 706                 Mutability::Not,
 707                 tcx.mk_ref(
 708                     tcx.lifetimes.re_erased,
 709                     ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 710                 ),
 711                 span,
 712             ));
 713             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 714             statements.push(Statement {
 715                 source_info,
 716                 kind: StatementKind::Assign(box (
 717                     Place::from(ref_rcvr),
 718                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_place()),
 719                 )),
 720             });
 721             Operand::Move(Place::from(ref_rcvr))
 722         }
 723     });
 724
 725     let (callee, mut args) = match call_kind {
 726         CallKind::Indirect => (rcvr.unwrap(), vec![]),
 727         CallKind::Direct(def_id) => {
 728             let ty = tcx.type_of(def_id);
 729             (
 730                 Operand::Constant(box Constant {
 731                     span,
 732                     user_ty: None,
 733                     literal: ty::Const::zero_sized(tcx, ty),
 734                 }),
 735                 rcvr.into_iter().collect::<Vec<_>>(),
 736             )
 737         }
 738     };
 739
 740     let mut arg_range = 0..sig.inputs().len();
 741
 742     // Take the `self` ("receiver") argument out of the range (it's adjusted above).
 743     if rcvr_adjustment.is_some() {
 744         arg_range.start += 1;
 745     }
 746
 747     // Take the last argument, if we need to untuple it (handled below).
 748     if untuple_args.is_some() {
 749         arg_range.end -= 1;
 750     }
 751
 752     // Pass all of the non-special arguments directly.
 753     args.extend(arg_range.map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 754
 755     // Untuple the last argument, if we have to.
 756     if let Some(untuple_args) = untuple_args {
 757         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
 758         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 759             Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
 760         }));
 761     }
 762
 763     let n_blocks = if let Some(Adjustment::RefMut) = rcvr_adjustment { 5 } else { 2 };
 764     let mut blocks = IndexVec::with_capacity(n_blocks);
 765     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 766         blocks.push(BasicBlockData {
 767             statements,
 768             terminator: Some(Terminator { source_info, kind }),
 769             is_cleanup,
 770         })
 771     };
 772
 773     // BB #0
 774     block(
 775         &mut blocks,
 776         statements,
 777         TerminatorKind::Call {
 778             func: callee,
 779             args,
 780             destination: Some((Place::return_place(), BasicBlock::new(1))),
 781             cleanup: if let Some(Adjustment::RefMut) = rcvr_adjustment {
 782                 Some(BasicBlock::new(3))
 783             } else {
 784                 None
 785             },
 786             from_hir_call: true,
 787         },
 788         false,
 789     );
 790
 791     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 792         // BB #1 - drop for Self
 793         block(
 794             &mut blocks,
 795             vec![],
 796             TerminatorKind::Drop {
 797                 location: rcvr_place(),
 798                 target: BasicBlock::new(2),
 799                 unwind: None,
 800             },
 801             false,
 802         );
 803     }
 804     // BB #1/#2 - return
 805     block(&mut blocks, vec![], TerminatorKind::Return, false);
 806     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 807         // BB #3 - drop if closure panics
 808         block(
 809             &mut blocks,
 810             vec![],
 811             TerminatorKind::Drop {
 812                 location: rcvr_place(),
 813                 target: BasicBlock::new(4),
 814                 unwind: None,
 815             },
 816             true,
 817         );
 818
 819         // BB #4 - resume
 820         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 821     }
 822
 823     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 824
 825     if let Abi::RustCall = sig.abi {
 826         body.spread_arg = Some(Local::new(sig.inputs().len()));
 827     }
 828     BodyAndCache::new(body)
 829 }
 830
 831 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &BodyAndCache<'_> {
 832     debug_assert!(tcx.is_constructor(ctor_id));
 833
 834     let span =
 835         tcx.hir().span_if_local(ctor_id).unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 836
 837     let param_env = tcx.param_env(ctor_id);
 838
 839     // Normalize the sig.
 840     let sig = tcx.fn_sig(ctor_id).no_bound_vars().expect("LBR in ADT constructor signature");
 841     let sig = tcx.normalize_erasing_regions(param_env, sig);
 842
 843     let (adt_def, substs) = match sig.output().kind {
 844         ty::Adt(adt_def, substs) => (adt_def, substs),
 845         _ => bug!("unexpected type for ADT ctor {:?}", sig.output()),
 846     };
 847
 848     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 849
 850     let local_decls = local_decls_for_sig(&sig, span);
 851
 852     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 853
 854     let variant_index = if adt_def.is_enum() {
 855         adt_def.variant_index_with_ctor_id(ctor_id)
 856     } else {
 857         VariantIdx::new(0)
 858     };
 859
 860     // Generate the following MIR:
 861     //
 862     // (return as Variant).field0 = arg0;
 863     // (return as Variant).field1 = arg1;
 864     //
 865     // return;
 866     debug!("build_ctor: variant_index={:?}", variant_index);
 867
 868     let statements = expand_aggregate(
 869         Place::return_place(),
 870         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
 871             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
 872         }),
 873         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 874         source_info,
 875         tcx,
 876     )
 877     .collect();
 878
 879     let start_block = BasicBlockData {
 880         statements,
 881         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
 882         is_cleanup: false,
 883     };
 884
 885     let body =
 886         new_body(IndexVec::from_elem_n(start_block, 1), local_decls, sig.inputs().len(), span);
 887
 888     crate::util::dump_mir(
 889         tcx,
 890         None,
 891         "mir_map",
 892         &0,
 893         crate::transform::MirSource::item(ctor_id),
 894         &body,
 895         |_, _| Ok(()),
 896     );
 897
 898     let mut body = BodyAndCache::new(body);
 899     body.ensure_predecessors();
 900     tcx.arena.alloc(body)
 901 }