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.fn_trait_kind_from_lang_item(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                 .in_definition_order()
  72                 .find(|it| it.kind == ty::AssocKind::Method)
  73                 .unwrap()
  74                 .def_id;
  75
  76             build_call_shim(
  77                 tcx,
  78                 instance,
  79                 Some(Adjustment::RefMut),
  80                 CallKind::Direct(call_mut),
  81                 None,
  82             )
  83         }
  84         ty::InstanceDef::DropGlue(def_id, ty) => build_drop_shim(tcx, def_id, ty),
  85         ty::InstanceDef::CloneShim(def_id, ty) => {
  86             let name = tcx.item_name(def_id);
  87             if name == sym::clone {
  88                 build_clone_shim(tcx, def_id, ty)
  89             } else if name == sym::clone_from {
  90                 debug!("make_shim({:?}: using default trait implementation", instance);
  91                 return tcx.optimized_mir(def_id);
  92             } else {
  93                 bug!("builtin clone shim {:?} not supported", instance)
  94             }
  95         }
  96         ty::InstanceDef::Virtual(..) => {
  97             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
  98         }
  99         ty::InstanceDef::Intrinsic(_) => {
 100             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 101         }
 102     };
 103     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 104
 105     run_passes(
 106         tcx,
 107         &mut result,
 108         instance,
 109         None,
 110         MirPhase::Const,
 111         &[
 112             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 113             &no_landing_pads::NoLandingPads::new(tcx),
 114             &remove_noop_landing_pads::RemoveNoopLandingPads,
 115             &simplify::SimplifyCfg::new("make_shim"),
 116             &add_call_guards::CriticalCallEdges,
 117         ],
 118     );
 119
 120     debug!("make_shim({:?}) = {:?}", instance, result);
 121
 122     result.ensure_predecessors();
 123     tcx.arena.alloc(result)
 124 }
 125
 126 #[derive(Copy, Clone, Debug, PartialEq)]
 127 enum Adjustment {
 128     Identity,
 129     Deref,
 130     DerefMove,
 131     RefMut,
 132 }
 133
 134 #[derive(Copy, Clone, Debug, PartialEq)]
 135 enum CallKind {
 136     Indirect,
 137     Direct(DefId),
 138 }
 139
 140 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 141     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 142     LocalDecl {
 143         mutability,
 144         ty,
 145         user_ty: UserTypeProjections::none(),
 146         source_info,
 147         internal: false,
 148         local_info: LocalInfo::Other,
 149         is_block_tail: None,
 150     }
 151 }
 152
 153 fn local_decls_for_sig<'tcx>(
 154     sig: &ty::FnSig<'tcx>,
 155     span: Span,
 156 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 157     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 158         .chain(sig.inputs().iter().map(|ity| temp_decl(Mutability::Not, ity, span)))
 159         .collect()
 160 }
 161
 162 fn build_drop_shim<'tcx>(
 163     tcx: TyCtxt<'tcx>,
 164     def_id: DefId,
 165     ty: Option<Ty<'tcx>>,
 166 ) -> BodyAndCache<'tcx> {
 167     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 168
 169     // Check if this is a generator, if so, return the drop glue for it
 170     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 171         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 172         return body.subst(tcx, substs);
 173     }
 174
 175     let substs = if let Some(ty) = ty {
 176         tcx.intern_substs(&[ty.into()])
 177     } else {
 178         InternalSubsts::identity_for_item(tcx, def_id)
 179     };
 180     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 181     let sig = tcx.erase_late_bound_regions(&sig);
 182     let span = tcx.def_span(def_id);
 183
 184     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 185
 186     let return_block = BasicBlock::new(1);
 187     let mut blocks = IndexVec::with_capacity(2);
 188     let block = |blocks: &mut IndexVec<_, _>, kind| {
 189         blocks.push(BasicBlockData {
 190             statements: vec![],
 191             terminator: Some(Terminator { source_info, kind }),
 192             is_cleanup: false,
 193         })
 194     };
 195     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 196     block(&mut blocks, TerminatorKind::Return);
 197
 198     let body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 199
 200     let mut body = BodyAndCache::new(body);
 201
 202     if let Some(..) = ty {
 203         // The first argument (index 0), but add 1 for the return value.
 204         let dropee_ptr = Place::from(Local::new(1 + 0));
 205         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 206             // Function arguments should be retagged, and we make this one raw.
 207             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 208                 0,
 209                 Statement {
 210                     source_info,
 211                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr)),
 212                 },
 213             );
 214         }
 215         let patch = {
 216             let param_env = tcx.param_env(def_id).with_reveal_all();
 217             let mut elaborator =
 218                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 219             let dropee = tcx.mk_place_deref(dropee_ptr);
 220             let resume_block = elaborator.patch.resume_block();
 221             elaborate_drops::elaborate_drop(
 222                 &mut elaborator,
 223                 source_info,
 224                 &dropee,
 225                 (),
 226                 return_block,
 227                 elaborate_drops::Unwind::To(resume_block),
 228                 START_BLOCK,
 229             );
 230             elaborator.patch
 231         };
 232         patch.apply(&mut body);
 233     }
 234
 235     body
 236 }
 237
 238 fn new_body<'tcx>(
 239     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 240     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 241     arg_count: usize,
 242     span: Span,
 243 ) -> Body<'tcx> {
 244     Body::new(
 245         basic_blocks,
 246         IndexVec::from_elem_n(
 247             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 248             1,
 249         ),
 250         local_decls,
 251         IndexVec::new(),
 252         arg_count,
 253         vec![],
 254         span,
 255         vec![],
 256         None,
 257     )
 258 }
 259
 260 pub struct DropShimElaborator<'a, 'tcx> {
 261     pub body: &'a Body<'tcx>,
 262     pub patch: MirPatch<'tcx>,
 263     pub tcx: TyCtxt<'tcx>,
 264     pub param_env: ty::ParamEnv<'tcx>,
 265 }
 266
 267 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 268     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 269         Ok(())
 270     }
 271 }
 272
 273 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 274     type Path = ();
 275
 276     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 277         &mut self.patch
 278     }
 279     fn body(&self) -> &'a Body<'tcx> {
 280         self.body
 281     }
 282     fn tcx(&self) -> TyCtxt<'tcx> {
 283         self.tcx
 284     }
 285     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 286         self.param_env
 287     }
 288
 289     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 290         if let DropFlagMode::Shallow = mode { DropStyle::Static } else { DropStyle::Open }
 291     }
 292
 293     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 294         None
 295     }
 296
 297     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 298
 299     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 300         None
 301     }
 302     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 303         None
 304     }
 305     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 306         Some(())
 307     }
 308     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 309         None
 310     }
 311 }
 312
 313 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 314 fn build_clone_shim<'tcx>(
 315     tcx: TyCtxt<'tcx>,
 316     def_id: DefId,
 317     self_ty: Ty<'tcx>,
 318 ) -> BodyAndCache<'tcx> {
 319     debug!("build_clone_shim(def_id={:?})", def_id);
 320
 321     let param_env = tcx.param_env(def_id);
 322
 323     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 324     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 325
 326     let dest = Place::return_place();
 327     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 328
 329     match self_ty.kind {
 330         _ if is_copy => builder.copy_shim(),
 331         ty::Array(ty, len) => {
 332             let len = len.eval_usize(tcx, param_env);
 333             builder.array_shim(dest, src, ty, len)
 334         }
 335         ty::Closure(def_id, substs) => {
 336             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys(def_id, tcx))
 337         }
 338         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 339         _ => bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty),
 340     };
 341
 342     BodyAndCache::new(builder.into_mir())
 343 }
 344
 345 struct CloneShimBuilder<'tcx> {
 346     tcx: TyCtxt<'tcx>,
 347     def_id: DefId,
 348     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 349     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 350     span: Span,
 351     sig: ty::FnSig<'tcx>,
 352 }
 353
 354 impl CloneShimBuilder<'tcx> {
 355     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 356         // we must subst the self_ty because it's
 357         // otherwise going to be TySelf and we can't index
 358         // or access fields of a Place of type TySelf.
 359         let substs = tcx.mk_substs_trait(self_ty, &[]);
 360         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 361         let sig = tcx.erase_late_bound_regions(&sig);
 362         let span = tcx.def_span(def_id);
 363
 364         CloneShimBuilder {
 365             tcx,
 366             def_id,
 367             local_decls: local_decls_for_sig(&sig, span),
 368             blocks: IndexVec::new(),
 369             span,
 370             sig,
 371         }
 372     }
 373
 374     fn into_mir(self) -> Body<'tcx> {
 375         new_body(self.blocks, self.local_decls, self.sig.inputs().len(), self.span)
 376     }
 377
 378     fn source_info(&self) -> SourceInfo {
 379         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 380     }
 381
 382     fn block(
 383         &mut self,
 384         statements: Vec<Statement<'tcx>>,
 385         kind: TerminatorKind<'tcx>,
 386         is_cleanup: bool,
 387     ) -> BasicBlock {
 388         let source_info = self.source_info();
 389         self.blocks.push(BasicBlockData {
 390             statements,
 391             terminator: Some(Terminator { source_info, kind }),
 392             is_cleanup,
 393         })
 394     }
 395
 396     /// Gives the index of an upcoming BasicBlock, with an offset.
 397     /// offset=0 will give you the index of the next BasicBlock,
 398     /// offset=1 will give the index of the next-to-next block,
 399     /// offset=-1 will give you the index of the last-created block
 400     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 401         BasicBlock::new(self.blocks.len() + offset)
 402     }
 403
 404     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 405         Statement { source_info: self.source_info(), kind }
 406     }
 407
 408     fn copy_shim(&mut self) {
 409         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 410         let ret_statement = self.make_statement(StatementKind::Assign(box (
 411             Place::return_place(),
 412             Rvalue::Use(Operand::Copy(rcvr)),
 413         )));
 414         self.block(vec![ret_statement], TerminatorKind::Return, false);
 415     }
 416
 417     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 418         let span = self.span;
 419         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 420     }
 421
 422     fn make_clone_call(
 423         &mut self,
 424         dest: Place<'tcx>,
 425         src: Place<'tcx>,
 426         ty: Ty<'tcx>,
 427         next: BasicBlock,
 428         cleanup: BasicBlock,
 429     ) {
 430         let tcx = self.tcx;
 431
 432         let substs = tcx.mk_substs_trait(ty, &[]);
 433
 434         // `func == Clone::clone(&ty) -> ty`
 435         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 436         let func = Operand::Constant(box Constant {
 437             span: self.span,
 438             user_ty: None,
 439             literal: ty::Const::zero_sized(tcx, func_ty),
 440         });
 441
 442         let ref_loc = self.make_place(
 443             Mutability::Not,
 444             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 445         );
 446
 447         // `let ref_loc: &ty = &src;`
 448         let statement = self.make_statement(StatementKind::Assign(box (
 449             ref_loc,
 450             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 451         )));
 452
 453         // `let loc = Clone::clone(ref_loc);`
 454         self.block(
 455             vec![statement],
 456             TerminatorKind::Call {
 457                 func,
 458                 args: vec![Operand::Move(ref_loc)],
 459                 destination: Some((dest, next)),
 460                 cleanup: Some(cleanup),
 461                 from_hir_call: true,
 462             },
 463             false,
 464         );
 465     }
 466
 467     fn loop_header(
 468         &mut self,
 469         beg: Place<'tcx>,
 470         end: Place<'tcx>,
 471         loop_body: BasicBlock,
 472         loop_end: BasicBlock,
 473         is_cleanup: bool,
 474     ) {
 475         let tcx = self.tcx;
 476
 477         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 478         let compute_cond = self.make_statement(StatementKind::Assign(box (
 479             cond,
 480             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 481         )));
 482
 483         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 484         self.block(
 485             vec![compute_cond],
 486             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 487             is_cleanup,
 488         );
 489     }
 490
 491     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 492         box Constant {
 493             span: self.span,
 494             user_ty: None,
 495             literal: ty::Const::from_usize(self.tcx, value),
 496         }
 497     }
 498
 499     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 500         let tcx = self.tcx;
 501         let span = self.span;
 502
 503         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 504         let end = self.make_place(Mutability::Not, tcx.types.usize);
 505
 506         // BB #0
 507         // `let mut beg = 0;`
 508         // `let end = len;`
 509         // `goto #1;`
 510         let inits = vec![
 511             self.make_statement(StatementKind::Assign(box (
 512                 Place::from(beg),
 513                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 514             ))),
 515             self.make_statement(StatementKind::Assign(box (
 516                 end,
 517                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 518             ))),
 519         ];
 520         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 521
 522         // BB #1: loop {
 523         //     BB #2;
 524         //     BB #3;
 525         // }
 526         // BB #4;
 527         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 528
 529         // BB #2
 530         // `dest[i] = Clone::clone(src[beg])`;
 531         // Goto #3 if ok, #5 if unwinding happens.
 532         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 533         let src_field = self.tcx.mk_place_index(src, beg);
 534         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 535
 536         // BB #3
 537         // `beg = beg + 1;`
 538         // `goto #1`;
 539         let statements = vec![self.make_statement(StatementKind::Assign(box (
 540             Place::from(beg),
 541             Rvalue::BinaryOp(
 542                 BinOp::Add,
 543                 Operand::Copy(Place::from(beg)),
 544                 Operand::Constant(self.make_usize(1)),
 545             ),
 546         )))];
 547         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 548
 549         // BB #4
 550         // `return dest;`
 551         self.block(vec![], TerminatorKind::Return, false);
 552
 553         // BB #5 (cleanup)
 554         // `let end = beg;`
 555         // `let mut beg = 0;`
 556         // goto #6;
 557         let end = beg;
 558         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 559         let init = self.make_statement(StatementKind::Assign(box (
 560             Place::from(beg),
 561             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 562         )));
 563         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 564
 565         // BB #6 (cleanup): loop {
 566         //     BB #7;
 567         //     BB #8;
 568         // }
 569         // BB #9;
 570         self.loop_header(
 571             Place::from(beg),
 572             Place::from(end),
 573             BasicBlock::new(7),
 574             BasicBlock::new(9),
 575             true,
 576         );
 577
 578         // BB #7 (cleanup)
 579         // `drop(dest[beg])`;
 580         self.block(
 581             vec![],
 582             TerminatorKind::Drop {
 583                 location: self.tcx.mk_place_index(dest, beg),
 584                 target: BasicBlock::new(8),
 585                 unwind: None,
 586             },
 587             true,
 588         );
 589
 590         // BB #8 (cleanup)
 591         // `beg = beg + 1;`
 592         // `goto #6;`
 593         let statement = self.make_statement(StatementKind::Assign(box (
 594             Place::from(beg),
 595             Rvalue::BinaryOp(
 596                 BinOp::Add,
 597                 Operand::Copy(Place::from(beg)),
 598                 Operand::Constant(self.make_usize(1)),
 599             ),
 600         )));
 601         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 602
 603         // BB #9 (resume)
 604         self.block(vec![], TerminatorKind::Resume, true);
 605     }
 606
 607     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 608     where
 609         I: Iterator<Item = Ty<'tcx>>,
 610     {
 611         let mut previous_field = None;
 612         for (i, ity) in tys.enumerate() {
 613             let field = Field::new(i);
 614             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 615
 616             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 617
 618             // #(2i + 1) is the cleanup block for the previous clone operation
 619             let cleanup_block = self.block_index_offset(1);
 620             // #(2i + 2) is the next cloning block
 621             // (or the Return terminator if this is the last block)
 622             let next_block = self.block_index_offset(2);
 623
 624             // BB #(2i)
 625             // `dest.i = Clone::clone(&src.i);`
 626             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 627             self.make_clone_call(dest_field.clone(), src_field, ity, next_block, cleanup_block);
 628
 629             // BB #(2i + 1) (cleanup)
 630             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 631                 // Drop previous field and goto previous cleanup block.
 632                 self.block(
 633                     vec![],
 634                     TerminatorKind::Drop {
 635                         location: previous_field,
 636                         target: previous_cleanup,
 637                         unwind: None,
 638                     },
 639                     true,
 640                 );
 641             } else {
 642                 // Nothing to drop, just resume.
 643                 self.block(vec![], TerminatorKind::Resume, true);
 644             }
 645
 646             previous_field = Some((dest_field, cleanup_block));
 647         }
 648
 649         self.block(vec![], TerminatorKind::Return, false);
 650     }
 651 }
 652
 653 /// Builds a "call" shim for `instance`. The shim calls the
 654 /// function specified by `call_kind`, first adjusting its first
 655 /// argument according to `rcvr_adjustment`.
 656 ///
 657 /// If `untuple_args` is a vec of types, the second argument of the
 658 /// function will be untupled as these types.
 659 fn build_call_shim<'tcx>(
 660     tcx: TyCtxt<'tcx>,
 661     instance: ty::InstanceDef<'tcx>,
 662     rcvr_adjustment: Option<Adjustment>,
 663     call_kind: CallKind,
 664     untuple_args: Option<&[Ty<'tcx>]>,
 665 ) -> BodyAndCache<'tcx> {
 666     debug!(
 667         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 668             call_kind={:?}, untuple_args={:?})",
 669         instance, rcvr_adjustment, call_kind, untuple_args
 670     );
 671
 672     let def_id = instance.def_id();
 673     let sig = tcx.fn_sig(def_id);
 674     let mut sig = tcx.erase_late_bound_regions(&sig);
 675
 676     // FIXME(eddyb) avoid having this snippet both here and in
 677     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 678     if let ty::InstanceDef::VtableShim(..) = instance {
 679         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 680         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 681         let self_arg = &mut inputs_and_output[0];
 682         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 683         *self_arg = tcx.mk_mut_ptr(*self_arg);
 684         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 685     }
 686
 687     let span = tcx.def_span(def_id);
 688
 689     debug!("build_call_shim: sig={:?}", sig);
 690
 691     let mut local_decls = local_decls_for_sig(&sig, span);
 692     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 693
 694     let rcvr_place = || {
 695         assert!(rcvr_adjustment.is_some());
 696         Place::from(Local::new(1 + 0))
 697     };
 698     let mut statements = vec![];
 699
 700     let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
 701         Adjustment::Identity => Operand::Move(rcvr_place()),
 702         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_place())),
 703         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_place())),
 704         Adjustment::RefMut => {
 705             // let rcvr = &mut rcvr;
 706             let ref_rcvr = local_decls.push(temp_decl(
 707                 Mutability::Not,
 708                 tcx.mk_ref(
 709                     tcx.lifetimes.re_erased,
 710                     ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 711                 ),
 712                 span,
 713             ));
 714             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 715             statements.push(Statement {
 716                 source_info,
 717                 kind: StatementKind::Assign(box (
 718                     Place::from(ref_rcvr),
 719                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_place()),
 720                 )),
 721             });
 722             Operand::Move(Place::from(ref_rcvr))
 723         }
 724     });
 725
 726     let (callee, mut args) = match call_kind {
 727         CallKind::Indirect => (rcvr.unwrap(), vec![]),
 728         CallKind::Direct(def_id) => {
 729             let ty = tcx.type_of(def_id);
 730             (
 731                 Operand::Constant(box Constant {
 732                     span,
 733                     user_ty: None,
 734                     literal: ty::Const::zero_sized(tcx, ty),
 735                 }),
 736                 rcvr.into_iter().collect::<Vec<_>>(),
 737             )
 738         }
 739     };
 740
 741     let mut arg_range = 0..sig.inputs().len();
 742
 743     // Take the `self` ("receiver") argument out of the range (it's adjusted above).
 744     if rcvr_adjustment.is_some() {
 745         arg_range.start += 1;
 746     }
 747
 748     // Take the last argument, if we need to untuple it (handled below).
 749     if untuple_args.is_some() {
 750         arg_range.end -= 1;
 751     }
 752
 753     // Pass all of the non-special arguments directly.
 754     args.extend(arg_range.map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 755
 756     // Untuple the last argument, if we have to.
 757     if let Some(untuple_args) = untuple_args {
 758         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
 759         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 760             Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
 761         }));
 762     }
 763
 764     let n_blocks = if let Some(Adjustment::RefMut) = rcvr_adjustment { 5 } else { 2 };
 765     let mut blocks = IndexVec::with_capacity(n_blocks);
 766     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 767         blocks.push(BasicBlockData {
 768             statements,
 769             terminator: Some(Terminator { source_info, kind }),
 770             is_cleanup,
 771         })
 772     };
 773
 774     // BB #0
 775     block(
 776         &mut blocks,
 777         statements,
 778         TerminatorKind::Call {
 779             func: callee,
 780             args,
 781             destination: Some((Place::return_place(), BasicBlock::new(1))),
 782             cleanup: if let Some(Adjustment::RefMut) = rcvr_adjustment {
 783                 Some(BasicBlock::new(3))
 784             } else {
 785                 None
 786             },
 787             from_hir_call: true,
 788         },
 789         false,
 790     );
 791
 792     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 793         // BB #1 - drop for Self
 794         block(
 795             &mut blocks,
 796             vec![],
 797             TerminatorKind::Drop {
 798                 location: rcvr_place(),
 799                 target: BasicBlock::new(2),
 800                 unwind: None,
 801             },
 802             false,
 803         );
 804     }
 805     // BB #1/#2 - return
 806     block(&mut blocks, vec![], TerminatorKind::Return, false);
 807     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 808         // BB #3 - drop if closure panics
 809         block(
 810             &mut blocks,
 811             vec![],
 812             TerminatorKind::Drop {
 813                 location: rcvr_place(),
 814                 target: BasicBlock::new(4),
 815                 unwind: None,
 816             },
 817             true,
 818         );
 819
 820         // BB #4 - resume
 821         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 822     }
 823
 824     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 825
 826     if let Abi::RustCall = sig.abi {
 827         body.spread_arg = Some(Local::new(sig.inputs().len()));
 828     }
 829     BodyAndCache::new(body)
 830 }
 831
 832 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &BodyAndCache<'_> {
 833     debug_assert!(tcx.is_constructor(ctor_id));
 834
 835     let span =
 836         tcx.hir().span_if_local(ctor_id).unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 837
 838     let param_env = tcx.param_env(ctor_id);
 839
 840     // Normalize the sig.
 841     let sig = tcx.fn_sig(ctor_id).no_bound_vars().expect("LBR in ADT constructor signature");
 842     let sig = tcx.normalize_erasing_regions(param_env, sig);
 843
 844     let (adt_def, substs) = match sig.output().kind {
 845         ty::Adt(adt_def, substs) => (adt_def, substs),
 846         _ => bug!("unexpected type for ADT ctor {:?}", sig.output()),
 847     };
 848
 849     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 850
 851     let local_decls = local_decls_for_sig(&sig, span);
 852
 853     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 854
 855     let variant_index = if adt_def.is_enum() {
 856         adt_def.variant_index_with_ctor_id(ctor_id)
 857     } else {
 858         VariantIdx::new(0)
 859     };
 860
 861     // Generate the following MIR:
 862     //
 863     // (return as Variant).field0 = arg0;
 864     // (return as Variant).field1 = arg1;
 865     //
 866     // return;
 867     debug!("build_ctor: variant_index={:?}", variant_index);
 868
 869     let statements = expand_aggregate(
 870         Place::return_place(),
 871         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
 872             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
 873         }),
 874         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 875         source_info,
 876         tcx,
 877     )
 878     .collect();
 879
 880     let start_block = BasicBlockData {
 881         statements,
 882         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
 883         is_cleanup: false,
 884     };
 885
 886     let body =
 887         new_body(IndexVec::from_elem_n(start_block, 1), local_decls, sig.inputs().len(), span);
 888
 889     crate::util::dump_mir(
 890         tcx,
 891         None,
 892         "mir_map",
 893         &0,
 894         crate::transform::MirSource::item(ctor_id),
 895         &body,
 896         |_, _| Ok(()),
 897     );
 898
 899     let mut body = BodyAndCache::new(body);
 900     body.ensure_predecessors();
 901     tcx.arena.alloc(body)
 902 }