compiler/rustc_mir/src/shim.rs

   1 use rustc_hir as hir;
   2 use rustc_hir::def_id::DefId;
   3 use rustc_hir::lang_items::LangItem;
   4 use rustc_middle::mir::*;
   5 use rustc_middle::ty::query::Providers;
   6 use rustc_middle::ty::subst::{InternalSubsts, Subst};
   7 use rustc_middle::ty::{self, Ty, TyCtxt};
   8 use rustc_target::abi::VariantIdx;
   9
  10 use rustc_index::vec::{Idx, IndexVec};
  11
  12 use rustc_span::Span;
  13 use rustc_target::spec::abi::Abi;
  14
  15 use std::fmt;
  16 use std::iter;
  17
  18 use crate::transform::{
  19     add_call_guards, add_moves_for_packed_drops, no_landing_pads, remove_noop_landing_pads,
  20     run_passes, simplify,
  21 };
  22 use crate::util::elaborate_drops::{self, DropElaborator, DropFlagMode, DropStyle};
  23 use crate::util::expand_aggregate;
  24 use crate::util::patch::MirPatch;
  25
  26 pub fn provide(providers: &mut Providers) {
  27     providers.mir_shims = make_shim;
  28 }
  29
  30 fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'tcx> {
  31     debug!("make_shim({:?})", instance);
  32
  33     let mut result = match instance {
  34         ty::InstanceDef::Item(..) => bug!("item {:?} passed to make_shim", instance),
  35         ty::InstanceDef::VtableShim(def_id) => {
  36             build_call_shim(tcx, instance, Some(Adjustment::Deref), CallKind::Direct(def_id))
  37         }
  38         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  39             let trait_ = tcx.trait_of_item(def_id).unwrap();
  40             let adjustment = match tcx.fn_trait_kind_from_lang_item(trait_) {
  41                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  42                 Some(ty::ClosureKind::FnMut | ty::ClosureKind::Fn) => Adjustment::Deref,
  43                 None => bug!("fn pointer {:?} is not an fn", ty),
  44             };
  45
  46             build_call_shim(tcx, instance, Some(adjustment), CallKind::Indirect(ty))
  47         }
  48         // We are generating a call back to our def-id, which the
  49         // codegen backend knows to turn to an actual call, be it
  50         // a virtual call, or a direct call to a function for which
  51         // indirect calls must be codegen'd differently than direct ones
  52         // (such as `#[track_caller]`).
  53         ty::InstanceDef::ReifyShim(def_id) => {
  54             build_call_shim(tcx, instance, None, CallKind::Direct(def_id))
  55         }
  56         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
  57             let fn_mut = tcx.require_lang_item(LangItem::FnMut, None);
  58             let call_mut = tcx
  59                 .associated_items(fn_mut)
  60                 .in_definition_order()
  61                 .find(|it| it.kind == ty::AssocKind::Fn)
  62                 .unwrap()
  63                 .def_id;
  64
  65             build_call_shim(tcx, instance, Some(Adjustment::RefMut), CallKind::Direct(call_mut))
  66         }
  67         ty::InstanceDef::DropGlue(def_id, ty) => build_drop_shim(tcx, def_id, ty),
  68         ty::InstanceDef::CloneShim(def_id, ty) => build_clone_shim(tcx, def_id, ty),
  69         ty::InstanceDef::Virtual(..) => {
  70             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
  71         }
  72         ty::InstanceDef::Intrinsic(_) => {
  73             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
  74         }
  75     };
  76     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
  77
  78     run_passes(
  79         tcx,
  80         &mut result,
  81         instance,
  82         None,
  83         MirPhase::Const,
  84         &[&[
  85             &add_moves_for_packed_drops::AddMovesForPackedDrops,
  86             &no_landing_pads::NoLandingPads::new(tcx),
  87             &remove_noop_landing_pads::RemoveNoopLandingPads,
  88             &simplify::SimplifyCfg::new("make_shim"),
  89             &add_call_guards::CriticalCallEdges,
  90         ]],
  91     );
  92
  93     debug!("make_shim({:?}) = {:?}", instance, result);
  94
  95     result
  96 }
  97
  98 #[derive(Copy, Clone, Debug, PartialEq)]
  99 enum Adjustment {
 100     /// Pass the receiver as-is.
 101     Identity,
 102
 103     /// We get passed `&[mut] self` and call the target with `*self`.
 104     ///
 105     /// This either copies `self` (if `Self: Copy`, eg. for function items), or moves out of it
 106     /// (for `VtableShim`, which effectively is passed `&own Self`).
 107     Deref,
 108
 109     /// We get passed `self: Self` and call the target with `&mut self`.
 110     ///
 111     /// In this case we need to ensure that the `Self` is dropped after the call, as the callee
 112     /// won't do it for us.
 113     RefMut,
 114 }
 115
 116 #[derive(Copy, Clone, Debug, PartialEq)]
 117 enum CallKind<'tcx> {
 118     /// Call the `FnPtr` that was passed as the receiver.
 119     Indirect(Ty<'tcx>),
 120
 121     /// Call a known `FnDef`.
 122     Direct(DefId),
 123 }
 124
 125 fn local_decls_for_sig<'tcx>(
 126     sig: &ty::FnSig<'tcx>,
 127     span: Span,
 128 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 129     iter::once(LocalDecl::new(sig.output(), span))
 130         .chain(sig.inputs().iter().map(|ity| LocalDecl::new(ity, span).immutable()))
 131         .collect()
 132 }
 133
 134 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 135     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 136
 137     // Check if this is a generator, if so, return the drop glue for it
 138     if let Some(&ty::Generator(gen_def_id, substs, _)) = ty.map(|ty| ty.kind()) {
 139         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 140         return body.subst(tcx, substs);
 141     }
 142
 143     let substs = if let Some(ty) = ty {
 144         tcx.intern_substs(&[ty.into()])
 145     } else {
 146         InternalSubsts::identity_for_item(tcx, def_id)
 147     };
 148     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 149     let sig = tcx.erase_late_bound_regions(&sig);
 150     let span = tcx.def_span(def_id);
 151
 152     let source_info = SourceInfo::outermost(span);
 153
 154     let return_block = BasicBlock::new(1);
 155     let mut blocks = IndexVec::with_capacity(2);
 156     let block = |blocks: &mut IndexVec<_, _>, kind| {
 157         blocks.push(BasicBlockData {
 158             statements: vec![],
 159             terminator: Some(Terminator { source_info, kind }),
 160             is_cleanup: false,
 161         })
 162     };
 163     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 164     block(&mut blocks, TerminatorKind::Return);
 165
 166     let mut body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 167
 168     if let Some(..) = ty {
 169         // The first argument (index 0), but add 1 for the return value.
 170         let dropee_ptr = Place::from(Local::new(1 + 0));
 171         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 172             // Function arguments should be retagged, and we make this one raw.
 173             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 174                 0,
 175                 Statement {
 176                     source_info,
 177                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr)),
 178                 },
 179             );
 180         }
 181         let patch = {
 182             let param_env = tcx.param_env_reveal_all_normalized(def_id);
 183             let mut elaborator =
 184                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 185             let dropee = tcx.mk_place_deref(dropee_ptr);
 186             let resume_block = elaborator.patch.resume_block();
 187             elaborate_drops::elaborate_drop(
 188                 &mut elaborator,
 189                 source_info,
 190                 dropee,
 191                 (),
 192                 return_block,
 193                 elaborate_drops::Unwind::To(resume_block),
 194                 START_BLOCK,
 195             );
 196             elaborator.patch
 197         };
 198         patch.apply(&mut body);
 199     }
 200
 201     body
 202 }
 203
 204 fn new_body<'tcx>(
 205     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 206     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 207     arg_count: usize,
 208     span: Span,
 209 ) -> Body<'tcx> {
 210     Body::new(
 211         basic_blocks,
 212         IndexVec::from_elem_n(
 213             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 214             1,
 215         ),
 216         local_decls,
 217         IndexVec::new(),
 218         arg_count,
 219         vec![],
 220         span,
 221         None,
 222     )
 223 }
 224
 225 pub struct DropShimElaborator<'a, 'tcx> {
 226     pub body: &'a Body<'tcx>,
 227     pub patch: MirPatch<'tcx>,
 228     pub tcx: TyCtxt<'tcx>,
 229     pub param_env: ty::ParamEnv<'tcx>,
 230 }
 231
 232 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 233     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 234         Ok(())
 235     }
 236 }
 237
 238 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 239     type Path = ();
 240
 241     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 242         &mut self.patch
 243     }
 244     fn body(&self) -> &'a Body<'tcx> {
 245         self.body
 246     }
 247     fn tcx(&self) -> TyCtxt<'tcx> {
 248         self.tcx
 249     }
 250     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 251         self.param_env
 252     }
 253
 254     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 255         match mode {
 256             DropFlagMode::Shallow => {
 257                 // Drops for the contained fields are "shallow" and "static" - they will simply call
 258                 // the field's own drop glue.
 259                 DropStyle::Static
 260             }
 261             DropFlagMode::Deep => {
 262                 // The top-level drop is "deep" and "open" - it will be elaborated to a drop ladder
 263                 // dropping each field contained in the value.
 264                 DropStyle::Open
 265             }
 266         }
 267     }
 268
 269     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 270         None
 271     }
 272
 273     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 274
 275     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 276         None
 277     }
 278     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 279         None
 280     }
 281     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 282         Some(())
 283     }
 284     fn array_subpath(&self, _path: Self::Path, _index: u64, _size: u64) -> Option<Self::Path> {
 285         None
 286     }
 287 }
 288
 289 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 290 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
 291     debug!("build_clone_shim(def_id={:?})", def_id);
 292
 293     let param_env = tcx.param_env(def_id);
 294
 295     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 296     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(builder.span), param_env);
 297
 298     let dest = Place::return_place();
 299     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 300
 301     match self_ty.kind() {
 302         _ if is_copy => builder.copy_shim(),
 303         ty::Array(ty, len) => {
 304             let len = len.eval_usize(tcx, param_env);
 305             builder.array_shim(dest, src, ty, len)
 306         }
 307         ty::Closure(_, substs) => {
 308             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys())
 309         }
 310         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 311         _ => bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty),
 312     };
 313
 314     builder.into_mir()
 315 }
 316
 317 struct CloneShimBuilder<'tcx> {
 318     tcx: TyCtxt<'tcx>,
 319     def_id: DefId,
 320     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 321     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 322     span: Span,
 323     sig: ty::FnSig<'tcx>,
 324 }
 325
 326 impl CloneShimBuilder<'tcx> {
 327     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 328         // we must subst the self_ty because it's
 329         // otherwise going to be TySelf and we can't index
 330         // or access fields of a Place of type TySelf.
 331         let substs = tcx.mk_substs_trait(self_ty, &[]);
 332         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 333         let sig = tcx.erase_late_bound_regions(&sig);
 334         let span = tcx.def_span(def_id);
 335
 336         CloneShimBuilder {
 337             tcx,
 338             def_id,
 339             local_decls: local_decls_for_sig(&sig, span),
 340             blocks: IndexVec::new(),
 341             span,
 342             sig,
 343         }
 344     }
 345
 346     fn into_mir(self) -> Body<'tcx> {
 347         new_body(self.blocks, self.local_decls, self.sig.inputs().len(), self.span)
 348     }
 349
 350     fn source_info(&self) -> SourceInfo {
 351         SourceInfo::outermost(self.span)
 352     }
 353
 354     fn block(
 355         &mut self,
 356         statements: Vec<Statement<'tcx>>,
 357         kind: TerminatorKind<'tcx>,
 358         is_cleanup: bool,
 359     ) -> BasicBlock {
 360         let source_info = self.source_info();
 361         self.blocks.push(BasicBlockData {
 362             statements,
 363             terminator: Some(Terminator { source_info, kind }),
 364             is_cleanup,
 365         })
 366     }
 367
 368     /// Gives the index of an upcoming BasicBlock, with an offset.
 369     /// offset=0 will give you the index of the next BasicBlock,
 370     /// offset=1 will give the index of the next-to-next block,
 371     /// offset=-1 will give you the index of the last-created block
 372     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 373         BasicBlock::new(self.blocks.len() + offset)
 374     }
 375
 376     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 377         Statement { source_info: self.source_info(), kind }
 378     }
 379
 380     fn copy_shim(&mut self) {
 381         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 382         let ret_statement = self.make_statement(StatementKind::Assign(box (
 383             Place::return_place(),
 384             Rvalue::Use(Operand::Copy(rcvr)),
 385         )));
 386         self.block(vec![ret_statement], TerminatorKind::Return, false);
 387     }
 388
 389     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 390         let span = self.span;
 391         let mut local = LocalDecl::new(ty, span);
 392         if mutability == Mutability::Not {
 393             local = local.immutable();
 394         }
 395         Place::from(self.local_decls.push(local))
 396     }
 397
 398     fn make_clone_call(
 399         &mut self,
 400         dest: Place<'tcx>,
 401         src: Place<'tcx>,
 402         ty: Ty<'tcx>,
 403         next: BasicBlock,
 404         cleanup: BasicBlock,
 405     ) {
 406         let tcx = self.tcx;
 407
 408         let substs = tcx.mk_substs_trait(ty, &[]);
 409
 410         // `func == Clone::clone(&ty) -> ty`
 411         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 412         let func = Operand::Constant(box Constant {
 413             span: self.span,
 414             user_ty: None,
 415             literal: ty::Const::zero_sized(tcx, func_ty),
 416         });
 417
 418         let ref_loc = self.make_place(
 419             Mutability::Not,
 420             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 421         );
 422
 423         // `let ref_loc: &ty = &src;`
 424         let statement = self.make_statement(StatementKind::Assign(box (
 425             ref_loc,
 426             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 427         )));
 428
 429         // `let loc = Clone::clone(ref_loc);`
 430         self.block(
 431             vec![statement],
 432             TerminatorKind::Call {
 433                 func,
 434                 args: vec![Operand::Move(ref_loc)],
 435                 destination: Some((dest, next)),
 436                 cleanup: Some(cleanup),
 437                 from_hir_call: true,
 438                 fn_span: self.span,
 439             },
 440             false,
 441         );
 442     }
 443
 444     fn loop_header(
 445         &mut self,
 446         beg: Place<'tcx>,
 447         end: Place<'tcx>,
 448         loop_body: BasicBlock,
 449         loop_end: BasicBlock,
 450         is_cleanup: bool,
 451     ) {
 452         let tcx = self.tcx;
 453
 454         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 455         let compute_cond = self.make_statement(StatementKind::Assign(box (
 456             cond,
 457             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 458         )));
 459
 460         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 461         self.block(
 462             vec![compute_cond],
 463             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 464             is_cleanup,
 465         );
 466     }
 467
 468     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 469         box Constant {
 470             span: self.span,
 471             user_ty: None,
 472             literal: ty::Const::from_usize(self.tcx, value),
 473         }
 474     }
 475
 476     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 477         let tcx = self.tcx;
 478         let span = self.span;
 479
 480         let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
 481         let end = self.make_place(Mutability::Not, tcx.types.usize);
 482
 483         // BB #0
 484         // `let mut beg = 0;`
 485         // `let end = len;`
 486         // `goto #1;`
 487         let inits = vec![
 488             self.make_statement(StatementKind::Assign(box (
 489                 Place::from(beg),
 490                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 491             ))),
 492             self.make_statement(StatementKind::Assign(box (
 493                 end,
 494                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 495             ))),
 496         ];
 497         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 498
 499         // BB #1: loop {
 500         //     BB #2;
 501         //     BB #3;
 502         // }
 503         // BB #4;
 504         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 505
 506         // BB #2
 507         // `dest[i] = Clone::clone(src[beg])`;
 508         // Goto #3 if ok, #5 if unwinding happens.
 509         let dest_field = self.tcx.mk_place_index(dest, beg);
 510         let src_field = self.tcx.mk_place_index(src, beg);
 511         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 512
 513         // BB #3
 514         // `beg = beg + 1;`
 515         // `goto #1`;
 516         let statements = vec![self.make_statement(StatementKind::Assign(box (
 517             Place::from(beg),
 518             Rvalue::BinaryOp(
 519                 BinOp::Add,
 520                 Operand::Copy(Place::from(beg)),
 521                 Operand::Constant(self.make_usize(1)),
 522             ),
 523         )))];
 524         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 525
 526         // BB #4
 527         // `return dest;`
 528         self.block(vec![], TerminatorKind::Return, false);
 529
 530         // BB #5 (cleanup)
 531         // `let end = beg;`
 532         // `let mut beg = 0;`
 533         // goto #6;
 534         let end = beg;
 535         let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
 536         let init = self.make_statement(StatementKind::Assign(box (
 537             Place::from(beg),
 538             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 539         )));
 540         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 541
 542         // BB #6 (cleanup): loop {
 543         //     BB #7;
 544         //     BB #8;
 545         // }
 546         // BB #9;
 547         self.loop_header(
 548             Place::from(beg),
 549             Place::from(end),
 550             BasicBlock::new(7),
 551             BasicBlock::new(9),
 552             true,
 553         );
 554
 555         // BB #7 (cleanup)
 556         // `drop(dest[beg])`;
 557         self.block(
 558             vec![],
 559             TerminatorKind::Drop {
 560                 place: self.tcx.mk_place_index(dest, beg),
 561                 target: BasicBlock::new(8),
 562                 unwind: None,
 563             },
 564             true,
 565         );
 566
 567         // BB #8 (cleanup)
 568         // `beg = beg + 1;`
 569         // `goto #6;`
 570         let statement = self.make_statement(StatementKind::Assign(box (
 571             Place::from(beg),
 572             Rvalue::BinaryOp(
 573                 BinOp::Add,
 574                 Operand::Copy(Place::from(beg)),
 575                 Operand::Constant(self.make_usize(1)),
 576             ),
 577         )));
 578         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 579
 580         // BB #9 (resume)
 581         self.block(vec![], TerminatorKind::Resume, true);
 582     }
 583
 584     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 585     where
 586         I: Iterator<Item = Ty<'tcx>>,
 587     {
 588         let mut previous_field = None;
 589         for (i, ity) in tys.enumerate() {
 590             let field = Field::new(i);
 591             let src_field = self.tcx.mk_place_field(src, field, ity);
 592
 593             let dest_field = self.tcx.mk_place_field(dest, field, ity);
 594
 595             // #(2i + 1) is the cleanup block for the previous clone operation
 596             let cleanup_block = self.block_index_offset(1);
 597             // #(2i + 2) is the next cloning block
 598             // (or the Return terminator if this is the last block)
 599             let next_block = self.block_index_offset(2);
 600
 601             // BB #(2i)
 602             // `dest.i = Clone::clone(&src.i);`
 603             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 604             self.make_clone_call(dest_field, src_field, ity, next_block, cleanup_block);
 605
 606             // BB #(2i + 1) (cleanup)
 607             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 608                 // Drop previous field and goto previous cleanup block.
 609                 self.block(
 610                     vec![],
 611                     TerminatorKind::Drop {
 612                         place: previous_field,
 613                         target: previous_cleanup,
 614                         unwind: None,
 615                     },
 616                     true,
 617                 );
 618             } else {
 619                 // Nothing to drop, just resume.
 620                 self.block(vec![], TerminatorKind::Resume, true);
 621             }
 622
 623             previous_field = Some((dest_field, cleanup_block));
 624         }
 625
 626         self.block(vec![], TerminatorKind::Return, false);
 627     }
 628 }
 629
 630 /// Builds a "call" shim for `instance`. The shim calls the function specified by `call_kind`,
 631 /// first adjusting its first argument according to `rcvr_adjustment`.
 632 fn build_call_shim<'tcx>(
 633     tcx: TyCtxt<'tcx>,
 634     instance: ty::InstanceDef<'tcx>,
 635     rcvr_adjustment: Option<Adjustment>,
 636     call_kind: CallKind<'tcx>,
 637 ) -> Body<'tcx> {
 638     debug!(
 639         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, call_kind={:?})",
 640         instance, rcvr_adjustment, call_kind
 641     );
 642
 643     // `FnPtrShim` contains the fn pointer type that a call shim is being built for - this is used
 644     // to substitute into the signature of the shim. It is not necessary for users of this
 645     // MIR body to perform further substitutions (see `InstanceDef::has_polymorphic_mir_body`).
 646     let (sig_substs, untuple_args) = if let ty::InstanceDef::FnPtrShim(_, ty) = instance {
 647         let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
 648
 649         let untuple_args = sig.inputs();
 650
 651         // Create substitutions for the `Self` and `Args` generic parameters of the shim body.
 652         let arg_tup = tcx.mk_tup(untuple_args.iter());
 653         let sig_substs = tcx.mk_substs_trait(ty, &[ty::subst::GenericArg::from(arg_tup)]);
 654
 655         (Some(sig_substs), Some(untuple_args))
 656     } else {
 657         (None, None)
 658     };
 659
 660     let def_id = instance.def_id();
 661     let sig = tcx.fn_sig(def_id);
 662     let mut sig = tcx.erase_late_bound_regions(&sig);
 663
 664     assert_eq!(sig_substs.is_some(), !instance.has_polymorphic_mir_body());
 665     if let Some(sig_substs) = sig_substs {
 666         sig = sig.subst(tcx, sig_substs);
 667     }
 668
 669     if let CallKind::Indirect(fnty) = call_kind {
 670         // `sig` determines our local decls, and thus the callee type in the `Call` terminator. This
 671         // can only be an `FnDef` or `FnPtr`, but currently will be `Self` since the types come from
 672         // the implemented `FnX` trait.
 673
 674         // Apply the opposite adjustment to the MIR input.
 675         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 676
 677         // Initial signature is `fn(&? Self, Args) -> Self::Output` where `Args` is a tuple of the
 678         // fn arguments. `Self` may be passed via (im)mutable reference or by-value.
 679         assert_eq!(inputs_and_output.len(), 3);
 680
 681         // `Self` is always the original fn type `ty`. The MIR call terminator is only defined for
 682         // `FnDef` and `FnPtr` callees, not the `Self` type param.
 683         let self_arg = &mut inputs_and_output[0];
 684         *self_arg = match rcvr_adjustment.unwrap() {
 685             Adjustment::Identity => fnty,
 686             Adjustment::Deref => tcx.mk_imm_ptr(fnty),
 687             Adjustment::RefMut => tcx.mk_mut_ptr(fnty),
 688         };
 689         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 690     }
 691
 692     // FIXME(eddyb) avoid having this snippet both here and in
 693     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 694     if let ty::InstanceDef::VtableShim(..) = instance {
 695         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 696         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 697         let self_arg = &mut inputs_and_output[0];
 698         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 699         *self_arg = tcx.mk_mut_ptr(*self_arg);
 700         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 701     }
 702
 703     let span = tcx.def_span(def_id);
 704
 705     debug!("build_call_shim: sig={:?}", sig);
 706
 707     let mut local_decls = local_decls_for_sig(&sig, span);
 708     let source_info = SourceInfo::outermost(span);
 709
 710     let rcvr_place = || {
 711         assert!(rcvr_adjustment.is_some());
 712         Place::from(Local::new(1 + 0))
 713     };
 714     let mut statements = vec![];
 715
 716     let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
 717         Adjustment::Identity => Operand::Move(rcvr_place()),
 718         Adjustment::Deref => Operand::Move(tcx.mk_place_deref(rcvr_place())),
 719         Adjustment::RefMut => {
 720             // let rcvr = &mut rcvr;
 721             let ref_rcvr = local_decls.push(
 722                 LocalDecl::new(
 723                     tcx.mk_ref(
 724                         tcx.lifetimes.re_erased,
 725                         ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 726                     ),
 727                     span,
 728                 )
 729                 .immutable(),
 730             );
 731             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 732             statements.push(Statement {
 733                 source_info,
 734                 kind: StatementKind::Assign(box (
 735                     Place::from(ref_rcvr),
 736                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_place()),
 737                 )),
 738             });
 739             Operand::Move(Place::from(ref_rcvr))
 740         }
 741     });
 742
 743     let (callee, mut args) = match call_kind {
 744         // `FnPtr` call has no receiver. Args are untupled below.
 745         CallKind::Indirect(_) => (rcvr.unwrap(), vec![]),
 746
 747         // `FnDef` call with optional receiver.
 748         CallKind::Direct(def_id) => {
 749             let ty = tcx.type_of(def_id);
 750             (
 751                 Operand::Constant(box Constant {
 752                     span,
 753                     user_ty: None,
 754                     literal: ty::Const::zero_sized(tcx, ty),
 755                 }),
 756                 rcvr.into_iter().collect::<Vec<_>>(),
 757             )
 758         }
 759     };
 760
 761     let mut arg_range = 0..sig.inputs().len();
 762
 763     // Take the `self` ("receiver") argument out of the range (it's adjusted above).
 764     if rcvr_adjustment.is_some() {
 765         arg_range.start += 1;
 766     }
 767
 768     // Take the last argument, if we need to untuple it (handled below).
 769     if untuple_args.is_some() {
 770         arg_range.end -= 1;
 771     }
 772
 773     // Pass all of the non-special arguments directly.
 774     args.extend(arg_range.map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 775
 776     // Untuple the last argument, if we have to.
 777     if let Some(untuple_args) = untuple_args {
 778         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
 779         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 780             Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
 781         }));
 782     }
 783
 784     let n_blocks = if let Some(Adjustment::RefMut) = rcvr_adjustment { 5 } else { 2 };
 785     let mut blocks = IndexVec::with_capacity(n_blocks);
 786     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 787         blocks.push(BasicBlockData {
 788             statements,
 789             terminator: Some(Terminator { source_info, kind }),
 790             is_cleanup,
 791         })
 792     };
 793
 794     // BB #0
 795     block(
 796         &mut blocks,
 797         statements,
 798         TerminatorKind::Call {
 799             func: callee,
 800             args,
 801             destination: Some((Place::return_place(), BasicBlock::new(1))),
 802             cleanup: if let Some(Adjustment::RefMut) = rcvr_adjustment {
 803                 Some(BasicBlock::new(3))
 804             } else {
 805                 None
 806             },
 807             from_hir_call: true,
 808             fn_span: span,
 809         },
 810         false,
 811     );
 812
 813     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 814         // BB #1 - drop for Self
 815         block(
 816             &mut blocks,
 817             vec![],
 818             TerminatorKind::Drop { place: rcvr_place(), target: BasicBlock::new(2), unwind: None },
 819             false,
 820         );
 821     }
 822     // BB #1/#2 - return
 823     block(&mut blocks, vec![], TerminatorKind::Return, false);
 824     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 825         // BB #3 - drop if closure panics
 826         block(
 827             &mut blocks,
 828             vec![],
 829             TerminatorKind::Drop { place: rcvr_place(), target: BasicBlock::new(4), unwind: None },
 830             true,
 831         );
 832
 833         // BB #4 - resume
 834         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 835     }
 836
 837     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 838
 839     if let Abi::RustCall = sig.abi {
 840         body.spread_arg = Some(Local::new(sig.inputs().len()));
 841     }
 842
 843     body
 844 }
 845
 846 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
 847     debug_assert!(tcx.is_constructor(ctor_id));
 848
 849     let span =
 850         tcx.hir().span_if_local(ctor_id).unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 851
 852     let param_env = tcx.param_env(ctor_id);
 853
 854     // Normalize the sig.
 855     let sig = tcx.fn_sig(ctor_id).no_bound_vars().expect("LBR in ADT constructor signature");
 856     let sig = tcx.normalize_erasing_regions(param_env, sig);
 857
 858     let (adt_def, substs) = match sig.output().kind() {
 859         ty::Adt(adt_def, substs) => (adt_def, substs),
 860         _ => bug!("unexpected type for ADT ctor {:?}", sig.output()),
 861     };
 862
 863     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 864
 865     let local_decls = local_decls_for_sig(&sig, span);
 866
 867     let source_info = SourceInfo::outermost(span);
 868
 869     let variant_index = if adt_def.is_enum() {
 870         adt_def.variant_index_with_ctor_id(ctor_id)
 871     } else {
 872         VariantIdx::new(0)
 873     };
 874
 875     // Generate the following MIR:
 876     //
 877     // (return as Variant).field0 = arg0;
 878     // (return as Variant).field1 = arg1;
 879     //
 880     // return;
 881     debug!("build_ctor: variant_index={:?}", variant_index);
 882
 883     let statements = expand_aggregate(
 884         Place::return_place(),
 885         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
 886             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
 887         }),
 888         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 889         source_info,
 890         tcx,
 891     )
 892     .collect();
 893
 894     let start_block = BasicBlockData {
 895         statements,
 896         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
 897         is_cleanup: false,
 898     };
 899
 900     let body =
 901         new_body(IndexVec::from_elem_n(start_block, 1), local_decls, sig.inputs().len(), span);
 902
 903     crate::util::dump_mir(
 904         tcx,
 905         None,
 906         "mir_map",
 907         &0,
 908         crate::transform::MirSource::item(ctor_id),
 909         &body,
 910         |_, _| Ok(()),
 911     );
 912
 913     body
 914 }