src/librustc_mir/shim.rs

   1 use rustc_hir as hir;
   2 use rustc_hir::def_id::DefId;
   3 use rustc_middle::mir::*;
   4 use rustc_middle::ty::query::Providers;
   5 use rustc_middle::ty::subst::{InternalSubsts, Subst};
   6 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
   7 use rustc_target::abi::VariantIdx;
   8
   9 use rustc_index::vec::{Idx, IndexVec};
  10
  11 use rustc_span::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             // FIXME(eddyb) support generating shims for a "shallow type",
  43             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
  44             // `Foo<Bar>` or `[String]` etc.
  45             assert!(!ty.needs_subst());
  46
  47             let trait_ = tcx.trait_of_item(def_id).unwrap();
  48             let adjustment = match tcx.fn_trait_kind_from_lang_item(trait_) {
  49                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  50                 Some(ty::ClosureKind::FnMut) | Some(ty::ClosureKind::Fn) => Adjustment::Deref,
  51                 None => bug!("fn pointer {:?} is not an fn", ty),
  52             };
  53             // HACK: we need the "real" argument types for the MIR,
  54             // but because our substs are (Self, Args), where Args
  55             // is a tuple, we must include the *concrete* argument
  56             // types in the MIR. They will be substituted again with
  57             // the param-substs, but because they are concrete, this
  58             // will not do any harm.
  59             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  60             let arg_tys = sig.inputs();
  61
  62             build_call_shim(tcx, instance, Some(adjustment), CallKind::Indirect, Some(arg_tys))
  63         }
  64         // We are generating a call back to our def-id, which the
  65         // codegen backend knows to turn to an actual call, be it
  66         // a virtual call, or a direct call to a function for which
  67         // indirect calls must be codegen'd differently than direct ones
  68         // (such as `#[track_caller]`).
  69         ty::InstanceDef::ReifyShim(def_id) => {
  70             build_call_shim(tcx, instance, None, CallKind::Direct(def_id), None)
  71         }
  72         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
  73             let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
  74             let call_mut = tcx
  75                 .associated_items(fn_mut)
  76                 .in_definition_order()
  77                 .find(|it| it.kind == ty::AssocKind::Method)
  78                 .unwrap()
  79                 .def_id;
  80
  81             build_call_shim(
  82                 tcx,
  83                 instance,
  84                 Some(Adjustment::RefMut),
  85                 CallKind::Direct(call_mut),
  86                 None,
  87             )
  88         }
  89         ty::InstanceDef::DropGlue(def_id, ty) => {
  90             // FIXME(eddyb) support generating shims for a "shallow type",
  91             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
  92             // `Foo<Bar>` or `[String]` etc.
  93             assert!(!ty.needs_subst());
  94
  95             build_drop_shim(tcx, def_id, ty)
  96         }
  97         ty::InstanceDef::CloneShim(def_id, ty) => {
  98             // FIXME(eddyb) support generating shims for a "shallow type",
  99             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
 100             // `Foo<Bar>` or `[String]` etc.
 101             assert!(!ty.needs_subst());
 102
 103             build_clone_shim(tcx, def_id, ty)
 104         }
 105         ty::InstanceDef::Virtual(..) => {
 106             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
 107         }
 108         ty::InstanceDef::Intrinsic(_) => {
 109             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 110         }
 111     };
 112     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 113
 114     run_passes(
 115         tcx,
 116         &mut result,
 117         instance,
 118         None,
 119         MirPhase::Const,
 120         &[
 121             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 122             &no_landing_pads::NoLandingPads::new(tcx),
 123             &remove_noop_landing_pads::RemoveNoopLandingPads,
 124             &simplify::SimplifyCfg::new("make_shim"),
 125             &add_call_guards::CriticalCallEdges,
 126         ],
 127     );
 128
 129     debug!("make_shim({:?}) = {:?}", instance, result);
 130
 131     result.ensure_predecessors();
 132     tcx.arena.alloc(result)
 133 }
 134
 135 #[derive(Copy, Clone, Debug, PartialEq)]
 136 enum Adjustment {
 137     Identity,
 138     Deref,
 139     DerefMove,
 140     RefMut,
 141 }
 142
 143 #[derive(Copy, Clone, Debug, PartialEq)]
 144 enum CallKind {
 145     Indirect,
 146     Direct(DefId),
 147 }
 148
 149 fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
 150     let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
 151     LocalDecl {
 152         mutability,
 153         ty,
 154         user_ty: UserTypeProjections::none(),
 155         source_info,
 156         internal: false,
 157         local_info: LocalInfo::Other,
 158         is_block_tail: None,
 159     }
 160 }
 161
 162 fn local_decls_for_sig<'tcx>(
 163     sig: &ty::FnSig<'tcx>,
 164     span: Span,
 165 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 166     iter::once(temp_decl(Mutability::Mut, sig.output(), span))
 167         .chain(sig.inputs().iter().map(|ity| temp_decl(Mutability::Not, ity, span)))
 168         .collect()
 169 }
 170
 171 fn build_drop_shim<'tcx>(
 172     tcx: TyCtxt<'tcx>,
 173     def_id: DefId,
 174     ty: Option<Ty<'tcx>>,
 175 ) -> BodyAndCache<'tcx> {
 176     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 177
 178     // Check if this is a generator, if so, return the drop glue for it
 179     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 180         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 181         return body.subst(tcx, substs);
 182     }
 183
 184     let substs = if let Some(ty) = ty {
 185         tcx.intern_substs(&[ty.into()])
 186     } else {
 187         InternalSubsts::identity_for_item(tcx, def_id)
 188     };
 189     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 190     let sig = tcx.erase_late_bound_regions(&sig);
 191     let span = tcx.def_span(def_id);
 192
 193     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 194
 195     let return_block = BasicBlock::new(1);
 196     let mut blocks = IndexVec::with_capacity(2);
 197     let block = |blocks: &mut IndexVec<_, _>, kind| {
 198         blocks.push(BasicBlockData {
 199             statements: vec![],
 200             terminator: Some(Terminator { source_info, kind }),
 201             is_cleanup: false,
 202         })
 203     };
 204     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 205     block(&mut blocks, TerminatorKind::Return);
 206
 207     let body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 208
 209     let mut body = BodyAndCache::new(body);
 210
 211     if let Some(..) = ty {
 212         // The first argument (index 0), but add 1 for the return value.
 213         let dropee_ptr = Place::from(Local::new(1 + 0));
 214         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 215             // Function arguments should be retagged, and we make this one raw.
 216             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 217                 0,
 218                 Statement {
 219                     source_info,
 220                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr)),
 221                 },
 222             );
 223         }
 224         let patch = {
 225             let param_env = tcx.param_env(def_id).with_reveal_all();
 226             let mut elaborator =
 227                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 228             let dropee = tcx.mk_place_deref(dropee_ptr);
 229             let resume_block = elaborator.patch.resume_block();
 230             elaborate_drops::elaborate_drop(
 231                 &mut elaborator,
 232                 source_info,
 233                 dropee,
 234                 (),
 235                 return_block,
 236                 elaborate_drops::Unwind::To(resume_block),
 237                 START_BLOCK,
 238             );
 239             elaborator.patch
 240         };
 241         patch.apply(&mut body);
 242     }
 243
 244     body
 245 }
 246
 247 fn new_body<'tcx>(
 248     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 249     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 250     arg_count: usize,
 251     span: Span,
 252 ) -> Body<'tcx> {
 253     Body::new(
 254         basic_blocks,
 255         IndexVec::from_elem_n(
 256             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 257             1,
 258         ),
 259         local_decls,
 260         IndexVec::new(),
 261         arg_count,
 262         vec![],
 263         span,
 264         vec![],
 265         None,
 266     )
 267 }
 268
 269 pub struct DropShimElaborator<'a, 'tcx> {
 270     pub body: &'a Body<'tcx>,
 271     pub patch: MirPatch<'tcx>,
 272     pub tcx: TyCtxt<'tcx>,
 273     pub param_env: ty::ParamEnv<'tcx>,
 274 }
 275
 276 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 277     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 278         Ok(())
 279     }
 280 }
 281
 282 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 283     type Path = ();
 284
 285     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 286         &mut self.patch
 287     }
 288     fn body(&self) -> &'a Body<'tcx> {
 289         self.body
 290     }
 291     fn tcx(&self) -> TyCtxt<'tcx> {
 292         self.tcx
 293     }
 294     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 295         self.param_env
 296     }
 297
 298     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 299         if let DropFlagMode::Shallow = mode { DropStyle::Static } else { DropStyle::Open }
 300     }
 301
 302     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 303         None
 304     }
 305
 306     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 307
 308     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 309         None
 310     }
 311     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 312         None
 313     }
 314     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 315         Some(())
 316     }
 317     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 318         None
 319     }
 320 }
 321
 322 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 323 fn build_clone_shim<'tcx>(
 324     tcx: TyCtxt<'tcx>,
 325     def_id: DefId,
 326     self_ty: Ty<'tcx>,
 327 ) -> BodyAndCache<'tcx> {
 328     debug!("build_clone_shim(def_id={:?})", def_id);
 329
 330     let param_env = tcx.param_env(def_id);
 331
 332     let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
 333     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env, builder.span);
 334
 335     let dest = Place::return_place();
 336     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 337
 338     match self_ty.kind {
 339         _ if is_copy => builder.copy_shim(),
 340         ty::Array(ty, len) => {
 341             let len = len.eval_usize(tcx, param_env);
 342             builder.array_shim(dest, src, ty, len)
 343         }
 344         ty::Closure(_, substs) => {
 345             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys())
 346         }
 347         ty::Tuple(..) => builder.tuple_like_shim(dest, src, self_ty.tuple_fields()),
 348         _ => bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty),
 349     };
 350
 351     BodyAndCache::new(builder.into_mir())
 352 }
 353
 354 struct CloneShimBuilder<'tcx> {
 355     tcx: TyCtxt<'tcx>,
 356     def_id: DefId,
 357     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 358     blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 359     span: Span,
 360     sig: ty::FnSig<'tcx>,
 361 }
 362
 363 impl CloneShimBuilder<'tcx> {
 364     fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Self {
 365         // we must subst the self_ty because it's
 366         // otherwise going to be TySelf and we can't index
 367         // or access fields of a Place of type TySelf.
 368         let substs = tcx.mk_substs_trait(self_ty, &[]);
 369         let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 370         let sig = tcx.erase_late_bound_regions(&sig);
 371         let span = tcx.def_span(def_id);
 372
 373         CloneShimBuilder {
 374             tcx,
 375             def_id,
 376             local_decls: local_decls_for_sig(&sig, span),
 377             blocks: IndexVec::new(),
 378             span,
 379             sig,
 380         }
 381     }
 382
 383     fn into_mir(self) -> Body<'tcx> {
 384         new_body(self.blocks, self.local_decls, self.sig.inputs().len(), self.span)
 385     }
 386
 387     fn source_info(&self) -> SourceInfo {
 388         SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
 389     }
 390
 391     fn block(
 392         &mut self,
 393         statements: Vec<Statement<'tcx>>,
 394         kind: TerminatorKind<'tcx>,
 395         is_cleanup: bool,
 396     ) -> BasicBlock {
 397         let source_info = self.source_info();
 398         self.blocks.push(BasicBlockData {
 399             statements,
 400             terminator: Some(Terminator { source_info, kind }),
 401             is_cleanup,
 402         })
 403     }
 404
 405     /// Gives the index of an upcoming BasicBlock, with an offset.
 406     /// offset=0 will give you the index of the next BasicBlock,
 407     /// offset=1 will give the index of the next-to-next block,
 408     /// offset=-1 will give you the index of the last-created block
 409     fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
 410         BasicBlock::new(self.blocks.len() + offset)
 411     }
 412
 413     fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
 414         Statement { source_info: self.source_info(), kind }
 415     }
 416
 417     fn copy_shim(&mut self) {
 418         let rcvr = self.tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 419         let ret_statement = self.make_statement(StatementKind::Assign(box (
 420             Place::return_place(),
 421             Rvalue::Use(Operand::Copy(rcvr)),
 422         )));
 423         self.block(vec![ret_statement], TerminatorKind::Return, false);
 424     }
 425
 426     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
 427         let span = self.span;
 428         Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
 429     }
 430
 431     fn make_clone_call(
 432         &mut self,
 433         dest: Place<'tcx>,
 434         src: Place<'tcx>,
 435         ty: Ty<'tcx>,
 436         next: BasicBlock,
 437         cleanup: BasicBlock,
 438     ) {
 439         let tcx = self.tcx;
 440
 441         let substs = tcx.mk_substs_trait(ty, &[]);
 442
 443         // `func == Clone::clone(&ty) -> ty`
 444         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 445         let func = Operand::Constant(box Constant {
 446             span: self.span,
 447             user_ty: None,
 448             literal: ty::Const::zero_sized(tcx, func_ty),
 449         });
 450
 451         let ref_loc = self.make_place(
 452             Mutability::Not,
 453             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 454         );
 455
 456         // `let ref_loc: &ty = &src;`
 457         let statement = self.make_statement(StatementKind::Assign(box (
 458             ref_loc,
 459             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 460         )));
 461
 462         // `let loc = Clone::clone(ref_loc);`
 463         self.block(
 464             vec![statement],
 465             TerminatorKind::Call {
 466                 func,
 467                 args: vec![Operand::Move(ref_loc)],
 468                 destination: Some((dest, next)),
 469                 cleanup: Some(cleanup),
 470                 from_hir_call: true,
 471             },
 472             false,
 473         );
 474     }
 475
 476     fn loop_header(
 477         &mut self,
 478         beg: Place<'tcx>,
 479         end: Place<'tcx>,
 480         loop_body: BasicBlock,
 481         loop_end: BasicBlock,
 482         is_cleanup: bool,
 483     ) {
 484         let tcx = self.tcx;
 485
 486         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 487         let compute_cond = self.make_statement(StatementKind::Assign(box (
 488             cond,
 489             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 490         )));
 491
 492         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 493         self.block(
 494             vec![compute_cond],
 495             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 496             is_cleanup,
 497         );
 498     }
 499
 500     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 501         box Constant {
 502             span: self.span,
 503             user_ty: None,
 504             literal: ty::Const::from_usize(self.tcx, value),
 505         }
 506     }
 507
 508     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 509         let tcx = self.tcx;
 510         let span = self.span;
 511
 512         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 513         let end = self.make_place(Mutability::Not, tcx.types.usize);
 514
 515         // BB #0
 516         // `let mut beg = 0;`
 517         // `let end = len;`
 518         // `goto #1;`
 519         let inits = vec![
 520             self.make_statement(StatementKind::Assign(box (
 521                 Place::from(beg),
 522                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 523             ))),
 524             self.make_statement(StatementKind::Assign(box (
 525                 end,
 526                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 527             ))),
 528         ];
 529         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 530
 531         // BB #1: loop {
 532         //     BB #2;
 533         //     BB #3;
 534         // }
 535         // BB #4;
 536         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 537
 538         // BB #2
 539         // `dest[i] = Clone::clone(src[beg])`;
 540         // Goto #3 if ok, #5 if unwinding happens.
 541         let dest_field = self.tcx.mk_place_index(dest.clone(), beg);
 542         let src_field = self.tcx.mk_place_index(src, beg);
 543         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 544
 545         // BB #3
 546         // `beg = beg + 1;`
 547         // `goto #1`;
 548         let statements = vec![self.make_statement(StatementKind::Assign(box (
 549             Place::from(beg),
 550             Rvalue::BinaryOp(
 551                 BinOp::Add,
 552                 Operand::Copy(Place::from(beg)),
 553                 Operand::Constant(self.make_usize(1)),
 554             ),
 555         )))];
 556         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 557
 558         // BB #4
 559         // `return dest;`
 560         self.block(vec![], TerminatorKind::Return, false);
 561
 562         // BB #5 (cleanup)
 563         // `let end = beg;`
 564         // `let mut beg = 0;`
 565         // goto #6;
 566         let end = beg;
 567         let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
 568         let init = self.make_statement(StatementKind::Assign(box (
 569             Place::from(beg),
 570             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 571         )));
 572         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 573
 574         // BB #6 (cleanup): loop {
 575         //     BB #7;
 576         //     BB #8;
 577         // }
 578         // BB #9;
 579         self.loop_header(
 580             Place::from(beg),
 581             Place::from(end),
 582             BasicBlock::new(7),
 583             BasicBlock::new(9),
 584             true,
 585         );
 586
 587         // BB #7 (cleanup)
 588         // `drop(dest[beg])`;
 589         self.block(
 590             vec![],
 591             TerminatorKind::Drop {
 592                 location: self.tcx.mk_place_index(dest, beg),
 593                 target: BasicBlock::new(8),
 594                 unwind: None,
 595             },
 596             true,
 597         );
 598
 599         // BB #8 (cleanup)
 600         // `beg = beg + 1;`
 601         // `goto #6;`
 602         let statement = self.make_statement(StatementKind::Assign(box (
 603             Place::from(beg),
 604             Rvalue::BinaryOp(
 605                 BinOp::Add,
 606                 Operand::Copy(Place::from(beg)),
 607                 Operand::Constant(self.make_usize(1)),
 608             ),
 609         )));
 610         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 611
 612         // BB #9 (resume)
 613         self.block(vec![], TerminatorKind::Resume, true);
 614     }
 615
 616     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 617     where
 618         I: Iterator<Item = Ty<'tcx>>,
 619     {
 620         let mut previous_field = None;
 621         for (i, ity) in tys.enumerate() {
 622             let field = Field::new(i);
 623             let src_field = self.tcx.mk_place_field(src.clone(), field, ity);
 624
 625             let dest_field = self.tcx.mk_place_field(dest.clone(), field, ity);
 626
 627             // #(2i + 1) is the cleanup block for the previous clone operation
 628             let cleanup_block = self.block_index_offset(1);
 629             // #(2i + 2) is the next cloning block
 630             // (or the Return terminator if this is the last block)
 631             let next_block = self.block_index_offset(2);
 632
 633             // BB #(2i)
 634             // `dest.i = Clone::clone(&src.i);`
 635             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 636             self.make_clone_call(dest_field.clone(), src_field, ity, next_block, cleanup_block);
 637
 638             // BB #(2i + 1) (cleanup)
 639             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 640                 // Drop previous field and goto previous cleanup block.
 641                 self.block(
 642                     vec![],
 643                     TerminatorKind::Drop {
 644                         location: previous_field,
 645                         target: previous_cleanup,
 646                         unwind: None,
 647                     },
 648                     true,
 649                 );
 650             } else {
 651                 // Nothing to drop, just resume.
 652                 self.block(vec![], TerminatorKind::Resume, true);
 653             }
 654
 655             previous_field = Some((dest_field, cleanup_block));
 656         }
 657
 658         self.block(vec![], TerminatorKind::Return, false);
 659     }
 660 }
 661
 662 /// Builds a "call" shim for `instance`. The shim calls the
 663 /// function specified by `call_kind`, first adjusting its first
 664 /// argument according to `rcvr_adjustment`.
 665 ///
 666 /// If `untuple_args` is a vec of types, the second argument of the
 667 /// function will be untupled as these types.
 668 fn build_call_shim<'tcx>(
 669     tcx: TyCtxt<'tcx>,
 670     instance: ty::InstanceDef<'tcx>,
 671     rcvr_adjustment: Option<Adjustment>,
 672     call_kind: CallKind,
 673     untuple_args: Option<&[Ty<'tcx>]>,
 674 ) -> BodyAndCache<'tcx> {
 675     debug!(
 676         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 677             call_kind={:?}, untuple_args={:?})",
 678         instance, rcvr_adjustment, call_kind, untuple_args
 679     );
 680
 681     let def_id = instance.def_id();
 682     let sig = tcx.fn_sig(def_id);
 683     let mut sig = tcx.erase_late_bound_regions(&sig);
 684
 685     // FIXME(eddyb) avoid having this snippet both here and in
 686     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 687     if let ty::InstanceDef::VtableShim(..) = instance {
 688         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 689         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 690         let self_arg = &mut inputs_and_output[0];
 691         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 692         *self_arg = tcx.mk_mut_ptr(*self_arg);
 693         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 694     }
 695
 696     let span = tcx.def_span(def_id);
 697
 698     debug!("build_call_shim: sig={:?}", sig);
 699
 700     let mut local_decls = local_decls_for_sig(&sig, span);
 701     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 702
 703     let rcvr_place = || {
 704         assert!(rcvr_adjustment.is_some());
 705         Place::from(Local::new(1 + 0))
 706     };
 707     let mut statements = vec![];
 708
 709     let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
 710         Adjustment::Identity => Operand::Move(rcvr_place()),
 711         Adjustment::Deref => Operand::Copy(tcx.mk_place_deref(rcvr_place())),
 712         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_place())),
 713         Adjustment::RefMut => {
 714             // let rcvr = &mut rcvr;
 715             let ref_rcvr = local_decls.push(temp_decl(
 716                 Mutability::Not,
 717                 tcx.mk_ref(
 718                     tcx.lifetimes.re_erased,
 719                     ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 720                 ),
 721                 span,
 722             ));
 723             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 724             statements.push(Statement {
 725                 source_info,
 726                 kind: StatementKind::Assign(box (
 727                     Place::from(ref_rcvr),
 728                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_place()),
 729                 )),
 730             });
 731             Operand::Move(Place::from(ref_rcvr))
 732         }
 733     });
 734
 735     let (callee, mut args) = match call_kind {
 736         CallKind::Indirect => (rcvr.unwrap(), vec![]),
 737         CallKind::Direct(def_id) => {
 738             let ty = tcx.type_of(def_id);
 739             (
 740                 Operand::Constant(box Constant {
 741                     span,
 742                     user_ty: None,
 743                     literal: ty::Const::zero_sized(tcx, ty),
 744                 }),
 745                 rcvr.into_iter().collect::<Vec<_>>(),
 746             )
 747         }
 748     };
 749
 750     let mut arg_range = 0..sig.inputs().len();
 751
 752     // Take the `self` ("receiver") argument out of the range (it's adjusted above).
 753     if rcvr_adjustment.is_some() {
 754         arg_range.start += 1;
 755     }
 756
 757     // Take the last argument, if we need to untuple it (handled below).
 758     if untuple_args.is_some() {
 759         arg_range.end -= 1;
 760     }
 761
 762     // Pass all of the non-special arguments directly.
 763     args.extend(arg_range.map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 764
 765     // Untuple the last argument, if we have to.
 766     if let Some(untuple_args) = untuple_args {
 767         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
 768         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 769             Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
 770         }));
 771     }
 772
 773     let n_blocks = if let Some(Adjustment::RefMut) = rcvr_adjustment { 5 } else { 2 };
 774     let mut blocks = IndexVec::with_capacity(n_blocks);
 775     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 776         blocks.push(BasicBlockData {
 777             statements,
 778             terminator: Some(Terminator { source_info, kind }),
 779             is_cleanup,
 780         })
 781     };
 782
 783     // BB #0
 784     block(
 785         &mut blocks,
 786         statements,
 787         TerminatorKind::Call {
 788             func: callee,
 789             args,
 790             destination: Some((Place::return_place(), BasicBlock::new(1))),
 791             cleanup: if let Some(Adjustment::RefMut) = rcvr_adjustment {
 792                 Some(BasicBlock::new(3))
 793             } else {
 794                 None
 795             },
 796             from_hir_call: true,
 797         },
 798         false,
 799     );
 800
 801     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 802         // BB #1 - drop for Self
 803         block(
 804             &mut blocks,
 805             vec![],
 806             TerminatorKind::Drop {
 807                 location: rcvr_place(),
 808                 target: BasicBlock::new(2),
 809                 unwind: None,
 810             },
 811             false,
 812         );
 813     }
 814     // BB #1/#2 - return
 815     block(&mut blocks, vec![], TerminatorKind::Return, false);
 816     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 817         // BB #3 - drop if closure panics
 818         block(
 819             &mut blocks,
 820             vec![],
 821             TerminatorKind::Drop {
 822                 location: rcvr_place(),
 823                 target: BasicBlock::new(4),
 824                 unwind: None,
 825             },
 826             true,
 827         );
 828
 829         // BB #4 - resume
 830         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 831     }
 832
 833     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 834
 835     if let Abi::RustCall = sig.abi {
 836         body.spread_arg = Some(Local::new(sig.inputs().len()));
 837     }
 838     BodyAndCache::new(body)
 839 }
 840
 841 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> &BodyAndCache<'_> {
 842     debug_assert!(tcx.is_constructor(ctor_id));
 843
 844     let span =
 845         tcx.hir().span_if_local(ctor_id).unwrap_or_else(|| bug!("no span for ctor {:?}", ctor_id));
 846
 847     let param_env = tcx.param_env(ctor_id);
 848
 849     // Normalize the sig.
 850     let sig = tcx.fn_sig(ctor_id).no_bound_vars().expect("LBR in ADT constructor signature");
 851     let sig = tcx.normalize_erasing_regions(param_env, sig);
 852
 853     let (adt_def, substs) = match sig.output().kind {
 854         ty::Adt(adt_def, substs) => (adt_def, substs),
 855         _ => bug!("unexpected type for ADT ctor {:?}", sig.output()),
 856     };
 857
 858     debug!("build_ctor: ctor_id={:?} sig={:?}", ctor_id, sig);
 859
 860     let local_decls = local_decls_for_sig(&sig, span);
 861
 862     let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
 863
 864     let variant_index = if adt_def.is_enum() {
 865         adt_def.variant_index_with_ctor_id(ctor_id)
 866     } else {
 867         VariantIdx::new(0)
 868     };
 869
 870     // Generate the following MIR:
 871     //
 872     // (return as Variant).field0 = arg0;
 873     // (return as Variant).field1 = arg1;
 874     //
 875     // return;
 876     debug!("build_ctor: variant_index={:?}", variant_index);
 877
 878     let statements = expand_aggregate(
 879         Place::return_place(),
 880         adt_def.variants[variant_index].fields.iter().enumerate().map(|(idx, field_def)| {
 881             (Operand::Move(Place::from(Local::new(idx + 1))), field_def.ty(tcx, substs))
 882         }),
 883         AggregateKind::Adt(adt_def, variant_index, substs, None, None),
 884         source_info,
 885         tcx,
 886     )
 887     .collect();
 888
 889     let start_block = BasicBlockData {
 890         statements,
 891         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
 892         is_cleanup: false,
 893     };
 894
 895     let body =
 896         new_body(IndexVec::from_elem_n(start_block, 1), local_decls, sig.inputs().len(), span);
 897
 898     crate::util::dump_mir(
 899         tcx,
 900         None,
 901         "mir_map",
 902         &0,
 903         crate::transform::MirSource::item(ctor_id),
 904         &body,
 905         |_, _| Ok(()),
 906     );
 907
 908     let mut body = BodyAndCache::new(body);
 909     body.ensure_predecessors();
 910     tcx.arena.alloc(body)
 911 }