src/librustc_mir/shim.rs

   1 use rustc_hir as hir;
   2 use rustc_hir::def_id::DefId;
   3 use rustc_hir::lang_items::FnMutTraitLangItem;
   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, TypeFoldable};
   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) => build_call_shim(
  36             tcx,
  37             instance,
  38             Some(Adjustment::DerefMove),
  39             CallKind::Direct(def_id),
  40             None,
  41         ),
  42         ty::InstanceDef::FnPtrShim(def_id, ty) => {
  43             // FIXME(eddyb) support generating shims for a "shallow type",
  44             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
  45             // `Foo<Bar>` or `[String]` etc.
  46             assert!(!ty.needs_subst());
  47
  48             let trait_ = tcx.trait_of_item(def_id).unwrap();
  49             let adjustment = match tcx.fn_trait_kind_from_lang_item(trait_) {
  50                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
  51                 Some(ty::ClosureKind::FnMut | ty::ClosureKind::Fn) => Adjustment::Deref,
  52                 None => bug!("fn pointer {:?} is not an fn", ty),
  53             };
  54             // HACK: we need the "real" argument types for the MIR,
  55             // but because our substs are (Self, Args), where Args
  56             // is a tuple, we must include the *concrete* argument
  57             // types in the MIR. They will be substituted again with
  58             // the param-substs, but because they are concrete, this
  59             // will not do any harm.
  60             let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
  61             let arg_tys = sig.inputs();
  62
  63             build_call_shim(tcx, instance, Some(adjustment), CallKind::Indirect, Some(arg_tys))
  64         }
  65         // We are generating a call back to our def-id, which the
  66         // codegen backend knows to turn to an actual call, be it
  67         // a virtual call, or a direct call to a function for which
  68         // indirect calls must be codegen'd differently than direct ones
  69         // (such as `#[track_caller]`).
  70         ty::InstanceDef::ReifyShim(def_id) => {
  71             build_call_shim(tcx, instance, None, CallKind::Direct(def_id), None)
  72         }
  73         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
  74             let fn_mut = tcx.require_lang_item(FnMutTraitLangItem, None);
  75             let call_mut = tcx
  76                 .associated_items(fn_mut)
  77                 .in_definition_order()
  78                 .find(|it| it.kind == ty::AssocKind::Fn)
  79                 .unwrap()
  80                 .def_id;
  81
  82             build_call_shim(
  83                 tcx,
  84                 instance,
  85                 Some(Adjustment::RefMut),
  86                 CallKind::Direct(call_mut),
  87                 None,
  88             )
  89         }
  90         ty::InstanceDef::DropGlue(def_id, ty) => {
  91             // FIXME(eddyb) support generating shims for a "shallow type",
  92             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
  93             // `Foo<Bar>` or `[String]` etc.
  94             assert!(!ty.needs_subst());
  95
  96             build_drop_shim(tcx, def_id, ty)
  97         }
  98         ty::InstanceDef::CloneShim(def_id, ty) => {
  99             // FIXME(eddyb) support generating shims for a "shallow type",
 100             // e.g. `Foo<_>` or `[_]` instead of requiring a fully monomorphic
 101             // `Foo<Bar>` or `[String]` etc.
 102             assert!(!ty.needs_subst());
 103
 104             build_clone_shim(tcx, def_id, ty)
 105         }
 106         ty::InstanceDef::Virtual(..) => {
 107             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
 108         }
 109         ty::InstanceDef::Intrinsic(_) => {
 110             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
 111         }
 112         ty::InstanceDef::InjectedCode(_) => {
 113             bug!("creating shims from injected code ({:?}) is unsupported", instance)
 114         }
 115     };
 116     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 117
 118     run_passes(
 119         tcx,
 120         &mut result,
 121         instance,
 122         None,
 123         MirPhase::Const,
 124         &[&[
 125             &add_moves_for_packed_drops::AddMovesForPackedDrops,
 126             &no_landing_pads::NoLandingPads::new(tcx),
 127             &remove_noop_landing_pads::RemoveNoopLandingPads,
 128             &simplify::SimplifyCfg::new("make_shim"),
 129             &add_call_guards::CriticalCallEdges,
 130         ]],
 131     );
 132
 133     debug!("make_shim({:?}) = {:?}", instance, result);
 134
 135     result
 136 }
 137
 138 #[derive(Copy, Clone, Debug, PartialEq)]
 139 enum Adjustment {
 140     Identity,
 141     Deref,
 142     DerefMove,
 143     RefMut,
 144 }
 145
 146 #[derive(Copy, Clone, Debug, PartialEq)]
 147 enum CallKind {
 148     Indirect,
 149     Direct(DefId),
 150 }
 151
 152 fn local_decls_for_sig<'tcx>(
 153     sig: &ty::FnSig<'tcx>,
 154     span: Span,
 155 ) -> IndexVec<Local, LocalDecl<'tcx>> {
 156     iter::once(LocalDecl::new(sig.output(), span))
 157         .chain(sig.inputs().iter().map(|ity| LocalDecl::new(ity, span).immutable()))
 158         .collect()
 159 }
 160
 161 fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>) -> Body<'tcx> {
 162     debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
 163
 164     // Check if this is a generator, if so, return the drop glue for it
 165     if let Some(&ty::TyS { kind: ty::Generator(gen_def_id, substs, _), .. }) = ty {
 166         let body = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
 167         return body.subst(tcx, substs);
 168     }
 169
 170     let substs = if let Some(ty) = ty {
 171         tcx.intern_substs(&[ty.into()])
 172     } else {
 173         InternalSubsts::identity_for_item(tcx, def_id)
 174     };
 175     let sig = tcx.fn_sig(def_id).subst(tcx, substs);
 176     let sig = tcx.erase_late_bound_regions(&sig);
 177     let span = tcx.def_span(def_id);
 178
 179     let source_info = SourceInfo::outermost(span);
 180
 181     let return_block = BasicBlock::new(1);
 182     let mut blocks = IndexVec::with_capacity(2);
 183     let block = |blocks: &mut IndexVec<_, _>, kind| {
 184         blocks.push(BasicBlockData {
 185             statements: vec![],
 186             terminator: Some(Terminator { source_info, kind }),
 187             is_cleanup: false,
 188         })
 189     };
 190     block(&mut blocks, TerminatorKind::Goto { target: return_block });
 191     block(&mut blocks, TerminatorKind::Return);
 192
 193     let mut body = new_body(blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 194
 195     if let Some(..) = ty {
 196         // The first argument (index 0), but add 1 for the return value.
 197         let dropee_ptr = Place::from(Local::new(1 + 0));
 198         if tcx.sess.opts.debugging_opts.mir_emit_retag {
 199             // Function arguments should be retagged, and we make this one raw.
 200             body.basic_blocks_mut()[START_BLOCK].statements.insert(
 201                 0,
 202                 Statement {
 203                     source_info,
 204                     kind: StatementKind::Retag(RetagKind::Raw, box (dropee_ptr)),
 205                 },
 206             );
 207         }
 208         let patch = {
 209             let param_env = tcx.param_env(def_id).with_reveal_all();
 210             let mut elaborator =
 211                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
 212             let dropee = tcx.mk_place_deref(dropee_ptr);
 213             let resume_block = elaborator.patch.resume_block();
 214             elaborate_drops::elaborate_drop(
 215                 &mut elaborator,
 216                 source_info,
 217                 dropee,
 218                 (),
 219                 return_block,
 220                 elaborate_drops::Unwind::To(resume_block),
 221                 START_BLOCK,
 222             );
 223             elaborator.patch
 224         };
 225         patch.apply(&mut body);
 226     }
 227
 228     body
 229 }
 230
 231 fn new_body<'tcx>(
 232     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 233     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 234     arg_count: usize,
 235     span: Span,
 236 ) -> Body<'tcx> {
 237     Body::new(
 238         basic_blocks,
 239         IndexVec::from_elem_n(
 240             SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
 241             1,
 242         ),
 243         local_decls,
 244         IndexVec::new(),
 245         arg_count,
 246         vec![],
 247         span,
 248         vec![],
 249         None,
 250     )
 251 }
 252
 253 pub struct DropShimElaborator<'a, 'tcx> {
 254     pub body: &'a Body<'tcx>,
 255     pub patch: MirPatch<'tcx>,
 256     pub tcx: TyCtxt<'tcx>,
 257     pub param_env: ty::ParamEnv<'tcx>,
 258 }
 259
 260 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
 261     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
 262         Ok(())
 263     }
 264 }
 265
 266 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 267     type Path = ();
 268
 269     fn patch(&mut self) -> &mut MirPatch<'tcx> {
 270         &mut self.patch
 271     }
 272     fn body(&self) -> &'a Body<'tcx> {
 273         self.body
 274     }
 275     fn tcx(&self) -> TyCtxt<'tcx> {
 276         self.tcx
 277     }
 278     fn param_env(&self) -> ty::ParamEnv<'tcx> {
 279         self.param_env
 280     }
 281
 282     fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
 283         match mode {
 284             DropFlagMode::Shallow => {
 285                 // Drops for the contained fields are "shallow" and "static" - they will simply call
 286                 // the field's own drop glue.
 287                 DropStyle::Static
 288             }
 289             DropFlagMode::Deep => {
 290                 // The top-level drop is "deep" and "open" - it will be elaborated to a drop ladder
 291                 // dropping each field contained in the value.
 292                 DropStyle::Open
 293             }
 294         }
 295     }
 296
 297     fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
 298         None
 299     }
 300
 301     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 302
 303     fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
 304         None
 305     }
 306     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
 307         None
 308     }
 309     fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
 310         Some(())
 311     }
 312     fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
 313         None
 314     }
 315 }
 316
 317 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 318 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'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(_, substs) => {
 336             builder.tuple_like_shim(dest, src, substs.as_closure().upvar_tys())
 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     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::outermost(self.span)
 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         let mut local = LocalDecl::new(ty, span);
 420         if mutability == Mutability::Not {
 421             local = local.immutable();
 422         }
 423         Place::from(self.local_decls.push(local))
 424     }
 425
 426     fn make_clone_call(
 427         &mut self,
 428         dest: Place<'tcx>,
 429         src: Place<'tcx>,
 430         ty: Ty<'tcx>,
 431         next: BasicBlock,
 432         cleanup: BasicBlock,
 433     ) {
 434         let tcx = self.tcx;
 435
 436         let substs = tcx.mk_substs_trait(ty, &[]);
 437
 438         // `func == Clone::clone(&ty) -> ty`
 439         let func_ty = tcx.mk_fn_def(self.def_id, substs);
 440         let func = Operand::Constant(box Constant {
 441             span: self.span,
 442             user_ty: None,
 443             literal: ty::Const::zero_sized(tcx, func_ty),
 444         });
 445
 446         let ref_loc = self.make_place(
 447             Mutability::Not,
 448             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }),
 449         );
 450
 451         // `let ref_loc: &ty = &src;`
 452         let statement = self.make_statement(StatementKind::Assign(box (
 453             ref_loc,
 454             Rvalue::Ref(tcx.lifetimes.re_erased, BorrowKind::Shared, src),
 455         )));
 456
 457         // `let loc = Clone::clone(ref_loc);`
 458         self.block(
 459             vec![statement],
 460             TerminatorKind::Call {
 461                 func,
 462                 args: vec![Operand::Move(ref_loc)],
 463                 destination: Some((dest, next)),
 464                 cleanup: Some(cleanup),
 465                 from_hir_call: true,
 466                 fn_span: self.span,
 467             },
 468             false,
 469         );
 470     }
 471
 472     fn loop_header(
 473         &mut self,
 474         beg: Place<'tcx>,
 475         end: Place<'tcx>,
 476         loop_body: BasicBlock,
 477         loop_end: BasicBlock,
 478         is_cleanup: bool,
 479     ) {
 480         let tcx = self.tcx;
 481
 482         let cond = self.make_place(Mutability::Mut, tcx.types.bool);
 483         let compute_cond = self.make_statement(StatementKind::Assign(box (
 484             cond,
 485             Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg)),
 486         )));
 487
 488         // `if end != beg { goto loop_body; } else { goto loop_end; }`
 489         self.block(
 490             vec![compute_cond],
 491             TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
 492             is_cleanup,
 493         );
 494     }
 495
 496     fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
 497         box Constant {
 498             span: self.span,
 499             user_ty: None,
 500             literal: ty::Const::from_usize(self.tcx, value),
 501         }
 502     }
 503
 504     fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
 505         let tcx = self.tcx;
 506         let span = self.span;
 507
 508         let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
 509         let end = self.make_place(Mutability::Not, tcx.types.usize);
 510
 511         // BB #0
 512         // `let mut beg = 0;`
 513         // `let end = len;`
 514         // `goto #1;`
 515         let inits = vec![
 516             self.make_statement(StatementKind::Assign(box (
 517                 Place::from(beg),
 518                 Rvalue::Use(Operand::Constant(self.make_usize(0))),
 519             ))),
 520             self.make_statement(StatementKind::Assign(box (
 521                 end,
 522                 Rvalue::Use(Operand::Constant(self.make_usize(len))),
 523             ))),
 524         ];
 525         self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 526
 527         // BB #1: loop {
 528         //     BB #2;
 529         //     BB #3;
 530         // }
 531         // BB #4;
 532         self.loop_header(Place::from(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
 533
 534         // BB #2
 535         // `dest[i] = Clone::clone(src[beg])`;
 536         // Goto #3 if ok, #5 if unwinding happens.
 537         let dest_field = self.tcx.mk_place_index(dest, beg);
 538         let src_field = self.tcx.mk_place_index(src, beg);
 539         self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3), BasicBlock::new(5));
 540
 541         // BB #3
 542         // `beg = beg + 1;`
 543         // `goto #1`;
 544         let statements = vec![self.make_statement(StatementKind::Assign(box (
 545             Place::from(beg),
 546             Rvalue::BinaryOp(
 547                 BinOp::Add,
 548                 Operand::Copy(Place::from(beg)),
 549                 Operand::Constant(self.make_usize(1)),
 550             ),
 551         )))];
 552         self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
 553
 554         // BB #4
 555         // `return dest;`
 556         self.block(vec![], TerminatorKind::Return, false);
 557
 558         // BB #5 (cleanup)
 559         // `let end = beg;`
 560         // `let mut beg = 0;`
 561         // goto #6;
 562         let end = beg;
 563         let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
 564         let init = self.make_statement(StatementKind::Assign(box (
 565             Place::from(beg),
 566             Rvalue::Use(Operand::Constant(self.make_usize(0))),
 567         )));
 568         self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 569
 570         // BB #6 (cleanup): loop {
 571         //     BB #7;
 572         //     BB #8;
 573         // }
 574         // BB #9;
 575         self.loop_header(
 576             Place::from(beg),
 577             Place::from(end),
 578             BasicBlock::new(7),
 579             BasicBlock::new(9),
 580             true,
 581         );
 582
 583         // BB #7 (cleanup)
 584         // `drop(dest[beg])`;
 585         self.block(
 586             vec![],
 587             TerminatorKind::Drop {
 588                 location: self.tcx.mk_place_index(dest, beg),
 589                 target: BasicBlock::new(8),
 590                 unwind: None,
 591             },
 592             true,
 593         );
 594
 595         // BB #8 (cleanup)
 596         // `beg = beg + 1;`
 597         // `goto #6;`
 598         let statement = self.make_statement(StatementKind::Assign(box (
 599             Place::from(beg),
 600             Rvalue::BinaryOp(
 601                 BinOp::Add,
 602                 Operand::Copy(Place::from(beg)),
 603                 Operand::Constant(self.make_usize(1)),
 604             ),
 605         )));
 606         self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
 607
 608         // BB #9 (resume)
 609         self.block(vec![], TerminatorKind::Resume, true);
 610     }
 611
 612     fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>, src: Place<'tcx>, tys: I)
 613     where
 614         I: Iterator<Item = Ty<'tcx>>,
 615     {
 616         let mut previous_field = None;
 617         for (i, ity) in tys.enumerate() {
 618             let field = Field::new(i);
 619             let src_field = self.tcx.mk_place_field(src, field, ity);
 620
 621             let dest_field = self.tcx.mk_place_field(dest, field, ity);
 622
 623             // #(2i + 1) is the cleanup block for the previous clone operation
 624             let cleanup_block = self.block_index_offset(1);
 625             // #(2i + 2) is the next cloning block
 626             // (or the Return terminator if this is the last block)
 627             let next_block = self.block_index_offset(2);
 628
 629             // BB #(2i)
 630             // `dest.i = Clone::clone(&src.i);`
 631             // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
 632             self.make_clone_call(dest_field, src_field, ity, next_block, cleanup_block);
 633
 634             // BB #(2i + 1) (cleanup)
 635             if let Some((previous_field, previous_cleanup)) = previous_field.take() {
 636                 // Drop previous field and goto previous cleanup block.
 637                 self.block(
 638                     vec![],
 639                     TerminatorKind::Drop {
 640                         location: previous_field,
 641                         target: previous_cleanup,
 642                         unwind: None,
 643                     },
 644                     true,
 645                 );
 646             } else {
 647                 // Nothing to drop, just resume.
 648                 self.block(vec![], TerminatorKind::Resume, true);
 649             }
 650
 651             previous_field = Some((dest_field, cleanup_block));
 652         }
 653
 654         self.block(vec![], TerminatorKind::Return, false);
 655     }
 656 }
 657
 658 /// Builds a "call" shim for `instance`. The shim calls the
 659 /// function specified by `call_kind`, first adjusting its first
 660 /// argument according to `rcvr_adjustment`.
 661 ///
 662 /// If `untuple_args` is a vec of types, the second argument of the
 663 /// function will be untupled as these types.
 664 fn build_call_shim<'tcx>(
 665     tcx: TyCtxt<'tcx>,
 666     instance: ty::InstanceDef<'tcx>,
 667     rcvr_adjustment: Option<Adjustment>,
 668     call_kind: CallKind,
 669     untuple_args: Option<&[Ty<'tcx>]>,
 670 ) -> Body<'tcx> {
 671     debug!(
 672         "build_call_shim(instance={:?}, rcvr_adjustment={:?}, \
 673             call_kind={:?}, untuple_args={:?})",
 674         instance, rcvr_adjustment, call_kind, untuple_args
 675     );
 676
 677     let def_id = instance.def_id();
 678     let sig = tcx.fn_sig(def_id);
 679     let mut sig = tcx.erase_late_bound_regions(&sig);
 680
 681     // FIXME(eddyb) avoid having this snippet both here and in
 682     // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
 683     if let ty::InstanceDef::VtableShim(..) = instance {
 684         // Modify fn(self, ...) to fn(self: *mut Self, ...)
 685         let mut inputs_and_output = sig.inputs_and_output.to_vec();
 686         let self_arg = &mut inputs_and_output[0];
 687         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
 688         *self_arg = tcx.mk_mut_ptr(*self_arg);
 689         sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
 690     }
 691
 692     let span = tcx.def_span(def_id);
 693
 694     debug!("build_call_shim: sig={:?}", sig);
 695
 696     let mut local_decls = local_decls_for_sig(&sig, span);
 697     let source_info = SourceInfo::outermost(span);
 698
 699     let rcvr_place = || {
 700         assert!(rcvr_adjustment.is_some());
 701         Place::from(Local::new(1 + 0))
 702     };
 703     let mut statements = vec![];
 704
 705     let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
 706         Adjustment::Identity => Operand::Move(rcvr_place()),
 707         Adjustment::Deref => Operand::Move(tcx.mk_place_deref(rcvr_place())), // Can't copy `&mut`
 708         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_place())),
 709         Adjustment::RefMut => {
 710             // let rcvr = &mut rcvr;
 711             let ref_rcvr = local_decls.push(
 712                 LocalDecl::new(
 713                     tcx.mk_ref(
 714                         tcx.lifetimes.re_erased,
 715                         ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
 716                     ),
 717                     span,
 718                 )
 719                 .immutable(),
 720             );
 721             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
 722             statements.push(Statement {
 723                 source_info,
 724                 kind: StatementKind::Assign(box (
 725                     Place::from(ref_rcvr),
 726                     Rvalue::Ref(tcx.lifetimes.re_erased, borrow_kind, rcvr_place()),
 727                 )),
 728             });
 729             Operand::Move(Place::from(ref_rcvr))
 730         }
 731     });
 732
 733     let (callee, mut args) = match call_kind {
 734         CallKind::Indirect => (rcvr.unwrap(), vec![]),
 735         CallKind::Direct(def_id) => {
 736             let ty = tcx.type_of(def_id);
 737             (
 738                 Operand::Constant(box Constant {
 739                     span,
 740                     user_ty: None,
 741                     literal: ty::Const::zero_sized(tcx, ty),
 742                 }),
 743                 rcvr.into_iter().collect::<Vec<_>>(),
 744             )
 745         }
 746     };
 747
 748     let mut arg_range = 0..sig.inputs().len();
 749
 750     // Take the `self` ("receiver") argument out of the range (it's adjusted above).
 751     if rcvr_adjustment.is_some() {
 752         arg_range.start += 1;
 753     }
 754
 755     // Take the last argument, if we need to untuple it (handled below).
 756     if untuple_args.is_some() {
 757         arg_range.end -= 1;
 758     }
 759
 760     // Pass all of the non-special arguments directly.
 761     args.extend(arg_range.map(|i| Operand::Move(Place::from(Local::new(1 + i)))));
 762
 763     // Untuple the last argument, if we have to.
 764     if let Some(untuple_args) = untuple_args {
 765         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
 766         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
 767             Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
 768         }));
 769     }
 770
 771     let n_blocks = if let Some(Adjustment::RefMut) = rcvr_adjustment { 5 } else { 2 };
 772     let mut blocks = IndexVec::with_capacity(n_blocks);
 773     let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
 774         blocks.push(BasicBlockData {
 775             statements,
 776             terminator: Some(Terminator { source_info, kind }),
 777             is_cleanup,
 778         })
 779     };
 780
 781     // BB #0
 782     block(
 783         &mut blocks,
 784         statements,
 785         TerminatorKind::Call {
 786             func: callee,
 787             args,
 788             destination: Some((Place::return_place(), BasicBlock::new(1))),
 789             cleanup: if let Some(Adjustment::RefMut) = rcvr_adjustment {
 790                 Some(BasicBlock::new(3))
 791             } else {
 792                 None
 793             },
 794             from_hir_call: true,
 795             fn_span: span,
 796         },
 797         false,
 798     );
 799
 800     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 801         // BB #1 - drop for Self
 802         block(
 803             &mut blocks,
 804             vec![],
 805             TerminatorKind::Drop {
 806                 location: rcvr_place(),
 807                 target: BasicBlock::new(2),
 808                 unwind: None,
 809             },
 810             false,
 811         );
 812     }
 813     // BB #1/#2 - return
 814     block(&mut blocks, vec![], TerminatorKind::Return, false);
 815     if let Some(Adjustment::RefMut) = rcvr_adjustment {
 816         // BB #3 - drop if closure panics
 817         block(
 818             &mut blocks,
 819             vec![],
 820             TerminatorKind::Drop {
 821                 location: rcvr_place(),
 822                 target: BasicBlock::new(4),
 823                 unwind: None,
 824             },
 825             true,
 826         );
 827
 828         // BB #4 - resume
 829         block(&mut blocks, vec![], TerminatorKind::Resume, true);
 830     }
 831
 832     let mut body = new_body(blocks, local_decls, sig.inputs().len(), span);
 833
 834     if let Abi::RustCall = sig.abi {
 835         body.spread_arg = Some(Local::new(sig.inputs().len()));
 836     }
 837
 838     body
 839 }
 840
 841 pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
 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::outermost(span);
 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     body
 909 }