compiler/rustc_codegen_cranelift/src/abi/mod.rs

   1 //! Handling of everything related to the calling convention. Also fills `fx.local_map`.
   2
   3 mod comments;
   4 mod pass_mode;
   5 mod returning;
   6
   7 use cranelift_module::ModuleError;
   8 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
   9 use rustc_middle::ty::layout::FnAbiOf;
  10 use rustc_target::abi::call::{Conv, FnAbi};
  11 use rustc_target::spec::abi::Abi;
  12
  13 use cranelift_codegen::ir::{AbiParam, SigRef};
  14
  15 use self::pass_mode::*;
  16 use crate::prelude::*;
  17
  18 pub(crate) use self::returning::codegen_return;
  19
  20 fn clif_sig_from_fn_abi<'tcx>(
  21     tcx: TyCtxt<'tcx>,
  22     default_call_conv: CallConv,
  23     fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
  24 ) -> Signature {
  25     let call_conv = match fn_abi.conv {
  26         Conv::Rust | Conv::C => default_call_conv,
  27         Conv::RustCold => CallConv::Cold,
  28         Conv::X86_64SysV => CallConv::SystemV,
  29         Conv::X86_64Win64 => CallConv::WindowsFastcall,
  30         Conv::ArmAapcs
  31         | Conv::CCmseNonSecureCall
  32         | Conv::Msp430Intr
  33         | Conv::PtxKernel
  34         | Conv::X86Fastcall
  35         | Conv::X86Intr
  36         | Conv::X86Stdcall
  37         | Conv::X86ThisCall
  38         | Conv::X86VectorCall
  39         | Conv::AmdGpuKernel
  40         | Conv::AvrInterrupt
  41         | Conv::AvrNonBlockingInterrupt => todo!("{:?}", fn_abi.conv),
  42     };
  43     let inputs = fn_abi.args.iter().map(|arg_abi| arg_abi.get_abi_param(tcx).into_iter()).flatten();
  44
  45     let (return_ptr, returns) = fn_abi.ret.get_abi_return(tcx);
  46     // Sometimes the first param is an pointer to the place where the return value needs to be stored.
  47     let params: Vec<_> = return_ptr.into_iter().chain(inputs).collect();
  48
  49     Signature { params, returns, call_conv }
  50 }
  51
  52 pub(crate) fn get_function_sig<'tcx>(
  53     tcx: TyCtxt<'tcx>,
  54     triple: &target_lexicon::Triple,
  55     inst: Instance<'tcx>,
  56 ) -> Signature {
  57     assert!(!inst.substs.needs_infer());
  58     clif_sig_from_fn_abi(
  59         tcx,
  60         CallConv::triple_default(triple),
  61         &RevealAllLayoutCx(tcx).fn_abi_of_instance(inst, ty::List::empty()),
  62     )
  63 }
  64
  65 /// Instance must be monomorphized
  66 pub(crate) fn import_function<'tcx>(
  67     tcx: TyCtxt<'tcx>,
  68     module: &mut dyn Module,
  69     inst: Instance<'tcx>,
  70 ) -> FuncId {
  71     let name = tcx.symbol_name(inst).name;
  72     let sig = get_function_sig(tcx, module.isa().triple(), inst);
  73     match module.declare_function(name, Linkage::Import, &sig) {
  74         Ok(func_id) => func_id,
  75         Err(ModuleError::IncompatibleDeclaration(_)) => tcx.sess.fatal(&format!(
  76             "attempt to declare `{name}` as function, but it was already declared as static"
  77         )),
  78         Err(ModuleError::IncompatibleSignature(_, prev_sig, new_sig)) => tcx.sess.fatal(&format!(
  79             "attempt to declare `{name}` with signature {new_sig:?}, \
  80              but it was already declared with signature {prev_sig:?}"
  81         )),
  82         Err(err) => Err::<_, _>(err).unwrap(),
  83     }
  84 }
  85
  86 impl<'tcx> FunctionCx<'_, '_, 'tcx> {
  87     /// Instance must be monomorphized
  88     pub(crate) fn get_function_ref(&mut self, inst: Instance<'tcx>) -> FuncRef {
  89         let func_id = import_function(self.tcx, self.module, inst);
  90         let func_ref = self.module.declare_func_in_func(func_id, &mut self.bcx.func);
  91
  92         if self.clif_comments.enabled() {
  93             self.add_comment(func_ref, format!("{:?}", inst));
  94         }
  95
  96         func_ref
  97     }
  98
  99     pub(crate) fn lib_call(
 100         &mut self,
 101         name: &str,
 102         params: Vec<AbiParam>,
 103         returns: Vec<AbiParam>,
 104         args: &[Value],
 105     ) -> &[Value] {
 106         let sig = Signature { params, returns, call_conv: self.target_config.default_call_conv };
 107         let func_id = self.module.declare_function(name, Linkage::Import, &sig).unwrap();
 108         let func_ref = self.module.declare_func_in_func(func_id, &mut self.bcx.func);
 109         if self.clif_comments.enabled() {
 110             self.add_comment(func_ref, format!("{:?}", name));
 111         }
 112         let call_inst = self.bcx.ins().call(func_ref, args);
 113         if self.clif_comments.enabled() {
 114             self.add_comment(call_inst, format!("easy_call {}", name));
 115         }
 116         let results = self.bcx.inst_results(call_inst);
 117         assert!(results.len() <= 2, "{}", results.len());
 118         results
 119     }
 120
 121     pub(crate) fn easy_call(
 122         &mut self,
 123         name: &str,
 124         args: &[CValue<'tcx>],
 125         return_ty: Ty<'tcx>,
 126     ) -> CValue<'tcx> {
 127         let (input_tys, args): (Vec<_>, Vec<_>) = args
 128             .iter()
 129             .map(|arg| {
 130                 (AbiParam::new(self.clif_type(arg.layout().ty).unwrap()), arg.load_scalar(self))
 131             })
 132             .unzip();
 133         let return_layout = self.layout_of(return_ty);
 134         let return_tys = if let ty::Tuple(tup) = return_ty.kind() {
 135             tup.iter().map(|ty| AbiParam::new(self.clif_type(ty).unwrap())).collect()
 136         } else {
 137             vec![AbiParam::new(self.clif_type(return_ty).unwrap())]
 138         };
 139         let ret_vals = self.lib_call(name, input_tys, return_tys, &args);
 140         match *ret_vals {
 141             [] => CValue::by_ref(
 142                 Pointer::const_addr(self, i64::from(self.pointer_type.bytes())),
 143                 return_layout,
 144             ),
 145             [val] => CValue::by_val(val, return_layout),
 146             [val, extra] => CValue::by_val_pair(val, extra, return_layout),
 147             _ => unreachable!(),
 148         }
 149     }
 150 }
 151
 152 /// Make a [`CPlace`] capable of holding value of the specified type.
 153 fn make_local_place<'tcx>(
 154     fx: &mut FunctionCx<'_, '_, 'tcx>,
 155     local: Local,
 156     layout: TyAndLayout<'tcx>,
 157     is_ssa: bool,
 158 ) -> CPlace<'tcx> {
 159     let place = if is_ssa {
 160         if let rustc_target::abi::Abi::ScalarPair(_, _) = layout.abi {
 161             CPlace::new_var_pair(fx, local, layout)
 162         } else {
 163             CPlace::new_var(fx, local, layout)
 164         }
 165     } else {
 166         CPlace::new_stack_slot(fx, layout)
 167     };
 168
 169     self::comments::add_local_place_comments(fx, place, local);
 170
 171     place
 172 }
 173
 174 pub(crate) fn codegen_fn_prelude<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, start_block: Block) {
 175     fx.bcx.append_block_params_for_function_params(start_block);
 176
 177     fx.bcx.switch_to_block(start_block);
 178     fx.bcx.ins().nop();
 179
 180     let ssa_analyzed = crate::analyze::analyze(fx);
 181
 182     self::comments::add_args_header_comment(fx);
 183
 184     let mut block_params_iter = fx.bcx.func.dfg.block_params(start_block).to_vec().into_iter();
 185     let ret_place =
 186         self::returning::codegen_return_param(fx, &ssa_analyzed, &mut block_params_iter);
 187     assert_eq!(fx.local_map.push(ret_place), RETURN_PLACE);
 188
 189     // None means pass_mode == NoPass
 190     enum ArgKind<'tcx> {
 191         Normal(Option<CValue<'tcx>>),
 192         Spread(Vec<Option<CValue<'tcx>>>),
 193     }
 194
 195     let fn_abi = fx.fn_abi.take().unwrap();
 196
 197     // FIXME implement variadics in cranelift
 198     if fn_abi.c_variadic {
 199         fx.tcx.sess.span_fatal(
 200             fx.mir.span,
 201             "Defining variadic functions is not yet supported by Cranelift",
 202         );
 203     }
 204
 205     let mut arg_abis_iter = fn_abi.args.iter();
 206
 207     let func_params = fx
 208         .mir
 209         .args_iter()
 210         .map(|local| {
 211             let arg_ty = fx.monomorphize(fx.mir.local_decls[local].ty);
 212
 213             // Adapted from https://github.com/rust-lang/rust/blob/145155dc96757002c7b2e9de8489416e2fdbbd57/src/librustc_codegen_llvm/mir/mod.rs#L442-L482
 214             if Some(local) == fx.mir.spread_arg {
 215                 // This argument (e.g. the last argument in the "rust-call" ABI)
 216                 // is a tuple that was spread at the ABI level and now we have
 217                 // to reconstruct it into a tuple local variable, from multiple
 218                 // individual function arguments.
 219
 220                 let tupled_arg_tys = match arg_ty.kind() {
 221                     ty::Tuple(ref tys) => tys,
 222                     _ => bug!("spread argument isn't a tuple?! but {:?}", arg_ty),
 223                 };
 224
 225                 let mut params = Vec::new();
 226                 for (i, _arg_ty) in tupled_arg_tys.iter().enumerate() {
 227                     let arg_abi = arg_abis_iter.next().unwrap();
 228                     let param =
 229                         cvalue_for_param(fx, Some(local), Some(i), arg_abi, &mut block_params_iter);
 230                     params.push(param);
 231                 }
 232
 233                 (local, ArgKind::Spread(params), arg_ty)
 234             } else {
 235                 let arg_abi = arg_abis_iter.next().unwrap();
 236                 let param =
 237                     cvalue_for_param(fx, Some(local), None, arg_abi, &mut block_params_iter);
 238                 (local, ArgKind::Normal(param), arg_ty)
 239             }
 240         })
 241         .collect::<Vec<(Local, ArgKind<'tcx>, Ty<'tcx>)>>();
 242
 243     assert!(fx.caller_location.is_none());
 244     if fx.instance.def.requires_caller_location(fx.tcx) {
 245         // Store caller location for `#[track_caller]`.
 246         let arg_abi = arg_abis_iter.next().unwrap();
 247         fx.caller_location =
 248             Some(cvalue_for_param(fx, None, None, arg_abi, &mut block_params_iter).unwrap());
 249     }
 250
 251     assert!(arg_abis_iter.next().is_none(), "ArgAbi left behind");
 252     fx.fn_abi = Some(fn_abi);
 253     assert!(block_params_iter.next().is_none(), "arg_value left behind");
 254
 255     self::comments::add_locals_header_comment(fx);
 256
 257     for (local, arg_kind, ty) in func_params {
 258         let layout = fx.layout_of(ty);
 259
 260         let is_ssa = ssa_analyzed[local] == crate::analyze::SsaKind::Ssa;
 261
 262         // While this is normally an optimization to prevent an unnecessary copy when an argument is
 263         // not mutated by the current function, this is necessary to support unsized arguments.
 264         if let ArgKind::Normal(Some(val)) = arg_kind {
 265             if let Some((addr, meta)) = val.try_to_ptr() {
 266                 // Ownership of the value at the backing storage for an argument is passed to the
 267                 // callee per the ABI, so it is fine to borrow the backing storage of this argument
 268                 // to prevent a copy.
 269
 270                 let place = if let Some(meta) = meta {
 271                     CPlace::for_ptr_with_extra(addr, meta, val.layout())
 272                 } else {
 273                     CPlace::for_ptr(addr, val.layout())
 274                 };
 275
 276                 self::comments::add_local_place_comments(fx, place, local);
 277
 278                 assert_eq!(fx.local_map.push(place), local);
 279                 continue;
 280             }
 281         }
 282
 283         let place = make_local_place(fx, local, layout, is_ssa);
 284         assert_eq!(fx.local_map.push(place), local);
 285
 286         match arg_kind {
 287             ArgKind::Normal(param) => {
 288                 if let Some(param) = param {
 289                     place.write_cvalue(fx, param);
 290                 }
 291             }
 292             ArgKind::Spread(params) => {
 293                 for (i, param) in params.into_iter().enumerate() {
 294                     if let Some(param) = param {
 295                         place.place_field(fx, mir::Field::new(i)).write_cvalue(fx, param);
 296                     }
 297                 }
 298             }
 299         }
 300     }
 301
 302     for local in fx.mir.vars_and_temps_iter() {
 303         let ty = fx.monomorphize(fx.mir.local_decls[local].ty);
 304         let layout = fx.layout_of(ty);
 305
 306         let is_ssa = ssa_analyzed[local] == crate::analyze::SsaKind::Ssa;
 307
 308         let place = make_local_place(fx, local, layout, is_ssa);
 309         assert_eq!(fx.local_map.push(place), local);
 310     }
 311
 312     fx.bcx.ins().jump(*fx.block_map.get(START_BLOCK).unwrap(), &[]);
 313 }
 314
 315 struct CallArgument<'tcx> {
 316     value: CValue<'tcx>,
 317     is_owned: bool,
 318 }
 319
 320 // FIXME avoid intermediate `CValue` before calling `adjust_arg_for_abi`
 321 fn codegen_call_argument_operand<'tcx>(
 322     fx: &mut FunctionCx<'_, '_, 'tcx>,
 323     operand: &Operand<'tcx>,
 324 ) -> CallArgument<'tcx> {
 325     CallArgument {
 326         value: codegen_operand(fx, operand),
 327         is_owned: matches!(operand, Operand::Move(_)),
 328     }
 329 }
 330
 331 pub(crate) fn codegen_terminator_call<'tcx>(
 332     fx: &mut FunctionCx<'_, '_, 'tcx>,
 333     source_info: mir::SourceInfo,
 334     func: &Operand<'tcx>,
 335     args: &[Operand<'tcx>],
 336     destination: Place<'tcx>,
 337     target: Option<BasicBlock>,
 338 ) {
 339     let fn_ty = fx.monomorphize(func.ty(fx.mir, fx.tcx));
 340     let fn_sig =
 341         fx.tcx.normalize_erasing_late_bound_regions(ParamEnv::reveal_all(), fn_ty.fn_sig(fx.tcx));
 342
 343     let ret_place = codegen_place(fx, destination);
 344
 345     // Handle special calls like intrinsics and empty drop glue.
 346     let instance = if let ty::FnDef(def_id, substs) = *fn_ty.kind() {
 347         let instance = ty::Instance::resolve(fx.tcx, ty::ParamEnv::reveal_all(), def_id, substs)
 348             .unwrap()
 349             .unwrap()
 350             .polymorphize(fx.tcx);
 351
 352         if fx.tcx.symbol_name(instance).name.starts_with("llvm.") {
 353             crate::intrinsics::codegen_llvm_intrinsic_call(
 354                 fx,
 355                 &fx.tcx.symbol_name(instance).name,
 356                 substs,
 357                 args,
 358                 ret_place,
 359                 target,
 360             );
 361             return;
 362         }
 363
 364         match instance.def {
 365             InstanceDef::Intrinsic(_) => {
 366                 crate::intrinsics::codegen_intrinsic_call(
 367                     fx,
 368                     instance,
 369                     args,
 370                     ret_place,
 371                     target,
 372                     source_info,
 373                 );
 374                 return;
 375             }
 376             InstanceDef::DropGlue(_, None) => {
 377                 // empty drop glue - a nop.
 378                 let dest = target.expect("Non terminating drop_in_place_real???");
 379                 let ret_block = fx.get_block(dest);
 380                 fx.bcx.ins().jump(ret_block, &[]);
 381                 return;
 382             }
 383             _ => Some(instance),
 384         }
 385     } else {
 386         None
 387     };
 388
 389     let extra_args = &args[fn_sig.inputs().len()..];
 390     let extra_args = fx
 391         .tcx
 392         .mk_type_list(extra_args.iter().map(|op_arg| fx.monomorphize(op_arg.ty(fx.mir, fx.tcx))));
 393     let fn_abi = if let Some(instance) = instance {
 394         RevealAllLayoutCx(fx.tcx).fn_abi_of_instance(instance, extra_args)
 395     } else {
 396         RevealAllLayoutCx(fx.tcx).fn_abi_of_fn_ptr(fn_ty.fn_sig(fx.tcx), extra_args)
 397     };
 398
 399     let is_cold = if fn_sig.abi == Abi::RustCold {
 400         true
 401     } else {
 402         instance
 403             .map(|inst| {
 404                 fx.tcx.codegen_fn_attrs(inst.def_id()).flags.contains(CodegenFnAttrFlags::COLD)
 405             })
 406             .unwrap_or(false)
 407     };
 408     if is_cold {
 409         fx.bcx.set_cold_block(fx.bcx.current_block().unwrap());
 410         if let Some(destination_block) = target {
 411             fx.bcx.set_cold_block(fx.get_block(destination_block));
 412         }
 413     }
 414
 415     // Unpack arguments tuple for closures
 416     let mut args = if fn_sig.abi == Abi::RustCall {
 417         assert_eq!(args.len(), 2, "rust-call abi requires two arguments");
 418         let self_arg = codegen_call_argument_operand(fx, &args[0]);
 419         let pack_arg = codegen_call_argument_operand(fx, &args[1]);
 420
 421         let tupled_arguments = match pack_arg.value.layout().ty.kind() {
 422             ty::Tuple(ref tupled_arguments) => tupled_arguments,
 423             _ => bug!("argument to function with \"rust-call\" ABI is not a tuple"),
 424         };
 425
 426         let mut args = Vec::with_capacity(1 + tupled_arguments.len());
 427         args.push(self_arg);
 428         for i in 0..tupled_arguments.len() {
 429             args.push(CallArgument {
 430                 value: pack_arg.value.value_field(fx, mir::Field::new(i)),
 431                 is_owned: pack_arg.is_owned,
 432             });
 433         }
 434         args
 435     } else {
 436         args.iter().map(|arg| codegen_call_argument_operand(fx, arg)).collect::<Vec<_>>()
 437     };
 438
 439     // Pass the caller location for `#[track_caller]`.
 440     if instance.map(|inst| inst.def.requires_caller_location(fx.tcx)).unwrap_or(false) {
 441         let caller_location = fx.get_caller_location(source_info);
 442         args.push(CallArgument { value: caller_location, is_owned: false });
 443     }
 444
 445     let args = args;
 446     assert_eq!(fn_abi.args.len(), args.len());
 447
 448     enum CallTarget {
 449         Direct(FuncRef),
 450         Indirect(SigRef, Value),
 451     }
 452
 453     let (func_ref, first_arg_override) = match instance {
 454         // Trait object call
 455         Some(Instance { def: InstanceDef::Virtual(_, idx), .. }) => {
 456             if fx.clif_comments.enabled() {
 457                 let nop_inst = fx.bcx.ins().nop();
 458                 fx.add_comment(
 459                     nop_inst,
 460                     format!("virtual call; self arg pass mode: {:?}", &fn_abi.args[0]),
 461                 );
 462             }
 463
 464             let (ptr, method) = crate::vtable::get_ptr_and_method_ref(fx, args[0].value, idx);
 465             let sig = clif_sig_from_fn_abi(fx.tcx, fx.target_config.default_call_conv, &fn_abi);
 466             let sig = fx.bcx.import_signature(sig);
 467
 468             (CallTarget::Indirect(sig, method), Some(ptr.get_addr(fx)))
 469         }
 470
 471         // Normal call
 472         Some(instance) => {
 473             let func_ref = fx.get_function_ref(instance);
 474             (CallTarget::Direct(func_ref), None)
 475         }
 476
 477         // Indirect call
 478         None => {
 479             if fx.clif_comments.enabled() {
 480                 let nop_inst = fx.bcx.ins().nop();
 481                 fx.add_comment(nop_inst, "indirect call");
 482             }
 483
 484             let func = codegen_operand(fx, func).load_scalar(fx);
 485             let sig = clif_sig_from_fn_abi(fx.tcx, fx.target_config.default_call_conv, &fn_abi);
 486             let sig = fx.bcx.import_signature(sig);
 487
 488             (CallTarget::Indirect(sig, func), None)
 489         }
 490     };
 491
 492     self::returning::codegen_with_call_return_arg(fx, &fn_abi.ret, ret_place, |fx, return_ptr| {
 493         let call_args = return_ptr
 494             .into_iter()
 495             .chain(first_arg_override.into_iter())
 496             .chain(
 497                 args.into_iter()
 498                     .enumerate()
 499                     .skip(if first_arg_override.is_some() { 1 } else { 0 })
 500                     .map(|(i, arg)| {
 501                         adjust_arg_for_abi(fx, arg.value, &fn_abi.args[i], arg.is_owned).into_iter()
 502                     })
 503                     .flatten(),
 504             )
 505             .collect::<Vec<Value>>();
 506
 507         let call_inst = match func_ref {
 508             CallTarget::Direct(func_ref) => fx.bcx.ins().call(func_ref, &call_args),
 509             CallTarget::Indirect(sig, func_ptr) => {
 510                 fx.bcx.ins().call_indirect(sig, func_ptr, &call_args)
 511             }
 512         };
 513
 514         // FIXME find a cleaner way to support varargs
 515         if fn_sig.c_variadic {
 516             if !matches!(fn_sig.abi, Abi::C { .. }) {
 517                 fx.tcx.sess.span_fatal(
 518                     source_info.span,
 519                     &format!("Variadic call for non-C abi {:?}", fn_sig.abi),
 520                 );
 521             }
 522             let sig_ref = fx.bcx.func.dfg.call_signature(call_inst).unwrap();
 523             let abi_params = call_args
 524                 .into_iter()
 525                 .map(|arg| {
 526                     let ty = fx.bcx.func.dfg.value_type(arg);
 527                     if !ty.is_int() {
 528                         // FIXME set %al to upperbound on float args once floats are supported
 529                         fx.tcx.sess.span_fatal(
 530                             source_info.span,
 531                             &format!("Non int ty {:?} for variadic call", ty),
 532                         );
 533                     }
 534                     AbiParam::new(ty)
 535                 })
 536                 .collect::<Vec<AbiParam>>();
 537             fx.bcx.func.dfg.signatures[sig_ref].params = abi_params;
 538         }
 539
 540         call_inst
 541     });
 542
 543     if let Some(dest) = target {
 544         let ret_block = fx.get_block(dest);
 545         fx.bcx.ins().jump(ret_block, &[]);
 546     } else {
 547         fx.bcx.ins().trap(TrapCode::UnreachableCodeReached);
 548     }
 549 }
 550
 551 pub(crate) fn codegen_drop<'tcx>(
 552     fx: &mut FunctionCx<'_, '_, 'tcx>,
 553     source_info: mir::SourceInfo,
 554     drop_place: CPlace<'tcx>,
 555 ) {
 556     let ty = drop_place.layout().ty;
 557     let drop_instance = Instance::resolve_drop_in_place(fx.tcx, ty).polymorphize(fx.tcx);
 558
 559     if let ty::InstanceDef::DropGlue(_, None) = drop_instance.def {
 560         // we don't actually need to drop anything
 561     } else {
 562         match ty.kind() {
 563             ty::Dynamic(_, _, ty::Dyn) => {
 564                 // IN THIS ARM, WE HAVE:
 565                 // ty = *mut (dyn Trait)
 566                 // which is: exists<T> ( *mut T,    Vtable<T: Trait> )
 567                 //                       args[0]    args[1]
 568                 //
 569                 // args = ( Data, Vtable )
 570                 //                  |
 571                 //                  v
 572                 //                /-------\
 573                 //                | ...   |
 574                 //                \-------/
 575                 //
 576                 let (ptr, vtable) = drop_place.to_ptr_maybe_unsized();
 577                 let ptr = ptr.get_addr(fx);
 578                 let drop_fn = crate::vtable::drop_fn_of_obj(fx, vtable.unwrap());
 579
 580                 // FIXME(eddyb) perhaps move some of this logic into
 581                 // `Instance::resolve_drop_in_place`?
 582                 let virtual_drop = Instance {
 583                     def: ty::InstanceDef::Virtual(drop_instance.def_id(), 0),
 584                     substs: drop_instance.substs,
 585                 };
 586                 let fn_abi =
 587                     RevealAllLayoutCx(fx.tcx).fn_abi_of_instance(virtual_drop, ty::List::empty());
 588
 589                 let sig = clif_sig_from_fn_abi(fx.tcx, fx.target_config.default_call_conv, &fn_abi);
 590                 let sig = fx.bcx.import_signature(sig);
 591                 fx.bcx.ins().call_indirect(sig, drop_fn, &[ptr]);
 592             }
 593             ty::Dynamic(_, _, ty::DynStar) => {
 594                 // IN THIS ARM, WE HAVE:
 595                 // ty = *mut (dyn* Trait)
 596                 // which is: *mut exists<T: sizeof(T) == sizeof(usize)> (T, Vtable<T: Trait>)
 597                 //
 598                 // args = [ * ]
 599                 //          |
 600                 //          v
 601                 //      ( Data, Vtable )
 602                 //                |
 603                 //                v
 604                 //              /-------\
 605                 //              | ...   |
 606                 //              \-------/
 607                 //
 608                 //
 609                 // WE CAN CONVERT THIS INTO THE ABOVE LOGIC BY DOING
 610                 //
 611                 // data = &(*args[0]).0    // gives a pointer to Data above (really the same pointer)
 612                 // vtable = (*args[0]).1   // loads the vtable out
 613                 // (data, vtable)          // an equivalent Rust `*mut dyn Trait`
 614                 //
 615                 // SO THEN WE CAN USE THE ABOVE CODE.
 616                 let (data, vtable) = drop_place.to_cvalue(fx).dyn_star_force_data_on_stack(fx);
 617                 let drop_fn = crate::vtable::drop_fn_of_obj(fx, vtable);
 618
 619                 let virtual_drop = Instance {
 620                     def: ty::InstanceDef::Virtual(drop_instance.def_id(), 0),
 621                     substs: drop_instance.substs,
 622                 };
 623                 let fn_abi =
 624                     RevealAllLayoutCx(fx.tcx).fn_abi_of_instance(virtual_drop, ty::List::empty());
 625
 626                 let sig = clif_sig_from_fn_abi(fx.tcx, fx.target_config.default_call_conv, &fn_abi);
 627                 let sig = fx.bcx.import_signature(sig);
 628                 fx.bcx.ins().call_indirect(sig, drop_fn, &[data]);
 629             }
 630             _ => {
 631                 assert!(!matches!(drop_instance.def, InstanceDef::Virtual(_, _)));
 632
 633                 let fn_abi =
 634                     RevealAllLayoutCx(fx.tcx).fn_abi_of_instance(drop_instance, ty::List::empty());
 635
 636                 let arg_value = drop_place.place_ref(
 637                     fx,
 638                     fx.layout_of(fx.tcx.mk_ref(
 639                         fx.tcx.lifetimes.re_erased,
 640                         TypeAndMut { ty, mutbl: crate::rustc_hir::Mutability::Mut },
 641                     )),
 642                 );
 643                 let arg_value = adjust_arg_for_abi(fx, arg_value, &fn_abi.args[0], true);
 644
 645                 let mut call_args: Vec<Value> = arg_value.into_iter().collect::<Vec<_>>();
 646
 647                 if drop_instance.def.requires_caller_location(fx.tcx) {
 648                     // Pass the caller location for `#[track_caller]`.
 649                     let caller_location = fx.get_caller_location(source_info);
 650                     call_args.extend(
 651                         adjust_arg_for_abi(fx, caller_location, &fn_abi.args[1], false).into_iter(),
 652                     );
 653                 }
 654
 655                 let func_ref = fx.get_function_ref(drop_instance);
 656                 fx.bcx.ins().call(func_ref, &call_args);
 657             }
 658         }
 659     }
 660 }