src/interpreter.rs

   1 use arena::TypedArena;
   2 use rustc::infer;
   3 use rustc::middle::const_eval;
   4 use rustc::middle::def_id::DefId;
   5 use rustc::mir::mir_map::MirMap;
   6 use rustc::mir::repr as mir;
   7 use rustc::traits::{self, ProjectionMode};
   8 use rustc::ty::fold::TypeFoldable;
   9 use rustc::ty::subst::{self, Subst, Substs};
  10 use rustc::ty::{self, TyCtxt};
  11 use rustc::util::nodemap::DefIdMap;
  12 use rustc_data_structures::fnv::FnvHashMap;
  13 use std::cell::RefCell;
  14 use std::iter;
  15 use std::ops::Deref;
  16 use std::rc::Rc;
  17 use syntax::ast;
  18 use syntax::attr;
  19 use syntax::codemap::DUMMY_SP;
  20
  21 use error::{EvalError, EvalResult};
  22 use memory::{self, FieldRepr, Memory, Pointer, Repr};
  23 use primval::{self, PrimVal};
  24
  25 const TRACE_EXECUTION: bool = false;
  26
  27 struct Interpreter<'a, 'tcx: 'a, 'arena> {
  28     /// The results of the type checker, from rustc.
  29     tcx: &'a TyCtxt<'tcx>,
  30
  31     /// A mapping from NodeIds to Mir, from rustc. Only contains MIR for crate-local items.
  32     mir_map: &'a MirMap<'tcx>,
  33
  34     /// A local cache from DefIds to Mir for non-crate-local items.
  35     mir_cache: RefCell<DefIdMap<Rc<mir::Mir<'tcx>>>>,
  36
  37     /// An arena allocator for type representations.
  38     repr_arena: &'arena TypedArena<Repr>,
  39
  40     /// A cache for in-memory representations of types.
  41     repr_cache: RefCell<FnvHashMap<ty::Ty<'tcx>, &'arena Repr>>,
  42
  43     /// The virtual memory system.
  44     memory: Memory,
  45
  46     /// The virtual call stack.
  47     stack: Vec<Frame<'a, 'tcx>>,
  48
  49     /// Another stack containing the type substitutions for the current function invocation. It
  50     /// exists separately from `stack` because it must contain the `Substs` for a function while
  51     /// *creating* the `Frame` for that same function.
  52     substs_stack: Vec<&'tcx Substs<'tcx>>,
  53 }
  54
  55 /// A stack frame.
  56 struct Frame<'a, 'tcx: 'a> {
  57     /// The MIR for the function called on this frame.
  58     mir: CachedMir<'a, 'tcx>,
  59
  60     /// The block this frame will execute when a function call returns back to this frame.
  61     next_block: mir::BasicBlock,
  62
  63     /// A pointer for writing the return value of the current call if it's not a diverging call.
  64     return_ptr: Option<Pointer>,
  65
  66     /// The list of locals for the current function, stored in order as
  67     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  68     /// and the temporaries at `self.temp_offset`.
  69     locals: Vec<Pointer>,
  70
  71     /// The offset of the first variable in `self.locals`.
  72     var_offset: usize,
  73
  74     /// The offset of the first temporary in `self.locals`.
  75     temp_offset: usize,
  76 }
  77
  78 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  79 struct Lvalue {
  80     ptr: Pointer,
  81     extra: LvalueExtra,
  82 }
  83
  84 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  85 enum LvalueExtra {
  86     None,
  87     Length(u64),
  88     // Vtable(memory::AllocId),
  89 }
  90
  91 #[derive(Clone)]
  92 enum CachedMir<'mir, 'tcx: 'mir> {
  93     Ref(&'mir mir::Mir<'tcx>),
  94     Owned(Rc<mir::Mir<'tcx>>)
  95 }
  96
  97 /// Represents the action to be taken in the main loop as a result of executing a terminator.
  98 enum TerminatorTarget {
  99     /// Make a local jump to the given block.
 100     Block(mir::BasicBlock),
 101
 102     /// Start executing from the new current frame. (For function calls.)
 103     Call,
 104
 105     /// Stop executing the current frame and resume the previous frame.
 106     Return,
 107 }
 108
 109 impl<'a, 'tcx: 'a, 'arena> Interpreter<'a, 'tcx, 'arena> {
 110     fn new(tcx: &'a TyCtxt<'tcx>, mir_map: &'a MirMap<'tcx>, repr_arena: &'arena TypedArena<Repr>)
 111         -> Self
 112     {
 113         Interpreter {
 114             tcx: tcx,
 115             mir_map: mir_map,
 116             mir_cache: RefCell::new(DefIdMap()),
 117             repr_arena: repr_arena,
 118             repr_cache: RefCell::new(FnvHashMap()),
 119             memory: Memory::new(),
 120             stack: Vec::new(),
 121             substs_stack: Vec::new(),
 122         }
 123     }
 124
 125     fn run(&mut self) -> EvalResult<()> {
 126         use std::fmt::Debug;
 127         fn print_trace<T: Debug>(t: &T, suffix: &'static str, indent: usize) {
 128             if !TRACE_EXECUTION { return; }
 129             for _ in 0..indent { print!("  "); }
 130             println!("{:?}{}", t, suffix);
 131         }
 132
 133         'outer: while !self.stack.is_empty() {
 134             let mut current_block = self.frame().next_block;
 135
 136             loop {
 137                 print_trace(&current_block, ":", self.stack.len());
 138                 let current_mir = self.mir().clone(); // Cloning a reference.
 139                 let block_data = current_mir.basic_block_data(current_block);
 140
 141                 for stmt in &block_data.statements {
 142                     print_trace(stmt, "", self.stack.len() + 1);
 143                     let mir::StatementKind::Assign(ref lvalue, ref rvalue) = stmt.kind;
 144                     try!(self.eval_assignment(lvalue, rvalue));
 145                 }
 146
 147                 let terminator = block_data.terminator();
 148                 print_trace(terminator, "", self.stack.len() + 1);
 149
 150                 match try!(self.eval_terminator(terminator)) {
 151                     TerminatorTarget::Block(block) => current_block = block,
 152                     TerminatorTarget::Return => {
 153                         self.pop_stack_frame();
 154                         self.substs_stack.pop();
 155                         continue 'outer;
 156                     }
 157                     TerminatorTarget::Call => continue 'outer,
 158                 }
 159             }
 160         }
 161
 162         Ok(())
 163     }
 164
 165     fn push_stack_frame(&mut self, mir: CachedMir<'a, 'tcx>, return_ptr: Option<Pointer>)
 166         -> EvalResult<()>
 167     {
 168         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 169         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 170         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 171
 172         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 173             let size = self.ty_size(ty);
 174             self.memory.allocate(size)
 175         }).collect();
 176
 177         let num_args = mir.arg_decls.len();
 178         let num_vars = mir.var_decls.len();
 179
 180         self.stack.push(Frame {
 181             mir: mir.clone(),
 182             next_block: mir::START_BLOCK,
 183             return_ptr: return_ptr,
 184             locals: locals,
 185             var_offset: num_args,
 186             temp_offset: num_args + num_vars,
 187         });
 188
 189         Ok(())
 190     }
 191
 192     fn pop_stack_frame(&mut self) {
 193         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 194         // TODO(tsion): Deallocate local variables.
 195     }
 196
 197     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 198             -> EvalResult<TerminatorTarget> {
 199         use rustc::mir::repr::TerminatorKind::*;
 200         let target = match terminator.kind {
 201             Return => TerminatorTarget::Return,
 202
 203             Goto { target } => TerminatorTarget::Block(target),
 204
 205             If { ref cond, targets: (then_target, else_target) } => {
 206                 let cond_ptr = try!(self.eval_operand(cond));
 207                 let cond_val = try!(self.memory.read_bool(cond_ptr));
 208                 TerminatorTarget::Block(if cond_val { then_target } else { else_target })
 209             }
 210
 211             SwitchInt { ref discr, ref values, ref targets, .. } => {
 212                 let discr_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 213                 let discr_size = self.lvalue_repr(discr).size();
 214                 let discr_val = try!(self.memory.read_uint(discr_ptr, discr_size));
 215
 216                 // Branch to the `otherwise` case by default, if no match is found.
 217                 let mut target_block = targets[targets.len() - 1];
 218
 219                 for (index, val_const) in values.iter().enumerate() {
 220                     let ptr = try!(self.const_to_ptr(val_const));
 221                     let val = try!(self.memory.read_uint(ptr, discr_size));
 222                     if discr_val == val {
 223                         target_block = targets[index];
 224                         break;
 225                     }
 226                 }
 227
 228                 TerminatorTarget::Block(target_block)
 229             }
 230
 231             Switch { ref discr, ref targets, adt_def } => {
 232                 let adt_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 233                 let adt_repr = self.lvalue_repr(discr);
 234                 let discr_size = match *adt_repr {
 235                     Repr::Aggregate { discr_size, .. } => discr_size,
 236                     _ => panic!("attmpted to switch on non-aggregate type"),
 237                 };
 238                 let discr_val = try!(self.memory.read_uint(adt_ptr, discr_size));
 239
 240                 let matching = adt_def.variants.iter()
 241                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 242
 243                 match matching {
 244                     Some(i) => TerminatorTarget::Block(targets[i]),
 245                     None => return Err(EvalError::InvalidDiscriminant),
 246                 }
 247             }
 248
 249             Call { ref func, ref args, ref destination, .. } => {
 250                 let mut return_ptr = None;
 251                 if let Some((ref lv, target)) = *destination {
 252                     self.frame_mut().next_block = target;
 253                     return_ptr = Some(try!(self.eval_lvalue(lv)).to_ptr());
 254                 }
 255
 256                 let func_ty = self.operand_ty(func);
 257                 match func_ty.sty {
 258                     ty::TyFnDef(def_id, substs, fn_ty) => {
 259                         use syntax::abi::Abi;
 260                         match fn_ty.abi {
 261                             Abi::RustIntrinsic => {
 262                                 let name = self.tcx.item_name(def_id).as_str();
 263                                 match fn_ty.sig.0.output {
 264                                     ty::FnConverging(ty) => {
 265                                         let size = self.ty_size(ty);
 266                                         try!(self.call_intrinsic(&name, substs, args,
 267                                             return_ptr.unwrap(), size))
 268                                     }
 269                                     ty::FnDiverging => unimplemented!(),
 270                                 }
 271                             }
 272
 273                             Abi::C =>
 274                                 try!(self.call_c_abi(def_id, args, return_ptr.unwrap())),
 275
 276                             Abi::Rust | Abi::RustCall => {
 277                                 // TODO(tsion): Adjust the first argument when calling a Fn or
 278                                 // FnMut closure via FnOnce::call_once.
 279
 280                                 // Only trait methods can have a Self parameter.
 281                                 let (def_id, substs) = if substs.self_ty().is_some() {
 282                                     self.trait_method(def_id, substs)
 283                                 } else {
 284                                     (def_id, substs)
 285                                 };
 286
 287                                 let mut arg_srcs = Vec::new();
 288                                 for arg in args {
 289                                     let (src, repr) = try!(self.eval_operand_and_repr(arg));
 290                                     arg_srcs.push((src, repr.size()));
 291                                 }
 292
 293                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 294                                     arg_srcs.pop();
 295                                     let last_arg = args.last().unwrap();
 296                                     let (last_src, last_repr) =
 297                                         try!(self.eval_operand_and_repr(last_arg));
 298                                     match *last_repr {
 299                                         Repr::Aggregate { discr_size: 0, ref variants, .. } => {
 300                                             assert_eq!(variants.len(), 1);
 301                                             for field in &variants[0] {
 302                                                 let src = last_src.offset(field.offset as isize);
 303                                                 arg_srcs.push((src, field.size));
 304                                             }
 305                                         }
 306
 307                                         _ => panic!("expected tuple as last argument in function with 'rust-call' ABI"),
 308                                     }
 309                                 }
 310
 311                                 let mir = self.load_mir(def_id);
 312                                 self.substs_stack.push(substs);
 313                                 try!(self.push_stack_frame(mir, return_ptr));
 314
 315                                 for (i, (src, size)) in arg_srcs.into_iter().enumerate() {
 316                                     let dest = self.frame().locals[i];
 317                                     try!(self.memory.copy(src, dest, size));
 318                                 }
 319
 320                                 TerminatorTarget::Call
 321                             }
 322
 323                             abi => panic!("can't handle function with {:?} ABI", abi),
 324                         }
 325                     }
 326
 327                     _ => panic!("can't handle callee of type {:?}", func_ty),
 328                 }
 329             }
 330
 331             Drop { target, .. } => {
 332                 // TODO: Handle destructors and dynamic drop.
 333                 TerminatorTarget::Block(target)
 334             }
 335
 336             Resume => unimplemented!(),
 337         };
 338
 339         Ok(target)
 340     }
 341
 342     fn call_intrinsic(&mut self, name: &str, substs: &'tcx Substs<'tcx>,
 343         args: &[mir::Operand<'tcx>], dest: Pointer, dest_size: usize)
 344         -> EvalResult<TerminatorTarget>
 345     {
 346         match name {
 347             "assume" => {}
 348
 349             "copy_nonoverlapping" => {
 350                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 351                 let elem_size = self.ty_size(elem_ty);
 352
 353                 let src_arg   = try!(self.eval_operand(&args[0]));
 354                 let dest_arg  = try!(self.eval_operand(&args[1]));
 355                 let count_arg = try!(self.eval_operand(&args[2]));
 356
 357                 let src   = try!(self.memory.read_ptr(src_arg));
 358                 let dest  = try!(self.memory.read_ptr(dest_arg));
 359                 let count = try!(self.memory.read_isize(count_arg));
 360
 361                 try!(self.memory.copy(src, dest, count as usize * elem_size));
 362             }
 363
 364             // TODO(tsion): Mark as dropped?
 365             "forget" => {}
 366
 367             "min_align_of" => {
 368                 try!(self.memory.write_int(dest, 1, dest_size));
 369             }
 370
 371             "move_val_init" => {
 372                 let ty = *substs.types.get(subst::FnSpace, 0);
 373                 let size = self.ty_size(ty);
 374
 375                 let ptr_arg = try!(self.eval_operand(&args[0]));
 376                 let ptr = try!(self.memory.read_ptr(ptr_arg));
 377
 378                 let val = try!(self.eval_operand(&args[1]));
 379                 try!(self.memory.copy(val, ptr, size));
 380             }
 381
 382             // FIXME(tsion): Handle different integer types correctly.
 383             "mul_with_overflow" => {
 384                 let ty = *substs.types.get(subst::FnSpace, 0);
 385                 let size = self.ty_size(ty);
 386
 387                 let left_arg  = try!(self.eval_operand(&args[0]));
 388                 let right_arg = try!(self.eval_operand(&args[1]));
 389
 390                 let left = try!(self.memory.read_int(left_arg, size));
 391                 let right = try!(self.memory.read_int(right_arg, size));
 392
 393                 let (n, overflowed) = unsafe {
 394                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 395                 };
 396
 397                 try!(self.memory.write_int(dest, n, size));
 398                 try!(self.memory.write_bool(dest.offset(size as isize), overflowed));
 399             }
 400
 401             "offset" => {
 402                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 403                 let pointee_size = self.ty_size(pointee_ty) as isize;
 404
 405                 let ptr_arg    = try!(self.eval_operand(&args[0]));
 406                 let offset_arg = try!(self.eval_operand(&args[1]));
 407
 408                 let offset = try!(self.memory.read_isize(offset_arg));
 409
 410                 match self.memory.read_ptr(ptr_arg) {
 411                     Ok(ptr) => {
 412                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 413                         try!(self.memory.write_ptr(dest, result_ptr));
 414                     }
 415                     Err(EvalError::ReadBytesAsPointer) => {
 416                         let addr = try!(self.memory.read_isize(ptr_arg));
 417                         let result_addr = addr + offset * pointee_size as i64;
 418                         try!(self.memory.write_isize(dest, result_addr));
 419                     }
 420                     Err(e) => return Err(e),
 421                 }
 422             }
 423
 424             // FIXME(tsion): Handle different integer types correctly. Use primvals?
 425             "overflowing_sub" => {
 426                 let ty = *substs.types.get(subst::FnSpace, 0);
 427                 let size = self.ty_size(ty);
 428
 429                 let left_arg  = try!(self.eval_operand(&args[0]));
 430                 let right_arg = try!(self.eval_operand(&args[1]));
 431
 432                 let left = try!(self.memory.read_int(left_arg, size));
 433                 let right = try!(self.memory.read_int(right_arg, size));
 434
 435                 let n = left.wrapping_sub(right);
 436                 try!(self.memory.write_int(dest, n, size));
 437             }
 438
 439             "size_of" => {
 440                 let ty = *substs.types.get(subst::FnSpace, 0);
 441                 let size = self.ty_size(ty) as u64;
 442                 try!(self.memory.write_uint(dest, size, dest_size));
 443             }
 444
 445             "transmute" => {
 446                 let src = try!(self.eval_operand(&args[0]));
 447                 try!(self.memory.copy(src, dest, dest_size));
 448             }
 449
 450             "uninit" => {
 451                 try!(self.memory.mark_definedness(dest, dest_size, false));
 452             }
 453
 454             name => panic!("can't handle intrinsic: {}", name),
 455         }
 456
 457         // Since we pushed no stack frame, the main loop will act
 458         // as if the call just completed and it's returning to the
 459         // current frame.
 460         Ok(TerminatorTarget::Call)
 461     }
 462
 463     fn call_c_abi(&mut self, def_id: DefId, args: &[mir::Operand<'tcx>], dest: Pointer)
 464         -> EvalResult<TerminatorTarget>
 465     {
 466         let name = self.tcx.item_name(def_id);
 467         let attrs = self.tcx.get_attrs(def_id);
 468         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 469             Some(ln) => ln.clone(),
 470             None => name.as_str(),
 471         };
 472
 473         match &link_name[..] {
 474             "__rust_allocate" => {
 475                 let size_arg  = try!(self.eval_operand(&args[0]));
 476                 let _align_arg = try!(self.eval_operand(&args[1]));
 477                 let size = try!(self.memory.read_usize(size_arg));
 478                 let ptr = self.memory.allocate(size as usize);
 479                 try!(self.memory.write_ptr(dest, ptr));
 480             }
 481
 482             _ => panic!("can't call C ABI function: {}", link_name),
 483         }
 484
 485         // Since we pushed no stack frame, the main loop will act
 486         // as if the call just completed and it's returning to the
 487         // current frame.
 488         Ok(TerminatorTarget::Call)
 489     }
 490
 491     fn assign_to_aggregate(
 492         &mut self,
 493         dest: Pointer,
 494         dest_repr: &Repr,
 495         variant: usize,
 496         discr: Option<u64>,
 497         operands: &[mir::Operand<'tcx>],
 498     ) -> EvalResult<()> {
 499         match *dest_repr {
 500             Repr::Aggregate { discr_size, ref variants, .. } => {
 501                 if discr_size > 0 {
 502                     try!(self.memory.write_uint(dest, discr.unwrap(), discr_size));
 503                 }
 504                 let after_discr = dest.offset(discr_size as isize);
 505                 for (field, operand) in variants[variant].iter().zip(operands) {
 506                     let src = try!(self.eval_operand(operand));
 507                     let field_dest = after_discr.offset(field.offset as isize);
 508                     try!(self.memory.copy(src, field_dest, field.size));
 509                 }
 510             }
 511             _ => panic!("expected Repr::Aggregate target"),
 512         }
 513         Ok(())
 514     }
 515
 516     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 517         -> EvalResult<()>
 518     {
 519         let dest = try!(self.eval_lvalue(lvalue)).to_ptr();
 520         let dest_repr = self.lvalue_repr(lvalue);
 521
 522         use rustc::mir::repr::Rvalue::*;
 523         match *rvalue {
 524             Use(ref operand) => {
 525                 let src = try!(self.eval_operand(operand));
 526                 try!(self.memory.copy(src, dest, dest_repr.size()));
 527             }
 528
 529             BinaryOp(bin_op, ref left, ref right) => {
 530                 let left_ptr = try!(self.eval_operand(left));
 531                 let left_ty = self.operand_ty(left);
 532                 let left_val = try!(self.read_primval(left_ptr, left_ty));
 533
 534                 let right_ptr = try!(self.eval_operand(right));
 535                 let right_ty = self.operand_ty(right);
 536                 let right_val = try!(self.read_primval(right_ptr, right_ty));
 537
 538                 let val = try!(primval::binary_op(bin_op, left_val, right_val));
 539                 try!(self.memory.write_primval(dest, val));
 540             }
 541
 542             UnaryOp(un_op, ref operand) => {
 543                 let ptr = try!(self.eval_operand(operand));
 544                 let ty = self.operand_ty(operand);
 545                 let val = try!(self.read_primval(ptr, ty));
 546                 try!(self.memory.write_primval(dest, primval::unary_op(un_op, val)));
 547             }
 548
 549             Aggregate(ref kind, ref operands) => {
 550                 use rustc::mir::repr::AggregateKind::*;
 551                 match *kind {
 552                     Tuple | Closure(..) =>
 553                         try!(self.assign_to_aggregate(dest, &dest_repr, 0, None, operands)),
 554
 555                     Adt(adt_def, variant, _) => {
 556                         let discr = Some(adt_def.variants[variant].disr_val.to_u64_unchecked());
 557                         try!(self.assign_to_aggregate(dest, &dest_repr, variant, discr, operands));
 558                     }
 559
 560                     Vec => if let Repr::Array { elem_size, length } = *dest_repr {
 561                         assert_eq!(length, operands.len());
 562                         for (i, operand) in operands.iter().enumerate() {
 563                             let src = try!(self.eval_operand(operand));
 564                             let elem_dest = dest.offset((i * elem_size) as isize);
 565                             try!(self.memory.copy(src, elem_dest, elem_size));
 566                         }
 567                     } else {
 568                         panic!("expected Repr::Array target");
 569                     },
 570                 }
 571             }
 572
 573             Repeat(ref operand, _) => {
 574                 if let Repr::Array { elem_size, length } = *dest_repr {
 575                     let src = try!(self.eval_operand(operand));
 576                     for i in 0..length {
 577                         let elem_dest = dest.offset((i * elem_size) as isize);
 578                         try!(self.memory.copy(src, elem_dest, elem_size));
 579                     }
 580                 } else {
 581                     panic!("expected Repr::Array target");
 582                 }
 583             }
 584
 585             Len(ref lvalue) => {
 586                 let src = try!(self.eval_lvalue(lvalue));
 587                 let ty = self.lvalue_ty(lvalue);
 588                 let len = match ty.sty {
 589                     ty::TyArray(_, n) => n as u64,
 590                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
 591                         n
 592                     } else {
 593                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
 594                     },
 595                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
 596                 };
 597                 try!(self.memory.write_usize(dest, len));
 598             }
 599
 600             Ref(_, _, ref lvalue) => {
 601                 let lv = try!(self.eval_lvalue(lvalue));
 602                 try!(self.memory.write_ptr(dest, lv.ptr));
 603                 match lv.extra {
 604                     LvalueExtra::None => {},
 605                     LvalueExtra::Length(len) => {
 606                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
 607                         try!(self.memory.write_usize(len_ptr, len));
 608                     }
 609                 }
 610             }
 611
 612             Box(ty) => {
 613                 let size = self.ty_size(ty);
 614                 let ptr = self.memory.allocate(size);
 615                 try!(self.memory.write_ptr(dest, ptr));
 616             }
 617
 618             Cast(kind, ref operand, dest_ty) => {
 619                 let src = try!(self.eval_operand(operand));
 620                 let src_ty = self.operand_ty(operand);
 621
 622                 use rustc::mir::repr::CastKind::*;
 623                 match kind {
 624                     Unsize => {
 625                         try!(self.memory.copy(src, dest, 8));
 626                         let src_pointee_ty = pointee_type(src_ty).unwrap();
 627                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
 628
 629                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
 630                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
 631                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
 632                                 try!(self.memory.write_usize(len_ptr, length as u64));
 633                             }
 634
 635                             _ => panic!("can't handle cast: {:?}", rvalue),
 636                         }
 637                     }
 638
 639                     Misc => {
 640                         // FIXME(tsion): Wrong for almost everything.
 641                         let size = dest_repr.size();
 642                         try!(self.memory.copy(src, dest, size));
 643                     }
 644
 645                     _ => panic!("can't handle cast: {:?}", rvalue),
 646                 }
 647             }
 648
 649             Slice { .. } => unimplemented!(),
 650             InlineAsm { .. } => unimplemented!(),
 651         }
 652
 653         Ok(())
 654     }
 655
 656     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
 657         self.eval_operand_and_repr(op).map(|(p, _)| p)
 658     }
 659
 660     fn eval_operand_and_repr(&mut self, op: &mir::Operand<'tcx>)
 661         -> EvalResult<(Pointer, &'arena Repr)>
 662     {
 663         use rustc::mir::repr::Operand::*;
 664         match *op {
 665             Consume(ref lvalue) =>
 666                 Ok((try!(self.eval_lvalue(lvalue)).to_ptr(), self.lvalue_repr(lvalue))),
 667             Constant(mir::Constant { ref literal, ty, .. }) => {
 668                 use rustc::mir::repr::Literal::*;
 669                 match *literal {
 670                     Value { ref value } => Ok((
 671                         try!(self.const_to_ptr(value)),
 672                         self.ty_to_repr(ty),
 673                     )),
 674                     Item { .. } => unimplemented!(),
 675                 }
 676             }
 677         }
 678     }
 679
 680     // TODO(tsion): Replace this inefficient hack with a wrapper like LvalueTy (e.g. LvalueRepr).
 681     fn lvalue_repr(&self, lvalue: &mir::Lvalue<'tcx>) -> &'arena Repr {
 682         use rustc::mir::tcx::LvalueTy;
 683         match self.mir().lvalue_ty(self.tcx, lvalue) {
 684             LvalueTy::Ty { ty } => self.ty_to_repr(ty),
 685             LvalueTy::Downcast { adt_def, substs, variant_index } => {
 686                 let field_tys = adt_def.variants[variant_index].fields.iter()
 687                     .map(|f| f.ty(self.tcx, substs));
 688                 self.repr_arena.alloc(self.make_aggregate_repr(iter::once(field_tys)))
 689             }
 690         }
 691     }
 692
 693     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
 694         use rustc::mir::repr::Lvalue::*;
 695         let ptr = match *lvalue {
 696             ReturnPointer => self.frame().return_ptr
 697                 .expect("ReturnPointer used in a function with no return value"),
 698             Arg(i) => self.frame().locals[i as usize],
 699             Var(i) => self.frame().locals[self.frame().var_offset + i as usize],
 700             Temp(i) => self.frame().locals[self.frame().temp_offset + i as usize],
 701
 702             Static(_def_id) => unimplemented!(),
 703
 704             Projection(ref proj) => {
 705                 let base_ptr = try!(self.eval_lvalue(&proj.base)).to_ptr();
 706                 let base_repr = self.lvalue_repr(&proj.base);
 707                 let base_ty = self.lvalue_ty(&proj.base);
 708                 use rustc::mir::repr::ProjectionElem::*;
 709                 match proj.elem {
 710                     Field(field, _) => match *base_repr {
 711                         Repr::Aggregate { discr_size: 0, ref variants, .. } => {
 712                             let fields = &variants[0];
 713                             base_ptr.offset(fields[field.index()].offset as isize)
 714                         }
 715                         _ => panic!("field access on non-product type: {:?}", base_repr),
 716                     },
 717
 718                     Downcast(..) => match *base_repr {
 719                         Repr::Aggregate { discr_size, .. } => base_ptr.offset(discr_size as isize),
 720                         _ => panic!("variant downcast on non-aggregate type: {:?}", base_repr),
 721                     },
 722
 723                     Deref => {
 724                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
 725                         let ptr = try!(self.memory.read_ptr(base_ptr));
 726                         let extra = match pointee_ty.sty {
 727                             ty::TySlice(_) | ty::TyStr => {
 728                                 let len_ptr = base_ptr.offset(self.memory.pointer_size as isize);
 729                                 let len = try!(self.memory.read_usize(len_ptr));
 730                                 LvalueExtra::Length(len)
 731                             }
 732                             ty::TyTrait(_) => unimplemented!(),
 733                             _ => LvalueExtra::None,
 734                         };
 735                         return Ok(Lvalue { ptr: ptr, extra: extra });
 736                     }
 737
 738                     Index(ref operand) => {
 739                         let elem_size = match base_ty.sty {
 740                             ty::TyArray(elem_ty, _) => self.ty_size(elem_ty),
 741                             ty::TySlice(elem_ty) => self.ty_size(elem_ty),
 742                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
 743                         };
 744                         let n_ptr = try!(self.eval_operand(operand));
 745                         let n = try!(self.memory.read_usize(n_ptr));
 746                         base_ptr.offset(n as isize * elem_size as isize)
 747                     }
 748
 749                     ConstantIndex { .. } => unimplemented!(),
 750                 }
 751             }
 752         };
 753
 754         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
 755     }
 756
 757     // TODO(tsion): Try making const_to_primval instead.
 758     fn const_to_ptr(&mut self, const_val: &const_eval::ConstVal) -> EvalResult<Pointer> {
 759         use rustc::middle::const_eval::ConstVal::*;
 760         match *const_val {
 761             Float(_f) => unimplemented!(),
 762             Integral(int) => {
 763                 // TODO(tsion): Check int constant type.
 764                 let ptr = self.memory.allocate(8);
 765                 try!(self.memory.write_uint(ptr, int.to_u64_unchecked(), 8));
 766                 Ok(ptr)
 767             }
 768             Str(ref s) => {
 769                 let psize = self.memory.pointer_size;
 770                 let static_ptr = self.memory.allocate(s.len());
 771                 let ptr = self.memory.allocate(psize * 2);
 772                 try!(self.memory.write_bytes(static_ptr, s.as_bytes()));
 773                 try!(self.memory.write_ptr(ptr, static_ptr));
 774                 try!(self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64));
 775                 Ok(ptr)
 776             }
 777             ByteStr(ref bs) => {
 778                 let psize = self.memory.pointer_size;
 779                 let static_ptr = self.memory.allocate(bs.len());
 780                 let ptr = self.memory.allocate(psize);
 781                 try!(self.memory.write_bytes(static_ptr, bs));
 782                 try!(self.memory.write_ptr(ptr, static_ptr));
 783                 Ok(ptr)
 784             }
 785             Bool(b) => {
 786                 let ptr = self.memory.allocate(1);
 787                 try!(self.memory.write_bool(ptr, b));
 788                 Ok(ptr)
 789             }
 790             Char(_c)          => unimplemented!(),
 791             Struct(_node_id)  => unimplemented!(),
 792             Tuple(_node_id)   => unimplemented!(),
 793             Function(_def_id) => unimplemented!(),
 794             Array(_, _)       => unimplemented!(),
 795             Repeat(_, _)      => unimplemented!(),
 796             Dummy             => unimplemented!(),
 797         }
 798     }
 799
 800     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> ty::Ty<'tcx> {
 801         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx))
 802     }
 803
 804     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> ty::Ty<'tcx> {
 805         self.monomorphize(self.mir().operand_ty(self.tcx, operand))
 806     }
 807
 808     fn monomorphize(&self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
 809         let substituted = ty.subst(self.tcx, self.substs());
 810         infer::normalize_associated_type(self.tcx, &substituted)
 811     }
 812
 813     fn type_is_sized(&self, ty: ty::Ty<'tcx>) -> bool {
 814         ty.is_sized(&self.tcx.empty_parameter_environment(), DUMMY_SP)
 815     }
 816
 817     fn ty_size(&self, ty: ty::Ty<'tcx>) -> usize {
 818         self.ty_to_repr(ty).size()
 819     }
 820
 821     fn ty_to_repr(&self, ty: ty::Ty<'tcx>) -> &'arena Repr {
 822         let ty = self.monomorphize(ty);
 823
 824         if let Some(repr) = self.repr_cache.borrow().get(ty) {
 825             return repr;
 826         }
 827
 828         use syntax::ast::{IntTy, UintTy};
 829         let repr = match ty.sty {
 830             ty::TyBool => Repr::Primitive { size: 1 },
 831
 832             ty::TyInt(IntTy::I8)  | ty::TyUint(UintTy::U8)  => Repr::Primitive { size: 1 },
 833             ty::TyInt(IntTy::I16) | ty::TyUint(UintTy::U16) => Repr::Primitive { size: 2 },
 834             ty::TyInt(IntTy::I32) | ty::TyUint(UintTy::U32) => Repr::Primitive { size: 4 },
 835             ty::TyInt(IntTy::I64) | ty::TyUint(UintTy::U64) => Repr::Primitive { size: 8 },
 836
 837             ty::TyInt(IntTy::Is) | ty::TyUint(UintTy::Us) =>
 838                 Repr::Primitive { size: self.memory.pointer_size },
 839
 840             ty::TyTuple(ref fields) =>
 841                 self.make_aggregate_repr(iter::once(fields.iter().cloned())),
 842
 843             ty::TyEnum(adt_def, substs) | ty::TyStruct(adt_def, substs) => {
 844                 let variants = adt_def.variants.iter().map(|v| {
 845                     v.fields.iter().map(|f| f.ty(self.tcx, substs))
 846                 });
 847                 self.make_aggregate_repr(variants)
 848             }
 849
 850             ty::TyArray(elem_ty, length) => Repr::Array {
 851                 elem_size: self.ty_size(elem_ty),
 852                 length: length,
 853             },
 854
 855             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
 856             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
 857             ty::TyBox(ty) => {
 858                 if self.type_is_sized(ty) {
 859                     Repr::Primitive { size: self.memory.pointer_size }
 860                 } else {
 861                     Repr::Primitive { size: self.memory.pointer_size * 2 }
 862                 }
 863             }
 864
 865             ty::TyFnPtr(..) => Repr::Primitive { size: self.memory.pointer_size },
 866
 867             ty::TyClosure(_, ref closure_substs) =>
 868                 self.make_aggregate_repr(iter::once(closure_substs.upvar_tys.iter().cloned())),
 869
 870             ref t => panic!("can't convert type to repr: {:?}", t),
 871         };
 872
 873         let repr_ref = self.repr_arena.alloc(repr);
 874         self.repr_cache.borrow_mut().insert(ty, repr_ref);
 875         repr_ref
 876     }
 877
 878     fn make_aggregate_repr<V>(&self, variant_fields: V) -> Repr
 879         where V: IntoIterator, V::Item: IntoIterator<Item = ty::Ty<'tcx>>
 880     {
 881         let mut variants = Vec::new();
 882         let mut max_variant_size = 0;
 883
 884         for field_tys in variant_fields {
 885             let mut fields = Vec::new();
 886             let mut size = 0;
 887
 888             for ty in field_tys {
 889                 let field_size = self.ty_size(ty);
 890                 let offest = size;
 891                 size += field_size;
 892                 fields.push(FieldRepr { offset: offest, size: field_size });
 893             }
 894
 895             if size > max_variant_size { max_variant_size = size; }
 896             variants.push(fields);
 897         }
 898
 899         let discr_size = match variants.len() {
 900             n if n <= 1       => 0,
 901             n if n <= 1 << 8  => 1,
 902             n if n <= 1 << 16 => 2,
 903             n if n <= 1 << 32 => 4,
 904             _                 => 8,
 905         };
 906         Repr::Aggregate {
 907             discr_size: discr_size,
 908             size: max_variant_size + discr_size,
 909             variants: variants,
 910         }
 911     }
 912
 913     pub fn read_primval(&mut self, ptr: Pointer, ty: ty::Ty<'tcx>) -> EvalResult<PrimVal> {
 914         use syntax::ast::{IntTy, UintTy};
 915         let val = match ty.sty {
 916             ty::TyBool              => PrimVal::Bool(try!(self.memory.read_bool(ptr))),
 917             ty::TyInt(IntTy::I8)    => PrimVal::I8(try!(self.memory.read_int(ptr, 1)) as i8),
 918             ty::TyInt(IntTy::I16)   => PrimVal::I16(try!(self.memory.read_int(ptr, 2)) as i16),
 919             ty::TyInt(IntTy::I32)   => PrimVal::I32(try!(self.memory.read_int(ptr, 4)) as i32),
 920             ty::TyInt(IntTy::I64)   => PrimVal::I64(try!(self.memory.read_int(ptr, 8)) as i64),
 921             ty::TyUint(UintTy::U8)  => PrimVal::U8(try!(self.memory.read_uint(ptr, 1)) as u8),
 922             ty::TyUint(UintTy::U16) => PrimVal::U16(try!(self.memory.read_uint(ptr, 2)) as u16),
 923             ty::TyUint(UintTy::U32) => PrimVal::U32(try!(self.memory.read_uint(ptr, 4)) as u32),
 924             ty::TyUint(UintTy::U64) => PrimVal::U64(try!(self.memory.read_uint(ptr, 8)) as u64),
 925
 926             // TODO(tsion): Pick the PrimVal dynamically.
 927             ty::TyInt(IntTy::Is)   => PrimVal::I64(try!(self.memory.read_isize(ptr))),
 928             ty::TyUint(UintTy::Us) => PrimVal::U64(try!(self.memory.read_usize(ptr))),
 929
 930             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
 931             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) => {
 932                 if self.type_is_sized(ty) {
 933                     match self.memory.read_ptr(ptr) {
 934                         Ok(p) => PrimVal::AbstractPtr(p),
 935                         Err(EvalError::ReadBytesAsPointer) => {
 936                             let n = try!(self.memory.read_usize(ptr));
 937                             PrimVal::IntegerPtr(n)
 938                         }
 939                         Err(e) => return Err(e),
 940                     }
 941                 } else {
 942                     panic!("unimplemented: primitive read of fat pointer type: {:?}", ty);
 943                 }
 944             }
 945
 946             _ => panic!("primitive read of non-primitive type: {:?}", ty),
 947         };
 948         Ok(val)
 949     }
 950
 951     fn frame(&self) -> &Frame<'a, 'tcx> {
 952         self.stack.last().expect("no call frames exist")
 953     }
 954
 955     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
 956         self.stack.last_mut().expect("no call frames exist")
 957     }
 958
 959     fn mir(&self) -> &mir::Mir<'tcx> {
 960         &self.frame().mir
 961     }
 962
 963     fn substs(&self) -> &'tcx Substs<'tcx> {
 964         self.substs_stack.last().cloned().unwrap_or_else(|| self.tcx.mk_substs(Substs::empty()))
 965     }
 966
 967     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
 968         match self.tcx.map.as_local_node_id(def_id) {
 969             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
 970             None => {
 971                 let mut mir_cache = self.mir_cache.borrow_mut();
 972                 if let Some(mir) = mir_cache.get(&def_id) {
 973                     return CachedMir::Owned(mir.clone());
 974                 }
 975
 976                 use rustc::middle::cstore::CrateStore;
 977                 let cs = &self.tcx.sess.cstore;
 978                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
 979                     panic!("no mir for {:?}", def_id);
 980                 });
 981                 let cached = Rc::new(mir);
 982                 mir_cache.insert(def_id, cached.clone());
 983                 CachedMir::Owned(cached)
 984             }
 985         }
 986     }
 987
 988     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
 989         // Do the initial selection for the obligation. This yields the shallow result we are
 990         // looking for -- that is, what specific impl.
 991         let infcx = infer::normalizing_infer_ctxt(self.tcx, &self.tcx.tables, ProjectionMode::Any);
 992         let mut selcx = traits::SelectionContext::new(&infcx);
 993
 994         let obligation = traits::Obligation::new(
 995             traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
 996             trait_ref.to_poly_trait_predicate(),
 997         );
 998         let selection = selcx.select(&obligation).unwrap().unwrap();
 999
1000         // Currently, we use a fulfillment context to completely resolve all nested obligations.
1001         // This is because they can inform the inference of the impl's type parameters.
1002         let mut fulfill_cx = traits::FulfillmentContext::new();
1003         let vtable = selection.map(|predicate| {
1004             fulfill_cx.register_predicate_obligation(&infcx, predicate);
1005         });
1006         let vtable = infer::drain_fulfillment_cx_or_panic(
1007             DUMMY_SP, &infcx, &mut fulfill_cx, &vtable
1008         );
1009
1010         vtable
1011     }
1012
1013     /// Trait method, which has to be resolved to an impl method.
1014     pub fn trait_method(&self, def_id: DefId, substs: &'tcx Substs<'tcx>)
1015         -> (DefId, &'tcx Substs<'tcx>)
1016     {
1017         let method_item = self.tcx.impl_or_trait_item(def_id);
1018         let trait_id = method_item.container().id();
1019         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
1020         match self.fulfill_obligation(trait_ref) {
1021             traits::VtableImpl(vtable_impl) => {
1022                 let impl_did = vtable_impl.impl_def_id;
1023                 let mname = self.tcx.item_name(def_id);
1024                 // Create a concatenated set of substitutions which includes those from the impl
1025                 // and those from the method:
1026                 let impl_substs = vtable_impl.substs.with_method_from(substs);
1027                 let substs = self.tcx.mk_substs(impl_substs);
1028                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
1029
1030                 (mth.method.def_id, mth.substs)
1031             }
1032
1033             traits::VtableClosure(vtable_closure) =>
1034                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
1035
1036             traits::VtableFnPointer(_fn_ty) => {
1037                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
1038                 unimplemented!()
1039                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
1040
1041                 // let method_ty = def_ty(tcx, def_id, substs);
1042                 // let fn_ptr_ty = match method_ty.sty {
1043                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
1044                 //     _ => unreachable!("expected fn item type, found {}",
1045                 //                       method_ty)
1046                 // };
1047                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
1048             }
1049
1050             traits::VtableObject(ref _data) => {
1051                 unimplemented!()
1052                 // Callee {
1053                 //     data: Virtual(traits::get_vtable_index_of_object_method(
1054                 //                   tcx, data, def_id)),
1055                 //                   ty: def_ty(tcx, def_id, substs)
1056                 // }
1057             }
1058             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
1059         }
1060     }
1061 }
1062
1063 fn pointee_type<'tcx>(ptr_ty: ty::Ty<'tcx>) -> Option<ty::Ty<'tcx>> {
1064     match ptr_ty.sty {
1065         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1066         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1067         ty::TyBox(ty) => {
1068             Some(ty)
1069         }
1070         _ => None,
1071     }
1072 }
1073
1074 impl Lvalue {
1075     fn to_ptr(self) -> Pointer {
1076         assert_eq!(self.extra, LvalueExtra::None);
1077         self.ptr
1078     }
1079 }
1080
1081 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1082     type Target = mir::Mir<'tcx>;
1083     fn deref(&self) -> &mir::Mir<'tcx> {
1084         match *self {
1085             CachedMir::Ref(r) => r,
1086             CachedMir::Owned(ref rc) => &rc,
1087         }
1088     }
1089 }
1090
1091 #[derive(Debug)]
1092 pub struct ImplMethod<'tcx> {
1093     pub method: Rc<ty::Method<'tcx>>,
1094     pub substs: &'tcx Substs<'tcx>,
1095     pub is_provided: bool,
1096 }
1097
1098 /// Locates the applicable definition of a method, given its name.
1099 pub fn get_impl_method<'tcx>(
1100     tcx: &TyCtxt<'tcx>,
1101     impl_def_id: DefId,
1102     substs: &'tcx Substs<'tcx>,
1103     name: ast::Name,
1104 ) -> ImplMethod<'tcx> {
1105     assert!(!substs.types.needs_infer());
1106
1107     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1108     let trait_def = tcx.lookup_trait_def(trait_def_id);
1109     let infcx = infer::normalizing_infer_ctxt(tcx, &tcx.tables, ProjectionMode::Any);
1110
1111     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1112         Some(node_item) => {
1113             ImplMethod {
1114                 method: node_item.item,
1115                 substs: traits::translate_substs(&infcx, impl_def_id, substs, node_item.node),
1116                 is_provided: node_item.node.is_from_trait(),
1117             }
1118         }
1119         None => {
1120             tcx.sess.bug(&format!("method {:?} not found in {:?}", name, impl_def_id))
1121         }
1122     }
1123 }
1124
1125 pub fn interpret_start_points<'tcx>(tcx: &TyCtxt<'tcx>, mir_map: &MirMap<'tcx>) {
1126     /// Print the given allocation and all allocations it depends on.
1127     fn print_allocation_tree(memory: &Memory, alloc_id: memory::AllocId) {
1128         let alloc = memory.get(alloc_id).unwrap();
1129         println!("  {:?}: {:?}", alloc_id, alloc);
1130         for &target_alloc in alloc.relocations.values() {
1131             print_allocation_tree(memory, target_alloc);
1132         }
1133     }
1134
1135     for (&id, mir) in &mir_map.map {
1136         for attr in tcx.map.attrs(id) {
1137             use syntax::attr::AttrMetaMethods;
1138             if attr.check_name("miri_run") {
1139                 let item = tcx.map.expect_item(id);
1140
1141                 println!("Interpreting: {}", item.name);
1142
1143                 let repr_arena = TypedArena::new();
1144                 let mut miri = Interpreter::new(tcx, mir_map, &repr_arena);
1145                 let return_ptr = match mir.return_ty {
1146                     ty::FnConverging(ty) => {
1147                         let size = miri.ty_size(ty);
1148                         Some(miri.memory.allocate(size))
1149                     }
1150                     ty::FnDiverging => None,
1151                 };
1152                 miri.push_stack_frame(CachedMir::Ref(mir), return_ptr).unwrap();
1153                 miri.run().unwrap();
1154
1155                 if let Some(ret) = return_ptr {
1156                     println!("Result:");
1157                     print_allocation_tree(&miri.memory, ret.alloc_id);
1158                     println!("");
1159                 }
1160             }
1161         }
1162     }
1163 }