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::{self, 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     // TODO(tsion): Merge with `substs_stack`. Also try restructuring `Frame` to accomodate.
  55     /// A stack of the things necessary to print good strack traces:
  56     ///   * Function DefIds and Substs to print proper substituted function names.
  57     ///   * Spans pointing to specific function calls in the source.
  58     name_stack: Vec<(DefId, &'tcx Substs<'tcx>, codemap::Span)>,
  59 }
  60
  61 /// A stack frame.
  62 struct Frame<'a, 'tcx: 'a> {
  63     /// The MIR for the function called on this frame.
  64     mir: CachedMir<'a, 'tcx>,
  65
  66     /// The block this frame will execute when a function call returns back to this frame.
  67     next_block: mir::BasicBlock,
  68
  69     /// A pointer for writing the return value of the current call if it's not a diverging call.
  70     return_ptr: Option<Pointer>,
  71
  72     /// The list of locals for the current function, stored in order as
  73     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  74     /// and the temporaries at `self.temp_offset`.
  75     locals: Vec<Pointer>,
  76
  77     /// The offset of the first variable in `self.locals`.
  78     var_offset: usize,
  79
  80     /// The offset of the first temporary in `self.locals`.
  81     temp_offset: usize,
  82 }
  83
  84 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  85 struct Lvalue {
  86     ptr: Pointer,
  87     extra: LvalueExtra,
  88 }
  89
  90 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  91 enum LvalueExtra {
  92     None,
  93     Length(u64),
  94     // Vtable(memory::AllocId),
  95 }
  96
  97 #[derive(Clone)]
  98 enum CachedMir<'mir, 'tcx: 'mir> {
  99     Ref(&'mir mir::Mir<'tcx>),
 100     Owned(Rc<mir::Mir<'tcx>>)
 101 }
 102
 103 /// Represents the action to be taken in the main loop as a result of executing a terminator.
 104 enum TerminatorTarget {
 105     /// Make a local jump to the given block.
 106     Block(mir::BasicBlock),
 107
 108     /// Start executing from the new current frame. (For function calls.)
 109     Call,
 110
 111     /// Stop executing the current frame and resume the previous frame.
 112     Return,
 113 }
 114
 115 impl<'a, 'tcx: 'a, 'arena> Interpreter<'a, 'tcx, 'arena> {
 116     fn new(tcx: &'a TyCtxt<'tcx>, mir_map: &'a MirMap<'tcx>, repr_arena: &'arena TypedArena<Repr>)
 117         -> Self
 118     {
 119         Interpreter {
 120             tcx: tcx,
 121             mir_map: mir_map,
 122             mir_cache: RefCell::new(DefIdMap()),
 123             repr_arena: repr_arena,
 124             repr_cache: RefCell::new(FnvHashMap()),
 125             memory: Memory::new(),
 126             stack: Vec::new(),
 127             substs_stack: Vec::new(),
 128             name_stack: Vec::new(),
 129         }
 130     }
 131
 132     fn maybe_report<T>(&self, span: codemap::Span, r: EvalResult<T>) -> EvalResult<T> {
 133         if let Err(ref e) = r {
 134             let mut err = self.tcx.sess.struct_span_err(span, &e.to_string());
 135             for &(def_id, substs, span) in self.name_stack.iter().rev() {
 136                 // FIXME(tsion): Find a way to do this without this Display impl hack.
 137                 use rustc::util::ppaux;
 138                 use std::fmt;
 139                 struct Instance<'tcx>(DefId, &'tcx Substs<'tcx>);
 140                 impl<'tcx> fmt::Display for Instance<'tcx> {
 141                     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 142                         ppaux::parameterized(f, self.1, self.0, ppaux::Ns::Value, &[],
 143                             |tcx| tcx.lookup_item_type(self.0).generics)
 144                     }
 145                 }
 146                 err.span_note(span, &format!("inside call to {}", Instance(def_id, substs)));
 147             }
 148             err.emit();
 149         }
 150         r
 151     }
 152
 153     fn run(&mut self) -> EvalResult<()> {
 154         use std::fmt::Debug;
 155         fn print_trace<T: Debug>(t: &T, suffix: &'static str, indent: usize) {
 156             if !TRACE_EXECUTION { return; }
 157             for _ in 0..indent { print!("  "); }
 158             println!("{:?}{}", t, suffix);
 159         }
 160
 161         'outer: while !self.stack.is_empty() {
 162             let mut current_block = self.frame().next_block;
 163
 164             loop {
 165                 print_trace(&current_block, ":", self.stack.len());
 166                 let current_mir = self.mir().clone(); // Cloning a reference.
 167                 let block_data = current_mir.basic_block_data(current_block);
 168
 169                 for stmt in &block_data.statements {
 170                     print_trace(stmt, "", self.stack.len() + 1);
 171                     let mir::StatementKind::Assign(ref lvalue, ref rvalue) = stmt.kind;
 172                     let result = self.eval_assignment(lvalue, rvalue);
 173                     try!(self.maybe_report(stmt.span, result));
 174                 }
 175
 176                 let terminator = block_data.terminator();
 177                 print_trace(terminator, "", self.stack.len() + 1);
 178
 179                 let result = self.eval_terminator(terminator);
 180                 match try!(self.maybe_report(terminator.span, result)) {
 181                     TerminatorTarget::Block(block) => current_block = block,
 182                     TerminatorTarget::Return => {
 183                         self.pop_stack_frame();
 184                         self.name_stack.pop();
 185                         continue 'outer;
 186                     }
 187                     TerminatorTarget::Call => continue 'outer,
 188                 }
 189             }
 190         }
 191
 192         Ok(())
 193     }
 194
 195     fn push_stack_frame(&mut self, mir: CachedMir<'a, 'tcx>, substs: &'tcx Substs<'tcx>,
 196         return_ptr: Option<Pointer>)
 197     {
 198         self.substs_stack.push(substs);
 199
 200         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 201         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 202         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 203
 204         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 205             let size = self.ty_size(ty);
 206             self.memory.allocate(size)
 207         }).collect();
 208
 209         let num_args = mir.arg_decls.len();
 210         let num_vars = mir.var_decls.len();
 211
 212         self.stack.push(Frame {
 213             mir: mir.clone(),
 214             next_block: mir::START_BLOCK,
 215             return_ptr: return_ptr,
 216             locals: locals,
 217             var_offset: num_args,
 218             temp_offset: num_args + num_vars,
 219         });
 220     }
 221
 222     fn pop_stack_frame(&mut self) {
 223         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 224         // TODO(tsion): Deallocate local variables.
 225         self.substs_stack.pop();
 226     }
 227
 228     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 229             -> EvalResult<TerminatorTarget> {
 230         use rustc::mir::repr::TerminatorKind::*;
 231         let target = match terminator.kind {
 232             Return => TerminatorTarget::Return,
 233
 234             Goto { target } => TerminatorTarget::Block(target),
 235
 236             If { ref cond, targets: (then_target, else_target) } => {
 237                 let cond_ptr = try!(self.eval_operand(cond));
 238                 let cond_val = try!(self.memory.read_bool(cond_ptr));
 239                 TerminatorTarget::Block(if cond_val { then_target } else { else_target })
 240             }
 241
 242             SwitchInt { ref discr, ref values, ref targets, .. } => {
 243                 let discr_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 244                 let discr_size = self.lvalue_repr(discr).size();
 245                 let discr_val = try!(self.memory.read_uint(discr_ptr, discr_size));
 246
 247                 // Branch to the `otherwise` case by default, if no match is found.
 248                 let mut target_block = targets[targets.len() - 1];
 249
 250                 for (index, val_const) in values.iter().enumerate() {
 251                     let ptr = try!(self.const_to_ptr(val_const));
 252                     let val = try!(self.memory.read_uint(ptr, discr_size));
 253                     if discr_val == val {
 254                         target_block = targets[index];
 255                         break;
 256                     }
 257                 }
 258
 259                 TerminatorTarget::Block(target_block)
 260             }
 261
 262             Switch { ref discr, ref targets, adt_def } => {
 263                 let adt_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 264                 let adt_repr = self.lvalue_repr(discr);
 265                 let discr_size = match *adt_repr {
 266                     Repr::Aggregate { discr_size, .. } => discr_size,
 267                     _ => panic!("attmpted to switch on non-aggregate type"),
 268                 };
 269                 let discr_val = try!(self.memory.read_uint(adt_ptr, discr_size));
 270
 271                 let matching = adt_def.variants.iter()
 272                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 273
 274                 match matching {
 275                     Some(i) => TerminatorTarget::Block(targets[i]),
 276                     None => return Err(EvalError::InvalidDiscriminant),
 277                 }
 278             }
 279
 280             Call { ref func, ref args, ref destination, .. } => {
 281                 let mut return_ptr = None;
 282                 if let Some((ref lv, target)) = *destination {
 283                     self.frame_mut().next_block = target;
 284                     return_ptr = Some(try!(self.eval_lvalue(lv)).to_ptr());
 285                 }
 286
 287                 let func_ty = self.operand_ty(func);
 288                 match func_ty.sty {
 289                     ty::TyFnDef(def_id, substs, fn_ty) => {
 290                         use syntax::abi::Abi;
 291                         match fn_ty.abi {
 292                             Abi::RustIntrinsic => {
 293                                 let name = self.tcx.item_name(def_id).as_str();
 294                                 match fn_ty.sig.0.output {
 295                                     ty::FnConverging(ty) => {
 296                                         let size = self.ty_size(ty);
 297                                         try!(self.call_intrinsic(&name, substs, args,
 298                                             return_ptr.unwrap(), size))
 299                                     }
 300                                     ty::FnDiverging => unimplemented!(),
 301                                 }
 302                             }
 303
 304                             Abi::C =>
 305                                 try!(self.call_c_abi(def_id, args, return_ptr.unwrap())),
 306
 307                             Abi::Rust | Abi::RustCall => {
 308                                 // TODO(tsion): Adjust the first argument when calling a Fn or
 309                                 // FnMut closure via FnOnce::call_once.
 310
 311                                 // Only trait methods can have a Self parameter.
 312                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 313                                     self.trait_method(def_id, substs)
 314                                 } else {
 315                                     (def_id, substs)
 316                                 };
 317
 318                                 let mut arg_srcs = Vec::new();
 319                                 for arg in args {
 320                                     let (src, repr) = try!(self.eval_operand_and_repr(arg));
 321                                     arg_srcs.push((src, repr.size()));
 322                                 }
 323
 324                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 325                                     arg_srcs.pop();
 326                                     let last_arg = args.last().unwrap();
 327                                     let (last_src, last_repr) =
 328                                         try!(self.eval_operand_and_repr(last_arg));
 329                                     match *last_repr {
 330                                         Repr::Aggregate { discr_size: 0, ref variants, .. } => {
 331                                             assert_eq!(variants.len(), 1);
 332                                             for field in &variants[0] {
 333                                                 let src = last_src.offset(field.offset as isize);
 334                                                 arg_srcs.push((src, field.size));
 335                                             }
 336                                         }
 337
 338                                         _ => panic!("expected tuple as last argument in function with 'rust-call' ABI"),
 339                                     }
 340                                 }
 341
 342                                 let mir = self.load_mir(resolved_def_id);
 343                                 self.name_stack.push((def_id, substs, terminator.span));
 344                                 self.push_stack_frame(mir, resolved_substs, return_ptr);
 345
 346                                 for (i, (src, size)) in arg_srcs.into_iter().enumerate() {
 347                                     let dest = self.frame().locals[i];
 348                                     try!(self.memory.copy(src, dest, size));
 349                                 }
 350
 351                                 TerminatorTarget::Call
 352                             }
 353
 354                             abi => panic!("can't handle function with {:?} ABI", abi),
 355                         }
 356                     }
 357
 358                     _ => panic!("can't handle callee of type {:?}", func_ty),
 359                 }
 360             }
 361
 362             Drop { target, .. } => {
 363                 // TODO: Handle destructors and dynamic drop.
 364                 TerminatorTarget::Block(target)
 365             }
 366
 367             Resume => unimplemented!(),
 368         };
 369
 370         Ok(target)
 371     }
 372
 373     fn call_intrinsic(&mut self, name: &str, substs: &'tcx Substs<'tcx>,
 374         args: &[mir::Operand<'tcx>], dest: Pointer, dest_size: usize)
 375         -> EvalResult<TerminatorTarget>
 376     {
 377         match name {
 378             "assume" => {}
 379
 380             "copy_nonoverlapping" => {
 381                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 382                 let elem_size = self.ty_size(elem_ty);
 383
 384                 let src_arg   = try!(self.eval_operand(&args[0]));
 385                 let dest_arg  = try!(self.eval_operand(&args[1]));
 386                 let count_arg = try!(self.eval_operand(&args[2]));
 387
 388                 let src   = try!(self.memory.read_ptr(src_arg));
 389                 let dest  = try!(self.memory.read_ptr(dest_arg));
 390                 let count = try!(self.memory.read_isize(count_arg));
 391
 392                 try!(self.memory.copy(src, dest, count as usize * elem_size));
 393             }
 394
 395             // TODO(tsion): Mark as dropped?
 396             "forget" => {}
 397
 398             "min_align_of" => {
 399                 try!(self.memory.write_int(dest, 1, dest_size));
 400             }
 401
 402             "move_val_init" => {
 403                 let ty = *substs.types.get(subst::FnSpace, 0);
 404                 let size = self.ty_size(ty);
 405
 406                 let ptr_arg = try!(self.eval_operand(&args[0]));
 407                 let ptr = try!(self.memory.read_ptr(ptr_arg));
 408
 409                 let val = try!(self.eval_operand(&args[1]));
 410                 try!(self.memory.copy(val, ptr, size));
 411             }
 412
 413             // FIXME(tsion): Handle different integer types correctly.
 414             "mul_with_overflow" => {
 415                 let ty = *substs.types.get(subst::FnSpace, 0);
 416                 let size = self.ty_size(ty);
 417
 418                 let left_arg  = try!(self.eval_operand(&args[0]));
 419                 let right_arg = try!(self.eval_operand(&args[1]));
 420
 421                 let left = try!(self.memory.read_int(left_arg, size));
 422                 let right = try!(self.memory.read_int(right_arg, size));
 423
 424                 let (n, overflowed) = unsafe {
 425                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 426                 };
 427
 428                 try!(self.memory.write_int(dest, n, size));
 429                 try!(self.memory.write_bool(dest.offset(size as isize), overflowed));
 430             }
 431
 432             "offset" => {
 433                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 434                 let pointee_size = self.ty_size(pointee_ty) as isize;
 435
 436                 let ptr_arg    = try!(self.eval_operand(&args[0]));
 437                 let offset_arg = try!(self.eval_operand(&args[1]));
 438
 439                 let offset = try!(self.memory.read_isize(offset_arg));
 440
 441                 match self.memory.read_ptr(ptr_arg) {
 442                     Ok(ptr) => {
 443                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 444                         try!(self.memory.write_ptr(dest, result_ptr));
 445                     }
 446                     Err(EvalError::ReadBytesAsPointer) => {
 447                         let addr = try!(self.memory.read_isize(ptr_arg));
 448                         let result_addr = addr + offset * pointee_size as i64;
 449                         try!(self.memory.write_isize(dest, result_addr));
 450                     }
 451                     Err(e) => return Err(e),
 452                 }
 453             }
 454
 455             // FIXME(tsion): Handle different integer types correctly. Use primvals?
 456             "overflowing_sub" => {
 457                 let ty = *substs.types.get(subst::FnSpace, 0);
 458                 let size = self.ty_size(ty);
 459
 460                 let left_arg  = try!(self.eval_operand(&args[0]));
 461                 let right_arg = try!(self.eval_operand(&args[1]));
 462
 463                 let left = try!(self.memory.read_int(left_arg, size));
 464                 let right = try!(self.memory.read_int(right_arg, size));
 465
 466                 let n = left.wrapping_sub(right);
 467                 try!(self.memory.write_int(dest, n, size));
 468             }
 469
 470             "size_of" => {
 471                 let ty = *substs.types.get(subst::FnSpace, 0);
 472                 let size = self.ty_size(ty) as u64;
 473                 try!(self.memory.write_uint(dest, size, dest_size));
 474             }
 475
 476             "transmute" => {
 477                 let src = try!(self.eval_operand(&args[0]));
 478                 try!(self.memory.copy(src, dest, dest_size));
 479             }
 480
 481             "uninit" => {
 482                 try!(self.memory.mark_definedness(dest, dest_size, false));
 483             }
 484
 485             name => panic!("can't handle intrinsic: {}", name),
 486         }
 487
 488         // Since we pushed no stack frame, the main loop will act
 489         // as if the call just completed and it's returning to the
 490         // current frame.
 491         Ok(TerminatorTarget::Call)
 492     }
 493
 494     fn call_c_abi(&mut self, def_id: DefId, args: &[mir::Operand<'tcx>], dest: Pointer)
 495         -> EvalResult<TerminatorTarget>
 496     {
 497         let name = self.tcx.item_name(def_id);
 498         let attrs = self.tcx.get_attrs(def_id);
 499         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 500             Some(ln) => ln.clone(),
 501             None => name.as_str(),
 502         };
 503
 504         match &link_name[..] {
 505             "__rust_allocate" => {
 506                 let size_arg  = try!(self.eval_operand(&args[0]));
 507                 let _align_arg = try!(self.eval_operand(&args[1]));
 508                 let size = try!(self.memory.read_usize(size_arg));
 509                 let ptr = self.memory.allocate(size as usize);
 510                 try!(self.memory.write_ptr(dest, ptr));
 511             }
 512
 513             _ => panic!("can't call C ABI function: {}", link_name),
 514         }
 515
 516         // Since we pushed no stack frame, the main loop will act
 517         // as if the call just completed and it's returning to the
 518         // current frame.
 519         Ok(TerminatorTarget::Call)
 520     }
 521
 522     fn assign_to_aggregate(
 523         &mut self,
 524         dest: Pointer,
 525         dest_repr: &Repr,
 526         variant: usize,
 527         discr: Option<u64>,
 528         operands: &[mir::Operand<'tcx>],
 529     ) -> EvalResult<()> {
 530         match *dest_repr {
 531             Repr::Aggregate { discr_size, ref variants, .. } => {
 532                 if discr_size > 0 {
 533                     try!(self.memory.write_uint(dest, discr.unwrap(), discr_size));
 534                 }
 535                 let after_discr = dest.offset(discr_size as isize);
 536                 for (field, operand) in variants[variant].iter().zip(operands) {
 537                     let src = try!(self.eval_operand(operand));
 538                     let field_dest = after_discr.offset(field.offset as isize);
 539                     try!(self.memory.copy(src, field_dest, field.size));
 540                 }
 541             }
 542             _ => panic!("expected Repr::Aggregate target"),
 543         }
 544         Ok(())
 545     }
 546
 547     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 548         -> EvalResult<()>
 549     {
 550         let dest = try!(self.eval_lvalue(lvalue)).to_ptr();
 551         let dest_repr = self.lvalue_repr(lvalue);
 552
 553         use rustc::mir::repr::Rvalue::*;
 554         match *rvalue {
 555             Use(ref operand) => {
 556                 let src = try!(self.eval_operand(operand));
 557                 try!(self.memory.copy(src, dest, dest_repr.size()));
 558             }
 559
 560             BinaryOp(bin_op, ref left, ref right) => {
 561                 let left_ptr = try!(self.eval_operand(left));
 562                 let left_ty = self.operand_ty(left);
 563                 let left_val = try!(self.read_primval(left_ptr, left_ty));
 564
 565                 let right_ptr = try!(self.eval_operand(right));
 566                 let right_ty = self.operand_ty(right);
 567                 let right_val = try!(self.read_primval(right_ptr, right_ty));
 568
 569                 let val = try!(primval::binary_op(bin_op, left_val, right_val));
 570                 try!(self.memory.write_primval(dest, val));
 571             }
 572
 573             UnaryOp(un_op, ref operand) => {
 574                 let ptr = try!(self.eval_operand(operand));
 575                 let ty = self.operand_ty(operand);
 576                 let val = try!(self.read_primval(ptr, ty));
 577                 try!(self.memory.write_primval(dest, primval::unary_op(un_op, val)));
 578             }
 579
 580             Aggregate(ref kind, ref operands) => {
 581                 use rustc::mir::repr::AggregateKind::*;
 582                 match *kind {
 583                     Tuple | Closure(..) =>
 584                         try!(self.assign_to_aggregate(dest, &dest_repr, 0, None, operands)),
 585
 586                     Adt(adt_def, variant, _) => {
 587                         let discr = Some(adt_def.variants[variant].disr_val.to_u64_unchecked());
 588                         try!(self.assign_to_aggregate(dest, &dest_repr, variant, discr, operands));
 589                     }
 590
 591                     Vec => if let Repr::Array { elem_size, length } = *dest_repr {
 592                         assert_eq!(length, operands.len());
 593                         for (i, operand) in operands.iter().enumerate() {
 594                             let src = try!(self.eval_operand(operand));
 595                             let elem_dest = dest.offset((i * elem_size) as isize);
 596                             try!(self.memory.copy(src, elem_dest, elem_size));
 597                         }
 598                     } else {
 599                         panic!("expected Repr::Array target");
 600                     },
 601                 }
 602             }
 603
 604             Repeat(ref operand, _) => {
 605                 if let Repr::Array { elem_size, length } = *dest_repr {
 606                     let src = try!(self.eval_operand(operand));
 607                     for i in 0..length {
 608                         let elem_dest = dest.offset((i * elem_size) as isize);
 609                         try!(self.memory.copy(src, elem_dest, elem_size));
 610                     }
 611                 } else {
 612                     panic!("expected Repr::Array target");
 613                 }
 614             }
 615
 616             Len(ref lvalue) => {
 617                 let src = try!(self.eval_lvalue(lvalue));
 618                 let ty = self.lvalue_ty(lvalue);
 619                 let len = match ty.sty {
 620                     ty::TyArray(_, n) => n as u64,
 621                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
 622                         n
 623                     } else {
 624                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
 625                     },
 626                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
 627                 };
 628                 try!(self.memory.write_usize(dest, len));
 629             }
 630
 631             Ref(_, _, ref lvalue) => {
 632                 let lv = try!(self.eval_lvalue(lvalue));
 633                 try!(self.memory.write_ptr(dest, lv.ptr));
 634                 match lv.extra {
 635                     LvalueExtra::None => {},
 636                     LvalueExtra::Length(len) => {
 637                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
 638                         try!(self.memory.write_usize(len_ptr, len));
 639                     }
 640                 }
 641             }
 642
 643             Box(ty) => {
 644                 let size = self.ty_size(ty);
 645                 let ptr = self.memory.allocate(size);
 646                 try!(self.memory.write_ptr(dest, ptr));
 647             }
 648
 649             Cast(kind, ref operand, dest_ty) => {
 650                 let src = try!(self.eval_operand(operand));
 651                 let src_ty = self.operand_ty(operand);
 652
 653                 use rustc::mir::repr::CastKind::*;
 654                 match kind {
 655                     Unsize => {
 656                         try!(self.memory.copy(src, dest, 8));
 657                         let src_pointee_ty = pointee_type(src_ty).unwrap();
 658                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
 659
 660                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
 661                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
 662                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
 663                                 try!(self.memory.write_usize(len_ptr, length as u64));
 664                             }
 665
 666                             _ => panic!("can't handle cast: {:?}", rvalue),
 667                         }
 668                     }
 669
 670                     Misc => {
 671                         // FIXME(tsion): Wrong for almost everything.
 672                         let size = dest_repr.size();
 673                         try!(self.memory.copy(src, dest, size));
 674                     }
 675
 676                     _ => panic!("can't handle cast: {:?}", rvalue),
 677                 }
 678             }
 679
 680             Slice { .. } => unimplemented!(),
 681             InlineAsm { .. } => unimplemented!(),
 682         }
 683
 684         Ok(())
 685     }
 686
 687     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
 688         self.eval_operand_and_repr(op).map(|(p, _)| p)
 689     }
 690
 691     fn eval_operand_and_repr(&mut self, op: &mir::Operand<'tcx>)
 692         -> EvalResult<(Pointer, &'arena Repr)>
 693     {
 694         use rustc::mir::repr::Operand::*;
 695         match *op {
 696             Consume(ref lvalue) =>
 697                 Ok((try!(self.eval_lvalue(lvalue)).to_ptr(), self.lvalue_repr(lvalue))),
 698             Constant(mir::Constant { ref literal, ty, .. }) => {
 699                 use rustc::mir::repr::Literal::*;
 700                 match *literal {
 701                     Value { ref value } => Ok((
 702                         try!(self.const_to_ptr(value)),
 703                         self.ty_to_repr(ty),
 704                     )),
 705                     Item { .. } => unimplemented!(),
 706                 }
 707             }
 708         }
 709     }
 710
 711     // TODO(tsion): Replace this inefficient hack with a wrapper like LvalueTy (e.g. LvalueRepr).
 712     fn lvalue_repr(&self, lvalue: &mir::Lvalue<'tcx>) -> &'arena Repr {
 713         use rustc::mir::tcx::LvalueTy;
 714         match self.mir().lvalue_ty(self.tcx, lvalue) {
 715             LvalueTy::Ty { ty } => self.ty_to_repr(ty),
 716             LvalueTy::Downcast { adt_def, substs, variant_index } => {
 717                 let field_tys = adt_def.variants[variant_index].fields.iter()
 718                     .map(|f| f.ty(self.tcx, substs));
 719                 self.repr_arena.alloc(self.make_aggregate_repr(iter::once(field_tys)))
 720             }
 721         }
 722     }
 723
 724     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
 725         use rustc::mir::repr::Lvalue::*;
 726         let ptr = match *lvalue {
 727             ReturnPointer => self.frame().return_ptr
 728                 .expect("ReturnPointer used in a function with no return value"),
 729             Arg(i) => self.frame().locals[i as usize],
 730             Var(i) => self.frame().locals[self.frame().var_offset + i as usize],
 731             Temp(i) => self.frame().locals[self.frame().temp_offset + i as usize],
 732
 733             Static(_def_id) => unimplemented!(),
 734
 735             Projection(ref proj) => {
 736                 let base_ptr = try!(self.eval_lvalue(&proj.base)).to_ptr();
 737                 let base_repr = self.lvalue_repr(&proj.base);
 738                 let base_ty = self.lvalue_ty(&proj.base);
 739                 use rustc::mir::repr::ProjectionElem::*;
 740                 match proj.elem {
 741                     Field(field, _) => match *base_repr {
 742                         Repr::Aggregate { discr_size: 0, ref variants, .. } => {
 743                             let fields = &variants[0];
 744                             base_ptr.offset(fields[field.index()].offset as isize)
 745                         }
 746                         _ => panic!("field access on non-product type: {:?}", base_repr),
 747                     },
 748
 749                     Downcast(..) => match *base_repr {
 750                         Repr::Aggregate { discr_size, .. } => base_ptr.offset(discr_size as isize),
 751                         _ => panic!("variant downcast on non-aggregate type: {:?}", base_repr),
 752                     },
 753
 754                     Deref => {
 755                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
 756                         let ptr = try!(self.memory.read_ptr(base_ptr));
 757                         let extra = match pointee_ty.sty {
 758                             ty::TySlice(_) | ty::TyStr => {
 759                                 let len_ptr = base_ptr.offset(self.memory.pointer_size as isize);
 760                                 let len = try!(self.memory.read_usize(len_ptr));
 761                                 LvalueExtra::Length(len)
 762                             }
 763                             ty::TyTrait(_) => unimplemented!(),
 764                             _ => LvalueExtra::None,
 765                         };
 766                         return Ok(Lvalue { ptr: ptr, extra: extra });
 767                     }
 768
 769                     Index(ref operand) => {
 770                         let elem_size = match base_ty.sty {
 771                             ty::TyArray(elem_ty, _) => self.ty_size(elem_ty),
 772                             ty::TySlice(elem_ty) => self.ty_size(elem_ty),
 773                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
 774                         };
 775                         let n_ptr = try!(self.eval_operand(operand));
 776                         let n = try!(self.memory.read_usize(n_ptr));
 777                         base_ptr.offset(n as isize * elem_size as isize)
 778                     }
 779
 780                     ConstantIndex { .. } => unimplemented!(),
 781                 }
 782             }
 783         };
 784
 785         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
 786     }
 787
 788     // TODO(tsion): Try making const_to_primval instead.
 789     fn const_to_ptr(&mut self, const_val: &const_eval::ConstVal) -> EvalResult<Pointer> {
 790         use rustc::middle::const_eval::ConstVal::*;
 791         match *const_val {
 792             Float(_f) => unimplemented!(),
 793             Integral(int) => {
 794                 // TODO(tsion): Check int constant type.
 795                 let ptr = self.memory.allocate(8);
 796                 try!(self.memory.write_uint(ptr, int.to_u64_unchecked(), 8));
 797                 Ok(ptr)
 798             }
 799             Str(ref s) => {
 800                 let psize = self.memory.pointer_size;
 801                 let static_ptr = self.memory.allocate(s.len());
 802                 let ptr = self.memory.allocate(psize * 2);
 803                 try!(self.memory.write_bytes(static_ptr, s.as_bytes()));
 804                 try!(self.memory.write_ptr(ptr, static_ptr));
 805                 try!(self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64));
 806                 Ok(ptr)
 807             }
 808             ByteStr(ref bs) => {
 809                 let psize = self.memory.pointer_size;
 810                 let static_ptr = self.memory.allocate(bs.len());
 811                 let ptr = self.memory.allocate(psize);
 812                 try!(self.memory.write_bytes(static_ptr, bs));
 813                 try!(self.memory.write_ptr(ptr, static_ptr));
 814                 Ok(ptr)
 815             }
 816             Bool(b) => {
 817                 let ptr = self.memory.allocate(1);
 818                 try!(self.memory.write_bool(ptr, b));
 819                 Ok(ptr)
 820             }
 821             Char(_c)          => unimplemented!(),
 822             Struct(_node_id)  => unimplemented!(),
 823             Tuple(_node_id)   => unimplemented!(),
 824             Function(_def_id) => unimplemented!(),
 825             Array(_, _)       => unimplemented!(),
 826             Repeat(_, _)      => unimplemented!(),
 827             Dummy             => unimplemented!(),
 828         }
 829     }
 830
 831     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> ty::Ty<'tcx> {
 832         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx))
 833     }
 834
 835     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> ty::Ty<'tcx> {
 836         self.monomorphize(self.mir().operand_ty(self.tcx, operand))
 837     }
 838
 839     fn monomorphize(&self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
 840         let substituted = ty.subst(self.tcx, self.substs());
 841         infer::normalize_associated_type(self.tcx, &substituted)
 842     }
 843
 844     fn type_is_sized(&self, ty: ty::Ty<'tcx>) -> bool {
 845         ty.is_sized(&self.tcx.empty_parameter_environment(), DUMMY_SP)
 846     }
 847
 848     fn ty_size(&self, ty: ty::Ty<'tcx>) -> usize {
 849         self.ty_to_repr(ty).size()
 850     }
 851
 852     fn ty_to_repr(&self, ty: ty::Ty<'tcx>) -> &'arena Repr {
 853         let ty = self.monomorphize(ty);
 854
 855         if let Some(repr) = self.repr_cache.borrow().get(ty) {
 856             return repr;
 857         }
 858
 859         use syntax::ast::{IntTy, UintTy};
 860         let repr = match ty.sty {
 861             ty::TyBool => Repr::Primitive { size: 1 },
 862
 863             ty::TyInt(IntTy::I8)  | ty::TyUint(UintTy::U8)  => Repr::Primitive { size: 1 },
 864             ty::TyInt(IntTy::I16) | ty::TyUint(UintTy::U16) => Repr::Primitive { size: 2 },
 865             ty::TyInt(IntTy::I32) | ty::TyUint(UintTy::U32) => Repr::Primitive { size: 4 },
 866             ty::TyInt(IntTy::I64) | ty::TyUint(UintTy::U64) => Repr::Primitive { size: 8 },
 867
 868             ty::TyInt(IntTy::Is) | ty::TyUint(UintTy::Us) =>
 869                 Repr::Primitive { size: self.memory.pointer_size },
 870
 871             ty::TyTuple(ref fields) =>
 872                 self.make_aggregate_repr(iter::once(fields.iter().cloned())),
 873
 874             ty::TyEnum(adt_def, substs) | ty::TyStruct(adt_def, substs) => {
 875                 let variants = adt_def.variants.iter().map(|v| {
 876                     v.fields.iter().map(|f| f.ty(self.tcx, substs))
 877                 });
 878                 self.make_aggregate_repr(variants)
 879             }
 880
 881             ty::TyArray(elem_ty, length) => Repr::Array {
 882                 elem_size: self.ty_size(elem_ty),
 883                 length: length,
 884             },
 885
 886             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
 887             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
 888             ty::TyBox(ty) => {
 889                 if self.type_is_sized(ty) {
 890                     Repr::Primitive { size: self.memory.pointer_size }
 891                 } else {
 892                     Repr::Primitive { size: self.memory.pointer_size * 2 }
 893                 }
 894             }
 895
 896             ty::TyFnPtr(..) => Repr::Primitive { size: self.memory.pointer_size },
 897
 898             ty::TyClosure(_, ref closure_substs) =>
 899                 self.make_aggregate_repr(iter::once(closure_substs.upvar_tys.iter().cloned())),
 900
 901             ref t => panic!("can't convert type to repr: {:?}", t),
 902         };
 903
 904         let repr_ref = self.repr_arena.alloc(repr);
 905         self.repr_cache.borrow_mut().insert(ty, repr_ref);
 906         repr_ref
 907     }
 908
 909     fn make_aggregate_repr<V>(&self, variant_fields: V) -> Repr
 910         where V: IntoIterator, V::Item: IntoIterator<Item = ty::Ty<'tcx>>
 911     {
 912         let mut variants = Vec::new();
 913         let mut max_variant_size = 0;
 914
 915         for field_tys in variant_fields {
 916             let mut fields = Vec::new();
 917             let mut size = 0;
 918
 919             for ty in field_tys {
 920                 let field_size = self.ty_size(ty);
 921                 let offest = size;
 922                 size += field_size;
 923                 fields.push(FieldRepr { offset: offest, size: field_size });
 924             }
 925
 926             if size > max_variant_size { max_variant_size = size; }
 927             variants.push(fields);
 928         }
 929
 930         let discr_size = match variants.len() {
 931             n if n <= 1       => 0,
 932             n if n <= 1 << 8  => 1,
 933             n if n <= 1 << 16 => 2,
 934             n if n <= 1 << 32 => 4,
 935             _                 => 8,
 936         };
 937         Repr::Aggregate {
 938             discr_size: discr_size,
 939             size: max_variant_size + discr_size,
 940             variants: variants,
 941         }
 942     }
 943
 944     pub fn read_primval(&mut self, ptr: Pointer, ty: ty::Ty<'tcx>) -> EvalResult<PrimVal> {
 945         use syntax::ast::{IntTy, UintTy};
 946         let val = match ty.sty {
 947             ty::TyBool              => PrimVal::Bool(try!(self.memory.read_bool(ptr))),
 948             ty::TyInt(IntTy::I8)    => PrimVal::I8(try!(self.memory.read_int(ptr, 1)) as i8),
 949             ty::TyInt(IntTy::I16)   => PrimVal::I16(try!(self.memory.read_int(ptr, 2)) as i16),
 950             ty::TyInt(IntTy::I32)   => PrimVal::I32(try!(self.memory.read_int(ptr, 4)) as i32),
 951             ty::TyInt(IntTy::I64)   => PrimVal::I64(try!(self.memory.read_int(ptr, 8)) as i64),
 952             ty::TyUint(UintTy::U8)  => PrimVal::U8(try!(self.memory.read_uint(ptr, 1)) as u8),
 953             ty::TyUint(UintTy::U16) => PrimVal::U16(try!(self.memory.read_uint(ptr, 2)) as u16),
 954             ty::TyUint(UintTy::U32) => PrimVal::U32(try!(self.memory.read_uint(ptr, 4)) as u32),
 955             ty::TyUint(UintTy::U64) => PrimVal::U64(try!(self.memory.read_uint(ptr, 8)) as u64),
 956
 957             // TODO(tsion): Pick the PrimVal dynamically.
 958             ty::TyInt(IntTy::Is)   => PrimVal::I64(try!(self.memory.read_isize(ptr))),
 959             ty::TyUint(UintTy::Us) => PrimVal::U64(try!(self.memory.read_usize(ptr))),
 960
 961             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
 962             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) => {
 963                 if self.type_is_sized(ty) {
 964                     match self.memory.read_ptr(ptr) {
 965                         Ok(p) => PrimVal::AbstractPtr(p),
 966                         Err(EvalError::ReadBytesAsPointer) => {
 967                             let n = try!(self.memory.read_usize(ptr));
 968                             PrimVal::IntegerPtr(n)
 969                         }
 970                         Err(e) => return Err(e),
 971                     }
 972                 } else {
 973                     panic!("unimplemented: primitive read of fat pointer type: {:?}", ty);
 974                 }
 975             }
 976
 977             _ => panic!("primitive read of non-primitive type: {:?}", ty),
 978         };
 979         Ok(val)
 980     }
 981
 982     fn frame(&self) -> &Frame<'a, 'tcx> {
 983         self.stack.last().expect("no call frames exist")
 984     }
 985
 986     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
 987         self.stack.last_mut().expect("no call frames exist")
 988     }
 989
 990     fn mir(&self) -> &mir::Mir<'tcx> {
 991         &self.frame().mir
 992     }
 993
 994     fn substs(&self) -> &'tcx Substs<'tcx> {
 995         self.substs_stack.last().cloned().unwrap_or_else(|| self.tcx.mk_substs(Substs::empty()))
 996     }
 997
 998     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
 999         match self.tcx.map.as_local_node_id(def_id) {
1000             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
1001             None => {
1002                 let mut mir_cache = self.mir_cache.borrow_mut();
1003                 if let Some(mir) = mir_cache.get(&def_id) {
1004                     return CachedMir::Owned(mir.clone());
1005                 }
1006
1007                 use rustc::middle::cstore::CrateStore;
1008                 let cs = &self.tcx.sess.cstore;
1009                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
1010                     panic!("no mir for {:?}", def_id);
1011                 });
1012                 let cached = Rc::new(mir);
1013                 mir_cache.insert(def_id, cached.clone());
1014                 CachedMir::Owned(cached)
1015             }
1016         }
1017     }
1018
1019     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
1020         // Do the initial selection for the obligation. This yields the shallow result we are
1021         // looking for -- that is, what specific impl.
1022         let infcx = infer::normalizing_infer_ctxt(self.tcx, &self.tcx.tables, ProjectionMode::Any);
1023         let mut selcx = traits::SelectionContext::new(&infcx);
1024
1025         let obligation = traits::Obligation::new(
1026             traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
1027             trait_ref.to_poly_trait_predicate(),
1028         );
1029         let selection = selcx.select(&obligation).unwrap().unwrap();
1030
1031         // Currently, we use a fulfillment context to completely resolve all nested obligations.
1032         // This is because they can inform the inference of the impl's type parameters.
1033         let mut fulfill_cx = traits::FulfillmentContext::new();
1034         let vtable = selection.map(|predicate| {
1035             fulfill_cx.register_predicate_obligation(&infcx, predicate);
1036         });
1037         let vtable = infer::drain_fulfillment_cx_or_panic(
1038             DUMMY_SP, &infcx, &mut fulfill_cx, &vtable
1039         );
1040
1041         vtable
1042     }
1043
1044     /// Trait method, which has to be resolved to an impl method.
1045     pub fn trait_method(&self, def_id: DefId, substs: &'tcx Substs<'tcx>)
1046         -> (DefId, &'tcx Substs<'tcx>)
1047     {
1048         let method_item = self.tcx.impl_or_trait_item(def_id);
1049         let trait_id = method_item.container().id();
1050         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
1051         match self.fulfill_obligation(trait_ref) {
1052             traits::VtableImpl(vtable_impl) => {
1053                 let impl_did = vtable_impl.impl_def_id;
1054                 let mname = self.tcx.item_name(def_id);
1055                 // Create a concatenated set of substitutions which includes those from the impl
1056                 // and those from the method:
1057                 let impl_substs = vtable_impl.substs.with_method_from(substs);
1058                 let substs = self.tcx.mk_substs(impl_substs);
1059                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
1060
1061                 (mth.method.def_id, mth.substs)
1062             }
1063
1064             traits::VtableClosure(vtable_closure) =>
1065                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
1066
1067             traits::VtableFnPointer(_fn_ty) => {
1068                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
1069                 unimplemented!()
1070                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
1071
1072                 // let method_ty = def_ty(tcx, def_id, substs);
1073                 // let fn_ptr_ty = match method_ty.sty {
1074                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
1075                 //     _ => unreachable!("expected fn item type, found {}",
1076                 //                       method_ty)
1077                 // };
1078                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
1079             }
1080
1081             traits::VtableObject(ref _data) => {
1082                 unimplemented!()
1083                 // Callee {
1084                 //     data: Virtual(traits::get_vtable_index_of_object_method(
1085                 //                   tcx, data, def_id)),
1086                 //                   ty: def_ty(tcx, def_id, substs)
1087                 // }
1088             }
1089             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
1090         }
1091     }
1092 }
1093
1094 fn pointee_type<'tcx>(ptr_ty: ty::Ty<'tcx>) -> Option<ty::Ty<'tcx>> {
1095     match ptr_ty.sty {
1096         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1097         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1098         ty::TyBox(ty) => {
1099             Some(ty)
1100         }
1101         _ => None,
1102     }
1103 }
1104
1105 impl Lvalue {
1106     fn to_ptr(self) -> Pointer {
1107         assert_eq!(self.extra, LvalueExtra::None);
1108         self.ptr
1109     }
1110 }
1111
1112 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1113     type Target = mir::Mir<'tcx>;
1114     fn deref(&self) -> &mir::Mir<'tcx> {
1115         match *self {
1116             CachedMir::Ref(r) => r,
1117             CachedMir::Owned(ref rc) => &rc,
1118         }
1119     }
1120 }
1121
1122 #[derive(Debug)]
1123 pub struct ImplMethod<'tcx> {
1124     pub method: Rc<ty::Method<'tcx>>,
1125     pub substs: &'tcx Substs<'tcx>,
1126     pub is_provided: bool,
1127 }
1128
1129 /// Locates the applicable definition of a method, given its name.
1130 pub fn get_impl_method<'tcx>(
1131     tcx: &TyCtxt<'tcx>,
1132     impl_def_id: DefId,
1133     substs: &'tcx Substs<'tcx>,
1134     name: ast::Name,
1135 ) -> ImplMethod<'tcx> {
1136     assert!(!substs.types.needs_infer());
1137
1138     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1139     let trait_def = tcx.lookup_trait_def(trait_def_id);
1140     let infcx = infer::normalizing_infer_ctxt(tcx, &tcx.tables, ProjectionMode::Any);
1141
1142     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1143         Some(node_item) => {
1144             ImplMethod {
1145                 method: node_item.item,
1146                 substs: traits::translate_substs(&infcx, impl_def_id, substs, node_item.node),
1147                 is_provided: node_item.node.is_from_trait(),
1148             }
1149         }
1150         None => {
1151             tcx.sess.bug(&format!("method {:?} not found in {:?}", name, impl_def_id))
1152         }
1153     }
1154 }
1155
1156 pub fn interpret_start_points<'tcx>(tcx: &TyCtxt<'tcx>, mir_map: &MirMap<'tcx>) {
1157     /// Print the given allocation and all allocations it depends on.
1158     fn print_allocation_tree(memory: &Memory, alloc_id: memory::AllocId) {
1159         let alloc = memory.get(alloc_id).unwrap();
1160         println!("  {:?}: {:?}", alloc_id, alloc);
1161         for &target_alloc in alloc.relocations.values() {
1162             print_allocation_tree(memory, target_alloc);
1163         }
1164     }
1165
1166     for (&id, mir) in &mir_map.map {
1167         for attr in tcx.map.attrs(id) {
1168             use syntax::attr::AttrMetaMethods;
1169             if attr.check_name("miri_run") {
1170                 let item = tcx.map.expect_item(id);
1171
1172                 println!("Interpreting: {}", item.name);
1173
1174                 let repr_arena = TypedArena::new();
1175                 let mut miri = Interpreter::new(tcx, mir_map, &repr_arena);
1176                 let return_ptr = match mir.return_ty {
1177                     ty::FnConverging(ty) => {
1178                         let size = miri.ty_size(ty);
1179                         Some(miri.memory.allocate(size))
1180                     }
1181                     ty::FnDiverging => None,
1182                 };
1183                 let substs = miri.tcx.mk_substs(Substs::empty());
1184                 miri.push_stack_frame(CachedMir::Ref(mir), substs, return_ptr);
1185                 if let Err(e) = miri.run() {
1186                     tcx.sess.err(&e.to_string());
1187                 }
1188                 tcx.sess.abort_if_errors();
1189
1190                 if let Some(ret) = return_ptr {
1191                     println!("Result:");
1192                     print_allocation_tree(&miri.memory, ret.alloc_id);
1193                     println!("");
1194                 }
1195             }
1196         }
1197     }
1198 }