src/interpreter.rs

   1 use rustc::infer;
   2 use rustc::middle::const_val;
   3 use rustc::hir::def_id::DefId;
   4 use rustc::mir::mir_map::MirMap;
   5 use rustc::mir::repr as mir;
   6 use rustc::traits::{self, ProjectionMode};
   7 use rustc::ty::fold::TypeFoldable;
   8 use rustc::ty::layout::{self, Layout, Size};
   9 use rustc::ty::subst::{self, Subst, Substs};
  10 use rustc::ty::{self, TyCtxt};
  11 use rustc::util::nodemap::DefIdMap;
  12 use std::cell::RefCell;
  13 use std::ops::Deref;
  14 use std::rc::Rc;
  15 use std::{iter, mem};
  16 use syntax::ast;
  17 use syntax::attr;
  18 use syntax::codemap::{self, DUMMY_SP};
  19
  20 use error::{EvalError, EvalResult};
  21 use memory::{Memory, Pointer};
  22 use primval::{self, PrimVal};
  23
  24 const TRACE_EXECUTION: bool = false;
  25
  26 struct Interpreter<'a, 'tcx: 'a> {
  27     /// The results of the type checker, from rustc.
  28     tcx: &'a TyCtxt<'tcx>,
  29
  30     /// A mapping from NodeIds to Mir, from rustc. Only contains MIR for crate-local items.
  31     mir_map: &'a MirMap<'tcx>,
  32
  33     /// A local cache from DefIds to Mir for non-crate-local items.
  34     mir_cache: RefCell<DefIdMap<Rc<mir::Mir<'tcx>>>>,
  35
  36     /// The virtual memory system.
  37     memory: Memory,
  38
  39     /// The virtual call stack.
  40     stack: Vec<Frame<'a, 'tcx>>,
  41
  42     /// Another stack containing the type substitutions for the current function invocation. It
  43     /// exists separately from `stack` because it must contain the `Substs` for a function while
  44     /// *creating* the `Frame` for that same function.
  45     substs_stack: Vec<&'tcx Substs<'tcx>>,
  46
  47     // TODO(tsion): Merge with `substs_stack`. Also try restructuring `Frame` to accomodate.
  48     /// A stack of the things necessary to print good strack traces:
  49     ///   * Function DefIds and Substs to print proper substituted function names.
  50     ///   * Spans pointing to specific function calls in the source.
  51     name_stack: Vec<(DefId, &'tcx Substs<'tcx>, codemap::Span)>,
  52 }
  53
  54 /// A stack frame.
  55 struct Frame<'a, 'tcx: 'a> {
  56     /// The MIR for the function called on this frame.
  57     mir: CachedMir<'a, 'tcx>,
  58
  59     /// The block this frame will execute when a function call returns back to this frame.
  60     next_block: mir::BasicBlock,
  61
  62     /// A pointer for writing the return value of the current call if it's not a diverging call.
  63     return_ptr: Option<Pointer>,
  64
  65     /// The list of locals for the current function, stored in order as
  66     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  67     /// and the temporaries at `self.temp_offset`.
  68     locals: Vec<Pointer>,
  69
  70     /// The offset of the first variable in `self.locals`.
  71     var_offset: usize,
  72
  73     /// The offset of the first temporary in `self.locals`.
  74     temp_offset: usize,
  75 }
  76
  77 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  78 struct Lvalue {
  79     ptr: Pointer,
  80     extra: LvalueExtra,
  81 }
  82
  83 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  84 enum LvalueExtra {
  85     None,
  86     Length(u64),
  87     // TODO(tsion): Vtable(memory::AllocId),
  88     DowncastVariant(usize),
  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> Interpreter<'a, 'tcx> {
 110     fn new(tcx: &'a TyCtxt<'tcx>, mir_map: &'a MirMap<'tcx>) -> Self {
 111         Interpreter {
 112             tcx: tcx,
 113             mir_map: mir_map,
 114             mir_cache: RefCell::new(DefIdMap()),
 115             memory: Memory::new(),
 116             stack: Vec::new(),
 117             substs_stack: Vec::new(),
 118             name_stack: Vec::new(),
 119         }
 120     }
 121
 122     fn maybe_report<T>(&self, span: codemap::Span, r: EvalResult<T>) -> EvalResult<T> {
 123         if let Err(ref e) = r {
 124             let mut err = self.tcx.sess.struct_span_err(span, &e.to_string());
 125             for &(def_id, substs, span) in self.name_stack.iter().rev() {
 126                 // FIXME(tsion): Find a way to do this without this Display impl hack.
 127                 use rustc::util::ppaux;
 128                 use std::fmt;
 129                 struct Instance<'tcx>(DefId, &'tcx Substs<'tcx>);
 130                 impl<'tcx> fmt::Display for Instance<'tcx> {
 131                     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 132                         ppaux::parameterized(f, self.1, self.0, ppaux::Ns::Value, &[],
 133                             |tcx| tcx.lookup_item_type(self.0).generics)
 134                     }
 135                 }
 136                 err.span_note(span, &format!("inside call to {}", Instance(def_id, substs)));
 137             }
 138             err.emit();
 139         }
 140         r
 141     }
 142
 143     fn log<F>(&self, extra_indent: usize, f: F) where F: FnOnce() {
 144         let indent = self.stack.len() + extra_indent;
 145         if !TRACE_EXECUTION { return; }
 146         for _ in 0..indent { print!("    "); }
 147         f();
 148         println!("");
 149     }
 150
 151     fn run(&mut self) -> EvalResult<()> {
 152         'outer: while !self.stack.is_empty() {
 153             let mut current_block = self.frame().next_block;
 154
 155             loop {
 156                 self.log(0, || print!("// {:?}", current_block));
 157                 let current_mir = self.mir().clone(); // Cloning a reference.
 158                 let block_data = current_mir.basic_block_data(current_block);
 159
 160                 for stmt in &block_data.statements {
 161                     self.log(0, || print!("{:?}", stmt));
 162                     let mir::StatementKind::Assign(ref lvalue, ref rvalue) = stmt.kind;
 163                     let result = self.eval_assignment(lvalue, rvalue);
 164                     try!(self.maybe_report(stmt.span, result));
 165                 }
 166
 167                 let terminator = block_data.terminator();
 168                 self.log(0, || print!("{:?}", terminator.kind));
 169
 170                 let result = self.eval_terminator(terminator);
 171                 match try!(self.maybe_report(terminator.span, result)) {
 172                     TerminatorTarget::Block(block) => current_block = block,
 173                     TerminatorTarget::Return => {
 174                         self.pop_stack_frame();
 175                         self.name_stack.pop();
 176                         continue 'outer;
 177                     }
 178                     TerminatorTarget::Call => continue 'outer,
 179                 }
 180             }
 181         }
 182
 183         Ok(())
 184     }
 185
 186     fn push_stack_frame(&mut self, mir: CachedMir<'a, 'tcx>, substs: &'tcx Substs<'tcx>,
 187         return_ptr: Option<Pointer>)
 188     {
 189         self.substs_stack.push(substs);
 190
 191         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 192         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 193         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 194
 195         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 196             let size = self.type_size(ty);
 197             self.memory.allocate(size)
 198         }).collect();
 199
 200         let num_args = mir.arg_decls.len();
 201         let num_vars = mir.var_decls.len();
 202
 203         self.stack.push(Frame {
 204             mir: mir.clone(),
 205             next_block: mir::START_BLOCK,
 206             return_ptr: return_ptr,
 207             locals: locals,
 208             var_offset: num_args,
 209             temp_offset: num_args + num_vars,
 210         });
 211     }
 212
 213     fn pop_stack_frame(&mut self) {
 214         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 215         // TODO(tsion): Deallocate local variables.
 216         self.substs_stack.pop();
 217     }
 218
 219     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 220             -> EvalResult<TerminatorTarget> {
 221         use rustc::mir::repr::TerminatorKind::*;
 222         let target = match terminator.kind {
 223             Return => TerminatorTarget::Return,
 224
 225             Goto { target } => TerminatorTarget::Block(target),
 226
 227             If { ref cond, targets: (then_target, else_target) } => {
 228                 let cond_ptr = try!(self.eval_operand(cond));
 229                 let cond_val = try!(self.memory.read_bool(cond_ptr));
 230                 TerminatorTarget::Block(if cond_val { then_target } else { else_target })
 231             }
 232
 233             SwitchInt { ref discr, ref values, ref targets, .. } => {
 234                 let discr_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 235                 let discr_size = self
 236                     .type_layout(self.lvalue_ty(discr))
 237                     .size(&self.tcx.data_layout)
 238                     .bytes() as usize;
 239                 let discr_val = try!(self.memory.read_uint(discr_ptr, discr_size));
 240
 241                 // Branch to the `otherwise` case by default, if no match is found.
 242                 let mut target_block = targets[targets.len() - 1];
 243
 244                 for (index, val_const) in values.iter().enumerate() {
 245                     let ptr = try!(self.const_to_ptr(val_const));
 246                     let val = try!(self.memory.read_uint(ptr, discr_size));
 247                     if discr_val == val {
 248                         target_block = targets[index];
 249                         break;
 250                     }
 251                 }
 252
 253                 TerminatorTarget::Block(target_block)
 254             }
 255
 256             Switch { ref discr, ref targets, adt_def } => {
 257                 let adt_ptr = try!(self.eval_lvalue(discr)).to_ptr();
 258                 let adt_layout = self.type_layout(self.lvalue_ty(discr));
 259
 260                  match *adt_layout {
 261                     Layout::General { discr, .. } | Layout::CEnum { discr, .. } => {
 262                         let discr_size = discr.size().bytes();
 263                         let discr_val = try!(self.memory.read_uint(adt_ptr, discr_size as usize));
 264
 265                         let matching = adt_def.variants.iter()
 266                             .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 267
 268                         match matching {
 269                             Some(i) => TerminatorTarget::Block(targets[i]),
 270                             None => return Err(EvalError::InvalidDiscriminant),
 271                         }
 272                     }
 273
 274                     Layout::RawNullablePointer { nndiscr, .. } => {
 275                         let is_null = match self.memory.read_usize(adt_ptr) {
 276                             Ok(0) => true,
 277                             Ok(_) | Err(EvalError::ReadPointerAsBytes) => false,
 278                             Err(e) => return Err(e),
 279                         };
 280
 281                         assert!(nndiscr == 0 || nndiscr == 1);
 282                         let target = if is_null { 1 - nndiscr } else { nndiscr };
 283                         TerminatorTarget::Block(targets[target as usize])
 284                     }
 285
 286                     _ => panic!("attempted to switch on non-aggregate type"),
 287                 }
 288             }
 289
 290             Call { ref func, ref args, ref destination, .. } => {
 291                 let mut return_ptr = None;
 292                 if let Some((ref lv, target)) = *destination {
 293                     self.frame_mut().next_block = target;
 294                     return_ptr = Some(try!(self.eval_lvalue(lv)).to_ptr());
 295                 }
 296
 297                 let func_ty = self.operand_ty(func);
 298                 match func_ty.sty {
 299                     ty::TyFnDef(def_id, substs, fn_ty) => {
 300                         use syntax::abi::Abi;
 301                         match fn_ty.abi {
 302                             Abi::RustIntrinsic => {
 303                                 let name = self.tcx.item_name(def_id).as_str();
 304                                 match fn_ty.sig.0.output {
 305                                     ty::FnConverging(ty) => {
 306                                         let size = self.type_size(ty);
 307                                         try!(self.call_intrinsic(&name, substs, args,
 308                                             return_ptr.unwrap(), size))
 309                                     }
 310                                     ty::FnDiverging => unimplemented!(),
 311                                 }
 312                             }
 313
 314                             Abi::C =>
 315                                 try!(self.call_c_abi(def_id, args, return_ptr.unwrap())),
 316
 317                             Abi::Rust | Abi::RustCall => {
 318                                 // TODO(tsion): Adjust the first argument when calling a Fn or
 319                                 // FnMut closure via FnOnce::call_once.
 320
 321                                 // Only trait methods can have a Self parameter.
 322                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 323                                     self.trait_method(def_id, substs)
 324                                 } else {
 325                                     (def_id, substs)
 326                                 };
 327
 328                                 let mut arg_srcs = Vec::new();
 329                                 for arg in args {
 330                                     let src = try!(self.eval_operand(arg));
 331                                     let src_ty = self.operand_ty(arg);
 332                                     arg_srcs.push((src, src_ty));
 333                                 }
 334
 335                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 336                                     arg_srcs.pop();
 337                                     let last_arg = args.last().unwrap();
 338                                     let last = try!(self.eval_operand(last_arg));
 339                                     let last_ty = self.operand_ty(last_arg);
 340                                     let last_layout = self.type_layout(last_ty);
 341                                     match (&last_ty.sty, last_layout) {
 342                                         (&ty::TyTuple(ref fields),
 343                                          &Layout::Univariant { ref variant, .. }) => {
 344                                             let offsets = iter::once(0)
 345                                                 .chain(variant.offset_after_field.iter()
 346                                                     .map(|s| s.bytes()));
 347                                             for (offset, ty) in offsets.zip(fields) {
 348                                                 let src = last.offset(offset as isize);
 349                                                 arg_srcs.push((src, ty));
 350                                             }
 351                                         }
 352                                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 353                                     }
 354                                 }
 355
 356                                 let mir = self.load_mir(resolved_def_id);
 357                                 self.name_stack.push((def_id, substs, terminator.span));
 358                                 self.push_stack_frame(mir, resolved_substs, return_ptr);
 359
 360                                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 361                                     let dest = self.frame().locals[i];
 362                                     try!(self.move_(src, dest, src_ty));
 363                                 }
 364
 365                                 TerminatorTarget::Call
 366                             }
 367
 368                             abi => panic!("can't handle function with {:?} ABI", abi),
 369                         }
 370                     }
 371
 372                     _ => panic!("can't handle callee of type {:?}", func_ty),
 373                 }
 374             }
 375
 376             Drop { ref value, target, .. } => {
 377                 let ptr = try!(self.eval_lvalue(value)).to_ptr();
 378                 let ty = self.lvalue_ty(value);
 379                 try!(self.drop(ptr, ty));
 380                 TerminatorTarget::Block(target)
 381             }
 382
 383             Resume => unimplemented!(),
 384         };
 385
 386         Ok(target)
 387     }
 388
 389     fn drop(&mut self, ptr: Pointer, ty: ty::Ty<'tcx>) -> EvalResult<()> {
 390         if !self.type_needs_drop(ty) {
 391             self.log(1, || print!("no need to drop {:?}", ty));
 392             return Ok(());
 393         }
 394         self.log(1, || print!("need to drop {:?}", ty));
 395
 396         // TODO(tsion): Call user-defined Drop::drop impls.
 397
 398         match ty.sty {
 399             ty::TyBox(contents_ty) => {
 400                 match self.memory.read_ptr(ptr) {
 401                     Ok(contents_ptr) => {
 402                         try!(self.drop(contents_ptr, contents_ty));
 403                         self.log(1, || print!("deallocating box"));
 404                         try!(self.memory.deallocate(contents_ptr));
 405                     }
 406                     Err(EvalError::ReadBytesAsPointer) => {
 407                         let size = self.memory.pointer_size;
 408                         let possible_drop_fill = try!(self.memory.read_bytes(ptr, size));
 409                         if possible_drop_fill.iter().all(|&b| b == mem::POST_DROP_U8) {
 410                             return Ok(());
 411                         } else {
 412                             return Err(EvalError::ReadBytesAsPointer);
 413                         }
 414                     }
 415                     Err(e) => return Err(e),
 416                 }
 417             }
 418
 419             // TODO(tsion): Implement drop for other relevant types (e.g. aggregates).
 420             _ => {}
 421         }
 422
 423         // Filling drop.
 424         // FIXME(tsion): Trait objects (with no static size) probably get filled, too.
 425         let size = self.type_size(ty);
 426         try!(self.memory.drop_fill(ptr, size));
 427
 428         Ok(())
 429     }
 430
 431     fn call_intrinsic(
 432         &mut self,
 433         name: &str,
 434         substs: &'tcx Substs<'tcx>,
 435         args: &[mir::Operand<'tcx>],
 436         dest: Pointer,
 437         dest_size: usize
 438     ) -> EvalResult<TerminatorTarget> {
 439         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 440             .map(|arg| self.eval_operand(arg))
 441             .collect();
 442         let args = try!(args_res);
 443
 444         match name {
 445             "assume" => {}
 446
 447             "copy_nonoverlapping" => {
 448                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 449                 let elem_size = self.type_size(elem_ty);
 450                 let src = try!(self.memory.read_ptr(args[0]));
 451                 let dest = try!(self.memory.read_ptr(args[1]));
 452                 let count = try!(self.memory.read_isize(args[2]));
 453                 try!(self.memory.copy(src, dest, count as usize * elem_size));
 454             }
 455
 456             "forget" => {
 457                 let arg_ty = *substs.types.get(subst::FnSpace, 0);
 458                 let arg_size = self.type_size(arg_ty);
 459                 try!(self.memory.drop_fill(args[0], arg_size));
 460             }
 461
 462             "init" => try!(self.memory.write_repeat(dest, 0, dest_size)),
 463
 464             "min_align_of" => {
 465                 try!(self.memory.write_int(dest, 1, dest_size));
 466             }
 467
 468             "move_val_init" => {
 469                 let ty = *substs.types.get(subst::FnSpace, 0);
 470                 let ptr = try!(self.memory.read_ptr(args[0]));
 471                 try!(self.move_(args[1], ptr, ty));
 472             }
 473
 474             // FIXME(tsion): Handle different integer types correctly.
 475             "add_with_overflow" => {
 476                 let ty = *substs.types.get(subst::FnSpace, 0);
 477                 let size = self.type_size(ty);
 478                 let left = try!(self.memory.read_int(args[0], size));
 479                 let right = try!(self.memory.read_int(args[1], size));
 480                 let (n, overflowed) = unsafe {
 481                     ::std::intrinsics::add_with_overflow::<i64>(left, right)
 482                 };
 483                 try!(self.memory.write_int(dest, n, size));
 484                 try!(self.memory.write_bool(dest.offset(size as isize), overflowed));
 485             }
 486
 487             // FIXME(tsion): Handle different integer types correctly.
 488             "mul_with_overflow" => {
 489                 let ty = *substs.types.get(subst::FnSpace, 0);
 490                 let size = self.type_size(ty);
 491                 let left = try!(self.memory.read_int(args[0], size));
 492                 let right = try!(self.memory.read_int(args[1], size));
 493                 let (n, overflowed) = unsafe {
 494                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 495                 };
 496                 try!(self.memory.write_int(dest, n, size));
 497                 try!(self.memory.write_bool(dest.offset(size as isize), overflowed));
 498             }
 499
 500             "offset" => {
 501                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 502                 let pointee_size = self.type_size(pointee_ty) as isize;
 503                 let ptr_arg = args[0];
 504                 let offset = try!(self.memory.read_isize(args[1]));
 505
 506                 match self.memory.read_ptr(ptr_arg) {
 507                     Ok(ptr) => {
 508                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 509                         try!(self.memory.write_ptr(dest, result_ptr));
 510                     }
 511                     Err(EvalError::ReadBytesAsPointer) => {
 512                         let addr = try!(self.memory.read_isize(ptr_arg));
 513                         let result_addr = addr + offset * pointee_size as i64;
 514                         try!(self.memory.write_isize(dest, result_addr));
 515                     }
 516                     Err(e) => return Err(e),
 517                 }
 518             }
 519
 520             // FIXME(tsion): Handle different integer types correctly. Use primvals?
 521             "overflowing_sub" => {
 522                 let ty = *substs.types.get(subst::FnSpace, 0);
 523                 let size = self.type_size(ty);
 524                 let left = try!(self.memory.read_int(args[0], size));
 525                 let right = try!(self.memory.read_int(args[1], size));
 526                 let n = left.wrapping_sub(right);
 527                 try!(self.memory.write_int(dest, n, size));
 528             }
 529
 530             "size_of" => {
 531                 let ty = *substs.types.get(subst::FnSpace, 0);
 532                 let size = self.type_size(ty) as u64;
 533                 try!(self.memory.write_uint(dest, size, dest_size));
 534             }
 535
 536             "transmute" => {
 537                 let ty = *substs.types.get(subst::FnSpace, 0);
 538                 try!(self.move_(args[0], dest, ty));
 539             }
 540             "uninit" => try!(self.memory.mark_definedness(dest, dest_size, false)),
 541
 542             name => panic!("can't handle intrinsic: {}", name),
 543         }
 544
 545         // Since we pushed no stack frame, the main loop will act
 546         // as if the call just completed and it's returning to the
 547         // current frame.
 548         Ok(TerminatorTarget::Call)
 549     }
 550
 551     fn call_c_abi(
 552         &mut self,
 553         def_id: DefId,
 554         args: &[mir::Operand<'tcx>],
 555         dest: Pointer
 556     ) -> EvalResult<TerminatorTarget> {
 557         let name = self.tcx.item_name(def_id);
 558         let attrs = self.tcx.get_attrs(def_id);
 559         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 560             Some(ln) => ln.clone(),
 561             None => name.as_str(),
 562         };
 563
 564         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 565             .map(|arg| self.eval_operand(arg))
 566             .collect();
 567         let args = try!(args_res);
 568
 569         match &link_name[..] {
 570             "__rust_allocate" => {
 571                 let size = try!(self.memory.read_usize(args[0]));
 572                 let ptr = self.memory.allocate(size as usize);
 573                 try!(self.memory.write_ptr(dest, ptr));
 574             }
 575
 576             "__rust_reallocate" => {
 577                 let ptr = try!(self.memory.read_ptr(args[0]));
 578                 let size = try!(self.memory.read_usize(args[2]));
 579                 try!(self.memory.reallocate(ptr, size as usize));
 580                 try!(self.memory.write_ptr(dest, ptr));
 581             }
 582
 583             _ => panic!("can't call C ABI function: {}", link_name),
 584         }
 585
 586         // Since we pushed no stack frame, the main loop will act
 587         // as if the call just completed and it's returning to the
 588         // current frame.
 589         Ok(TerminatorTarget::Call)
 590     }
 591
 592     fn assign_fields<I: IntoIterator<Item = u64>>(
 593         &mut self,
 594         dest: Pointer,
 595         offsets: I,
 596         operands: &[mir::Operand<'tcx>],
 597     ) -> EvalResult<()> {
 598         for (offset, operand) in offsets.into_iter().zip(operands) {
 599             let src = try!(self.eval_operand(operand));
 600             let src_ty = self.operand_ty(operand);
 601             let field_dest = dest.offset(offset as isize);
 602             try!(self.move_(src, field_dest, src_ty));
 603         }
 604         Ok(())
 605     }
 606
 607     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 608         -> EvalResult<()>
 609     {
 610         let dest = try!(self.eval_lvalue(lvalue)).to_ptr();
 611         let dest_ty = self.lvalue_ty(lvalue);
 612         let dest_layout = self.type_layout(dest_ty);
 613
 614         use rustc::mir::repr::Rvalue::*;
 615         match *rvalue {
 616             Use(ref operand) => {
 617                 let src = try!(self.eval_operand(operand));
 618                 try!(self.move_(src, dest, dest_ty));
 619             }
 620
 621             BinaryOp(bin_op, ref left, ref right) => {
 622                 let left_ptr = try!(self.eval_operand(left));
 623                 let left_ty = self.operand_ty(left);
 624                 let left_val = try!(self.read_primval(left_ptr, left_ty));
 625
 626                 let right_ptr = try!(self.eval_operand(right));
 627                 let right_ty = self.operand_ty(right);
 628                 let right_val = try!(self.read_primval(right_ptr, right_ty));
 629
 630                 let val = try!(primval::binary_op(bin_op, left_val, right_val));
 631                 try!(self.memory.write_primval(dest, val));
 632             }
 633
 634             UnaryOp(un_op, ref operand) => {
 635                 let ptr = try!(self.eval_operand(operand));
 636                 let ty = self.operand_ty(operand);
 637                 let val = try!(self.read_primval(ptr, ty));
 638                 try!(self.memory.write_primval(dest, primval::unary_op(un_op, val)));
 639             }
 640
 641             Aggregate(ref kind, ref operands) => {
 642                 use rustc::ty::layout::Layout::*;
 643                 match *dest_layout {
 644                     Univariant { ref variant, .. } => {
 645                         let offsets = iter::once(0)
 646                             .chain(variant.offset_after_field.iter().map(|s| s.bytes()));
 647                         try!(self.assign_fields(dest, offsets, operands));
 648                     }
 649
 650                     Array { .. } => {
 651                         let elem_size = match dest_ty.sty {
 652                             ty::TyArray(elem_ty, _) => self.type_size(elem_ty) as u64,
 653                             _ => panic!("tried to assign {:?} to non-array type {:?}",
 654                                         kind, dest_ty),
 655                         };
 656                         let offsets = (0..).map(|i| i * elem_size);
 657                         try!(self.assign_fields(dest, offsets, operands));
 658                     }
 659
 660                     General { discr, ref variants, .. } => {
 661                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 662                             let discr_val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 663                             let discr_size = discr.size().bytes() as usize;
 664                             try!(self.memory.write_uint(dest, discr_val, discr_size));
 665
 666                             let offsets = variants[variant].offset_after_field.iter()
 667                                 .map(|s| s.bytes());
 668                             try!(self.assign_fields(dest, offsets, operands));
 669                         } else {
 670                             panic!("tried to assign {:?} to Layout::General", kind);
 671                         }
 672                     }
 673
 674                     RawNullablePointer { nndiscr, .. } => {
 675                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 676                             if nndiscr == variant as u64 {
 677                                 assert_eq!(operands.len(), 1);
 678                                 let operand = &operands[0];
 679                                 let src = try!(self.eval_operand(operand));
 680                                 let src_ty = self.operand_ty(operand);
 681                                 try!(self.move_(src, dest, src_ty));
 682                             } else {
 683                                 assert_eq!(operands.len(), 0);
 684                                 try!(self.memory.write_isize(dest, 0));
 685                             }
 686                         } else {
 687                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 688                         }
 689                     }
 690
 691                     CEnum { discr, signed, .. } => {
 692                         assert_eq!(operands.len(), 0);
 693                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 694                             let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 695                             let size = discr.size().bytes() as usize;
 696
 697                             if signed {
 698                                 try!(self.memory.write_int(dest, val as i64, size));
 699                             } else {
 700                                 try!(self.memory.write_uint(dest, val, size));
 701                             }
 702                         } else {
 703                             panic!("tried to assign {:?} to Layout::CEnum", kind);
 704                         }
 705                     }
 706
 707                     _ => panic!("can't handle destination layout {:?} when assigning {:?}",
 708                                 dest_layout, kind),
 709                 }
 710             }
 711
 712             Repeat(ref operand, _) => {
 713                 let (elem_size, length) = match dest_ty.sty {
 714                     ty::TyArray(elem_ty, n) => (self.type_size(elem_ty), n),
 715                     _ => panic!("tried to assign array-repeat to non-array type {:?}", dest_ty),
 716                 };
 717
 718                 let src = try!(self.eval_operand(operand));
 719                 for i in 0..length {
 720                     let elem_dest = dest.offset((i * elem_size) as isize);
 721                     try!(self.memory.copy(src, elem_dest, elem_size));
 722                 }
 723             }
 724
 725             Len(ref lvalue) => {
 726                 let src = try!(self.eval_lvalue(lvalue));
 727                 let ty = self.lvalue_ty(lvalue);
 728                 let len = match ty.sty {
 729                     ty::TyArray(_, n) => n as u64,
 730                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
 731                         n
 732                     } else {
 733                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
 734                     },
 735                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
 736                 };
 737                 try!(self.memory.write_usize(dest, len));
 738             }
 739
 740             Ref(_, _, ref lvalue) => {
 741                 let lv = try!(self.eval_lvalue(lvalue));
 742                 try!(self.memory.write_ptr(dest, lv.ptr));
 743                 match lv.extra {
 744                     LvalueExtra::None => {},
 745                     LvalueExtra::Length(len) => {
 746                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
 747                         try!(self.memory.write_usize(len_ptr, len));
 748                     }
 749                     LvalueExtra::DowncastVariant(..) =>
 750                         panic!("attempted to take a reference to an enum downcast lvalue"),
 751                 }
 752             }
 753
 754             Box(ty) => {
 755                 let size = self.type_size(ty);
 756                 let ptr = self.memory.allocate(size);
 757                 try!(self.memory.write_ptr(dest, ptr));
 758             }
 759
 760             Cast(kind, ref operand, dest_ty) => {
 761                 let src = try!(self.eval_operand(operand));
 762                 let src_ty = self.operand_ty(operand);
 763
 764                 use rustc::mir::repr::CastKind::*;
 765                 match kind {
 766                     Unsize => {
 767                         try!(self.move_(src, dest, src_ty));
 768                         let src_pointee_ty = pointee_type(src_ty).unwrap();
 769                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
 770
 771                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
 772                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
 773                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
 774                                 try!(self.memory.write_usize(len_ptr, length as u64));
 775                             }
 776
 777                             _ => panic!("can't handle cast: {:?}", rvalue),
 778                         }
 779                     }
 780
 781                     Misc => {
 782                         // FIXME(tsion): Wrong for almost everything.
 783                         let size = dest_layout.size(&self.tcx.data_layout).bytes() as usize;
 784                         try!(self.memory.copy(src, dest, size));
 785                     }
 786
 787                     _ => panic!("can't handle cast: {:?}", rvalue),
 788                 }
 789             }
 790
 791             Slice { .. } => unimplemented!(),
 792             InlineAsm { .. } => unimplemented!(),
 793         }
 794
 795         Ok(())
 796     }
 797
 798     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
 799         use rustc::mir::repr::Operand::*;
 800         match *op {
 801             Consume(ref lvalue) =>
 802                 Ok(try!(self.eval_lvalue(lvalue)).to_ptr()),
 803             Constant(mir::Constant { ref literal, .. }) => {
 804                 use rustc::mir::repr::Literal::*;
 805                 match *literal {
 806                     Value { ref value } => Ok(try!(self.const_to_ptr(value))),
 807                     Item { .. } => unimplemented!(),
 808                     Promoted { .. } => unimplemented!(),
 809                 }
 810             }
 811         }
 812     }
 813
 814     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
 815         use rustc::mir::repr::Lvalue::*;
 816         let ptr = match *lvalue {
 817             ReturnPointer => self.frame().return_ptr
 818                 .expect("ReturnPointer used in a function with no return value"),
 819             Arg(i) => self.frame().locals[i as usize],
 820             Var(i) => self.frame().locals[self.frame().var_offset + i as usize],
 821             Temp(i) => self.frame().locals[self.frame().temp_offset + i as usize],
 822
 823             Static(_def_id) => unimplemented!(),
 824
 825             Projection(ref proj) => {
 826                 let base = try!(self.eval_lvalue(&proj.base));
 827                 let base_ty = self.lvalue_ty(&proj.base);
 828                 let base_layout = self.type_layout(base_ty);
 829
 830                 use rustc::mir::repr::ProjectionElem::*;
 831                 match proj.elem {
 832                     Field(field, _) => {
 833                         let variant = match *base_layout {
 834                             Layout::Univariant { ref variant, .. } => variant,
 835                             Layout::General { ref variants, .. } => {
 836                                 if let LvalueExtra::DowncastVariant(variant_idx) = base.extra {
 837                                     &variants[variant_idx]
 838                                 } else {
 839                                     panic!("field access on enum had no variant index");
 840                                 }
 841                             }
 842                             Layout::RawNullablePointer { .. } => {
 843                                 assert_eq!(field.index(), 0);
 844                                 return Ok(base);
 845                             }
 846                             _ => panic!("field access on non-product type: {:?}", base_layout),
 847                         };
 848
 849                         let offset = variant.field_offset(field.index()).bytes();
 850                         base.ptr.offset(offset as isize)
 851                     },
 852
 853                     Downcast(_, variant) => match *base_layout {
 854                         Layout::General { discr, .. } => {
 855                             return Ok(Lvalue {
 856                                 ptr: base.ptr.offset(discr.size().bytes() as isize),
 857                                 extra: LvalueExtra::DowncastVariant(variant),
 858                             });
 859                         }
 860                         Layout::RawNullablePointer { .. } => return Ok(base),
 861                         _ => panic!("variant downcast on non-aggregate type: {:?}", base_layout),
 862                     },
 863
 864                     Deref => {
 865                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
 866                         let ptr = try!(self.memory.read_ptr(base.ptr));
 867                         let extra = match pointee_ty.sty {
 868                             ty::TySlice(_) | ty::TyStr => {
 869                                 let len_ptr = base.ptr.offset(self.memory.pointer_size as isize);
 870                                 let len = try!(self.memory.read_usize(len_ptr));
 871                                 LvalueExtra::Length(len)
 872                             }
 873                             ty::TyTrait(_) => unimplemented!(),
 874                             _ => LvalueExtra::None,
 875                         };
 876                         return Ok(Lvalue { ptr: ptr, extra: extra });
 877                     }
 878
 879                     Index(ref operand) => {
 880                         let elem_size = match base_ty.sty {
 881                             ty::TyArray(elem_ty, _) |
 882                             ty::TySlice(elem_ty) => self.type_size(elem_ty),
 883                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
 884                         };
 885                         let n_ptr = try!(self.eval_operand(operand));
 886                         let n = try!(self.memory.read_usize(n_ptr));
 887                         base.ptr.offset(n as isize * elem_size as isize)
 888                     }
 889
 890                     ConstantIndex { .. } => unimplemented!(),
 891                 }
 892             }
 893         };
 894
 895         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
 896     }
 897
 898     // TODO(tsion): Try making const_to_primval instead.
 899     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<Pointer> {
 900         use rustc::middle::const_val::ConstVal::*;
 901         match *const_val {
 902             Float(_f) => unimplemented!(),
 903             Integral(int) => {
 904                 // TODO(tsion): Check int constant type.
 905                 let ptr = self.memory.allocate(8);
 906                 try!(self.memory.write_uint(ptr, int.to_u64_unchecked(), 8));
 907                 Ok(ptr)
 908             }
 909             Str(ref s) => {
 910                 let psize = self.memory.pointer_size;
 911                 let static_ptr = self.memory.allocate(s.len());
 912                 let ptr = self.memory.allocate(psize * 2);
 913                 try!(self.memory.write_bytes(static_ptr, s.as_bytes()));
 914                 try!(self.memory.write_ptr(ptr, static_ptr));
 915                 try!(self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64));
 916                 Ok(ptr)
 917             }
 918             ByteStr(ref bs) => {
 919                 let psize = self.memory.pointer_size;
 920                 let static_ptr = self.memory.allocate(bs.len());
 921                 let ptr = self.memory.allocate(psize);
 922                 try!(self.memory.write_bytes(static_ptr, bs));
 923                 try!(self.memory.write_ptr(ptr, static_ptr));
 924                 Ok(ptr)
 925             }
 926             Bool(b) => {
 927                 let ptr = self.memory.allocate(1);
 928                 try!(self.memory.write_bool(ptr, b));
 929                 Ok(ptr)
 930             }
 931             Char(_c)          => unimplemented!(),
 932             Struct(_node_id)  => unimplemented!(),
 933             Tuple(_node_id)   => unimplemented!(),
 934             Function(_def_id) => unimplemented!(),
 935             Array(_, _)       => unimplemented!(),
 936             Repeat(_, _)      => unimplemented!(),
 937             Dummy             => unimplemented!(),
 938         }
 939     }
 940
 941     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> ty::Ty<'tcx> {
 942         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx))
 943     }
 944
 945     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> ty::Ty<'tcx> {
 946         self.monomorphize(self.mir().operand_ty(self.tcx, operand))
 947     }
 948
 949     fn monomorphize(&self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
 950         let substituted = ty.subst(self.tcx, self.substs());
 951         infer::normalize_associated_type(self.tcx, &substituted)
 952     }
 953
 954     fn type_needs_drop(&self, ty: ty::Ty<'tcx>) -> bool {
 955         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
 956     }
 957
 958     fn move_(&mut self, src: Pointer, dest: Pointer, ty: ty::Ty<'tcx>) -> EvalResult<()> {
 959         let size = self.type_size(ty);
 960         try!(self.memory.copy(src, dest, size));
 961         if self.type_needs_drop(ty) {
 962             try!(self.memory.drop_fill(src, size));
 963         }
 964         Ok(())
 965     }
 966
 967     fn type_is_sized(&self, ty: ty::Ty<'tcx>) -> bool {
 968         ty.is_sized(&self.tcx.empty_parameter_environment(), DUMMY_SP)
 969     }
 970
 971     fn type_size(&self, ty: ty::Ty<'tcx>) -> usize {
 972         self.type_layout(ty).size(&self.tcx.data_layout).bytes() as usize
 973     }
 974
 975     fn type_layout(&self, ty: ty::Ty<'tcx>) -> &'tcx Layout {
 976         // TODO(tsion): Is this inefficient? Needs investigation.
 977         let ty = self.monomorphize(ty);
 978
 979         let infcx = infer::normalizing_infer_ctxt(self.tcx, &self.tcx.tables, ProjectionMode::Any);
 980
 981         // TODO(tsion): Report this error properly.
 982         ty.layout(&infcx).unwrap()
 983     }
 984
 985     pub fn read_primval(&mut self, ptr: Pointer, ty: ty::Ty<'tcx>) -> EvalResult<PrimVal> {
 986         use syntax::ast::{IntTy, UintTy};
 987         let val = match ty.sty {
 988             ty::TyBool              => PrimVal::Bool(try!(self.memory.read_bool(ptr))),
 989             ty::TyInt(IntTy::I8)    => PrimVal::I8(try!(self.memory.read_int(ptr, 1)) as i8),
 990             ty::TyInt(IntTy::I16)   => PrimVal::I16(try!(self.memory.read_int(ptr, 2)) as i16),
 991             ty::TyInt(IntTy::I32)   => PrimVal::I32(try!(self.memory.read_int(ptr, 4)) as i32),
 992             ty::TyInt(IntTy::I64)   => PrimVal::I64(try!(self.memory.read_int(ptr, 8)) as i64),
 993             ty::TyUint(UintTy::U8)  => PrimVal::U8(try!(self.memory.read_uint(ptr, 1)) as u8),
 994             ty::TyUint(UintTy::U16) => PrimVal::U16(try!(self.memory.read_uint(ptr, 2)) as u16),
 995             ty::TyUint(UintTy::U32) => PrimVal::U32(try!(self.memory.read_uint(ptr, 4)) as u32),
 996             ty::TyUint(UintTy::U64) => PrimVal::U64(try!(self.memory.read_uint(ptr, 8)) as u64),
 997
 998             // TODO(tsion): Pick the PrimVal dynamically.
 999             ty::TyInt(IntTy::Is)   => PrimVal::I64(try!(self.memory.read_isize(ptr))),
1000             ty::TyUint(UintTy::Us) => PrimVal::U64(try!(self.memory.read_usize(ptr))),
1001
1002             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1003             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) => {
1004                 if self.type_is_sized(ty) {
1005                     match self.memory.read_ptr(ptr) {
1006                         Ok(p) => PrimVal::AbstractPtr(p),
1007                         Err(EvalError::ReadBytesAsPointer) => {
1008                             let n = try!(self.memory.read_usize(ptr));
1009                             PrimVal::IntegerPtr(n)
1010                         }
1011                         Err(e) => return Err(e),
1012                     }
1013                 } else {
1014                     panic!("unimplemented: primitive read of fat pointer type: {:?}", ty);
1015                 }
1016             }
1017
1018             _ => panic!("primitive read of non-primitive type: {:?}", ty),
1019         };
1020         Ok(val)
1021     }
1022
1023     fn frame(&self) -> &Frame<'a, 'tcx> {
1024         self.stack.last().expect("no call frames exist")
1025     }
1026
1027     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
1028         self.stack.last_mut().expect("no call frames exist")
1029     }
1030
1031     fn mir(&self) -> &mir::Mir<'tcx> {
1032         &self.frame().mir
1033     }
1034
1035     fn substs(&self) -> &'tcx Substs<'tcx> {
1036         self.substs_stack.last().cloned().unwrap_or_else(|| self.tcx.mk_substs(Substs::empty()))
1037     }
1038
1039     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
1040         match self.tcx.map.as_local_node_id(def_id) {
1041             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
1042             None => {
1043                 let mut mir_cache = self.mir_cache.borrow_mut();
1044                 if let Some(mir) = mir_cache.get(&def_id) {
1045                     return CachedMir::Owned(mir.clone());
1046                 }
1047
1048                 let cs = &self.tcx.sess.cstore;
1049                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
1050                     panic!("no mir for {:?}", def_id);
1051                 });
1052                 let cached = Rc::new(mir);
1053                 mir_cache.insert(def_id, cached.clone());
1054                 CachedMir::Owned(cached)
1055             }
1056         }
1057     }
1058
1059     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
1060         // Do the initial selection for the obligation. This yields the shallow result we are
1061         // looking for -- that is, what specific impl.
1062         let infcx = infer::normalizing_infer_ctxt(self.tcx, &self.tcx.tables, ProjectionMode::Any);
1063         let mut selcx = traits::SelectionContext::new(&infcx);
1064
1065         let obligation = traits::Obligation::new(
1066             traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
1067             trait_ref.to_poly_trait_predicate(),
1068         );
1069         let selection = selcx.select(&obligation).unwrap().unwrap();
1070
1071         // Currently, we use a fulfillment context to completely resolve all nested obligations.
1072         // This is because they can inform the inference of the impl's type parameters.
1073         let mut fulfill_cx = traits::FulfillmentContext::new();
1074         let vtable = selection.map(|predicate| {
1075             fulfill_cx.register_predicate_obligation(&infcx, predicate);
1076         });
1077         infer::drain_fulfillment_cx_or_panic(
1078             DUMMY_SP, &infcx, &mut fulfill_cx, &vtable
1079         )
1080     }
1081
1082     /// Trait method, which has to be resolved to an impl method.
1083     pub fn trait_method(&self, def_id: DefId, substs: &'tcx Substs<'tcx>)
1084         -> (DefId, &'tcx Substs<'tcx>)
1085     {
1086         let method_item = self.tcx.impl_or_trait_item(def_id);
1087         let trait_id = method_item.container().id();
1088         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
1089         match self.fulfill_obligation(trait_ref) {
1090             traits::VtableImpl(vtable_impl) => {
1091                 let impl_did = vtable_impl.impl_def_id;
1092                 let mname = self.tcx.item_name(def_id);
1093                 // Create a concatenated set of substitutions which includes those from the impl
1094                 // and those from the method:
1095                 let impl_substs = vtable_impl.substs.with_method_from(substs);
1096                 let substs = self.tcx.mk_substs(impl_substs);
1097                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
1098
1099                 (mth.method.def_id, mth.substs)
1100             }
1101
1102             traits::VtableClosure(vtable_closure) =>
1103                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
1104
1105             traits::VtableFnPointer(_fn_ty) => {
1106                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
1107                 unimplemented!()
1108                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
1109
1110                 // let method_ty = def_ty(tcx, def_id, substs);
1111                 // let fn_ptr_ty = match method_ty.sty {
1112                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
1113                 //     _ => unreachable!("expected fn item type, found {}",
1114                 //                       method_ty)
1115                 // };
1116                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
1117             }
1118
1119             traits::VtableObject(ref _data) => {
1120                 unimplemented!()
1121                 // Callee {
1122                 //     data: Virtual(traits::get_vtable_index_of_object_method(
1123                 //                   tcx, data, def_id)),
1124                 //                   ty: def_ty(tcx, def_id, substs)
1125                 // }
1126             }
1127             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
1128         }
1129     }
1130 }
1131
1132 fn pointee_type(ptr_ty: ty::Ty) -> Option<ty::Ty> {
1133     match ptr_ty.sty {
1134         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1135         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1136         ty::TyBox(ty) => {
1137             Some(ty)
1138         }
1139         _ => None,
1140     }
1141 }
1142
1143 impl Lvalue {
1144     fn to_ptr(self) -> Pointer {
1145         assert_eq!(self.extra, LvalueExtra::None);
1146         self.ptr
1147     }
1148 }
1149
1150 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1151     type Target = mir::Mir<'tcx>;
1152     fn deref(&self) -> &mir::Mir<'tcx> {
1153         match *self {
1154             CachedMir::Ref(r) => r,
1155             CachedMir::Owned(ref rc) => &rc,
1156         }
1157     }
1158 }
1159
1160 #[derive(Debug)]
1161 pub struct ImplMethod<'tcx> {
1162     pub method: Rc<ty::Method<'tcx>>,
1163     pub substs: &'tcx Substs<'tcx>,
1164     pub is_provided: bool,
1165 }
1166
1167 /// Locates the applicable definition of a method, given its name.
1168 pub fn get_impl_method<'tcx>(
1169     tcx: &TyCtxt<'tcx>,
1170     impl_def_id: DefId,
1171     substs: &'tcx Substs<'tcx>,
1172     name: ast::Name,
1173 ) -> ImplMethod<'tcx> {
1174     assert!(!substs.types.needs_infer());
1175
1176     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1177     let trait_def = tcx.lookup_trait_def(trait_def_id);
1178     let infcx = infer::normalizing_infer_ctxt(tcx, &tcx.tables, ProjectionMode::Any);
1179
1180     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1181         Some(node_item) => {
1182             ImplMethod {
1183                 method: node_item.item,
1184                 substs: traits::translate_substs(&infcx, impl_def_id, substs, node_item.node),
1185                 is_provided: node_item.node.is_from_trait(),
1186             }
1187         }
1188         None => {
1189             bug!("method {:?} not found in {:?}", name, impl_def_id);
1190         }
1191     }
1192 }
1193
1194 pub fn interpret_start_points<'tcx>(tcx: &TyCtxt<'tcx>, mir_map: &MirMap<'tcx>) {
1195     for (&id, mir) in &mir_map.map {
1196         for attr in tcx.map.attrs(id) {
1197             use syntax::attr::AttrMetaMethods;
1198             if attr.check_name("miri_run") {
1199                 let item = tcx.map.expect_item(id);
1200
1201                 println!("Interpreting: {}", item.name);
1202
1203                 let mut miri = Interpreter::new(tcx, mir_map);
1204                 let return_ptr = match mir.return_ty {
1205                     ty::FnConverging(ty) => {
1206                         let size = miri.type_size(ty);
1207                         Some(miri.memory.allocate(size))
1208                     }
1209                     ty::FnDiverging => None,
1210                 };
1211                 let substs = miri.tcx.mk_substs(Substs::empty());
1212                 miri.push_stack_frame(CachedMir::Ref(mir), substs, return_ptr);
1213                 if let Err(_e) = miri.run() {
1214                     // TODO(tsion): Detect whether the error was already reported or not.
1215                     // tcx.sess.err(&e.to_string());
1216                 } else if let Some(ret) = return_ptr {
1217                     miri.memory.dump(ret.alloc_id);
1218                 }
1219                 println!("");
1220             }
1221         }
1222     }
1223 }
1224
1225 // TODO(tsion): Upstream these methods into rustc::ty::layout.
1226
1227 trait IntegerExt {
1228     fn size(self) -> Size;
1229 }
1230
1231 impl IntegerExt for layout::Integer {
1232     fn size(self) -> Size {
1233         use rustc::ty::layout::Integer::*;
1234         match self {
1235             I1 | I8 => Size::from_bits(8),
1236             I16 => Size::from_bits(16),
1237             I32 => Size::from_bits(32),
1238             I64 => Size::from_bits(64),
1239         }
1240     }
1241 }
1242
1243 trait StructExt {
1244     fn field_offset(&self, index: usize) -> Size;
1245 }
1246
1247 impl StructExt for layout::Struct {
1248     fn field_offset(&self, index: usize) -> Size {
1249         if index == 0 {
1250             Size::from_bytes(0)
1251         } else {
1252             self.offset_after_field[index - 1]
1253         }
1254     }
1255 }