src/interpreter/mod.rs

   1 use rustc::middle::const_val;
   2 use rustc::hir::def_id::DefId;
   3 use rustc::mir::mir_map::MirMap;
   4 use rustc::mir::repr as mir;
   5 use rustc::traits::{self, ProjectionMode};
   6 use rustc::ty::fold::TypeFoldable;
   7 use rustc::ty::layout::{self, Layout, Size};
   8 use rustc::ty::subst::{self, Subst, Substs};
   9 use rustc::ty::{self, Ty, TyCtxt};
  10 use rustc::util::nodemap::DefIdMap;
  11 use std::cell::RefCell;
  12 use std::ops::Deref;
  13 use std::rc::Rc;
  14 use std::{iter, mem};
  15 use syntax::ast;
  16 use syntax::attr;
  17 use syntax::codemap::{self, DUMMY_SP};
  18
  19 use error::{EvalError, EvalResult};
  20 use memory::{Memory, Pointer};
  21 use primval::{self, PrimVal};
  22
  23 use std::collections::HashMap;
  24
  25 mod stepper;
  26
  27 pub fn step<'fncx, 'a: 'fncx, 'tcx: 'a>(gecx: &'fncx mut EvalContext<'a, 'tcx>) -> EvalResult<bool> {
  28     stepper::Stepper::new(gecx).step()
  29 }
  30
  31 pub struct EvalContext<'a, 'tcx: 'a> {
  32     /// The results of the type checker, from rustc.
  33     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  34
  35     /// A mapping from NodeIds to Mir, from rustc. Only contains MIR for crate-local items.
  36     mir_map: &'a MirMap<'tcx>,
  37
  38     /// A local cache from DefIds to Mir for non-crate-local items.
  39     mir_cache: RefCell<DefIdMap<Rc<mir::Mir<'tcx>>>>,
  40
  41     /// The virtual memory system.
  42     memory: Memory,
  43
  44     /// Precomputed statics, constants and promoteds
  45     statics: HashMap<ConstantId<'tcx>, Pointer>,
  46
  47     /// The virtual call stack.
  48     stack: Vec<Frame<'a, 'tcx>>,
  49 }
  50
  51 /// A stack frame.
  52 pub struct Frame<'a, 'tcx: 'a> {
  53     /// The def_id of the current function
  54     pub def_id: DefId,
  55
  56     /// The span of the call site
  57     pub span: codemap::Span,
  58
  59     /// type substitutions for the current function invocation
  60     pub substs: &'tcx Substs<'tcx>,
  61
  62     /// The MIR for the function called on this frame.
  63     pub mir: CachedMir<'a, 'tcx>,
  64
  65     /// The block that is currently executed (or will be executed after the above call stacks return)
  66     pub next_block: mir::BasicBlock,
  67
  68     /// A pointer for writing the return value of the current call if it's not a diverging call.
  69     pub return_ptr: Option<Pointer>,
  70
  71     /// The list of locals for the current function, stored in order as
  72     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  73     /// and the temporaries at `self.temp_offset`.
  74     pub locals: Vec<Pointer>,
  75
  76     /// The offset of the first variable in `self.locals`.
  77     pub var_offset: usize,
  78
  79     /// The offset of the first temporary in `self.locals`.
  80     pub temp_offset: usize,
  81
  82     /// The index of the currently evaluated statment
  83     pub stmt: usize,
  84 }
  85
  86 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  87 struct Lvalue {
  88     ptr: Pointer,
  89     extra: LvalueExtra,
  90 }
  91
  92 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  93 enum LvalueExtra {
  94     None,
  95     Length(u64),
  96     // TODO(solson): Vtable(memory::AllocId),
  97     DowncastVariant(usize),
  98 }
  99
 100 #[derive(Clone)]
 101 pub enum CachedMir<'mir, 'tcx: 'mir> {
 102     Ref(&'mir mir::Mir<'tcx>),
 103     Owned(Rc<mir::Mir<'tcx>>)
 104 }
 105
 106 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 107 /// Uniquely identifies a specific constant or static
 108 struct ConstantId<'tcx> {
 109     /// the def id of the constant/static or in case of promoteds, the def id of the function they belong to
 110     def_id: DefId,
 111     /// In case of statics and constants this is `Substs::empty()`, so only promoteds and associated
 112     /// constants actually have something useful here. We could special case statics and constants,
 113     /// but that would only require more branching when working with constants, and not bring any
 114     /// real benefits.
 115     substs: &'tcx Substs<'tcx>,
 116     kind: ConstantKind,
 117 }
 118
 119 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 120 enum ConstantKind {
 121     Promoted(usize),
 122     /// Statics, constants and associated constants
 123     Global,
 124 }
 125
 126 impl<'a, 'tcx> EvalContext<'a, 'tcx> {
 127     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>, mir_map: &'a MirMap<'tcx>) -> Self {
 128         EvalContext {
 129             tcx: tcx,
 130             mir_map: mir_map,
 131             mir_cache: RefCell::new(DefIdMap()),
 132             memory: Memory::new(tcx.sess
 133                                    .target
 134                                    .uint_type
 135                                    .bit_width()
 136                                    .expect("Session::target::uint_type was usize")/8),
 137             statics: HashMap::new(),
 138             stack: Vec::new(),
 139         }
 140     }
 141
 142     pub fn alloc_ret_ptr(&mut self, output_ty: ty::FnOutput<'tcx>, substs: &'tcx Substs<'tcx>) -> Option<Pointer> {
 143         match output_ty {
 144             ty::FnConverging(ty) => {
 145                 let size = self.type_size(ty, substs);
 146                 Some(self.memory.allocate(size))
 147             }
 148             ty::FnDiverging => None,
 149         }
 150     }
 151
 152     pub fn memory(&self) -> &Memory {
 153         &self.memory
 154     }
 155
 156     pub fn stack(&self) -> &[Frame] {
 157         &self.stack
 158     }
 159
 160     // TODO(solson): Try making const_to_primval instead.
 161     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<Pointer> {
 162         use rustc::middle::const_val::ConstVal::*;
 163         match *const_val {
 164             Float(_f) => unimplemented!(),
 165             Integral(int) => {
 166                 // TODO(solson): Check int constant type.
 167                 let ptr = self.memory.allocate(8);
 168                 self.memory.write_uint(ptr, int.to_u64_unchecked(), 8)?;
 169                 Ok(ptr)
 170             }
 171             Str(ref s) => {
 172                 let psize = self.memory.pointer_size;
 173                 let static_ptr = self.memory.allocate(s.len());
 174                 let ptr = self.memory.allocate(psize * 2);
 175                 self.memory.write_bytes(static_ptr, s.as_bytes())?;
 176                 self.memory.write_ptr(ptr, static_ptr)?;
 177                 self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64)?;
 178                 Ok(ptr)
 179             }
 180             ByteStr(ref bs) => {
 181                 let psize = self.memory.pointer_size;
 182                 let static_ptr = self.memory.allocate(bs.len());
 183                 let ptr = self.memory.allocate(psize);
 184                 self.memory.write_bytes(static_ptr, bs)?;
 185                 self.memory.write_ptr(ptr, static_ptr)?;
 186                 Ok(ptr)
 187             }
 188             Bool(b) => {
 189                 let ptr = self.memory.allocate(1);
 190                 self.memory.write_bool(ptr, b)?;
 191                 Ok(ptr)
 192             }
 193             Char(_c)          => unimplemented!(),
 194             Struct(_node_id)  => unimplemented!(),
 195             Tuple(_node_id)   => unimplemented!(),
 196             Function(_def_id) => unimplemented!(),
 197             Array(_, _)       => unimplemented!(),
 198             Repeat(_, _)      => unimplemented!(),
 199             Dummy             => unimplemented!(),
 200         }
 201     }
 202
 203     fn type_needs_drop(&self, ty: Ty<'tcx>) -> bool {
 204         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
 205     }
 206
 207     fn type_is_sized(&self, ty: Ty<'tcx>) -> bool {
 208         ty.is_sized(self.tcx, &self.tcx.empty_parameter_environment(), DUMMY_SP)
 209     }
 210
 211     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
 212         // Do the initial selection for the obligation. This yields the shallow result we are
 213         // looking for -- that is, what specific impl.
 214         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 215             let mut selcx = traits::SelectionContext::new(&infcx);
 216
 217             let obligation = traits::Obligation::new(
 218                 traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
 219                 trait_ref.to_poly_trait_predicate(),
 220             );
 221             let selection = selcx.select(&obligation).unwrap().unwrap();
 222
 223             // Currently, we use a fulfillment context to completely resolve all nested obligations.
 224             // This is because they can inform the inference of the impl's type parameters.
 225             let mut fulfill_cx = traits::FulfillmentContext::new();
 226             let vtable = selection.map(|predicate| {
 227                 fulfill_cx.register_predicate_obligation(&infcx, predicate);
 228             });
 229             infcx.drain_fulfillment_cx_or_panic(DUMMY_SP, &mut fulfill_cx, &vtable)
 230         })
 231     }
 232
 233     /// Trait method, which has to be resolved to an impl method.
 234     pub fn trait_method(
 235         &self,
 236         def_id: DefId,
 237         substs: &'tcx Substs<'tcx>
 238     ) -> (DefId, &'tcx Substs<'tcx>) {
 239         let method_item = self.tcx.impl_or_trait_item(def_id);
 240         let trait_id = method_item.container().id();
 241         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
 242         match self.fulfill_obligation(trait_ref) {
 243             traits::VtableImpl(vtable_impl) => {
 244                 let impl_did = vtable_impl.impl_def_id;
 245                 let mname = self.tcx.item_name(def_id);
 246                 // Create a concatenated set of substitutions which includes those from the impl
 247                 // and those from the method:
 248                 let impl_substs = vtable_impl.substs.with_method_from(substs);
 249                 let substs = self.tcx.mk_substs(impl_substs);
 250                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
 251
 252                 (mth.method.def_id, mth.substs)
 253             }
 254
 255             traits::VtableClosure(vtable_closure) =>
 256                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
 257
 258             traits::VtableFnPointer(_fn_ty) => {
 259                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
 260                 unimplemented!()
 261                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
 262
 263                 // let method_ty = def_ty(tcx, def_id, substs);
 264                 // let fn_ptr_ty = match method_ty.sty {
 265                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
 266                 //     _ => unreachable!("expected fn item type, found {}",
 267                 //                       method_ty)
 268                 // };
 269                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 270             }
 271
 272             traits::VtableObject(ref _data) => {
 273                 unimplemented!()
 274                 // Callee {
 275                 //     data: Virtual(traits::get_vtable_index_of_object_method(
 276                 //                   tcx, data, def_id)),
 277                 //                   ty: def_ty(tcx, def_id, substs)
 278                 // }
 279             }
 280             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
 281         }
 282     }
 283
 284     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
 285         match self.tcx.map.as_local_node_id(def_id) {
 286             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
 287             None => {
 288                 let mut mir_cache = self.mir_cache.borrow_mut();
 289                 if let Some(mir) = mir_cache.get(&def_id) {
 290                     return CachedMir::Owned(mir.clone());
 291                 }
 292
 293                 let cs = &self.tcx.sess.cstore;
 294                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
 295                     panic!("no mir for {:?}", def_id);
 296                 });
 297                 let cached = Rc::new(mir);
 298                 mir_cache.insert(def_id, cached.clone());
 299                 CachedMir::Owned(cached)
 300             }
 301         }
 302     }
 303
 304     fn monomorphize(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> Ty<'tcx> {
 305         let substituted = ty.subst(self.tcx, substs);
 306         self.tcx.normalize_associated_type(&substituted)
 307     }
 308
 309     fn type_size(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> usize {
 310         self.type_layout(ty, substs).size(&self.tcx.data_layout).bytes() as usize
 311     }
 312
 313     fn type_layout(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> &'tcx Layout {
 314         // TODO(solson): Is this inefficient? Needs investigation.
 315         let ty = self.monomorphize(ty, substs);
 316
 317         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 318             // TODO(solson): Report this error properly.
 319             ty.layout(&infcx).unwrap()
 320         })
 321     }
 322
 323     pub fn push_stack_frame(&mut self, def_id: DefId, span: codemap::Span, mir: CachedMir<'a, 'tcx>, substs: &'tcx Substs<'tcx>,
 324         return_ptr: Option<Pointer>)
 325     {
 326         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 327         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 328         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 329
 330         let num_args = mir.arg_decls.len();
 331         let num_vars = mir.var_decls.len();
 332
 333         ::log_settings::settings().indentation += 1;
 334
 335         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 336             let size = self.type_size(ty, substs);
 337             self.memory.allocate(size)
 338         }).collect();
 339
 340         self.stack.push(Frame {
 341             mir: mir.clone(),
 342             next_block: mir::START_BLOCK,
 343             return_ptr: return_ptr,
 344             locals: locals,
 345             var_offset: num_args,
 346             temp_offset: num_args + num_vars,
 347             span: span,
 348             def_id: def_id,
 349             substs: substs,
 350             stmt: 0,
 351         });
 352     }
 353
 354     fn pop_stack_frame(&mut self) {
 355         ::log_settings::settings().indentation -= 1;
 356         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 357         // TODO(solson): Deallocate local variables.
 358     }
 359
 360     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 361             -> EvalResult<()> {
 362         use rustc::mir::repr::TerminatorKind::*;
 363         match terminator.kind {
 364             Return => self.pop_stack_frame(),
 365
 366             Goto { target } => {
 367                 self.frame_mut().next_block = target;
 368             },
 369
 370             If { ref cond, targets: (then_target, else_target) } => {
 371                 let cond_ptr = self.eval_operand(cond)?;
 372                 let cond_val = self.memory.read_bool(cond_ptr)?;
 373                 self.frame_mut().next_block = if cond_val { then_target } else { else_target };
 374             }
 375
 376             SwitchInt { ref discr, ref values, ref targets, .. } => {
 377                 let discr_ptr = self.eval_lvalue(discr)?.to_ptr();
 378                 let discr_size = self
 379                     .type_layout(self.lvalue_ty(discr), self.substs())
 380                     .size(&self.tcx.data_layout)
 381                     .bytes() as usize;
 382                 let discr_val = self.memory.read_uint(discr_ptr, discr_size)?;
 383
 384                 // Branch to the `otherwise` case by default, if no match is found.
 385                 let mut target_block = targets[targets.len() - 1];
 386
 387                 for (index, val_const) in values.iter().enumerate() {
 388                     let ptr = self.const_to_ptr(val_const)?;
 389                     let val = self.memory.read_uint(ptr, discr_size)?;
 390                     if discr_val == val {
 391                         target_block = targets[index];
 392                         break;
 393                     }
 394                 }
 395
 396                 self.frame_mut().next_block = target_block;
 397             }
 398
 399             Switch { ref discr, ref targets, adt_def } => {
 400                 let adt_ptr = self.eval_lvalue(discr)?.to_ptr();
 401                 let adt_ty = self.lvalue_ty(discr);
 402                 let discr_val = self.read_discriminant_value(adt_ptr, adt_ty)?;
 403                 let matching = adt_def.variants.iter()
 404                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 405
 406                 match matching {
 407                     Some(i) => {
 408                         self.frame_mut().next_block = targets[i];
 409                     },
 410                     None => return Err(EvalError::InvalidDiscriminant),
 411                 }
 412             }
 413
 414             Call { ref func, ref args, ref destination, .. } => {
 415                 let mut return_ptr = None;
 416                 if let Some((ref lv, target)) = *destination {
 417                     self.frame_mut().next_block = target;
 418                     return_ptr = Some(self.eval_lvalue(lv)?.to_ptr());
 419                 }
 420
 421                 let func_ty = self.operand_ty(func);
 422                 match func_ty.sty {
 423                     ty::TyFnDef(def_id, substs, fn_ty) => {
 424                         use syntax::abi::Abi;
 425                         match fn_ty.abi {
 426                             Abi::RustIntrinsic => {
 427                                 let name = self.tcx.item_name(def_id).as_str();
 428                                 match fn_ty.sig.0.output {
 429                                     ty::FnConverging(ty) => {
 430                                         let size = self.type_size(ty, self.substs());
 431                                         let ret = return_ptr.unwrap();
 432                                         self.call_intrinsic(&name, substs, args, ret, size)?
 433                                     }
 434                                     ty::FnDiverging => unimplemented!(),
 435                                 }
 436                             }
 437
 438                             Abi::C => {
 439                                 match fn_ty.sig.0.output {
 440                                     ty::FnConverging(ty) => {
 441                                         let size = self.type_size(ty, self.substs());
 442                                         self.call_c_abi(def_id, args, return_ptr.unwrap(), size)?
 443                                     }
 444                                     ty::FnDiverging => unimplemented!(),
 445                                 }
 446                             }
 447
 448                             Abi::Rust | Abi::RustCall => {
 449                                 // TODO(solson): Adjust the first argument when calling a Fn or
 450                                 // FnMut closure via FnOnce::call_once.
 451
 452                                 // Only trait methods can have a Self parameter.
 453                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 454                                     self.trait_method(def_id, substs)
 455                                 } else {
 456                                     (def_id, substs)
 457                                 };
 458
 459                                 let mut arg_srcs = Vec::new();
 460                                 for arg in args {
 461                                     let src = self.eval_operand(arg)?;
 462                                     let src_ty = self.operand_ty(arg);
 463                                     arg_srcs.push((src, src_ty));
 464                                 }
 465
 466                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 467                                     arg_srcs.pop();
 468                                     let last_arg = args.last().unwrap();
 469                                     let last = self.eval_operand(last_arg)?;
 470                                     let last_ty = self.operand_ty(last_arg);
 471                                     let last_layout = self.type_layout(last_ty, self.substs());
 472                                     match (&last_ty.sty, last_layout) {
 473                                         (&ty::TyTuple(fields),
 474                                          &Layout::Univariant { ref variant, .. }) => {
 475                                             let offsets = iter::once(0)
 476                                                 .chain(variant.offset_after_field.iter()
 477                                                     .map(|s| s.bytes()));
 478                                             for (offset, ty) in offsets.zip(fields) {
 479                                                 let src = last.offset(offset as isize);
 480                                                 arg_srcs.push((src, ty));
 481                                             }
 482                                         }
 483                                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 484                                     }
 485                                 }
 486
 487                                 let mir = self.load_mir(resolved_def_id);
 488                                 self.push_stack_frame(def_id, terminator.span, mir, resolved_substs, return_ptr);
 489
 490                                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 491                                     let dest = self.frame().locals[i];
 492                                     self.move_(src, dest, src_ty)?;
 493                                 }
 494                             }
 495
 496                             abi => return Err(EvalError::Unimplemented(format!("can't handle function with {:?} ABI", abi))),
 497                         }
 498                     }
 499
 500                     _ => return Err(EvalError::Unimplemented(format!("can't handle callee of type {:?}", func_ty))),
 501                 }
 502             }
 503
 504             Drop { ref value, target, .. } => {
 505                 let ptr = self.eval_lvalue(value)?.to_ptr();
 506                 let ty = self.lvalue_ty(value);
 507                 self.drop(ptr, ty)?;
 508                 self.frame_mut().next_block = target;
 509             }
 510
 511             Resume => unimplemented!(),
 512         }
 513
 514         Ok(())
 515     }
 516
 517     fn drop(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
 518         if !self.type_needs_drop(ty) {
 519             debug!("no need to drop {:?}", ty);
 520             return Ok(());
 521         }
 522         trace!("-need to drop {:?}", ty);
 523
 524         // TODO(solson): Call user-defined Drop::drop impls.
 525
 526         match ty.sty {
 527             ty::TyBox(contents_ty) => {
 528                 match self.memory.read_ptr(ptr) {
 529                     Ok(contents_ptr) => {
 530                         self.drop(contents_ptr, contents_ty)?;
 531                         trace!("-deallocating box");
 532                         self.memory.deallocate(contents_ptr)?;
 533                     }
 534                     Err(EvalError::ReadBytesAsPointer) => {
 535                         let size = self.memory.pointer_size;
 536                         let possible_drop_fill = self.memory.read_bytes(ptr, size)?;
 537                         if possible_drop_fill.iter().all(|&b| b == mem::POST_DROP_U8) {
 538                             return Ok(());
 539                         } else {
 540                             return Err(EvalError::ReadBytesAsPointer);
 541                         }
 542                     }
 543                     Err(e) => return Err(e),
 544                 }
 545             }
 546
 547             // TODO(solson): Implement drop for other relevant types (e.g. aggregates).
 548             _ => {}
 549         }
 550
 551         // Filling drop.
 552         // FIXME(solson): Trait objects (with no static size) probably get filled, too.
 553         let size = self.type_size(ty, self.substs());
 554         self.memory.drop_fill(ptr, size)?;
 555
 556         Ok(())
 557     }
 558
 559     fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalResult<u64> {
 560         use rustc::ty::layout::Layout::*;
 561         let adt_layout = self.type_layout(adt_ty, self.substs());
 562
 563         let discr_val = match *adt_layout {
 564             General { discr, .. } | CEnum { discr, .. } => {
 565                 let discr_size = discr.size().bytes();
 566                 self.memory.read_uint(adt_ptr, discr_size as usize)?
 567             }
 568
 569             RawNullablePointer { nndiscr, .. } => {
 570                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
 571             }
 572
 573             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
 574                 let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
 575                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
 576                 self.read_nonnull_discriminant_value(nonnull, nndiscr)?
 577             }
 578
 579             // The discriminant_value intrinsic returns 0 for non-sum types.
 580             Array { .. } | FatPointer { .. } | Scalar { .. } | Univariant { .. } |
 581             Vector { .. } => 0,
 582         };
 583
 584         Ok(discr_val)
 585     }
 586
 587     fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<u64> {
 588         let not_null = match self.memory.read_usize(ptr) {
 589             Ok(0) => false,
 590             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
 591             Err(e) => return Err(e),
 592         };
 593         assert!(nndiscr == 0 || nndiscr == 1);
 594         Ok(if not_null { nndiscr } else { 1 - nndiscr })
 595     }
 596
 597     fn call_intrinsic(
 598         &mut self,
 599         name: &str,
 600         substs: &'tcx Substs<'tcx>,
 601         args: &[mir::Operand<'tcx>],
 602         dest: Pointer,
 603         dest_size: usize
 604     ) -> EvalResult<()> {
 605         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 606             .map(|arg| self.eval_operand(arg))
 607             .collect();
 608         let args = args_res?;
 609
 610         match name {
 611             // FIXME(solson): Handle different integer types correctly.
 612             "add_with_overflow" => {
 613                 let ty = *substs.types.get(subst::FnSpace, 0);
 614                 let size = self.type_size(ty, self.substs());
 615                 let left = self.memory.read_int(args[0], size)?;
 616                 let right = self.memory.read_int(args[1], size)?;
 617                 let (n, overflowed) = unsafe {
 618                     ::std::intrinsics::add_with_overflow::<i64>(left, right)
 619                 };
 620                 self.memory.write_int(dest, n, size)?;
 621                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 622             }
 623
 624             "assume" => {}
 625
 626             "copy_nonoverlapping" => {
 627                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 628                 let elem_size = self.type_size(elem_ty, self.substs());
 629                 let src = self.memory.read_ptr(args[0])?;
 630                 let dest = self.memory.read_ptr(args[1])?;
 631                 let count = self.memory.read_isize(args[2])?;
 632                 self.memory.copy(src, dest, count as usize * elem_size)?;
 633             }
 634
 635             "discriminant_value" => {
 636                 let ty = *substs.types.get(subst::FnSpace, 0);
 637                 let adt_ptr = self.memory.read_ptr(args[0])?;
 638                 let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
 639                 self.memory.write_uint(dest, discr_val, dest_size)?;
 640             }
 641
 642             "forget" => {
 643                 let arg_ty = *substs.types.get(subst::FnSpace, 0);
 644                 let arg_size = self.type_size(arg_ty, self.substs());
 645                 self.memory.drop_fill(args[0], arg_size)?;
 646             }
 647
 648             "init" => self.memory.write_repeat(dest, 0, dest_size)?,
 649
 650             "min_align_of" => {
 651                 self.memory.write_int(dest, 1, dest_size)?;
 652             }
 653
 654             "move_val_init" => {
 655                 let ty = *substs.types.get(subst::FnSpace, 0);
 656                 let ptr = self.memory.read_ptr(args[0])?;
 657                 self.move_(args[1], ptr, ty)?;
 658             }
 659
 660             // FIXME(solson): Handle different integer types correctly.
 661             "mul_with_overflow" => {
 662                 let ty = *substs.types.get(subst::FnSpace, 0);
 663                 let size = self.type_size(ty, self.substs());
 664                 let left = self.memory.read_int(args[0], size)?;
 665                 let right = self.memory.read_int(args[1], size)?;
 666                 let (n, overflowed) = unsafe {
 667                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 668                 };
 669                 self.memory.write_int(dest, n, size)?;
 670                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 671             }
 672
 673             "offset" => {
 674                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 675                 let pointee_size = self.type_size(pointee_ty, self.substs()) as isize;
 676                 let ptr_arg = args[0];
 677                 let offset = self.memory.read_isize(args[1])?;
 678
 679                 match self.memory.read_ptr(ptr_arg) {
 680                     Ok(ptr) => {
 681                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 682                         self.memory.write_ptr(dest, result_ptr)?;
 683                     }
 684                     Err(EvalError::ReadBytesAsPointer) => {
 685                         let addr = self.memory.read_isize(ptr_arg)?;
 686                         let result_addr = addr + offset * pointee_size as i64;
 687                         self.memory.write_isize(dest, result_addr)?;
 688                     }
 689                     Err(e) => return Err(e),
 690                 }
 691             }
 692
 693             // FIXME(solson): Handle different integer types correctly. Use primvals?
 694             "overflowing_sub" => {
 695                 let ty = *substs.types.get(subst::FnSpace, 0);
 696                 let size = self.type_size(ty, self.substs());
 697                 let left = self.memory.read_int(args[0], size)?;
 698                 let right = self.memory.read_int(args[1], size)?;
 699                 let n = left.wrapping_sub(right);
 700                 self.memory.write_int(dest, n, size)?;
 701             }
 702
 703             "size_of" => {
 704                 let ty = *substs.types.get(subst::FnSpace, 0);
 705                 let size = self.type_size(ty, self.substs()) as u64;
 706                 self.memory.write_uint(dest, size, dest_size)?;
 707             }
 708
 709             "size_of_val" => {
 710                 let ty = *substs.types.get(subst::FnSpace, 0);
 711                 if self.type_is_sized(ty) {
 712                     let size = self.type_size(ty, self.substs()) as u64;
 713                     self.memory.write_uint(dest, size, dest_size)?;
 714                 } else {
 715                     match ty.sty {
 716                         ty::TySlice(_) | ty::TyStr => {
 717                             let elem_ty = ty.sequence_element_type(self.tcx);
 718                             let elem_size = self.type_size(elem_ty, self.substs()) as u64;
 719                             let ptr_size = self.memory.pointer_size as isize;
 720                             let n = self.memory.read_usize(args[0].offset(ptr_size))?;
 721                             self.memory.write_uint(dest, n * elem_size, dest_size)?;
 722                         }
 723
 724                         _ => return Err(EvalError::Unimplemented(format!("unimplemented: size_of_val::<{:?}>", ty))),
 725                     }
 726                 }
 727             }
 728
 729             "transmute" => {
 730                 let ty = *substs.types.get(subst::FnSpace, 0);
 731                 self.move_(args[0], dest, ty)?;
 732             }
 733             "uninit" => self.memory.mark_definedness(dest, dest_size, false)?,
 734
 735             name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
 736         }
 737
 738         // Since we pushed no stack frame, the main loop will act
 739         // as if the call just completed and it's returning to the
 740         // current frame.
 741         Ok(())
 742     }
 743
 744     fn call_c_abi(
 745         &mut self,
 746         def_id: DefId,
 747         args: &[mir::Operand<'tcx>],
 748         dest: Pointer,
 749         dest_size: usize,
 750     ) -> EvalResult<()> {
 751         let name = self.tcx.item_name(def_id);
 752         let attrs = self.tcx.get_attrs(def_id);
 753         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 754             Some(ln) => ln.clone(),
 755             None => name.as_str(),
 756         };
 757
 758         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 759             .map(|arg| self.eval_operand(arg))
 760             .collect();
 761         let args = args_res?;
 762
 763         match &link_name[..] {
 764             "__rust_allocate" => {
 765                 let size = self.memory.read_usize(args[0])?;
 766                 let ptr = self.memory.allocate(size as usize);
 767                 self.memory.write_ptr(dest, ptr)?;
 768             }
 769
 770             "__rust_reallocate" => {
 771                 let ptr = self.memory.read_ptr(args[0])?;
 772                 let size = self.memory.read_usize(args[2])?;
 773                 self.memory.reallocate(ptr, size as usize)?;
 774                 self.memory.write_ptr(dest, ptr)?;
 775             }
 776
 777             "memcmp" => {
 778                 let left = self.memory.read_ptr(args[0])?;
 779                 let right = self.memory.read_ptr(args[1])?;
 780                 let n = self.memory.read_usize(args[2])? as usize;
 781
 782                 let result = {
 783                     let left_bytes = self.memory.read_bytes(left, n)?;
 784                     let right_bytes = self.memory.read_bytes(right, n)?;
 785
 786                     use std::cmp::Ordering::*;
 787                     match left_bytes.cmp(right_bytes) {
 788                         Less => -1,
 789                         Equal => 0,
 790                         Greater => 1,
 791                     }
 792                 };
 793
 794                 self.memory.write_int(dest, result, dest_size)?;
 795             }
 796
 797             _ => return Err(EvalError::Unimplemented(format!("can't call C ABI function: {}", link_name))),
 798         }
 799
 800         // Since we pushed no stack frame, the main loop will act
 801         // as if the call just completed and it's returning to the
 802         // current frame.
 803         Ok(())
 804     }
 805
 806     fn assign_fields<I: IntoIterator<Item = u64>>(
 807         &mut self,
 808         dest: Pointer,
 809         offsets: I,
 810         operands: &[mir::Operand<'tcx>],
 811     ) -> EvalResult<()> {
 812         for (offset, operand) in offsets.into_iter().zip(operands) {
 813             let src = self.eval_operand(operand)?;
 814             let src_ty = self.operand_ty(operand);
 815             let field_dest = dest.offset(offset as isize);
 816             self.move_(src, field_dest, src_ty)?;
 817         }
 818         Ok(())
 819     }
 820
 821     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 822         -> EvalResult<()>
 823     {
 824         let dest = self.eval_lvalue(lvalue)?.to_ptr();
 825         let dest_ty = self.lvalue_ty(lvalue);
 826         let dest_layout = self.type_layout(dest_ty, self.substs());
 827
 828         use rustc::mir::repr::Rvalue::*;
 829         match *rvalue {
 830             Use(ref operand) => {
 831                 let src = self.eval_operand(operand)?;
 832                 self.move_(src, dest, dest_ty)?;
 833             }
 834
 835             BinaryOp(bin_op, ref left, ref right) => {
 836                 let left_ptr = self.eval_operand(left)?;
 837                 let left_ty = self.operand_ty(left);
 838                 let left_val = self.read_primval(left_ptr, left_ty)?;
 839
 840                 let right_ptr = self.eval_operand(right)?;
 841                 let right_ty = self.operand_ty(right);
 842                 let right_val = self.read_primval(right_ptr, right_ty)?;
 843
 844                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 845                 self.memory.write_primval(dest, val)?;
 846             }
 847
 848             UnaryOp(un_op, ref operand) => {
 849                 let ptr = self.eval_operand(operand)?;
 850                 let ty = self.operand_ty(operand);
 851                 let val = self.read_primval(ptr, ty)?;
 852                 self.memory.write_primval(dest, primval::unary_op(un_op, val)?)?;
 853             }
 854
 855             Aggregate(ref kind, ref operands) => {
 856                 use rustc::ty::layout::Layout::*;
 857                 match *dest_layout {
 858                     Univariant { ref variant, .. } => {
 859                         let offsets = iter::once(0)
 860                             .chain(variant.offset_after_field.iter().map(|s| s.bytes()));
 861                         self.assign_fields(dest, offsets, operands)?;
 862                     }
 863
 864                     Array { .. } => {
 865                         let elem_size = match dest_ty.sty {
 866                             ty::TyArray(elem_ty, _) => self.type_size(elem_ty, self.substs()) as u64,
 867                             _ => panic!("tried to assign {:?} to non-array type {:?}",
 868                                         kind, dest_ty),
 869                         };
 870                         let offsets = (0..).map(|i| i * elem_size);
 871                         self.assign_fields(dest, offsets, operands)?;
 872                     }
 873
 874                     General { discr, ref variants, .. } => {
 875                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 876                             let discr_val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 877                             let discr_size = discr.size().bytes() as usize;
 878                             self.memory.write_uint(dest, discr_val, discr_size)?;
 879
 880                             let offsets = variants[variant].offset_after_field.iter()
 881                                 .map(|s| s.bytes());
 882                             self.assign_fields(dest, offsets, operands)?;
 883                         } else {
 884                             panic!("tried to assign {:?} to Layout::General", kind);
 885                         }
 886                     }
 887
 888                     RawNullablePointer { nndiscr, .. } => {
 889                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 890                             if nndiscr == variant as u64 {
 891                                 assert_eq!(operands.len(), 1);
 892                                 let operand = &operands[0];
 893                                 let src = self.eval_operand(operand)?;
 894                                 let src_ty = self.operand_ty(operand);
 895                                 self.move_(src, dest, src_ty)?;
 896                             } else {
 897                                 assert_eq!(operands.len(), 0);
 898                                 self.memory.write_isize(dest, 0)?;
 899                             }
 900                         } else {
 901                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 902                         }
 903                     }
 904
 905                     StructWrappedNullablePointer { nndiscr, ref nonnull, ref discrfield } => {
 906                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 907                             if nndiscr == variant as u64 {
 908                                 let offsets = iter::once(0)
 909                                     .chain(nonnull.offset_after_field.iter().map(|s| s.bytes()));
 910                                 try!(self.assign_fields(dest, offsets, operands));
 911                             } else {
 912                                 assert_eq!(operands.len(), 0);
 913                                 let offset = self.nonnull_offset(dest_ty, nndiscr, discrfield)?;
 914                                 let dest = dest.offset(offset.bytes() as isize);
 915                                 try!(self.memory.write_isize(dest, 0));
 916                             }
 917                         } else {
 918                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 919                         }
 920                     }
 921
 922                     CEnum { discr, signed, .. } => {
 923                         assert_eq!(operands.len(), 0);
 924                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 925                             let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 926                             let size = discr.size().bytes() as usize;
 927
 928                             if signed {
 929                                 self.memory.write_int(dest, val as i64, size)?;
 930                             } else {
 931                                 self.memory.write_uint(dest, val, size)?;
 932                             }
 933                         } else {
 934                             panic!("tried to assign {:?} to Layout::CEnum", kind);
 935                         }
 936                     }
 937
 938                     _ => return Err(EvalError::Unimplemented(format!("can't handle destination layout {:?} when assigning {:?}", dest_layout, kind))),
 939                 }
 940             }
 941
 942             Repeat(ref operand, _) => {
 943                 let (elem_size, length) = match dest_ty.sty {
 944                     ty::TyArray(elem_ty, n) => (self.type_size(elem_ty, self.substs()), n),
 945                     _ => panic!("tried to assign array-repeat to non-array type {:?}", dest_ty),
 946                 };
 947
 948                 let src = self.eval_operand(operand)?;
 949                 for i in 0..length {
 950                     let elem_dest = dest.offset((i * elem_size) as isize);
 951                     self.memory.copy(src, elem_dest, elem_size)?;
 952                 }
 953             }
 954
 955             Len(ref lvalue) => {
 956                 let src = self.eval_lvalue(lvalue)?;
 957                 let ty = self.lvalue_ty(lvalue);
 958                 let len = match ty.sty {
 959                     ty::TyArray(_, n) => n as u64,
 960                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
 961                         n
 962                     } else {
 963                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
 964                     },
 965                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
 966                 };
 967                 self.memory.write_usize(dest, len)?;
 968             }
 969
 970             Ref(_, _, ref lvalue) => {
 971                 let lv = self.eval_lvalue(lvalue)?;
 972                 self.memory.write_ptr(dest, lv.ptr)?;
 973                 match lv.extra {
 974                     LvalueExtra::None => {},
 975                     LvalueExtra::Length(len) => {
 976                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
 977                         self.memory.write_usize(len_ptr, len)?;
 978                     }
 979                     LvalueExtra::DowncastVariant(..) =>
 980                         panic!("attempted to take a reference to an enum downcast lvalue"),
 981                 }
 982             }
 983
 984             Box(ty) => {
 985                 let size = self.type_size(ty, self.substs());
 986                 let ptr = self.memory.allocate(size);
 987                 self.memory.write_ptr(dest, ptr)?;
 988             }
 989
 990             Cast(kind, ref operand, dest_ty) => {
 991                 let src = self.eval_operand(operand)?;
 992                 let src_ty = self.operand_ty(operand);
 993
 994                 use rustc::mir::repr::CastKind::*;
 995                 match kind {
 996                     Unsize => {
 997                         self.move_(src, dest, src_ty)?;
 998                         let src_pointee_ty = pointee_type(src_ty).unwrap();
 999                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
1000
1001                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
1002                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
1003                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
1004                                 self.memory.write_usize(len_ptr, length as u64)?;
1005                             }
1006
1007                             _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1008                         }
1009                     }
1010
1011                     Misc => {
1012                         // FIXME(solson): Wrong for almost everything.
1013                         let size = dest_layout.size(&self.tcx.data_layout).bytes() as usize;
1014                         self.memory.copy(src, dest, size)?;
1015                     }
1016
1017                     _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1018                 }
1019             }
1020
1021             Slice { .. } => unimplemented!(),
1022             InlineAsm { .. } => unimplemented!(),
1023         }
1024
1025         Ok(())
1026     }
1027
1028     fn nonnull_offset(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<Size> {
1029         // Skip the constant 0 at the start meant for LLVM GEP.
1030         let mut path = discrfield.iter().skip(1).map(|&i| i as usize);
1031
1032         // Handle the field index for the outer non-null variant.
1033         let inner_ty = match ty.sty {
1034             ty::TyEnum(adt_def, substs) => {
1035                 let variant = &adt_def.variants[nndiscr as usize];
1036                 let index = path.next().unwrap();
1037                 let field = &variant.fields[index];
1038                 field.ty(self.tcx, substs)
1039             }
1040             _ => panic!(
1041                 "non-enum for StructWrappedNullablePointer: {}",
1042                 ty,
1043             ),
1044         };
1045
1046         self.field_path_offset(inner_ty, path)
1047     }
1048
1049     fn field_path_offset<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<Size> {
1050         let mut offset = Size::from_bytes(0);
1051
1052         // Skip the initial 0 intended for LLVM GEP.
1053         for field_index in path {
1054             let field_offset = self.get_field_offset(ty, field_index)?;
1055             ty = self.get_field_ty(ty, field_index)?;
1056             offset = offset.checked_add(field_offset, &self.tcx.data_layout).unwrap();
1057         }
1058
1059         Ok(offset)
1060     }
1061
1062     fn get_field_ty(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Ty<'tcx>> {
1063         match ty.sty {
1064             ty::TyStruct(adt_def, substs) => {
1065                 Ok(adt_def.struct_variant().fields[field_index].ty(self.tcx, substs))
1066             }
1067
1068             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1069             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1070             ty::TyBox(ty) => {
1071                 assert_eq!(field_index, 0);
1072                 Ok(ty)
1073             }
1074             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}", ty))),
1075         }
1076     }
1077
1078     fn get_field_offset(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Size> {
1079         let layout = self.type_layout(ty, self.substs());
1080
1081         use rustc::ty::layout::Layout::*;
1082         match *layout {
1083             Univariant { .. } => {
1084                 assert_eq!(field_index, 0);
1085                 Ok(Size::from_bytes(0))
1086             }
1087             FatPointer { .. } => {
1088                 let bytes = layout::FAT_PTR_ADDR * self.memory.pointer_size;
1089                 Ok(Size::from_bytes(bytes as u64))
1090             }
1091             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}, with layout: {:?}", ty, layout))),
1092         }
1093     }
1094
1095     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
1096         use rustc::mir::repr::Operand::*;
1097         match *op {
1098             Consume(ref lvalue) => Ok(self.eval_lvalue(lvalue)?.to_ptr()),
1099             Constant(mir::Constant { ref literal, ty, .. }) => {
1100                 use rustc::mir::repr::Literal::*;
1101                 match *literal {
1102                     Value { ref value } => Ok(self.const_to_ptr(value)?),
1103                     Item { def_id, substs } => {
1104                         if let ty::TyFnDef(..) = ty.sty {
1105                             Err(EvalError::Unimplemented("unimplemented: mentions of function items".to_string()))
1106                         } else {
1107                             let cid = ConstantId {
1108                                 def_id: def_id,
1109                                 substs: substs,
1110                                 kind: ConstantKind::Global,
1111                             };
1112                             Ok(*self.statics.get(&cid).expect("static should have been cached (rvalue)"))
1113                         }
1114                     },
1115                     Promoted { index } => {
1116                         let cid = ConstantId {
1117                             def_id: self.frame().def_id,
1118                             substs: self.substs(),
1119                             kind: ConstantKind::Promoted(index),
1120                         };
1121                         Ok(*self.statics.get(&cid).expect("a promoted constant hasn't been precomputed"))
1122                     },
1123                 }
1124             }
1125         }
1126     }
1127
1128     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
1129         use rustc::mir::repr::Lvalue::*;
1130         let ptr = match *lvalue {
1131             ReturnPointer => self.frame().return_ptr
1132                 .expect("ReturnPointer used in a function with no return value"),
1133             Arg(i) => self.frame().locals[i as usize],
1134             Var(i) => self.frame().locals[self.frame().var_offset + i as usize],
1135             Temp(i) => self.frame().locals[self.frame().temp_offset + i as usize],
1136
1137             Static(def_id) => {
1138                 let substs = self.tcx.mk_substs(subst::Substs::empty());
1139                 let cid = ConstantId {
1140                     def_id: def_id,
1141                     substs: substs,
1142                     kind: ConstantKind::Global,
1143                 };
1144                 *self.statics.get(&cid).expect("static should have been cached (lvalue)")
1145             },
1146
1147             Projection(ref proj) => {
1148                 let base = self.eval_lvalue(&proj.base)?;
1149                 let base_ty = self.lvalue_ty(&proj.base);
1150                 let base_layout = self.type_layout(base_ty, self.substs());
1151
1152                 use rustc::mir::repr::ProjectionElem::*;
1153                 match proj.elem {
1154                     Field(field, _) => {
1155                         use rustc::ty::layout::Layout::*;
1156                         let variant = match *base_layout {
1157                             Univariant { ref variant, .. } => variant,
1158                             General { ref variants, .. } => {
1159                                 if let LvalueExtra::DowncastVariant(variant_idx) = base.extra {
1160                                     &variants[variant_idx]
1161                                 } else {
1162                                     panic!("field access on enum had no variant index");
1163                                 }
1164                             }
1165                             RawNullablePointer { .. } => {
1166                                 assert_eq!(field.index(), 0);
1167                                 return Ok(base);
1168                             }
1169                             StructWrappedNullablePointer { ref nonnull, .. } => nonnull,
1170                             _ => panic!("field access on non-product type: {:?}", base_layout),
1171                         };
1172
1173                         let offset = variant.field_offset(field.index()).bytes();
1174                         base.ptr.offset(offset as isize)
1175                     },
1176
1177                     Downcast(_, variant) => {
1178                         use rustc::ty::layout::Layout::*;
1179                         match *base_layout {
1180                             General { discr, .. } => {
1181                                 return Ok(Lvalue {
1182                                     ptr: base.ptr.offset(discr.size().bytes() as isize),
1183                                     extra: LvalueExtra::DowncastVariant(variant),
1184                                 });
1185                             }
1186                             RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
1187                                 return Ok(base);
1188                             }
1189                             _ => panic!("variant downcast on non-aggregate: {:?}", base_layout),
1190                         }
1191                     },
1192
1193                     Deref => {
1194                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
1195                         let ptr = self.memory.read_ptr(base.ptr)?;
1196                         let extra = match pointee_ty.sty {
1197                             ty::TySlice(_) | ty::TyStr => {
1198                                 let len_ptr = base.ptr.offset(self.memory.pointer_size as isize);
1199                                 let len = self.memory.read_usize(len_ptr)?;
1200                                 LvalueExtra::Length(len)
1201                             }
1202                             ty::TyTrait(_) => unimplemented!(),
1203                             _ => LvalueExtra::None,
1204                         };
1205                         return Ok(Lvalue { ptr: ptr, extra: extra });
1206                     }
1207
1208                     Index(ref operand) => {
1209                         let elem_size = match base_ty.sty {
1210                             ty::TyArray(elem_ty, _) |
1211                             ty::TySlice(elem_ty) => self.type_size(elem_ty, self.substs()),
1212                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
1213                         };
1214                         let n_ptr = self.eval_operand(operand)?;
1215                         let n = self.memory.read_usize(n_ptr)?;
1216                         base.ptr.offset(n as isize * elem_size as isize)
1217                     }
1218
1219                     ConstantIndex { .. } => unimplemented!(),
1220                 }
1221             }
1222         };
1223
1224         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
1225     }
1226
1227     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> Ty<'tcx> {
1228         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx), self.substs())
1229     }
1230
1231     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> Ty<'tcx> {
1232         self.monomorphize(self.mir().operand_ty(self.tcx, operand), self.substs())
1233     }
1234
1235     fn move_(&mut self, src: Pointer, dest: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
1236         let size = self.type_size(ty, self.substs());
1237         self.memory.copy(src, dest, size)?;
1238         if self.type_needs_drop(ty) {
1239             self.memory.drop_fill(src, size)?;
1240         }
1241         Ok(())
1242     }
1243
1244     pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<PrimVal> {
1245         use syntax::ast::{IntTy, UintTy};
1246         let val = match (self.memory.pointer_size, &ty.sty) {
1247             (_, &ty::TyBool)              => PrimVal::Bool(self.memory.read_bool(ptr)?),
1248             (_, &ty::TyInt(IntTy::I8))    => PrimVal::I8(self.memory.read_int(ptr, 1)? as i8),
1249             (2, &ty::TyInt(IntTy::Is)) |
1250             (_, &ty::TyInt(IntTy::I16))   => PrimVal::I16(self.memory.read_int(ptr, 2)? as i16),
1251             (4, &ty::TyInt(IntTy::Is)) |
1252             (_, &ty::TyInt(IntTy::I32))   => PrimVal::I32(self.memory.read_int(ptr, 4)? as i32),
1253             (8, &ty::TyInt(IntTy::Is)) |
1254             (_, &ty::TyInt(IntTy::I64))   => PrimVal::I64(self.memory.read_int(ptr, 8)? as i64),
1255             (_, &ty::TyUint(UintTy::U8))  => PrimVal::U8(self.memory.read_uint(ptr, 1)? as u8),
1256             (2, &ty::TyUint(UintTy::Us)) |
1257             (_, &ty::TyUint(UintTy::U16)) => PrimVal::U16(self.memory.read_uint(ptr, 2)? as u16),
1258             (4, &ty::TyUint(UintTy::Us)) |
1259             (_, &ty::TyUint(UintTy::U32)) => PrimVal::U32(self.memory.read_uint(ptr, 4)? as u32),
1260             (8, &ty::TyUint(UintTy::Us)) |
1261             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
1262
1263             (_, &ty::TyRef(_, ty::TypeAndMut { ty, .. })) |
1264             (_, &ty::TyRawPtr(ty::TypeAndMut { ty, .. })) => {
1265                 if self.type_is_sized(ty) {
1266                     match self.memory.read_ptr(ptr) {
1267                         Ok(p) => PrimVal::AbstractPtr(p),
1268                         Err(EvalError::ReadBytesAsPointer) => {
1269                             PrimVal::IntegerPtr(self.memory.read_usize(ptr)?)
1270                         }
1271                         Err(e) => return Err(e),
1272                     }
1273                 } else {
1274                     return Err(EvalError::Unimplemented(format!("unimplemented: primitive read of fat pointer type: {:?}", ty)));
1275                 }
1276             }
1277
1278             _ => panic!("primitive read of non-primitive type: {:?}", ty),
1279         };
1280         Ok(val)
1281     }
1282
1283     fn frame(&self) -> &Frame<'a, 'tcx> {
1284         self.stack.last().expect("no call frames exist")
1285     }
1286
1287     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
1288         self.stack.last_mut().expect("no call frames exist")
1289     }
1290
1291     fn mir(&self) -> CachedMir<'a, 'tcx> {
1292         self.frame().mir.clone()
1293     }
1294
1295     fn substs(&self) -> &'tcx Substs<'tcx> {
1296         self.frame().substs
1297     }
1298 }
1299
1300 fn pointee_type(ptr_ty: ty::Ty) -> Option<ty::Ty> {
1301     match ptr_ty.sty {
1302         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1303         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1304         ty::TyBox(ty) => {
1305             Some(ty)
1306         }
1307         _ => None,
1308     }
1309 }
1310
1311 impl Lvalue {
1312     fn to_ptr(self) -> Pointer {
1313         assert_eq!(self.extra, LvalueExtra::None);
1314         self.ptr
1315     }
1316 }
1317
1318 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1319     type Target = mir::Mir<'tcx>;
1320     fn deref(&self) -> &mir::Mir<'tcx> {
1321         match *self {
1322             CachedMir::Ref(r) => r,
1323             CachedMir::Owned(ref rc) => rc,
1324         }
1325     }
1326 }
1327
1328 #[derive(Debug)]
1329 pub struct ImplMethod<'tcx> {
1330     pub method: Rc<ty::Method<'tcx>>,
1331     pub substs: &'tcx Substs<'tcx>,
1332     pub is_provided: bool,
1333 }
1334
1335 /// Locates the applicable definition of a method, given its name.
1336 pub fn get_impl_method<'a, 'tcx>(
1337     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1338     impl_def_id: DefId,
1339     substs: &'tcx Substs<'tcx>,
1340     name: ast::Name,
1341 ) -> ImplMethod<'tcx> {
1342     assert!(!substs.types.needs_infer());
1343
1344     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1345     let trait_def = tcx.lookup_trait_def(trait_def_id);
1346
1347     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1348         Some(node_item) => {
1349             let substs = tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
1350                 let substs = traits::translate_substs(&infcx, impl_def_id,
1351                                                       substs, node_item.node);
1352                 tcx.lift(&substs).unwrap_or_else(|| {
1353                     bug!("trans::meth::get_impl_method: translate_substs \
1354                           returned {:?} which contains inference types/regions",
1355                          substs);
1356                 })
1357             });
1358             ImplMethod {
1359                 method: node_item.item,
1360                 substs: substs,
1361                 is_provided: node_item.node.is_from_trait(),
1362             }
1363         }
1364         None => {
1365             bug!("method {:?} not found in {:?}", name, impl_def_id)
1366         }
1367     }
1368 }
1369
1370 // TODO(solson): Upstream these methods into rustc::ty::layout.
1371
1372 trait IntegerExt {
1373     fn size(self) -> Size;
1374 }
1375
1376 impl IntegerExt for layout::Integer {
1377     fn size(self) -> Size {
1378         use rustc::ty::layout::Integer::*;
1379         match self {
1380             I1 | I8 => Size::from_bits(8),
1381             I16 => Size::from_bits(16),
1382             I32 => Size::from_bits(32),
1383             I64 => Size::from_bits(64),
1384         }
1385     }
1386 }
1387
1388 trait StructExt {
1389     fn field_offset(&self, index: usize) -> Size;
1390 }
1391
1392 impl StructExt for layout::Struct {
1393     fn field_offset(&self, index: usize) -> Size {
1394         if index == 0 {
1395             Size::from_bytes(0)
1396         } else {
1397             self.offset_after_field[index - 1]
1398         }
1399     }
1400 }