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 rustc_data_structures::indexed_vec::Idx;
  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 use std::collections::HashMap;
  25
  26 mod stepper;
  27
  28 pub fn step<'ecx, 'a: 'ecx, 'tcx: 'a>(ecx: &'ecx mut EvalContext<'a, 'tcx>) -> EvalResult<bool> {
  29     stepper::Stepper::new(ecx).step()
  30 }
  31
  32 pub struct EvalContext<'a, 'tcx: 'a> {
  33     /// The results of the type checker, from rustc.
  34     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  35
  36     /// A mapping from NodeIds to Mir, from rustc. Only contains MIR for crate-local items.
  37     mir_map: &'a MirMap<'tcx>,
  38
  39     /// A local cache from DefIds to Mir for non-crate-local items.
  40     mir_cache: RefCell<DefIdMap<Rc<mir::Mir<'tcx>>>>,
  41
  42     /// The virtual memory system.
  43     memory: Memory,
  44
  45     /// Precomputed statics, constants and promoteds
  46     statics: HashMap<ConstantId<'tcx>, Pointer>,
  47
  48     /// The virtual call stack.
  49     stack: Vec<Frame<'a, 'tcx>>,
  50 }
  51
  52 /// A stack frame.
  53 pub struct Frame<'a, 'tcx: 'a> {
  54     /// The def_id of the current function
  55     pub def_id: DefId,
  56
  57     /// The span of the call site
  58     pub span: codemap::Span,
  59
  60     /// type substitutions for the current function invocation
  61     pub substs: &'tcx Substs<'tcx>,
  62
  63     /// The MIR for the function called on this frame.
  64     pub mir: CachedMir<'a, 'tcx>,
  65
  66     /// The block that is currently executed (or will be executed after the above call stacks return)
  67     pub next_block: mir::BasicBlock,
  68
  69     /// A pointer for writing the return value of the current call if it's not a diverging call.
  70     pub return_ptr: Option<Pointer>,
  71
  72     /// The list of locals for the current function, stored in order as
  73     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  74     /// and the temporaries at `self.temp_offset`.
  75     pub locals: Vec<Pointer>,
  76
  77     /// The offset of the first variable in `self.locals`.
  78     pub var_offset: usize,
  79
  80     /// The offset of the first temporary in `self.locals`.
  81     pub temp_offset: usize,
  82
  83     /// The index of the currently evaluated statment
  84     pub stmt: usize,
  85 }
  86
  87 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  88 struct Lvalue {
  89     ptr: Pointer,
  90     extra: LvalueExtra,
  91 }
  92
  93 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  94 enum LvalueExtra {
  95     None,
  96     Length(u64),
  97     // TODO(solson): Vtable(memory::AllocId),
  98     DowncastVariant(usize),
  99 }
 100
 101 #[derive(Clone)]
 102 pub enum CachedMir<'mir, 'tcx: 'mir> {
 103     Ref(&'mir mir::Mir<'tcx>),
 104     Owned(Rc<mir::Mir<'tcx>>)
 105 }
 106
 107 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 108 /// Uniquely identifies a specific constant or static
 109 struct ConstantId<'tcx> {
 110     /// the def id of the constant/static or in case of promoteds, the def id of the function they belong to
 111     def_id: DefId,
 112     /// In case of statics and constants this is `Substs::empty()`, so only promoteds and associated
 113     /// constants actually have something useful here. We could special case statics and constants,
 114     /// but that would only require more branching when working with constants, and not bring any
 115     /// real benefits.
 116     substs: &'tcx Substs<'tcx>,
 117     kind: ConstantKind,
 118 }
 119
 120 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 121 enum ConstantKind {
 122     Promoted(mir::Promoted),
 123     /// Statics, constants and associated constants
 124     Global,
 125 }
 126
 127 impl<'a, 'tcx> EvalContext<'a, 'tcx> {
 128     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>, mir_map: &'a MirMap<'tcx>) -> Self {
 129         EvalContext {
 130             tcx: tcx,
 131             mir_map: mir_map,
 132             mir_cache: RefCell::new(DefIdMap()),
 133             memory: Memory::new(tcx.sess
 134                                    .target
 135                                    .uint_type
 136                                    .bit_width()
 137                                    .expect("Session::target::uint_type was usize")/8),
 138             statics: HashMap::new(),
 139             stack: Vec::new(),
 140         }
 141     }
 142
 143     pub fn alloc_ret_ptr(&mut self, output_ty: ty::FnOutput<'tcx>, substs: &'tcx Substs<'tcx>) -> Option<Pointer> {
 144         match output_ty {
 145             ty::FnConverging(ty) => {
 146                 let size = self.type_size_with_substs(ty, substs);
 147                 Some(self.memory.allocate(size))
 148             }
 149             ty::FnDiverging => None,
 150         }
 151     }
 152
 153     pub fn memory(&self) -> &Memory {
 154         &self.memory
 155     }
 156
 157     pub fn stack(&self) -> &[Frame] {
 158         &self.stack
 159     }
 160
 161     // TODO(solson): Try making const_to_primval instead.
 162     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<Pointer> {
 163         use rustc::middle::const_val::ConstVal::*;
 164         match *const_val {
 165             Float(_f) => unimplemented!(),
 166             Integral(int) => {
 167                 // TODO(solson): Check int constant type.
 168                 let ptr = self.memory.allocate(8);
 169                 self.memory.write_uint(ptr, int.to_u64_unchecked(), 8)?;
 170                 Ok(ptr)
 171             }
 172             Str(ref s) => {
 173                 let psize = self.memory.pointer_size;
 174                 let static_ptr = self.memory.allocate(s.len());
 175                 let ptr = self.memory.allocate(psize * 2);
 176                 self.memory.write_bytes(static_ptr, s.as_bytes())?;
 177                 self.memory.write_ptr(ptr, static_ptr)?;
 178                 self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64)?;
 179                 Ok(ptr)
 180             }
 181             ByteStr(ref bs) => {
 182                 let psize = self.memory.pointer_size;
 183                 let static_ptr = self.memory.allocate(bs.len());
 184                 let ptr = self.memory.allocate(psize);
 185                 self.memory.write_bytes(static_ptr, bs)?;
 186                 self.memory.write_ptr(ptr, static_ptr)?;
 187                 Ok(ptr)
 188             }
 189             Bool(b) => {
 190                 let ptr = self.memory.allocate(1);
 191                 self.memory.write_bool(ptr, b)?;
 192                 Ok(ptr)
 193             }
 194             Char(_c)          => unimplemented!(),
 195             Struct(_node_id)  => unimplemented!(),
 196             Tuple(_node_id)   => unimplemented!(),
 197             Function(_def_id) => unimplemented!(),
 198             Array(_, _)       => unimplemented!(),
 199             Repeat(_, _)      => unimplemented!(),
 200             Dummy             => unimplemented!(),
 201         }
 202     }
 203
 204     fn type_needs_drop(&self, ty: Ty<'tcx>) -> bool {
 205         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
 206     }
 207
 208     fn type_is_sized(&self, ty: Ty<'tcx>) -> bool {
 209         ty.is_sized(self.tcx, &self.tcx.empty_parameter_environment(), DUMMY_SP)
 210     }
 211
 212     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
 213         // Do the initial selection for the obligation. This yields the shallow result we are
 214         // looking for -- that is, what specific impl.
 215         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 216             let mut selcx = traits::SelectionContext::new(&infcx);
 217
 218             let obligation = traits::Obligation::new(
 219                 traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
 220                 trait_ref.to_poly_trait_predicate(),
 221             );
 222             let selection = selcx.select(&obligation).unwrap().unwrap();
 223
 224             // Currently, we use a fulfillment context to completely resolve all nested obligations.
 225             // This is because they can inform the inference of the impl's type parameters.
 226             let mut fulfill_cx = traits::FulfillmentContext::new();
 227             let vtable = selection.map(|predicate| {
 228                 fulfill_cx.register_predicate_obligation(&infcx, predicate);
 229             });
 230             infcx.drain_fulfillment_cx_or_panic(DUMMY_SP, &mut fulfill_cx, &vtable)
 231         })
 232     }
 233
 234     /// Trait method, which has to be resolved to an impl method.
 235     pub fn trait_method(
 236         &self,
 237         def_id: DefId,
 238         substs: &'tcx Substs<'tcx>
 239     ) -> (DefId, &'tcx Substs<'tcx>) {
 240         let method_item = self.tcx.impl_or_trait_item(def_id);
 241         let trait_id = method_item.container().id();
 242         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
 243         match self.fulfill_obligation(trait_ref) {
 244             traits::VtableImpl(vtable_impl) => {
 245                 let impl_did = vtable_impl.impl_def_id;
 246                 let mname = self.tcx.item_name(def_id);
 247                 // Create a concatenated set of substitutions which includes those from the impl
 248                 // and those from the method:
 249                 let impl_substs = vtable_impl.substs.with_method_from(substs);
 250                 let substs = self.tcx.mk_substs(impl_substs);
 251                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
 252
 253                 (mth.method.def_id, mth.substs)
 254             }
 255
 256             traits::VtableClosure(vtable_closure) =>
 257                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
 258
 259             traits::VtableFnPointer(_fn_ty) => {
 260                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
 261                 unimplemented!()
 262                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
 263
 264                 // let method_ty = def_ty(tcx, def_id, substs);
 265                 // let fn_ptr_ty = match method_ty.sty {
 266                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
 267                 //     _ => unreachable!("expected fn item type, found {}",
 268                 //                       method_ty)
 269                 // };
 270                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 271             }
 272
 273             traits::VtableObject(ref _data) => {
 274                 unimplemented!()
 275                 // Callee {
 276                 //     data: Virtual(traits::get_vtable_index_of_object_method(
 277                 //                   tcx, data, def_id)),
 278                 //                   ty: def_ty(tcx, def_id, substs)
 279                 // }
 280             }
 281             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
 282         }
 283     }
 284
 285     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
 286         match self.tcx.map.as_local_node_id(def_id) {
 287             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
 288             None => {
 289                 let mut mir_cache = self.mir_cache.borrow_mut();
 290                 if let Some(mir) = mir_cache.get(&def_id) {
 291                     return CachedMir::Owned(mir.clone());
 292                 }
 293
 294                 let cs = &self.tcx.sess.cstore;
 295                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
 296                     panic!("no mir for {:?}", def_id);
 297                 });
 298                 let cached = Rc::new(mir);
 299                 mir_cache.insert(def_id, cached.clone());
 300                 CachedMir::Owned(cached)
 301             }
 302         }
 303     }
 304
 305     fn monomorphize(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> Ty<'tcx> {
 306         let substituted = ty.subst(self.tcx, substs);
 307         self.tcx.normalize_associated_type(&substituted)
 308     }
 309
 310     fn type_size(&self, ty: Ty<'tcx>) -> usize {
 311         self.type_size_with_substs(ty, self.substs())
 312     }
 313
 314     fn type_size_with_substs(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> usize {
 315         self.type_layout_with_substs(ty, substs).size(&self.tcx.data_layout).bytes() as usize
 316     }
 317
 318     fn type_layout(&self, ty: Ty<'tcx>) -> &'tcx Layout {
 319         self.type_layout_with_substs(ty, self.substs())
 320     }
 321
 322     fn type_layout_with_substs(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> &'tcx Layout {
 323         // TODO(solson): Is this inefficient? Needs investigation.
 324         let ty = self.monomorphize(ty, substs);
 325
 326         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 327             // TODO(solson): Report this error properly.
 328             ty.layout(&infcx).unwrap()
 329         })
 330     }
 331
 332     pub fn push_stack_frame(&mut self, def_id: DefId, span: codemap::Span, mir: CachedMir<'a, 'tcx>, substs: &'tcx Substs<'tcx>,
 333         return_ptr: Option<Pointer>)
 334     {
 335         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 336         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 337         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 338
 339         let num_args = mir.arg_decls.len();
 340         let num_vars = mir.var_decls.len();
 341
 342         ::log_settings::settings().indentation += 1;
 343
 344         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 345             let size = self.type_size_with_substs(ty, substs);
 346             self.memory.allocate(size)
 347         }).collect();
 348
 349         self.stack.push(Frame {
 350             mir: mir.clone(),
 351             next_block: mir::START_BLOCK,
 352             return_ptr: return_ptr,
 353             locals: locals,
 354             var_offset: num_args,
 355             temp_offset: num_args + num_vars,
 356             span: span,
 357             def_id: def_id,
 358             substs: substs,
 359             stmt: 0,
 360         });
 361     }
 362
 363     fn pop_stack_frame(&mut self) {
 364         ::log_settings::settings().indentation -= 1;
 365         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 366         // TODO(solson): Deallocate local variables.
 367     }
 368
 369     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 370             -> EvalResult<()> {
 371         use rustc::mir::repr::TerminatorKind::*;
 372         match terminator.kind {
 373             Return => self.pop_stack_frame(),
 374
 375             Goto { target } => {
 376                 self.frame_mut().next_block = target;
 377             },
 378
 379             If { ref cond, targets: (then_target, else_target) } => {
 380                 let cond_ptr = self.eval_operand(cond)?;
 381                 let cond_val = self.memory.read_bool(cond_ptr)?;
 382                 self.frame_mut().next_block = if cond_val { then_target } else { else_target };
 383             }
 384
 385             SwitchInt { ref discr, ref values, ref targets, .. } => {
 386                 let discr_ptr = self.eval_lvalue(discr)?.to_ptr();
 387                 let discr_size = self
 388                     .type_layout(self.lvalue_ty(discr))
 389                     .size(&self.tcx.data_layout)
 390                     .bytes() as usize;
 391                 let discr_val = self.memory.read_uint(discr_ptr, discr_size)?;
 392
 393                 // Branch to the `otherwise` case by default, if no match is found.
 394                 let mut target_block = targets[targets.len() - 1];
 395
 396                 for (index, val_const) in values.iter().enumerate() {
 397                     let ptr = self.const_to_ptr(val_const)?;
 398                     let val = self.memory.read_uint(ptr, discr_size)?;
 399                     if discr_val == val {
 400                         target_block = targets[index];
 401                         break;
 402                     }
 403                 }
 404
 405                 self.frame_mut().next_block = target_block;
 406             }
 407
 408             Switch { ref discr, ref targets, adt_def } => {
 409                 let adt_ptr = self.eval_lvalue(discr)?.to_ptr();
 410                 let adt_ty = self.lvalue_ty(discr);
 411                 let discr_val = self.read_discriminant_value(adt_ptr, adt_ty)?;
 412                 let matching = adt_def.variants.iter()
 413                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 414
 415                 match matching {
 416                     Some(i) => {
 417                         self.frame_mut().next_block = targets[i];
 418                     },
 419                     None => return Err(EvalError::InvalidDiscriminant),
 420                 }
 421             }
 422
 423             Call { ref func, ref args, ref destination, .. } => {
 424                 let mut return_ptr = None;
 425                 if let Some((ref lv, target)) = *destination {
 426                     self.frame_mut().next_block = target;
 427                     return_ptr = Some(self.eval_lvalue(lv)?.to_ptr());
 428                 }
 429
 430                 let func_ty = self.operand_ty(func);
 431                 match func_ty.sty {
 432                     ty::TyFnDef(def_id, substs, fn_ty) => {
 433                         use syntax::abi::Abi;
 434                         match fn_ty.abi {
 435                             Abi::RustIntrinsic => {
 436                                 let name = self.tcx.item_name(def_id).as_str();
 437                                 match fn_ty.sig.0.output {
 438                                     ty::FnConverging(ty) => {
 439                                         let size = self.type_size(ty);
 440                                         let ret = return_ptr.unwrap();
 441                                         self.call_intrinsic(&name, substs, args, ret, size)?
 442                                     }
 443                                     ty::FnDiverging => unimplemented!(),
 444                                 }
 445                             }
 446
 447                             Abi::C => {
 448                                 match fn_ty.sig.0.output {
 449                                     ty::FnConverging(ty) => {
 450                                         let size = self.type_size(ty);
 451                                         self.call_c_abi(def_id, args, return_ptr.unwrap(), size)?
 452                                     }
 453                                     ty::FnDiverging => unimplemented!(),
 454                                 }
 455                             }
 456
 457                             Abi::Rust | Abi::RustCall => {
 458                                 // TODO(solson): Adjust the first argument when calling a Fn or
 459                                 // FnMut closure via FnOnce::call_once.
 460
 461                                 // Only trait methods can have a Self parameter.
 462                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 463                                     self.trait_method(def_id, substs)
 464                                 } else {
 465                                     (def_id, substs)
 466                                 };
 467
 468                                 let mut arg_srcs = Vec::new();
 469                                 for arg in args {
 470                                     let src = self.eval_operand(arg)?;
 471                                     let src_ty = self.operand_ty(arg);
 472                                     arg_srcs.push((src, src_ty));
 473                                 }
 474
 475                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 476                                     arg_srcs.pop();
 477                                     let last_arg = args.last().unwrap();
 478                                     let last = self.eval_operand(last_arg)?;
 479                                     let last_ty = self.operand_ty(last_arg);
 480                                     let last_layout = self.type_layout(last_ty);
 481                                     match (&last_ty.sty, last_layout) {
 482                                         (&ty::TyTuple(fields),
 483                                          &Layout::Univariant { ref variant, .. }) => {
 484                                             let offsets = iter::once(0)
 485                                                 .chain(variant.offset_after_field.iter()
 486                                                     .map(|s| s.bytes()));
 487                                             for (offset, ty) in offsets.zip(fields) {
 488                                                 let src = last.offset(offset as isize);
 489                                                 arg_srcs.push((src, ty));
 490                                             }
 491                                         }
 492                                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 493                                     }
 494                                 }
 495
 496                                 let mir = self.load_mir(resolved_def_id);
 497                                 self.push_stack_frame(
 498                                     def_id, terminator.source_info.span, mir, resolved_substs,
 499                                     return_ptr
 500                                 );
 501
 502                                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 503                                     let dest = self.frame().locals[i];
 504                                     self.move_(src, dest, src_ty)?;
 505                                 }
 506                             }
 507
 508                             abi => return Err(EvalError::Unimplemented(format!("can't handle function with {:?} ABI", abi))),
 509                         }
 510                     }
 511
 512                     _ => return Err(EvalError::Unimplemented(format!("can't handle callee of type {:?}", func_ty))),
 513                 }
 514             }
 515
 516             Drop { ref location, target, .. } => {
 517                 let ptr = self.eval_lvalue(location)?.to_ptr();
 518                 let ty = self.lvalue_ty(location);
 519                 self.drop(ptr, ty)?;
 520                 self.frame_mut().next_block = target;
 521             }
 522
 523             Assert { ref cond, expected, ref msg, target, cleanup } => {
 524                 let actual_ptr = self.eval_operand(cond)?;
 525                 let actual = self.memory.read_bool(actual_ptr)?;
 526                 if actual == expected {
 527                     self.frame_mut().next_block = target;
 528                 } else {
 529                     panic!("unimplemented: jump to {:?} and print {:?}", cleanup, msg);
 530                 }
 531             }
 532
 533             DropAndReplace { .. } => unimplemented!(),
 534             Resume => unimplemented!(),
 535             Unreachable => unimplemented!(),
 536         }
 537
 538         Ok(())
 539     }
 540
 541     fn drop(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
 542         if !self.type_needs_drop(ty) {
 543             debug!("no need to drop {:?}", ty);
 544             return Ok(());
 545         }
 546         trace!("-need to drop {:?}", ty);
 547
 548         // TODO(solson): Call user-defined Drop::drop impls.
 549
 550         match ty.sty {
 551             ty::TyBox(contents_ty) => {
 552                 match self.memory.read_ptr(ptr) {
 553                     Ok(contents_ptr) => {
 554                         self.drop(contents_ptr, contents_ty)?;
 555                         trace!("-deallocating box");
 556                         self.memory.deallocate(contents_ptr)?;
 557                     }
 558                     Err(EvalError::ReadBytesAsPointer) => {
 559                         let size = self.memory.pointer_size;
 560                         let possible_drop_fill = self.memory.read_bytes(ptr, size)?;
 561                         if possible_drop_fill.iter().all(|&b| b == mem::POST_DROP_U8) {
 562                             return Ok(());
 563                         } else {
 564                             return Err(EvalError::ReadBytesAsPointer);
 565                         }
 566                     }
 567                     Err(e) => return Err(e),
 568                 }
 569             }
 570
 571             // TODO(solson): Implement drop for other relevant types (e.g. aggregates).
 572             _ => {}
 573         }
 574
 575         // Filling drop.
 576         // FIXME(solson): Trait objects (with no static size) probably get filled, too.
 577         let size = self.type_size(ty);
 578         self.memory.drop_fill(ptr, size)?;
 579
 580         Ok(())
 581     }
 582
 583     fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalResult<u64> {
 584         use rustc::ty::layout::Layout::*;
 585         let adt_layout = self.type_layout(adt_ty);
 586
 587         let discr_val = match *adt_layout {
 588             General { discr, .. } | CEnum { discr, .. } => {
 589                 let discr_size = discr.size().bytes();
 590                 self.memory.read_uint(adt_ptr, discr_size as usize)?
 591             }
 592
 593             RawNullablePointer { nndiscr, .. } => {
 594                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
 595             }
 596
 597             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
 598                 let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
 599                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
 600                 self.read_nonnull_discriminant_value(nonnull, nndiscr)?
 601             }
 602
 603             // The discriminant_value intrinsic returns 0 for non-sum types.
 604             Array { .. } | FatPointer { .. } | Scalar { .. } | Univariant { .. } |
 605             Vector { .. } => 0,
 606         };
 607
 608         Ok(discr_val)
 609     }
 610
 611     fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<u64> {
 612         let not_null = match self.memory.read_usize(ptr) {
 613             Ok(0) => false,
 614             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
 615             Err(e) => return Err(e),
 616         };
 617         assert!(nndiscr == 0 || nndiscr == 1);
 618         Ok(if not_null { nndiscr } else { 1 - nndiscr })
 619     }
 620
 621     fn call_intrinsic(
 622         &mut self,
 623         name: &str,
 624         substs: &'tcx Substs<'tcx>,
 625         args: &[mir::Operand<'tcx>],
 626         dest: Pointer,
 627         dest_size: usize
 628     ) -> EvalResult<()> {
 629         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 630             .map(|arg| self.eval_operand(arg))
 631             .collect();
 632         let args = args_res?;
 633
 634         match name {
 635             // FIXME(solson): Handle different integer types correctly.
 636             "add_with_overflow" => {
 637                 let ty = *substs.types.get(subst::FnSpace, 0);
 638                 let size = self.type_size(ty);
 639                 let left = self.memory.read_int(args[0], size)?;
 640                 let right = self.memory.read_int(args[1], size)?;
 641                 let (n, overflowed) = unsafe {
 642                     ::std::intrinsics::add_with_overflow::<i64>(left, right)
 643                 };
 644                 self.memory.write_int(dest, n, size)?;
 645                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 646             }
 647
 648             "assume" => {}
 649
 650             "copy_nonoverlapping" => {
 651                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 652                 let elem_size = self.type_size(elem_ty);
 653                 let src = self.memory.read_ptr(args[0])?;
 654                 let dest = self.memory.read_ptr(args[1])?;
 655                 let count = self.memory.read_isize(args[2])?;
 656                 self.memory.copy(src, dest, count as usize * elem_size)?;
 657             }
 658
 659             "discriminant_value" => {
 660                 let ty = *substs.types.get(subst::FnSpace, 0);
 661                 let adt_ptr = self.memory.read_ptr(args[0])?;
 662                 let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
 663                 self.memory.write_uint(dest, discr_val, dest_size)?;
 664             }
 665
 666             "forget" => {
 667                 let arg_ty = *substs.types.get(subst::FnSpace, 0);
 668                 let arg_size = self.type_size(arg_ty);
 669                 self.memory.drop_fill(args[0], arg_size)?;
 670             }
 671
 672             "init" => self.memory.write_repeat(dest, 0, dest_size)?,
 673
 674             "min_align_of" => {
 675                 self.memory.write_int(dest, 1, dest_size)?;
 676             }
 677
 678             "move_val_init" => {
 679                 let ty = *substs.types.get(subst::FnSpace, 0);
 680                 let ptr = self.memory.read_ptr(args[0])?;
 681                 self.move_(args[1], ptr, ty)?;
 682             }
 683
 684             // FIXME(solson): Handle different integer types correctly.
 685             "mul_with_overflow" => {
 686                 let ty = *substs.types.get(subst::FnSpace, 0);
 687                 let size = self.type_size(ty);
 688                 let left = self.memory.read_int(args[0], size)?;
 689                 let right = self.memory.read_int(args[1], size)?;
 690                 let (n, overflowed) = unsafe {
 691                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 692                 };
 693                 self.memory.write_int(dest, n, size)?;
 694                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 695             }
 696
 697             "offset" => {
 698                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 699                 let pointee_size = self.type_size(pointee_ty) as isize;
 700                 let ptr_arg = args[0];
 701                 let offset = self.memory.read_isize(args[1])?;
 702
 703                 match self.memory.read_ptr(ptr_arg) {
 704                     Ok(ptr) => {
 705                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 706                         self.memory.write_ptr(dest, result_ptr)?;
 707                     }
 708                     Err(EvalError::ReadBytesAsPointer) => {
 709                         let addr = self.memory.read_isize(ptr_arg)?;
 710                         let result_addr = addr + offset * pointee_size as i64;
 711                         self.memory.write_isize(dest, result_addr)?;
 712                     }
 713                     Err(e) => return Err(e),
 714                 }
 715             }
 716
 717             // FIXME(solson): Handle different integer types correctly. Use primvals?
 718             "overflowing_sub" => {
 719                 let ty = *substs.types.get(subst::FnSpace, 0);
 720                 let size = self.type_size(ty);
 721                 let left = self.memory.read_int(args[0], size)?;
 722                 let right = self.memory.read_int(args[1], size)?;
 723                 let n = left.wrapping_sub(right);
 724                 self.memory.write_int(dest, n, size)?;
 725             }
 726
 727             "size_of" => {
 728                 let ty = *substs.types.get(subst::FnSpace, 0);
 729                 let size = self.type_size(ty) as u64;
 730                 self.memory.write_uint(dest, size, dest_size)?;
 731             }
 732
 733             "size_of_val" => {
 734                 let ty = *substs.types.get(subst::FnSpace, 0);
 735                 if self.type_is_sized(ty) {
 736                     let size = self.type_size(ty) as u64;
 737                     self.memory.write_uint(dest, size, dest_size)?;
 738                 } else {
 739                     match ty.sty {
 740                         ty::TySlice(_) | ty::TyStr => {
 741                             let elem_ty = ty.sequence_element_type(self.tcx);
 742                             let elem_size = self.type_size(elem_ty) as u64;
 743                             let ptr_size = self.memory.pointer_size as isize;
 744                             let n = self.memory.read_usize(args[0].offset(ptr_size))?;
 745                             self.memory.write_uint(dest, n * elem_size, dest_size)?;
 746                         }
 747
 748                         _ => return Err(EvalError::Unimplemented(format!("unimplemented: size_of_val::<{:?}>", ty))),
 749                     }
 750                 }
 751             }
 752
 753             "transmute" => {
 754                 let ty = *substs.types.get(subst::FnSpace, 0);
 755                 self.move_(args[0], dest, ty)?;
 756             }
 757             "uninit" => self.memory.mark_definedness(dest, dest_size, false)?,
 758
 759             name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
 760         }
 761
 762         // Since we pushed no stack frame, the main loop will act
 763         // as if the call just completed and it's returning to the
 764         // current frame.
 765         Ok(())
 766     }
 767
 768     fn call_c_abi(
 769         &mut self,
 770         def_id: DefId,
 771         args: &[mir::Operand<'tcx>],
 772         dest: Pointer,
 773         dest_size: usize,
 774     ) -> EvalResult<()> {
 775         let name = self.tcx.item_name(def_id);
 776         let attrs = self.tcx.get_attrs(def_id);
 777         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 778             Some(ln) => ln.clone(),
 779             None => name.as_str(),
 780         };
 781
 782         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 783             .map(|arg| self.eval_operand(arg))
 784             .collect();
 785         let args = args_res?;
 786
 787         match &link_name[..] {
 788             "__rust_allocate" => {
 789                 let size = self.memory.read_usize(args[0])?;
 790                 let ptr = self.memory.allocate(size as usize);
 791                 self.memory.write_ptr(dest, ptr)?;
 792             }
 793
 794             "__rust_reallocate" => {
 795                 let ptr = self.memory.read_ptr(args[0])?;
 796                 let size = self.memory.read_usize(args[2])?;
 797                 self.memory.reallocate(ptr, size as usize)?;
 798                 self.memory.write_ptr(dest, ptr)?;
 799             }
 800
 801             "memcmp" => {
 802                 let left = self.memory.read_ptr(args[0])?;
 803                 let right = self.memory.read_ptr(args[1])?;
 804                 let n = self.memory.read_usize(args[2])? as usize;
 805
 806                 let result = {
 807                     let left_bytes = self.memory.read_bytes(left, n)?;
 808                     let right_bytes = self.memory.read_bytes(right, n)?;
 809
 810                     use std::cmp::Ordering::*;
 811                     match left_bytes.cmp(right_bytes) {
 812                         Less => -1,
 813                         Equal => 0,
 814                         Greater => 1,
 815                     }
 816                 };
 817
 818                 self.memory.write_int(dest, result, dest_size)?;
 819             }
 820
 821             _ => {
 822                 return Err(EvalError::Unimplemented(format!("can't call C ABI function: {}", link_name)));
 823             }
 824         }
 825
 826         // Since we pushed no stack frame, the main loop will act
 827         // as if the call just completed and it's returning to the
 828         // current frame.
 829         Ok(())
 830     }
 831
 832     fn assign_fields<I: IntoIterator<Item = u64>>(
 833         &mut self,
 834         dest: Pointer,
 835         offsets: I,
 836         operands: &[mir::Operand<'tcx>],
 837     ) -> EvalResult<()> {
 838         for (offset, operand) in offsets.into_iter().zip(operands) {
 839             let src = self.eval_operand(operand)?;
 840             let src_ty = self.operand_ty(operand);
 841             let field_dest = dest.offset(offset as isize);
 842             self.move_(src, field_dest, src_ty)?;
 843         }
 844         Ok(())
 845     }
 846
 847     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 848         -> EvalResult<()>
 849     {
 850         let dest = self.eval_lvalue(lvalue)?.to_ptr();
 851         let dest_ty = self.lvalue_ty(lvalue);
 852         let dest_layout = self.type_layout(dest_ty);
 853
 854         use rustc::mir::repr::Rvalue::*;
 855         match *rvalue {
 856             Use(ref operand) => {
 857                 let src = self.eval_operand(operand)?;
 858                 self.move_(src, dest, dest_ty)?;
 859             }
 860
 861             BinaryOp(bin_op, ref left, ref right) => {
 862                 let left_ptr = self.eval_operand(left)?;
 863                 let left_ty = self.operand_ty(left);
 864                 let left_val = self.read_primval(left_ptr, left_ty)?;
 865
 866                 let right_ptr = self.eval_operand(right)?;
 867                 let right_ty = self.operand_ty(right);
 868                 let right_val = self.read_primval(right_ptr, right_ty)?;
 869
 870                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 871                 self.memory.write_primval(dest, val)?;
 872             }
 873
 874             // FIXME(solson): Factor this out with BinaryOp.
 875             CheckedBinaryOp(bin_op, ref left, ref right) => {
 876                 let left_ptr = self.eval_operand(left)?;
 877                 let left_ty = self.operand_ty(left);
 878                 let left_val = self.read_primval(left_ptr, left_ty)?;
 879
 880                 let right_ptr = self.eval_operand(right)?;
 881                 let right_ty = self.operand_ty(right);
 882                 let right_val = self.read_primval(right_ptr, right_ty)?;
 883
 884                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 885                 self.memory.write_primval(dest, val)?;
 886
 887                 // FIXME(solson): Find the result type size properly. Perhaps refactor out
 888                 // Projection calculations so we can do the equivalent of `dest.1` here.
 889                 let s = self.type_size(left_ty);
 890                 self.memory.write_bool(dest.offset(s as isize), false)?;
 891             }
 892
 893             UnaryOp(un_op, ref operand) => {
 894                 let ptr = self.eval_operand(operand)?;
 895                 let ty = self.operand_ty(operand);
 896                 let val = self.read_primval(ptr, ty)?;
 897                 self.memory.write_primval(dest, primval::unary_op(un_op, val)?)?;
 898             }
 899
 900             Aggregate(ref kind, ref operands) => {
 901                 use rustc::ty::layout::Layout::*;
 902                 match *dest_layout {
 903                     Univariant { ref variant, .. } => {
 904                         let offsets = iter::once(0)
 905                             .chain(variant.offset_after_field.iter().map(|s| s.bytes()));
 906                         self.assign_fields(dest, offsets, operands)?;
 907                     }
 908
 909                     Array { .. } => {
 910                         let elem_size = match dest_ty.sty {
 911                             ty::TyArray(elem_ty, _) => self.type_size(elem_ty) as u64,
 912                             _ => panic!("tried to assign {:?} to non-array type {:?}",
 913                                         kind, dest_ty),
 914                         };
 915                         let offsets = (0..).map(|i| i * elem_size);
 916                         self.assign_fields(dest, offsets, operands)?;
 917                     }
 918
 919                     General { discr, ref variants, .. } => {
 920                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 921                             let discr_val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 922                             let discr_size = discr.size().bytes() as usize;
 923                             self.memory.write_uint(dest, discr_val, discr_size)?;
 924
 925                             let offsets = variants[variant].offset_after_field.iter()
 926                                 .map(|s| s.bytes());
 927                             self.assign_fields(dest, offsets, operands)?;
 928                         } else {
 929                             panic!("tried to assign {:?} to Layout::General", kind);
 930                         }
 931                     }
 932
 933                     RawNullablePointer { nndiscr, .. } => {
 934                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 935                             if nndiscr == variant as u64 {
 936                                 assert_eq!(operands.len(), 1);
 937                                 let operand = &operands[0];
 938                                 let src = self.eval_operand(operand)?;
 939                                 let src_ty = self.operand_ty(operand);
 940                                 self.move_(src, dest, src_ty)?;
 941                             } else {
 942                                 assert_eq!(operands.len(), 0);
 943                                 self.memory.write_isize(dest, 0)?;
 944                             }
 945                         } else {
 946                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 947                         }
 948                     }
 949
 950                     StructWrappedNullablePointer { nndiscr, ref nonnull, ref discrfield } => {
 951                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 952                             if nndiscr == variant as u64 {
 953                                 let offsets = iter::once(0)
 954                                     .chain(nonnull.offset_after_field.iter().map(|s| s.bytes()));
 955                                 try!(self.assign_fields(dest, offsets, operands));
 956                             } else {
 957                                 assert_eq!(operands.len(), 0);
 958                                 let offset = self.nonnull_offset(dest_ty, nndiscr, discrfield)?;
 959                                 let dest = dest.offset(offset.bytes() as isize);
 960                                 try!(self.memory.write_isize(dest, 0));
 961                             }
 962                         } else {
 963                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 964                         }
 965                     }
 966
 967                     CEnum { discr, signed, .. } => {
 968                         assert_eq!(operands.len(), 0);
 969                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 970                             let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 971                             let size = discr.size().bytes() as usize;
 972
 973                             if signed {
 974                                 self.memory.write_int(dest, val as i64, size)?;
 975                             } else {
 976                                 self.memory.write_uint(dest, val, size)?;
 977                             }
 978                         } else {
 979                             panic!("tried to assign {:?} to Layout::CEnum", kind);
 980                         }
 981                     }
 982
 983                     _ => return Err(EvalError::Unimplemented(format!("can't handle destination layout {:?} when assigning {:?}", dest_layout, kind))),
 984                 }
 985             }
 986
 987             Repeat(ref operand, _) => {
 988                 let (elem_size, length) = match dest_ty.sty {
 989                     ty::TyArray(elem_ty, n) => (self.type_size(elem_ty), n),
 990                     _ => panic!("tried to assign array-repeat to non-array type {:?}", dest_ty),
 991                 };
 992
 993                 let src = self.eval_operand(operand)?;
 994                 for i in 0..length {
 995                     let elem_dest = dest.offset((i * elem_size) as isize);
 996                     self.memory.copy(src, elem_dest, elem_size)?;
 997                 }
 998             }
 999
1000             Len(ref lvalue) => {
1001                 let src = self.eval_lvalue(lvalue)?;
1002                 let ty = self.lvalue_ty(lvalue);
1003                 let len = match ty.sty {
1004                     ty::TyArray(_, n) => n as u64,
1005                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
1006                         n
1007                     } else {
1008                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
1009                     },
1010                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
1011                 };
1012                 self.memory.write_usize(dest, len)?;
1013             }
1014
1015             Ref(_, _, ref lvalue) => {
1016                 let lv = self.eval_lvalue(lvalue)?;
1017                 self.memory.write_ptr(dest, lv.ptr)?;
1018                 match lv.extra {
1019                     LvalueExtra::None => {},
1020                     LvalueExtra::Length(len) => {
1021                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
1022                         self.memory.write_usize(len_ptr, len)?;
1023                     }
1024                     LvalueExtra::DowncastVariant(..) =>
1025                         panic!("attempted to take a reference to an enum downcast lvalue"),
1026                 }
1027             }
1028
1029             Box(ty) => {
1030                 let size = self.type_size(ty);
1031                 let ptr = self.memory.allocate(size);
1032                 self.memory.write_ptr(dest, ptr)?;
1033             }
1034
1035             Cast(kind, ref operand, dest_ty) => {
1036                 let src = self.eval_operand(operand)?;
1037                 let src_ty = self.operand_ty(operand);
1038
1039                 use rustc::mir::repr::CastKind::*;
1040                 match kind {
1041                     Unsize => {
1042                         self.move_(src, dest, src_ty)?;
1043                         let src_pointee_ty = pointee_type(src_ty).unwrap();
1044                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
1045
1046                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
1047                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
1048                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
1049                                 self.memory.write_usize(len_ptr, length as u64)?;
1050                             }
1051
1052                             _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1053                         }
1054                     }
1055
1056                     Misc => {
1057                         // FIXME(solson): Wrong for almost everything.
1058                         let dest_size = self.type_size(dest_ty);
1059                         let src_size = self.type_size(src_ty);
1060                         if dest_size == src_size {
1061                             warn!("performing fishy cast from {:?} to {:?}", src_ty, dest_ty);
1062                             self.memory.copy(src, dest, dest_size)?;
1063                         } else {
1064                             return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue)));
1065                         }
1066                     }
1067
1068                     _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1069                 }
1070             }
1071
1072             InlineAsm { .. } => unimplemented!(),
1073         }
1074
1075         Ok(())
1076     }
1077
1078     fn nonnull_offset(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<Size> {
1079         // Skip the constant 0 at the start meant for LLVM GEP.
1080         let mut path = discrfield.iter().skip(1).map(|&i| i as usize);
1081
1082         // Handle the field index for the outer non-null variant.
1083         let inner_ty = match ty.sty {
1084             ty::TyEnum(adt_def, substs) => {
1085                 let variant = &adt_def.variants[nndiscr as usize];
1086                 let index = path.next().unwrap();
1087                 let field = &variant.fields[index];
1088                 field.ty(self.tcx, substs)
1089             }
1090             _ => panic!(
1091                 "non-enum for StructWrappedNullablePointer: {}",
1092                 ty,
1093             ),
1094         };
1095
1096         self.field_path_offset(inner_ty, path)
1097     }
1098
1099     fn field_path_offset<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<Size> {
1100         let mut offset = Size::from_bytes(0);
1101
1102         // Skip the initial 0 intended for LLVM GEP.
1103         for field_index in path {
1104             let field_offset = self.get_field_offset(ty, field_index)?;
1105             ty = self.get_field_ty(ty, field_index)?;
1106             offset = offset.checked_add(field_offset, &self.tcx.data_layout).unwrap();
1107         }
1108
1109         Ok(offset)
1110     }
1111
1112     fn get_field_ty(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Ty<'tcx>> {
1113         match ty.sty {
1114             ty::TyStruct(adt_def, substs) => {
1115                 Ok(adt_def.struct_variant().fields[field_index].ty(self.tcx, substs))
1116             }
1117
1118             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1119             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1120             ty::TyBox(ty) => {
1121                 assert_eq!(field_index, 0);
1122                 Ok(ty)
1123             }
1124             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}", ty))),
1125         }
1126     }
1127
1128     fn get_field_offset(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Size> {
1129         let layout = self.type_layout(ty);
1130
1131         use rustc::ty::layout::Layout::*;
1132         match *layout {
1133             Univariant { .. } => {
1134                 assert_eq!(field_index, 0);
1135                 Ok(Size::from_bytes(0))
1136             }
1137             FatPointer { .. } => {
1138                 let bytes = layout::FAT_PTR_ADDR * self.memory.pointer_size;
1139                 Ok(Size::from_bytes(bytes as u64))
1140             }
1141             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}, with layout: {:?}", ty, layout))),
1142         }
1143     }
1144
1145     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
1146         use rustc::mir::repr::Operand::*;
1147         match *op {
1148             Consume(ref lvalue) => Ok(self.eval_lvalue(lvalue)?.to_ptr()),
1149             Constant(mir::Constant { ref literal, ty, .. }) => {
1150                 use rustc::mir::repr::Literal::*;
1151                 match *literal {
1152                     Value { ref value } => Ok(self.const_to_ptr(value)?),
1153                     Item { def_id, substs } => {
1154                         if let ty::TyFnDef(..) = ty.sty {
1155                             Err(EvalError::Unimplemented("unimplemented: mentions of function items".to_string()))
1156                         } else {
1157                             let cid = ConstantId {
1158                                 def_id: def_id,
1159                                 substs: substs,
1160                                 kind: ConstantKind::Global,
1161                             };
1162                             Ok(*self.statics.get(&cid).expect("static should have been cached (rvalue)"))
1163                         }
1164                     },
1165                     Promoted { index } => {
1166                         let cid = ConstantId {
1167                             def_id: self.frame().def_id,
1168                             substs: self.substs(),
1169                             kind: ConstantKind::Promoted(index),
1170                         };
1171                         Ok(*self.statics.get(&cid).expect("a promoted constant hasn't been precomputed"))
1172                     },
1173                 }
1174             }
1175         }
1176     }
1177
1178     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
1179         use rustc::mir::repr::Lvalue::*;
1180         let ptr = match *lvalue {
1181             ReturnPointer => self.frame().return_ptr
1182                 .expect("ReturnPointer used in a function with no return value"),
1183             Arg(i) => self.frame().locals[i.index()],
1184             Var(i) => self.frame().locals[self.frame().var_offset + i.index()],
1185             Temp(i) => self.frame().locals[self.frame().temp_offset + i.index()],
1186
1187             Static(def_id) => {
1188                 let substs = self.tcx.mk_substs(subst::Substs::empty());
1189                 let cid = ConstantId {
1190                     def_id: def_id,
1191                     substs: substs,
1192                     kind: ConstantKind::Global,
1193                 };
1194                 *self.statics.get(&cid).expect("static should have been cached (lvalue)")
1195             },
1196
1197             Projection(ref proj) => {
1198                 let base = self.eval_lvalue(&proj.base)?;
1199                 let base_ty = self.lvalue_ty(&proj.base);
1200                 let base_layout = self.type_layout(base_ty);
1201
1202                 use rustc::mir::repr::ProjectionElem::*;
1203                 match proj.elem {
1204                     Field(field, _) => {
1205                         use rustc::ty::layout::Layout::*;
1206                         let variant = match *base_layout {
1207                             Univariant { ref variant, .. } => variant,
1208                             General { ref variants, .. } => {
1209                                 if let LvalueExtra::DowncastVariant(variant_idx) = base.extra {
1210                                     &variants[variant_idx]
1211                                 } else {
1212                                     panic!("field access on enum had no variant index");
1213                                 }
1214                             }
1215                             RawNullablePointer { .. } => {
1216                                 assert_eq!(field.index(), 0);
1217                                 return Ok(base);
1218                             }
1219                             StructWrappedNullablePointer { ref nonnull, .. } => nonnull,
1220                             _ => panic!("field access on non-product type: {:?}", base_layout),
1221                         };
1222
1223                         let offset = variant.field_offset(field.index()).bytes();
1224                         base.ptr.offset(offset as isize)
1225                     },
1226
1227                     Downcast(_, variant) => {
1228                         use rustc::ty::layout::Layout::*;
1229                         match *base_layout {
1230                             General { discr, .. } => {
1231                                 return Ok(Lvalue {
1232                                     ptr: base.ptr.offset(discr.size().bytes() as isize),
1233                                     extra: LvalueExtra::DowncastVariant(variant),
1234                                 });
1235                             }
1236                             RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
1237                                 return Ok(base);
1238                             }
1239                             _ => panic!("variant downcast on non-aggregate: {:?}", base_layout),
1240                         }
1241                     },
1242
1243                     Deref => {
1244                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
1245                         let ptr = self.memory.read_ptr(base.ptr)?;
1246                         let extra = match pointee_ty.sty {
1247                             ty::TySlice(_) | ty::TyStr => {
1248                                 let len_ptr = base.ptr.offset(self.memory.pointer_size as isize);
1249                                 let len = self.memory.read_usize(len_ptr)?;
1250                                 LvalueExtra::Length(len)
1251                             }
1252                             ty::TyTrait(_) => unimplemented!(),
1253                             _ => LvalueExtra::None,
1254                         };
1255                         return Ok(Lvalue { ptr: ptr, extra: extra });
1256                     }
1257
1258                     Index(ref operand) => {
1259                         let elem_size = match base_ty.sty {
1260                             ty::TyArray(elem_ty, _) |
1261                             ty::TySlice(elem_ty) => self.type_size(elem_ty),
1262                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
1263                         };
1264                         let n_ptr = self.eval_operand(operand)?;
1265                         let n = self.memory.read_usize(n_ptr)?;
1266                         base.ptr.offset(n as isize * elem_size as isize)
1267                     }
1268
1269                     ConstantIndex { .. } => unimplemented!(),
1270                     Subslice { .. } => unimplemented!(),
1271                 }
1272             }
1273         };
1274
1275         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
1276     }
1277
1278     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> Ty<'tcx> {
1279         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx), self.substs())
1280     }
1281
1282     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> Ty<'tcx> {
1283         self.monomorphize(self.mir().operand_ty(self.tcx, operand), self.substs())
1284     }
1285
1286     fn move_(&mut self, src: Pointer, dest: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
1287         let size = self.type_size(ty);
1288         self.memory.copy(src, dest, size)?;
1289         if self.type_needs_drop(ty) {
1290             self.memory.drop_fill(src, size)?;
1291         }
1292         Ok(())
1293     }
1294
1295     pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<PrimVal> {
1296         use syntax::ast::{IntTy, UintTy};
1297         let val = match (self.memory.pointer_size, &ty.sty) {
1298             (_, &ty::TyBool)              => PrimVal::Bool(self.memory.read_bool(ptr)?),
1299             (_, &ty::TyInt(IntTy::I8))    => PrimVal::I8(self.memory.read_int(ptr, 1)? as i8),
1300             (2, &ty::TyInt(IntTy::Is)) |
1301             (_, &ty::TyInt(IntTy::I16))   => PrimVal::I16(self.memory.read_int(ptr, 2)? as i16),
1302             (4, &ty::TyInt(IntTy::Is)) |
1303             (_, &ty::TyInt(IntTy::I32))   => PrimVal::I32(self.memory.read_int(ptr, 4)? as i32),
1304             (8, &ty::TyInt(IntTy::Is)) |
1305             (_, &ty::TyInt(IntTy::I64))   => PrimVal::I64(self.memory.read_int(ptr, 8)? as i64),
1306             (_, &ty::TyUint(UintTy::U8))  => PrimVal::U8(self.memory.read_uint(ptr, 1)? as u8),
1307             (2, &ty::TyUint(UintTy::Us)) |
1308             (_, &ty::TyUint(UintTy::U16)) => PrimVal::U16(self.memory.read_uint(ptr, 2)? as u16),
1309             (4, &ty::TyUint(UintTy::Us)) |
1310             (_, &ty::TyUint(UintTy::U32)) => PrimVal::U32(self.memory.read_uint(ptr, 4)? as u32),
1311             (8, &ty::TyUint(UintTy::Us)) |
1312             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
1313
1314             (_, &ty::TyRef(_, ty::TypeAndMut { ty, .. })) |
1315             (_, &ty::TyRawPtr(ty::TypeAndMut { ty, .. })) => {
1316                 if self.type_is_sized(ty) {
1317                     match self.memory.read_ptr(ptr) {
1318                         Ok(p) => PrimVal::AbstractPtr(p),
1319                         Err(EvalError::ReadBytesAsPointer) => {
1320                             PrimVal::IntegerPtr(self.memory.read_usize(ptr)?)
1321                         }
1322                         Err(e) => return Err(e),
1323                     }
1324                 } else {
1325                     return Err(EvalError::Unimplemented(format!("unimplemented: primitive read of fat pointer type: {:?}", ty)));
1326                 }
1327             }
1328
1329             _ => panic!("primitive read of non-primitive type: {:?}", ty),
1330         };
1331         Ok(val)
1332     }
1333
1334     fn frame(&self) -> &Frame<'a, 'tcx> {
1335         self.stack.last().expect("no call frames exist")
1336     }
1337
1338     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
1339         self.stack.last_mut().expect("no call frames exist")
1340     }
1341
1342     fn mir(&self) -> CachedMir<'a, 'tcx> {
1343         self.frame().mir.clone()
1344     }
1345
1346     fn substs(&self) -> &'tcx Substs<'tcx> {
1347         self.frame().substs
1348     }
1349 }
1350
1351 fn pointee_type(ptr_ty: ty::Ty) -> Option<ty::Ty> {
1352     match ptr_ty.sty {
1353         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1354         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1355         ty::TyBox(ty) => {
1356             Some(ty)
1357         }
1358         _ => None,
1359     }
1360 }
1361
1362 impl Lvalue {
1363     fn to_ptr(self) -> Pointer {
1364         assert_eq!(self.extra, LvalueExtra::None);
1365         self.ptr
1366     }
1367 }
1368
1369 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1370     type Target = mir::Mir<'tcx>;
1371     fn deref(&self) -> &mir::Mir<'tcx> {
1372         match *self {
1373             CachedMir::Ref(r) => r,
1374             CachedMir::Owned(ref rc) => rc,
1375         }
1376     }
1377 }
1378
1379 #[derive(Debug)]
1380 pub struct ImplMethod<'tcx> {
1381     pub method: Rc<ty::Method<'tcx>>,
1382     pub substs: &'tcx Substs<'tcx>,
1383     pub is_provided: bool,
1384 }
1385
1386 /// Locates the applicable definition of a method, given its name.
1387 pub fn get_impl_method<'a, 'tcx>(
1388     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1389     impl_def_id: DefId,
1390     substs: &'tcx Substs<'tcx>,
1391     name: ast::Name,
1392 ) -> ImplMethod<'tcx> {
1393     assert!(!substs.types.needs_infer());
1394
1395     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1396     let trait_def = tcx.lookup_trait_def(trait_def_id);
1397
1398     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1399         Some(node_item) => {
1400             let substs = tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
1401                 let substs = traits::translate_substs(&infcx, impl_def_id,
1402                                                       substs, node_item.node);
1403                 tcx.lift(&substs).unwrap_or_else(|| {
1404                     bug!("trans::meth::get_impl_method: translate_substs \
1405                           returned {:?} which contains inference types/regions",
1406                          substs);
1407                 })
1408             });
1409             ImplMethod {
1410                 method: node_item.item,
1411                 substs: substs,
1412                 is_provided: node_item.node.is_from_trait(),
1413             }
1414         }
1415         None => {
1416             bug!("method {:?} not found in {:?}", name, impl_def_id)
1417         }
1418     }
1419 }
1420
1421 // TODO(solson): Upstream these methods into rustc::ty::layout.
1422
1423 trait IntegerExt {
1424     fn size(self) -> Size;
1425 }
1426
1427 impl IntegerExt for layout::Integer {
1428     fn size(self) -> Size {
1429         use rustc::ty::layout::Integer::*;
1430         match self {
1431             I1 | I8 => Size::from_bits(8),
1432             I16 => Size::from_bits(16),
1433             I32 => Size::from_bits(32),
1434             I64 => Size::from_bits(64),
1435         }
1436     }
1437 }
1438
1439 trait StructExt {
1440     fn field_offset(&self, index: usize) -> Size;
1441 }
1442
1443 impl StructExt for layout::Struct {
1444     fn field_offset(&self, index: usize) -> Size {
1445         if index == 0 {
1446             Size::from_bytes(0)
1447         } else {
1448             self.offset_after_field[index - 1]
1449         }
1450     }
1451 }