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(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>, substs: &'tcx Substs<'tcx>) -> usize {
 311         self.type_layout(ty, substs).size(&self.tcx.data_layout).bytes() as usize
 312     }
 313
 314     fn type_layout(&self, ty: Ty<'tcx>, substs: &'tcx Substs<'tcx>) -> &'tcx Layout {
 315         // TODO(solson): Is this inefficient? Needs investigation.
 316         let ty = self.monomorphize(ty, substs);
 317
 318         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 319             // TODO(solson): Report this error properly.
 320             ty.layout(&infcx).unwrap()
 321         })
 322     }
 323
 324     pub fn push_stack_frame(&mut self, def_id: DefId, span: codemap::Span, mir: CachedMir<'a, 'tcx>, substs: &'tcx Substs<'tcx>,
 325         return_ptr: Option<Pointer>)
 326     {
 327         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 328         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 329         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 330
 331         let num_args = mir.arg_decls.len();
 332         let num_vars = mir.var_decls.len();
 333
 334         ::log_settings::settings().indentation += 1;
 335
 336         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 337             let size = self.type_size(ty, substs);
 338             self.memory.allocate(size)
 339         }).collect();
 340
 341         self.stack.push(Frame {
 342             mir: mir.clone(),
 343             next_block: mir::START_BLOCK,
 344             return_ptr: return_ptr,
 345             locals: locals,
 346             var_offset: num_args,
 347             temp_offset: num_args + num_vars,
 348             span: span,
 349             def_id: def_id,
 350             substs: substs,
 351             stmt: 0,
 352         });
 353     }
 354
 355     fn pop_stack_frame(&mut self) {
 356         ::log_settings::settings().indentation -= 1;
 357         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 358         // TODO(solson): Deallocate local variables.
 359     }
 360
 361     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 362             -> EvalResult<()> {
 363         use rustc::mir::repr::TerminatorKind::*;
 364         match terminator.kind {
 365             Return => self.pop_stack_frame(),
 366
 367             Goto { target } => {
 368                 self.frame_mut().next_block = target;
 369             },
 370
 371             If { ref cond, targets: (then_target, else_target) } => {
 372                 let cond_ptr = self.eval_operand(cond)?;
 373                 let cond_val = self.memory.read_bool(cond_ptr)?;
 374                 self.frame_mut().next_block = if cond_val { then_target } else { else_target };
 375             }
 376
 377             SwitchInt { ref discr, ref values, ref targets, .. } => {
 378                 let discr_ptr = self.eval_lvalue(discr)?.to_ptr();
 379                 let discr_size = self
 380                     .type_layout(self.lvalue_ty(discr), self.substs())
 381                     .size(&self.tcx.data_layout)
 382                     .bytes() as usize;
 383                 let discr_val = self.memory.read_uint(discr_ptr, discr_size)?;
 384
 385                 // Branch to the `otherwise` case by default, if no match is found.
 386                 let mut target_block = targets[targets.len() - 1];
 387
 388                 for (index, val_const) in values.iter().enumerate() {
 389                     let ptr = self.const_to_ptr(val_const)?;
 390                     let val = self.memory.read_uint(ptr, discr_size)?;
 391                     if discr_val == val {
 392                         target_block = targets[index];
 393                         break;
 394                     }
 395                 }
 396
 397                 self.frame_mut().next_block = target_block;
 398             }
 399
 400             Switch { ref discr, ref targets, adt_def } => {
 401                 let adt_ptr = self.eval_lvalue(discr)?.to_ptr();
 402                 let adt_ty = self.lvalue_ty(discr);
 403                 let discr_val = self.read_discriminant_value(adt_ptr, adt_ty)?;
 404                 let matching = adt_def.variants.iter()
 405                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 406
 407                 match matching {
 408                     Some(i) => {
 409                         self.frame_mut().next_block = targets[i];
 410                     },
 411                     None => return Err(EvalError::InvalidDiscriminant),
 412                 }
 413             }
 414
 415             Call { ref func, ref args, ref destination, .. } => {
 416                 let mut return_ptr = None;
 417                 if let Some((ref lv, target)) = *destination {
 418                     self.frame_mut().next_block = target;
 419                     return_ptr = Some(self.eval_lvalue(lv)?.to_ptr());
 420                 }
 421
 422                 let func_ty = self.operand_ty(func);
 423                 match func_ty.sty {
 424                     ty::TyFnDef(def_id, substs, fn_ty) => {
 425                         use syntax::abi::Abi;
 426                         match fn_ty.abi {
 427                             Abi::RustIntrinsic => {
 428                                 let name = self.tcx.item_name(def_id).as_str();
 429                                 match fn_ty.sig.0.output {
 430                                     ty::FnConverging(ty) => {
 431                                         let size = self.type_size(ty, self.substs());
 432                                         let ret = return_ptr.unwrap();
 433                                         self.call_intrinsic(&name, substs, args, ret, size)?
 434                                     }
 435                                     ty::FnDiverging => unimplemented!(),
 436                                 }
 437                             }
 438
 439                             Abi::C => {
 440                                 match fn_ty.sig.0.output {
 441                                     ty::FnConverging(ty) => {
 442                                         let size = self.type_size(ty, self.substs());
 443                                         self.call_c_abi(def_id, args, return_ptr.unwrap(), size)?
 444                                     }
 445                                     ty::FnDiverging => unimplemented!(),
 446                                 }
 447                             }
 448
 449                             Abi::Rust | Abi::RustCall => {
 450                                 // TODO(solson): Adjust the first argument when calling a Fn or
 451                                 // FnMut closure via FnOnce::call_once.
 452
 453                                 // Only trait methods can have a Self parameter.
 454                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 455                                     self.trait_method(def_id, substs)
 456                                 } else {
 457                                     (def_id, substs)
 458                                 };
 459
 460                                 let mut arg_srcs = Vec::new();
 461                                 for arg in args {
 462                                     let src = self.eval_operand(arg)?;
 463                                     let src_ty = self.operand_ty(arg);
 464                                     arg_srcs.push((src, src_ty));
 465                                 }
 466
 467                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 468                                     arg_srcs.pop();
 469                                     let last_arg = args.last().unwrap();
 470                                     let last = self.eval_operand(last_arg)?;
 471                                     let last_ty = self.operand_ty(last_arg);
 472                                     let last_layout = self.type_layout(last_ty, self.substs());
 473                                     match (&last_ty.sty, last_layout) {
 474                                         (&ty::TyTuple(fields),
 475                                          &Layout::Univariant { ref variant, .. }) => {
 476                                             let offsets = iter::once(0)
 477                                                 .chain(variant.offset_after_field.iter()
 478                                                     .map(|s| s.bytes()));
 479                                             for (offset, ty) in offsets.zip(fields) {
 480                                                 let src = last.offset(offset as isize);
 481                                                 arg_srcs.push((src, ty));
 482                                             }
 483                                         }
 484                                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 485                                     }
 486                                 }
 487
 488                                 let mir = self.load_mir(resolved_def_id);
 489                                 self.push_stack_frame(
 490                                     def_id, terminator.source_info.span, mir, resolved_substs,
 491                                     return_ptr
 492                                 );
 493
 494                                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 495                                     let dest = self.frame().locals[i];
 496                                     self.move_(src, dest, src_ty)?;
 497                                 }
 498                             }
 499
 500                             abi => return Err(EvalError::Unimplemented(format!("can't handle function with {:?} ABI", abi))),
 501                         }
 502                     }
 503
 504                     _ => return Err(EvalError::Unimplemented(format!("can't handle callee of type {:?}", func_ty))),
 505                 }
 506             }
 507
 508             Drop { ref location, target, .. } => {
 509                 let ptr = self.eval_lvalue(location)?.to_ptr();
 510                 let ty = self.lvalue_ty(location);
 511                 self.drop(ptr, ty)?;
 512                 self.frame_mut().next_block = target;
 513             }
 514
 515             Assert { ref cond, expected, ref msg, target, cleanup } => {
 516                 let actual_ptr = self.eval_operand(cond)?;
 517                 let actual = self.memory.read_bool(actual_ptr)?;
 518                 if actual == expected {
 519                     self.frame_mut().next_block = target;
 520                 } else {
 521                     panic!("unimplemented: jump to {:?} and print {:?}", cleanup, msg);
 522                 }
 523             }
 524
 525             DropAndReplace { .. } => unimplemented!(),
 526             Resume => unimplemented!(),
 527             Unreachable => unimplemented!(),
 528         }
 529
 530         Ok(())
 531     }
 532
 533     fn drop(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
 534         if !self.type_needs_drop(ty) {
 535             debug!("no need to drop {:?}", ty);
 536             return Ok(());
 537         }
 538         trace!("-need to drop {:?}", ty);
 539
 540         // TODO(solson): Call user-defined Drop::drop impls.
 541
 542         match ty.sty {
 543             ty::TyBox(contents_ty) => {
 544                 match self.memory.read_ptr(ptr) {
 545                     Ok(contents_ptr) => {
 546                         self.drop(contents_ptr, contents_ty)?;
 547                         trace!("-deallocating box");
 548                         self.memory.deallocate(contents_ptr)?;
 549                     }
 550                     Err(EvalError::ReadBytesAsPointer) => {
 551                         let size = self.memory.pointer_size;
 552                         let possible_drop_fill = self.memory.read_bytes(ptr, size)?;
 553                         if possible_drop_fill.iter().all(|&b| b == mem::POST_DROP_U8) {
 554                             return Ok(());
 555                         } else {
 556                             return Err(EvalError::ReadBytesAsPointer);
 557                         }
 558                     }
 559                     Err(e) => return Err(e),
 560                 }
 561             }
 562
 563             // TODO(solson): Implement drop for other relevant types (e.g. aggregates).
 564             _ => {}
 565         }
 566
 567         // Filling drop.
 568         // FIXME(solson): Trait objects (with no static size) probably get filled, too.
 569         let size = self.type_size(ty, self.substs());
 570         self.memory.drop_fill(ptr, size)?;
 571
 572         Ok(())
 573     }
 574
 575     fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalResult<u64> {
 576         use rustc::ty::layout::Layout::*;
 577         let adt_layout = self.type_layout(adt_ty, self.substs());
 578
 579         let discr_val = match *adt_layout {
 580             General { discr, .. } | CEnum { discr, .. } => {
 581                 let discr_size = discr.size().bytes();
 582                 self.memory.read_uint(adt_ptr, discr_size as usize)?
 583             }
 584
 585             RawNullablePointer { nndiscr, .. } => {
 586                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
 587             }
 588
 589             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
 590                 let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
 591                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
 592                 self.read_nonnull_discriminant_value(nonnull, nndiscr)?
 593             }
 594
 595             // The discriminant_value intrinsic returns 0 for non-sum types.
 596             Array { .. } | FatPointer { .. } | Scalar { .. } | Univariant { .. } |
 597             Vector { .. } => 0,
 598         };
 599
 600         Ok(discr_val)
 601     }
 602
 603     fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<u64> {
 604         let not_null = match self.memory.read_usize(ptr) {
 605             Ok(0) => false,
 606             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
 607             Err(e) => return Err(e),
 608         };
 609         assert!(nndiscr == 0 || nndiscr == 1);
 610         Ok(if not_null { nndiscr } else { 1 - nndiscr })
 611     }
 612
 613     fn call_intrinsic(
 614         &mut self,
 615         name: &str,
 616         substs: &'tcx Substs<'tcx>,
 617         args: &[mir::Operand<'tcx>],
 618         dest: Pointer,
 619         dest_size: usize
 620     ) -> EvalResult<()> {
 621         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 622             .map(|arg| self.eval_operand(arg))
 623             .collect();
 624         let args = args_res?;
 625
 626         match name {
 627             // FIXME(solson): Handle different integer types correctly.
 628             "add_with_overflow" => {
 629                 let ty = *substs.types.get(subst::FnSpace, 0);
 630                 let size = self.type_size(ty, self.substs());
 631                 let left = self.memory.read_int(args[0], size)?;
 632                 let right = self.memory.read_int(args[1], size)?;
 633                 let (n, overflowed) = unsafe {
 634                     ::std::intrinsics::add_with_overflow::<i64>(left, right)
 635                 };
 636                 self.memory.write_int(dest, n, size)?;
 637                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 638             }
 639
 640             "assume" => {}
 641
 642             "copy_nonoverlapping" => {
 643                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 644                 let elem_size = self.type_size(elem_ty, self.substs());
 645                 let src = self.memory.read_ptr(args[0])?;
 646                 let dest = self.memory.read_ptr(args[1])?;
 647                 let count = self.memory.read_isize(args[2])?;
 648                 self.memory.copy(src, dest, count as usize * elem_size)?;
 649             }
 650
 651             "discriminant_value" => {
 652                 let ty = *substs.types.get(subst::FnSpace, 0);
 653                 let adt_ptr = self.memory.read_ptr(args[0])?;
 654                 let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
 655                 self.memory.write_uint(dest, discr_val, dest_size)?;
 656             }
 657
 658             "forget" => {
 659                 let arg_ty = *substs.types.get(subst::FnSpace, 0);
 660                 let arg_size = self.type_size(arg_ty, self.substs());
 661                 self.memory.drop_fill(args[0], arg_size)?;
 662             }
 663
 664             "init" => self.memory.write_repeat(dest, 0, dest_size)?,
 665
 666             "min_align_of" => {
 667                 self.memory.write_int(dest, 1, dest_size)?;
 668             }
 669
 670             "move_val_init" => {
 671                 let ty = *substs.types.get(subst::FnSpace, 0);
 672                 let ptr = self.memory.read_ptr(args[0])?;
 673                 self.move_(args[1], ptr, ty)?;
 674             }
 675
 676             // FIXME(solson): Handle different integer types correctly.
 677             "mul_with_overflow" => {
 678                 let ty = *substs.types.get(subst::FnSpace, 0);
 679                 let size = self.type_size(ty, self.substs());
 680                 let left = self.memory.read_int(args[0], size)?;
 681                 let right = self.memory.read_int(args[1], size)?;
 682                 let (n, overflowed) = unsafe {
 683                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 684                 };
 685                 self.memory.write_int(dest, n, size)?;
 686                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 687             }
 688
 689             "offset" => {
 690                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 691                 let pointee_size = self.type_size(pointee_ty, self.substs()) as isize;
 692                 let ptr_arg = args[0];
 693                 let offset = self.memory.read_isize(args[1])?;
 694
 695                 match self.memory.read_ptr(ptr_arg) {
 696                     Ok(ptr) => {
 697                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 698                         self.memory.write_ptr(dest, result_ptr)?;
 699                     }
 700                     Err(EvalError::ReadBytesAsPointer) => {
 701                         let addr = self.memory.read_isize(ptr_arg)?;
 702                         let result_addr = addr + offset * pointee_size as i64;
 703                         self.memory.write_isize(dest, result_addr)?;
 704                     }
 705                     Err(e) => return Err(e),
 706                 }
 707             }
 708
 709             // FIXME(solson): Handle different integer types correctly. Use primvals?
 710             "overflowing_sub" => {
 711                 let ty = *substs.types.get(subst::FnSpace, 0);
 712                 let size = self.type_size(ty, self.substs());
 713                 let left = self.memory.read_int(args[0], size)?;
 714                 let right = self.memory.read_int(args[1], size)?;
 715                 let n = left.wrapping_sub(right);
 716                 self.memory.write_int(dest, n, size)?;
 717             }
 718
 719             "size_of" => {
 720                 let ty = *substs.types.get(subst::FnSpace, 0);
 721                 let size = self.type_size(ty, self.substs()) as u64;
 722                 self.memory.write_uint(dest, size, dest_size)?;
 723             }
 724
 725             "size_of_val" => {
 726                 let ty = *substs.types.get(subst::FnSpace, 0);
 727                 if self.type_is_sized(ty) {
 728                     let size = self.type_size(ty, self.substs()) as u64;
 729                     self.memory.write_uint(dest, size, dest_size)?;
 730                 } else {
 731                     match ty.sty {
 732                         ty::TySlice(_) | ty::TyStr => {
 733                             let elem_ty = ty.sequence_element_type(self.tcx);
 734                             let elem_size = self.type_size(elem_ty, self.substs()) as u64;
 735                             let ptr_size = self.memory.pointer_size as isize;
 736                             let n = self.memory.read_usize(args[0].offset(ptr_size))?;
 737                             self.memory.write_uint(dest, n * elem_size, dest_size)?;
 738                         }
 739
 740                         _ => return Err(EvalError::Unimplemented(format!("unimplemented: size_of_val::<{:?}>", ty))),
 741                     }
 742                 }
 743             }
 744
 745             "transmute" => {
 746                 let ty = *substs.types.get(subst::FnSpace, 0);
 747                 self.move_(args[0], dest, ty)?;
 748             }
 749             "uninit" => self.memory.mark_definedness(dest, dest_size, false)?,
 750
 751             name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
 752         }
 753
 754         // Since we pushed no stack frame, the main loop will act
 755         // as if the call just completed and it's returning to the
 756         // current frame.
 757         Ok(())
 758     }
 759
 760     fn call_c_abi(
 761         &mut self,
 762         def_id: DefId,
 763         args: &[mir::Operand<'tcx>],
 764         dest: Pointer,
 765         dest_size: usize,
 766     ) -> EvalResult<()> {
 767         let name = self.tcx.item_name(def_id);
 768         let attrs = self.tcx.get_attrs(def_id);
 769         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 770             Some(ln) => ln.clone(),
 771             None => name.as_str(),
 772         };
 773
 774         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 775             .map(|arg| self.eval_operand(arg))
 776             .collect();
 777         let args = args_res?;
 778
 779         match &link_name[..] {
 780             "__rust_allocate" => {
 781                 let size = self.memory.read_usize(args[0])?;
 782                 let ptr = self.memory.allocate(size as usize);
 783                 self.memory.write_ptr(dest, ptr)?;
 784             }
 785
 786             "__rust_reallocate" => {
 787                 let ptr = self.memory.read_ptr(args[0])?;
 788                 let size = self.memory.read_usize(args[2])?;
 789                 self.memory.reallocate(ptr, size as usize)?;
 790                 self.memory.write_ptr(dest, ptr)?;
 791             }
 792
 793             "memcmp" => {
 794                 let left = self.memory.read_ptr(args[0])?;
 795                 let right = self.memory.read_ptr(args[1])?;
 796                 let n = self.memory.read_usize(args[2])? as usize;
 797
 798                 let result = {
 799                     let left_bytes = self.memory.read_bytes(left, n)?;
 800                     let right_bytes = self.memory.read_bytes(right, n)?;
 801
 802                     use std::cmp::Ordering::*;
 803                     match left_bytes.cmp(right_bytes) {
 804                         Less => -1,
 805                         Equal => 0,
 806                         Greater => 1,
 807                     }
 808                 };
 809
 810                 self.memory.write_int(dest, result, dest_size)?;
 811             }
 812
 813             _ => return Err(EvalError::Unimplemented(format!("can't call C ABI function: {}", link_name))),
 814         }
 815
 816         // Since we pushed no stack frame, the main loop will act
 817         // as if the call just completed and it's returning to the
 818         // current frame.
 819         Ok(())
 820     }
 821
 822     fn assign_fields<I: IntoIterator<Item = u64>>(
 823         &mut self,
 824         dest: Pointer,
 825         offsets: I,
 826         operands: &[mir::Operand<'tcx>],
 827     ) -> EvalResult<()> {
 828         for (offset, operand) in offsets.into_iter().zip(operands) {
 829             let src = self.eval_operand(operand)?;
 830             let src_ty = self.operand_ty(operand);
 831             let field_dest = dest.offset(offset as isize);
 832             self.move_(src, field_dest, src_ty)?;
 833         }
 834         Ok(())
 835     }
 836
 837     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 838         -> EvalResult<()>
 839     {
 840         let dest = self.eval_lvalue(lvalue)?.to_ptr();
 841         let dest_ty = self.lvalue_ty(lvalue);
 842         let dest_layout = self.type_layout(dest_ty, self.substs());
 843
 844         use rustc::mir::repr::Rvalue::*;
 845         match *rvalue {
 846             Use(ref operand) => {
 847                 let src = self.eval_operand(operand)?;
 848                 self.move_(src, dest, dest_ty)?;
 849             }
 850
 851             BinaryOp(bin_op, ref left, ref right) => {
 852                 let left_ptr = self.eval_operand(left)?;
 853                 let left_ty = self.operand_ty(left);
 854                 let left_val = self.read_primval(left_ptr, left_ty)?;
 855
 856                 let right_ptr = self.eval_operand(right)?;
 857                 let right_ty = self.operand_ty(right);
 858                 let right_val = self.read_primval(right_ptr, right_ty)?;
 859
 860                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 861                 self.memory.write_primval(dest, val)?;
 862             }
 863
 864             // FIXME(solson): Factor this out with BinaryOp.
 865             CheckedBinaryOp(bin_op, ref left, ref right) => {
 866                 let left_ptr = self.eval_operand(left)?;
 867                 let left_ty = self.operand_ty(left);
 868                 let left_val = self.read_primval(left_ptr, left_ty)?;
 869
 870                 let right_ptr = self.eval_operand(right)?;
 871                 let right_ty = self.operand_ty(right);
 872                 let right_val = self.read_primval(right_ptr, right_ty)?;
 873
 874                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 875                 self.memory.write_primval(dest, val)?;
 876
 877                 // FIXME(solson): Find the result type size properly. Perhaps refactor out
 878                 // Projection calculations so we can do the equivalent of `dest.1` here.
 879                 let s = self.type_size(left_ty, self.substs());
 880                 self.memory.write_bool(dest.offset(s as isize), false)?;
 881             }
 882
 883             UnaryOp(un_op, ref operand) => {
 884                 let ptr = self.eval_operand(operand)?;
 885                 let ty = self.operand_ty(operand);
 886                 let val = self.read_primval(ptr, ty)?;
 887                 self.memory.write_primval(dest, primval::unary_op(un_op, val)?)?;
 888             }
 889
 890             Aggregate(ref kind, ref operands) => {
 891                 use rustc::ty::layout::Layout::*;
 892                 match *dest_layout {
 893                     Univariant { ref variant, .. } => {
 894                         let offsets = iter::once(0)
 895                             .chain(variant.offset_after_field.iter().map(|s| s.bytes()));
 896                         self.assign_fields(dest, offsets, operands)?;
 897                     }
 898
 899                     Array { .. } => {
 900                         let elem_size = match dest_ty.sty {
 901                             ty::TyArray(elem_ty, _) => self.type_size(elem_ty, self.substs()) as u64,
 902                             _ => panic!("tried to assign {:?} to non-array type {:?}",
 903                                         kind, dest_ty),
 904                         };
 905                         let offsets = (0..).map(|i| i * elem_size);
 906                         self.assign_fields(dest, offsets, operands)?;
 907                     }
 908
 909                     General { discr, ref variants, .. } => {
 910                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 911                             let discr_val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 912                             let discr_size = discr.size().bytes() as usize;
 913                             self.memory.write_uint(dest, discr_val, discr_size)?;
 914
 915                             let offsets = variants[variant].offset_after_field.iter()
 916                                 .map(|s| s.bytes());
 917                             self.assign_fields(dest, offsets, operands)?;
 918                         } else {
 919                             panic!("tried to assign {:?} to Layout::General", kind);
 920                         }
 921                     }
 922
 923                     RawNullablePointer { nndiscr, .. } => {
 924                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 925                             if nndiscr == variant as u64 {
 926                                 assert_eq!(operands.len(), 1);
 927                                 let operand = &operands[0];
 928                                 let src = self.eval_operand(operand)?;
 929                                 let src_ty = self.operand_ty(operand);
 930                                 self.move_(src, dest, src_ty)?;
 931                             } else {
 932                                 assert_eq!(operands.len(), 0);
 933                                 self.memory.write_isize(dest, 0)?;
 934                             }
 935                         } else {
 936                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 937                         }
 938                     }
 939
 940                     StructWrappedNullablePointer { nndiscr, ref nonnull, ref discrfield } => {
 941                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 942                             if nndiscr == variant as u64 {
 943                                 let offsets = iter::once(0)
 944                                     .chain(nonnull.offset_after_field.iter().map(|s| s.bytes()));
 945                                 try!(self.assign_fields(dest, offsets, operands));
 946                             } else {
 947                                 assert_eq!(operands.len(), 0);
 948                                 let offset = self.nonnull_offset(dest_ty, nndiscr, discrfield)?;
 949                                 let dest = dest.offset(offset.bytes() as isize);
 950                                 try!(self.memory.write_isize(dest, 0));
 951                             }
 952                         } else {
 953                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 954                         }
 955                     }
 956
 957                     CEnum { discr, signed, .. } => {
 958                         assert_eq!(operands.len(), 0);
 959                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 960                             let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 961                             let size = discr.size().bytes() as usize;
 962
 963                             if signed {
 964                                 self.memory.write_int(dest, val as i64, size)?;
 965                             } else {
 966                                 self.memory.write_uint(dest, val, size)?;
 967                             }
 968                         } else {
 969                             panic!("tried to assign {:?} to Layout::CEnum", kind);
 970                         }
 971                     }
 972
 973                     _ => return Err(EvalError::Unimplemented(format!("can't handle destination layout {:?} when assigning {:?}", dest_layout, kind))),
 974                 }
 975             }
 976
 977             Repeat(ref operand, _) => {
 978                 let (elem_size, length) = match dest_ty.sty {
 979                     ty::TyArray(elem_ty, n) => (self.type_size(elem_ty, self.substs()), n),
 980                     _ => panic!("tried to assign array-repeat to non-array type {:?}", dest_ty),
 981                 };
 982
 983                 let src = self.eval_operand(operand)?;
 984                 for i in 0..length {
 985                     let elem_dest = dest.offset((i * elem_size) as isize);
 986                     self.memory.copy(src, elem_dest, elem_size)?;
 987                 }
 988             }
 989
 990             Len(ref lvalue) => {
 991                 let src = self.eval_lvalue(lvalue)?;
 992                 let ty = self.lvalue_ty(lvalue);
 993                 let len = match ty.sty {
 994                     ty::TyArray(_, n) => n as u64,
 995                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
 996                         n
 997                     } else {
 998                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
 999                     },
1000                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
1001                 };
1002                 self.memory.write_usize(dest, len)?;
1003             }
1004
1005             Ref(_, _, ref lvalue) => {
1006                 let lv = self.eval_lvalue(lvalue)?;
1007                 self.memory.write_ptr(dest, lv.ptr)?;
1008                 match lv.extra {
1009                     LvalueExtra::None => {},
1010                     LvalueExtra::Length(len) => {
1011                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
1012                         self.memory.write_usize(len_ptr, len)?;
1013                     }
1014                     LvalueExtra::DowncastVariant(..) =>
1015                         panic!("attempted to take a reference to an enum downcast lvalue"),
1016                 }
1017             }
1018
1019             Box(ty) => {
1020                 let size = self.type_size(ty, self.substs());
1021                 let ptr = self.memory.allocate(size);
1022                 self.memory.write_ptr(dest, ptr)?;
1023             }
1024
1025             Cast(kind, ref operand, dest_ty) => {
1026                 let src = self.eval_operand(operand)?;
1027                 let src_ty = self.operand_ty(operand);
1028
1029                 use rustc::mir::repr::CastKind::*;
1030                 match kind {
1031                     Unsize => {
1032                         self.move_(src, dest, src_ty)?;
1033                         let src_pointee_ty = pointee_type(src_ty).unwrap();
1034                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
1035
1036                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
1037                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
1038                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
1039                                 self.memory.write_usize(len_ptr, length as u64)?;
1040                             }
1041
1042                             _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1043                         }
1044                     }
1045
1046                     Misc => {
1047                         // FIXME(solson): Wrong for almost everything.
1048                         let dest_size = self.type_size(dest_ty, self.substs());
1049                         let src_size = self.type_size(src_ty, self.substs());
1050                         if dest_size == src_size {
1051                             warn!("performing fishy cast from {:?} to {:?}", src_ty, dest_ty);
1052                             self.memory.copy(src, dest, dest_size)?;
1053                         } else {
1054                             return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue)));
1055                         }
1056                     }
1057
1058                     _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1059                 }
1060             }
1061
1062             InlineAsm { .. } => unimplemented!(),
1063         }
1064
1065         Ok(())
1066     }
1067
1068     fn nonnull_offset(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<Size> {
1069         // Skip the constant 0 at the start meant for LLVM GEP.
1070         let mut path = discrfield.iter().skip(1).map(|&i| i as usize);
1071
1072         // Handle the field index for the outer non-null variant.
1073         let inner_ty = match ty.sty {
1074             ty::TyEnum(adt_def, substs) => {
1075                 let variant = &adt_def.variants[nndiscr as usize];
1076                 let index = path.next().unwrap();
1077                 let field = &variant.fields[index];
1078                 field.ty(self.tcx, substs)
1079             }
1080             _ => panic!(
1081                 "non-enum for StructWrappedNullablePointer: {}",
1082                 ty,
1083             ),
1084         };
1085
1086         self.field_path_offset(inner_ty, path)
1087     }
1088
1089     fn field_path_offset<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<Size> {
1090         let mut offset = Size::from_bytes(0);
1091
1092         // Skip the initial 0 intended for LLVM GEP.
1093         for field_index in path {
1094             let field_offset = self.get_field_offset(ty, field_index)?;
1095             ty = self.get_field_ty(ty, field_index)?;
1096             offset = offset.checked_add(field_offset, &self.tcx.data_layout).unwrap();
1097         }
1098
1099         Ok(offset)
1100     }
1101
1102     fn get_field_ty(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Ty<'tcx>> {
1103         match ty.sty {
1104             ty::TyStruct(adt_def, substs) => {
1105                 Ok(adt_def.struct_variant().fields[field_index].ty(self.tcx, substs))
1106             }
1107
1108             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1109             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1110             ty::TyBox(ty) => {
1111                 assert_eq!(field_index, 0);
1112                 Ok(ty)
1113             }
1114             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}", ty))),
1115         }
1116     }
1117
1118     fn get_field_offset(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Size> {
1119         let layout = self.type_layout(ty, self.substs());
1120
1121         use rustc::ty::layout::Layout::*;
1122         match *layout {
1123             Univariant { .. } => {
1124                 assert_eq!(field_index, 0);
1125                 Ok(Size::from_bytes(0))
1126             }
1127             FatPointer { .. } => {
1128                 let bytes = layout::FAT_PTR_ADDR * self.memory.pointer_size;
1129                 Ok(Size::from_bytes(bytes as u64))
1130             }
1131             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}, with layout: {:?}", ty, layout))),
1132         }
1133     }
1134
1135     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
1136         use rustc::mir::repr::Operand::*;
1137         match *op {
1138             Consume(ref lvalue) => Ok(self.eval_lvalue(lvalue)?.to_ptr()),
1139             Constant(mir::Constant { ref literal, ty, .. }) => {
1140                 use rustc::mir::repr::Literal::*;
1141                 match *literal {
1142                     Value { ref value } => Ok(self.const_to_ptr(value)?),
1143                     Item { def_id, substs } => {
1144                         if let ty::TyFnDef(..) = ty.sty {
1145                             Err(EvalError::Unimplemented("unimplemented: mentions of function items".to_string()))
1146                         } else {
1147                             let cid = ConstantId {
1148                                 def_id: def_id,
1149                                 substs: substs,
1150                                 kind: ConstantKind::Global,
1151                             };
1152                             Ok(*self.statics.get(&cid).expect("static should have been cached (rvalue)"))
1153                         }
1154                     },
1155                     Promoted { index } => {
1156                         let cid = ConstantId {
1157                             def_id: self.frame().def_id,
1158                             substs: self.substs(),
1159                             kind: ConstantKind::Promoted(index),
1160                         };
1161                         Ok(*self.statics.get(&cid).expect("a promoted constant hasn't been precomputed"))
1162                     },
1163                 }
1164             }
1165         }
1166     }
1167
1168     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
1169         use rustc::mir::repr::Lvalue::*;
1170         let ptr = match *lvalue {
1171             ReturnPointer => self.frame().return_ptr
1172                 .expect("ReturnPointer used in a function with no return value"),
1173             Arg(i) => self.frame().locals[i.index()],
1174             Var(i) => self.frame().locals[self.frame().var_offset + i.index()],
1175             Temp(i) => self.frame().locals[self.frame().temp_offset + i.index()],
1176
1177             Static(def_id) => {
1178                 let substs = self.tcx.mk_substs(subst::Substs::empty());
1179                 let cid = ConstantId {
1180                     def_id: def_id,
1181                     substs: substs,
1182                     kind: ConstantKind::Global,
1183                 };
1184                 *self.statics.get(&cid).expect("static should have been cached (lvalue)")
1185             },
1186
1187             Projection(ref proj) => {
1188                 let base = self.eval_lvalue(&proj.base)?;
1189                 let base_ty = self.lvalue_ty(&proj.base);
1190                 let base_layout = self.type_layout(base_ty, self.substs());
1191
1192                 use rustc::mir::repr::ProjectionElem::*;
1193                 match proj.elem {
1194                     Field(field, _) => {
1195                         use rustc::ty::layout::Layout::*;
1196                         let variant = match *base_layout {
1197                             Univariant { ref variant, .. } => variant,
1198                             General { ref variants, .. } => {
1199                                 if let LvalueExtra::DowncastVariant(variant_idx) = base.extra {
1200                                     &variants[variant_idx]
1201                                 } else {
1202                                     panic!("field access on enum had no variant index");
1203                                 }
1204                             }
1205                             RawNullablePointer { .. } => {
1206                                 assert_eq!(field.index(), 0);
1207                                 return Ok(base);
1208                             }
1209                             StructWrappedNullablePointer { ref nonnull, .. } => nonnull,
1210                             _ => panic!("field access on non-product type: {:?}", base_layout),
1211                         };
1212
1213                         let offset = variant.field_offset(field.index()).bytes();
1214                         base.ptr.offset(offset as isize)
1215                     },
1216
1217                     Downcast(_, variant) => {
1218                         use rustc::ty::layout::Layout::*;
1219                         match *base_layout {
1220                             General { discr, .. } => {
1221                                 return Ok(Lvalue {
1222                                     ptr: base.ptr.offset(discr.size().bytes() as isize),
1223                                     extra: LvalueExtra::DowncastVariant(variant),
1224                                 });
1225                             }
1226                             RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
1227                                 return Ok(base);
1228                             }
1229                             _ => panic!("variant downcast on non-aggregate: {:?}", base_layout),
1230                         }
1231                     },
1232
1233                     Deref => {
1234                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
1235                         let ptr = self.memory.read_ptr(base.ptr)?;
1236                         let extra = match pointee_ty.sty {
1237                             ty::TySlice(_) | ty::TyStr => {
1238                                 let len_ptr = base.ptr.offset(self.memory.pointer_size as isize);
1239                                 let len = self.memory.read_usize(len_ptr)?;
1240                                 LvalueExtra::Length(len)
1241                             }
1242                             ty::TyTrait(_) => unimplemented!(),
1243                             _ => LvalueExtra::None,
1244                         };
1245                         return Ok(Lvalue { ptr: ptr, extra: extra });
1246                     }
1247
1248                     Index(ref operand) => {
1249                         let elem_size = match base_ty.sty {
1250                             ty::TyArray(elem_ty, _) |
1251                             ty::TySlice(elem_ty) => self.type_size(elem_ty, self.substs()),
1252                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
1253                         };
1254                         let n_ptr = self.eval_operand(operand)?;
1255                         let n = self.memory.read_usize(n_ptr)?;
1256                         base.ptr.offset(n as isize * elem_size as isize)
1257                     }
1258
1259                     ConstantIndex { .. } => unimplemented!(),
1260                     Subslice { .. } => unimplemented!(),
1261                 }
1262             }
1263         };
1264
1265         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
1266     }
1267
1268     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> Ty<'tcx> {
1269         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx), self.substs())
1270     }
1271
1272     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> Ty<'tcx> {
1273         self.monomorphize(self.mir().operand_ty(self.tcx, operand), self.substs())
1274     }
1275
1276     fn move_(&mut self, src: Pointer, dest: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
1277         let size = self.type_size(ty, self.substs());
1278         self.memory.copy(src, dest, size)?;
1279         if self.type_needs_drop(ty) {
1280             self.memory.drop_fill(src, size)?;
1281         }
1282         Ok(())
1283     }
1284
1285     pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<PrimVal> {
1286         use syntax::ast::{IntTy, UintTy};
1287         let val = match (self.memory.pointer_size, &ty.sty) {
1288             (_, &ty::TyBool)              => PrimVal::Bool(self.memory.read_bool(ptr)?),
1289             (_, &ty::TyInt(IntTy::I8))    => PrimVal::I8(self.memory.read_int(ptr, 1)? as i8),
1290             (2, &ty::TyInt(IntTy::Is)) |
1291             (_, &ty::TyInt(IntTy::I16))   => PrimVal::I16(self.memory.read_int(ptr, 2)? as i16),
1292             (4, &ty::TyInt(IntTy::Is)) |
1293             (_, &ty::TyInt(IntTy::I32))   => PrimVal::I32(self.memory.read_int(ptr, 4)? as i32),
1294             (8, &ty::TyInt(IntTy::Is)) |
1295             (_, &ty::TyInt(IntTy::I64))   => PrimVal::I64(self.memory.read_int(ptr, 8)? as i64),
1296             (_, &ty::TyUint(UintTy::U8))  => PrimVal::U8(self.memory.read_uint(ptr, 1)? as u8),
1297             (2, &ty::TyUint(UintTy::Us)) |
1298             (_, &ty::TyUint(UintTy::U16)) => PrimVal::U16(self.memory.read_uint(ptr, 2)? as u16),
1299             (4, &ty::TyUint(UintTy::Us)) |
1300             (_, &ty::TyUint(UintTy::U32)) => PrimVal::U32(self.memory.read_uint(ptr, 4)? as u32),
1301             (8, &ty::TyUint(UintTy::Us)) |
1302             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
1303
1304             (_, &ty::TyRef(_, ty::TypeAndMut { ty, .. })) |
1305             (_, &ty::TyRawPtr(ty::TypeAndMut { ty, .. })) => {
1306                 if self.type_is_sized(ty) {
1307                     match self.memory.read_ptr(ptr) {
1308                         Ok(p) => PrimVal::AbstractPtr(p),
1309                         Err(EvalError::ReadBytesAsPointer) => {
1310                             PrimVal::IntegerPtr(self.memory.read_usize(ptr)?)
1311                         }
1312                         Err(e) => return Err(e),
1313                     }
1314                 } else {
1315                     return Err(EvalError::Unimplemented(format!("unimplemented: primitive read of fat pointer type: {:?}", ty)));
1316                 }
1317             }
1318
1319             _ => panic!("primitive read of non-primitive type: {:?}", ty),
1320         };
1321         Ok(val)
1322     }
1323
1324     fn frame(&self) -> &Frame<'a, 'tcx> {
1325         self.stack.last().expect("no call frames exist")
1326     }
1327
1328     fn frame_mut(&mut self) -> &mut Frame<'a, 'tcx> {
1329         self.stack.last_mut().expect("no call frames exist")
1330     }
1331
1332     fn mir(&self) -> CachedMir<'a, 'tcx> {
1333         self.frame().mir.clone()
1334     }
1335
1336     fn substs(&self) -> &'tcx Substs<'tcx> {
1337         self.frame().substs
1338     }
1339 }
1340
1341 fn pointee_type(ptr_ty: ty::Ty) -> Option<ty::Ty> {
1342     match ptr_ty.sty {
1343         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1344         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1345         ty::TyBox(ty) => {
1346             Some(ty)
1347         }
1348         _ => None,
1349     }
1350 }
1351
1352 impl Lvalue {
1353     fn to_ptr(self) -> Pointer {
1354         assert_eq!(self.extra, LvalueExtra::None);
1355         self.ptr
1356     }
1357 }
1358
1359 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1360     type Target = mir::Mir<'tcx>;
1361     fn deref(&self) -> &mir::Mir<'tcx> {
1362         match *self {
1363             CachedMir::Ref(r) => r,
1364             CachedMir::Owned(ref rc) => rc,
1365         }
1366     }
1367 }
1368
1369 #[derive(Debug)]
1370 pub struct ImplMethod<'tcx> {
1371     pub method: Rc<ty::Method<'tcx>>,
1372     pub substs: &'tcx Substs<'tcx>,
1373     pub is_provided: bool,
1374 }
1375
1376 /// Locates the applicable definition of a method, given its name.
1377 pub fn get_impl_method<'a, 'tcx>(
1378     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1379     impl_def_id: DefId,
1380     substs: &'tcx Substs<'tcx>,
1381     name: ast::Name,
1382 ) -> ImplMethod<'tcx> {
1383     assert!(!substs.types.needs_infer());
1384
1385     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1386     let trait_def = tcx.lookup_trait_def(trait_def_id);
1387
1388     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1389         Some(node_item) => {
1390             let substs = tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
1391                 let substs = traits::translate_substs(&infcx, impl_def_id,
1392                                                       substs, node_item.node);
1393                 tcx.lift(&substs).unwrap_or_else(|| {
1394                     bug!("trans::meth::get_impl_method: translate_substs \
1395                           returned {:?} which contains inference types/regions",
1396                          substs);
1397                 })
1398             });
1399             ImplMethod {
1400                 method: node_item.item,
1401                 substs: substs,
1402                 is_provided: node_item.node.is_from_trait(),
1403             }
1404         }
1405         None => {
1406             bug!("method {:?} not found in {:?}", name, impl_def_id)
1407         }
1408     }
1409 }
1410
1411 // TODO(solson): Upstream these methods into rustc::ty::layout.
1412
1413 trait IntegerExt {
1414     fn size(self) -> Size;
1415 }
1416
1417 impl IntegerExt for layout::Integer {
1418     fn size(self) -> Size {
1419         use rustc::ty::layout::Integer::*;
1420         match self {
1421             I1 | I8 => Size::from_bits(8),
1422             I16 => Size::from_bits(16),
1423             I32 => Size::from_bits(32),
1424             I64 => Size::from_bits(64),
1425         }
1426     }
1427 }
1428
1429 trait StructExt {
1430     fn field_offset(&self, index: usize) -> Size;
1431 }
1432
1433 impl StructExt for layout::Struct {
1434     fn field_offset(&self, index: usize) -> Size {
1435         if index == 0 {
1436             Size::from_bytes(0)
1437         } else {
1438             self.offset_after_field[index - 1]
1439         }
1440     }
1441 }