src/interpreter/mod.rs

   1 use rustc::middle::const_val;
   2 use rustc::hir::def_id::DefId;
   3 use rustc::mir::mir_map::MirMap;
   4 use rustc::mir::repr as mir;
   5 use rustc::traits::{self, ProjectionMode};
   6 use rustc::ty::fold::TypeFoldable;
   7 use rustc::ty::layout::{self, Layout, Size};
   8 use rustc::ty::subst::{self, Subst, Substs};
   9 use rustc::ty::{self, Ty, TyCtxt};
  10 use rustc::util::nodemap::DefIdMap;
  11 use std::cell::RefCell;
  12 use std::ops::{Deref, DerefMut};
  13 use std::rc::Rc;
  14 use std::{iter, mem};
  15 use syntax::ast;
  16 use syntax::attr;
  17 use syntax::codemap::{self, DUMMY_SP, Span};
  18
  19 use error::{EvalError, EvalResult};
  20 use memory::{Memory, Pointer};
  21 use primval::{self, PrimVal};
  22
  23 use std::collections::HashMap;
  24
  25 mod stepper;
  26
  27 struct GlobalEvalContext<'a, 'tcx: 'a> {
  28     /// The results of the type checker, from rustc.
  29     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  30
  31     /// A mapping from NodeIds to Mir, from rustc. Only contains MIR for crate-local items.
  32     mir_map: &'a MirMap<'tcx>,
  33
  34     /// A local cache from DefIds to Mir for non-crate-local items.
  35     mir_cache: RefCell<DefIdMap<Rc<mir::Mir<'tcx>>>>,
  36
  37     /// The virtual memory system.
  38     memory: Memory,
  39
  40     /// Precomputed statics, constants and promoteds
  41     statics: HashMap<ConstantId<'tcx>, Pointer>,
  42 }
  43
  44 struct FnEvalContext<'a, 'b: 'a + 'mir, 'mir, 'tcx: 'b> {
  45     gecx: &'a mut GlobalEvalContext<'b, 'tcx>,
  46
  47     /// The virtual call stack.
  48     stack: Vec<Frame<'mir, 'tcx>>,
  49 }
  50
  51 impl<'a, 'b, 'mir, 'tcx> Deref for FnEvalContext<'a, 'b, 'mir, 'tcx> {
  52     type Target = GlobalEvalContext<'b, 'tcx>;
  53     fn deref(&self) -> &Self::Target {
  54         self.gecx
  55     }
  56 }
  57
  58 impl<'a, 'b, 'mir, 'tcx> DerefMut for FnEvalContext<'a, 'b, 'mir, 'tcx> {
  59     fn deref_mut(&mut self) -> &mut Self::Target {
  60         self.gecx
  61     }
  62 }
  63
  64 /// A stack frame.
  65 struct Frame<'a, 'tcx: 'a> {
  66     /// The def_id of the current function
  67     def_id: DefId,
  68
  69     /// The span of the call site
  70     span: codemap::Span,
  71
  72     /// type substitutions for the current function invocation
  73     substs: &'tcx Substs<'tcx>,
  74
  75     /// The MIR for the function called on this frame.
  76     mir: CachedMir<'a, 'tcx>,
  77
  78     /// The block that is currently executed (or will be executed after the above call stacks return)
  79     next_block: mir::BasicBlock,
  80
  81     /// A pointer for writing the return value of the current call if it's not a diverging call.
  82     return_ptr: Option<Pointer>,
  83
  84     /// The list of locals for the current function, stored in order as
  85     /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
  86     /// and the temporaries at `self.temp_offset`.
  87     locals: Vec<Pointer>,
  88
  89     /// The offset of the first variable in `self.locals`.
  90     var_offset: usize,
  91
  92     /// The offset of the first temporary in `self.locals`.
  93     temp_offset: usize,
  94
  95     /// The index of the currently evaluated statment
  96     stmt: usize,
  97
  98     // Constants that need to be evaluated before the next statement can be evaluated
  99     constants: Vec<(ConstantId<'tcx>, Span, Pointer, CachedMir<'a, 'tcx>)>,
 100 }
 101
 102 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 103 struct Lvalue {
 104     ptr: Pointer,
 105     extra: LvalueExtra,
 106 }
 107
 108 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 109 enum LvalueExtra {
 110     None,
 111     Length(u64),
 112     // TODO(solson): Vtable(memory::AllocId),
 113     DowncastVariant(usize),
 114 }
 115
 116 #[derive(Clone)]
 117 enum CachedMir<'mir, 'tcx: 'mir> {
 118     Ref(&'mir mir::Mir<'tcx>),
 119     Owned(Rc<mir::Mir<'tcx>>)
 120 }
 121
 122 /// Represents the action to be taken in the main loop as a result of executing a terminator.
 123 enum TerminatorTarget {
 124     /// Make a local jump to the next block
 125     Block,
 126
 127     /// Start executing from the new current frame. (For function calls.)
 128     Call,
 129
 130     /// Stop executing the current frame and resume the previous frame.
 131     Return,
 132 }
 133
 134 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 135 enum ConstantId<'tcx> {
 136     Promoted { def_id: DefId, substs: &'tcx Substs<'tcx>, index: usize },
 137     Static { def_id: DefId, substs: &'tcx Substs<'tcx> },
 138 }
 139
 140 impl<'tcx> ConstantId<'tcx> {
 141     fn substs(&self) -> &'tcx Substs<'tcx> {
 142         use self::ConstantId::*;
 143         match *self {
 144             Promoted { substs, .. } |
 145             Static { substs, .. } => substs
 146         }
 147     }
 148
 149     fn def_id(&self) -> DefId {
 150         use self::ConstantId::*;
 151         match *self {
 152             Promoted { def_id, .. } |
 153             Static { def_id, .. } => def_id,
 154         }
 155     }
 156 }
 157
 158
 159 impl<'a, 'tcx> GlobalEvalContext<'a, 'tcx> {
 160     fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>, mir_map: &'a MirMap<'tcx>) -> Self {
 161         GlobalEvalContext {
 162             tcx: tcx,
 163             mir_map: mir_map,
 164             mir_cache: RefCell::new(DefIdMap()),
 165             memory: Memory::new(tcx.sess
 166                                    .target
 167                                    .uint_type
 168                                    .bit_width()
 169                                    .expect("Session::target::uint_type was usize")/8),
 170             statics: HashMap::new(),
 171         }
 172     }
 173
 174     fn call(&mut self, mir: &mir::Mir<'tcx>, def_id: DefId) -> EvalResult<Option<Pointer>> {
 175         let substs = self.tcx.mk_substs(subst::Substs::empty());
 176         let return_ptr = self.alloc_ret_ptr(mir.return_ty, substs);
 177
 178         let mut nested_fecx = FnEvalContext::new(self);
 179
 180         nested_fecx.push_stack_frame(def_id, mir.span, CachedMir::Ref(mir), substs, None);
 181
 182         nested_fecx.frame_mut().return_ptr = return_ptr;
 183
 184         nested_fecx.run()?;
 185         Ok(return_ptr)
 186     }
 187
 188     fn alloc_ret_ptr(&mut self, ty: ty::FnOutput<'tcx>, substs: &'tcx Substs<'tcx>) -> Option<Pointer> {
 189         match ty {
 190             ty::FnConverging(ty) => {
 191                 let size = self.type_size(ty, substs);
 192                 Some(self.memory.allocate(size))
 193             }
 194             ty::FnDiverging => None,
 195         }
 196     }
 197     // TODO(solson): Try making const_to_primval instead.
 198     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<Pointer> {
 199         use rustc::middle::const_val::ConstVal::*;
 200         match *const_val {
 201             Float(_f) => unimplemented!(),
 202             Integral(int) => {
 203                 // TODO(solson): Check int constant type.
 204                 let ptr = self.memory.allocate(8);
 205                 self.memory.write_uint(ptr, int.to_u64_unchecked(), 8)?;
 206                 Ok(ptr)
 207             }
 208             Str(ref s) => {
 209                 let psize = self.memory.pointer_size;
 210                 let static_ptr = self.memory.allocate(s.len());
 211                 let ptr = self.memory.allocate(psize * 2);
 212                 self.memory.write_bytes(static_ptr, s.as_bytes())?;
 213                 self.memory.write_ptr(ptr, static_ptr)?;
 214                 self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64)?;
 215                 Ok(ptr)
 216             }
 217             ByteStr(ref bs) => {
 218                 let psize = self.memory.pointer_size;
 219                 let static_ptr = self.memory.allocate(bs.len());
 220                 let ptr = self.memory.allocate(psize);
 221                 self.memory.write_bytes(static_ptr, bs)?;
 222                 self.memory.write_ptr(ptr, static_ptr)?;
 223                 Ok(ptr)
 224             }
 225             Bool(b) => {
 226                 let ptr = self.memory.allocate(1);
 227                 self.memory.write_bool(ptr, b)?;
 228                 Ok(ptr)
 229             }
 230             Char(_c)          => unimplemented!(),
 231             Struct(_node_id)  => unimplemented!(),
 232             Tuple(_node_id)   => unimplemented!(),
 233             Function(_def_id) => unimplemented!(),
 234             Array(_, _)       => unimplemented!(),
 235             Repeat(_, _)      => unimplemented!(),
 236             Dummy             => unimplemented!(),
 237         }
 238     }
 239
 240     fn type_needs_drop(&self, ty: Ty<'tcx>) -> bool {
 241         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
 242     }
 243
 244     fn type_is_sized(&self, ty: Ty<'tcx>) -> bool {
 245         ty.is_sized(self.tcx, &self.tcx.empty_parameter_environment(), DUMMY_SP)
 246     }
 247
 248     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
 249         // Do the initial selection for the obligation. This yields the shallow result we are
 250         // looking for -- that is, what specific impl.
 251         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 252             let mut selcx = traits::SelectionContext::new(&infcx);
 253
 254             let obligation = traits::Obligation::new(
 255                 traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
 256                 trait_ref.to_poly_trait_predicate(),
 257             );
 258             let selection = selcx.select(&obligation).unwrap().unwrap();
 259
 260             // Currently, we use a fulfillment context to completely resolve all nested obligations.
 261             // This is because they can inform the inference of the impl's type parameters.
 262             let mut fulfill_cx = traits::FulfillmentContext::new();
 263             let vtable = selection.map(|predicate| {
 264                 fulfill_cx.register_predicate_obligation(&infcx, predicate);
 265             });
 266             infcx.drain_fulfillment_cx_or_panic(DUMMY_SP, &mut fulfill_cx, &vtable)
 267         })
 268     }
 269
 270     /// Trait method, which has to be resolved to an impl method.
 271     pub fn trait_method(
 272         &self,
 273         def_id: DefId,
 274         substs: &'tcx Substs<'tcx>
 275     ) -> (DefId, &'tcx Substs<'tcx>) {
 276         let method_item = self.tcx.impl_or_trait_item(def_id);
 277         let trait_id = method_item.container().id();
 278         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
 279         match self.fulfill_obligation(trait_ref) {
 280             traits::VtableImpl(vtable_impl) => {
 281                 let impl_did = vtable_impl.impl_def_id;
 282                 let mname = self.tcx.item_name(def_id);
 283                 // Create a concatenated set of substitutions which includes those from the impl
 284                 // and those from the method:
 285                 let impl_substs = vtable_impl.substs.with_method_from(substs);
 286                 let substs = self.tcx.mk_substs(impl_substs);
 287                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
 288
 289                 (mth.method.def_id, mth.substs)
 290             }
 291
 292             traits::VtableClosure(vtable_closure) =>
 293                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
 294
 295             traits::VtableFnPointer(_fn_ty) => {
 296                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
 297                 unimplemented!()
 298                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
 299
 300                 // let method_ty = def_ty(tcx, def_id, substs);
 301                 // let fn_ptr_ty = match method_ty.sty {
 302                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
 303                 //     _ => unreachable!("expected fn item type, found {}",
 304                 //                       method_ty)
 305                 // };
 306                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 307             }
 308
 309             traits::VtableObject(ref _data) => {
 310                 unimplemented!()
 311                 // Callee {
 312                 //     data: Virtual(traits::get_vtable_index_of_object_method(
 313                 //                   tcx, data, def_id)),
 314                 //                   ty: def_ty(tcx, def_id, substs)
 315                 // }
 316             }
 317             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
 318         }
 319     }
 320 }
 321
 322 impl<'a, 'b, 'mir, 'tcx> FnEvalContext<'a, 'b, 'mir, 'tcx> {
 323     fn new(gecx: &'a mut GlobalEvalContext<'b, 'tcx>) -> Self {
 324         FnEvalContext {
 325             gecx: gecx,
 326             stack: Vec::new(),
 327         }
 328     }
 329
 330     #[inline(never)]
 331     #[cold]
 332     fn report(&self, e: &EvalError) {
 333         let stmt = self.frame().stmt;
 334         let block = self.basic_block();
 335         let span = if stmt < block.statements.len() {
 336             block.statements[stmt].span
 337         } else {
 338             block.terminator().span
 339         };
 340         let mut err = self.tcx.sess.struct_span_err(span, &e.to_string());
 341         for &Frame{ def_id, substs, span, .. } in self.stack.iter().rev() {
 342             // FIXME(solson): Find a way to do this without this Display impl hack.
 343             use rustc::util::ppaux;
 344             use std::fmt;
 345             struct Instance<'tcx>(DefId, &'tcx Substs<'tcx>);
 346             impl<'tcx> fmt::Display for Instance<'tcx> {
 347                 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 348                     ppaux::parameterized(f, self.1, self.0, ppaux::Ns::Value, &[],
 349                         |tcx| tcx.lookup_item_type(self.0).generics)
 350                 }
 351             }
 352             err.span_note(span, &format!("inside call to {}", Instance(def_id, substs)));
 353         }
 354         err.emit();
 355     }
 356
 357     fn maybe_report<T>(&self, r: EvalResult<T>) -> EvalResult<T> {
 358         if let Err(ref e) = r {
 359             self.report(e);
 360         }
 361         r
 362     }
 363
 364     fn run(&mut self) -> EvalResult<()> {
 365         let mut stepper = stepper::Stepper::new(self);
 366         'outer: loop {
 367             use self::stepper::Event::*;
 368             trace!("// {:?}", stepper.block());
 369
 370             loop {
 371                 match stepper.step()? {
 372                     Constant => trace!("next statement requires the computation of a constant"),
 373                     Assignment => trace!("{:?}", stepper.stmt()),
 374                     Terminator => {
 375                         trace!("{:?}", stepper.term().kind);
 376                         continue 'outer;
 377                     },
 378                     Done => return Ok(()),
 379                 }
 380             }
 381         }
 382     }
 383
 384     fn push_stack_frame(&mut self, def_id: DefId, span: codemap::Span, mir: CachedMir<'mir, 'tcx>, substs: &'tcx Substs<'tcx>,
 385         return_ptr: Option<Pointer>)
 386     {
 387         let arg_tys = mir.arg_decls.iter().map(|a| a.ty);
 388         let var_tys = mir.var_decls.iter().map(|v| v.ty);
 389         let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
 390
 391         let num_args = mir.arg_decls.len();
 392         let num_vars = mir.var_decls.len();
 393
 394         ::log_settings::settings().indentation += 1;
 395
 396         self.stack.push(Frame {
 397             mir: mir.clone(),
 398             next_block: mir::START_BLOCK,
 399             return_ptr: return_ptr,
 400             locals: Vec::new(),
 401             var_offset: num_args,
 402             temp_offset: num_args + num_vars,
 403             span: span,
 404             def_id: def_id,
 405             substs: substs,
 406             stmt: 0,
 407             constants: Vec::new(),
 408         });
 409
 410         let locals: Vec<Pointer> = arg_tys.chain(var_tys).chain(temp_tys).map(|ty| {
 411             let size = self.type_size(ty);
 412             self.memory.allocate(size)
 413         }).collect();
 414
 415         self.frame_mut().locals = locals;
 416     }
 417
 418     fn pop_stack_frame(&mut self) {
 419         ::log_settings::settings().indentation -= 1;
 420         let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
 421         // TODO(solson): Deallocate local variables.
 422     }
 423
 424     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>)
 425             -> EvalResult<TerminatorTarget> {
 426         use rustc::mir::repr::TerminatorKind::*;
 427         let target = match terminator.kind {
 428             Return => TerminatorTarget::Return,
 429
 430             Goto { target } => {
 431                 self.frame_mut().next_block = target;
 432                 TerminatorTarget::Block
 433             },
 434
 435             If { ref cond, targets: (then_target, else_target) } => {
 436                 let cond_ptr = self.eval_operand(cond)?;
 437                 let cond_val = self.memory.read_bool(cond_ptr)?;
 438                 self.frame_mut().next_block = if cond_val { then_target } else { else_target };
 439                 TerminatorTarget::Block
 440             }
 441
 442             SwitchInt { ref discr, ref values, ref targets, .. } => {
 443                 let discr_ptr = self.eval_lvalue(discr)?.to_ptr();
 444                 let discr_size = self
 445                     .type_layout(self.lvalue_ty(discr))
 446                     .size(&self.tcx.data_layout)
 447                     .bytes() as usize;
 448                 let discr_val = self.memory.read_uint(discr_ptr, discr_size)?;
 449
 450                 // Branch to the `otherwise` case by default, if no match is found.
 451                 let mut target_block = targets[targets.len() - 1];
 452
 453                 for (index, val_const) in values.iter().enumerate() {
 454                     let ptr = self.const_to_ptr(val_const)?;
 455                     let val = self.memory.read_uint(ptr, discr_size)?;
 456                     if discr_val == val {
 457                         target_block = targets[index];
 458                         break;
 459                     }
 460                 }
 461
 462                 self.frame_mut().next_block = target_block;
 463                 TerminatorTarget::Block
 464             }
 465
 466             Switch { ref discr, ref targets, adt_def } => {
 467                 let adt_ptr = self.eval_lvalue(discr)?.to_ptr();
 468                 let adt_ty = self.lvalue_ty(discr);
 469                 let discr_val = self.read_discriminant_value(adt_ptr, adt_ty)?;
 470                 let matching = adt_def.variants.iter()
 471                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
 472
 473                 match matching {
 474                     Some(i) => {
 475                         self.frame_mut().next_block = targets[i];
 476                         TerminatorTarget::Block
 477                     },
 478                     None => return Err(EvalError::InvalidDiscriminant),
 479                 }
 480             }
 481
 482             Call { ref func, ref args, ref destination, .. } => {
 483                 let mut return_ptr = None;
 484                 if let Some((ref lv, target)) = *destination {
 485                     self.frame_mut().next_block = target;
 486                     return_ptr = Some(self.eval_lvalue(lv)?.to_ptr());
 487                 }
 488
 489                 let func_ty = self.operand_ty(func);
 490                 match func_ty.sty {
 491                     ty::TyFnDef(def_id, substs, fn_ty) => {
 492                         use syntax::abi::Abi;
 493                         match fn_ty.abi {
 494                             Abi::RustIntrinsic => {
 495                                 let name = self.tcx.item_name(def_id).as_str();
 496                                 match fn_ty.sig.0.output {
 497                                     ty::FnConverging(ty) => {
 498                                         let size = self.type_size(ty);
 499                                         let ret = return_ptr.unwrap();
 500                                         self.call_intrinsic(&name, substs, args, ret, size)?
 501                                     }
 502                                     ty::FnDiverging => unimplemented!(),
 503                                 }
 504                             }
 505
 506                             Abi::C => {
 507                                 match fn_ty.sig.0.output {
 508                                     ty::FnConverging(ty) => {
 509                                         let size = self.type_size(ty);
 510                                         self.call_c_abi(def_id, args, return_ptr.unwrap(), size)?
 511                                     }
 512                                     ty::FnDiverging => unimplemented!(),
 513                                 }
 514                             }
 515
 516                             Abi::Rust | Abi::RustCall => {
 517                                 // TODO(solson): Adjust the first argument when calling a Fn or
 518                                 // FnMut closure via FnOnce::call_once.
 519
 520                                 // Only trait methods can have a Self parameter.
 521                                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 522                                     self.trait_method(def_id, substs)
 523                                 } else {
 524                                     (def_id, substs)
 525                                 };
 526
 527                                 let mut arg_srcs = Vec::new();
 528                                 for arg in args {
 529                                     let src = self.eval_operand(arg)?;
 530                                     let src_ty = self.operand_ty(arg);
 531                                     arg_srcs.push((src, src_ty));
 532                                 }
 533
 534                                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 535                                     arg_srcs.pop();
 536                                     let last_arg = args.last().unwrap();
 537                                     let last = self.eval_operand(last_arg)?;
 538                                     let last_ty = self.operand_ty(last_arg);
 539                                     let last_layout = self.type_layout(last_ty);
 540                                     match (&last_ty.sty, last_layout) {
 541                                         (&ty::TyTuple(fields),
 542                                          &Layout::Univariant { ref variant, .. }) => {
 543                                             let offsets = iter::once(0)
 544                                                 .chain(variant.offset_after_field.iter()
 545                                                     .map(|s| s.bytes()));
 546                                             for (offset, ty) in offsets.zip(fields) {
 547                                                 let src = last.offset(offset as isize);
 548                                                 arg_srcs.push((src, ty));
 549                                             }
 550                                         }
 551                                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 552                                     }
 553                                 }
 554
 555                                 let mir = self.load_mir(resolved_def_id);
 556                                 self.push_stack_frame(def_id, terminator.span, mir, resolved_substs, return_ptr);
 557
 558                                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 559                                     let dest = self.frame().locals[i];
 560                                     self.move_(src, dest, src_ty)?;
 561                                 }
 562
 563                                 TerminatorTarget::Call
 564                             }
 565
 566                             abi => return Err(EvalError::Unimplemented(format!("can't handle function with {:?} ABI", abi))),
 567                         }
 568                     }
 569
 570                     _ => return Err(EvalError::Unimplemented(format!("can't handle callee of type {:?}", func_ty))),
 571                 }
 572             }
 573
 574             Drop { ref value, target, .. } => {
 575                 let ptr = self.eval_lvalue(value)?.to_ptr();
 576                 let ty = self.lvalue_ty(value);
 577                 self.drop(ptr, ty)?;
 578                 self.frame_mut().next_block = target;
 579                 TerminatorTarget::Block
 580             }
 581
 582             Resume => unimplemented!(),
 583         };
 584
 585         Ok(target)
 586     }
 587
 588     fn drop(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
 589         if !self.type_needs_drop(ty) {
 590             debug!("no need to drop {:?}", ty);
 591             return Ok(());
 592         }
 593         trace!("-need to drop {:?}", ty);
 594
 595         // TODO(solson): Call user-defined Drop::drop impls.
 596
 597         match ty.sty {
 598             ty::TyBox(contents_ty) => {
 599                 match self.memory.read_ptr(ptr) {
 600                     Ok(contents_ptr) => {
 601                         self.drop(contents_ptr, contents_ty)?;
 602                         trace!("-deallocating box");
 603                         self.memory.deallocate(contents_ptr)?;
 604                     }
 605                     Err(EvalError::ReadBytesAsPointer) => {
 606                         let size = self.memory.pointer_size;
 607                         let possible_drop_fill = self.memory.read_bytes(ptr, size)?;
 608                         if possible_drop_fill.iter().all(|&b| b == mem::POST_DROP_U8) {
 609                             return Ok(());
 610                         } else {
 611                             return Err(EvalError::ReadBytesAsPointer);
 612                         }
 613                     }
 614                     Err(e) => return Err(e),
 615                 }
 616             }
 617
 618             // TODO(solson): Implement drop for other relevant types (e.g. aggregates).
 619             _ => {}
 620         }
 621
 622         // Filling drop.
 623         // FIXME(solson): Trait objects (with no static size) probably get filled, too.
 624         let size = self.type_size(ty);
 625         self.memory.drop_fill(ptr, size)?;
 626
 627         Ok(())
 628     }
 629
 630     fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalResult<u64> {
 631         use rustc::ty::layout::Layout::*;
 632         let adt_layout = self.type_layout(adt_ty);
 633
 634         let discr_val = match *adt_layout {
 635             General { discr, .. } | CEnum { discr, .. } => {
 636                 let discr_size = discr.size().bytes();
 637                 self.memory.read_uint(adt_ptr, discr_size as usize)?
 638             }
 639
 640             RawNullablePointer { nndiscr, .. } => {
 641                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
 642             }
 643
 644             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
 645                 let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
 646                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
 647                 self.read_nonnull_discriminant_value(nonnull, nndiscr)?
 648             }
 649
 650             // The discriminant_value intrinsic returns 0 for non-sum types.
 651             Array { .. } | FatPointer { .. } | Scalar { .. } | Univariant { .. } |
 652             Vector { .. } => 0,
 653         };
 654
 655         Ok(discr_val)
 656     }
 657
 658     fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<u64> {
 659         let not_null = match self.memory.read_usize(ptr) {
 660             Ok(0) => false,
 661             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
 662             Err(e) => return Err(e),
 663         };
 664         assert!(nndiscr == 0 || nndiscr == 1);
 665         Ok(if not_null { nndiscr } else { 1 - nndiscr })
 666     }
 667
 668     fn call_intrinsic(
 669         &mut self,
 670         name: &str,
 671         substs: &'tcx Substs<'tcx>,
 672         args: &[mir::Operand<'tcx>],
 673         dest: Pointer,
 674         dest_size: usize
 675     ) -> EvalResult<TerminatorTarget> {
 676         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 677             .map(|arg| self.eval_operand(arg))
 678             .collect();
 679         let args = args_res?;
 680
 681         match name {
 682             // FIXME(solson): Handle different integer types correctly.
 683             "add_with_overflow" => {
 684                 let ty = *substs.types.get(subst::FnSpace, 0);
 685                 let size = self.type_size(ty);
 686                 let left = self.memory.read_int(args[0], size)?;
 687                 let right = self.memory.read_int(args[1], size)?;
 688                 let (n, overflowed) = unsafe {
 689                     ::std::intrinsics::add_with_overflow::<i64>(left, right)
 690                 };
 691                 self.memory.write_int(dest, n, size)?;
 692                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 693             }
 694
 695             "assume" => {}
 696
 697             "copy_nonoverlapping" => {
 698                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 699                 let elem_size = self.type_size(elem_ty);
 700                 let src = self.memory.read_ptr(args[0])?;
 701                 let dest = self.memory.read_ptr(args[1])?;
 702                 let count = self.memory.read_isize(args[2])?;
 703                 self.memory.copy(src, dest, count as usize * elem_size)?;
 704             }
 705
 706             "discriminant_value" => {
 707                 let ty = *substs.types.get(subst::FnSpace, 0);
 708                 let adt_ptr = self.memory.read_ptr(args[0])?;
 709                 let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
 710                 self.memory.write_uint(dest, discr_val, dest_size)?;
 711             }
 712
 713             "forget" => {
 714                 let arg_ty = *substs.types.get(subst::FnSpace, 0);
 715                 let arg_size = self.type_size(arg_ty);
 716                 self.memory.drop_fill(args[0], arg_size)?;
 717             }
 718
 719             "init" => self.memory.write_repeat(dest, 0, dest_size)?,
 720
 721             "min_align_of" => {
 722                 self.memory.write_int(dest, 1, dest_size)?;
 723             }
 724
 725             "move_val_init" => {
 726                 let ty = *substs.types.get(subst::FnSpace, 0);
 727                 let ptr = self.memory.read_ptr(args[0])?;
 728                 self.move_(args[1], ptr, ty)?;
 729             }
 730
 731             // FIXME(solson): Handle different integer types correctly.
 732             "mul_with_overflow" => {
 733                 let ty = *substs.types.get(subst::FnSpace, 0);
 734                 let size = self.type_size(ty);
 735                 let left = self.memory.read_int(args[0], size)?;
 736                 let right = self.memory.read_int(args[1], size)?;
 737                 let (n, overflowed) = unsafe {
 738                     ::std::intrinsics::mul_with_overflow::<i64>(left, right)
 739                 };
 740                 self.memory.write_int(dest, n, size)?;
 741                 self.memory.write_bool(dest.offset(size as isize), overflowed)?;
 742             }
 743
 744             "offset" => {
 745                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 746                 let pointee_size = self.type_size(pointee_ty) as isize;
 747                 let ptr_arg = args[0];
 748                 let offset = self.memory.read_isize(args[1])?;
 749
 750                 match self.memory.read_ptr(ptr_arg) {
 751                     Ok(ptr) => {
 752                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 753                         self.memory.write_ptr(dest, result_ptr)?;
 754                     }
 755                     Err(EvalError::ReadBytesAsPointer) => {
 756                         let addr = self.memory.read_isize(ptr_arg)?;
 757                         let result_addr = addr + offset * pointee_size as i64;
 758                         self.memory.write_isize(dest, result_addr)?;
 759                     }
 760                     Err(e) => return Err(e),
 761                 }
 762             }
 763
 764             // FIXME(solson): Handle different integer types correctly. Use primvals?
 765             "overflowing_sub" => {
 766                 let ty = *substs.types.get(subst::FnSpace, 0);
 767                 let size = self.type_size(ty);
 768                 let left = self.memory.read_int(args[0], size)?;
 769                 let right = self.memory.read_int(args[1], size)?;
 770                 let n = left.wrapping_sub(right);
 771                 self.memory.write_int(dest, n, size)?;
 772             }
 773
 774             "size_of" => {
 775                 let ty = *substs.types.get(subst::FnSpace, 0);
 776                 let size = self.type_size(ty) as u64;
 777                 self.memory.write_uint(dest, size, dest_size)?;
 778             }
 779
 780             "size_of_val" => {
 781                 let ty = *substs.types.get(subst::FnSpace, 0);
 782                 if self.type_is_sized(ty) {
 783                     let size = self.type_size(ty) as u64;
 784                     self.memory.write_uint(dest, size, dest_size)?;
 785                 } else {
 786                     match ty.sty {
 787                         ty::TySlice(_) | ty::TyStr => {
 788                             let elem_ty = ty.sequence_element_type(self.tcx);
 789                             let elem_size = self.type_size(elem_ty) as u64;
 790                             let ptr_size = self.memory.pointer_size as isize;
 791                             let n = self.memory.read_usize(args[0].offset(ptr_size))?;
 792                             self.memory.write_uint(dest, n * elem_size, dest_size)?;
 793                         }
 794
 795                         _ => return Err(EvalError::Unimplemented(format!("unimplemented: size_of_val::<{:?}>", ty))),
 796                     }
 797                 }
 798             }
 799
 800             "transmute" => {
 801                 let ty = *substs.types.get(subst::FnSpace, 0);
 802                 self.move_(args[0], dest, ty)?;
 803             }
 804             "uninit" => self.memory.mark_definedness(dest, dest_size, false)?,
 805
 806             name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
 807         }
 808
 809         // Since we pushed no stack frame, the main loop will act
 810         // as if the call just completed and it's returning to the
 811         // current frame.
 812         Ok(TerminatorTarget::Call)
 813     }
 814
 815     fn call_c_abi(
 816         &mut self,
 817         def_id: DefId,
 818         args: &[mir::Operand<'tcx>],
 819         dest: Pointer,
 820         dest_size: usize,
 821     ) -> EvalResult<TerminatorTarget> {
 822         let name = self.tcx.item_name(def_id);
 823         let attrs = self.tcx.get_attrs(def_id);
 824         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 825             Some(ln) => ln.clone(),
 826             None => name.as_str(),
 827         };
 828
 829         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 830             .map(|arg| self.eval_operand(arg))
 831             .collect();
 832         let args = args_res?;
 833
 834         match &link_name[..] {
 835             "__rust_allocate" => {
 836                 let size = self.memory.read_usize(args[0])?;
 837                 let ptr = self.memory.allocate(size as usize);
 838                 self.memory.write_ptr(dest, ptr)?;
 839             }
 840
 841             "__rust_reallocate" => {
 842                 let ptr = self.memory.read_ptr(args[0])?;
 843                 let size = self.memory.read_usize(args[2])?;
 844                 self.memory.reallocate(ptr, size as usize)?;
 845                 self.memory.write_ptr(dest, ptr)?;
 846             }
 847
 848             "memcmp" => {
 849                 let left = self.memory.read_ptr(args[0])?;
 850                 let right = self.memory.read_ptr(args[1])?;
 851                 let n = self.memory.read_usize(args[2])? as usize;
 852
 853                 let result = {
 854                     let left_bytes = self.memory.read_bytes(left, n)?;
 855                     let right_bytes = self.memory.read_bytes(right, n)?;
 856
 857                     use std::cmp::Ordering::*;
 858                     match left_bytes.cmp(right_bytes) {
 859                         Less => -1,
 860                         Equal => 0,
 861                         Greater => 1,
 862                     }
 863                 };
 864
 865                 self.memory.write_int(dest, result, dest_size)?;
 866             }
 867
 868             _ => return Err(EvalError::Unimplemented(format!("can't call C ABI function: {}", link_name))),
 869         }
 870
 871         // Since we pushed no stack frame, the main loop will act
 872         // as if the call just completed and it's returning to the
 873         // current frame.
 874         Ok(TerminatorTarget::Call)
 875     }
 876
 877     fn assign_fields<I: IntoIterator<Item = u64>>(
 878         &mut self,
 879         dest: Pointer,
 880         offsets: I,
 881         operands: &[mir::Operand<'tcx>],
 882     ) -> EvalResult<()> {
 883         for (offset, operand) in offsets.into_iter().zip(operands) {
 884             let src = self.eval_operand(operand)?;
 885             let src_ty = self.operand_ty(operand);
 886             let field_dest = dest.offset(offset as isize);
 887             self.move_(src, field_dest, src_ty)?;
 888         }
 889         Ok(())
 890     }
 891
 892     fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
 893         -> EvalResult<()>
 894     {
 895         let dest = self.eval_lvalue(lvalue)?.to_ptr();
 896         let dest_ty = self.lvalue_ty(lvalue);
 897         let dest_layout = self.type_layout(dest_ty);
 898
 899         use rustc::mir::repr::Rvalue::*;
 900         match *rvalue {
 901             Use(ref operand) => {
 902                 let src = self.eval_operand(operand)?;
 903                 self.move_(src, dest, dest_ty)?;
 904             }
 905
 906             BinaryOp(bin_op, ref left, ref right) => {
 907                 let left_ptr = self.eval_operand(left)?;
 908                 let left_ty = self.operand_ty(left);
 909                 let left_val = self.read_primval(left_ptr, left_ty)?;
 910
 911                 let right_ptr = self.eval_operand(right)?;
 912                 let right_ty = self.operand_ty(right);
 913                 let right_val = self.read_primval(right_ptr, right_ty)?;
 914
 915                 let val = primval::binary_op(bin_op, left_val, right_val)?;
 916                 self.memory.write_primval(dest, val)?;
 917             }
 918
 919             UnaryOp(un_op, ref operand) => {
 920                 let ptr = self.eval_operand(operand)?;
 921                 let ty = self.operand_ty(operand);
 922                 let val = self.read_primval(ptr, ty)?;
 923                 self.memory.write_primval(dest, primval::unary_op(un_op, val)?)?;
 924             }
 925
 926             Aggregate(ref kind, ref operands) => {
 927                 use rustc::ty::layout::Layout::*;
 928                 match *dest_layout {
 929                     Univariant { ref variant, .. } => {
 930                         let offsets = iter::once(0)
 931                             .chain(variant.offset_after_field.iter().map(|s| s.bytes()));
 932                         self.assign_fields(dest, offsets, operands)?;
 933                     }
 934
 935                     Array { .. } => {
 936                         let elem_size = match dest_ty.sty {
 937                             ty::TyArray(elem_ty, _) => self.type_size(elem_ty) as u64,
 938                             _ => panic!("tried to assign {:?} to non-array type {:?}",
 939                                         kind, dest_ty),
 940                         };
 941                         let offsets = (0..).map(|i| i * elem_size);
 942                         self.assign_fields(dest, offsets, operands)?;
 943                     }
 944
 945                     General { discr, ref variants, .. } => {
 946                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 947                             let discr_val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 948                             let discr_size = discr.size().bytes() as usize;
 949                             self.memory.write_uint(dest, discr_val, discr_size)?;
 950
 951                             let offsets = variants[variant].offset_after_field.iter()
 952                                 .map(|s| s.bytes());
 953                             self.assign_fields(dest, offsets, operands)?;
 954                         } else {
 955                             panic!("tried to assign {:?} to Layout::General", kind);
 956                         }
 957                     }
 958
 959                     RawNullablePointer { nndiscr, .. } => {
 960                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 961                             if nndiscr == variant as u64 {
 962                                 assert_eq!(operands.len(), 1);
 963                                 let operand = &operands[0];
 964                                 let src = self.eval_operand(operand)?;
 965                                 let src_ty = self.operand_ty(operand);
 966                                 self.move_(src, dest, src_ty)?;
 967                             } else {
 968                                 assert_eq!(operands.len(), 0);
 969                                 self.memory.write_isize(dest, 0)?;
 970                             }
 971                         } else {
 972                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 973                         }
 974                     }
 975
 976                     StructWrappedNullablePointer { nndiscr, ref nonnull, ref discrfield } => {
 977                         if let mir::AggregateKind::Adt(_, variant, _) = *kind {
 978                             if nndiscr == variant as u64 {
 979                                 let offsets = iter::once(0)
 980                                     .chain(nonnull.offset_after_field.iter().map(|s| s.bytes()));
 981                                 try!(self.assign_fields(dest, offsets, operands));
 982                             } else {
 983                                 assert_eq!(operands.len(), 0);
 984                                 let offset = self.nonnull_offset(dest_ty, nndiscr, discrfield)?;
 985                                 let dest = dest.offset(offset.bytes() as isize);
 986                                 try!(self.memory.write_isize(dest, 0));
 987                             }
 988                         } else {
 989                             panic!("tried to assign {:?} to Layout::RawNullablePointer", kind);
 990                         }
 991                     }
 992
 993                     CEnum { discr, signed, .. } => {
 994                         assert_eq!(operands.len(), 0);
 995                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
 996                             let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
 997                             let size = discr.size().bytes() as usize;
 998
 999                             if signed {
1000                                 self.memory.write_int(dest, val as i64, size)?;
1001                             } else {
1002                                 self.memory.write_uint(dest, val, size)?;
1003                             }
1004                         } else {
1005                             panic!("tried to assign {:?} to Layout::CEnum", kind);
1006                         }
1007                     }
1008
1009                     _ => return Err(EvalError::Unimplemented(format!("can't handle destination layout {:?} when assigning {:?}", dest_layout, kind))),
1010                 }
1011             }
1012
1013             Repeat(ref operand, _) => {
1014                 let (elem_size, length) = match dest_ty.sty {
1015                     ty::TyArray(elem_ty, n) => (self.type_size(elem_ty), n),
1016                     _ => panic!("tried to assign array-repeat to non-array type {:?}", dest_ty),
1017                 };
1018
1019                 let src = self.eval_operand(operand)?;
1020                 for i in 0..length {
1021                     let elem_dest = dest.offset((i * elem_size) as isize);
1022                     self.memory.copy(src, elem_dest, elem_size)?;
1023                 }
1024             }
1025
1026             Len(ref lvalue) => {
1027                 let src = self.eval_lvalue(lvalue)?;
1028                 let ty = self.lvalue_ty(lvalue);
1029                 let len = match ty.sty {
1030                     ty::TyArray(_, n) => n as u64,
1031                     ty::TySlice(_) => if let LvalueExtra::Length(n) = src.extra {
1032                         n
1033                     } else {
1034                         panic!("Rvalue::Len of a slice given non-slice pointer: {:?}", src);
1035                     },
1036                     _ => panic!("Rvalue::Len expected array or slice, got {:?}", ty),
1037                 };
1038                 self.memory.write_usize(dest, len)?;
1039             }
1040
1041             Ref(_, _, ref lvalue) => {
1042                 let lv = self.eval_lvalue(lvalue)?;
1043                 self.memory.write_ptr(dest, lv.ptr)?;
1044                 match lv.extra {
1045                     LvalueExtra::None => {},
1046                     LvalueExtra::Length(len) => {
1047                         let len_ptr = dest.offset(self.memory.pointer_size as isize);
1048                         self.memory.write_usize(len_ptr, len)?;
1049                     }
1050                     LvalueExtra::DowncastVariant(..) =>
1051                         panic!("attempted to take a reference to an enum downcast lvalue"),
1052                 }
1053             }
1054
1055             Box(ty) => {
1056                 let size = self.type_size(ty);
1057                 let ptr = self.memory.allocate(size);
1058                 self.memory.write_ptr(dest, ptr)?;
1059             }
1060
1061             Cast(kind, ref operand, dest_ty) => {
1062                 let src = self.eval_operand(operand)?;
1063                 let src_ty = self.operand_ty(operand);
1064
1065                 use rustc::mir::repr::CastKind::*;
1066                 match kind {
1067                     Unsize => {
1068                         self.move_(src, dest, src_ty)?;
1069                         let src_pointee_ty = pointee_type(src_ty).unwrap();
1070                         let dest_pointee_ty = pointee_type(dest_ty).unwrap();
1071
1072                         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
1073                             (&ty::TyArray(_, length), &ty::TySlice(_)) => {
1074                                 let len_ptr = dest.offset(self.memory.pointer_size as isize);
1075                                 self.memory.write_usize(len_ptr, length as u64)?;
1076                             }
1077
1078                             _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1079                         }
1080                     }
1081
1082                     Misc => {
1083                         // FIXME(solson): Wrong for almost everything.
1084                         let size = dest_layout.size(&self.tcx.data_layout).bytes() as usize;
1085                         self.memory.copy(src, dest, size)?;
1086                     }
1087
1088                     _ => return Err(EvalError::Unimplemented(format!("can't handle cast: {:?}", rvalue))),
1089                 }
1090             }
1091
1092             Slice { .. } => unimplemented!(),
1093             InlineAsm { .. } => unimplemented!(),
1094         }
1095
1096         Ok(())
1097     }
1098
1099     fn nonnull_offset(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<Size> {
1100         // Skip the constant 0 at the start meant for LLVM GEP.
1101         let mut path = discrfield.iter().skip(1).map(|&i| i as usize);
1102
1103         // Handle the field index for the outer non-null variant.
1104         let inner_ty = match ty.sty {
1105             ty::TyEnum(adt_def, substs) => {
1106                 let variant = &adt_def.variants[nndiscr as usize];
1107                 let index = path.next().unwrap();
1108                 let field = &variant.fields[index];
1109                 field.ty(self.tcx, substs)
1110             }
1111             _ => panic!(
1112                 "non-enum for StructWrappedNullablePointer: {}",
1113                 ty,
1114             ),
1115         };
1116
1117         self.field_path_offset(inner_ty, path)
1118     }
1119
1120     fn field_path_offset<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<Size> {
1121         let mut offset = Size::from_bytes(0);
1122
1123         // Skip the initial 0 intended for LLVM GEP.
1124         for field_index in path {
1125             let field_offset = self.get_field_offset(ty, field_index)?;
1126             ty = self.get_field_ty(ty, field_index)?;
1127             offset = offset.checked_add(field_offset, &self.tcx.data_layout).unwrap();
1128         }
1129
1130         Ok(offset)
1131     }
1132
1133     fn get_field_ty(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Ty<'tcx>> {
1134         match ty.sty {
1135             ty::TyStruct(adt_def, substs) => {
1136                 Ok(adt_def.struct_variant().fields[field_index].ty(self.tcx, substs))
1137             }
1138
1139             ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1140             ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1141             ty::TyBox(ty) => {
1142                 assert_eq!(field_index, 0);
1143                 Ok(ty)
1144             }
1145             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}", ty))),
1146         }
1147     }
1148
1149     fn get_field_offset(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<Size> {
1150         let layout = self.type_layout(ty);
1151
1152         use rustc::ty::layout::Layout::*;
1153         match *layout {
1154             Univariant { .. } => {
1155                 assert_eq!(field_index, 0);
1156                 Ok(Size::from_bytes(0))
1157             }
1158             FatPointer { .. } => {
1159                 let bytes = layout::FAT_PTR_ADDR * self.memory.pointer_size;
1160                 Ok(Size::from_bytes(bytes as u64))
1161             }
1162             _ => Err(EvalError::Unimplemented(format!("can't handle type: {:?}, with layout: {:?}", ty, layout))),
1163         }
1164     }
1165
1166     fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<Pointer> {
1167         use rustc::mir::repr::Operand::*;
1168         match *op {
1169             Consume(ref lvalue) => Ok(self.eval_lvalue(lvalue)?.to_ptr()),
1170             Constant(mir::Constant { ref literal, .. }) => {
1171                 use rustc::mir::repr::Literal::*;
1172                 match *literal {
1173                     Value { ref value } => Ok(self.const_to_ptr(value)?),
1174                     Item { def_id, substs } => {
1175                         let item_ty = self.tcx.lookup_item_type(def_id).subst(self.tcx, substs);
1176                         if item_ty.ty.is_fn() {
1177                             Err(EvalError::Unimplemented("unimplemented: mentions of function items".to_string()))
1178                         } else {
1179                             let cid = ConstantId::Static{ def_id: def_id, substs: substs };
1180                             Ok(*self.statics.get(&cid).expect("static should have been cached (rvalue)"))
1181                         }
1182                     },
1183                     Promoted { index } => {
1184                         let cid = ConstantId::Promoted {
1185                             def_id: self.frame().def_id,
1186                             substs: self.substs(),
1187                             index: index,
1188                         };
1189                         Ok(*self.statics.get(&cid).expect("a promoted constant hasn't been precomputed"))
1190                     },
1191                 }
1192             }
1193         }
1194     }
1195
1196     fn eval_lvalue(&mut self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<Lvalue> {
1197         use rustc::mir::repr::Lvalue::*;
1198         let ptr = match *lvalue {
1199             ReturnPointer => self.frame().return_ptr
1200                 .expect("ReturnPointer used in a function with no return value"),
1201             Arg(i) => self.frame().locals[i as usize],
1202             Var(i) => self.frame().locals[self.frame().var_offset + i as usize],
1203             Temp(i) => self.frame().locals[self.frame().temp_offset + i as usize],
1204
1205             Static(def_id) => {
1206                 let substs = self.tcx.mk_substs(subst::Substs::empty());
1207                 let cid = ConstantId::Static{ def_id: def_id, substs: substs };
1208                 *self.gecx.statics.get(&cid).expect("static should have been cached (lvalue)")
1209             },
1210
1211             Projection(ref proj) => {
1212                 let base = self.eval_lvalue(&proj.base)?;
1213                 let base_ty = self.lvalue_ty(&proj.base);
1214                 let base_layout = self.type_layout(base_ty);
1215
1216                 use rustc::mir::repr::ProjectionElem::*;
1217                 match proj.elem {
1218                     Field(field, _) => {
1219                         use rustc::ty::layout::Layout::*;
1220                         let variant = match *base_layout {
1221                             Univariant { ref variant, .. } => variant,
1222                             General { ref variants, .. } => {
1223                                 if let LvalueExtra::DowncastVariant(variant_idx) = base.extra {
1224                                     &variants[variant_idx]
1225                                 } else {
1226                                     panic!("field access on enum had no variant index");
1227                                 }
1228                             }
1229                             RawNullablePointer { .. } => {
1230                                 assert_eq!(field.index(), 0);
1231                                 return Ok(base);
1232                             }
1233                             StructWrappedNullablePointer { ref nonnull, .. } => nonnull,
1234                             _ => panic!("field access on non-product type: {:?}", base_layout),
1235                         };
1236
1237                         let offset = variant.field_offset(field.index()).bytes();
1238                         base.ptr.offset(offset as isize)
1239                     },
1240
1241                     Downcast(_, variant) => {
1242                         use rustc::ty::layout::Layout::*;
1243                         match *base_layout {
1244                             General { discr, .. } => {
1245                                 return Ok(Lvalue {
1246                                     ptr: base.ptr.offset(discr.size().bytes() as isize),
1247                                     extra: LvalueExtra::DowncastVariant(variant),
1248                                 });
1249                             }
1250                             RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
1251                                 return Ok(base);
1252                             }
1253                             _ => panic!("variant downcast on non-aggregate: {:?}", base_layout),
1254                         }
1255                     },
1256
1257                     Deref => {
1258                         let pointee_ty = pointee_type(base_ty).expect("Deref of non-pointer");
1259                         let ptr = self.memory.read_ptr(base.ptr)?;
1260                         let extra = match pointee_ty.sty {
1261                             ty::TySlice(_) | ty::TyStr => {
1262                                 let len_ptr = base.ptr.offset(self.memory.pointer_size as isize);
1263                                 let len = self.memory.read_usize(len_ptr)?;
1264                                 LvalueExtra::Length(len)
1265                             }
1266                             ty::TyTrait(_) => unimplemented!(),
1267                             _ => LvalueExtra::None,
1268                         };
1269                         return Ok(Lvalue { ptr: ptr, extra: extra });
1270                     }
1271
1272                     Index(ref operand) => {
1273                         let elem_size = match base_ty.sty {
1274                             ty::TyArray(elem_ty, _) |
1275                             ty::TySlice(elem_ty) => self.type_size(elem_ty),
1276                             _ => panic!("indexing expected an array or slice, got {:?}", base_ty),
1277                         };
1278                         let n_ptr = self.eval_operand(operand)?;
1279                         let n = self.memory.read_usize(n_ptr)?;
1280                         base.ptr.offset(n as isize * elem_size as isize)
1281                     }
1282
1283                     ConstantIndex { .. } => unimplemented!(),
1284                 }
1285             }
1286         };
1287
1288         Ok(Lvalue { ptr: ptr, extra: LvalueExtra::None })
1289     }
1290
1291     // TODO(solson): Try making const_to_primval instead.
1292     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<Pointer> {
1293         use rustc::middle::const_val::ConstVal::*;
1294         match *const_val {
1295             Float(_f) => unimplemented!(),
1296             Integral(int) => {
1297                 // TODO(solson): Check int constant type.
1298                 let ptr = self.memory.allocate(8);
1299                 self.memory.write_uint(ptr, int.to_u64_unchecked(), 8)?;
1300                 Ok(ptr)
1301             }
1302             Str(ref s) => {
1303                 let psize = self.memory.pointer_size;
1304                 let static_ptr = self.memory.allocate(s.len());
1305                 let ptr = self.memory.allocate(psize * 2);
1306                 self.memory.write_bytes(static_ptr, s.as_bytes())?;
1307                 self.memory.write_ptr(ptr, static_ptr)?;
1308                 self.memory.write_usize(ptr.offset(psize as isize), s.len() as u64)?;
1309                 Ok(ptr)
1310             }
1311             ByteStr(ref bs) => {
1312                 let psize = self.memory.pointer_size;
1313                 let static_ptr = self.memory.allocate(bs.len());
1314                 let ptr = self.memory.allocate(psize);
1315                 self.memory.write_bytes(static_ptr, bs)?;
1316                 self.memory.write_ptr(ptr, static_ptr)?;
1317                 Ok(ptr)
1318             }
1319             Bool(b) => {
1320                 let ptr = self.memory.allocate(1);
1321                 self.memory.write_bool(ptr, b)?;
1322                 Ok(ptr)
1323             }
1324             Char(_c)          => unimplemented!(),
1325             Struct(_node_id)  => unimplemented!(),
1326             Tuple(_node_id)   => unimplemented!(),
1327             Function(_def_id) => unimplemented!(),
1328             Array(_, _)       => unimplemented!(),
1329             Repeat(_, _)      => unimplemented!(),
1330             Dummy             => unimplemented!(),
1331         }
1332     }
1333
1334     fn lvalue_ty(&self, lvalue: &mir::Lvalue<'tcx>) -> Ty<'tcx> {
1335         self.monomorphize(self.mir().lvalue_ty(self.tcx, lvalue).to_ty(self.tcx))
1336     }
1337
1338     fn operand_ty(&self, operand: &mir::Operand<'tcx>) -> Ty<'tcx> {
1339         self.monomorphize(self.mir().operand_ty(self.tcx, operand))
1340     }
1341
1342     fn monomorphize(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
1343         let substituted = ty.subst(self.tcx, self.substs());
1344         self.tcx.normalize_associated_type(&substituted)
1345     }
1346
1347     fn type_needs_drop(&self, ty: Ty<'tcx>) -> bool {
1348         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
1349     }
1350
1351     fn move_(&mut self, src: Pointer, dest: Pointer, ty: Ty<'tcx>) -> EvalResult<()> {
1352         let size = self.type_size(ty);
1353         self.memory.copy(src, dest, size)?;
1354         if self.type_needs_drop(ty) {
1355             self.memory.drop_fill(src, size)?;
1356         }
1357         Ok(())
1358     }
1359
1360     fn type_is_sized(&self, ty: Ty<'tcx>) -> bool {
1361         ty.is_sized(self.tcx, &self.tcx.empty_parameter_environment(), DUMMY_SP)
1362     }
1363
1364     fn type_size(&self, ty: Ty<'tcx>) -> usize {
1365         self.type_layout(ty).size(&self.tcx.data_layout).bytes() as usize
1366     }
1367
1368     fn type_layout(&self, ty: Ty<'tcx>) -> &'tcx Layout {
1369         // TODO(solson): Is this inefficient? Needs investigation.
1370         let ty = self.monomorphize(ty);
1371
1372         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
1373             // TODO(solson): Report this error properly.
1374             ty.layout(&infcx).unwrap()
1375         })
1376     }
1377
1378     pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<PrimVal> {
1379         use syntax::ast::{IntTy, UintTy};
1380         let val = match (self.memory.pointer_size, &ty.sty) {
1381             (_, &ty::TyBool)              => PrimVal::Bool(self.memory.read_bool(ptr)?),
1382             (_, &ty::TyInt(IntTy::I8))    => PrimVal::I8(self.memory.read_int(ptr, 1)? as i8),
1383             (2, &ty::TyInt(IntTy::Is)) |
1384             (_, &ty::TyInt(IntTy::I16))   => PrimVal::I16(self.memory.read_int(ptr, 2)? as i16),
1385             (4, &ty::TyInt(IntTy::Is)) |
1386             (_, &ty::TyInt(IntTy::I32))   => PrimVal::I32(self.memory.read_int(ptr, 4)? as i32),
1387             (8, &ty::TyInt(IntTy::Is)) |
1388             (_, &ty::TyInt(IntTy::I64))   => PrimVal::I64(self.memory.read_int(ptr, 8)? as i64),
1389             (_, &ty::TyUint(UintTy::U8))  => PrimVal::U8(self.memory.read_uint(ptr, 1)? as u8),
1390             (2, &ty::TyUint(UintTy::Us)) |
1391             (_, &ty::TyUint(UintTy::U16)) => PrimVal::U16(self.memory.read_uint(ptr, 2)? as u16),
1392             (4, &ty::TyUint(UintTy::Us)) |
1393             (_, &ty::TyUint(UintTy::U32)) => PrimVal::U32(self.memory.read_uint(ptr, 4)? as u32),
1394             (8, &ty::TyUint(UintTy::Us)) |
1395             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
1396
1397             (_, &ty::TyRef(_, ty::TypeAndMut { ty, .. })) |
1398             (_, &ty::TyRawPtr(ty::TypeAndMut { ty, .. })) => {
1399                 if self.type_is_sized(ty) {
1400                     match self.memory.read_ptr(ptr) {
1401                         Ok(p) => PrimVal::AbstractPtr(p),
1402                         Err(EvalError::ReadBytesAsPointer) => {
1403                             PrimVal::IntegerPtr(self.memory.read_usize(ptr)?)
1404                         }
1405                         Err(e) => return Err(e),
1406                     }
1407                 } else {
1408                     return Err(EvalError::Unimplemented(format!("unimplemented: primitive read of fat pointer type: {:?}", ty)));
1409                 }
1410             }
1411
1412             _ => panic!("primitive read of non-primitive type: {:?}", ty),
1413         };
1414         Ok(val)
1415     }
1416
1417     fn frame(&self) -> &Frame<'mir, 'tcx> {
1418         self.stack.last().expect("no call frames exist")
1419     }
1420
1421     fn basic_block(&self) -> &mir::BasicBlockData<'tcx> {
1422         let frame = self.frame();
1423         frame.mir.basic_block_data(frame.next_block)
1424     }
1425
1426     fn frame_mut(&mut self) -> &mut Frame<'mir, 'tcx> {
1427         self.stack.last_mut().expect("no call frames exist")
1428     }
1429
1430     fn mir(&self) -> CachedMir<'mir, 'tcx> {
1431         self.frame().mir.clone()
1432     }
1433
1434     fn substs(&self) -> &'tcx Substs<'tcx> {
1435         self.frame().substs
1436     }
1437
1438     fn load_mir(&self, def_id: DefId) -> CachedMir<'mir, 'tcx> {
1439         match self.tcx.map.as_local_node_id(def_id) {
1440             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
1441             None => {
1442                 let mut mir_cache = self.mir_cache.borrow_mut();
1443                 if let Some(mir) = mir_cache.get(&def_id) {
1444                     return CachedMir::Owned(mir.clone());
1445                 }
1446
1447                 let cs = &self.tcx.sess.cstore;
1448                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
1449                     panic!("no mir for {:?}", def_id);
1450                 });
1451                 let cached = Rc::new(mir);
1452                 mir_cache.insert(def_id, cached.clone());
1453                 CachedMir::Owned(cached)
1454             }
1455         }
1456     }
1457 }
1458
1459 fn pointee_type(ptr_ty: ty::Ty) -> Option<ty::Ty> {
1460     match ptr_ty.sty {
1461         ty::TyRef(_, ty::TypeAndMut { ty, .. }) |
1462         ty::TyRawPtr(ty::TypeAndMut { ty, .. }) |
1463         ty::TyBox(ty) => {
1464             Some(ty)
1465         }
1466         _ => None,
1467     }
1468 }
1469
1470 impl Lvalue {
1471     fn to_ptr(self) -> Pointer {
1472         assert_eq!(self.extra, LvalueExtra::None);
1473         self.ptr
1474     }
1475 }
1476
1477 impl<'mir, 'tcx: 'mir> Deref for CachedMir<'mir, 'tcx> {
1478     type Target = mir::Mir<'tcx>;
1479     fn deref(&self) -> &mir::Mir<'tcx> {
1480         match *self {
1481             CachedMir::Ref(r) => r,
1482             CachedMir::Owned(ref rc) => rc,
1483         }
1484     }
1485 }
1486
1487 #[derive(Debug)]
1488 pub struct ImplMethod<'tcx> {
1489     pub method: Rc<ty::Method<'tcx>>,
1490     pub substs: &'tcx Substs<'tcx>,
1491     pub is_provided: bool,
1492 }
1493
1494 /// Locates the applicable definition of a method, given its name.
1495 pub fn get_impl_method<'a, 'tcx>(
1496     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1497     impl_def_id: DefId,
1498     substs: &'tcx Substs<'tcx>,
1499     name: ast::Name,
1500 ) -> ImplMethod<'tcx> {
1501     assert!(!substs.types.needs_infer());
1502
1503     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
1504     let trait_def = tcx.lookup_trait_def(trait_def_id);
1505
1506     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
1507         Some(node_item) => {
1508             let substs = tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
1509                 let substs = traits::translate_substs(&infcx, impl_def_id,
1510                                                       substs, node_item.node);
1511                 tcx.lift(&substs).unwrap_or_else(|| {
1512                     bug!("trans::meth::get_impl_method: translate_substs \
1513                           returned {:?} which contains inference types/regions",
1514                          substs);
1515                 })
1516             });
1517             ImplMethod {
1518                 method: node_item.item,
1519                 substs: substs,
1520                 is_provided: node_item.node.is_from_trait(),
1521             }
1522         }
1523         None => {
1524             bug!("method {:?} not found in {:?}", name, impl_def_id)
1525         }
1526     }
1527 }
1528
1529 pub fn interpret_start_points<'a, 'tcx>(
1530     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1531     mir_map: &MirMap<'tcx>,
1532 ) {
1533     let initial_indentation = ::log_settings::settings().indentation;
1534     for (&id, mir) in &mir_map.map {
1535         for attr in tcx.map.attrs(id) {
1536             use syntax::attr::AttrMetaMethods;
1537             if attr.check_name("miri_run") {
1538                 let item = tcx.map.expect_item(id);
1539
1540                 ::log_settings::settings().indentation = initial_indentation;
1541
1542                 debug!("Interpreting: {}", item.name);
1543
1544                 let mut gecx = GlobalEvalContext::new(tcx, mir_map);
1545                 match gecx.call(mir, tcx.map.local_def_id(id)) {
1546                     Ok(Some(return_ptr)) => if log_enabled!(::log::LogLevel::Debug) {
1547                         gecx.memory.dump(return_ptr.alloc_id);
1548                     },
1549                     Ok(None) => warn!("diverging function returned"),
1550                     Err(_e) => {
1551                         // TODO(solson): Detect whether the error was already reported or not.
1552                         // tcx.sess.err(&e.to_string());
1553                     }
1554                 }
1555             }
1556         }
1557     }
1558 }
1559
1560 // TODO(solson): Upstream these methods into rustc::ty::layout.
1561
1562 trait IntegerExt {
1563     fn size(self) -> Size;
1564 }
1565
1566 impl IntegerExt for layout::Integer {
1567     fn size(self) -> Size {
1568         use rustc::ty::layout::Integer::*;
1569         match self {
1570             I1 | I8 => Size::from_bits(8),
1571             I16 => Size::from_bits(16),
1572             I32 => Size::from_bits(32),
1573             I64 => Size::from_bits(64),
1574         }
1575     }
1576 }
1577
1578 trait StructExt {
1579     fn field_offset(&self, index: usize) -> Size;
1580 }
1581
1582 impl StructExt for layout::Struct {
1583     fn field_offset(&self, index: usize) -> Size {
1584         if index == 0 {
1585             Size::from_bytes(0)
1586         } else {
1587             self.offset_after_field[index - 1]
1588         }
1589     }
1590 }