src/librustc_mir/interpret/place.rs

   1 use rustc::mir;
   2 use rustc::ty::{self, Ty};
   3 use rustc::ty::layout::{self, Align, LayoutOf, TyLayout};
   4 use rustc_data_structures::indexed_vec::Idx;
   5
   6 use rustc::mir::interpret::{GlobalId, Value, PrimVal, EvalResult, Pointer, MemoryPointer};
   7 use super::{EvalContext, Machine, ValTy};
   8 use interpret::memory::HasMemory;
   9
  10 #[derive(Copy, Clone, Debug)]
  11 pub enum Place {
  12     /// A place referring to a value allocated in the `Memory` system.
  13     Ptr {
  14         /// A place may have an invalid (integral or undef) pointer,
  15         /// since it might be turned back into a reference
  16         /// before ever being dereferenced.
  17         ptr: Pointer,
  18         align: Align,
  19         extra: PlaceExtra,
  20     },
  21
  22     /// A place referring to a value on the stack. Represented by a stack frame index paired with
  23     /// a Mir local index.
  24     Local { frame: usize, local: mir::Local },
  25 }
  26
  27 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  28 pub enum PlaceExtra {
  29     None,
  30     Length(u64),
  31     Vtable(MemoryPointer),
  32     DowncastVariant(usize),
  33 }
  34
  35 impl<'tcx> Place {
  36     /// Produces a Place that will error if attempted to be read from
  37     pub fn undef() -> Self {
  38         Self::from_primval_ptr(PrimVal::Undef.into(), Align::from_bytes(1, 1).unwrap())
  39     }
  40
  41     pub fn from_primval_ptr(ptr: Pointer, align: Align) -> Self {
  42         Place::Ptr {
  43             ptr,
  44             align,
  45             extra: PlaceExtra::None,
  46         }
  47     }
  48
  49     pub fn from_ptr(ptr: MemoryPointer, align: Align) -> Self {
  50         Self::from_primval_ptr(ptr.into(), align)
  51     }
  52
  53     pub fn to_ptr_align_extra(self) -> (Pointer, Align, PlaceExtra) {
  54         match self {
  55             Place::Ptr { ptr, align, extra } => (ptr, align, extra),
  56             _ => bug!("to_ptr_and_extra: expected Place::Ptr, got {:?}", self),
  57
  58         }
  59     }
  60
  61     pub fn to_ptr_align(self) -> (Pointer, Align) {
  62         let (ptr, align, _extra) = self.to_ptr_align_extra();
  63         (ptr, align)
  64     }
  65
  66     pub fn to_ptr(self) -> EvalResult<'tcx, MemoryPointer> {
  67         // At this point, we forget about the alignment information -- the place has been turned into a reference,
  68         // and no matter where it came from, it now must be aligned.
  69         self.to_ptr_align().0.to_ptr()
  70     }
  71
  72     pub(super) fn elem_ty_and_len(self, ty: Ty<'tcx>) -> (Ty<'tcx>, u64) {
  73         match ty.sty {
  74             ty::TyArray(elem, n) => (elem, n.val.unwrap_u64() as u64),
  75
  76             ty::TySlice(elem) => {
  77                 match self {
  78                     Place::Ptr { extra: PlaceExtra::Length(len), .. } => (elem, len),
  79                     _ => {
  80                         bug!(
  81                             "elem_ty_and_len of a TySlice given non-slice place: {:?}",
  82                             self
  83                         )
  84                     }
  85                 }
  86             }
  87
  88             _ => bug!("elem_ty_and_len expected array or slice, got {:?}", ty),
  89         }
  90     }
  91 }
  92
  93 impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
  94     /// Reads a value from the place without going through the intermediate step of obtaining
  95     /// a `miri::Place`
  96     pub fn try_read_place(
  97         &mut self,
  98         place: &mir::Place<'tcx>,
  99     ) -> EvalResult<'tcx, Option<Value>> {
 100         use rustc::mir::Place::*;
 101         match *place {
 102             // Might allow this in the future, right now there's no way to do this from Rust code anyway
 103             Local(mir::RETURN_PLACE) => err!(ReadFromReturnPointer),
 104             // Directly reading a local will always succeed
 105             Local(local) => self.frame().get_local(local).map(Some),
 106             // No fast path for statics. Reading from statics is rare and would require another
 107             // Machine function to handle differently in miri.
 108             Static(_) => Ok(None),
 109             Projection(ref proj) => self.try_read_place_projection(proj),
 110         }
 111     }
 112
 113     pub fn read_field(
 114         &self,
 115         base: Value,
 116         variant: Option<usize>,
 117         field: mir::Field,
 118         base_ty: Ty<'tcx>,
 119     ) -> EvalResult<'tcx, Option<(Value, Ty<'tcx>)>> {
 120         let mut base_layout = self.layout_of(base_ty)?;
 121         if let Some(variant_index) = variant {
 122             base_layout = base_layout.for_variant(self, variant_index);
 123         }
 124         let field_index = field.index();
 125         let field = base_layout.field(self, field_index)?;
 126         if field.size.bytes() == 0 {
 127             return Ok(Some((Value::ByVal(PrimVal::Undef), field.ty)))
 128         }
 129         let offset = base_layout.fields.offset(field_index);
 130         match base {
 131             // the field covers the entire type
 132             Value::ByValPair(..) |
 133             Value::ByVal(_) if offset.bytes() == 0 && field.size == base_layout.size => Ok(Some((base, field.ty))),
 134             // split fat pointers, 2 element tuples, ...
 135             Value::ByValPair(a, b) if base_layout.fields.count() == 2 => {
 136                 let val = [a, b][field_index];
 137                 Ok(Some((Value::ByVal(val), field.ty)))
 138             },
 139             _ => Ok(None),
 140         }
 141     }
 142
 143     fn try_read_place_projection(
 144         &mut self,
 145         proj: &mir::PlaceProjection<'tcx>,
 146     ) -> EvalResult<'tcx, Option<Value>> {
 147         use rustc::mir::ProjectionElem::*;
 148         let base = match self.try_read_place(&proj.base)? {
 149             Some(base) => base,
 150             None => return Ok(None),
 151         };
 152         let base_ty = self.place_ty(&proj.base);
 153         match proj.elem {
 154             Field(field, _) => Ok(self.read_field(base, None, field, base_ty)?.map(|(f, _)| f)),
 155             // The NullablePointer cases should work fine, need to take care for normal enums
 156             Downcast(..) |
 157             Subslice { .. } |
 158             // reading index 0 or index 1 from a ByVal or ByVal pair could be optimized
 159             ConstantIndex { .. } | Index(_) |
 160             // No way to optimize this projection any better than the normal place path
 161             Deref => Ok(None),
 162         }
 163     }
 164
 165     /// Returns a value and (in case of a ByRef) if we are supposed to use aligned accesses.
 166     pub(super) fn eval_and_read_place(
 167         &mut self,
 168         place: &mir::Place<'tcx>,
 169     ) -> EvalResult<'tcx, Value> {
 170         // Shortcut for things like accessing a fat pointer's field,
 171         // which would otherwise (in the `eval_place` path) require moving a `ByValPair` to memory
 172         // and returning an `Place::Ptr` to it
 173         if let Some(val) = self.try_read_place(place)? {
 174             return Ok(val);
 175         }
 176         let place = self.eval_place(place)?;
 177         self.read_place(place)
 178     }
 179
 180     pub fn read_place(&self, place: Place) -> EvalResult<'tcx, Value> {
 181         match place {
 182             Place::Ptr { ptr, align, extra } => {
 183                 assert_eq!(extra, PlaceExtra::None);
 184                 Ok(Value::ByRef(ptr, align))
 185             }
 186             Place::Local { frame, local } => self.stack[frame].get_local(local),
 187         }
 188     }
 189
 190     pub fn eval_place(&mut self, mir_place: &mir::Place<'tcx>) -> EvalResult<'tcx, Place> {
 191         use rustc::mir::Place::*;
 192         let place = match *mir_place {
 193             Local(mir::RETURN_PLACE) => self.frame().return_place,
 194             Local(local) => Place::Local {
 195                 frame: self.cur_frame(),
 196                 local,
 197             },
 198
 199             Static(ref static_) => {
 200                 let layout = self.layout_of(self.place_ty(mir_place))?;
 201                 let instance = ty::Instance::mono(*self.tcx, static_.def_id);
 202                 let cid = GlobalId {
 203                     instance,
 204                     promoted: None
 205                 };
 206                 let alloc = Machine::init_static(self, cid)?;
 207                 Place::Ptr {
 208                     ptr: MemoryPointer::new(alloc, 0).into(),
 209                     align: layout.align,
 210                     extra: PlaceExtra::None,
 211                 }
 212             }
 213
 214             Projection(ref proj) => {
 215                 let ty = self.place_ty(&proj.base);
 216                 let place = self.eval_place(&proj.base)?;
 217                 return self.eval_place_projection(place, ty, &proj.elem);
 218             }
 219         };
 220
 221         if log_enabled!(::log::Level::Trace) {
 222             self.dump_local(place);
 223         }
 224
 225         Ok(place)
 226     }
 227
 228     pub fn place_field(
 229         &mut self,
 230         base: Place,
 231         field: mir::Field,
 232         mut base_layout: TyLayout<'tcx>,
 233     ) -> EvalResult<'tcx, (Place, TyLayout<'tcx>)> {
 234         match base {
 235             Place::Ptr { extra: PlaceExtra::DowncastVariant(variant_index), .. } => {
 236                 base_layout = base_layout.for_variant(&self, variant_index);
 237             }
 238             _ => {}
 239         }
 240         let field_index = field.index();
 241         let field = base_layout.field(&self, field_index)?;
 242         let offset = base_layout.fields.offset(field_index);
 243
 244         // Do not allocate in trivial cases
 245         let (base_ptr, base_align, base_extra) = match base {
 246             Place::Ptr { ptr, align, extra } => (ptr, align, extra),
 247             Place::Local { frame, local } => {
 248                 match (&self.stack[frame].get_local(local)?, &base_layout.abi) {
 249                     // in case the field covers the entire type, just return the value
 250                     (&Value::ByVal(_), &layout::Abi::Scalar(_)) |
 251                     (&Value::ByValPair(..), &layout::Abi::ScalarPair(..))
 252                         if offset.bytes() == 0 && field.size == base_layout.size =>
 253                     {
 254                         return Ok((base, field));
 255                     }
 256                     _ => self.force_allocation(base)?.to_ptr_align_extra(),
 257                 }
 258             }
 259         };
 260
 261         let offset = match base_extra {
 262             PlaceExtra::Vtable(tab) => {
 263                 let (_, align) = self.size_and_align_of_dst(
 264                     base_layout.ty,
 265                     base_ptr.to_value_with_vtable(tab),
 266                 )?;
 267                 offset.abi_align(align).bytes()
 268             }
 269             _ => offset.bytes(),
 270         };
 271
 272         let ptr = base_ptr.offset(offset, &self)?;
 273         let align = base_align.min(base_layout.align).min(field.align);
 274         let extra = if !field.is_unsized() {
 275             PlaceExtra::None
 276         } else {
 277             match base_extra {
 278                 PlaceExtra::None => bug!("expected fat pointer"),
 279                 PlaceExtra::DowncastVariant(..) => {
 280                     bug!("Rust doesn't support unsized fields in enum variants")
 281                 }
 282                 PlaceExtra::Vtable(_) |
 283                 PlaceExtra::Length(_) => {}
 284             }
 285             base_extra
 286         };
 287
 288         Ok((Place::Ptr { ptr, align, extra }, field))
 289     }
 290
 291     pub fn val_to_place(&self, val: Value, ty: Ty<'tcx>) -> EvalResult<'tcx, Place> {
 292         let layout = self.layout_of(ty)?;
 293         Ok(match self.tcx.struct_tail(ty).sty {
 294             ty::TyDynamic(..) => {
 295                 let (ptr, vtable) = self.into_ptr_vtable_pair(val)?;
 296                 Place::Ptr {
 297                     ptr,
 298                     align: layout.align,
 299                     extra: PlaceExtra::Vtable(vtable),
 300                 }
 301             }
 302             ty::TyStr | ty::TySlice(_) => {
 303                 let (ptr, len) = self.into_slice(val)?;
 304                 Place::Ptr {
 305                     ptr,
 306                     align: layout.align,
 307                     extra: PlaceExtra::Length(len),
 308                 }
 309             }
 310             _ => Place::from_primval_ptr(self.into_ptr(val)?, layout.align),
 311         })
 312     }
 313
 314     pub fn place_index(
 315         &mut self,
 316         base: Place,
 317         outer_ty: Ty<'tcx>,
 318         n: u64,
 319     ) -> EvalResult<'tcx, Place> {
 320         // Taking the outer type here may seem odd; it's needed because for array types, the outer type gives away the length.
 321         let base = self.force_allocation(base)?;
 322         let (base_ptr, align) = base.to_ptr_align();
 323
 324         let (elem_ty, len) = base.elem_ty_and_len(outer_ty);
 325         let elem_size = self.layout_of(elem_ty)?.size.bytes();
 326         assert!(
 327             n < len,
 328             "Tried to access element {} of array/slice with length {}",
 329             n,
 330             len
 331         );
 332         let ptr = base_ptr.offset(n * elem_size, &*self)?;
 333         Ok(Place::Ptr {
 334             ptr,
 335             align,
 336             extra: PlaceExtra::None,
 337         })
 338     }
 339
 340     pub(super) fn place_downcast(
 341         &mut self,
 342         base: Place,
 343         variant: usize,
 344     ) -> EvalResult<'tcx, Place> {
 345         // FIXME(solson)
 346         let base = self.force_allocation(base)?;
 347         let (ptr, align) = base.to_ptr_align();
 348         let extra = PlaceExtra::DowncastVariant(variant);
 349         Ok(Place::Ptr { ptr, align, extra })
 350     }
 351
 352     pub fn eval_place_projection(
 353         &mut self,
 354         base: Place,
 355         base_ty: Ty<'tcx>,
 356         proj_elem: &mir::ProjectionElem<'tcx, mir::Local, Ty<'tcx>>,
 357     ) -> EvalResult<'tcx, Place> {
 358         use rustc::mir::ProjectionElem::*;
 359         match *proj_elem {
 360             Field(field, _) => {
 361                 let layout = self.layout_of(base_ty)?;
 362                 Ok(self.place_field(base, field, layout)?.0)
 363             }
 364
 365             Downcast(_, variant) => {
 366                 self.place_downcast(base, variant)
 367             }
 368
 369             Deref => {
 370                 let val = self.read_place(base)?;
 371
 372                 let pointee_type = match base_ty.sty {
 373                     ty::TyRawPtr(ref tam) |
 374                     ty::TyRef(_, ref tam) => tam.ty,
 375                     ty::TyAdt(def, _) if def.is_box() => base_ty.boxed_ty(),
 376                     _ => bug!("can only deref pointer types"),
 377                 };
 378
 379                 trace!("deref to {} on {:?}", pointee_type, val);
 380
 381                 self.val_to_place(val, pointee_type)
 382             }
 383
 384             Index(local) => {
 385                 let value = self.frame().get_local(local)?;
 386                 let ty = self.tcx.types.usize;
 387                 let n = self.value_to_primval(ValTy { value, ty })?.to_u64()?;
 388                 self.place_index(base, base_ty, n)
 389             }
 390
 391             ConstantIndex {
 392                 offset,
 393                 min_length,
 394                 from_end,
 395             } => {
 396                 // FIXME(solson)
 397                 let base = self.force_allocation(base)?;
 398                 let (base_ptr, align) = base.to_ptr_align();
 399
 400                 let (elem_ty, n) = base.elem_ty_and_len(base_ty);
 401                 let elem_size = self.layout_of(elem_ty)?.size.bytes();
 402                 assert!(n >= min_length as u64);
 403
 404                 let index = if from_end {
 405                     n - u64::from(offset)
 406                 } else {
 407                     u64::from(offset)
 408                 };
 409
 410                 let ptr = base_ptr.offset(index * elem_size, &self)?;
 411                 Ok(Place::Ptr { ptr, align, extra: PlaceExtra::None })
 412             }
 413
 414             Subslice { from, to } => {
 415                 // FIXME(solson)
 416                 let base = self.force_allocation(base)?;
 417                 let (base_ptr, align) = base.to_ptr_align();
 418
 419                 let (elem_ty, n) = base.elem_ty_and_len(base_ty);
 420                 let elem_size = self.layout_of(elem_ty)?.size.bytes();
 421                 assert!(u64::from(from) <= n - u64::from(to));
 422                 let ptr = base_ptr.offset(u64::from(from) * elem_size, &self)?;
 423                 // sublicing arrays produces arrays
 424                 let extra = if self.type_is_sized(base_ty) {
 425                     PlaceExtra::None
 426                 } else {
 427                     PlaceExtra::Length(n - u64::from(to) - u64::from(from))
 428                 };
 429                 Ok(Place::Ptr { ptr, align, extra })
 430             }
 431         }
 432     }
 433
 434     pub fn place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 435         self.monomorphize(
 436             place.ty(self.mir(), *self.tcx).to_ty(*self.tcx),
 437             self.substs(),
 438         )
 439     }
 440 }