src/librustc_mir/interpret/cast.rs

   1 use rustc::ty::{self, Ty, TypeAndMut};
   2 use rustc::ty::layout::{self, TyLayout, Size};
   3 use rustc::ty::adjustment::{PointerCast};
   4 use syntax::ast::{FloatTy, IntTy, UintTy};
   5 use syntax::symbol::sym;
   6
   7 use rustc_apfloat::ieee::{Single, Double};
   8 use rustc::mir::interpret::{
   9     Scalar, EvalResult, Pointer, PointerArithmetic, InterpError,
  10 };
  11 use rustc::mir::CastKind;
  12 use rustc_apfloat::Float;
  13
  14 use super::{InterpretCx, Machine, PlaceTy, OpTy, ImmTy, Immediate};
  15
  16 impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M> {
  17     fn type_is_fat_ptr(&self, ty: Ty<'tcx>) -> bool {
  18         match ty.sty {
  19             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
  20             ty::Ref(_, ty, _) => !self.type_is_sized(ty),
  21             ty::Adt(def, _) if def.is_box() => !self.type_is_sized(ty.boxed_ty()),
  22             _ => false,
  23         }
  24     }
  25
  26     pub fn cast(
  27         &mut self,
  28         src: OpTy<'tcx, M::PointerTag>,
  29         kind: CastKind,
  30         dest: PlaceTy<'tcx, M::PointerTag>,
  31     ) -> EvalResult<'tcx> {
  32         use rustc::mir::CastKind::*;
  33         match kind {
  34             Pointer(PointerCast::Unsize) => {
  35                 self.unsize_into(src, dest)?;
  36             }
  37
  38             Misc | Pointer(PointerCast::MutToConstPointer) => {
  39                 let src = self.read_immediate(src)?;
  40
  41                 if self.type_is_fat_ptr(src.layout.ty) {
  42                     match (*src, self.type_is_fat_ptr(dest.layout.ty)) {
  43                         // pointers to extern types
  44                         (Immediate::Scalar(_),_) |
  45                         // slices and trait objects to other slices/trait objects
  46                         (Immediate::ScalarPair(..), true) => {
  47                             // No change to immediate
  48                             self.write_immediate(*src, dest)?;
  49                         }
  50                         // slices and trait objects to thin pointers (dropping the metadata)
  51                         (Immediate::ScalarPair(data, _), false) => {
  52                             self.write_scalar(data, dest)?;
  53                         }
  54                     }
  55                 } else {
  56                     match src.layout.variants {
  57                         layout::Variants::Single { index } => {
  58                             if let Some(discr) =
  59                                 src.layout.ty.discriminant_for_variant(*self.tcx, index)
  60                             {
  61                                 // Cast from a univariant enum
  62                                 assert!(src.layout.is_zst());
  63                                 return self.write_scalar(
  64                                     Scalar::from_uint(discr.val, dest.layout.size),
  65                                     dest);
  66                             }
  67                         }
  68                         layout::Variants::Multiple { .. } => {},
  69                     }
  70
  71                     let dest_val = self.cast_scalar(src.to_scalar()?, src.layout, dest.layout)?;
  72                     self.write_scalar(dest_val, dest)?;
  73                 }
  74             }
  75
  76             Pointer(PointerCast::ReifyFnPointer) => {
  77                 // The src operand does not matter, just its type
  78                 match src.layout.ty.sty {
  79                     ty::FnDef(def_id, substs) => {
  80                         if self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
  81                             bug!("reifying a fn ptr that requires const arguments");
  82                         }
  83                         let instance: EvalResult<'tcx, _> = ty::Instance::resolve(
  84                             *self.tcx,
  85                             self.param_env,
  86                             def_id,
  87                             substs,
  88                         ).ok_or_else(|| InterpError::TooGeneric.into());
  89                         let fn_ptr = self.memory.create_fn_alloc(instance?).with_default_tag();
  90                         self.write_scalar(Scalar::Ptr(fn_ptr.into()), dest)?;
  91                     }
  92                     _ => bug!("reify fn pointer on {:?}", src.layout.ty),
  93                 }
  94             }
  95
  96             Pointer(PointerCast::UnsafeFnPointer) => {
  97                 let src = self.read_immediate(src)?;
  98                 match dest.layout.ty.sty {
  99                     ty::FnPtr(_) => {
 100                         // No change to value
 101                         self.write_immediate(*src, dest)?;
 102                     }
 103                     _ => bug!("fn to unsafe fn cast on {:?}", dest.layout.ty),
 104                 }
 105             }
 106
 107             Pointer(PointerCast::ClosureFnPointer(_)) => {
 108                 // The src operand does not matter, just its type
 109                 match src.layout.ty.sty {
 110                     ty::Closure(def_id, substs) => {
 111                         let substs = self.subst_and_normalize_erasing_regions(substs)?;
 112                         let instance = ty::Instance::resolve_closure(
 113                             *self.tcx,
 114                             def_id,
 115                             substs,
 116                             ty::ClosureKind::FnOnce,
 117                         );
 118                         let fn_ptr = self.memory.create_fn_alloc(instance).with_default_tag();
 119                         let val = Immediate::Scalar(Scalar::Ptr(fn_ptr.into()).into());
 120                         self.write_immediate(val, dest)?;
 121                     }
 122                     _ => bug!("closure fn pointer on {:?}", src.layout.ty),
 123                 }
 124             }
 125         }
 126         Ok(())
 127     }
 128
 129     pub(super) fn cast_scalar(
 130         &self,
 131         val: Scalar<M::PointerTag>,
 132         src_layout: TyLayout<'tcx>,
 133         dest_layout: TyLayout<'tcx>,
 134     ) -> EvalResult<'tcx, Scalar<M::PointerTag>> {
 135         use rustc::ty::TyKind::*;
 136         trace!("Casting {:?}: {:?} to {:?}", val, src_layout.ty, dest_layout.ty);
 137
 138         match val.to_bits_or_ptr(src_layout.size, self) {
 139             Err(ptr) => self.cast_from_ptr(ptr, dest_layout.ty),
 140             Ok(data) => {
 141                 match src_layout.ty.sty {
 142                     Float(fty) => self.cast_from_float(data, fty, dest_layout.ty),
 143                     _ => self.cast_from_int(data, src_layout, dest_layout),
 144                 }
 145             }
 146         }
 147     }
 148
 149     fn cast_from_int(
 150         &self,
 151         v: u128,
 152         src_layout: TyLayout<'tcx>,
 153         dest_layout: TyLayout<'tcx>,
 154     ) -> EvalResult<'tcx, Scalar<M::PointerTag>> {
 155         let signed = src_layout.abi.is_signed();
 156         let v = if signed {
 157             self.sign_extend(v, src_layout)
 158         } else {
 159             v
 160         };
 161         trace!("cast_from_int: {}, {}, {}", v, src_layout.ty, dest_layout.ty);
 162         use rustc::ty::TyKind::*;
 163         match dest_layout.ty.sty {
 164             Int(_) | Uint(_) | RawPtr(_) => {
 165                 let v = self.truncate(v, dest_layout);
 166                 Ok(Scalar::from_uint(v, dest_layout.size))
 167             }
 168
 169             Float(FloatTy::F32) if signed => Ok(Scalar::from_uint(
 170                 Single::from_i128(v as i128).value.to_bits(),
 171                 Size::from_bits(32)
 172             )),
 173             Float(FloatTy::F64) if signed => Ok(Scalar::from_uint(
 174                 Double::from_i128(v as i128).value.to_bits(),
 175                 Size::from_bits(64)
 176             )),
 177             Float(FloatTy::F32) => Ok(Scalar::from_uint(
 178                 Single::from_u128(v).value.to_bits(),
 179                 Size::from_bits(32)
 180             )),
 181             Float(FloatTy::F64) => Ok(Scalar::from_uint(
 182                 Double::from_u128(v).value.to_bits(),
 183                 Size::from_bits(64)
 184             )),
 185
 186             Char => {
 187                 // `u8` to `char` cast
 188                 debug_assert_eq!(v as u8 as u128, v);
 189                 Ok(Scalar::from_uint(v, Size::from_bytes(4)))
 190             },
 191
 192             // Casts to bool are not permitted by rustc, no need to handle them here.
 193             _ => err!(Unimplemented(format!("int to {:?} cast", dest_layout.ty))),
 194         }
 195     }
 196
 197     fn cast_from_float(
 198         &self,
 199         bits: u128,
 200         fty: FloatTy,
 201         dest_ty: Ty<'tcx>
 202     ) -> EvalResult<'tcx, Scalar<M::PointerTag>> {
 203         use rustc::ty::TyKind::*;
 204         use rustc_apfloat::FloatConvert;
 205         match dest_ty.sty {
 206             // float -> uint
 207             Uint(t) => {
 208                 let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits() as usize);
 209                 let v = match fty {
 210                     FloatTy::F32 => Single::from_bits(bits).to_u128(width).value,
 211                     FloatTy::F64 => Double::from_bits(bits).to_u128(width).value,
 212                 };
 213                 // This should already fit the bit width
 214                 Ok(Scalar::from_uint(v, Size::from_bits(width as u64)))
 215             },
 216             // float -> int
 217             Int(t) => {
 218                 let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits() as usize);
 219                 let v = match fty {
 220                     FloatTy::F32 => Single::from_bits(bits).to_i128(width).value,
 221                     FloatTy::F64 => Double::from_bits(bits).to_i128(width).value,
 222                 };
 223                 Ok(Scalar::from_int(v, Size::from_bits(width as u64)))
 224             },
 225             // f64 -> f32
 226             Float(FloatTy::F32) if fty == FloatTy::F64 => {
 227                 Ok(Scalar::from_uint(
 228                     Single::to_bits(Double::from_bits(bits).convert(&mut false).value),
 229                     Size::from_bits(32),
 230                 ))
 231             },
 232             // f32 -> f64
 233             Float(FloatTy::F64) if fty == FloatTy::F32 => {
 234                 Ok(Scalar::from_uint(
 235                     Double::to_bits(Single::from_bits(bits).convert(&mut false).value),
 236                     Size::from_bits(64),
 237                 ))
 238             },
 239             // identity cast
 240             Float(FloatTy:: F64) => Ok(Scalar::from_uint(bits, Size::from_bits(64))),
 241             Float(FloatTy:: F32) => Ok(Scalar::from_uint(bits, Size::from_bits(32))),
 242             _ => err!(Unimplemented(format!("float to {:?} cast", dest_ty))),
 243         }
 244     }
 245
 246     fn cast_from_ptr(
 247         &self,
 248         ptr: Pointer<M::PointerTag>,
 249         ty: Ty<'tcx>
 250     ) -> EvalResult<'tcx, Scalar<M::PointerTag>> {
 251         use rustc::ty::TyKind::*;
 252         match ty.sty {
 253             // Casting to a reference or fn pointer is not permitted by rustc,
 254             // no need to support it here.
 255             RawPtr(_) |
 256             Int(IntTy::Isize) |
 257             Uint(UintTy::Usize) => Ok(ptr.into()),
 258             Int(_) | Uint(_) => err!(ReadPointerAsBytes),
 259             _ => err!(Unimplemented(format!("ptr to {:?} cast", ty))),
 260         }
 261     }
 262
 263     fn unsize_into_ptr(
 264         &mut self,
 265         src: OpTy<'tcx, M::PointerTag>,
 266         dest: PlaceTy<'tcx, M::PointerTag>,
 267         // The pointee types
 268         sty: Ty<'tcx>,
 269         dty: Ty<'tcx>,
 270     ) -> EvalResult<'tcx> {
 271         // A<Struct> -> A<Trait> conversion
 272         let (src_pointee_ty, dest_pointee_ty) = self.tcx.struct_lockstep_tails(sty, dty);
 273
 274         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
 275             (&ty::Array(_, length), &ty::Slice(_)) => {
 276                 let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
 277                 // u64 cast is from usize to u64, which is always good
 278                 let val = Immediate::new_slice(
 279                     ptr,
 280                     length.unwrap_usize(self.tcx.tcx),
 281                     self,
 282                 );
 283                 self.write_immediate(val, dest)
 284             }
 285             (&ty::Dynamic(..), &ty::Dynamic(..)) => {
 286                 // For now, upcasts are limited to changes in marker
 287                 // traits, and hence never actually require an actual
 288                 // change to the vtable.
 289                 let val = self.read_immediate(src)?;
 290                 self.write_immediate(*val, dest)
 291             }
 292             (_, &ty::Dynamic(ref data, _)) => {
 293                 // Initial cast from sized to dyn trait
 294                 let vtable = self.get_vtable(src_pointee_ty, data.principal())?;
 295                 let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
 296                 let val = Immediate::new_dyn_trait(ptr, vtable);
 297                 self.write_immediate(val, dest)
 298             }
 299
 300             _ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, dest.layout.ty),
 301         }
 302     }
 303
 304     fn unsize_into(
 305         &mut self,
 306         src: OpTy<'tcx, M::PointerTag>,
 307         dest: PlaceTy<'tcx, M::PointerTag>,
 308     ) -> EvalResult<'tcx> {
 309         match (&src.layout.ty.sty, &dest.layout.ty.sty) {
 310             (&ty::Ref(_, s, _), &ty::Ref(_, d, _)) |
 311             (&ty::Ref(_, s, _), &ty::RawPtr(TypeAndMut { ty: d, .. })) |
 312             (&ty::RawPtr(TypeAndMut { ty: s, .. }),
 313              &ty::RawPtr(TypeAndMut { ty: d, .. })) => {
 314                 self.unsize_into_ptr(src, dest, s, d)
 315             }
 316             (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
 317                 assert_eq!(def_a, def_b);
 318                 if def_a.is_box() || def_b.is_box() {
 319                     if !def_a.is_box() || !def_b.is_box() {
 320                         bug!("invalid unsizing between {:?} -> {:?}", src.layout, dest.layout);
 321                     }
 322                     return self.unsize_into_ptr(
 323                         src,
 324                         dest,
 325                         src.layout.ty.boxed_ty(),
 326                         dest.layout.ty.boxed_ty(),
 327                     );
 328                 }
 329
 330                 // unsizing of generic struct with pointer fields
 331                 // Example: `Arc<T>` -> `Arc<Trait>`
 332                 // here we need to increase the size of every &T thin ptr field to a fat ptr
 333                 for i in 0..src.layout.fields.count() {
 334                     let dst_field = self.place_field(dest, i as u64)?;
 335                     if dst_field.layout.is_zst() {
 336                         continue;
 337                     }
 338                     let src_field = match src.try_as_mplace() {
 339                         Ok(mplace) => {
 340                             let src_field = self.mplace_field(mplace, i as u64)?;
 341                             src_field.into()
 342                         }
 343                         Err(..) => {
 344                             let src_field_layout = src.layout.field(self, i)?;
 345                             // this must be a field covering the entire thing
 346                             assert_eq!(src.layout.fields.offset(i).bytes(), 0);
 347                             assert_eq!(src_field_layout.size, src.layout.size);
 348                             // just sawp out the layout
 349                             OpTy::from(ImmTy { imm: src.to_immediate(), layout: src_field_layout })
 350                         }
 351                     };
 352                     if src_field.layout.ty == dst_field.layout.ty {
 353                         self.copy_op(src_field, dst_field)?;
 354                     } else {
 355                         self.unsize_into(src_field, dst_field)?;
 356                     }
 357                 }
 358                 Ok(())
 359             }
 360             _ => {
 361                 bug!(
 362                     "unsize_into: invalid conversion: {:?} -> {:?}",
 363                     src.layout,
 364                     dest.layout
 365                 )
 366             }
 367         }
 368     }
 369 }