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_apfloat::{Float, FloatConvert};
   9 use rustc::mir::interpret::{
  10     Scalar, InterpResult, Pointer, PointerArithmetic, InterpError,
  11 };
  12 use rustc::mir::CastKind;
  13
  14 use super::{InterpretCx, Machine, PlaceTy, OpTy, 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     ) -> InterpResult<'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: InterpResult<'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?);
  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);
 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     fn cast_scalar(
 130         &self,
 131         val: Scalar<M::PointerTag>,
 132         src_layout: TyLayout<'tcx>,
 133         dest_layout: TyLayout<'tcx>,
 134     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 135         use rustc::ty::TyKind::*;
 136         trace!("Casting {:?}: {:?} to {:?}", val, src_layout.ty, dest_layout.ty);
 137
 138         match src_layout.ty.sty {
 139             // Floating point
 140             Float(FloatTy::F32) => self.cast_from_float(val.to_f32()?, dest_layout.ty),
 141             Float(FloatTy::F64) => self.cast_from_float(val.to_f64()?, dest_layout.ty),
 142             // Integer(-like), including fn ptr casts and casts from enums that
 143             // are represented as integers (this excludes univariant enums, which
 144             // are handled in `cast` directly).
 145             _ => {
 146                 assert!(
 147                     src_layout.ty.is_bool()       || src_layout.ty.is_char()     ||
 148                     src_layout.ty.is_enum()       || src_layout.ty.is_integral() ||
 149                     src_layout.ty.is_unsafe_ptr() || src_layout.ty.is_fn_ptr()   ||
 150                     src_layout.ty.is_region_ptr(),
 151                     "Unexpected cast from type {:?}", src_layout.ty
 152                 );
 153                 match val.to_bits_or_ptr(src_layout.size, self) {
 154                     Err(ptr) => self.cast_from_ptr(ptr, dest_layout.ty),
 155                     Ok(data) => self.cast_from_int(data, src_layout, dest_layout),
 156                 }
 157             }
 158         }
 159     }
 160
 161     fn cast_from_int(
 162         &self,
 163         v: u128, // raw bits
 164         src_layout: TyLayout<'tcx>,
 165         dest_layout: TyLayout<'tcx>,
 166     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 167         // Let's make sure v is sign-extended *if* it has a signed type.
 168         let signed = src_layout.abi.is_signed();
 169         let v = if signed {
 170             self.sign_extend(v, src_layout)
 171         } else {
 172             v
 173         };
 174         trace!("cast_from_int: {}, {}, {}", v, src_layout.ty, dest_layout.ty);
 175         use rustc::ty::TyKind::*;
 176         match dest_layout.ty.sty {
 177             Int(_) | Uint(_) | RawPtr(_) => {
 178                 let v = self.truncate(v, dest_layout);
 179                 Ok(Scalar::from_uint(v, dest_layout.size))
 180             }
 181
 182             Float(FloatTy::F32) if signed => Ok(Scalar::from_f32(
 183                 Single::from_i128(v as i128).value
 184             )),
 185             Float(FloatTy::F64) if signed => Ok(Scalar::from_f64(
 186                 Double::from_i128(v as i128).value
 187             )),
 188             Float(FloatTy::F32) => Ok(Scalar::from_f32(
 189                 Single::from_u128(v).value
 190             )),
 191             Float(FloatTy::F64) => Ok(Scalar::from_f64(
 192                 Double::from_u128(v).value
 193             )),
 194
 195             Char => {
 196                 // `u8` to `char` cast
 197                 debug_assert_eq!(v as u8 as u128, v);
 198                 Ok(Scalar::from_uint(v, Size::from_bytes(4)))
 199             },
 200
 201             // Casts to bool are not permitted by rustc, no need to handle them here.
 202             _ => err!(Unimplemented(format!("int to {:?} cast", dest_layout.ty))),
 203         }
 204     }
 205
 206     fn cast_from_float<F>(
 207         &self,
 208         f: F,
 209         dest_ty: Ty<'tcx>
 210     ) -> InterpResult<'tcx, Scalar<M::PointerTag>>
 211     where F: Float + Into<Scalar<M::PointerTag>> + FloatConvert<Single> + FloatConvert<Double>
 212     {
 213         use rustc::ty::TyKind::*;
 214         match dest_ty.sty {
 215             // float -> uint
 216             Uint(t) => {
 217                 let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits() as usize);
 218                 let v = f.to_u128(width).value;
 219                 // This should already fit the bit width
 220                 Ok(Scalar::from_uint(v, Size::from_bits(width as u64)))
 221             },
 222             // float -> int
 223             Int(t) => {
 224                 let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits() as usize);
 225                 let v = f.to_i128(width).value;
 226                 Ok(Scalar::from_int(v, Size::from_bits(width as u64)))
 227             },
 228             // float -> f32
 229             Float(FloatTy::F32) =>
 230                 Ok(Scalar::from_f32(f.convert(&mut false).value)),
 231             // float -> f64
 232             Float(FloatTy::F64) =>
 233                 Ok(Scalar::from_f64(f.convert(&mut false).value)),
 234             // That's it.
 235             _ => bug!("invalid float to {:?} cast", dest_ty),
 236         }
 237     }
 238
 239     fn cast_from_ptr(
 240         &self,
 241         ptr: Pointer<M::PointerTag>,
 242         ty: Ty<'tcx>
 243     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 244         use rustc::ty::TyKind::*;
 245         match ty.sty {
 246             // Casting to a reference or fn pointer is not permitted by rustc,
 247             // no need to support it here.
 248             RawPtr(_) |
 249             Int(IntTy::Isize) |
 250             Uint(UintTy::Usize) => Ok(ptr.into()),
 251             Int(_) | Uint(_) => err!(ReadPointerAsBytes),
 252             _ => err!(Unimplemented(format!("ptr to {:?} cast", ty))),
 253         }
 254     }
 255
 256     fn unsize_into_ptr(
 257         &mut self,
 258         src: OpTy<'tcx, M::PointerTag>,
 259         dest: PlaceTy<'tcx, M::PointerTag>,
 260         // The pointee types
 261         sty: Ty<'tcx>,
 262         dty: Ty<'tcx>,
 263     ) -> InterpResult<'tcx> {
 264         // A<Struct> -> A<Trait> conversion
 265         let (src_pointee_ty, dest_pointee_ty) = self.tcx.struct_lockstep_tails(sty, dty);
 266
 267         match (&src_pointee_ty.sty, &dest_pointee_ty.sty) {
 268             (&ty::Array(_, length), &ty::Slice(_)) => {
 269                 let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
 270                 // u64 cast is from usize to u64, which is always good
 271                 let val = Immediate::new_slice(
 272                     ptr,
 273                     length.unwrap_usize(self.tcx.tcx),
 274                     self,
 275                 );
 276                 self.write_immediate(val, dest)
 277             }
 278             (&ty::Dynamic(..), &ty::Dynamic(..)) => {
 279                 // For now, upcasts are limited to changes in marker
 280                 // traits, and hence never actually require an actual
 281                 // change to the vtable.
 282                 let val = self.read_immediate(src)?;
 283                 self.write_immediate(*val, dest)
 284             }
 285             (_, &ty::Dynamic(ref data, _)) => {
 286                 // Initial cast from sized to dyn trait
 287                 let vtable = self.get_vtable(src_pointee_ty, data.principal())?;
 288                 let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
 289                 let val = Immediate::new_dyn_trait(ptr, vtable);
 290                 self.write_immediate(val, dest)
 291             }
 292
 293             _ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, dest.layout.ty),
 294         }
 295     }
 296
 297     fn unsize_into(
 298         &mut self,
 299         src: OpTy<'tcx, M::PointerTag>,
 300         dest: PlaceTy<'tcx, M::PointerTag>,
 301     ) -> InterpResult<'tcx> {
 302         trace!("Unsizing {:?} into {:?}", src, dest);
 303         match (&src.layout.ty.sty, &dest.layout.ty.sty) {
 304             (&ty::Ref(_, s, _), &ty::Ref(_, d, _)) |
 305             (&ty::Ref(_, s, _), &ty::RawPtr(TypeAndMut { ty: d, .. })) |
 306             (&ty::RawPtr(TypeAndMut { ty: s, .. }),
 307              &ty::RawPtr(TypeAndMut { ty: d, .. })) => {
 308                 self.unsize_into_ptr(src, dest, s, d)
 309             }
 310             (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
 311                 assert_eq!(def_a, def_b);
 312                 if def_a.is_box() || def_b.is_box() {
 313                     if !def_a.is_box() || !def_b.is_box() {
 314                         bug!("invalid unsizing between {:?} -> {:?}", src.layout, dest.layout);
 315                     }
 316                     return self.unsize_into_ptr(
 317                         src,
 318                         dest,
 319                         src.layout.ty.boxed_ty(),
 320                         dest.layout.ty.boxed_ty(),
 321                     );
 322                 }
 323
 324                 // unsizing of generic struct with pointer fields
 325                 // Example: `Arc<T>` -> `Arc<Trait>`
 326                 // here we need to increase the size of every &T thin ptr field to a fat ptr
 327                 for i in 0..src.layout.fields.count() {
 328                     let dst_field = self.place_field(dest, i as u64)?;
 329                     if dst_field.layout.is_zst() {
 330                         continue;
 331                     }
 332                     let src_field = self.operand_field(src, i as u64)?;
 333                     if src_field.layout.ty == dst_field.layout.ty {
 334                         self.copy_op(src_field, dst_field)?;
 335                     } else {
 336                         self.unsize_into(src_field, dst_field)?;
 337                     }
 338                 }
 339                 Ok(())
 340             }
 341             _ => {
 342                 bug!(
 343                     "unsize_into: invalid conversion: {:?} -> {:?}",
 344                     src.layout,
 345                     dest.layout
 346                 )
 347             }
 348         }
 349     }
 350 }