src/librustc_mir/interpret/intrinsics.rs

   1 //! Intrinsics and other functions that the miri engine executes without
   2 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
   3 //! and miri.
   4
   5 use rustc::mir::{
   6     self,
   7     interpret::{ConstValue, GlobalId, InterpResult, Scalar},
   8     BinOp,
   9 };
  10 use rustc::ty;
  11 use rustc::ty::layout::{LayoutOf, Primitive, Size};
  12 use rustc::ty::subst::SubstsRef;
  13 use rustc::ty::TyCtxt;
  14 use rustc_hir::def_id::DefId;
  15 use rustc_span::symbol::{sym, Symbol};
  16 use rustc_span::Span;
  17
  18 use super::{ImmTy, InterpCx, Machine, OpTy, PlaceTy};
  19
  20 mod caller_location;
  21 mod type_name;
  22
  23 fn numeric_intrinsic<'tcx, Tag>(
  24     name: Symbol,
  25     bits: u128,
  26     kind: Primitive,
  27 ) -> InterpResult<'tcx, Scalar<Tag>> {
  28     let size = match kind {
  29         Primitive::Int(integer, _) => integer.size(),
  30         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  31     };
  32     let extra = 128 - size.bits() as u128;
  33     let bits_out = match name {
  34         sym::ctpop => bits.count_ones() as u128,
  35         sym::ctlz => bits.leading_zeros() as u128 - extra,
  36         sym::cttz => (bits << extra).trailing_zeros() as u128 - extra,
  37         sym::bswap => (bits << extra).swap_bytes(),
  38         sym::bitreverse => (bits << extra).reverse_bits(),
  39         _ => bug!("not a numeric intrinsic: {}", name),
  40     };
  41     Ok(Scalar::from_uint(bits_out, size))
  42 }
  43
  44 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  45 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  46 crate fn eval_nullary_intrinsic<'tcx>(
  47     tcx: TyCtxt<'tcx>,
  48     param_env: ty::ParamEnv<'tcx>,
  49     def_id: DefId,
  50     substs: SubstsRef<'tcx>,
  51 ) -> InterpResult<'tcx, &'tcx ty::Const<'tcx>> {
  52     let tp_ty = substs.type_at(0);
  53     let name = tcx.item_name(def_id);
  54     Ok(match name {
  55         sym::type_name => {
  56             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  57             tcx.mk_const(ty::Const {
  58                 val: ty::ConstKind::Value(ConstValue::Slice {
  59                     data: alloc,
  60                     start: 0,
  61                     end: alloc.len(),
  62                 }),
  63                 ty: tcx.mk_static_str(),
  64             })
  65         }
  66         sym::needs_drop => ty::Const::from_bool(tcx, tp_ty.needs_drop(tcx, param_env)),
  67         sym::size_of | sym::min_align_of | sym::pref_align_of => {
  68             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  69             let n = match name {
  70                 sym::pref_align_of => layout.align.pref.bytes(),
  71                 sym::min_align_of => layout.align.abi.bytes(),
  72                 sym::size_of => layout.size.bytes(),
  73                 _ => bug!(),
  74             };
  75             ty::Const::from_usize(tcx, n)
  76         }
  77         sym::type_id => {
  78             ty::Const::from_bits(tcx, tcx.type_id_hash(tp_ty).into(), param_env.and(tcx.types.u64))
  79         }
  80         other => bug!("`{}` is not a zero arg intrinsic", other),
  81     })
  82 }
  83
  84 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  85     /// Returns `true` if emulation happened.
  86     pub fn emulate_intrinsic(
  87         &mut self,
  88         span: Span,
  89         instance: ty::Instance<'tcx>,
  90         args: &[OpTy<'tcx, M::PointerTag>],
  91         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
  92     ) -> InterpResult<'tcx, bool> {
  93         let substs = instance.substs;
  94         let intrinsic_name = self.tcx.item_name(instance.def_id());
  95
  96         // We currently do not handle any intrinsics that are *allowed* to diverge,
  97         // but `transmute` could lack a return place in case of UB.
  98         let (dest, ret) = match ret {
  99             Some(p) => p,
 100             None => match intrinsic_name {
 101                 sym::transmute => throw_ub!(Unreachable),
 102                 _ => return Ok(false),
 103             },
 104         };
 105
 106         // Keep the patterns in this match ordered the same as the list in
 107         // `src/librustc/ty/constness.rs`
 108         match intrinsic_name {
 109             sym::caller_location => {
 110                 let span = self.find_closest_untracked_caller_location().unwrap_or(span);
 111                 let location = self.alloc_caller_location_for_span(span);
 112                 self.write_scalar(location.ptr, dest)?;
 113             }
 114
 115             sym::min_align_of
 116             | sym::pref_align_of
 117             | sym::needs_drop
 118             | sym::size_of
 119             | sym::type_id
 120             | sym::type_name => {
 121                 let gid = GlobalId { instance, promoted: None };
 122                 let val = self.const_eval(gid)?;
 123                 self.copy_op(val, dest)?;
 124             }
 125
 126             sym::ctpop
 127             | sym::cttz
 128             | sym::cttz_nonzero
 129             | sym::ctlz
 130             | sym::ctlz_nonzero
 131             | sym::bswap
 132             | sym::bitreverse => {
 133                 let ty = substs.type_at(0);
 134                 let layout_of = self.layout_of(ty)?;
 135                 let val = self.read_scalar(args[0])?.not_undef()?;
 136                 let bits = self.force_bits(val, layout_of.size)?;
 137                 let kind = match layout_of.abi {
 138                     ty::layout::Abi::Scalar(ref scalar) => scalar.value,
 139                     _ => throw_unsup!(TypeNotPrimitive(ty)),
 140                 };
 141                 let (nonzero, intrinsic_name) = match intrinsic_name {
 142                     sym::cttz_nonzero => (true, sym::cttz),
 143                     sym::ctlz_nonzero => (true, sym::ctlz),
 144                     other => (false, other),
 145                 };
 146                 if nonzero && bits == 0 {
 147                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 148                 }
 149                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 150                 self.write_scalar(out_val, dest)?;
 151             }
 152             sym::wrapping_add
 153             | sym::wrapping_sub
 154             | sym::wrapping_mul
 155             | sym::add_with_overflow
 156             | sym::sub_with_overflow
 157             | sym::mul_with_overflow => {
 158                 let lhs = self.read_immediate(args[0])?;
 159                 let rhs = self.read_immediate(args[1])?;
 160                 let (bin_op, ignore_overflow) = match intrinsic_name {
 161                     sym::wrapping_add => (BinOp::Add, true),
 162                     sym::wrapping_sub => (BinOp::Sub, true),
 163                     sym::wrapping_mul => (BinOp::Mul, true),
 164                     sym::add_with_overflow => (BinOp::Add, false),
 165                     sym::sub_with_overflow => (BinOp::Sub, false),
 166                     sym::mul_with_overflow => (BinOp::Mul, false),
 167                     _ => bug!("Already checked for int ops"),
 168                 };
 169                 if ignore_overflow {
 170                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 171                 } else {
 172                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 173                 }
 174             }
 175             sym::saturating_add | sym::saturating_sub => {
 176                 let l = self.read_immediate(args[0])?;
 177                 let r = self.read_immediate(args[1])?;
 178                 let is_add = intrinsic_name == sym::saturating_add;
 179                 let (val, overflowed, _ty) =
 180                     self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
 181                 let val = if overflowed {
 182                     let num_bits = l.layout.size.bits();
 183                     if l.layout.abi.is_signed() {
 184                         // For signed ints the saturated value depends on the sign of the first
 185                         // term since the sign of the second term can be inferred from this and
 186                         // the fact that the operation has overflowed (if either is 0 no
 187                         // overflow can occur)
 188                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 189                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 190                         if first_term_positive {
 191                             // Negative overflow not possible since the positive first term
 192                             // can only increase an (in range) negative term for addition
 193                             // or corresponding negated positive term for subtraction
 194                             Scalar::from_uint(
 195                                 (1u128 << (num_bits - 1)) - 1, // max positive
 196                                 Size::from_bits(num_bits),
 197                             )
 198                         } else {
 199                             // Positive overflow not possible for similar reason
 200                             // max negative
 201                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 202                         }
 203                     } else {
 204                         // unsigned
 205                         if is_add {
 206                             // max unsigned
 207                             Scalar::from_uint(
 208                                 u128::max_value() >> (128 - num_bits),
 209                                 Size::from_bits(num_bits),
 210                             )
 211                         } else {
 212                             // underflow to 0
 213                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 214                         }
 215                     }
 216                 } else {
 217                     val
 218                 };
 219                 self.write_scalar(val, dest)?;
 220             }
 221             sym::unchecked_shl
 222             | sym::unchecked_shr
 223             | sym::unchecked_add
 224             | sym::unchecked_sub
 225             | sym::unchecked_mul
 226             | sym::unchecked_div
 227             | sym::unchecked_rem => {
 228                 let l = self.read_immediate(args[0])?;
 229                 let r = self.read_immediate(args[1])?;
 230                 let bin_op = match intrinsic_name {
 231                     sym::unchecked_shl => BinOp::Shl,
 232                     sym::unchecked_shr => BinOp::Shr,
 233                     sym::unchecked_add => BinOp::Add,
 234                     sym::unchecked_sub => BinOp::Sub,
 235                     sym::unchecked_mul => BinOp::Mul,
 236                     sym::unchecked_div => BinOp::Div,
 237                     sym::unchecked_rem => BinOp::Rem,
 238                     _ => bug!("Already checked for int ops"),
 239                 };
 240                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 241                 if overflowed {
 242                     let layout = self.layout_of(substs.type_at(0))?;
 243                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 244                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 245                         throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
 246                     } else {
 247                         throw_ub_format!("Overflow executing `{}`", intrinsic_name);
 248                     }
 249                 }
 250                 self.write_scalar(val, dest)?;
 251             }
 252             sym::rotate_left | sym::rotate_right => {
 253                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 254                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 255                 let layout = self.layout_of(substs.type_at(0))?;
 256                 let val = self.read_scalar(args[0])?.not_undef()?;
 257                 let val_bits = self.force_bits(val, layout.size)?;
 258                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 259                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 260                 let width_bits = layout.size.bits() as u128;
 261                 let shift_bits = raw_shift_bits % width_bits;
 262                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 263                 let result_bits = if intrinsic_name == sym::rotate_left {
 264                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 265                 } else {
 266                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 267                 };
 268                 let truncated_bits = self.truncate(result_bits, layout);
 269                 let result = Scalar::from_uint(truncated_bits, layout.size);
 270                 self.write_scalar(result, dest)?;
 271             }
 272
 273             sym::ptr_offset_from => {
 274                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 275                 let a = self.read_immediate(args[0])?.to_scalar()?;
 276                 let b = self.read_immediate(args[1])?.to_scalar()?;
 277
 278                 // Special case: if both scalars are *equal integers*
 279                 // and not NULL, we pretend there is an allocation of size 0 right there,
 280                 // and their offset is 0. (There's never a valid object at NULL, making it an
 281                 // exception from the exception.)
 282                 // This is the dual to the special exception for offset-by-0
 283                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 284                 //
 285                 // Control flow is weird because we cannot early-return (to reach the
 286                 // `go_to_block` at the end).
 287                 let done = if a.is_bits() && b.is_bits() {
 288                     let a = a.to_machine_usize(self)?;
 289                     let b = b.to_machine_usize(self)?;
 290                     if a == b && a != 0 {
 291                         self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
 292                         true
 293                     } else {
 294                         false
 295                     }
 296                 } else {
 297                     false
 298                 };
 299
 300                 if !done {
 301                     // General case: we need two pointers.
 302                     let a = self.force_ptr(a)?;
 303                     let b = self.force_ptr(b)?;
 304                     if a.alloc_id != b.alloc_id {
 305                         throw_ub_format!(
 306                             "ptr_offset_from cannot compute offset of pointers into different \
 307                             allocations.",
 308                         );
 309                     }
 310                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 311                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 312                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 313                     let (val, _overflowed, _ty) =
 314                         self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
 315                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 316                     let val = ImmTy::from_scalar(val, isize_layout);
 317                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 318                     self.exact_div(val, size, dest)?;
 319                 }
 320             }
 321
 322             sym::transmute => {
 323                 self.copy_op_transmute(args[0], dest)?;
 324             }
 325             sym::simd_insert => {
 326                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 327                 let elem = args[2];
 328                 let input = args[0];
 329                 let (len, e_ty) = input.layout.ty.simd_size_and_type(self.tcx.tcx);
 330                 assert!(
 331                     index < len,
 332                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 333                     index,
 334                     e_ty,
 335                     len
 336                 );
 337                 assert_eq!(
 338                     input.layout, dest.layout,
 339                     "Return type `{}` must match vector type `{}`",
 340                     dest.layout.ty, input.layout.ty
 341                 );
 342                 assert_eq!(
 343                     elem.layout.ty, e_ty,
 344                     "Scalar element type `{}` must match vector element type `{}`",
 345                     elem.layout.ty, e_ty
 346                 );
 347
 348                 for i in 0..len {
 349                     let place = self.place_field(dest, i)?;
 350                     let value = if i == index { elem } else { self.operand_field(input, i)? };
 351                     self.copy_op(value, place)?;
 352                 }
 353             }
 354             sym::simd_extract => {
 355                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 356                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(self.tcx.tcx);
 357                 assert!(
 358                     index < len,
 359                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 360                     index,
 361                     e_ty,
 362                     len
 363                 );
 364                 assert_eq!(
 365                     e_ty, dest.layout.ty,
 366                     "Return type `{}` must match vector element type `{}`",
 367                     dest.layout.ty, e_ty
 368                 );
 369                 self.copy_op(self.operand_field(args[0], index)?, dest)?;
 370             }
 371             _ => return Ok(false),
 372         }
 373
 374         self.dump_place(*dest);
 375         self.go_to_block(ret);
 376         Ok(true)
 377     }
 378
 379     pub fn exact_div(
 380         &mut self,
 381         a: ImmTy<'tcx, M::PointerTag>,
 382         b: ImmTy<'tcx, M::PointerTag>,
 383         dest: PlaceTy<'tcx, M::PointerTag>,
 384     ) -> InterpResult<'tcx> {
 385         // Performs an exact division, resulting in undefined behavior where
 386         // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
 387         // First, check x % y != 0 (or if that computation overflows).
 388         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
 389         if overflow || res.to_bits(a.layout.size)? != 0 {
 390             // Then, check if `b` is -1, which is the "min_value / -1" case.
 391             let minus1 = Scalar::from_int(-1, dest.layout.size);
 392             let b_scalar = b.to_scalar().unwrap();
 393             if b_scalar == minus1 {
 394                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 395             } else {
 396                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 397             }
 398         }
 399         // `Rem` says this is all right, so we can let `Div` do its job.
 400         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 401     }
 402 }