compiler/rustc_const_eval/src/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 std::convert::TryFrom;
   6
   7 use rustc_hir::def_id::DefId;
   8 use rustc_middle::mir::{
   9     self,
  10     interpret::{ConstValue, GlobalId, InterpResult, Scalar},
  11     BinOp,
  12 };
  13 use rustc_middle::ty;
  14 use rustc_middle::ty::layout::LayoutOf as _;
  15 use rustc_middle::ty::subst::SubstsRef;
  16 use rustc_middle::ty::{Ty, TyCtxt};
  17 use rustc_span::symbol::{sym, Symbol};
  18 use rustc_target::abi::{Abi, Align, Primitive, Size};
  19
  20 use super::{
  21     util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
  22     Pointer,
  23 };
  24
  25 mod caller_location;
  26 mod type_name;
  27
  28 fn numeric_intrinsic<Tag>(name: Symbol, bits: u128, kind: Primitive) -> Scalar<Tag> {
  29     let size = match kind {
  30         Primitive::Int(integer, _) => integer.size(),
  31         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  32     };
  33     let extra = 128 - u128::from(size.bits());
  34     let bits_out = match name {
  35         sym::ctpop => u128::from(bits.count_ones()),
  36         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  37         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  38         sym::bswap => (bits << extra).swap_bytes(),
  39         sym::bitreverse => (bits << extra).reverse_bits(),
  40         _ => bug!("not a numeric intrinsic: {}", name),
  41     };
  42     Scalar::from_uint(bits_out, size)
  43 }
  44
  45 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  46 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  47 crate fn eval_nullary_intrinsic<'tcx>(
  48     tcx: TyCtxt<'tcx>,
  49     param_env: ty::ParamEnv<'tcx>,
  50     def_id: DefId,
  51     substs: SubstsRef<'tcx>,
  52 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  53     let tp_ty = substs.type_at(0);
  54     let name = tcx.item_name(def_id);
  55     Ok(match name {
  56         sym::type_name => {
  57             ensure_monomorphic_enough(tcx, tp_ty)?;
  58             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  59             ConstValue::Slice { data: alloc, start: 0, end: alloc.inner().len() }
  60         }
  61         sym::needs_drop => {
  62             ensure_monomorphic_enough(tcx, tp_ty)?;
  63             ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env))
  64         }
  65         sym::pref_align_of => {
  66             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  67             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  68             ConstValue::from_machine_usize(layout.align.pref.bytes(), &tcx)
  69         }
  70         sym::type_id => {
  71             ensure_monomorphic_enough(tcx, tp_ty)?;
  72             ConstValue::from_u64(tcx.type_id_hash(tp_ty))
  73         }
  74         sym::variant_count => match tp_ty.kind() {
  75             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  76             ty::Adt(ref adt, _) => ConstValue::from_machine_usize(adt.variants.len() as u64, &tcx),
  77             ty::Projection(_)
  78             | ty::Opaque(_, _)
  79             | ty::Param(_)
  80             | ty::Bound(_, _)
  81             | ty::Placeholder(_)
  82             | ty::Infer(_) => throw_inval!(TooGeneric),
  83             ty::Bool
  84             | ty::Char
  85             | ty::Int(_)
  86             | ty::Uint(_)
  87             | ty::Float(_)
  88             | ty::Foreign(_)
  89             | ty::Str
  90             | ty::Array(_, _)
  91             | ty::Slice(_)
  92             | ty::RawPtr(_)
  93             | ty::Ref(_, _, _)
  94             | ty::FnDef(_, _)
  95             | ty::FnPtr(_)
  96             | ty::Dynamic(_, _)
  97             | ty::Closure(_, _)
  98             | ty::Generator(_, _, _)
  99             | ty::GeneratorWitness(_)
 100             | ty::Never
 101             | ty::Tuple(_)
 102             | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
 103         },
 104         other => bug!("`{}` is not a zero arg intrinsic", other),
 105     })
 106 }
 107
 108 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 109     /// Returns `true` if emulation happened.
 110     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
 111     /// intrinsic handling.
 112     pub fn emulate_intrinsic(
 113         &mut self,
 114         instance: ty::Instance<'tcx>,
 115         args: &[OpTy<'tcx, M::PointerTag>],
 116         ret: Option<(&PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
 117     ) -> InterpResult<'tcx, bool> {
 118         let substs = instance.substs;
 119         let intrinsic_name = self.tcx.item_name(instance.def_id());
 120
 121         // First handle intrinsics without return place.
 122         let (dest, ret) = match ret {
 123             None => match intrinsic_name {
 124                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 125                 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
 126                 // Unsupported diverging intrinsic.
 127                 _ => return Ok(false),
 128             },
 129             Some(p) => p,
 130         };
 131
 132         // Keep the patterns in this match ordered the same as the list in
 133         // `src/librustc_middle/ty/constness.rs`
 134         match intrinsic_name {
 135             sym::caller_location => {
 136                 let span = self.find_closest_untracked_caller_location();
 137                 let location = self.alloc_caller_location_for_span(span);
 138                 self.write_immediate(location.to_ref(self), dest)?;
 139             }
 140
 141             sym::min_align_of_val | sym::size_of_val => {
 142                 // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
 143                 // dereferenceable!
 144                 let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
 145                 let (size, align) = self
 146                     .size_and_align_of_mplace(&place)?
 147                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 148
 149                 let result = match intrinsic_name {
 150                     sym::min_align_of_val => align.bytes(),
 151                     sym::size_of_val => size.bytes(),
 152                     _ => bug!(),
 153                 };
 154
 155                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
 156             }
 157
 158             sym::pref_align_of
 159             | sym::needs_drop
 160             | sym::type_id
 161             | sym::type_name
 162             | sym::variant_count => {
 163                 let gid = GlobalId { instance, promoted: None };
 164                 let ty = match intrinsic_name {
 165                     sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
 166                     sym::needs_drop => self.tcx.types.bool,
 167                     sym::type_id => self.tcx.types.u64,
 168                     sym::type_name => self.tcx.mk_static_str(),
 169                     _ => bug!("already checked for nullary intrinsics"),
 170                 };
 171                 let val =
 172                     self.tcx.const_eval_global_id(self.param_env, gid, Some(self.tcx.span))?;
 173                 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
 174                 self.copy_op(&val, dest)?;
 175             }
 176
 177             sym::ctpop
 178             | sym::cttz
 179             | sym::cttz_nonzero
 180             | sym::ctlz
 181             | sym::ctlz_nonzero
 182             | sym::bswap
 183             | sym::bitreverse => {
 184                 let ty = substs.type_at(0);
 185                 let layout_of = self.layout_of(ty)?;
 186                 let val = self.read_scalar(&args[0])?.check_init()?;
 187                 let bits = val.to_bits(layout_of.size)?;
 188                 let kind = match layout_of.abi {
 189                     Abi::Scalar(scalar) => scalar.value,
 190                     _ => span_bug!(
 191                         self.cur_span(),
 192                         "{} called on invalid type {:?}",
 193                         intrinsic_name,
 194                         ty
 195                     ),
 196                 };
 197                 let (nonzero, intrinsic_name) = match intrinsic_name {
 198                     sym::cttz_nonzero => (true, sym::cttz),
 199                     sym::ctlz_nonzero => (true, sym::ctlz),
 200                     other => (false, other),
 201                 };
 202                 if nonzero && bits == 0 {
 203                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 204                 }
 205                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
 206                 self.write_scalar(out_val, dest)?;
 207             }
 208             sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
 209                 let lhs = self.read_immediate(&args[0])?;
 210                 let rhs = self.read_immediate(&args[1])?;
 211                 let bin_op = match intrinsic_name {
 212                     sym::add_with_overflow => BinOp::Add,
 213                     sym::sub_with_overflow => BinOp::Sub,
 214                     sym::mul_with_overflow => BinOp::Mul,
 215                     _ => bug!("Already checked for int ops"),
 216                 };
 217                 self.binop_with_overflow(bin_op, &lhs, &rhs, dest)?;
 218             }
 219             sym::saturating_add | sym::saturating_sub => {
 220                 let l = self.read_immediate(&args[0])?;
 221                 let r = self.read_immediate(&args[1])?;
 222                 let val = self.saturating_arith(
 223                     if intrinsic_name == sym::saturating_add { BinOp::Add } else { BinOp::Sub },
 224                     &l,
 225                     &r,
 226                 )?;
 227                 self.write_scalar(val, dest)?;
 228             }
 229             sym::discriminant_value => {
 230                 let place = self.deref_operand(&args[0])?;
 231                 let discr_val = self.read_discriminant(&place.into())?.0;
 232                 self.write_scalar(discr_val, dest)?;
 233             }
 234             sym::unchecked_shl
 235             | sym::unchecked_shr
 236             | sym::unchecked_add
 237             | sym::unchecked_sub
 238             | sym::unchecked_mul
 239             | sym::unchecked_div
 240             | sym::unchecked_rem => {
 241                 let l = self.read_immediate(&args[0])?;
 242                 let r = self.read_immediate(&args[1])?;
 243                 let bin_op = match intrinsic_name {
 244                     sym::unchecked_shl => BinOp::Shl,
 245                     sym::unchecked_shr => BinOp::Shr,
 246                     sym::unchecked_add => BinOp::Add,
 247                     sym::unchecked_sub => BinOp::Sub,
 248                     sym::unchecked_mul => BinOp::Mul,
 249                     sym::unchecked_div => BinOp::Div,
 250                     sym::unchecked_rem => BinOp::Rem,
 251                     _ => bug!("Already checked for int ops"),
 252                 };
 253                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
 254                 if overflowed {
 255                     let layout = self.layout_of(substs.type_at(0))?;
 256                     let r_val = r.to_scalar()?.to_bits(layout.size)?;
 257                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 258                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 259                     } else {
 260                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 261                     }
 262                 }
 263                 self.write_scalar(val, dest)?;
 264             }
 265             sym::rotate_left | sym::rotate_right => {
 266                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 267                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 268                 let layout = self.layout_of(substs.type_at(0))?;
 269                 let val = self.read_scalar(&args[0])?.check_init()?;
 270                 let val_bits = val.to_bits(layout.size)?;
 271                 let raw_shift = self.read_scalar(&args[1])?.check_init()?;
 272                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
 273                 let width_bits = u128::from(layout.size.bits());
 274                 let shift_bits = raw_shift_bits % width_bits;
 275                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 276                 let result_bits = if intrinsic_name == sym::rotate_left {
 277                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 278                 } else {
 279                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 280                 };
 281                 let truncated_bits = self.truncate(result_bits, layout);
 282                 let result = Scalar::from_uint(truncated_bits, layout.size);
 283                 self.write_scalar(result, dest)?;
 284             }
 285             sym::copy => {
 286                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
 287             }
 288             sym::write_bytes => {
 289                 self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
 290             }
 291             sym::offset => {
 292                 let ptr = self.read_pointer(&args[0])?;
 293                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 294                 let pointee_ty = substs.type_at(0);
 295
 296                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 297                 self.write_pointer(offset_ptr, dest)?;
 298             }
 299             sym::arith_offset => {
 300                 let ptr = self.read_pointer(&args[0])?;
 301                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 302                 let pointee_ty = substs.type_at(0);
 303
 304                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 305                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 306                 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
 307                 self.write_pointer(offset_ptr, dest)?;
 308             }
 309             sym::ptr_offset_from => {
 310                 let a = self.read_immediate(&args[0])?.to_scalar()?;
 311                 let b = self.read_immediate(&args[1])?.to_scalar()?;
 312
 313                 // Special case: if both scalars are *equal integers*
 314                 // and not null, we pretend there is an allocation of size 0 right there,
 315                 // and their offset is 0. (There's never a valid object at null, making it an
 316                 // exception from the exception.)
 317                 // This is the dual to the special exception for offset-by-0
 318                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 319                 //
 320                 // Control flow is weird because we cannot early-return (to reach the
 321                 // `go_to_block` at the end).
 322                 let done = if let (Ok(a), Ok(b)) = (a.try_to_int(), b.try_to_int()) {
 323                     let a = a.try_to_machine_usize(*self.tcx).unwrap();
 324                     let b = b.try_to_machine_usize(*self.tcx).unwrap();
 325                     if a == b && a != 0 {
 326                         self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
 327                         true
 328                     } else {
 329                         false
 330                     }
 331                 } else {
 332                     false
 333                 };
 334
 335                 if !done {
 336                     // General case: we need two pointers.
 337                     let a = self.scalar_to_ptr(a);
 338                     let b = self.scalar_to_ptr(b);
 339                     let (a_alloc_id, a_offset, _) = self.memory.ptr_get_alloc(a)?;
 340                     let (b_alloc_id, b_offset, _) = self.memory.ptr_get_alloc(b)?;
 341                     if a_alloc_id != b_alloc_id {
 342                         throw_ub_format!(
 343                             "ptr_offset_from cannot compute offset of pointers into different \
 344                             allocations.",
 345                         );
 346                     }
 347                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 348                     let isize_layout = self.layout_of(self.tcx.types.isize)?;
 349                     let a_offset = ImmTy::from_uint(a_offset.bytes(), usize_layout);
 350                     let b_offset = ImmTy::from_uint(b_offset.bytes(), usize_layout);
 351                     let (val, _overflowed, _ty) =
 352                         self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?;
 353                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 354                     let val = ImmTy::from_scalar(val, isize_layout);
 355                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 356                     self.exact_div(&val, &size, dest)?;
 357                 }
 358             }
 359
 360             sym::transmute => {
 361                 self.copy_op_transmute(&args[0], dest)?;
 362             }
 363             sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
 364                 let ty = instance.substs.type_at(0);
 365                 let layout = self.layout_of(ty)?;
 366
 367                 // For *all* intrinsics we first check `is_uninhabited` to give a more specific
 368                 // error message.
 369                 if layout.abi.is_uninhabited() {
 370                     // The run-time intrinsic panics just to get a good backtrace; here we abort
 371                     // since there is no problem showing a backtrace even for aborts.
 372                     M::abort(
 373                         self,
 374                         format!(
 375                             "aborted execution: attempted to instantiate uninhabited type `{}`",
 376                             ty
 377                         ),
 378                     )?;
 379                 }
 380                 if intrinsic_name == sym::assert_zero_valid
 381                     && !layout.might_permit_raw_init(self, /*zero:*/ true)
 382                 {
 383                     M::abort(
 384                         self,
 385                         format!(
 386                             "aborted execution: attempted to zero-initialize type `{}`, which is invalid",
 387                             ty
 388                         ),
 389                     )?;
 390                 }
 391                 if intrinsic_name == sym::assert_uninit_valid
 392                     && !layout.might_permit_raw_init(self, /*zero:*/ false)
 393                 {
 394                     M::abort(
 395                         self,
 396                         format!(
 397                             "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
 398                             ty
 399                         ),
 400                     )?;
 401                 }
 402             }
 403             sym::simd_insert => {
 404                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 405                 let elem = &args[2];
 406                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 407                 let (dest, dest_len) = self.place_to_simd(dest)?;
 408                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
 409                 assert!(
 410                     index < dest_len,
 411                     "Index `{}` must be in bounds of vector with length {}`",
 412                     index,
 413                     dest_len
 414                 );
 415
 416                 for i in 0..dest_len {
 417                     let place = self.mplace_index(&dest, i)?;
 418                     let value =
 419                         if i == index { *elem } else { self.mplace_index(&input, i)?.into() };
 420                     self.copy_op(&value, &place.into())?;
 421                 }
 422             }
 423             sym::simd_extract => {
 424                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 425                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 426                 assert!(
 427                     index < input_len,
 428                     "index `{}` must be in bounds of vector with length `{}`",
 429                     index,
 430                     input_len
 431                 );
 432                 self.copy_op(&self.mplace_index(&input, index)?.into(), dest)?;
 433             }
 434             sym::likely | sym::unlikely | sym::black_box => {
 435                 // These just return their argument
 436                 self.copy_op(&args[0], dest)?;
 437             }
 438             sym::assume => {
 439                 let cond = self.read_scalar(&args[0])?.check_init()?.to_bool()?;
 440                 if !cond {
 441                     throw_ub_format!("`assume` intrinsic called with `false`");
 442                 }
 443             }
 444             sym::raw_eq => {
 445                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
 446                 self.write_scalar(result, dest)?;
 447             }
 448             _ => return Ok(false),
 449         }
 450
 451         trace!("{:?}", self.dump_place(**dest));
 452         self.go_to_block(ret);
 453         Ok(true)
 454     }
 455
 456     pub fn exact_div(
 457         &mut self,
 458         a: &ImmTy<'tcx, M::PointerTag>,
 459         b: &ImmTy<'tcx, M::PointerTag>,
 460         dest: &PlaceTy<'tcx, M::PointerTag>,
 461     ) -> InterpResult<'tcx> {
 462         // Performs an exact division, resulting in undefined behavior where
 463         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 464         // First, check x % y != 0 (or if that computation overflows).
 465         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
 466         assert!(!overflow); // All overflow is UB, so this should never return on overflow.
 467         if res.assert_bits(a.layout.size) != 0 {
 468             throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
 469         }
 470         // `Rem` says this is all right, so we can let `Div` do its job.
 471         self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
 472     }
 473
 474     pub fn saturating_arith(
 475         &self,
 476         mir_op: BinOp,
 477         l: &ImmTy<'tcx, M::PointerTag>,
 478         r: &ImmTy<'tcx, M::PointerTag>,
 479     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 480         assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
 481         let (val, overflowed, _ty) = self.overflowing_binary_op(mir_op, l, r)?;
 482         Ok(if overflowed {
 483             let size = l.layout.size;
 484             let num_bits = size.bits();
 485             if l.layout.abi.is_signed() {
 486                 // For signed ints the saturated value depends on the sign of the first
 487                 // term since the sign of the second term can be inferred from this and
 488                 // the fact that the operation has overflowed (if either is 0 no
 489                 // overflow can occur)
 490                 let first_term: u128 = l.to_scalar()?.to_bits(l.layout.size)?;
 491                 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 492                 if first_term_positive {
 493                     // Negative overflow not possible since the positive first term
 494                     // can only increase an (in range) negative term for addition
 495                     // or corresponding negated positive term for subtraction
 496                     Scalar::from_int(size.signed_int_max(), size)
 497                 } else {
 498                     // Positive overflow not possible for similar reason
 499                     // max negative
 500                     Scalar::from_int(size.signed_int_min(), size)
 501                 }
 502             } else {
 503                 // unsigned
 504                 if matches!(mir_op, BinOp::Add) {
 505                     // max unsigned
 506                     Scalar::from_uint(size.unsigned_int_max(), size)
 507                 } else {
 508                     // underflow to 0
 509                     Scalar::from_uint(0u128, size)
 510                 }
 511             }
 512         } else {
 513             val
 514         })
 515     }
 516
 517     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 518     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 519     /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
 520     pub fn ptr_offset_inbounds(
 521         &self,
 522         ptr: Pointer<Option<M::PointerTag>>,
 523         pointee_ty: Ty<'tcx>,
 524         offset_count: i64,
 525     ) -> InterpResult<'tcx, Pointer<Option<M::PointerTag>>> {
 526         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 527         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 528         // The computed offset, in bytes, cannot overflow an isize.
 529         let offset_bytes =
 530             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 531         // The offset being in bounds cannot rely on "wrapping around" the address space.
 532         // So, first rule out overflows in the pointer arithmetic.
 533         let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
 534         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 535         // memory between these pointers must be accessible. Note that we do not require the
 536         // pointers to be properly aligned (unlike a read/write operation).
 537         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 538         let size = offset_bytes.unsigned_abs();
 539         // This call handles checking for integer/null pointers.
 540         self.memory.check_ptr_access_align(
 541             min_ptr,
 542             Size::from_bytes(size),
 543             Align::ONE,
 544             CheckInAllocMsg::PointerArithmeticTest,
 545         )?;
 546         Ok(offset_ptr)
 547     }
 548
 549     /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
 550     pub(crate) fn copy_intrinsic(
 551         &mut self,
 552         src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 553         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 554         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 555         nonoverlapping: bool,
 556     ) -> InterpResult<'tcx> {
 557         let count = self.read_scalar(&count)?.to_machine_usize(self)?;
 558         let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
 559         let (size, align) = (layout.size, layout.align.abi);
 560         let size = size.checked_mul(count, self).ok_or_else(|| {
 561             err_ub_format!(
 562                 "overflow computing total size of `{}`",
 563                 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
 564             )
 565         })?;
 566
 567         let src = self.read_pointer(&src)?;
 568         let dst = self.read_pointer(&dst)?;
 569
 570         self.memory.copy(src, align, dst, align, size, nonoverlapping)
 571     }
 572
 573     pub(crate) fn write_bytes_intrinsic(
 574         &mut self,
 575         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 576         byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 577         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 578     ) -> InterpResult<'tcx> {
 579         let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
 580
 581         let dst = self.read_pointer(&dst)?;
 582         let byte = self.read_scalar(&byte)?.to_u8()?;
 583         let count = self.read_scalar(&count)?.to_machine_usize(self)?;
 584
 585         let len = layout
 586             .size
 587             .checked_mul(count, self)
 588             .ok_or_else(|| err_ub_format!("overflow computing total size of `write_bytes`"))?;
 589
 590         let bytes = std::iter::repeat(byte).take(len.bytes_usize());
 591         self.memory.write_bytes(dst, bytes)
 592     }
 593
 594     pub(crate) fn raw_eq_intrinsic(
 595         &mut self,
 596         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 597         rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 598     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 599         let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
 600         assert!(!layout.is_unsized());
 601
 602         let lhs = self.read_pointer(lhs)?;
 603         let rhs = self.read_pointer(rhs)?;
 604         let lhs_bytes = self.memory.read_bytes(lhs, layout.size)?;
 605         let rhs_bytes = self.memory.read_bytes(rhs, layout.size)?;
 606         Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
 607     }
 608 }