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.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                 // dereferencable!
 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 is_add = intrinsic_name == sym::saturating_add;
 223                 let (val, overflowed, _ty) = self.overflowing_binary_op(
 224                     if is_add { BinOp::Add } else { BinOp::Sub },
 225                     &l,
 226                     &r,
 227                 )?;
 228                 let val = if overflowed {
 229                     let size = l.layout.size;
 230                     let num_bits = size.bits();
 231                     if l.layout.abi.is_signed() {
 232                         // For signed ints the saturated value depends on the sign of the first
 233                         // term since the sign of the second term can be inferred from this and
 234                         // the fact that the operation has overflowed (if either is 0 no
 235                         // overflow can occur)
 236                         let first_term: u128 = l.to_scalar()?.to_bits(l.layout.size)?;
 237                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 238                         if first_term_positive {
 239                             // Negative overflow not possible since the positive first term
 240                             // can only increase an (in range) negative term for addition
 241                             // or corresponding negated positive term for subtraction
 242                             Scalar::from_uint(
 243                                 (1u128 << (num_bits - 1)) - 1, // max positive
 244                                 Size::from_bits(num_bits),
 245                             )
 246                         } else {
 247                             // Positive overflow not possible for similar reason
 248                             // max negative
 249                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 250                         }
 251                     } else {
 252                         // unsigned
 253                         if is_add {
 254                             // max unsigned
 255                             Scalar::from_uint(size.unsigned_int_max(), Size::from_bits(num_bits))
 256                         } else {
 257                             // underflow to 0
 258                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 259                         }
 260                     }
 261                 } else {
 262                     val
 263                 };
 264                 self.write_scalar(val, dest)?;
 265             }
 266             sym::discriminant_value => {
 267                 let place = self.deref_operand(&args[0])?;
 268                 let discr_val = self.read_discriminant(&place.into())?.0;
 269                 self.write_scalar(discr_val, dest)?;
 270             }
 271             sym::unchecked_shl
 272             | sym::unchecked_shr
 273             | sym::unchecked_add
 274             | sym::unchecked_sub
 275             | sym::unchecked_mul
 276             | sym::unchecked_div
 277             | sym::unchecked_rem => {
 278                 let l = self.read_immediate(&args[0])?;
 279                 let r = self.read_immediate(&args[1])?;
 280                 let bin_op = match intrinsic_name {
 281                     sym::unchecked_shl => BinOp::Shl,
 282                     sym::unchecked_shr => BinOp::Shr,
 283                     sym::unchecked_add => BinOp::Add,
 284                     sym::unchecked_sub => BinOp::Sub,
 285                     sym::unchecked_mul => BinOp::Mul,
 286                     sym::unchecked_div => BinOp::Div,
 287                     sym::unchecked_rem => BinOp::Rem,
 288                     _ => bug!("Already checked for int ops"),
 289                 };
 290                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
 291                 if overflowed {
 292                     let layout = self.layout_of(substs.type_at(0))?;
 293                     let r_val = r.to_scalar()?.to_bits(layout.size)?;
 294                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 295                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 296                     } else {
 297                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 298                     }
 299                 }
 300                 self.write_scalar(val, dest)?;
 301             }
 302             sym::rotate_left | sym::rotate_right => {
 303                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 304                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 305                 let layout = self.layout_of(substs.type_at(0))?;
 306                 let val = self.read_scalar(&args[0])?.check_init()?;
 307                 let val_bits = val.to_bits(layout.size)?;
 308                 let raw_shift = self.read_scalar(&args[1])?.check_init()?;
 309                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
 310                 let width_bits = u128::from(layout.size.bits());
 311                 let shift_bits = raw_shift_bits % width_bits;
 312                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 313                 let result_bits = if intrinsic_name == sym::rotate_left {
 314                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 315                 } else {
 316                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 317                 };
 318                 let truncated_bits = self.truncate(result_bits, layout);
 319                 let result = Scalar::from_uint(truncated_bits, layout.size);
 320                 self.write_scalar(result, dest)?;
 321             }
 322             sym::copy => {
 323                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
 324             }
 325             sym::offset => {
 326                 let ptr = self.read_pointer(&args[0])?;
 327                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 328                 let pointee_ty = substs.type_at(0);
 329
 330                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 331                 self.write_pointer(offset_ptr, dest)?;
 332             }
 333             sym::arith_offset => {
 334                 let ptr = self.read_pointer(&args[0])?;
 335                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 336                 let pointee_ty = substs.type_at(0);
 337
 338                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 339                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 340                 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
 341                 self.write_pointer(offset_ptr, dest)?;
 342             }
 343             sym::ptr_offset_from => {
 344                 let a = self.read_immediate(&args[0])?.to_scalar()?;
 345                 let b = self.read_immediate(&args[1])?.to_scalar()?;
 346
 347                 // Special case: if both scalars are *equal integers*
 348                 // and not null, we pretend there is an allocation of size 0 right there,
 349                 // and their offset is 0. (There's never a valid object at null, making it an
 350                 // exception from the exception.)
 351                 // This is the dual to the special exception for offset-by-0
 352                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 353                 //
 354                 // Control flow is weird because we cannot early-return (to reach the
 355                 // `go_to_block` at the end).
 356                 let done = if let (Ok(a), Ok(b)) = (a.try_to_int(), b.try_to_int()) {
 357                     let a = a.try_to_machine_usize(*self.tcx).unwrap();
 358                     let b = b.try_to_machine_usize(*self.tcx).unwrap();
 359                     if a == b && a != 0 {
 360                         self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
 361                         true
 362                     } else {
 363                         false
 364                     }
 365                 } else {
 366                     false
 367                 };
 368
 369                 if !done {
 370                     // General case: we need two pointers.
 371                     let a = self.scalar_to_ptr(a);
 372                     let b = self.scalar_to_ptr(b);
 373                     let (a_alloc_id, a_offset, _) = self.memory.ptr_get_alloc(a)?;
 374                     let (b_alloc_id, b_offset, _) = self.memory.ptr_get_alloc(b)?;
 375                     if a_alloc_id != b_alloc_id {
 376                         throw_ub_format!(
 377                             "ptr_offset_from cannot compute offset of pointers into different \
 378                             allocations.",
 379                         );
 380                     }
 381                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 382                     let isize_layout = self.layout_of(self.tcx.types.isize)?;
 383                     let a_offset = ImmTy::from_uint(a_offset.bytes(), usize_layout);
 384                     let b_offset = ImmTy::from_uint(b_offset.bytes(), usize_layout);
 385                     let (val, _overflowed, _ty) =
 386                         self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?;
 387                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 388                     let val = ImmTy::from_scalar(val, isize_layout);
 389                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 390                     self.exact_div(&val, &size, dest)?;
 391                 }
 392             }
 393
 394             sym::transmute => {
 395                 self.copy_op_transmute(&args[0], dest)?;
 396             }
 397             sym::assert_inhabited => {
 398                 let ty = instance.substs.type_at(0);
 399                 let layout = self.layout_of(ty)?;
 400
 401                 if layout.abi.is_uninhabited() {
 402                     // The run-time intrinsic panics just to get a good backtrace; here we abort
 403                     // since there is no problem showing a backtrace even for aborts.
 404                     M::abort(
 405                         self,
 406                         format!(
 407                             "aborted execution: attempted to instantiate uninhabited type `{}`",
 408                             ty
 409                         ),
 410                     )?;
 411                 }
 412             }
 413             sym::simd_insert => {
 414                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 415                 let elem = &args[2];
 416                 let input = &args[0];
 417                 let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx);
 418                 assert!(
 419                     index < len,
 420                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 421                     index,
 422                     e_ty,
 423                     len
 424                 );
 425                 assert_eq!(
 426                     input.layout, dest.layout,
 427                     "Return type `{}` must match vector type `{}`",
 428                     dest.layout.ty, input.layout.ty
 429                 );
 430                 assert_eq!(
 431                     elem.layout.ty, e_ty,
 432                     "Scalar element type `{}` must match vector element type `{}`",
 433                     elem.layout.ty, e_ty
 434                 );
 435
 436                 for i in 0..len {
 437                     let place = self.place_index(dest, i)?;
 438                     let value = if i == index { *elem } else { self.operand_index(input, i)? };
 439                     self.copy_op(&value, &place)?;
 440                 }
 441             }
 442             sym::simd_extract => {
 443                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 444                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx);
 445                 assert!(
 446                     index < len,
 447                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 448                     index,
 449                     e_ty,
 450                     len
 451                 );
 452                 assert_eq!(
 453                     e_ty, dest.layout.ty,
 454                     "Return type `{}` must match vector element type `{}`",
 455                     dest.layout.ty, e_ty
 456                 );
 457                 self.copy_op(&self.operand_index(&args[0], index)?, dest)?;
 458             }
 459             sym::likely | sym::unlikely | sym::black_box => {
 460                 // These just return their argument
 461                 self.copy_op(&args[0], dest)?;
 462             }
 463             sym::assume => {
 464                 let cond = self.read_scalar(&args[0])?.check_init()?.to_bool()?;
 465                 if !cond {
 466                     throw_ub_format!("`assume` intrinsic called with `false`");
 467                 }
 468             }
 469             sym::raw_eq => {
 470                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
 471                 self.write_scalar(result, dest)?;
 472             }
 473             _ => return Ok(false),
 474         }
 475
 476         trace!("{:?}", self.dump_place(**dest));
 477         self.go_to_block(ret);
 478         Ok(true)
 479     }
 480
 481     pub fn exact_div(
 482         &mut self,
 483         a: &ImmTy<'tcx, M::PointerTag>,
 484         b: &ImmTy<'tcx, M::PointerTag>,
 485         dest: &PlaceTy<'tcx, M::PointerTag>,
 486     ) -> InterpResult<'tcx> {
 487         // Performs an exact division, resulting in undefined behavior where
 488         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 489         // First, check x % y != 0 (or if that computation overflows).
 490         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
 491         if overflow || res.assert_bits(a.layout.size) != 0 {
 492             // Then, check if `b` is -1, which is the "MIN / -1" case.
 493             let minus1 = Scalar::from_int(-1, dest.layout.size);
 494             let b_scalar = b.to_scalar().unwrap();
 495             if b_scalar == minus1 {
 496                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 497             } else {
 498                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 499             }
 500         }
 501         // `Rem` says this is all right, so we can let `Div` do its job.
 502         self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
 503     }
 504
 505     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 506     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 507     /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
 508     pub fn ptr_offset_inbounds(
 509         &self,
 510         ptr: Pointer<Option<M::PointerTag>>,
 511         pointee_ty: Ty<'tcx>,
 512         offset_count: i64,
 513     ) -> InterpResult<'tcx, Pointer<Option<M::PointerTag>>> {
 514         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 515         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 516         // The computed offset, in bytes, cannot overflow an isize.
 517         let offset_bytes =
 518             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 519         // The offset being in bounds cannot rely on "wrapping around" the address space.
 520         // So, first rule out overflows in the pointer arithmetic.
 521         let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
 522         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 523         // memory between these pointers must be accessible. Note that we do not require the
 524         // pointers to be properly aligned (unlike a read/write operation).
 525         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 526         let size = offset_bytes.unsigned_abs();
 527         // This call handles checking for integer/null pointers.
 528         self.memory.check_ptr_access_align(
 529             min_ptr,
 530             Size::from_bytes(size),
 531             Align::ONE,
 532             CheckInAllocMsg::PointerArithmeticTest,
 533         )?;
 534         Ok(offset_ptr)
 535     }
 536
 537     /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
 538     pub(crate) fn copy_intrinsic(
 539         &mut self,
 540         src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 541         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 542         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 543         nonoverlapping: bool,
 544     ) -> InterpResult<'tcx> {
 545         let count = self.read_scalar(&count)?.to_machine_usize(self)?;
 546         let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
 547         let (size, align) = (layout.size, layout.align.abi);
 548         let size = size.checked_mul(count, self).ok_or_else(|| {
 549             err_ub_format!(
 550                 "overflow computing total size of `{}`",
 551                 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
 552             )
 553         })?;
 554
 555         let src = self.read_pointer(&src)?;
 556         let dst = self.read_pointer(&dst)?;
 557
 558         self.memory.copy(src, align, dst, align, size, nonoverlapping)
 559     }
 560
 561     pub(crate) fn raw_eq_intrinsic(
 562         &mut self,
 563         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 564         rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
 565     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 566         let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
 567         assert!(!layout.is_unsized());
 568
 569         let lhs = self.read_pointer(lhs)?;
 570         let rhs = self.read_pointer(rhs)?;
 571         let lhs_bytes = self.memory.read_bytes(lhs, layout.size)?;
 572         let rhs_bytes = self.memory.read_bytes(rhs, layout.size)?;
 573         Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
 574     }
 575 }