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 rustc_hir::def_id::DefId;
   6 use rustc_middle::mir::{
   7     self,
   8     interpret::{
   9         Allocation, ConstAllocation, ConstValue, GlobalId, InterpResult, PointerArithmetic, Scalar,
  10     },
  11     BinOp, NonDivergingIntrinsic,
  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
  27 fn numeric_intrinsic<Prov>(name: Symbol, bits: u128, kind: Primitive) -> Scalar<Prov> {
  28     let size = match kind {
  29         Primitive::Int(integer, _) => integer.size(),
  30         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  31     };
  32     let extra = 128 - u128::from(size.bits());
  33     let bits_out = match name {
  34         sym::ctpop => u128::from(bits.count_ones()),
  35         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  36         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  37         sym::bswap => (bits << extra).swap_bytes(),
  38         sym::bitreverse => (bits << extra).reverse_bits(),
  39         _ => bug!("not a numeric intrinsic: {}", name),
  40     };
  41     Scalar::from_uint(bits_out, size)
  42 }
  43
  44 /// Directly returns an `Allocation` containing an absolute path representation of the given type.
  45 pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAllocation<'tcx> {
  46     let path = crate::util::type_name(tcx, ty);
  47     let alloc = Allocation::from_bytes_byte_aligned_immutable(path.into_bytes());
  48     tcx.intern_const_alloc(alloc)
  49 }
  50
  51 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  52 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  53 pub(crate) fn eval_nullary_intrinsic<'tcx>(
  54     tcx: TyCtxt<'tcx>,
  55     param_env: ty::ParamEnv<'tcx>,
  56     def_id: DefId,
  57     substs: SubstsRef<'tcx>,
  58 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  59     let tp_ty = substs.type_at(0);
  60     let name = tcx.item_name(def_id);
  61     Ok(match name {
  62         sym::type_name => {
  63             ensure_monomorphic_enough(tcx, tp_ty)?;
  64             let alloc = alloc_type_name(tcx, tp_ty);
  65             ConstValue::Slice { data: alloc, start: 0, end: alloc.inner().len() }
  66         }
  67         sym::needs_drop => {
  68             ensure_monomorphic_enough(tcx, tp_ty)?;
  69             ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env))
  70         }
  71         sym::pref_align_of => {
  72             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  73             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  74             ConstValue::from_machine_usize(layout.align.pref.bytes(), &tcx)
  75         }
  76         sym::type_id => {
  77             ensure_monomorphic_enough(tcx, tp_ty)?;
  78             ConstValue::from_u64(tcx.type_id_hash(tp_ty))
  79         }
  80         sym::variant_count => match tp_ty.kind() {
  81             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  82             ty::Adt(adt, _) => ConstValue::from_machine_usize(adt.variants().len() as u64, &tcx),
  83             ty::Alias(..) | ty::Param(_) | ty::Placeholder(_) | ty::Infer(_) => {
  84                 throw_inval!(TooGeneric)
  85             }
  86             ty::Bound(_, _) => bug!("bound ty during ctfe"),
  87             ty::Bool
  88             | ty::Char
  89             | ty::Int(_)
  90             | ty::Uint(_)
  91             | ty::Float(_)
  92             | ty::Foreign(_)
  93             | ty::Str
  94             | ty::Array(_, _)
  95             | ty::Slice(_)
  96             | ty::RawPtr(_)
  97             | ty::Ref(_, _, _)
  98             | ty::FnDef(_, _)
  99             | ty::FnPtr(_)
 100             | ty::Dynamic(_, _, _)
 101             | ty::Closure(_, _)
 102             | ty::Generator(_, _, _)
 103             | ty::GeneratorWitness(_)
 104             | ty::Never
 105             | ty::Tuple(_)
 106             | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
 107         },
 108         other => bug!("`{}` is not a zero arg intrinsic", other),
 109     })
 110 }
 111
 112 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 113     /// Returns `true` if emulation happened.
 114     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
 115     /// intrinsic handling.
 116     pub fn emulate_intrinsic(
 117         &mut self,
 118         instance: ty::Instance<'tcx>,
 119         args: &[OpTy<'tcx, M::Provenance>],
 120         dest: &PlaceTy<'tcx, M::Provenance>,
 121         ret: Option<mir::BasicBlock>,
 122     ) -> InterpResult<'tcx, bool> {
 123         let substs = instance.substs;
 124         let intrinsic_name = self.tcx.item_name(instance.def_id());
 125
 126         // First handle intrinsics without return place.
 127         let ret = match ret {
 128             None => match intrinsic_name {
 129                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 130                 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
 131                 // Unsupported diverging intrinsic.
 132                 _ => return Ok(false),
 133             },
 134             Some(p) => p,
 135         };
 136
 137         match intrinsic_name {
 138             sym::caller_location => {
 139                 let span = self.find_closest_untracked_caller_location();
 140                 let location = self.alloc_caller_location_for_span(span);
 141                 self.write_immediate(location.to_ref(self), dest)?;
 142             }
 143
 144             sym::min_align_of_val | sym::size_of_val => {
 145                 // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
 146                 // dereferenceable!
 147                 let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
 148                 let (size, align) = self
 149                     .size_and_align_of_mplace(&place)?
 150                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 151
 152                 let result = match intrinsic_name {
 153                     sym::min_align_of_val => align.bytes(),
 154                     sym::size_of_val => size.bytes(),
 155                     _ => bug!(),
 156                 };
 157
 158                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
 159             }
 160
 161             sym::pref_align_of
 162             | sym::needs_drop
 163             | sym::type_id
 164             | sym::type_name
 165             | sym::variant_count => {
 166                 let gid = GlobalId { instance, promoted: None };
 167                 let ty = match intrinsic_name {
 168                     sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
 169                     sym::needs_drop => self.tcx.types.bool,
 170                     sym::type_id => self.tcx.types.u64,
 171                     sym::type_name => self.tcx.mk_static_str(),
 172                     _ => bug!(),
 173                 };
 174                 let val = self.ctfe_query(None, |tcx| {
 175                     tcx.const_eval_global_id(self.param_env, gid, Some(tcx.span))
 176                 })?;
 177                 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
 178                 self.copy_op(&val, dest, /*allow_transmute*/ false)?;
 179             }
 180
 181             sym::ctpop
 182             | sym::cttz
 183             | sym::cttz_nonzero
 184             | sym::ctlz
 185             | sym::ctlz_nonzero
 186             | sym::bswap
 187             | sym::bitreverse => {
 188                 let ty = substs.type_at(0);
 189                 let layout_of = self.layout_of(ty)?;
 190                 let val = self.read_scalar(&args[0])?;
 191                 let bits = val.to_bits(layout_of.size)?;
 192                 let kind = match layout_of.abi {
 193                     Abi::Scalar(scalar) => scalar.primitive(),
 194                     _ => span_bug!(
 195                         self.cur_span(),
 196                         "{} called on invalid type {:?}",
 197                         intrinsic_name,
 198                         ty
 199                     ),
 200                 };
 201                 let (nonzero, intrinsic_name) = match intrinsic_name {
 202                     sym::cttz_nonzero => (true, sym::cttz),
 203                     sym::ctlz_nonzero => (true, sym::ctlz),
 204                     other => (false, other),
 205                 };
 206                 if nonzero && bits == 0 {
 207                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 208                 }
 209                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
 210                 self.write_scalar(out_val, dest)?;
 211             }
 212             sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
 213                 let lhs = self.read_immediate(&args[0])?;
 214                 let rhs = self.read_immediate(&args[1])?;
 215                 let bin_op = match intrinsic_name {
 216                     sym::add_with_overflow => BinOp::Add,
 217                     sym::sub_with_overflow => BinOp::Sub,
 218                     sym::mul_with_overflow => BinOp::Mul,
 219                     _ => bug!(),
 220                 };
 221                 self.binop_with_overflow(
 222                     bin_op, /*force_overflow_checks*/ true, &lhs, &rhs, dest,
 223                 )?;
 224             }
 225             sym::saturating_add | sym::saturating_sub => {
 226                 let l = self.read_immediate(&args[0])?;
 227                 let r = self.read_immediate(&args[1])?;
 228                 let val = self.saturating_arith(
 229                     if intrinsic_name == sym::saturating_add { BinOp::Add } else { BinOp::Sub },
 230                     &l,
 231                     &r,
 232                 )?;
 233                 self.write_scalar(val, dest)?;
 234             }
 235             sym::discriminant_value => {
 236                 let place = self.deref_operand(&args[0])?;
 237                 let discr_val = self.read_discriminant(&place.into())?.0;
 238                 self.write_scalar(discr_val, dest)?;
 239             }
 240             sym::exact_div => {
 241                 let l = self.read_immediate(&args[0])?;
 242                 let r = self.read_immediate(&args[1])?;
 243                 self.exact_div(&l, &r, dest)?;
 244             }
 245             sym::unchecked_shl
 246             | sym::unchecked_shr
 247             | sym::unchecked_add
 248             | sym::unchecked_sub
 249             | sym::unchecked_mul
 250             | sym::unchecked_div
 251             | sym::unchecked_rem => {
 252                 let l = self.read_immediate(&args[0])?;
 253                 let r = self.read_immediate(&args[1])?;
 254                 let bin_op = match intrinsic_name {
 255                     sym::unchecked_shl => BinOp::Shl,
 256                     sym::unchecked_shr => BinOp::Shr,
 257                     sym::unchecked_add => BinOp::Add,
 258                     sym::unchecked_sub => BinOp::Sub,
 259                     sym::unchecked_mul => BinOp::Mul,
 260                     sym::unchecked_div => BinOp::Div,
 261                     sym::unchecked_rem => BinOp::Rem,
 262                     _ => bug!(),
 263                 };
 264                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
 265                 if overflowed {
 266                     let layout = self.layout_of(substs.type_at(0))?;
 267                     let r_val = r.to_scalar().to_bits(layout.size)?;
 268                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 269                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 270                     } else {
 271                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 272                     }
 273                 }
 274                 self.write_scalar(val, dest)?;
 275             }
 276             sym::rotate_left | sym::rotate_right => {
 277                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 278                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 279                 let layout = self.layout_of(substs.type_at(0))?;
 280                 let val = self.read_scalar(&args[0])?;
 281                 let val_bits = val.to_bits(layout.size)?;
 282                 let raw_shift = self.read_scalar(&args[1])?;
 283                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
 284                 let width_bits = u128::from(layout.size.bits());
 285                 let shift_bits = raw_shift_bits % width_bits;
 286                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 287                 let result_bits = if intrinsic_name == sym::rotate_left {
 288                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 289                 } else {
 290                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 291                 };
 292                 let truncated_bits = self.truncate(result_bits, layout);
 293                 let result = Scalar::from_uint(truncated_bits, layout.size);
 294                 self.write_scalar(result, dest)?;
 295             }
 296             sym::copy => {
 297                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
 298             }
 299             sym::write_bytes => {
 300                 self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
 301             }
 302             sym::offset => {
 303                 let ptr = self.read_pointer(&args[0])?;
 304                 let offset_count = self.read_machine_isize(&args[1])?;
 305                 let pointee_ty = substs.type_at(0);
 306
 307                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 308                 self.write_pointer(offset_ptr, dest)?;
 309             }
 310             sym::arith_offset => {
 311                 let ptr = self.read_pointer(&args[0])?;
 312                 let offset_count = self.read_machine_isize(&args[1])?;
 313                 let pointee_ty = substs.type_at(0);
 314
 315                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 316                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 317                 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
 318                 self.write_pointer(offset_ptr, dest)?;
 319             }
 320             sym::ptr_offset_from | sym::ptr_offset_from_unsigned => {
 321                 let a = self.read_pointer(&args[0])?;
 322                 let b = self.read_pointer(&args[1])?;
 323
 324                 let usize_layout = self.layout_of(self.tcx.types.usize)?;
 325                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 326
 327                 // Get offsets for both that are at least relative to the same base.
 328                 let (a_offset, b_offset) =
 329                     match (self.ptr_try_get_alloc_id(a), self.ptr_try_get_alloc_id(b)) {
 330                         (Err(a), Err(b)) => {
 331                             // Neither pointer points to an allocation.
 332                             // If these are inequal or null, this *will* fail the deref check below.
 333                             (a, b)
 334                         }
 335                         (Err(_), _) | (_, Err(_)) => {
 336                             // We managed to find a valid allocation for one pointer, but not the other.
 337                             // That means they are definitely not pointing to the same allocation.
 338                             throw_ub_format!(
 339                                 "`{}` called on pointers into different allocations",
 340                                 intrinsic_name
 341                             );
 342                         }
 343                         (Ok((a_alloc_id, a_offset, _)), Ok((b_alloc_id, b_offset, _))) => {
 344                             // Found allocation for both. They must be into the same allocation.
 345                             if a_alloc_id != b_alloc_id {
 346                                 throw_ub_format!(
 347                                     "`{}` called on pointers into different allocations",
 348                                     intrinsic_name
 349                                 );
 350                             }
 351                             // Use these offsets for distance calculation.
 352                             (a_offset.bytes(), b_offset.bytes())
 353                         }
 354                     };
 355
 356                 // Compute distance.
 357                 let dist = {
 358                     // Addresses are unsigned, so this is a `usize` computation. We have to do the
 359                     // overflow check separately anyway.
 360                     let (val, overflowed, _ty) = {
 361                         let a_offset = ImmTy::from_uint(a_offset, usize_layout);
 362                         let b_offset = ImmTy::from_uint(b_offset, usize_layout);
 363                         self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?
 364                     };
 365                     if overflowed {
 366                         // a < b
 367                         if intrinsic_name == sym::ptr_offset_from_unsigned {
 368                             throw_ub_format!(
 369                                 "`{}` called when first pointer has smaller offset than second: {} < {}",
 370                                 intrinsic_name,
 371                                 a_offset,
 372                                 b_offset,
 373                             );
 374                         }
 375                         // The signed form of the intrinsic allows this. If we interpret the
 376                         // difference as isize, we'll get the proper signed difference. If that
 377                         // seems *positive*, they were more than isize::MAX apart.
 378                         let dist = val.to_machine_isize(self)?;
 379                         if dist >= 0 {
 380                             throw_ub_format!(
 381                                 "`{}` called when first pointer is too far before second",
 382                                 intrinsic_name
 383                             );
 384                         }
 385                         dist
 386                     } else {
 387                         // b >= a
 388                         let dist = val.to_machine_isize(self)?;
 389                         // If converting to isize produced a *negative* result, we had an overflow
 390                         // because they were more than isize::MAX apart.
 391                         if dist < 0 {
 392                             throw_ub_format!(
 393                                 "`{}` called when first pointer is too far ahead of second",
 394                                 intrinsic_name
 395                             );
 396                         }
 397                         dist
 398                     }
 399                 };
 400
 401                 // Check that the range between them is dereferenceable ("in-bounds or one past the
 402                 // end of the same allocation"). This is like the check in ptr_offset_inbounds.
 403                 let min_ptr = if dist >= 0 { b } else { a };
 404                 self.check_ptr_access_align(
 405                     min_ptr,
 406                     Size::from_bytes(dist.unsigned_abs()),
 407                     Align::ONE,
 408                     CheckInAllocMsg::OffsetFromTest,
 409                 )?;
 410
 411                 // Perform division by size to compute return value.
 412                 let ret_layout = if intrinsic_name == sym::ptr_offset_from_unsigned {
 413                     assert!(0 <= dist && dist <= self.machine_isize_max());
 414                     usize_layout
 415                 } else {
 416                     assert!(self.machine_isize_min() <= dist && dist <= self.machine_isize_max());
 417                     isize_layout
 418                 };
 419                 let pointee_layout = self.layout_of(substs.type_at(0))?;
 420                 // If ret_layout is unsigned, we checked that so is the distance, so we are good.
 421                 let val = ImmTy::from_int(dist, ret_layout);
 422                 let size = ImmTy::from_int(pointee_layout.size.bytes(), ret_layout);
 423                 self.exact_div(&val, &size, dest)?;
 424             }
 425
 426             sym::transmute => {
 427                 self.copy_op(&args[0], dest, /*allow_transmute*/ true)?;
 428             }
 429             sym::assert_inhabited
 430             | sym::assert_zero_valid
 431             | sym::assert_mem_uninitialized_valid => {
 432                 let ty = instance.substs.type_at(0);
 433                 let layout = self.layout_of(ty)?;
 434
 435                 // For *all* intrinsics we first check `is_uninhabited` to give a more specific
 436                 // error message.
 437                 if layout.abi.is_uninhabited() {
 438                     // The run-time intrinsic panics just to get a good backtrace; here we abort
 439                     // since there is no problem showing a backtrace even for aborts.
 440                     M::abort(
 441                         self,
 442                         format!(
 443                             "aborted execution: attempted to instantiate uninhabited type `{}`",
 444                             ty
 445                         ),
 446                     )?;
 447                 }
 448
 449                 if intrinsic_name == sym::assert_zero_valid {
 450                     let should_panic = !self.tcx.permits_zero_init(layout);
 451
 452                     if should_panic {
 453                         M::abort(
 454                             self,
 455                             format!(
 456                                 "aborted execution: attempted to zero-initialize type `{}`, which is invalid",
 457                                 ty
 458                             ),
 459                         )?;
 460                     }
 461                 }
 462
 463                 if intrinsic_name == sym::assert_mem_uninitialized_valid {
 464                     let should_panic = !self.tcx.permits_uninit_init(layout);
 465
 466                     if should_panic {
 467                         M::abort(
 468                             self,
 469                             format!(
 470                                 "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
 471                                 ty
 472                             ),
 473                         )?;
 474                     }
 475                 }
 476             }
 477             sym::simd_insert => {
 478                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 479                 let elem = &args[2];
 480                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 481                 let (dest, dest_len) = self.place_to_simd(dest)?;
 482                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
 483                 assert!(
 484                     index < dest_len,
 485                     "Index `{}` must be in bounds of vector with length {}`",
 486                     index,
 487                     dest_len
 488                 );
 489
 490                 for i in 0..dest_len {
 491                     let place = self.mplace_index(&dest, i)?;
 492                     let value = if i == index {
 493                         elem.clone()
 494                     } else {
 495                         self.mplace_index(&input, i)?.into()
 496                     };
 497                     self.copy_op(&value, &place.into(), /*allow_transmute*/ false)?;
 498                 }
 499             }
 500             sym::simd_extract => {
 501                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 502                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 503                 assert!(
 504                     index < input_len,
 505                     "index `{}` must be in bounds of vector with length `{}`",
 506                     index,
 507                     input_len
 508                 );
 509                 self.copy_op(
 510                     &self.mplace_index(&input, index)?.into(),
 511                     dest,
 512                     /*allow_transmute*/ false,
 513                 )?;
 514             }
 515             sym::likely | sym::unlikely | sym::black_box => {
 516                 // These just return their argument
 517                 self.copy_op(&args[0], dest, /*allow_transmute*/ false)?;
 518             }
 519             sym::raw_eq => {
 520                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
 521                 self.write_scalar(result, dest)?;
 522             }
 523
 524             sym::vtable_size => {
 525                 let ptr = self.read_pointer(&args[0])?;
 526                 let (size, _align) = self.get_vtable_size_and_align(ptr)?;
 527                 self.write_scalar(Scalar::from_machine_usize(size.bytes(), self), dest)?;
 528             }
 529             sym::vtable_align => {
 530                 let ptr = self.read_pointer(&args[0])?;
 531                 let (_size, align) = self.get_vtable_size_and_align(ptr)?;
 532                 self.write_scalar(Scalar::from_machine_usize(align.bytes(), self), dest)?;
 533             }
 534
 535             _ => return Ok(false),
 536         }
 537
 538         trace!("{:?}", self.dump_place(**dest));
 539         self.go_to_block(ret);
 540         Ok(true)
 541     }
 542
 543     pub(super) fn emulate_nondiverging_intrinsic(
 544         &mut self,
 545         intrinsic: &NonDivergingIntrinsic<'tcx>,
 546     ) -> InterpResult<'tcx> {
 547         match intrinsic {
 548             NonDivergingIntrinsic::Assume(op) => {
 549                 let op = self.eval_operand(op, None)?;
 550                 let cond = self.read_scalar(&op)?.to_bool()?;
 551                 if !cond {
 552                     throw_ub_format!("`assume` called with `false`");
 553                 }
 554                 Ok(())
 555             }
 556             NonDivergingIntrinsic::CopyNonOverlapping(mir::CopyNonOverlapping {
 557                 count,
 558                 src,
 559                 dst,
 560             }) => {
 561                 let src = self.eval_operand(src, None)?;
 562                 let dst = self.eval_operand(dst, None)?;
 563                 let count = self.eval_operand(count, None)?;
 564                 self.copy_intrinsic(&src, &dst, &count, /* nonoverlapping */ true)
 565             }
 566         }
 567     }
 568
 569     pub fn exact_div(
 570         &mut self,
 571         a: &ImmTy<'tcx, M::Provenance>,
 572         b: &ImmTy<'tcx, M::Provenance>,
 573         dest: &PlaceTy<'tcx, M::Provenance>,
 574     ) -> InterpResult<'tcx> {
 575         // Performs an exact division, resulting in undefined behavior where
 576         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 577         // First, check x % y != 0 (or if that computation overflows).
 578         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
 579         assert!(!overflow); // All overflow is UB, so this should never return on overflow.
 580         if res.assert_bits(a.layout.size) != 0 {
 581             throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
 582         }
 583         // `Rem` says this is all right, so we can let `Div` do its job.
 584         self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
 585     }
 586
 587     pub fn saturating_arith(
 588         &self,
 589         mir_op: BinOp,
 590         l: &ImmTy<'tcx, M::Provenance>,
 591         r: &ImmTy<'tcx, M::Provenance>,
 592     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 593         assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
 594         let (val, overflowed, _ty) = self.overflowing_binary_op(mir_op, l, r)?;
 595         Ok(if overflowed {
 596             let size = l.layout.size;
 597             let num_bits = size.bits();
 598             if l.layout.abi.is_signed() {
 599                 // For signed ints the saturated value depends on the sign of the first
 600                 // term since the sign of the second term can be inferred from this and
 601                 // the fact that the operation has overflowed (if either is 0 no
 602                 // overflow can occur)
 603                 let first_term: u128 = l.to_scalar().to_bits(l.layout.size)?;
 604                 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 605                 if first_term_positive {
 606                     // Negative overflow not possible since the positive first term
 607                     // can only increase an (in range) negative term for addition
 608                     // or corresponding negated positive term for subtraction
 609                     Scalar::from_int(size.signed_int_max(), size)
 610                 } else {
 611                     // Positive overflow not possible for similar reason
 612                     // max negative
 613                     Scalar::from_int(size.signed_int_min(), size)
 614                 }
 615             } else {
 616                 // unsigned
 617                 if matches!(mir_op, BinOp::Add) {
 618                     // max unsigned
 619                     Scalar::from_uint(size.unsigned_int_max(), size)
 620                 } else {
 621                     // underflow to 0
 622                     Scalar::from_uint(0u128, size)
 623                 }
 624             }
 625         } else {
 626             val
 627         })
 628     }
 629
 630     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 631     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 632     /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
 633     pub fn ptr_offset_inbounds(
 634         &self,
 635         ptr: Pointer<Option<M::Provenance>>,
 636         pointee_ty: Ty<'tcx>,
 637         offset_count: i64,
 638     ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> {
 639         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 640         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 641         // The computed offset, in bytes, must not overflow an isize.
 642         // `checked_mul` enforces a too small bound, but no actual allocation can be big enough for
 643         // the difference to be noticeable.
 644         let offset_bytes =
 645             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 646         // The offset being in bounds cannot rely on "wrapping around" the address space.
 647         // So, first rule out overflows in the pointer arithmetic.
 648         let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
 649         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 650         // memory between these pointers must be accessible. Note that we do not require the
 651         // pointers to be properly aligned (unlike a read/write operation).
 652         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 653         // This call handles checking for integer/null pointers.
 654         self.check_ptr_access_align(
 655             min_ptr,
 656             Size::from_bytes(offset_bytes.unsigned_abs()),
 657             Align::ONE,
 658             CheckInAllocMsg::PointerArithmeticTest,
 659         )?;
 660         Ok(offset_ptr)
 661     }
 662
 663     /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
 664     pub(crate) fn copy_intrinsic(
 665         &mut self,
 666         src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 667         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 668         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 669         nonoverlapping: bool,
 670     ) -> InterpResult<'tcx> {
 671         let count = self.read_machine_usize(&count)?;
 672         let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
 673         let (size, align) = (layout.size, layout.align.abi);
 674         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 675         // but no actual allocation can be big enough for the difference to be noticeable.
 676         let size = size.checked_mul(count, self).ok_or_else(|| {
 677             err_ub_format!(
 678                 "overflow computing total size of `{}`",
 679                 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
 680             )
 681         })?;
 682
 683         let src = self.read_pointer(&src)?;
 684         let dst = self.read_pointer(&dst)?;
 685
 686         self.mem_copy(src, align, dst, align, size, nonoverlapping)
 687     }
 688
 689     pub(crate) fn write_bytes_intrinsic(
 690         &mut self,
 691         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 692         byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 693         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 694     ) -> InterpResult<'tcx> {
 695         let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
 696
 697         let dst = self.read_pointer(&dst)?;
 698         let byte = self.read_scalar(&byte)?.to_u8()?;
 699         let count = self.read_machine_usize(&count)?;
 700
 701         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 702         // but no actual allocation can be big enough for the difference to be noticeable.
 703         let len = layout
 704             .size
 705             .checked_mul(count, self)
 706             .ok_or_else(|| err_ub_format!("overflow computing total size of `write_bytes`"))?;
 707
 708         let bytes = std::iter::repeat(byte).take(len.bytes_usize());
 709         self.write_bytes_ptr(dst, bytes)
 710     }
 711
 712     pub(crate) fn raw_eq_intrinsic(
 713         &mut self,
 714         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 715         rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 716     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 717         let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
 718         assert!(layout.is_sized());
 719
 720         let get_bytes = |this: &InterpCx<'mir, 'tcx, M>,
 721                          op: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 722                          size|
 723          -> InterpResult<'tcx, &[u8]> {
 724             let ptr = this.read_pointer(op)?;
 725             let Some(alloc_ref) = self.get_ptr_alloc(ptr, size, Align::ONE)? else {
 726                 // zero-sized access
 727                 return Ok(&[]);
 728             };
 729             if alloc_ref.has_provenance() {
 730                 throw_ub_format!("`raw_eq` on bytes with provenance");
 731             }
 732             alloc_ref.get_bytes_strip_provenance()
 733         };
 734
 735         let lhs_bytes = get_bytes(self, lhs, layout.size)?;
 736         let rhs_bytes = get_bytes(self, rhs, layout.size)?;
 737         Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
 738     }
 739 }