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(ref adt, _) => {
  83                 ConstValue::from_machine_usize(adt.variants().len() as u64, &tcx)
  84             }
  85             ty::Alias(..) | ty::Param(_) | ty::Placeholder(_) | ty::Infer(_) => {
  86                 throw_inval!(TooGeneric)
  87             }
  88             ty::Bound(_, _) => bug!("bound ty during ctfe"),
  89             ty::Bool
  90             | ty::Char
  91             | ty::Int(_)
  92             | ty::Uint(_)
  93             | ty::Float(_)
  94             | ty::Foreign(_)
  95             | ty::Str
  96             | ty::Array(_, _)
  97             | ty::Slice(_)
  98             | ty::RawPtr(_)
  99             | ty::Ref(_, _, _)
 100             | ty::FnDef(_, _)
 101             | ty::FnPtr(_)
 102             | ty::Dynamic(_, _, _)
 103             | ty::Closure(_, _)
 104             | ty::Generator(_, _, _)
 105             | ty::GeneratorWitness(_)
 106             | ty::Never
 107             | ty::Tuple(_)
 108             | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
 109         },
 110         other => bug!("`{}` is not a zero arg intrinsic", other),
 111     })
 112 }
 113
 114 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 115     /// Returns `true` if emulation happened.
 116     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
 117     /// intrinsic handling.
 118     pub fn emulate_intrinsic(
 119         &mut self,
 120         instance: ty::Instance<'tcx>,
 121         args: &[OpTy<'tcx, M::Provenance>],
 122         dest: &PlaceTy<'tcx, M::Provenance>,
 123         ret: Option<mir::BasicBlock>,
 124     ) -> InterpResult<'tcx, bool> {
 125         let substs = instance.substs;
 126         let intrinsic_name = self.tcx.item_name(instance.def_id());
 127
 128         // First handle intrinsics without return place.
 129         let ret = match ret {
 130             None => match intrinsic_name {
 131                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 132                 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
 133                 // Unsupported diverging intrinsic.
 134                 _ => return Ok(false),
 135             },
 136             Some(p) => p,
 137         };
 138
 139         match intrinsic_name {
 140             sym::caller_location => {
 141                 let span = self.find_closest_untracked_caller_location();
 142                 let location = self.alloc_caller_location_for_span(span);
 143                 self.write_immediate(location.to_ref(self), dest)?;
 144             }
 145
 146             sym::min_align_of_val | sym::size_of_val => {
 147                 // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
 148                 // dereferenceable!
 149                 let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
 150                 let (size, align) = self
 151                     .size_and_align_of_mplace(&place)?
 152                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 153
 154                 let result = match intrinsic_name {
 155                     sym::min_align_of_val => align.bytes(),
 156                     sym::size_of_val => size.bytes(),
 157                     _ => bug!(),
 158                 };
 159
 160                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
 161             }
 162
 163             sym::pref_align_of
 164             | sym::needs_drop
 165             | sym::type_id
 166             | sym::type_name
 167             | sym::variant_count => {
 168                 let gid = GlobalId { instance, promoted: None };
 169                 let ty = match intrinsic_name {
 170                     sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
 171                     sym::needs_drop => self.tcx.types.bool,
 172                     sym::type_id => self.tcx.types.u64,
 173                     sym::type_name => self.tcx.mk_static_str(),
 174                     _ => bug!(),
 175                 };
 176                 let val = self.ctfe_query(None, |tcx| {
 177                     tcx.const_eval_global_id(self.param_env, gid, Some(tcx.span))
 178                 })?;
 179                 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
 180                 self.copy_op(&val, dest, /*allow_transmute*/ false)?;
 181             }
 182
 183             sym::ctpop
 184             | sym::cttz
 185             | sym::cttz_nonzero
 186             | sym::ctlz
 187             | sym::ctlz_nonzero
 188             | sym::bswap
 189             | sym::bitreverse => {
 190                 let ty = substs.type_at(0);
 191                 let layout_of = self.layout_of(ty)?;
 192                 let val = self.read_scalar(&args[0])?;
 193                 let bits = val.to_bits(layout_of.size)?;
 194                 let kind = match layout_of.abi {
 195                     Abi::Scalar(scalar) => scalar.primitive(),
 196                     _ => span_bug!(
 197                         self.cur_span(),
 198                         "{} called on invalid type {:?}",
 199                         intrinsic_name,
 200                         ty
 201                     ),
 202                 };
 203                 let (nonzero, intrinsic_name) = match intrinsic_name {
 204                     sym::cttz_nonzero => (true, sym::cttz),
 205                     sym::ctlz_nonzero => (true, sym::ctlz),
 206                     other => (false, other),
 207                 };
 208                 if nonzero && bits == 0 {
 209                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 210                 }
 211                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
 212                 self.write_scalar(out_val, dest)?;
 213             }
 214             sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
 215                 let lhs = self.read_immediate(&args[0])?;
 216                 let rhs = self.read_immediate(&args[1])?;
 217                 let bin_op = match intrinsic_name {
 218                     sym::add_with_overflow => BinOp::Add,
 219                     sym::sub_with_overflow => BinOp::Sub,
 220                     sym::mul_with_overflow => BinOp::Mul,
 221                     _ => bug!(),
 222                 };
 223                 self.binop_with_overflow(
 224                     bin_op, /*force_overflow_checks*/ true, &lhs, &rhs, dest,
 225                 )?;
 226             }
 227             sym::saturating_add | sym::saturating_sub => {
 228                 let l = self.read_immediate(&args[0])?;
 229                 let r = self.read_immediate(&args[1])?;
 230                 let val = self.saturating_arith(
 231                     if intrinsic_name == sym::saturating_add { BinOp::Add } else { BinOp::Sub },
 232                     &l,
 233                     &r,
 234                 )?;
 235                 self.write_scalar(val, dest)?;
 236             }
 237             sym::discriminant_value => {
 238                 let place = self.deref_operand(&args[0])?;
 239                 let discr_val = self.read_discriminant(&place.into())?.0;
 240                 self.write_scalar(discr_val, dest)?;
 241             }
 242             sym::exact_div => {
 243                 let l = self.read_immediate(&args[0])?;
 244                 let r = self.read_immediate(&args[1])?;
 245                 self.exact_div(&l, &r, dest)?;
 246             }
 247             sym::unchecked_shl
 248             | sym::unchecked_shr
 249             | sym::unchecked_add
 250             | sym::unchecked_sub
 251             | sym::unchecked_mul
 252             | sym::unchecked_div
 253             | sym::unchecked_rem => {
 254                 let l = self.read_immediate(&args[0])?;
 255                 let r = self.read_immediate(&args[1])?;
 256                 let bin_op = match intrinsic_name {
 257                     sym::unchecked_shl => BinOp::Shl,
 258                     sym::unchecked_shr => BinOp::Shr,
 259                     sym::unchecked_add => BinOp::Add,
 260                     sym::unchecked_sub => BinOp::Sub,
 261                     sym::unchecked_mul => BinOp::Mul,
 262                     sym::unchecked_div => BinOp::Div,
 263                     sym::unchecked_rem => BinOp::Rem,
 264                     _ => bug!(),
 265                 };
 266                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
 267                 if overflowed {
 268                     let layout = self.layout_of(substs.type_at(0))?;
 269                     let r_val = r.to_scalar().to_bits(layout.size)?;
 270                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 271                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 272                     } else {
 273                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 274                     }
 275                 }
 276                 self.write_scalar(val, dest)?;
 277             }
 278             sym::rotate_left | sym::rotate_right => {
 279                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 280                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 281                 let layout = self.layout_of(substs.type_at(0))?;
 282                 let val = self.read_scalar(&args[0])?;
 283                 let val_bits = val.to_bits(layout.size)?;
 284                 let raw_shift = self.read_scalar(&args[1])?;
 285                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
 286                 let width_bits = u128::from(layout.size.bits());
 287                 let shift_bits = raw_shift_bits % width_bits;
 288                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 289                 let result_bits = if intrinsic_name == sym::rotate_left {
 290                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 291                 } else {
 292                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 293                 };
 294                 let truncated_bits = self.truncate(result_bits, layout);
 295                 let result = Scalar::from_uint(truncated_bits, layout.size);
 296                 self.write_scalar(result, dest)?;
 297             }
 298             sym::copy => {
 299                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
 300             }
 301             sym::write_bytes => {
 302                 self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
 303             }
 304             sym::offset => {
 305                 let ptr = self.read_pointer(&args[0])?;
 306                 let offset_count = self.read_machine_isize(&args[1])?;
 307                 let pointee_ty = substs.type_at(0);
 308
 309                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 310                 self.write_pointer(offset_ptr, dest)?;
 311             }
 312             sym::arith_offset => {
 313                 let ptr = self.read_pointer(&args[0])?;
 314                 let offset_count = self.read_machine_isize(&args[1])?;
 315                 let pointee_ty = substs.type_at(0);
 316
 317                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 318                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 319                 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
 320                 self.write_pointer(offset_ptr, dest)?;
 321             }
 322             sym::ptr_offset_from | sym::ptr_offset_from_unsigned => {
 323                 let a = self.read_pointer(&args[0])?;
 324                 let b = self.read_pointer(&args[1])?;
 325
 326                 let usize_layout = self.layout_of(self.tcx.types.usize)?;
 327                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 328
 329                 // Get offsets for both that are at least relative to the same base.
 330                 let (a_offset, b_offset) =
 331                     match (self.ptr_try_get_alloc_id(a), self.ptr_try_get_alloc_id(b)) {
 332                         (Err(a), Err(b)) => {
 333                             // Neither pointer points to an allocation.
 334                             // If these are inequal or null, this *will* fail the deref check below.
 335                             (a, b)
 336                         }
 337                         (Err(_), _) | (_, Err(_)) => {
 338                             // We managed to find a valid allocation for one pointer, but not the other.
 339                             // That means they are definitely not pointing to the same allocation.
 340                             throw_ub_format!(
 341                                 "`{}` called on pointers into different allocations",
 342                                 intrinsic_name
 343                             );
 344                         }
 345                         (Ok((a_alloc_id, a_offset, _)), Ok((b_alloc_id, b_offset, _))) => {
 346                             // Found allocation for both. They must be into the same allocation.
 347                             if a_alloc_id != b_alloc_id {
 348                                 throw_ub_format!(
 349                                     "`{}` called on pointers into different allocations",
 350                                     intrinsic_name
 351                                 );
 352                             }
 353                             // Use these offsets for distance calculation.
 354                             (a_offset.bytes(), b_offset.bytes())
 355                         }
 356                     };
 357
 358                 // Compute distance.
 359                 let dist = {
 360                     // Addresses are unsigned, so this is a `usize` computation. We have to do the
 361                     // overflow check separately anyway.
 362                     let (val, overflowed, _ty) = {
 363                         let a_offset = ImmTy::from_uint(a_offset, usize_layout);
 364                         let b_offset = ImmTy::from_uint(b_offset, usize_layout);
 365                         self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?
 366                     };
 367                     if overflowed {
 368                         // a < b
 369                         if intrinsic_name == sym::ptr_offset_from_unsigned {
 370                             throw_ub_format!(
 371                                 "`{}` called when first pointer has smaller offset than second: {} < {}",
 372                                 intrinsic_name,
 373                                 a_offset,
 374                                 b_offset,
 375                             );
 376                         }
 377                         // The signed form of the intrinsic allows this. If we interpret the
 378                         // difference as isize, we'll get the proper signed difference. If that
 379                         // seems *positive*, they were more than isize::MAX apart.
 380                         let dist = val.to_machine_isize(self)?;
 381                         if dist >= 0 {
 382                             throw_ub_format!(
 383                                 "`{}` called when first pointer is too far before second",
 384                                 intrinsic_name
 385                             );
 386                         }
 387                         dist
 388                     } else {
 389                         // b >= a
 390                         let dist = val.to_machine_isize(self)?;
 391                         // If converting to isize produced a *negative* result, we had an overflow
 392                         // because they were more than isize::MAX apart.
 393                         if dist < 0 {
 394                             throw_ub_format!(
 395                                 "`{}` called when first pointer is too far ahead of second",
 396                                 intrinsic_name
 397                             );
 398                         }
 399                         dist
 400                     }
 401                 };
 402
 403                 // Check that the range between them is dereferenceable ("in-bounds or one past the
 404                 // end of the same allocation"). This is like the check in ptr_offset_inbounds.
 405                 let min_ptr = if dist >= 0 { b } else { a };
 406                 self.check_ptr_access_align(
 407                     min_ptr,
 408                     Size::from_bytes(dist.unsigned_abs()),
 409                     Align::ONE,
 410                     CheckInAllocMsg::OffsetFromTest,
 411                 )?;
 412
 413                 // Perform division by size to compute return value.
 414                 let ret_layout = if intrinsic_name == sym::ptr_offset_from_unsigned {
 415                     assert!(0 <= dist && dist <= self.machine_isize_max());
 416                     usize_layout
 417                 } else {
 418                     assert!(self.machine_isize_min() <= dist && dist <= self.machine_isize_max());
 419                     isize_layout
 420                 };
 421                 let pointee_layout = self.layout_of(substs.type_at(0))?;
 422                 // If ret_layout is unsigned, we checked that so is the distance, so we are good.
 423                 let val = ImmTy::from_int(dist, ret_layout);
 424                 let size = ImmTy::from_int(pointee_layout.size.bytes(), ret_layout);
 425                 self.exact_div(&val, &size, dest)?;
 426             }
 427
 428             sym::transmute => {
 429                 self.copy_op(&args[0], dest, /*allow_transmute*/ true)?;
 430             }
 431             sym::assert_inhabited
 432             | sym::assert_zero_valid
 433             | sym::assert_mem_uninitialized_valid => {
 434                 let ty = instance.substs.type_at(0);
 435                 let layout = self.layout_of(ty)?;
 436
 437                 // For *all* intrinsics we first check `is_uninhabited` to give a more specific
 438                 // error message.
 439                 if layout.abi.is_uninhabited() {
 440                     // The run-time intrinsic panics just to get a good backtrace; here we abort
 441                     // since there is no problem showing a backtrace even for aborts.
 442                     M::abort(
 443                         self,
 444                         format!(
 445                             "aborted execution: attempted to instantiate uninhabited type `{}`",
 446                             ty
 447                         ),
 448                     )?;
 449                 }
 450
 451                 if intrinsic_name == sym::assert_zero_valid {
 452                     let should_panic = !self.tcx.permits_zero_init(layout);
 453
 454                     if should_panic {
 455                         M::abort(
 456                             self,
 457                             format!(
 458                                 "aborted execution: attempted to zero-initialize type `{}`, which is invalid",
 459                                 ty
 460                             ),
 461                         )?;
 462                     }
 463                 }
 464
 465                 if intrinsic_name == sym::assert_mem_uninitialized_valid {
 466                     let should_panic = !self.tcx.permits_uninit_init(layout);
 467
 468                     if should_panic {
 469                         M::abort(
 470                             self,
 471                             format!(
 472                                 "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
 473                                 ty
 474                             ),
 475                         )?;
 476                     }
 477                 }
 478             }
 479             sym::simd_insert => {
 480                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 481                 let elem = &args[2];
 482                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 483                 let (dest, dest_len) = self.place_to_simd(dest)?;
 484                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
 485                 assert!(
 486                     index < dest_len,
 487                     "Index `{}` must be in bounds of vector with length {}`",
 488                     index,
 489                     dest_len
 490                 );
 491
 492                 for i in 0..dest_len {
 493                     let place = self.mplace_index(&dest, i)?;
 494                     let value = if i == index {
 495                         elem.clone()
 496                     } else {
 497                         self.mplace_index(&input, i)?.into()
 498                     };
 499                     self.copy_op(&value, &place.into(), /*allow_transmute*/ false)?;
 500                 }
 501             }
 502             sym::simd_extract => {
 503                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 504                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 505                 assert!(
 506                     index < input_len,
 507                     "index `{}` must be in bounds of vector with length `{}`",
 508                     index,
 509                     input_len
 510                 );
 511                 self.copy_op(
 512                     &self.mplace_index(&input, index)?.into(),
 513                     dest,
 514                     /*allow_transmute*/ false,
 515                 )?;
 516             }
 517             sym::likely | sym::unlikely | sym::black_box => {
 518                 // These just return their argument
 519                 self.copy_op(&args[0], dest, /*allow_transmute*/ false)?;
 520             }
 521             sym::raw_eq => {
 522                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
 523                 self.write_scalar(result, dest)?;
 524             }
 525
 526             sym::vtable_size => {
 527                 let ptr = self.read_pointer(&args[0])?;
 528                 let (size, _align) = self.get_vtable_size_and_align(ptr)?;
 529                 self.write_scalar(Scalar::from_machine_usize(size.bytes(), self), dest)?;
 530             }
 531             sym::vtable_align => {
 532                 let ptr = self.read_pointer(&args[0])?;
 533                 let (_size, align) = self.get_vtable_size_and_align(ptr)?;
 534                 self.write_scalar(Scalar::from_machine_usize(align.bytes(), self), dest)?;
 535             }
 536
 537             _ => return Ok(false),
 538         }
 539
 540         trace!("{:?}", self.dump_place(**dest));
 541         self.go_to_block(ret);
 542         Ok(true)
 543     }
 544
 545     pub(super) fn emulate_nondiverging_intrinsic(
 546         &mut self,
 547         intrinsic: &NonDivergingIntrinsic<'tcx>,
 548     ) -> InterpResult<'tcx> {
 549         match intrinsic {
 550             NonDivergingIntrinsic::Assume(op) => {
 551                 let op = self.eval_operand(op, None)?;
 552                 let cond = self.read_scalar(&op)?.to_bool()?;
 553                 if !cond {
 554                     throw_ub_format!("`assume` called with `false`");
 555                 }
 556                 Ok(())
 557             }
 558             NonDivergingIntrinsic::CopyNonOverlapping(mir::CopyNonOverlapping {
 559                 count,
 560                 src,
 561                 dst,
 562             }) => {
 563                 let src = self.eval_operand(src, None)?;
 564                 let dst = self.eval_operand(dst, None)?;
 565                 let count = self.eval_operand(count, None)?;
 566                 self.copy_intrinsic(&src, &dst, &count, /* nonoverlapping */ true)
 567             }
 568         }
 569     }
 570
 571     pub fn exact_div(
 572         &mut self,
 573         a: &ImmTy<'tcx, M::Provenance>,
 574         b: &ImmTy<'tcx, M::Provenance>,
 575         dest: &PlaceTy<'tcx, M::Provenance>,
 576     ) -> InterpResult<'tcx> {
 577         // Performs an exact division, resulting in undefined behavior where
 578         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 579         // First, check x % y != 0 (or if that computation overflows).
 580         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
 581         assert!(!overflow); // All overflow is UB, so this should never return on overflow.
 582         if res.assert_bits(a.layout.size) != 0 {
 583             throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
 584         }
 585         // `Rem` says this is all right, so we can let `Div` do its job.
 586         self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
 587     }
 588
 589     pub fn saturating_arith(
 590         &self,
 591         mir_op: BinOp,
 592         l: &ImmTy<'tcx, M::Provenance>,
 593         r: &ImmTy<'tcx, M::Provenance>,
 594     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 595         assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
 596         let (val, overflowed, _ty) = self.overflowing_binary_op(mir_op, l, r)?;
 597         Ok(if overflowed {
 598             let size = l.layout.size;
 599             let num_bits = size.bits();
 600             if l.layout.abi.is_signed() {
 601                 // For signed ints the saturated value depends on the sign of the first
 602                 // term since the sign of the second term can be inferred from this and
 603                 // the fact that the operation has overflowed (if either is 0 no
 604                 // overflow can occur)
 605                 let first_term: u128 = l.to_scalar().to_bits(l.layout.size)?;
 606                 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 607                 if first_term_positive {
 608                     // Negative overflow not possible since the positive first term
 609                     // can only increase an (in range) negative term for addition
 610                     // or corresponding negated positive term for subtraction
 611                     Scalar::from_int(size.signed_int_max(), size)
 612                 } else {
 613                     // Positive overflow not possible for similar reason
 614                     // max negative
 615                     Scalar::from_int(size.signed_int_min(), size)
 616                 }
 617             } else {
 618                 // unsigned
 619                 if matches!(mir_op, BinOp::Add) {
 620                     // max unsigned
 621                     Scalar::from_uint(size.unsigned_int_max(), size)
 622                 } else {
 623                     // underflow to 0
 624                     Scalar::from_uint(0u128, size)
 625                 }
 626             }
 627         } else {
 628             val
 629         })
 630     }
 631
 632     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 633     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 634     /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
 635     pub fn ptr_offset_inbounds(
 636         &self,
 637         ptr: Pointer<Option<M::Provenance>>,
 638         pointee_ty: Ty<'tcx>,
 639         offset_count: i64,
 640     ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> {
 641         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 642         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 643         // The computed offset, in bytes, must not overflow an isize.
 644         // `checked_mul` enforces a too small bound, but no actual allocation can be big enough for
 645         // the difference to be noticeable.
 646         let offset_bytes =
 647             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 648         // The offset being in bounds cannot rely on "wrapping around" the address space.
 649         // So, first rule out overflows in the pointer arithmetic.
 650         let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
 651         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 652         // memory between these pointers must be accessible. Note that we do not require the
 653         // pointers to be properly aligned (unlike a read/write operation).
 654         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 655         // This call handles checking for integer/null pointers.
 656         self.check_ptr_access_align(
 657             min_ptr,
 658             Size::from_bytes(offset_bytes.unsigned_abs()),
 659             Align::ONE,
 660             CheckInAllocMsg::PointerArithmeticTest,
 661         )?;
 662         Ok(offset_ptr)
 663     }
 664
 665     /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
 666     pub(crate) fn copy_intrinsic(
 667         &mut self,
 668         src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 669         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 670         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 671         nonoverlapping: bool,
 672     ) -> InterpResult<'tcx> {
 673         let count = self.read_machine_usize(&count)?;
 674         let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
 675         let (size, align) = (layout.size, layout.align.abi);
 676         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 677         // but no actual allocation can be big enough for the difference to be noticeable.
 678         let size = size.checked_mul(count, self).ok_or_else(|| {
 679             err_ub_format!(
 680                 "overflow computing total size of `{}`",
 681                 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
 682             )
 683         })?;
 684
 685         let src = self.read_pointer(&src)?;
 686         let dst = self.read_pointer(&dst)?;
 687
 688         self.mem_copy(src, align, dst, align, size, nonoverlapping)
 689     }
 690
 691     pub(crate) fn write_bytes_intrinsic(
 692         &mut self,
 693         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 694         byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 695         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 696     ) -> InterpResult<'tcx> {
 697         let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
 698
 699         let dst = self.read_pointer(&dst)?;
 700         let byte = self.read_scalar(&byte)?.to_u8()?;
 701         let count = self.read_machine_usize(&count)?;
 702
 703         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 704         // but no actual allocation can be big enough for the difference to be noticeable.
 705         let len = layout
 706             .size
 707             .checked_mul(count, self)
 708             .ok_or_else(|| err_ub_format!("overflow computing total size of `write_bytes`"))?;
 709
 710         let bytes = std::iter::repeat(byte).take(len.bytes_usize());
 711         self.write_bytes_ptr(dst, bytes)
 712     }
 713
 714     pub(crate) fn raw_eq_intrinsic(
 715         &mut self,
 716         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 717         rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 718     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 719         let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
 720         assert!(layout.is_sized());
 721
 722         let get_bytes = |this: &InterpCx<'mir, 'tcx, M>,
 723                          op: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 724                          size|
 725          -> InterpResult<'tcx, &[u8]> {
 726             let ptr = this.read_pointer(op)?;
 727             let Some(alloc_ref) = self.get_ptr_alloc(ptr, size, Align::ONE)? else {
 728                 // zero-sized access
 729                 return Ok(&[]);
 730             };
 731             if alloc_ref.has_provenance() {
 732                 throw_ub_format!("`raw_eq` on bytes with provenance");
 733             }
 734             alloc_ref.get_bytes_strip_provenance()
 735         };
 736
 737         let lhs_bytes = get_bytes(self, lhs, layout.size)?;
 738         let rhs_bytes = get_bytes(self, rhs, layout.size)?;
 739         Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
 740     }
 741 }