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::{
  11         Allocation, ConstAllocation, ConstValue, GlobalId, InterpResult, PointerArithmetic, Scalar,
  12     },
  13     BinOp, NonDivergingIntrinsic,
  14 };
  15 use rustc_middle::ty;
  16 use rustc_middle::ty::layout::LayoutOf as _;
  17 use rustc_middle::ty::subst::SubstsRef;
  18 use rustc_middle::ty::{Ty, TyCtxt};
  19 use rustc_span::symbol::{sym, Symbol};
  20 use rustc_target::abi::{Abi, Align, Primitive, Size};
  21
  22 use super::{
  23     util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
  24     Pointer,
  25 };
  26
  27 mod caller_location;
  28
  29 fn numeric_intrinsic<Prov>(name: Symbol, bits: u128, kind: Primitive) -> Scalar<Prov> {
  30     let size = match kind {
  31         Primitive::Int(integer, _) => integer.size(),
  32         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  33     };
  34     let extra = 128 - u128::from(size.bits());
  35     let bits_out = match name {
  36         sym::ctpop => u128::from(bits.count_ones()),
  37         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  38         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  39         sym::bswap => (bits << extra).swap_bytes(),
  40         sym::bitreverse => (bits << extra).reverse_bits(),
  41         _ => bug!("not a numeric intrinsic: {}", name),
  42     };
  43     Scalar::from_uint(bits_out, size)
  44 }
  45
  46 /// Directly returns an `Allocation` containing an absolute path representation of the given type.
  47 pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAllocation<'tcx> {
  48     let path = crate::util::type_name(tcx, ty);
  49     let alloc = Allocation::from_bytes_byte_aligned_immutable(path.into_bytes());
  50     tcx.intern_const_alloc(alloc)
  51 }
  52
  53 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  54 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  55 pub(crate) fn eval_nullary_intrinsic<'tcx>(
  56     tcx: TyCtxt<'tcx>,
  57     param_env: ty::ParamEnv<'tcx>,
  58     def_id: DefId,
  59     substs: SubstsRef<'tcx>,
  60 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  61     let tp_ty = substs.type_at(0);
  62     let name = tcx.item_name(def_id);
  63     Ok(match name {
  64         sym::type_name => {
  65             ensure_monomorphic_enough(tcx, tp_ty)?;
  66             let alloc = alloc_type_name(tcx, tp_ty);
  67             ConstValue::Slice { data: alloc, start: 0, end: alloc.inner().len() }
  68         }
  69         sym::needs_drop => {
  70             ensure_monomorphic_enough(tcx, tp_ty)?;
  71             ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env))
  72         }
  73         sym::pref_align_of => {
  74             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  75             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  76             ConstValue::from_machine_usize(layout.align.pref.bytes(), &tcx)
  77         }
  78         sym::type_id => {
  79             ensure_monomorphic_enough(tcx, tp_ty)?;
  80             ConstValue::from_u64(tcx.type_id_hash(tp_ty))
  81         }
  82         sym::variant_count => match tp_ty.kind() {
  83             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
  84             ty::Adt(ref adt, _) => {
  85                 ConstValue::from_machine_usize(adt.variants().len() as u64, &tcx)
  86             }
  87             ty::Projection(_)
  88             | ty::Opaque(_, _)
  89             | ty::Param(_)
  90             | ty::Placeholder(_)
  91             | ty::Infer(_) => throw_inval!(TooGeneric),
  92             ty::Bound(_, _) => bug!("bound ty during ctfe"),
  93             ty::Bool
  94             | ty::Char
  95             | ty::Int(_)
  96             | ty::Uint(_)
  97             | ty::Float(_)
  98             | ty::Foreign(_)
  99             | ty::Str
 100             | ty::Array(_, _)
 101             | ty::Slice(_)
 102             | ty::RawPtr(_)
 103             | ty::Ref(_, _, _)
 104             | ty::FnDef(_, _)
 105             | ty::FnPtr(_)
 106             | ty::Dynamic(_, _, _)
 107             | ty::Closure(_, _)
 108             | ty::Generator(_, _, _)
 109             | ty::GeneratorWitness(_)
 110             | ty::Never
 111             | ty::Tuple(_)
 112             | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
 113         },
 114         other => bug!("`{}` is not a zero arg intrinsic", other),
 115     })
 116 }
 117
 118 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 119     /// Returns `true` if emulation happened.
 120     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
 121     /// intrinsic handling.
 122     pub fn emulate_intrinsic(
 123         &mut self,
 124         instance: ty::Instance<'tcx>,
 125         args: &[OpTy<'tcx, M::Provenance>],
 126         dest: &PlaceTy<'tcx, M::Provenance>,
 127         ret: Option<mir::BasicBlock>,
 128     ) -> InterpResult<'tcx, bool> {
 129         let substs = instance.substs;
 130         let intrinsic_name = self.tcx.item_name(instance.def_id());
 131
 132         // First handle intrinsics without return place.
 133         let ret = match ret {
 134             None => match intrinsic_name {
 135                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 136                 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
 137                 // Unsupported diverging intrinsic.
 138                 _ => return Ok(false),
 139             },
 140             Some(p) => p,
 141         };
 142
 143         match intrinsic_name {
 144             sym::caller_location => {
 145                 let span = self.find_closest_untracked_caller_location();
 146                 let location = self.alloc_caller_location_for_span(span);
 147                 self.write_immediate(location.to_ref(self), dest)?;
 148             }
 149
 150             sym::min_align_of_val | sym::size_of_val => {
 151                 // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
 152                 // dereferenceable!
 153                 let place = self.ref_to_mplace(&self.read_immediate(&args[0])?)?;
 154                 let (size, align) = self
 155                     .size_and_align_of_mplace(&place)?
 156                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 157
 158                 let result = match intrinsic_name {
 159                     sym::min_align_of_val => align.bytes(),
 160                     sym::size_of_val => size.bytes(),
 161                     _ => bug!(),
 162                 };
 163
 164                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
 165             }
 166
 167             sym::pref_align_of
 168             | sym::needs_drop
 169             | sym::type_id
 170             | sym::type_name
 171             | sym::variant_count => {
 172                 let gid = GlobalId { instance, promoted: None };
 173                 let ty = match intrinsic_name {
 174                     sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
 175                     sym::needs_drop => self.tcx.types.bool,
 176                     sym::type_id => self.tcx.types.u64,
 177                     sym::type_name => self.tcx.mk_static_str(),
 178                     _ => bug!(),
 179                 };
 180                 let val = self.ctfe_query(None, |tcx| {
 181                     tcx.const_eval_global_id(self.param_env, gid, Some(tcx.span))
 182                 })?;
 183                 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;
 184                 self.copy_op(&val, dest, /*allow_transmute*/ false)?;
 185             }
 186
 187             sym::ctpop
 188             | sym::cttz
 189             | sym::cttz_nonzero
 190             | sym::ctlz
 191             | sym::ctlz_nonzero
 192             | sym::bswap
 193             | sym::bitreverse => {
 194                 let ty = substs.type_at(0);
 195                 let layout_of = self.layout_of(ty)?;
 196                 let val = self.read_scalar(&args[0])?;
 197                 let bits = val.to_bits(layout_of.size)?;
 198                 let kind = match layout_of.abi {
 199                     Abi::Scalar(scalar) => scalar.primitive(),
 200                     _ => span_bug!(
 201                         self.cur_span(),
 202                         "{} called on invalid type {:?}",
 203                         intrinsic_name,
 204                         ty
 205                     ),
 206                 };
 207                 let (nonzero, intrinsic_name) = match intrinsic_name {
 208                     sym::cttz_nonzero => (true, sym::cttz),
 209                     sym::ctlz_nonzero => (true, sym::ctlz),
 210                     other => (false, other),
 211                 };
 212                 if nonzero && bits == 0 {
 213                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 214                 }
 215                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind);
 216                 self.write_scalar(out_val, dest)?;
 217             }
 218             sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
 219                 let lhs = self.read_immediate(&args[0])?;
 220                 let rhs = self.read_immediate(&args[1])?;
 221                 let bin_op = match intrinsic_name {
 222                     sym::add_with_overflow => BinOp::Add,
 223                     sym::sub_with_overflow => BinOp::Sub,
 224                     sym::mul_with_overflow => BinOp::Mul,
 225                     _ => bug!(),
 226                 };
 227                 self.binop_with_overflow(
 228                     bin_op, /*force_overflow_checks*/ true, &lhs, &rhs, dest,
 229                 )?;
 230             }
 231             sym::saturating_add | sym::saturating_sub => {
 232                 let l = self.read_immediate(&args[0])?;
 233                 let r = self.read_immediate(&args[1])?;
 234                 let val = self.saturating_arith(
 235                     if intrinsic_name == sym::saturating_add { BinOp::Add } else { BinOp::Sub },
 236                     &l,
 237                     &r,
 238                 )?;
 239                 self.write_scalar(val, dest)?;
 240             }
 241             sym::discriminant_value => {
 242                 let place = self.deref_operand(&args[0])?;
 243                 let discr_val = self.read_discriminant(&place.into())?.0;
 244                 self.write_scalar(discr_val, dest)?;
 245             }
 246             sym::exact_div => {
 247                 let l = self.read_immediate(&args[0])?;
 248                 let r = self.read_immediate(&args[1])?;
 249                 self.exact_div(&l, &r, dest)?;
 250             }
 251             sym::unchecked_shl
 252             | sym::unchecked_shr
 253             | sym::unchecked_add
 254             | sym::unchecked_sub
 255             | sym::unchecked_mul
 256             | sym::unchecked_div
 257             | sym::unchecked_rem => {
 258                 let l = self.read_immediate(&args[0])?;
 259                 let r = self.read_immediate(&args[1])?;
 260                 let bin_op = match intrinsic_name {
 261                     sym::unchecked_shl => BinOp::Shl,
 262                     sym::unchecked_shr => BinOp::Shr,
 263                     sym::unchecked_add => BinOp::Add,
 264                     sym::unchecked_sub => BinOp::Sub,
 265                     sym::unchecked_mul => BinOp::Mul,
 266                     sym::unchecked_div => BinOp::Div,
 267                     sym::unchecked_rem => BinOp::Rem,
 268                     _ => bug!(),
 269                 };
 270                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
 271                 if overflowed {
 272                     let layout = self.layout_of(substs.type_at(0))?;
 273                     let r_val = r.to_scalar().to_bits(layout.size)?;
 274                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 275                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 276                     } else {
 277                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 278                     }
 279                 }
 280                 self.write_scalar(val, dest)?;
 281             }
 282             sym::rotate_left | sym::rotate_right => {
 283                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 284                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 285                 let layout = self.layout_of(substs.type_at(0))?;
 286                 let val = self.read_scalar(&args[0])?;
 287                 let val_bits = val.to_bits(layout.size)?;
 288                 let raw_shift = self.read_scalar(&args[1])?;
 289                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
 290                 let width_bits = u128::from(layout.size.bits());
 291                 let shift_bits = raw_shift_bits % width_bits;
 292                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 293                 let result_bits = if intrinsic_name == sym::rotate_left {
 294                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 295                 } else {
 296                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 297                 };
 298                 let truncated_bits = self.truncate(result_bits, layout);
 299                 let result = Scalar::from_uint(truncated_bits, layout.size);
 300                 self.write_scalar(result, dest)?;
 301             }
 302             sym::copy => {
 303                 self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
 304             }
 305             sym::write_bytes => {
 306                 self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
 307             }
 308             sym::offset => {
 309                 let ptr = self.read_pointer(&args[0])?;
 310                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 311                 let pointee_ty = substs.type_at(0);
 312
 313                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 314                 self.write_pointer(offset_ptr, dest)?;
 315             }
 316             sym::arith_offset => {
 317                 let ptr = self.read_pointer(&args[0])?;
 318                 let offset_count = self.read_scalar(&args[1])?.to_machine_isize(self)?;
 319                 let pointee_ty = substs.type_at(0);
 320
 321                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 322                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 323                 let offset_ptr = ptr.wrapping_signed_offset(offset_bytes, self);
 324                 self.write_pointer(offset_ptr, dest)?;
 325             }
 326             sym::ptr_offset_from | sym::ptr_offset_from_unsigned => {
 327                 let a = self.read_pointer(&args[0])?;
 328                 let b = self.read_pointer(&args[1])?;
 329
 330                 let usize_layout = self.layout_of(self.tcx.types.usize)?;
 331                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 332
 333                 // Get offsets for both that are at least relative to the same base.
 334                 let (a_offset, b_offset) =
 335                     match (self.ptr_try_get_alloc_id(a), self.ptr_try_get_alloc_id(b)) {
 336                         (Err(a), Err(b)) => {
 337                             // Neither pointer points to an allocation.
 338                             // If these are inequal or null, this *will* fail the deref check below.
 339                             (a, b)
 340                         }
 341                         (Err(_), _) | (_, Err(_)) => {
 342                             // We managed to find a valid allocation for one pointer, but not the other.
 343                             // That means they are definitely not pointing to the same allocation.
 344                             throw_ub_format!(
 345                                 "`{}` called on pointers into different allocations",
 346                                 intrinsic_name
 347                             );
 348                         }
 349                         (Ok((a_alloc_id, a_offset, _)), Ok((b_alloc_id, b_offset, _))) => {
 350                             // Found allocation for both. They must be into the same allocation.
 351                             if a_alloc_id != b_alloc_id {
 352                                 throw_ub_format!(
 353                                     "`{}` called on pointers into different allocations",
 354                                     intrinsic_name
 355                                 );
 356                             }
 357                             // Use these offsets for distance calculation.
 358                             (a_offset.bytes(), b_offset.bytes())
 359                         }
 360                     };
 361
 362                 // Compute distance.
 363                 let dist = {
 364                     // Addresses are unsigned, so this is a `usize` computation. We have to do the
 365                     // overflow check separately anyway.
 366                     let (val, overflowed, _ty) = {
 367                         let a_offset = ImmTy::from_uint(a_offset, usize_layout);
 368                         let b_offset = ImmTy::from_uint(b_offset, usize_layout);
 369                         self.overflowing_binary_op(BinOp::Sub, &a_offset, &b_offset)?
 370                     };
 371                     if overflowed {
 372                         // a < b
 373                         if intrinsic_name == sym::ptr_offset_from_unsigned {
 374                             throw_ub_format!(
 375                                 "`{}` called when first pointer has smaller offset than second: {} < {}",
 376                                 intrinsic_name,
 377                                 a_offset,
 378                                 b_offset,
 379                             );
 380                         }
 381                         // The signed form of the intrinsic allows this. If we interpret the
 382                         // difference as isize, we'll get the proper signed difference. If that
 383                         // seems *positive*, they were more than isize::MAX apart.
 384                         let dist = val.to_machine_isize(self)?;
 385                         if dist >= 0 {
 386                             throw_ub_format!(
 387                                 "`{}` called when first pointer is too far before second",
 388                                 intrinsic_name
 389                             );
 390                         }
 391                         dist
 392                     } else {
 393                         // b >= a
 394                         let dist = val.to_machine_isize(self)?;
 395                         // If converting to isize produced a *negative* result, we had an overflow
 396                         // because they were more than isize::MAX apart.
 397                         if dist < 0 {
 398                             throw_ub_format!(
 399                                 "`{}` called when first pointer is too far ahead of second",
 400                                 intrinsic_name
 401                             );
 402                         }
 403                         dist
 404                     }
 405                 };
 406
 407                 // Check that the range between them is dereferenceable ("in-bounds or one past the
 408                 // end of the same allocation"). This is like the check in ptr_offset_inbounds.
 409                 let min_ptr = if dist >= 0 { b } else { a };
 410                 self.check_ptr_access_align(
 411                     min_ptr,
 412                     Size::from_bytes(dist.unsigned_abs()),
 413                     Align::ONE,
 414                     CheckInAllocMsg::OffsetFromTest,
 415                 )?;
 416
 417                 // Perform division by size to compute return value.
 418                 let ret_layout = if intrinsic_name == sym::ptr_offset_from_unsigned {
 419                     assert!(0 <= dist && dist <= self.machine_isize_max());
 420                     usize_layout
 421                 } else {
 422                     assert!(self.machine_isize_min() <= dist && dist <= self.machine_isize_max());
 423                     isize_layout
 424                 };
 425                 let pointee_layout = self.layout_of(substs.type_at(0))?;
 426                 // If ret_layout is unsigned, we checked that so is the distance, so we are good.
 427                 let val = ImmTy::from_int(dist, ret_layout);
 428                 let size = ImmTy::from_int(pointee_layout.size.bytes(), ret_layout);
 429                 self.exact_div(&val, &size, dest)?;
 430             }
 431
 432             sym::transmute => {
 433                 self.copy_op(&args[0], dest, /*allow_transmute*/ true)?;
 434             }
 435             sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
 436                 let ty = instance.substs.type_at(0);
 437                 let layout = self.layout_of(ty)?;
 438
 439                 // For *all* intrinsics we first check `is_uninhabited` to give a more specific
 440                 // error message.
 441                 if layout.abi.is_uninhabited() {
 442                     // The run-time intrinsic panics just to get a good backtrace; here we abort
 443                     // since there is no problem showing a backtrace even for aborts.
 444                     M::abort(
 445                         self,
 446                         format!(
 447                             "aborted execution: attempted to instantiate uninhabited type `{}`",
 448                             ty
 449                         ),
 450                     )?;
 451                 }
 452
 453                 if intrinsic_name == sym::assert_zero_valid {
 454                     let should_panic = !self.tcx.permits_zero_init(layout);
 455
 456                     if should_panic {
 457                         M::abort(
 458                             self,
 459                             format!(
 460                                 "aborted execution: attempted to zero-initialize type `{}`, which is invalid",
 461                                 ty
 462                             ),
 463                         )?;
 464                     }
 465                 }
 466
 467                 if intrinsic_name == sym::assert_uninit_valid {
 468                     let should_panic = !self.tcx.permits_uninit_init(layout);
 469
 470                     if should_panic {
 471                         M::abort(
 472                             self,
 473                             format!(
 474                                 "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
 475                                 ty
 476                             ),
 477                         )?;
 478                     }
 479                 }
 480             }
 481             sym::simd_insert => {
 482                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 483                 let elem = &args[2];
 484                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 485                 let (dest, dest_len) = self.place_to_simd(dest)?;
 486                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
 487                 assert!(
 488                     index < dest_len,
 489                     "Index `{}` must be in bounds of vector with length {}`",
 490                     index,
 491                     dest_len
 492                 );
 493
 494                 for i in 0..dest_len {
 495                     let place = self.mplace_index(&dest, i)?;
 496                     let value = if i == index {
 497                         elem.clone()
 498                     } else {
 499                         self.mplace_index(&input, i)?.into()
 500                     };
 501                     self.copy_op(&value, &place.into(), /*allow_transmute*/ false)?;
 502                 }
 503             }
 504             sym::simd_extract => {
 505                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
 506                 let (input, input_len) = self.operand_to_simd(&args[0])?;
 507                 assert!(
 508                     index < input_len,
 509                     "index `{}` must be in bounds of vector with length `{}`",
 510                     index,
 511                     input_len
 512                 );
 513                 self.copy_op(
 514                     &self.mplace_index(&input, index)?.into(),
 515                     dest,
 516                     /*allow_transmute*/ false,
 517                 )?;
 518             }
 519             sym::likely | sym::unlikely | sym::black_box => {
 520                 // These just return their argument
 521                 self.copy_op(&args[0], dest, /*allow_transmute*/ false)?;
 522             }
 523             sym::raw_eq => {
 524                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
 525                 self.write_scalar(result, dest)?;
 526             }
 527
 528             sym::vtable_size => {
 529                 let ptr = self.read_pointer(&args[0])?;
 530                 let (size, _align) = self.get_vtable_size_and_align(ptr)?;
 531                 self.write_scalar(Scalar::from_machine_usize(size.bytes(), self), dest)?;
 532             }
 533             sym::vtable_align => {
 534                 let ptr = self.read_pointer(&args[0])?;
 535                 let (_size, align) = self.get_vtable_size_and_align(ptr)?;
 536                 self.write_scalar(Scalar::from_machine_usize(align.bytes(), self), dest)?;
 537             }
 538
 539             _ => return Ok(false),
 540         }
 541
 542         trace!("{:?}", self.dump_place(**dest));
 543         self.go_to_block(ret);
 544         Ok(true)
 545     }
 546
 547     pub(super) fn emulate_nondiverging_intrinsic(
 548         &mut self,
 549         intrinsic: &NonDivergingIntrinsic<'tcx>,
 550     ) -> InterpResult<'tcx> {
 551         match intrinsic {
 552             NonDivergingIntrinsic::Assume(op) => {
 553                 let op = self.eval_operand(op, None)?;
 554                 let cond = self.read_scalar(&op)?.to_bool()?;
 555                 if !cond {
 556                     throw_ub_format!("`assume` called with `false`");
 557                 }
 558                 Ok(())
 559             }
 560             NonDivergingIntrinsic::CopyNonOverlapping(mir::CopyNonOverlapping {
 561                 count,
 562                 src,
 563                 dst,
 564             }) => {
 565                 let src = self.eval_operand(src, None)?;
 566                 let dst = self.eval_operand(dst, None)?;
 567                 let count = self.eval_operand(count, None)?;
 568                 self.copy_intrinsic(&src, &dst, &count, /* nonoverlapping */ true)
 569             }
 570         }
 571     }
 572
 573     pub fn exact_div(
 574         &mut self,
 575         a: &ImmTy<'tcx, M::Provenance>,
 576         b: &ImmTy<'tcx, M::Provenance>,
 577         dest: &PlaceTy<'tcx, M::Provenance>,
 578     ) -> InterpResult<'tcx> {
 579         // Performs an exact division, resulting in undefined behavior where
 580         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 581         // First, check x % y != 0 (or if that computation overflows).
 582         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, &a, &b)?;
 583         assert!(!overflow); // All overflow is UB, so this should never return on overflow.
 584         if res.assert_bits(a.layout.size) != 0 {
 585             throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
 586         }
 587         // `Rem` says this is all right, so we can let `Div` do its job.
 588         self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)
 589     }
 590
 591     pub fn saturating_arith(
 592         &self,
 593         mir_op: BinOp,
 594         l: &ImmTy<'tcx, M::Provenance>,
 595         r: &ImmTy<'tcx, M::Provenance>,
 596     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 597         assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
 598         let (val, overflowed, _ty) = self.overflowing_binary_op(mir_op, l, r)?;
 599         Ok(if overflowed {
 600             let size = l.layout.size;
 601             let num_bits = size.bits();
 602             if l.layout.abi.is_signed() {
 603                 // For signed ints the saturated value depends on the sign of the first
 604                 // term since the sign of the second term can be inferred from this and
 605                 // the fact that the operation has overflowed (if either is 0 no
 606                 // overflow can occur)
 607                 let first_term: u128 = l.to_scalar().to_bits(l.layout.size)?;
 608                 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 609                 if first_term_positive {
 610                     // Negative overflow not possible since the positive first term
 611                     // can only increase an (in range) negative term for addition
 612                     // or corresponding negated positive term for subtraction
 613                     Scalar::from_int(size.signed_int_max(), size)
 614                 } else {
 615                     // Positive overflow not possible for similar reason
 616                     // max negative
 617                     Scalar::from_int(size.signed_int_min(), size)
 618                 }
 619             } else {
 620                 // unsigned
 621                 if matches!(mir_op, BinOp::Add) {
 622                     // max unsigned
 623                     Scalar::from_uint(size.unsigned_int_max(), size)
 624                 } else {
 625                     // underflow to 0
 626                     Scalar::from_uint(0u128, size)
 627                 }
 628             }
 629         } else {
 630             val
 631         })
 632     }
 633
 634     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 635     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 636     /// 0, so offset-by-0 (and only 0) is okay -- except that null cannot be offset by _any_ value.
 637     pub fn ptr_offset_inbounds(
 638         &self,
 639         ptr: Pointer<Option<M::Provenance>>,
 640         pointee_ty: Ty<'tcx>,
 641         offset_count: i64,
 642     ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> {
 643         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 644         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 645         // The computed offset, in bytes, must not overflow an isize.
 646         // `checked_mul` enforces a too small bound, but no actual allocation can be big enough for
 647         // the difference to be noticeable.
 648         let offset_bytes =
 649             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 650         // The offset being in bounds cannot rely on "wrapping around" the address space.
 651         // So, first rule out overflows in the pointer arithmetic.
 652         let offset_ptr = ptr.signed_offset(offset_bytes, self)?;
 653         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 654         // memory between these pointers must be accessible. Note that we do not require the
 655         // pointers to be properly aligned (unlike a read/write operation).
 656         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 657         // This call handles checking for integer/null pointers.
 658         self.check_ptr_access_align(
 659             min_ptr,
 660             Size::from_bytes(offset_bytes.unsigned_abs()),
 661             Align::ONE,
 662             CheckInAllocMsg::PointerArithmeticTest,
 663         )?;
 664         Ok(offset_ptr)
 665     }
 666
 667     /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
 668     pub(crate) fn copy_intrinsic(
 669         &mut self,
 670         src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 671         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 672         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 673         nonoverlapping: bool,
 674     ) -> InterpResult<'tcx> {
 675         let count = self.read_scalar(&count)?.to_machine_usize(self)?;
 676         let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
 677         let (size, align) = (layout.size, layout.align.abi);
 678         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 679         // but no actual allocation can be big enough for the difference to be noticeable.
 680         let size = size.checked_mul(count, self).ok_or_else(|| {
 681             err_ub_format!(
 682                 "overflow computing total size of `{}`",
 683                 if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
 684             )
 685         })?;
 686
 687         let src = self.read_pointer(&src)?;
 688         let dst = self.read_pointer(&dst)?;
 689
 690         self.mem_copy(src, align, dst, align, size, nonoverlapping)
 691     }
 692
 693     pub(crate) fn write_bytes_intrinsic(
 694         &mut self,
 695         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 696         byte: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 697         count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 698     ) -> InterpResult<'tcx> {
 699         let layout = self.layout_of(dst.layout.ty.builtin_deref(true).unwrap().ty)?;
 700
 701         let dst = self.read_pointer(&dst)?;
 702         let byte = self.read_scalar(&byte)?.to_u8()?;
 703         let count = self.read_scalar(&count)?.to_machine_usize(self)?;
 704
 705         // `checked_mul` enforces a too small bound (the correct one would probably be machine_isize_max),
 706         // but no actual allocation can be big enough for the difference to be noticeable.
 707         let len = layout
 708             .size
 709             .checked_mul(count, self)
 710             .ok_or_else(|| err_ub_format!("overflow computing total size of `write_bytes`"))?;
 711
 712         let bytes = std::iter::repeat(byte).take(len.bytes_usize());
 713         self.write_bytes_ptr(dst, bytes)
 714     }
 715
 716     pub(crate) fn raw_eq_intrinsic(
 717         &mut self,
 718         lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 719         rhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 720     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
 721         let layout = self.layout_of(lhs.layout.ty.builtin_deref(true).unwrap().ty)?;
 722         assert!(layout.is_sized());
 723
 724         let get_bytes = |this: &InterpCx<'mir, 'tcx, M>,
 725                          op: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
 726                          size|
 727          -> InterpResult<'tcx, &[u8]> {
 728             let ptr = this.read_pointer(op)?;
 729             let Some(alloc_ref) = self.get_ptr_alloc(ptr, size, Align::ONE)? else {
 730                 // zero-sized access
 731                 return Ok(&[]);
 732             };
 733             if alloc_ref.has_provenance() {
 734                 throw_ub_format!("`raw_eq` on bytes with provenance");
 735             }
 736             alloc_ref.get_bytes_strip_provenance()
 737         };
 738
 739         let lhs_bytes = get_bytes(self, lhs, layout.size)?;
 740         let rhs_bytes = get_bytes(self, rhs, layout.size)?;
 741         Ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
 742     }
 743 }