src/librustc_mir/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::{uabs, ConstValue, GlobalId, InterpResult, Scalar},
  11     BinOp,
  12 };
  13 use rustc_middle::ty;
  14 use rustc_middle::ty::subst::SubstsRef;
  15 use rustc_middle::ty::{Ty, TyCtxt, TypeFoldable};
  16 use rustc_span::symbol::{sym, Symbol};
  17 use rustc_target::abi::{Abi, LayoutOf as _, Primitive, Size};
  18
  19 use super::{CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy};
  20
  21 mod caller_location;
  22 mod type_name;
  23
  24 fn numeric_intrinsic<'tcx, Tag>(
  25     name: Symbol,
  26     bits: u128,
  27     kind: Primitive,
  28 ) -> InterpResult<'tcx, Scalar<Tag>> {
  29     let size = match kind {
  30         Primitive::Int(integer, _) => integer.size(),
  31         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  32     };
  33     let extra = 128 - u128::from(size.bits());
  34     let bits_out = match name {
  35         sym::ctpop => u128::from(bits.count_ones()),
  36         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  37         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  38         sym::bswap => (bits << extra).swap_bytes(),
  39         sym::bitreverse => (bits << extra).reverse_bits(),
  40         _ => bug!("not a numeric intrinsic: {}", name),
  41     };
  42     Ok(Scalar::from_uint(bits_out, size))
  43 }
  44
  45 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  46 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  47 crate fn eval_nullary_intrinsic<'tcx>(
  48     tcx: TyCtxt<'tcx>,
  49     param_env: ty::ParamEnv<'tcx>,
  50     def_id: DefId,
  51     substs: SubstsRef<'tcx>,
  52 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  53     let tp_ty = substs.type_at(0);
  54     let name = tcx.item_name(def_id);
  55     Ok(match name {
  56         sym::type_name => {
  57             if tp_ty.needs_subst() {
  58                 throw_inval!(TooGeneric);
  59             }
  60             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  61             ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
  62         }
  63         sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)),
  64         sym::size_of | sym::min_align_of | sym::pref_align_of => {
  65             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  66             let n = match name {
  67                 sym::pref_align_of => layout.align.pref.bytes(),
  68                 sym::min_align_of => layout.align.abi.bytes(),
  69                 sym::size_of => layout.size.bytes(),
  70                 _ => bug!(),
  71             };
  72             ConstValue::from_machine_usize(n, &tcx)
  73         }
  74         sym::type_id => {
  75             if tp_ty.needs_subst() {
  76                 throw_inval!(TooGeneric);
  77             }
  78             ConstValue::from_u64(tcx.type_id_hash(tp_ty))
  79         }
  80         sym::variant_count => {
  81             if let ty::Adt(ref adt, _) = tp_ty.kind {
  82                 ConstValue::from_machine_usize(adt.variants.len() as u64, &tcx)
  83             } else {
  84                 ConstValue::from_machine_usize(0u64, &tcx)
  85             }
  86         }
  87         other => bug!("`{}` is not a zero arg intrinsic", other),
  88     })
  89 }
  90
  91 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  92     /// Returns `true` if emulation happened.
  93     pub fn emulate_intrinsic(
  94         &mut self,
  95         instance: ty::Instance<'tcx>,
  96         args: &[OpTy<'tcx, M::PointerTag>],
  97         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
  98     ) -> InterpResult<'tcx, bool> {
  99         let substs = instance.substs;
 100         let intrinsic_name = self.tcx.item_name(instance.def_id());
 101
 102         // First handle intrinsics without return place.
 103         let (dest, ret) = match ret {
 104             None => match intrinsic_name {
 105                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 106                 sym::unreachable => throw_ub!(Unreachable),
 107                 sym::abort => M::abort(self)?,
 108                 // Unsupported diverging intrinsic.
 109                 _ => return Ok(false),
 110             },
 111             Some(p) => p,
 112         };
 113
 114         // Keep the patterns in this match ordered the same as the list in
 115         // `src/librustc_middle/ty/constness.rs`
 116         match intrinsic_name {
 117             sym::caller_location => {
 118                 let span = self.find_closest_untracked_caller_location();
 119                 let location = self.alloc_caller_location_for_span(span);
 120                 self.write_scalar(location.ptr, dest)?;
 121             }
 122
 123             sym::min_align_of
 124             | sym::pref_align_of
 125             | sym::needs_drop
 126             | sym::size_of
 127             | sym::type_id
 128             | sym::type_name
 129             | sym::variant_count => {
 130                 let gid = GlobalId { instance, promoted: None };
 131                 let ty = match intrinsic_name {
 132                     sym::min_align_of | sym::pref_align_of | sym::size_of | sym::variant_count => {
 133                         self.tcx.types.usize
 134                     }
 135                     sym::needs_drop => self.tcx.types.bool,
 136                     sym::type_id => self.tcx.types.u64,
 137                     sym::type_name => self.tcx.mk_static_str(),
 138                     _ => bug!("already checked for nullary intrinsics"),
 139                 };
 140                 let val = self.const_eval(gid, ty)?;
 141                 self.copy_op(val, dest)?;
 142             }
 143
 144             sym::ctpop
 145             | sym::cttz
 146             | sym::cttz_nonzero
 147             | sym::ctlz
 148             | sym::ctlz_nonzero
 149             | sym::bswap
 150             | sym::bitreverse => {
 151                 let ty = substs.type_at(0);
 152                 let layout_of = self.layout_of(ty)?;
 153                 let val = self.read_scalar(args[0])?.not_undef()?;
 154                 let bits = self.force_bits(val, layout_of.size)?;
 155                 let kind = match layout_of.abi {
 156                     Abi::Scalar(ref scalar) => scalar.value,
 157                     _ => span_bug!(
 158                         self.cur_span(),
 159                         "{} called on invalid type {:?}",
 160                         intrinsic_name,
 161                         ty
 162                     ),
 163                 };
 164                 let (nonzero, intrinsic_name) = match intrinsic_name {
 165                     sym::cttz_nonzero => (true, sym::cttz),
 166                     sym::ctlz_nonzero => (true, sym::ctlz),
 167                     other => (false, other),
 168                 };
 169                 if nonzero && bits == 0 {
 170                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 171                 }
 172                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 173                 self.write_scalar(out_val, dest)?;
 174             }
 175             sym::wrapping_add
 176             | sym::wrapping_sub
 177             | sym::wrapping_mul
 178             | sym::add_with_overflow
 179             | sym::sub_with_overflow
 180             | sym::mul_with_overflow => {
 181                 let lhs = self.read_immediate(args[0])?;
 182                 let rhs = self.read_immediate(args[1])?;
 183                 let (bin_op, ignore_overflow) = match intrinsic_name {
 184                     sym::wrapping_add => (BinOp::Add, true),
 185                     sym::wrapping_sub => (BinOp::Sub, true),
 186                     sym::wrapping_mul => (BinOp::Mul, true),
 187                     sym::add_with_overflow => (BinOp::Add, false),
 188                     sym::sub_with_overflow => (BinOp::Sub, false),
 189                     sym::mul_with_overflow => (BinOp::Mul, false),
 190                     _ => bug!("Already checked for int ops"),
 191                 };
 192                 if ignore_overflow {
 193                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 194                 } else {
 195                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 196                 }
 197             }
 198             sym::saturating_add | sym::saturating_sub => {
 199                 let l = self.read_immediate(args[0])?;
 200                 let r = self.read_immediate(args[1])?;
 201                 let is_add = intrinsic_name == sym::saturating_add;
 202                 let (val, overflowed, _ty) =
 203                     self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
 204                 let val = if overflowed {
 205                     let num_bits = l.layout.size.bits();
 206                     if l.layout.abi.is_signed() {
 207                         // For signed ints the saturated value depends on the sign of the first
 208                         // term since the sign of the second term can be inferred from this and
 209                         // the fact that the operation has overflowed (if either is 0 no
 210                         // overflow can occur)
 211                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 212                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 213                         if first_term_positive {
 214                             // Negative overflow not possible since the positive first term
 215                             // can only increase an (in range) negative term for addition
 216                             // or corresponding negated positive term for subtraction
 217                             Scalar::from_uint(
 218                                 (1u128 << (num_bits - 1)) - 1, // max positive
 219                                 Size::from_bits(num_bits),
 220                             )
 221                         } else {
 222                             // Positive overflow not possible for similar reason
 223                             // max negative
 224                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 225                         }
 226                     } else {
 227                         // unsigned
 228                         if is_add {
 229                             // max unsigned
 230                             Scalar::from_uint(
 231                                 u128::MAX >> (128 - num_bits),
 232                                 Size::from_bits(num_bits),
 233                             )
 234                         } else {
 235                             // underflow to 0
 236                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 237                         }
 238                     }
 239                 } else {
 240                     val
 241                 };
 242                 self.write_scalar(val, dest)?;
 243             }
 244             sym::discriminant_value => {
 245                 let place = self.deref_operand(args[0])?;
 246                 let discr_val = self.read_discriminant(place.into())?.0;
 247                 self.write_scalar(discr_val, dest)?;
 248             }
 249             sym::unchecked_shl
 250             | sym::unchecked_shr
 251             | sym::unchecked_add
 252             | sym::unchecked_sub
 253             | sym::unchecked_mul
 254             | sym::unchecked_div
 255             | sym::unchecked_rem => {
 256                 let l = self.read_immediate(args[0])?;
 257                 let r = self.read_immediate(args[1])?;
 258                 let bin_op = match intrinsic_name {
 259                     sym::unchecked_shl => BinOp::Shl,
 260                     sym::unchecked_shr => BinOp::Shr,
 261                     sym::unchecked_add => BinOp::Add,
 262                     sym::unchecked_sub => BinOp::Sub,
 263                     sym::unchecked_mul => BinOp::Mul,
 264                     sym::unchecked_div => BinOp::Div,
 265                     sym::unchecked_rem => BinOp::Rem,
 266                     _ => bug!("Already checked for int ops"),
 267                 };
 268                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 269                 if overflowed {
 270                     let layout = self.layout_of(substs.type_at(0))?;
 271                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 272                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 273                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 274                     } else {
 275                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 276                     }
 277                 }
 278                 self.write_scalar(val, dest)?;
 279             }
 280             sym::rotate_left | sym::rotate_right => {
 281                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 282                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 283                 let layout = self.layout_of(substs.type_at(0))?;
 284                 let val = self.read_scalar(args[0])?.not_undef()?;
 285                 let val_bits = self.force_bits(val, layout.size)?;
 286                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 287                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 288                 let width_bits = u128::from(layout.size.bits());
 289                 let shift_bits = raw_shift_bits % width_bits;
 290                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 291                 let result_bits = if intrinsic_name == sym::rotate_left {
 292                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 293                 } else {
 294                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 295                 };
 296                 let truncated_bits = self.truncate(result_bits, layout);
 297                 let result = Scalar::from_uint(truncated_bits, layout.size);
 298                 self.write_scalar(result, dest)?;
 299             }
 300             sym::offset => {
 301                 let ptr = self.read_scalar(args[0])?.not_undef()?;
 302                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 303                 let pointee_ty = substs.type_at(0);
 304
 305                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 306                 self.write_scalar(offset_ptr, dest)?;
 307             }
 308             sym::arith_offset => {
 309                 let ptr = self.read_scalar(args[0])?.not_undef()?;
 310                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 311                 let pointee_ty = substs.type_at(0);
 312
 313                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 314                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 315                 let offset_ptr = ptr.ptr_wrapping_signed_offset(offset_bytes, self);
 316                 self.write_scalar(offset_ptr, dest)?;
 317             }
 318             sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {
 319                 // FIXME: return `true` for at least some comparisons where we can reliably
 320                 // determine the result of runtime (in)equality tests at compile-time.
 321                 self.write_scalar(Scalar::from_bool(false), dest)?;
 322             }
 323             sym::ptr_offset_from => {
 324                 let a = self.read_immediate(args[0])?.to_scalar()?;
 325                 let b = self.read_immediate(args[1])?.to_scalar()?;
 326
 327                 // Special case: if both scalars are *equal integers*
 328                 // and not NULL, we pretend there is an allocation of size 0 right there,
 329                 // and their offset is 0. (There's never a valid object at NULL, making it an
 330                 // exception from the exception.)
 331                 // This is the dual to the special exception for offset-by-0
 332                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 333                 //
 334                 // Control flow is weird because we cannot early-return (to reach the
 335                 // `go_to_block` at the end).
 336                 let done = if a.is_bits() && b.is_bits() {
 337                     let a = a.to_machine_usize(self)?;
 338                     let b = b.to_machine_usize(self)?;
 339                     if a == b && a != 0 {
 340                         self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
 341                         true
 342                     } else {
 343                         false
 344                     }
 345                 } else {
 346                     false
 347                 };
 348
 349                 if !done {
 350                     // General case: we need two pointers.
 351                     let a = self.force_ptr(a)?;
 352                     let b = self.force_ptr(b)?;
 353                     if a.alloc_id != b.alloc_id {
 354                         throw_ub_format!(
 355                             "ptr_offset_from cannot compute offset of pointers into different \
 356                             allocations.",
 357                         );
 358                     }
 359                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 360                     let isize_layout = self.layout_of(self.tcx.types.isize)?;
 361                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 362                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 363                     let (val, _overflowed, _ty) =
 364                         self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
 365                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 366                     let val = ImmTy::from_scalar(val, isize_layout);
 367                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 368                     self.exact_div(val, size, dest)?;
 369                 }
 370             }
 371
 372             sym::transmute => {
 373                 self.copy_op_transmute(args[0], dest)?;
 374             }
 375             sym::simd_insert => {
 376                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 377                 let elem = args[2];
 378                 let input = args[0];
 379                 let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx);
 380                 assert!(
 381                     index < len,
 382                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 383                     index,
 384                     e_ty,
 385                     len
 386                 );
 387                 assert_eq!(
 388                     input.layout, dest.layout,
 389                     "Return type `{}` must match vector type `{}`",
 390                     dest.layout.ty, input.layout.ty
 391                 );
 392                 assert_eq!(
 393                     elem.layout.ty, e_ty,
 394                     "Scalar element type `{}` must match vector element type `{}`",
 395                     elem.layout.ty, e_ty
 396                 );
 397
 398                 for i in 0..len {
 399                     let place = self.place_index(dest, i)?;
 400                     let value = if i == index { elem } else { self.operand_index(input, i)? };
 401                     self.copy_op(value, place)?;
 402                 }
 403             }
 404             sym::simd_extract => {
 405                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 406                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx);
 407                 assert!(
 408                     index < len,
 409                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 410                     index,
 411                     e_ty,
 412                     len
 413                 );
 414                 assert_eq!(
 415                     e_ty, dest.layout.ty,
 416                     "Return type `{}` must match vector element type `{}`",
 417                     dest.layout.ty, e_ty
 418                 );
 419                 self.copy_op(self.operand_index(args[0], index)?, dest)?;
 420             }
 421             sym::likely | sym::unlikely => {
 422                 // These just return their argument
 423                 self.copy_op(args[0], dest)?;
 424             }
 425             // FIXME(#73156): Handle source code coverage in const eval
 426             sym::count_code_region
 427             | sym::coverage_counter_add
 428             | sym::coverage_counter_subtract
 429             | sym::coverage_unreachable => (),
 430             _ => return Ok(false),
 431         }
 432
 433         self.dump_place(*dest);
 434         self.go_to_block(ret);
 435         Ok(true)
 436     }
 437
 438     pub fn exact_div(
 439         &mut self,
 440         a: ImmTy<'tcx, M::PointerTag>,
 441         b: ImmTy<'tcx, M::PointerTag>,
 442         dest: PlaceTy<'tcx, M::PointerTag>,
 443     ) -> InterpResult<'tcx> {
 444         // Performs an exact division, resulting in undefined behavior where
 445         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 446         // First, check x % y != 0 (or if that computation overflows).
 447         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
 448         if overflow || res.assert_bits(a.layout.size) != 0 {
 449             // Then, check if `b` is -1, which is the "MIN / -1" case.
 450             let minus1 = Scalar::from_int(-1, dest.layout.size);
 451             let b_scalar = b.to_scalar().unwrap();
 452             if b_scalar == minus1 {
 453                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 454             } else {
 455                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 456             }
 457         }
 458         // `Rem` says this is all right, so we can let `Div` do its job.
 459         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 460     }
 461
 462     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 463     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 464     /// 0, so offset-by-0 (and only 0) is okay -- except that NULL cannot be offset by _any_ value.
 465     pub fn ptr_offset_inbounds(
 466         &self,
 467         ptr: Scalar<M::PointerTag>,
 468         pointee_ty: Ty<'tcx>,
 469         offset_count: i64,
 470     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 471         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 472         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 473         // The computed offset, in bytes, cannot overflow an isize.
 474         let offset_bytes =
 475             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 476         // The offset being in bounds cannot rely on "wrapping around" the address space.
 477         // So, first rule out overflows in the pointer arithmetic.
 478         let offset_ptr = ptr.ptr_signed_offset(offset_bytes, self)?;
 479         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 480         // memory between these pointers must be accessible. Note that we do not require the
 481         // pointers to be properly aligned (unlike a read/write operation).
 482         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 483         let size: u64 = uabs(offset_bytes);
 484         // This call handles checking for integer/NULL pointers.
 485         self.memory.check_ptr_access_align(
 486             min_ptr,
 487             Size::from_bytes(size),
 488             None,
 489             CheckInAllocMsg::InboundsTest,
 490         )?;
 491         Ok(offset_ptr)
 492     }
 493 }