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 rustc::hir::def_id::DefId;
   6 use rustc::mir::{
   7     self,
   8     interpret::{ConstValue, InterpResult, Scalar},
   9     BinOp,
  10 };
  11 use rustc::ty;
  12 use rustc::ty::layout::{LayoutOf, Primitive, Size};
  13 use rustc::ty::subst::SubstsRef;
  14 use rustc::ty::TyCtxt;
  15 use syntax_pos::symbol::{sym, Symbol};
  16 use syntax_pos::Span;
  17
  18 use super::{ImmTy, InterpCx, Machine, OpTy, PlaceTy};
  19
  20 mod caller_location;
  21 mod type_name;
  22
  23 fn numeric_intrinsic<'tcx, Tag>(
  24     name: Symbol,
  25     bits: u128,
  26     kind: Primitive,
  27 ) -> InterpResult<'tcx, Scalar<Tag>> {
  28     let size = match kind {
  29         Primitive::Int(integer, _) => integer.size(),
  30         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  31     };
  32     let extra = 128 - size.bits() as u128;
  33     let bits_out = match name {
  34         sym::ctpop => bits.count_ones() as u128,
  35         sym::ctlz => bits.leading_zeros() as u128 - extra,
  36         sym::cttz => (bits << extra).trailing_zeros() as u128 - extra,
  37         sym::bswap => (bits << extra).swap_bytes(),
  38         sym::bitreverse => (bits << extra).reverse_bits(),
  39         _ => bug!("not a numeric intrinsic: {}", name),
  40     };
  41     Ok(Scalar::from_uint(bits_out, size))
  42 }
  43
  44 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  45 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  46 crate fn eval_nullary_intrinsic<'tcx>(
  47     tcx: TyCtxt<'tcx>,
  48     param_env: ty::ParamEnv<'tcx>,
  49     def_id: DefId,
  50     substs: SubstsRef<'tcx>,
  51 ) -> InterpResult<'tcx, &'tcx ty::Const<'tcx>> {
  52     let tp_ty = substs.type_at(0);
  53     let name = tcx.item_name(def_id);
  54     Ok(match name {
  55         sym::type_name => {
  56             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  57             tcx.mk_const(ty::Const {
  58                 val: ty::ConstKind::Value(ConstValue::Slice {
  59                     data: alloc,
  60                     start: 0,
  61                     end: alloc.len(),
  62                 }),
  63                 ty: tcx.mk_static_str(),
  64             })
  65         }
  66         sym::needs_drop => ty::Const::from_bool(tcx, tp_ty.needs_drop(tcx, param_env)),
  67         sym::size_of | sym::min_align_of | sym::pref_align_of => {
  68             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  69             let n = match name {
  70                 sym::pref_align_of => layout.align.pref.bytes(),
  71                 sym::min_align_of => layout.align.abi.bytes(),
  72                 sym::size_of => layout.size.bytes(),
  73                 _ => bug!(),
  74             };
  75             ty::Const::from_usize(tcx, n)
  76         }
  77         sym::type_id => {
  78             ty::Const::from_bits(tcx, tcx.type_id_hash(tp_ty).into(), param_env.and(tcx.types.u64))
  79         }
  80         other => bug!("`{}` is not a zero arg intrinsic", other),
  81     })
  82 }
  83
  84 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  85     /// Returns `true` if emulation happened.
  86     pub fn emulate_intrinsic(
  87         &mut self,
  88         span: Span,
  89         instance: ty::Instance<'tcx>,
  90         args: &[OpTy<'tcx, M::PointerTag>],
  91         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
  92     ) -> InterpResult<'tcx, bool> {
  93         let substs = instance.substs;
  94         let intrinsic_name = self.tcx.item_name(instance.def_id());
  95
  96         // We currently do not handle any intrinsics that are *allowed* to diverge,
  97         // but `transmute` could lack a return place in case of UB.
  98         let (dest, ret) = match ret {
  99             Some(p) => p,
 100             None => match intrinsic_name {
 101                 sym::transmute => throw_ub!(Unreachable),
 102                 _ => return Ok(false),
 103             },
 104         };
 105
 106         // Keep the patterns in this match ordered the same as the list in
 107         // `src/librustc/ty/constness.rs`
 108         match intrinsic_name {
 109             sym::caller_location => {
 110                 let span = self.find_closest_untracked_caller_location().unwrap_or(span);
 111                 let location = self.alloc_caller_location_for_span(span);
 112                 self.write_scalar(location.ptr, dest)?;
 113             }
 114
 115             sym::min_align_of
 116             | sym::pref_align_of
 117             | sym::needs_drop
 118             | sym::size_of
 119             | sym::type_id
 120             | sym::type_name => {
 121                 let gid = GlobalId { instance, promoted: None };
 122                 let val = self.const_eval(gid)?;
 123                 self.copy_op(val, dest)?;
 124             }
 125
 126             sym::ctpop
 127             | sym::cttz
 128             | sym::cttz_nonzero
 129             | sym::ctlz
 130             | sym::ctlz_nonzero
 131             | sym::bswap
 132             | sym::bitreverse => {
 133                 let ty = substs.type_at(0);
 134                 let layout_of = self.layout_of(ty)?;
 135                 let val = self.read_scalar(args[0])?.not_undef()?;
 136                 let bits = self.force_bits(val, layout_of.size)?;
 137                 let kind = match layout_of.abi {
 138                     ty::layout::Abi::Scalar(ref scalar) => scalar.value,
 139                     _ => throw_unsup!(TypeNotPrimitive(ty)),
 140                 };
 141                 let (nonzero, intrinsic_name) = match intrinsic_name {
 142                     sym::cttz_nonzero => (true, sym::cttz),
 143                     sym::ctlz_nonzero => (true, sym::ctlz),
 144                     other => (false, other),
 145                 };
 146                 if nonzero && bits == 0 {
 147                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 148                 }
 149                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 150                 self.write_scalar(out_val, dest)?;
 151             }
 152             sym::wrapping_add
 153             | sym::wrapping_sub
 154             | sym::wrapping_mul
 155             | sym::add_with_overflow
 156             | sym::sub_with_overflow
 157             | sym::mul_with_overflow => {
 158                 let lhs = self.read_immediate(args[0])?;
 159                 let rhs = self.read_immediate(args[1])?;
 160                 let (bin_op, ignore_overflow) = match intrinsic_name {
 161                     sym::wrapping_add => (BinOp::Add, true),
 162                     sym::wrapping_sub => (BinOp::Sub, true),
 163                     sym::wrapping_mul => (BinOp::Mul, true),
 164                     sym::add_with_overflow => (BinOp::Add, false),
 165                     sym::sub_with_overflow => (BinOp::Sub, false),
 166                     sym::mul_with_overflow => (BinOp::Mul, false),
 167                     _ => bug!("Already checked for int ops"),
 168                 };
 169                 if ignore_overflow {
 170                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 171                 } else {
 172                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 173                 }
 174             }
 175             sym::saturating_add | sym::saturating_sub => {
 176                 let l = self.read_immediate(args[0])?;
 177                 let r = self.read_immediate(args[1])?;
 178                 let is_add = intrinsic_name == sym::saturating_add;
 179                 let (val, overflowed, _ty) =
 180                     self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
 181                 let val = if overflowed {
 182                     let num_bits = l.layout.size.bits();
 183                     if l.layout.abi.is_signed() {
 184                         // For signed ints the saturated value depends on the sign of the first
 185                         // term since the sign of the second term can be inferred from this and
 186                         // the fact that the operation has overflowed (if either is 0 no
 187                         // overflow can occur)
 188                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 189                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 190                         if first_term_positive {
 191                             // Negative overflow not possible since the positive first term
 192                             // can only increase an (in range) negative term for addition
 193                             // or corresponding negated positive term for subtraction
 194                             Scalar::from_uint(
 195                                 (1u128 << (num_bits - 1)) - 1, // max positive
 196                                 Size::from_bits(num_bits),
 197                             )
 198                         } else {
 199                             // Positive overflow not possible for similar reason
 200                             // max negative
 201                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 202                         }
 203                     } else {
 204                         // unsigned
 205                         if is_add {
 206                             // max unsigned
 207                             Scalar::from_uint(
 208                                 u128::max_value() >> (128 - num_bits),
 209                                 Size::from_bits(num_bits),
 210                             )
 211                         } else {
 212                             // underflow to 0
 213                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 214                         }
 215                     }
 216                 } else {
 217                     val
 218                 };
 219                 self.write_scalar(val, dest)?;
 220             }
 221             sym::unchecked_shl | sym::unchecked_shr => {
 222                 let l = self.read_immediate(args[0])?;
 223                 let r = self.read_immediate(args[1])?;
 224                 let bin_op = match intrinsic_name {
 225                     sym::unchecked_shl => BinOp::Shl,
 226                     sym::unchecked_shr => BinOp::Shr,
 227                     _ => bug!("Already checked for int ops"),
 228                 };
 229                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 230                 if overflowed {
 231                     let layout = self.layout_of(substs.type_at(0))?;
 232                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 233                     throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
 234                 }
 235                 self.write_scalar(val, dest)?;
 236             }
 237             sym::rotate_left | sym::rotate_right => {
 238                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 239                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 240                 let layout = self.layout_of(substs.type_at(0))?;
 241                 let val = self.read_scalar(args[0])?.not_undef()?;
 242                 let val_bits = self.force_bits(val, layout.size)?;
 243                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 244                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 245                 let width_bits = layout.size.bits() as u128;
 246                 let shift_bits = raw_shift_bits % width_bits;
 247                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 248                 let result_bits = if intrinsic_name == sym::rotate_left {
 249                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 250                 } else {
 251                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 252                 };
 253                 let truncated_bits = self.truncate(result_bits, layout);
 254                 let result = Scalar::from_uint(truncated_bits, layout.size);
 255                 self.write_scalar(result, dest)?;
 256             }
 257
 258             sym::ptr_offset_from => {
 259                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 260                 let a = self.read_immediate(args[0])?.to_scalar()?;
 261                 let b = self.read_immediate(args[1])?.to_scalar()?;
 262
 263                 // Special case: if both scalars are *equal integers*
 264                 // and not NULL, we pretend there is an allocation of size 0 right there,
 265                 // and their offset is 0. (There's never a valid object at NULL, making it an
 266                 // exception from the exception.)
 267                 // This is the dual to the special exception for offset-by-0
 268                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 269                 //
 270                 // Control flow is weird because we cannot early-return (to reach the
 271                 // `go_to_block` at the end).
 272                 let done = if a.is_bits() && b.is_bits() {
 273                     let a = a.to_machine_usize(self)?;
 274                     let b = b.to_machine_usize(self)?;
 275                     if a == b && a != 0 {
 276                         self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
 277                         true
 278                     } else {
 279                         false
 280                     }
 281                 } else {
 282                     false
 283                 };
 284
 285                 if !done {
 286                     // General case: we need two pointers.
 287                     let a = self.force_ptr(a)?;
 288                     let b = self.force_ptr(b)?;
 289                     if a.alloc_id != b.alloc_id {
 290                         throw_ub_format!(
 291                             "ptr_offset_from cannot compute offset of pointers into different \
 292                             allocations.",
 293                         );
 294                     }
 295                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 296                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 297                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 298                     let (val, _overflowed, _ty) =
 299                         self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
 300                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 301                     let val = ImmTy::from_scalar(val, isize_layout);
 302                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 303                     self.exact_div(val, size, dest)?;
 304                 }
 305             }
 306
 307             sym::transmute => {
 308                 self.copy_op_transmute(args[0], dest)?;
 309             }
 310             sym::simd_insert => {
 311                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 312                 let elem = args[2];
 313                 let input = args[0];
 314                 let (len, e_ty) = input.layout.ty.simd_size_and_type(self.tcx.tcx);
 315                 assert!(
 316                     index < len,
 317                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 318                     index,
 319                     e_ty,
 320                     len
 321                 );
 322                 assert_eq!(
 323                     input.layout, dest.layout,
 324                     "Return type `{}` must match vector type `{}`",
 325                     dest.layout.ty, input.layout.ty
 326                 );
 327                 assert_eq!(
 328                     elem.layout.ty, e_ty,
 329                     "Scalar element type `{}` must match vector element type `{}`",
 330                     elem.layout.ty, e_ty
 331                 );
 332
 333                 for i in 0..len {
 334                     let place = self.place_field(dest, i)?;
 335                     let value = if i == index { elem } else { self.operand_field(input, i)? };
 336                     self.copy_op(value, place)?;
 337                 }
 338             }
 339             sym::simd_extract => {
 340                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 341                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(self.tcx.tcx);
 342                 assert!(
 343                     index < len,
 344                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 345                     index,
 346                     e_ty,
 347                     len
 348                 );
 349                 assert_eq!(
 350                     e_ty, dest.layout.ty,
 351                     "Return type `{}` must match vector element type `{}`",
 352                     dest.layout.ty, e_ty
 353                 );
 354                 self.copy_op(self.operand_field(args[0], index)?, dest)?;
 355             }
 356             _ => return Ok(false),
 357         }
 358
 359         self.dump_place(*dest);
 360         self.go_to_block(ret);
 361         Ok(true)
 362     }
 363
 364     /// "Intercept" a function call to a panic-related function
 365     /// because we have something special to do for it.
 366     /// Returns `true` if an intercept happened.
 367     pub fn hook_panic_fn(
 368         &mut self,
 369         instance: ty::Instance<'tcx>,
 370         args: &[OpTy<'tcx, M::PointerTag>],
 371         _ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
 372     ) -> InterpResult<'tcx, bool> {
 373         let def_id = instance.def_id();
 374         if Some(def_id) == self.tcx.lang_items().panic_fn() {
 375             // &'static str, &core::panic::Location { &'static str, u32, u32 }
 376             assert!(args.len() == 2);
 377
 378             let msg_place = self.deref_operand(args[0])?;
 379             let msg = Symbol::intern(self.read_str(msg_place)?);
 380
 381             let location = self.deref_operand(args[1])?;
 382             let (file, line, col) = (
 383                 self.mplace_field(location, 0)?,
 384                 self.mplace_field(location, 1)?,
 385                 self.mplace_field(location, 2)?,
 386             );
 387
 388             let file_place = self.deref_operand(file.into())?;
 389             let file = Symbol::intern(self.read_str(file_place)?);
 390             let line = self.read_scalar(line.into())?.to_u32()?;
 391             let col = self.read_scalar(col.into())?.to_u32()?;
 392             throw_panic!(Panic { msg, file, line, col })
 393         } else if Some(def_id) == self.tcx.lang_items().begin_panic_fn() {
 394             assert!(args.len() == 2);
 395             // &'static str, &(&'static str, u32, u32)
 396             let msg = args[0];
 397             let place = self.deref_operand(args[1])?;
 398             let (file, line, col) = (
 399                 self.mplace_field(place, 0)?,
 400                 self.mplace_field(place, 1)?,
 401                 self.mplace_field(place, 2)?,
 402             );
 403
 404             let msg_place = self.deref_operand(msg.into())?;
 405             let msg = Symbol::intern(self.read_str(msg_place)?);
 406             let file_place = self.deref_operand(file.into())?;
 407             let file = Symbol::intern(self.read_str(file_place)?);
 408             let line = self.read_scalar(line.into())?.to_u32()?;
 409             let col = self.read_scalar(col.into())?.to_u32()?;
 410             throw_panic!(Panic { msg, file, line, col })
 411         } else {
 412             return Ok(false);
 413         }
 414     }
 415
 416     pub fn exact_div(
 417         &mut self,
 418         a: ImmTy<'tcx, M::PointerTag>,
 419         b: ImmTy<'tcx, M::PointerTag>,
 420         dest: PlaceTy<'tcx, M::PointerTag>,
 421     ) -> InterpResult<'tcx> {
 422         // Performs an exact division, resulting in undefined behavior where
 423         // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
 424         // First, check x % y != 0.
 425         if self.binary_op(BinOp::Rem, a, b)?.to_bits()? != 0 {
 426             // Then, check if `b` is -1, which is the "min_value / -1" case.
 427             let minus1 = Scalar::from_int(-1, dest.layout.size);
 428             let b_scalar = b.to_scalar().unwrap();
 429             if b_scalar == minus1 {
 430                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 431             } else {
 432                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 433             }
 434         }
 435         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 436     }
 437 }