1 //! Intrinsics and other functions that the miri engine executes without
2 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
7 interpret::{ConstValue, GlobalId, InterpResult, Scalar},
11 use rustc::ty::layout::{LayoutOf, Primitive, Size};
12 use rustc::ty::subst::SubstsRef;
13 use rustc::ty::TyCtxt;
14 use rustc_hir::def_id::DefId;
15 use rustc_span::symbol::{sym, Symbol};
18 use super::{ImmTy, InterpCx, Machine, OpTy, PlaceTy};
23 fn numeric_intrinsic<'tcx, Tag>(
27 ) -> InterpResult<'tcx, Scalar<Tag>> {
28 let size = match kind {
29 Primitive::Int(integer, _) => integer.size(),
30 _ => bug!("invalid `{}` argument: {:?}", name, bits),
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),
41 Ok(Scalar::from_uint(bits_out, size))
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>(
48 param_env: ty::ParamEnv<'tcx>,
50 substs: SubstsRef<'tcx>,
51 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
52 let tp_ty = substs.type_at(0);
53 let name = tcx.item_name(def_id);
56 let alloc = type_name::alloc_type_name(tcx, tp_ty);
57 ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
59 sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)),
60 sym::size_of | sym::min_align_of | sym::pref_align_of => {
61 let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
63 sym::pref_align_of => layout.align.pref.bytes(),
64 sym::min_align_of => layout.align.abi.bytes(),
65 sym::size_of => layout.size.bytes(),
68 ConstValue::from_machine_usize(n, &tcx)
70 sym::type_id => ConstValue::from_u64(tcx.type_id_hash(tp_ty)),
71 other => bug!("`{}` is not a zero arg intrinsic", other),
75 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
76 /// Returns `true` if emulation happened.
77 pub fn emulate_intrinsic(
80 instance: ty::Instance<'tcx>,
81 args: &[OpTy<'tcx, M::PointerTag>],
82 ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
83 ) -> InterpResult<'tcx, bool> {
84 let substs = instance.substs;
85 let intrinsic_name = self.tcx.item_name(instance.def_id());
87 // We currently do not handle any intrinsics that are *allowed* to diverge,
88 // but `transmute` could lack a return place in case of UB.
89 let (dest, ret) = match ret {
91 None => match intrinsic_name {
92 sym::transmute => throw_ub!(Unreachable),
93 _ => return Ok(false),
97 // Keep the patterns in this match ordered the same as the list in
98 // `src/librustc/ty/constness.rs`
99 match intrinsic_name {
100 sym::caller_location => {
101 let span = self.find_closest_untracked_caller_location().unwrap_or(span);
102 let location = self.alloc_caller_location_for_span(span);
103 self.write_scalar(location.ptr, dest)?;
111 | sym::type_name => {
112 let gid = GlobalId { instance, promoted: None };
113 let ty = match intrinsic_name {
114 sym::min_align_of | sym::pref_align_of | sym::size_of => self.tcx.types.usize,
115 sym::needs_drop => self.tcx.types.bool,
116 sym::type_id => self.tcx.types.u64,
117 sym::type_name => self.tcx.mk_static_str(),
118 _ => span_bug!(span, "Already checked for nullary intrinsics"),
120 let val = self.const_eval(gid, ty)?;
121 self.copy_op(val, dest)?;
130 | sym::bitreverse => {
131 let ty = substs.type_at(0);
132 let layout_of = self.layout_of(ty)?;
133 let val = self.read_scalar(args[0])?.not_undef()?;
134 let bits = self.force_bits(val, layout_of.size)?;
135 let kind = match layout_of.abi {
136 ty::layout::Abi::Scalar(ref scalar) => scalar.value,
137 _ => throw_unsup!(TypeNotPrimitive(ty)),
139 let (nonzero, intrinsic_name) = match intrinsic_name {
140 sym::cttz_nonzero => (true, sym::cttz),
141 sym::ctlz_nonzero => (true, sym::ctlz),
142 other => (false, other),
144 if nonzero && bits == 0 {
145 throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
147 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
148 self.write_scalar(out_val, dest)?;
153 | sym::add_with_overflow
154 | sym::sub_with_overflow
155 | sym::mul_with_overflow => {
156 let lhs = self.read_immediate(args[0])?;
157 let rhs = self.read_immediate(args[1])?;
158 let (bin_op, ignore_overflow) = match intrinsic_name {
159 sym::wrapping_add => (BinOp::Add, true),
160 sym::wrapping_sub => (BinOp::Sub, true),
161 sym::wrapping_mul => (BinOp::Mul, true),
162 sym::add_with_overflow => (BinOp::Add, false),
163 sym::sub_with_overflow => (BinOp::Sub, false),
164 sym::mul_with_overflow => (BinOp::Mul, false),
165 _ => bug!("Already checked for int ops"),
168 self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
170 self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
173 sym::saturating_add | sym::saturating_sub => {
174 let l = self.read_immediate(args[0])?;
175 let r = self.read_immediate(args[1])?;
176 let is_add = intrinsic_name == sym::saturating_add;
177 let (val, overflowed, _ty) =
178 self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
179 let val = if overflowed {
180 let num_bits = l.layout.size.bits();
181 if l.layout.abi.is_signed() {
182 // For signed ints the saturated value depends on the sign of the first
183 // term since the sign of the second term can be inferred from this and
184 // the fact that the operation has overflowed (if either is 0 no
185 // overflow can occur)
186 let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
187 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
188 if first_term_positive {
189 // Negative overflow not possible since the positive first term
190 // can only increase an (in range) negative term for addition
191 // or corresponding negated positive term for subtraction
193 (1u128 << (num_bits - 1)) - 1, // max positive
194 Size::from_bits(num_bits),
197 // Positive overflow not possible for similar reason
199 Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
206 u128::max_value() >> (128 - num_bits),
207 Size::from_bits(num_bits),
211 Scalar::from_uint(0u128, Size::from_bits(num_bits))
217 self.write_scalar(val, dest)?;
225 | sym::unchecked_rem => {
226 let l = self.read_immediate(args[0])?;
227 let r = self.read_immediate(args[1])?;
228 let bin_op = match intrinsic_name {
229 sym::unchecked_shl => BinOp::Shl,
230 sym::unchecked_shr => BinOp::Shr,
231 sym::unchecked_add => BinOp::Add,
232 sym::unchecked_sub => BinOp::Sub,
233 sym::unchecked_mul => BinOp::Mul,
234 sym::unchecked_div => BinOp::Div,
235 sym::unchecked_rem => BinOp::Rem,
236 _ => bug!("Already checked for int ops"),
238 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
240 let layout = self.layout_of(substs.type_at(0))?;
241 let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
242 if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
243 throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
245 throw_ub_format!("Overflow executing `{}`", intrinsic_name);
248 self.write_scalar(val, dest)?;
250 sym::rotate_left | sym::rotate_right => {
251 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
252 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
253 let layout = self.layout_of(substs.type_at(0))?;
254 let val = self.read_scalar(args[0])?.not_undef()?;
255 let val_bits = self.force_bits(val, layout.size)?;
256 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
257 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
258 let width_bits = layout.size.bits() as u128;
259 let shift_bits = raw_shift_bits % width_bits;
260 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
261 let result_bits = if intrinsic_name == sym::rotate_left {
262 (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
264 (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
266 let truncated_bits = self.truncate(result_bits, layout);
267 let result = Scalar::from_uint(truncated_bits, layout.size);
268 self.write_scalar(result, dest)?;
271 sym::ptr_offset_from => {
272 let isize_layout = self.layout_of(self.tcx.types.isize)?;
273 let a = self.read_immediate(args[0])?.to_scalar()?;
274 let b = self.read_immediate(args[1])?.to_scalar()?;
276 // Special case: if both scalars are *equal integers*
277 // and not NULL, we pretend there is an allocation of size 0 right there,
278 // and their offset is 0. (There's never a valid object at NULL, making it an
279 // exception from the exception.)
280 // This is the dual to the special exception for offset-by-0
281 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
283 // Control flow is weird because we cannot early-return (to reach the
284 // `go_to_block` at the end).
285 let done = if a.is_bits() && b.is_bits() {
286 let a = a.to_machine_usize(self)?;
287 let b = b.to_machine_usize(self)?;
288 if a == b && a != 0 {
289 self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
299 // General case: we need two pointers.
300 let a = self.force_ptr(a)?;
301 let b = self.force_ptr(b)?;
302 if a.alloc_id != b.alloc_id {
304 "ptr_offset_from cannot compute offset of pointers into different \
308 let usize_layout = self.layout_of(self.tcx.types.usize)?;
309 let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
310 let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
311 let (val, _overflowed, _ty) =
312 self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
313 let pointee_layout = self.layout_of(substs.type_at(0))?;
314 let val = ImmTy::from_scalar(val, isize_layout);
315 let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
316 self.exact_div(val, size, dest)?;
321 self.copy_op_transmute(args[0], dest)?;
323 sym::simd_insert => {
324 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
327 let (len, e_ty) = input.layout.ty.simd_size_and_type(self.tcx.tcx);
330 "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
336 input.layout, dest.layout,
337 "Return type `{}` must match vector type `{}`",
338 dest.layout.ty, input.layout.ty
341 elem.layout.ty, e_ty,
342 "Scalar element type `{}` must match vector element type `{}`",
347 let place = self.place_field(dest, i)?;
348 let value = if i == index { elem } else { self.operand_field(input, i)? };
349 self.copy_op(value, place)?;
352 sym::simd_extract => {
353 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
354 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(self.tcx.tcx);
357 "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
363 e_ty, dest.layout.ty,
364 "Return type `{}` must match vector element type `{}`",
367 self.copy_op(self.operand_field(args[0], index)?, dest)?;
369 _ => return Ok(false),
372 self.dump_place(*dest);
373 self.go_to_block(ret);
379 a: ImmTy<'tcx, M::PointerTag>,
380 b: ImmTy<'tcx, M::PointerTag>,
381 dest: PlaceTy<'tcx, M::PointerTag>,
382 ) -> InterpResult<'tcx> {
383 // Performs an exact division, resulting in undefined behavior where
384 // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
385 // First, check x % y != 0 (or if that computation overflows).
386 let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
387 if overflow || res.assert_bits(a.layout.size) != 0 {
388 // Then, check if `b` is -1, which is the "min_value / -1" case.
389 let minus1 = Scalar::from_int(-1, dest.layout.size);
390 let b_scalar = b.to_scalar().unwrap();
391 if b_scalar == minus1 {
392 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
394 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
397 // `Rem` says this is all right, so we can let `Div` do its job.
398 self.binop_ignore_overflow(BinOp::Div, a, b, dest)