diff options
Diffstat (limited to 'compiler/rustc_mir/src/interpret/intrinsics.rs')
| -rw-r--r-- | compiler/rustc_mir/src/interpret/intrinsics.rs | 537 |
1 files changed, 537 insertions, 0 deletions
diff --git a/compiler/rustc_mir/src/interpret/intrinsics.rs b/compiler/rustc_mir/src/interpret/intrinsics.rs new file mode 100644 index 00000000000..b37dcd42f4c --- /dev/null +++ b/compiler/rustc_mir/src/interpret/intrinsics.rs @@ -0,0 +1,537 @@ +//! Intrinsics and other functions that the miri engine executes without +//! looking at their MIR. Intrinsics/functions supported here are shared by CTFE +//! and miri. + +use std::convert::TryFrom; + +use rustc_hir::def_id::DefId; +use rustc_middle::mir::{ + self, + interpret::{uabs, ConstValue, GlobalId, InterpResult, Scalar}, + BinOp, +}; +use rustc_middle::ty; +use rustc_middle::ty::subst::SubstsRef; +use rustc_middle::ty::{Ty, TyCtxt}; +use rustc_span::symbol::{sym, Symbol}; +use rustc_target::abi::{Abi, LayoutOf as _, Primitive, Size}; + +use super::{ + util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy, +}; + +mod caller_location; +mod type_name; + +fn numeric_intrinsic<'tcx, Tag>( + name: Symbol, + bits: u128, + kind: Primitive, +) -> InterpResult<'tcx, Scalar<Tag>> { + let size = match kind { + Primitive::Int(integer, _) => integer.size(), + _ => bug!("invalid `{}` argument: {:?}", name, bits), + }; + let extra = 128 - u128::from(size.bits()); + let bits_out = match name { + sym::ctpop => u128::from(bits.count_ones()), + sym::ctlz => u128::from(bits.leading_zeros()) - extra, + sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra, + sym::bswap => (bits << extra).swap_bytes(), + sym::bitreverse => (bits << extra).reverse_bits(), + _ => bug!("not a numeric intrinsic: {}", name), + }; + Ok(Scalar::from_uint(bits_out, size)) +} + +/// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated +/// inside an `InterpCx` and instead have their value computed directly from rustc internal info. +crate fn eval_nullary_intrinsic<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + def_id: DefId, + substs: SubstsRef<'tcx>, +) -> InterpResult<'tcx, ConstValue<'tcx>> { + let tp_ty = substs.type_at(0); + let name = tcx.item_name(def_id); + Ok(match name { + sym::type_name => { + ensure_monomorphic_enough(tcx, tp_ty)?; + let alloc = type_name::alloc_type_name(tcx, tp_ty); + ConstValue::Slice { data: alloc, start: 0, end: alloc.len() } + } + sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)), + sym::size_of | sym::min_align_of | sym::pref_align_of => { + let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?; + let n = match name { + sym::pref_align_of => layout.align.pref.bytes(), + sym::min_align_of => layout.align.abi.bytes(), + sym::size_of => layout.size.bytes(), + _ => bug!(), + }; + ConstValue::from_machine_usize(n, &tcx) + } + sym::type_id => { + ensure_monomorphic_enough(tcx, tp_ty)?; + ConstValue::from_u64(tcx.type_id_hash(tp_ty)) + } + sym::variant_count => { + if let ty::Adt(ref adt, _) = tp_ty.kind { + ConstValue::from_machine_usize(adt.variants.len() as u64, &tcx) + } else { + ConstValue::from_machine_usize(0u64, &tcx) + } + } + other => bug!("`{}` is not a zero arg intrinsic", other), + }) +} + +impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { + /// Returns `true` if emulation happened. + pub fn emulate_intrinsic( + &mut self, + instance: ty::Instance<'tcx>, + args: &[OpTy<'tcx, M::PointerTag>], + ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>, + ) -> InterpResult<'tcx, bool> { + let substs = instance.substs; + let intrinsic_name = self.tcx.item_name(instance.def_id()); + + // First handle intrinsics without return place. + let (dest, ret) = match ret { + None => match intrinsic_name { + sym::transmute => throw_ub_format!("transmuting to uninhabited type"), + sym::unreachable => throw_ub!(Unreachable), + sym::abort => M::abort(self)?, + // Unsupported diverging intrinsic. + _ => return Ok(false), + }, + Some(p) => p, + }; + + // Keep the patterns in this match ordered the same as the list in + // `src/librustc_middle/ty/constness.rs` + match intrinsic_name { + sym::caller_location => { + let span = self.find_closest_untracked_caller_location(); + let location = self.alloc_caller_location_for_span(span); + self.write_scalar(location.ptr, dest)?; + } + + sym::min_align_of_val | sym::size_of_val => { + let place = self.deref_operand(args[0])?; + let (size, align) = self + .size_and_align_of(place.meta, place.layout)? + .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?; + + let result = match intrinsic_name { + sym::min_align_of_val => align.bytes(), + sym::size_of_val => size.bytes(), + _ => bug!(), + }; + + self.write_scalar(Scalar::from_machine_usize(result, self), dest)?; + } + + sym::min_align_of + | sym::pref_align_of + | sym::needs_drop + | sym::size_of + | sym::type_id + | sym::type_name + | sym::variant_count => { + let gid = GlobalId { instance, promoted: None }; + let ty = match intrinsic_name { + sym::min_align_of | sym::pref_align_of | sym::size_of | sym::variant_count => { + self.tcx.types.usize + } + sym::needs_drop => self.tcx.types.bool, + sym::type_id => self.tcx.types.u64, + sym::type_name => self.tcx.mk_static_str(), + _ => bug!("already checked for nullary intrinsics"), + }; + let val = self.const_eval(gid, ty)?; + self.copy_op(val, dest)?; + } + + sym::ctpop + | sym::cttz + | sym::cttz_nonzero + | sym::ctlz + | sym::ctlz_nonzero + | sym::bswap + | sym::bitreverse => { + let ty = substs.type_at(0); + let layout_of = self.layout_of(ty)?; + let val = self.read_scalar(args[0])?.check_init()?; + let bits = self.force_bits(val, layout_of.size)?; + let kind = match layout_of.abi { + Abi::Scalar(ref scalar) => scalar.value, + _ => span_bug!( + self.cur_span(), + "{} called on invalid type {:?}", + intrinsic_name, + ty + ), + }; + let (nonzero, intrinsic_name) = match intrinsic_name { + sym::cttz_nonzero => (true, sym::cttz), + sym::ctlz_nonzero => (true, sym::ctlz), + other => (false, other), + }; + if nonzero && bits == 0 { + throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name); + } + let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?; + self.write_scalar(out_val, dest)?; + } + sym::wrapping_add + | sym::wrapping_sub + | sym::wrapping_mul + | sym::add_with_overflow + | sym::sub_with_overflow + | sym::mul_with_overflow => { + let lhs = self.read_immediate(args[0])?; + let rhs = self.read_immediate(args[1])?; + let (bin_op, ignore_overflow) = match intrinsic_name { + sym::wrapping_add => (BinOp::Add, true), + sym::wrapping_sub => (BinOp::Sub, true), + sym::wrapping_mul => (BinOp::Mul, true), + sym::add_with_overflow => (BinOp::Add, false), + sym::sub_with_overflow => (BinOp::Sub, false), + sym::mul_with_overflow => (BinOp::Mul, false), + _ => bug!("Already checked for int ops"), + }; + if ignore_overflow { + self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?; + } else { + self.binop_with_overflow(bin_op, lhs, rhs, dest)?; + } + } + sym::saturating_add | sym::saturating_sub => { + let l = self.read_immediate(args[0])?; + let r = self.read_immediate(args[1])?; + let is_add = intrinsic_name == sym::saturating_add; + let (val, overflowed, _ty) = + self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?; + let val = if overflowed { + let num_bits = l.layout.size.bits(); + if l.layout.abi.is_signed() { + // For signed ints the saturated value depends on the sign of the first + // term since the sign of the second term can be inferred from this and + // the fact that the operation has overflowed (if either is 0 no + // overflow can occur) + let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?; + let first_term_positive = first_term & (1 << (num_bits - 1)) == 0; + if first_term_positive { + // Negative overflow not possible since the positive first term + // can only increase an (in range) negative term for addition + // or corresponding negated positive term for subtraction + Scalar::from_uint( + (1u128 << (num_bits - 1)) - 1, // max positive + Size::from_bits(num_bits), + ) + } else { + // Positive overflow not possible for similar reason + // max negative + Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits)) + } + } else { + // unsigned + if is_add { + // max unsigned + Scalar::from_uint( + u128::MAX >> (128 - num_bits), + Size::from_bits(num_bits), + ) + } else { + // underflow to 0 + Scalar::from_uint(0u128, Size::from_bits(num_bits)) + } + } + } else { + val + }; + self.write_scalar(val, dest)?; + } + sym::discriminant_value => { + let place = self.deref_operand(args[0])?; + let discr_val = self.read_discriminant(place.into())?.0; + self.write_scalar(discr_val, dest)?; + } + sym::unchecked_shl + | sym::unchecked_shr + | sym::unchecked_add + | sym::unchecked_sub + | sym::unchecked_mul + | sym::unchecked_div + | sym::unchecked_rem => { + let l = self.read_immediate(args[0])?; + let r = self.read_immediate(args[1])?; + let bin_op = match intrinsic_name { + sym::unchecked_shl => BinOp::Shl, + sym::unchecked_shr => BinOp::Shr, + sym::unchecked_add => BinOp::Add, + sym::unchecked_sub => BinOp::Sub, + sym::unchecked_mul => BinOp::Mul, + sym::unchecked_div => BinOp::Div, + sym::unchecked_rem => BinOp::Rem, + _ => bug!("Already checked for int ops"), + }; + let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?; + if overflowed { + let layout = self.layout_of(substs.type_at(0))?; + let r_val = self.force_bits(r.to_scalar()?, layout.size)?; + if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name { + throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name); + } else { + throw_ub_format!("overflow executing `{}`", intrinsic_name); + } + } + self.write_scalar(val, dest)?; + } + sym::rotate_left | sym::rotate_right => { + // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW)) + // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW)) + let layout = self.layout_of(substs.type_at(0))?; + let val = self.read_scalar(args[0])?.check_init()?; + let val_bits = self.force_bits(val, layout.size)?; + let raw_shift = self.read_scalar(args[1])?.check_init()?; + let raw_shift_bits = self.force_bits(raw_shift, layout.size)?; + let width_bits = u128::from(layout.size.bits()); + let shift_bits = raw_shift_bits % width_bits; + let inv_shift_bits = (width_bits - shift_bits) % width_bits; + let result_bits = if intrinsic_name == sym::rotate_left { + (val_bits << shift_bits) | (val_bits >> inv_shift_bits) + } else { + (val_bits >> shift_bits) | (val_bits << inv_shift_bits) + }; + let truncated_bits = self.truncate(result_bits, layout); + let result = Scalar::from_uint(truncated_bits, layout.size); + self.write_scalar(result, dest)?; + } + sym::offset => { + let ptr = self.read_scalar(args[0])?.check_init()?; + let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?; + let pointee_ty = substs.type_at(0); + + let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?; + self.write_scalar(offset_ptr, dest)?; + } + sym::arith_offset => { + let ptr = self.read_scalar(args[0])?.check_init()?; + let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?; + let pointee_ty = substs.type_at(0); + + let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap(); + let offset_bytes = offset_count.wrapping_mul(pointee_size); + let offset_ptr = ptr.ptr_wrapping_signed_offset(offset_bytes, self); + self.write_scalar(offset_ptr, dest)?; + } + sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => { + let a = self.read_immediate(args[0])?.to_scalar()?; + let b = self.read_immediate(args[1])?.to_scalar()?; + let cmp = if intrinsic_name == sym::ptr_guaranteed_eq { + self.guaranteed_eq(a, b) + } else { + self.guaranteed_ne(a, b) + }; + self.write_scalar(Scalar::from_bool(cmp), dest)?; + } + sym::ptr_offset_from => { + let a = self.read_immediate(args[0])?.to_scalar()?; + let b = self.read_immediate(args[1])?.to_scalar()?; + + // Special case: if both scalars are *equal integers* + // and not NULL, we pretend there is an allocation of size 0 right there, + // and their offset is 0. (There's never a valid object at NULL, making it an + // exception from the exception.) + // This is the dual to the special exception for offset-by-0 + // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`). + // + // Control flow is weird because we cannot early-return (to reach the + // `go_to_block` at the end). + let done = if a.is_bits() && b.is_bits() { + let a = a.to_machine_usize(self)?; + let b = b.to_machine_usize(self)?; + if a == b && a != 0 { + self.write_scalar(Scalar::from_machine_isize(0, self), dest)?; + true + } else { + false + } + } else { + false + }; + + if !done { + // General case: we need two pointers. + let a = self.force_ptr(a)?; + let b = self.force_ptr(b)?; + if a.alloc_id != b.alloc_id { + throw_ub_format!( + "ptr_offset_from cannot compute offset of pointers into different \ + allocations.", + ); + } + let usize_layout = self.layout_of(self.tcx.types.usize)?; + let isize_layout = self.layout_of(self.tcx.types.isize)?; + let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout); + let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout); + let (val, _overflowed, _ty) = + self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?; + let pointee_layout = self.layout_of(substs.type_at(0))?; + let val = ImmTy::from_scalar(val, isize_layout); + let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout); + self.exact_div(val, size, dest)?; + } + } + + sym::transmute => { + self.copy_op_transmute(args[0], dest)?; + } + sym::simd_insert => { + let index = u64::from(self.read_scalar(args[1])?.to_u32()?); + let elem = args[2]; + let input = args[0]; + let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx); + assert!( + index < len, + "Index `{}` must be in bounds of vector type `{}`: `[0, {})`", + index, + e_ty, + len + ); + assert_eq!( + input.layout, dest.layout, + "Return type `{}` must match vector type `{}`", + dest.layout.ty, input.layout.ty + ); + assert_eq!( + elem.layout.ty, e_ty, + "Scalar element type `{}` must match vector element type `{}`", + elem.layout.ty, e_ty + ); + + for i in 0..len { + let place = self.place_index(dest, i)?; + let value = if i == index { elem } else { self.operand_index(input, i)? }; + self.copy_op(value, place)?; + } + } + sym::simd_extract => { + let index = u64::from(self.read_scalar(args[1])?.to_u32()?); + let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx); + assert!( + index < len, + "index `{}` is out-of-bounds of vector type `{}` with length `{}`", + index, + e_ty, + len + ); + assert_eq!( + e_ty, dest.layout.ty, + "Return type `{}` must match vector element type `{}`", + dest.layout.ty, e_ty + ); + self.copy_op(self.operand_index(args[0], index)?, dest)?; + } + sym::likely | sym::unlikely => { + // These just return their argument + self.copy_op(args[0], dest)?; + } + _ => return Ok(false), + } + + trace!("{:?}", self.dump_place(*dest)); + self.go_to_block(ret); + Ok(true) + } + + fn guaranteed_eq(&mut self, a: Scalar<M::PointerTag>, b: Scalar<M::PointerTag>) -> bool { + match (a, b) { + // Comparisons between integers are always known. + (Scalar::Raw { .. }, Scalar::Raw { .. }) => a == b, + // Equality with integers can never be known for sure. + (Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false, + // FIXME: return `true` for when both sides are the same pointer, *except* that + // some things (like functions and vtables) do not have stable addresses + // so we need to be careful around them. + (Scalar::Ptr(_), Scalar::Ptr(_)) => false, + } + } + + fn guaranteed_ne(&mut self, a: Scalar<M::PointerTag>, b: Scalar<M::PointerTag>) -> bool { + match (a, b) { + // Comparisons between integers are always known. + (Scalar::Raw { .. }, Scalar::Raw { .. }) => a != b, + // Comparisons of abstract pointers with null pointers are known if the pointer + // is in bounds, because if they are in bounds, the pointer can't be null. + (Scalar::Raw { data: 0, .. }, Scalar::Ptr(ptr)) + | (Scalar::Ptr(ptr), Scalar::Raw { data: 0, .. }) => !self.memory.ptr_may_be_null(ptr), + // Inequality with integers other than null can never be known for sure. + (Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false, + // FIXME: return `true` for at least some comparisons where we can reliably + // determine the result of runtime inequality tests at compile-time. + // Examples include comparison of addresses in static items, for these we can + // give reliable results. + (Scalar::Ptr(_), Scalar::Ptr(_)) => false, + } + } + + pub fn exact_div( + &mut self, + a: ImmTy<'tcx, M::PointerTag>, + b: ImmTy<'tcx, M::PointerTag>, + dest: PlaceTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx> { + // Performs an exact division, resulting in undefined behavior where + // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`. + // First, check x % y != 0 (or if that computation overflows). + let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?; + if overflow || res.assert_bits(a.layout.size) != 0 { + // Then, check if `b` is -1, which is the "MIN / -1" case. + let minus1 = Scalar::from_int(-1, dest.layout.size); + let b_scalar = b.to_scalar().unwrap(); + if b_scalar == minus1 { + throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented") + } else { + throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,) + } + } + // `Rem` says this is all right, so we can let `Div` do its job. + self.binop_ignore_overflow(BinOp::Div, a, b, dest) + } + + /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its + /// allocation. For integer pointers, we consider each of them their own tiny allocation of size + /// 0, so offset-by-0 (and only 0) is okay -- except that NULL cannot be offset by _any_ value. + pub fn ptr_offset_inbounds( + &self, + ptr: Scalar<M::PointerTag>, + pointee_ty: Ty<'tcx>, + offset_count: i64, + ) -> InterpResult<'tcx, Scalar<M::PointerTag>> { + // We cannot overflow i64 as a type's size must be <= isize::MAX. + let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap(); + // The computed offset, in bytes, cannot overflow an isize. + let offset_bytes = + offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?; + // The offset being in bounds cannot rely on "wrapping around" the address space. + // So, first rule out overflows in the pointer arithmetic. + let offset_ptr = ptr.ptr_signed_offset(offset_bytes, self)?; + // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the + // memory between these pointers must be accessible. Note that we do not require the + // pointers to be properly aligned (unlike a read/write operation). + let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr }; + let size: u64 = uabs(offset_bytes); + // This call handles checking for integer/NULL pointers. + self.memory.check_ptr_access_align( + min_ptr, + Size::from_bytes(size), + None, + CheckInAllocMsg::InboundsTest, + )?; + Ok(offset_ptr) + } +} |