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Diffstat (limited to 'compiler/rustc_const_eval/src/interpret/operand.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/operand.rs | 831 |
1 files changed, 831 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs new file mode 100644 index 000000000..94ba62c16 --- /dev/null +++ b/compiler/rustc_const_eval/src/interpret/operand.rs @@ -0,0 +1,831 @@ +//! Functions concerning immediate values and operands, and reading from operands. +//! All high-level functions to read from memory work on operands as sources. + +use std::fmt::Write; + +use rustc_hir::def::Namespace; +use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout}; +use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer}; +use rustc_middle::ty::{ConstInt, DelaySpanBugEmitted, Ty}; +use rustc_middle::{mir, ty}; +use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, TagEncoding}; +use rustc_target::abi::{VariantIdx, Variants}; + +use super::{ + alloc_range, from_known_layout, mir_assign_valid_types, AllocId, ConstValue, Frame, GlobalId, + InterpCx, InterpResult, MPlaceTy, Machine, MemPlace, MemPlaceMeta, Place, PlaceTy, Pointer, + Provenance, Scalar, ScalarMaybeUninit, +}; + +/// An `Immediate` represents a single immediate self-contained Rust value. +/// +/// For optimization of a few very common cases, there is also a representation for a pair of +/// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary +/// operations and wide pointers. This idea was taken from rustc's codegen. +/// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely +/// defined on `Immediate`, and do not have to work with a `Place`. +#[derive(Copy, Clone, Debug)] +pub enum Immediate<Prov: Provenance = AllocId> { + /// A single scalar value (must have *initialized* `Scalar` ABI). + /// FIXME: we also currently often use this for ZST. + /// `ScalarMaybeUninit` should reject ZST, and we should use `Uninit` for them instead. + Scalar(ScalarMaybeUninit<Prov>), + /// A pair of two scalar value (must have `ScalarPair` ABI where both fields are + /// `Scalar::Initialized`). + ScalarPair(ScalarMaybeUninit<Prov>, ScalarMaybeUninit<Prov>), + /// A value of fully uninitialized memory. Can have and size and layout. + Uninit, +} + +impl<Prov: Provenance> From<ScalarMaybeUninit<Prov>> for Immediate<Prov> { + #[inline(always)] + fn from(val: ScalarMaybeUninit<Prov>) -> Self { + Immediate::Scalar(val) + } +} + +impl<Prov: Provenance> From<Scalar<Prov>> for Immediate<Prov> { + #[inline(always)] + fn from(val: Scalar<Prov>) -> Self { + Immediate::Scalar(val.into()) + } +} + +impl<'tcx, Prov: Provenance> Immediate<Prov> { + pub fn from_pointer(p: Pointer<Prov>, cx: &impl HasDataLayout) -> Self { + Immediate::Scalar(ScalarMaybeUninit::from_pointer(p, cx)) + } + + pub fn from_maybe_pointer(p: Pointer<Option<Prov>>, cx: &impl HasDataLayout) -> Self { + Immediate::Scalar(ScalarMaybeUninit::from_maybe_pointer(p, cx)) + } + + pub fn new_slice(val: Scalar<Prov>, len: u64, cx: &impl HasDataLayout) -> Self { + Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into()) + } + + pub fn new_dyn_trait( + val: Scalar<Prov>, + vtable: Pointer<Option<Prov>>, + cx: &impl HasDataLayout, + ) -> Self { + Immediate::ScalarPair(val.into(), ScalarMaybeUninit::from_maybe_pointer(vtable, cx)) + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980) + pub fn to_scalar_or_uninit(self) -> ScalarMaybeUninit<Prov> { + match self { + Immediate::Scalar(val) => val, + Immediate::ScalarPair(..) => bug!("Got a scalar pair where a scalar was expected"), + Immediate::Uninit => ScalarMaybeUninit::Uninit, + } + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980) + pub fn to_scalar(self) -> InterpResult<'tcx, Scalar<Prov>> { + self.to_scalar_or_uninit().check_init() + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980) + pub fn to_scalar_or_uninit_pair(self) -> (ScalarMaybeUninit<Prov>, ScalarMaybeUninit<Prov>) { + match self { + Immediate::ScalarPair(val1, val2) => (val1, val2), + Immediate::Scalar(..) => bug!("Got a scalar where a scalar pair was expected"), + Immediate::Uninit => (ScalarMaybeUninit::Uninit, ScalarMaybeUninit::Uninit), + } + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980) + pub fn to_scalar_pair(self) -> InterpResult<'tcx, (Scalar<Prov>, Scalar<Prov>)> { + let (val1, val2) = self.to_scalar_or_uninit_pair(); + Ok((val1.check_init()?, val2.check_init()?)) + } +} + +// ScalarPair needs a type to interpret, so we often have an immediate and a type together +// as input for binary and cast operations. +#[derive(Clone, Debug)] +pub struct ImmTy<'tcx, Prov: Provenance = AllocId> { + imm: Immediate<Prov>, + pub layout: TyAndLayout<'tcx>, +} + +impl<Prov: Provenance> std::fmt::Display for ImmTy<'_, Prov> { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + /// Helper function for printing a scalar to a FmtPrinter + fn p<'a, 'tcx, Prov: Provenance>( + cx: FmtPrinter<'a, 'tcx>, + s: ScalarMaybeUninit<Prov>, + ty: Ty<'tcx>, + ) -> Result<FmtPrinter<'a, 'tcx>, std::fmt::Error> { + match s { + ScalarMaybeUninit::Scalar(Scalar::Int(int)) => { + cx.pretty_print_const_scalar_int(int, ty, true) + } + ScalarMaybeUninit::Scalar(Scalar::Ptr(ptr, _sz)) => { + // Just print the ptr value. `pretty_print_const_scalar_ptr` would also try to + // print what is points to, which would fail since it has no access to the local + // memory. + cx.pretty_print_const_pointer(ptr, ty, true) + } + ScalarMaybeUninit::Uninit => cx.typed_value( + |mut this| { + this.write_str("uninit ")?; + Ok(this) + }, + |this| this.print_type(ty), + " ", + ), + } + } + ty::tls::with(|tcx| { + match self.imm { + Immediate::Scalar(s) => { + if let Some(ty) = tcx.lift(self.layout.ty) { + let cx = FmtPrinter::new(tcx, Namespace::ValueNS); + f.write_str(&p(cx, s, ty)?.into_buffer())?; + return Ok(()); + } + write!(f, "{:x}: {}", s, self.layout.ty) + } + Immediate::ScalarPair(a, b) => { + // FIXME(oli-obk): at least print tuples and slices nicely + write!(f, "({:x}, {:x}): {}", a, b, self.layout.ty) + } + Immediate::Uninit => { + write!(f, "uninit: {}", self.layout.ty) + } + } + }) + } +} + +impl<'tcx, Prov: Provenance> std::ops::Deref for ImmTy<'tcx, Prov> { + type Target = Immediate<Prov>; + #[inline(always)] + fn deref(&self) -> &Immediate<Prov> { + &self.imm + } +} + +/// An `Operand` is the result of computing a `mir::Operand`. It can be immediate, +/// or still in memory. The latter is an optimization, to delay reading that chunk of +/// memory and to avoid having to store arbitrary-sized data here. +#[derive(Copy, Clone, Debug)] +pub enum Operand<Prov: Provenance = AllocId> { + Immediate(Immediate<Prov>), + Indirect(MemPlace<Prov>), +} + +#[derive(Clone, Debug)] +pub struct OpTy<'tcx, Prov: Provenance = AllocId> { + op: Operand<Prov>, // Keep this private; it helps enforce invariants. + pub layout: TyAndLayout<'tcx>, + /// rustc does not have a proper way to represent the type of a field of a `repr(packed)` struct: + /// it needs to have a different alignment than the field type would usually have. + /// So we represent this here with a separate field that "overwrites" `layout.align`. + /// This means `layout.align` should never be used for an `OpTy`! + /// `None` means "alignment does not matter since this is a by-value operand" + /// (`Operand::Immediate`); this field is only relevant for `Operand::Indirect`. + /// Also CTFE ignores alignment anyway, so this is for Miri only. + pub align: Option<Align>, +} + +impl<'tcx, Prov: Provenance> std::ops::Deref for OpTy<'tcx, Prov> { + type Target = Operand<Prov>; + #[inline(always)] + fn deref(&self) -> &Operand<Prov> { + &self.op + } +} + +impl<'tcx, Prov: Provenance> From<MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> { + #[inline(always)] + fn from(mplace: MPlaceTy<'tcx, Prov>) -> Self { + OpTy { op: Operand::Indirect(*mplace), layout: mplace.layout, align: Some(mplace.align) } + } +} + +impl<'tcx, Prov: Provenance> From<&'_ MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> { + #[inline(always)] + fn from(mplace: &MPlaceTy<'tcx, Prov>) -> Self { + OpTy { op: Operand::Indirect(**mplace), layout: mplace.layout, align: Some(mplace.align) } + } +} + +impl<'tcx, Prov: Provenance> From<&'_ mut MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> { + #[inline(always)] + fn from(mplace: &mut MPlaceTy<'tcx, Prov>) -> Self { + OpTy { op: Operand::Indirect(**mplace), layout: mplace.layout, align: Some(mplace.align) } + } +} + +impl<'tcx, Prov: Provenance> From<ImmTy<'tcx, Prov>> for OpTy<'tcx, Prov> { + #[inline(always)] + fn from(val: ImmTy<'tcx, Prov>) -> Self { + OpTy { op: Operand::Immediate(val.imm), layout: val.layout, align: None } + } +} + +impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> { + #[inline] + pub fn from_scalar(val: Scalar<Prov>, layout: TyAndLayout<'tcx>) -> Self { + ImmTy { imm: val.into(), layout } + } + + #[inline] + pub fn from_immediate(imm: Immediate<Prov>, layout: TyAndLayout<'tcx>) -> Self { + ImmTy { imm, layout } + } + + #[inline] + pub fn uninit(layout: TyAndLayout<'tcx>) -> Self { + ImmTy { imm: Immediate::Uninit, layout } + } + + #[inline] + pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> { + Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout)) + } + #[inline] + pub fn from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Self { + Self::from_scalar(Scalar::from_uint(i, layout.size), layout) + } + + #[inline] + pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> { + Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout)) + } + + #[inline] + pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self { + Self::from_scalar(Scalar::from_int(i, layout.size), layout) + } + + #[inline] + pub fn to_const_int(self) -> ConstInt { + assert!(self.layout.ty.is_integral()); + let int = self.to_scalar().expect("to_const_int doesn't work on scalar pairs").assert_int(); + ConstInt::new(int, self.layout.ty.is_signed(), self.layout.ty.is_ptr_sized_integral()) + } +} + +impl<'tcx, Prov: Provenance> OpTy<'tcx, Prov> { + pub fn len(&self, cx: &impl HasDataLayout) -> InterpResult<'tcx, u64> { + if self.layout.is_unsized() { + // There are no unsized immediates. + self.assert_mem_place().len(cx) + } else { + match self.layout.fields { + abi::FieldsShape::Array { count, .. } => Ok(count), + _ => bug!("len not supported on sized type {:?}", self.layout.ty), + } + } + } + + pub fn offset_with_meta( + &self, + offset: Size, + meta: MemPlaceMeta<Prov>, + layout: TyAndLayout<'tcx>, + cx: &impl HasDataLayout, + ) -> InterpResult<'tcx, Self> { + match self.try_as_mplace() { + Ok(mplace) => Ok(mplace.offset_with_meta(offset, meta, layout, cx)?.into()), + Err(imm) => { + assert!( + matches!(*imm, Immediate::Uninit), + "Scalar/ScalarPair cannot be offset into" + ); + assert!(!meta.has_meta()); // no place to store metadata here + // Every part of an uninit is uninit. + Ok(ImmTy::uninit(layout).into()) + } + } + } + + pub fn offset( + &self, + offset: Size, + layout: TyAndLayout<'tcx>, + cx: &impl HasDataLayout, + ) -> InterpResult<'tcx, Self> { + assert!(!layout.is_unsized()); + self.offset_with_meta(offset, MemPlaceMeta::None, layout, cx) + } +} + +impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { + /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`. + /// Returns `None` if the layout does not permit loading this as a value. + /// + /// This is an internal function; call `read_immediate` instead. + fn read_immediate_from_mplace_raw( + &self, + mplace: &MPlaceTy<'tcx, M::Provenance>, + force: bool, + ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::Provenance>>> { + if mplace.layout.is_unsized() { + // Don't touch unsized + return Ok(None); + } + + let Some(alloc) = self.get_place_alloc(mplace)? else { + // zero-sized type can be left uninit + return Ok(Some(ImmTy::uninit(mplace.layout))); + }; + + // It may seem like all types with `Scalar` or `ScalarPair` ABI are fair game at this point. + // However, `MaybeUninit<u64>` is considered a `Scalar` as far as its layout is concerned -- + // and yet cannot be represented by an interpreter `Scalar`, since we have to handle the + // case where some of the bytes are initialized and others are not. So, we need an extra + // check that walks over the type of `mplace` to make sure it is truly correct to treat this + // like a `Scalar` (or `ScalarPair`). + let scalar_layout = match mplace.layout.abi { + // `if` does not work nested inside patterns, making this a bit awkward to express. + Abi::Scalar(abi::Scalar::Initialized { value: s, .. }) => Some(s), + Abi::Scalar(s) if force => Some(s.primitive()), + _ => None, + }; + if let Some(s) = scalar_layout { + let size = s.size(self); + assert_eq!(size, mplace.layout.size, "abi::Scalar size does not match layout size"); + let scalar = alloc + .read_scalar(alloc_range(Size::ZERO, size), /*read_provenance*/ s.is_ptr())?; + return Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout })); + } + let scalar_pair_layout = match mplace.layout.abi { + Abi::ScalarPair( + abi::Scalar::Initialized { value: a, .. }, + abi::Scalar::Initialized { value: b, .. }, + ) => Some((a, b)), + Abi::ScalarPair(a, b) if force => Some((a.primitive(), b.primitive())), + _ => None, + }; + if let Some((a, b)) = scalar_pair_layout { + // We checked `ptr_align` above, so all fields will have the alignment they need. + // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`, + // which `ptr.offset(b_offset)` cannot possibly fail to satisfy. + let (a_size, b_size) = (a.size(self), b.size(self)); + let b_offset = a_size.align_to(b.align(self).abi); + assert!(b_offset.bytes() > 0); // in `operand_field` we use the offset to tell apart the fields + let a_val = alloc.read_scalar( + alloc_range(Size::ZERO, a_size), + /*read_provenance*/ a.is_ptr(), + )?; + let b_val = alloc + .read_scalar(alloc_range(b_offset, b_size), /*read_provenance*/ b.is_ptr())?; + return Ok(Some(ImmTy { + imm: Immediate::ScalarPair(a_val, b_val), + layout: mplace.layout, + })); + } + // Neither a scalar nor scalar pair. + return Ok(None); + } + + /// Try returning an immediate for the operand. If the layout does not permit loading this as an + /// immediate, return where in memory we can find the data. + /// Note that for a given layout, this operation will either always fail or always + /// succeed! Whether it succeeds depends on whether the layout can be represented + /// in an `Immediate`, not on which data is stored there currently. + /// + /// If `force` is `true`, then even scalars with fields that can be ununit will be + /// read. This means the load is lossy and should not be written back! + /// This flag exists only for validity checking. + /// + /// This is an internal function that should not usually be used; call `read_immediate` instead. + /// ConstProp needs it, though. + pub fn read_immediate_raw( + &self, + src: &OpTy<'tcx, M::Provenance>, + force: bool, + ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::Provenance>, MPlaceTy<'tcx, M::Provenance>>> { + Ok(match src.try_as_mplace() { + Ok(ref mplace) => { + if let Some(val) = self.read_immediate_from_mplace_raw(mplace, force)? { + Ok(val) + } else { + Err(*mplace) + } + } + Err(val) => Ok(val), + }) + } + + /// Read an immediate from a place, asserting that that is possible with the given layout. + #[inline(always)] + pub fn read_immediate( + &self, + op: &OpTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> { + if let Ok(imm) = self.read_immediate_raw(op, /*force*/ false)? { + Ok(imm) + } else { + span_bug!(self.cur_span(), "primitive read failed for type: {:?}", op.layout.ty); + } + } + + /// Read a scalar from a place + pub fn read_scalar( + &self, + op: &OpTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, ScalarMaybeUninit<M::Provenance>> { + Ok(self.read_immediate(op)?.to_scalar_or_uninit()) + } + + /// Read a pointer from a place. + pub fn read_pointer( + &self, + op: &OpTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> { + self.read_scalar(op)?.to_pointer(self) + } + + /// Turn the wide MPlace into a string (must already be dereferenced!) + pub fn read_str(&self, mplace: &MPlaceTy<'tcx, M::Provenance>) -> InterpResult<'tcx, &str> { + let len = mplace.len(self)?; + let bytes = self.read_bytes_ptr(mplace.ptr, Size::from_bytes(len))?; + let str = std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?; + Ok(str) + } + + /// Converts a repr(simd) operand into an operand where `place_index` accesses the SIMD elements. + /// Also returns the number of elements. + /// + /// Can (but does not always) trigger UB if `op` is uninitialized. + pub fn operand_to_simd( + &self, + op: &OpTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::Provenance>, u64)> { + // Basically we just transmute this place into an array following simd_size_and_type. + // This only works in memory, but repr(simd) types should never be immediates anyway. + assert!(op.layout.ty.is_simd()); + match op.try_as_mplace() { + Ok(mplace) => self.mplace_to_simd(&mplace), + Err(imm) => match *imm { + Immediate::Uninit => { + throw_ub!(InvalidUninitBytes(None)) + } + Immediate::Scalar(..) | Immediate::ScalarPair(..) => { + bug!("arrays/slices can never have Scalar/ScalarPair layout") + } + }, + } + } + + /// Read from a local. Will not actually access the local if reading from a ZST. + /// Will not access memory, instead an indirect `Operand` is returned. + /// + /// This is public because it is used by [priroda](https://github.com/oli-obk/priroda) to get an + /// OpTy from a local. + pub fn local_to_op( + &self, + frame: &Frame<'mir, 'tcx, M::Provenance, M::FrameExtra>, + local: mir::Local, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + let layout = self.layout_of_local(frame, local, layout)?; + let op = if layout.is_zst() { + // Bypass `access_local` (helps in ConstProp) + Operand::Immediate(Immediate::Uninit) + } else { + *M::access_local(frame, local)? + }; + Ok(OpTy { op, layout, align: Some(layout.align.abi) }) + } + + /// Every place can be read from, so we can turn them into an operand. + /// This will definitely return `Indirect` if the place is a `Ptr`, i.e., this + /// will never actually read from memory. + #[inline(always)] + pub fn place_to_op( + &self, + place: &PlaceTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + let op = match **place { + Place::Ptr(mplace) => Operand::Indirect(mplace), + Place::Local { frame, local } => { + *self.local_to_op(&self.stack()[frame], local, None)? + } + }; + Ok(OpTy { op, layout: place.layout, align: Some(place.align) }) + } + + /// Evaluate a place with the goal of reading from it. This lets us sometimes + /// avoid allocations. + pub fn eval_place_to_op( + &self, + mir_place: mir::Place<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + // Do not use the layout passed in as argument if the base we are looking at + // here is not the entire place. + let layout = if mir_place.projection.is_empty() { layout } else { None }; + + let mut op = self.local_to_op(self.frame(), mir_place.local, layout)?; + // Using `try_fold` turned out to be bad for performance, hence the loop. + for elem in mir_place.projection.iter() { + op = self.operand_projection(&op, elem)? + } + + trace!("eval_place_to_op: got {:?}", *op); + // Sanity-check the type we ended up with. + debug_assert!( + mir_assign_valid_types( + *self.tcx, + self.param_env, + self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions( + mir_place.ty(&self.frame().body.local_decls, *self.tcx).ty + )?)?, + op.layout, + ), + "eval_place of a MIR place with type {:?} produced an interpreter operand with type {:?}", + mir_place.ty(&self.frame().body.local_decls, *self.tcx).ty, + op.layout.ty, + ); + Ok(op) + } + + /// Evaluate the operand, returning a place where you can then find the data. + /// If you already know the layout, you can save two table lookups + /// by passing it in here. + #[inline] + pub fn eval_operand( + &self, + mir_op: &mir::Operand<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + use rustc_middle::mir::Operand::*; + let op = match *mir_op { + // FIXME: do some more logic on `move` to invalidate the old location + Copy(place) | Move(place) => self.eval_place_to_op(place, layout)?, + + Constant(ref constant) => { + let val = + self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal)?; + + // This can still fail: + // * During ConstProp, with `TooGeneric` or since the `required_consts` were not all + // checked yet. + // * During CTFE, since promoteds in `const`/`static` initializer bodies can fail. + self.mir_const_to_op(&val, layout)? + } + }; + trace!("{:?}: {:?}", mir_op, *op); + Ok(op) + } + + /// Evaluate a bunch of operands at once + pub(super) fn eval_operands( + &self, + ops: &[mir::Operand<'tcx>], + ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::Provenance>>> { + ops.iter().map(|op| self.eval_operand(op, None)).collect() + } + + // Used when the miri-engine runs into a constant and for extracting information from constants + // in patterns via the `const_eval` module + /// The `val` and `layout` are assumed to already be in our interpreter + /// "universe" (param_env). + pub fn const_to_op( + &self, + c: ty::Const<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + match c.kind() { + ty::ConstKind::Param(_) | ty::ConstKind::Bound(..) => throw_inval!(TooGeneric), + ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => { + throw_inval!(AlreadyReported(reported)) + } + ty::ConstKind::Unevaluated(uv) => { + let instance = self.resolve(uv.def, uv.substs)?; + Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into()) + } + ty::ConstKind::Infer(..) | ty::ConstKind::Placeholder(..) => { + span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", c) + } + ty::ConstKind::Value(valtree) => { + let ty = c.ty(); + let const_val = self.tcx.valtree_to_const_val((ty, valtree)); + self.const_val_to_op(const_val, ty, layout) + } + } + } + + pub fn mir_const_to_op( + &self, + val: &mir::ConstantKind<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + match val { + mir::ConstantKind::Ty(ct) => self.const_to_op(*ct, layout), + mir::ConstantKind::Val(val, ty) => self.const_val_to_op(*val, *ty, layout), + } + } + + pub(crate) fn const_val_to_op( + &self, + val_val: ConstValue<'tcx>, + ty: Ty<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + // Other cases need layout. + let adjust_scalar = |scalar| -> InterpResult<'tcx, _> { + Ok(match scalar { + Scalar::Ptr(ptr, size) => Scalar::Ptr(self.global_base_pointer(ptr)?, size), + Scalar::Int(int) => Scalar::Int(int), + }) + }; + let layout = from_known_layout(self.tcx, self.param_env, layout, || self.layout_of(ty))?; + let op = match val_val { + ConstValue::ByRef { alloc, offset } => { + let id = self.tcx.create_memory_alloc(alloc); + // We rely on mutability being set correctly in that allocation to prevent writes + // where none should happen. + let ptr = self.global_base_pointer(Pointer::new(id, offset))?; + Operand::Indirect(MemPlace::from_ptr(ptr.into())) + } + ConstValue::Scalar(x) => Operand::Immediate(adjust_scalar(x)?.into()), + ConstValue::ZeroSized => Operand::Immediate(Immediate::Uninit), + ConstValue::Slice { data, start, end } => { + // We rely on mutability being set correctly in `data` to prevent writes + // where none should happen. + let ptr = Pointer::new( + self.tcx.create_memory_alloc(data), + Size::from_bytes(start), // offset: `start` + ); + Operand::Immediate(Immediate::new_slice( + Scalar::from_pointer(self.global_base_pointer(ptr)?, &*self.tcx), + u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start` + self, + )) + } + }; + Ok(OpTy { op, layout, align: Some(layout.align.abi) }) + } + + /// Read discriminant, return the runtime value as well as the variant index. + /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)! + pub fn read_discriminant( + &self, + op: &OpTy<'tcx, M::Provenance>, + ) -> InterpResult<'tcx, (Scalar<M::Provenance>, VariantIdx)> { + trace!("read_discriminant_value {:#?}", op.layout); + // Get type and layout of the discriminant. + let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?; + trace!("discriminant type: {:?}", discr_layout.ty); + + // We use "discriminant" to refer to the value associated with a particular enum variant. + // This is not to be confused with its "variant index", which is just determining its position in the + // declared list of variants -- they can differ with explicitly assigned discriminants. + // We use "tag" to refer to how the discriminant is encoded in memory, which can be either + // straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`). + let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout.variants { + Variants::Single { index } => { + let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) { + Some(discr) => { + // This type actually has discriminants. + assert_eq!(discr.ty, discr_layout.ty); + Scalar::from_uint(discr.val, discr_layout.size) + } + None => { + // On a type without actual discriminants, variant is 0. + assert_eq!(index.as_u32(), 0); + Scalar::from_uint(index.as_u32(), discr_layout.size) + } + }; + return Ok((discr, index)); + } + Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => { + (tag, tag_encoding, tag_field) + } + }; + + // There are *three* layouts that come into play here: + // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for + // the `Scalar` we return. + // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type, + // and used to interpret the value we read from the tag field. + // For the return value, a cast to `discr_layout` is performed. + // - The field storing the tag has a layout, which is very similar to `tag_layout` but + // may be a pointer. This is `tag_val.layout`; we just use it for sanity checks. + + // Get layout for tag. + let tag_layout = self.layout_of(tag_scalar_layout.primitive().to_int_ty(*self.tcx))?; + + // Read tag and sanity-check `tag_layout`. + let tag_val = self.read_immediate(&self.operand_field(op, tag_field)?)?; + assert_eq!(tag_layout.size, tag_val.layout.size); + assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed()); + trace!("tag value: {}", tag_val); + + // Figure out which discriminant and variant this corresponds to. + Ok(match *tag_encoding { + TagEncoding::Direct => { + let scalar = tag_val.to_scalar()?; + // Generate a specific error if `tag_val` is not an integer. + // (`tag_bits` itself is only used for error messages below.) + let tag_bits = scalar + .try_to_int() + .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))? + .assert_bits(tag_layout.size); + // Cast bits from tag layout to discriminant layout. + // After the checks we did above, this cannot fail, as + // discriminants are int-like. + let discr_val = + self.cast_from_int_like(scalar, tag_val.layout, discr_layout.ty).unwrap(); + let discr_bits = discr_val.assert_bits(discr_layout.size); + // Convert discriminant to variant index, and catch invalid discriminants. + let index = match *op.layout.ty.kind() { + ty::Adt(adt, _) => { + adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits) + } + ty::Generator(def_id, substs, _) => { + let substs = substs.as_generator(); + substs + .discriminants(def_id, *self.tcx) + .find(|(_, var)| var.val == discr_bits) + } + _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"), + } + .ok_or_else(|| err_ub!(InvalidTag(Scalar::from_uint(tag_bits, tag_layout.size))))?; + // Return the cast value, and the index. + (discr_val, index.0) + } + TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start } => { + let tag_val = tag_val.to_scalar()?; + // Compute the variant this niche value/"tag" corresponds to. With niche layout, + // discriminant (encoded in niche/tag) and variant index are the same. + let variants_start = niche_variants.start().as_u32(); + let variants_end = niche_variants.end().as_u32(); + let variant = match tag_val.try_to_int() { + Err(dbg_val) => { + // So this is a pointer then, and casting to an int failed. + // Can only happen during CTFE. + // The niche must be just 0, and the ptr not null, then we know this is + // okay. Everything else, we conservatively reject. + let ptr_valid = niche_start == 0 + && variants_start == variants_end + && !self.scalar_may_be_null(tag_val)?; + if !ptr_valid { + throw_ub!(InvalidTag(dbg_val)) + } + dataful_variant + } + Ok(tag_bits) => { + let tag_bits = tag_bits.assert_bits(tag_layout.size); + // We need to use machine arithmetic to get the relative variant idx: + // variant_index_relative = tag_val - niche_start_val + let tag_val = ImmTy::from_uint(tag_bits, tag_layout); + let niche_start_val = ImmTy::from_uint(niche_start, tag_layout); + let variant_index_relative_val = + self.binary_op(mir::BinOp::Sub, &tag_val, &niche_start_val)?; + let variant_index_relative = variant_index_relative_val + .to_scalar()? + .assert_bits(tag_val.layout.size); + // Check if this is in the range that indicates an actual discriminant. + if variant_index_relative <= u128::from(variants_end - variants_start) { + let variant_index_relative = u32::try_from(variant_index_relative) + .expect("we checked that this fits into a u32"); + // Then computing the absolute variant idx should not overflow any more. + let variant_index = variants_start + .checked_add(variant_index_relative) + .expect("overflow computing absolute variant idx"); + let variants_len = op + .layout + .ty + .ty_adt_def() + .expect("tagged layout for non adt") + .variants() + .len(); + assert!(usize::try_from(variant_index).unwrap() < variants_len); + VariantIdx::from_u32(variant_index) + } else { + dataful_variant + } + } + }; + // Compute the size of the scalar we need to return. + // No need to cast, because the variant index directly serves as discriminant and is + // encoded in the tag. + (Scalar::from_uint(variant.as_u32(), discr_layout.size), variant) + } + }) + } +} + +// Some nodes are used a lot. Make sure they don't unintentionally get bigger. +#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] +mod size_asserts { + use super::*; + // These are in alphabetical order, which is easy to maintain. + rustc_data_structures::static_assert_size!(Immediate, 56); + rustc_data_structures::static_assert_size!(ImmTy<'_>, 72); + rustc_data_structures::static_assert_size!(Operand, 64); + rustc_data_structures::static_assert_size!(OpTy<'_>, 88); +} |