src/librustc/mir/interpret/value.rs - toolchain/rustc - Git at Google

 use std::fmt;
 use rustc_macros::HashStable;

 use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}, subst::SubstsRef};
 use crate::hir::def_id::DefId;

 use super::{EvalResult, Pointer, PointerArithmetic, Allocation, AllocId, sign_extend, truncate};

 /// Represents the result of a raw const operation, pre-validation.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, RustcEncodable, RustcDecodable, Hash, HashStable)]
 pub struct RawConst<'tcx> {
     // the value lives here, at offset 0, and that allocation definitely is a `AllocKind::Memory`
     // (so you can use `AllocMap::unwrap_memory`).
     pub alloc_id: AllocId,
     pub ty: Ty<'tcx>,
 }

 /// Represents a constant value in Rust. `Scalar` and `ScalarPair` are optimizations that
 /// match the `LocalState` optimizations for easy conversions between `Value` and `ConstValue`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord,
          RustcEncodable, RustcDecodable, Hash, HashStable)]
 pub enum ConstValue<'tcx> {
     /// A const generic parameter.
     Param(ParamConst),

     /// Infer the value of the const.
     Infer(InferConst<'tcx>),

     /// Used only for types with `layout::abi::Scalar` ABI and ZSTs.
     ///
     /// Not using the enum `Value` to encode that this must not be `Undef`.
     Scalar(Scalar),

     /// Used only for slices and strings (`&[T]`, `&str`, `*const [T]`, `*mut str`, `Box<str>`,
     /// etc.).
     ///
     /// Empty slices don't necessarily have an address backed by an `AllocId`, thus we also need to
     /// enable integer pointers. The `Scalar` type covers exactly those two cases. While we could
     /// create dummy-`AllocId`s, the additional code effort for the conversions doesn't seem worth
     /// it.
     Slice(Scalar, u64),

     /// An allocation together with a pointer into the allocation.
     /// Invariant: the pointer's `AllocId` resolves to the allocation.
     ByRef(Pointer, &'tcx Allocation),

     /// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other
     /// variants when the code is monomorphic enough for that.
     Unevaluated(DefId, SubstsRef<'tcx>),
 }

 #[cfg(target_arch = "x86_64")]
 static_assert!(CONST_SIZE: ::std::mem::size_of::<ConstValue<'static>>() == 40);

 impl<'tcx> ConstValue<'tcx> {
     #[inline]
     pub fn try_to_scalar(&self) -> Option<Scalar> {
         match *self {
             ConstValue::Param(_) |
             ConstValue::Infer(_) |
             ConstValue::ByRef(..) |
             ConstValue::Unevaluated(..) |
             ConstValue::Slice(..) => None,
             ConstValue::Scalar(val) => Some(val),
         }
     }

     #[inline]
     pub fn try_to_bits(&self, size: Size) -> Option<u128> {
         self.try_to_scalar()?.to_bits(size).ok()
     }

     #[inline]
     pub fn try_to_ptr(&self) -> Option<Pointer> {
         self.try_to_scalar()?.to_ptr().ok()
     }

     #[inline]
     pub fn new_slice(
         val: Scalar,
         len: u64,
     ) -> Self {
         ConstValue::Slice(val, len)
     }
 }

 /// A `Scalar` represents an immediate, primitive value existing outside of a
 /// `memory::Allocation`. It is in many ways like a small chunk of a `Allocation`, up to 8 bytes in
 /// size. Like a range of bytes in an `Allocation`, a `Scalar` can either represent the raw bytes
 /// of a simple value or a pointer into another `Allocation`
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd,
          RustcEncodable, RustcDecodable, Hash, HashStable)]
 pub enum Scalar<Tag=(), Id=AllocId> {
     /// The raw bytes of a simple value.
     Bits {
         /// The first `size` bytes are the value.
         /// Do not try to read less or more bytes than that. The remaining bytes must be 0.
         size: u8,
         bits: u128,
     },

     /// A pointer into an `Allocation`. An `Allocation` in the `memory` module has a list of
     /// relocations, but a `Scalar` is only large enough to contain one, so we just represent the
     /// relocation and its associated offset together as a `Pointer` here.
     Ptr(Pointer<Tag, Id>),
 }

 #[cfg(target_arch = "x86_64")]
 static_assert!(SCALAR_SIZE: ::std::mem::size_of::<Scalar>() == 24);

 impl<Tag> fmt::Display for Scalar<Tag> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Scalar::Ptr(_) => write!(f, "a pointer"),
             Scalar::Bits { bits, .. } => write!(f, "{}", bits),
         }
     }
 }

 impl<'tcx> Scalar<()> {
     #[inline]
     pub fn with_default_tag<Tag>(self) -> Scalar<Tag>
         where Tag: Default
     {
         match self {
             Scalar::Ptr(ptr) => Scalar::Ptr(ptr.with_default_tag()),
             Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
         }
     }
 }

 impl<'tcx, Tag> Scalar<Tag> {
     #[inline]
     pub fn erase_tag(self) -> Scalar {
         match self {
             Scalar::Ptr(ptr) => Scalar::Ptr(ptr.erase_tag()),
             Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
         }
     }

     #[inline]
     pub fn with_tag(self, new_tag: Tag) -> Self {
         match self {
             Scalar::Ptr(ptr) => Scalar::Ptr(Pointer { tag: new_tag, ..ptr }),
             Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
         }
     }

     #[inline]
     pub fn ptr_null(cx: &impl HasDataLayout) -> Self {
         Scalar::Bits {
             bits: 0,
             size: cx.data_layout().pointer_size.bytes() as u8,
         }
     }

     #[inline]
     pub fn zst() -> Self {
         Scalar::Bits { bits: 0, size: 0 }
     }

     #[inline]
     pub fn ptr_offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
                 Ok(Scalar::Bits {
                     bits: dl.offset(bits as u64, i.bytes())? as u128,
                     size,
                 })
             }
             Scalar::Ptr(ptr) => ptr.offset(i, dl).map(Scalar::Ptr),
         }
     }

     #[inline]
     pub fn ptr_wrapping_offset(self, i: Size, cx: &impl HasDataLayout) -> Self {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
                 Scalar::Bits {
                     bits: dl.overflowing_offset(bits as u64, i.bytes()).0 as u128,
                     size,
                 }
             }
             Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_offset(i, dl)),
         }
     }

     #[inline]
     pub fn ptr_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size().bytes());
                 Ok(Scalar::Bits {
                     bits: dl.signed_offset(bits as u64, i)? as u128,
                     size,
                 })
             }
             Scalar::Ptr(ptr) => ptr.signed_offset(i, dl).map(Scalar::Ptr),
         }
     }

     #[inline]
     pub fn ptr_wrapping_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> Self {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
                 Scalar::Bits {
                     bits: dl.overflowing_signed_offset(bits as u64, i128::from(i)).0 as u128,
                     size,
                 }
             }
             Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_signed_offset(i, dl)),
         }
     }

     /// Returns this pointers offset from the allocation base, or from NULL (for
     /// integer pointers).
     #[inline]
     pub fn get_ptr_offset(self, cx: &impl HasDataLayout) -> Size {
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, cx.pointer_size().bytes());
                 Size::from_bytes(bits as u64)
             }
             Scalar::Ptr(ptr) => ptr.offset,
         }
     }

     #[inline]
     pub fn is_null_ptr(self, cx: &impl HasDataLayout) -> bool {
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, cx.data_layout().pointer_size.bytes());
                 bits == 0
             },
             Scalar::Ptr(_) => false,
         }
     }

     #[inline]
     pub fn from_bool(b: bool) -> Self {
         Scalar::Bits { bits: b as u128, size: 1 }
     }

     #[inline]
     pub fn from_char(c: char) -> Self {
         Scalar::Bits { bits: c as u128, size: 4 }
     }

     #[inline]
     pub fn from_uint(i: impl Into<u128>, size: Size) -> Self {
         let i = i.into();
         debug_assert_eq!(truncate(i, size), i,
                          "Unsigned value {} does not fit in {} bits", i, size.bits());
         Scalar::Bits { bits: i, size: size.bytes() as u8 }
     }

     #[inline]
     pub fn from_int(i: impl Into<i128>, size: Size) -> Self {
         let i = i.into();
         // `into` performed sign extension, we have to truncate
         let truncated = truncate(i as u128, size);
         debug_assert_eq!(sign_extend(truncated, size) as i128, i,
                          "Signed value {} does not fit in {} bits", i, size.bits());
         Scalar::Bits { bits: truncated, size: size.bytes() as u8 }
     }

     #[inline]
     pub fn from_f32(f: f32) -> Self {
         Scalar::Bits { bits: f.to_bits() as u128, size: 4 }
     }

     #[inline]
     pub fn from_f64(f: f64) -> Self {
         Scalar::Bits { bits: f.to_bits() as u128, size: 8 }
     }

     #[inline]
     pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(target_size.bytes(), size as u64);
                 assert_ne!(size, 0, "to_bits cannot be used with zsts");
                 Ok(bits)
             }
             Scalar::Ptr(_) => err!(ReadPointerAsBytes),
         }
     }

     #[inline]
     pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
         match self {
             Scalar::Bits { bits: 0, .. } => err!(InvalidNullPointerUsage),
             Scalar::Bits { .. } => err!(ReadBytesAsPointer),
             Scalar::Ptr(p) => Ok(p),
         }
     }

     #[inline]
     pub fn is_bits(self) -> bool {
         match self {
             Scalar::Bits { .. } => true,
             _ => false,
         }
     }

     #[inline]
     pub fn is_ptr(self) -> bool {
         match self {
             Scalar::Ptr(_) => true,
             _ => false,
         }
     }

     pub fn to_bool(self) -> EvalResult<'tcx, bool> {
         match self {
             Scalar::Bits { bits: 0, size: 1 } => Ok(false),
             Scalar::Bits { bits: 1, size: 1 } => Ok(true),
             _ => err!(InvalidBool),
         }
     }

     pub fn to_char(self) -> EvalResult<'tcx, char> {
         let val = self.to_u32()?;
         match ::std::char::from_u32(val) {
             Some(c) => Ok(c),
             None => err!(InvalidChar(val as u128)),
         }
     }

     pub fn to_u8(self) -> EvalResult<'static, u8> {
         let sz = Size::from_bits(8);
         let b = self.to_bits(sz)?;
         assert_eq!(b as u8 as u128, b);
         Ok(b as u8)
     }

     pub fn to_u32(self) -> EvalResult<'static, u32> {
         let sz = Size::from_bits(32);
         let b = self.to_bits(sz)?;
         assert_eq!(b as u32 as u128, b);
         Ok(b as u32)
     }

     pub fn to_u64(self) -> EvalResult<'static, u64> {
         let sz = Size::from_bits(64);
         let b = self.to_bits(sz)?;
         assert_eq!(b as u64 as u128, b);
         Ok(b as u64)
     }

     pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'static, u64> {
         let b = self.to_bits(cx.data_layout().pointer_size)?;
         assert_eq!(b as u64 as u128, b);
         Ok(b as u64)
     }

     pub fn to_i8(self) -> EvalResult<'static, i8> {
         let sz = Size::from_bits(8);
         let b = self.to_bits(sz)?;
         let b = sign_extend(b, sz) as i128;
         assert_eq!(b as i8 as i128, b);
         Ok(b as i8)
     }

     pub fn to_i32(self) -> EvalResult<'static, i32> {
         let sz = Size::from_bits(32);
         let b = self.to_bits(sz)?;
         let b = sign_extend(b, sz) as i128;
         assert_eq!(b as i32 as i128, b);
         Ok(b as i32)
     }

     pub fn to_i64(self) -> EvalResult<'static, i64> {
         let sz = Size::from_bits(64);
         let b = self.to_bits(sz)?;
         let b = sign_extend(b, sz) as i128;
         assert_eq!(b as i64 as i128, b);
         Ok(b as i64)
     }

     pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'static, i64> {
         let b = self.to_bits(cx.data_layout().pointer_size)?;
         let b = sign_extend(b, cx.data_layout().pointer_size) as i128;
         assert_eq!(b as i64 as i128, b);
         Ok(b as i64)
     }

     #[inline]
     pub fn to_f32(self) -> EvalResult<'static, f32> {
         Ok(f32::from_bits(self.to_u32()?))
     }

     #[inline]
     pub fn to_f64(self) -> EvalResult<'static, f64> {
         Ok(f64::from_bits(self.to_u64()?))
     }
 }

 impl<Tag> From<Pointer<Tag>> for Scalar<Tag> {
     #[inline(always)]
     fn from(ptr: Pointer<Tag>) -> Self {
         Scalar::Ptr(ptr)
     }
 }

 #[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
 pub enum ScalarMaybeUndef<Tag=(), Id=AllocId> {
     Scalar(Scalar<Tag, Id>),
     Undef,
 }

 impl<Tag> From<Scalar<Tag>> for ScalarMaybeUndef<Tag> {
     #[inline(always)]
     fn from(s: Scalar<Tag>) -> Self {
         ScalarMaybeUndef::Scalar(s)
     }
 }

 impl<Tag> fmt::Display for ScalarMaybeUndef<Tag> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             ScalarMaybeUndef::Undef => write!(f, "uninitialized bytes"),
             ScalarMaybeUndef::Scalar(s) => write!(f, "{}", s),
         }
     }
 }

 impl<'tcx> ScalarMaybeUndef<()> {
     #[inline]
     pub fn with_default_tag<Tag>(self) -> ScalarMaybeUndef<Tag>
         where Tag: Default
     {
         match self {
             ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.with_default_tag()),
             ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
         }
     }
 }

 impl<'tcx, Tag> ScalarMaybeUndef<Tag> {
     #[inline]
     pub fn erase_tag(self) -> ScalarMaybeUndef
     {
         match self {
             ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.erase_tag()),
             ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
         }
     }

     #[inline]
     pub fn not_undef(self) -> EvalResult<'static, Scalar<Tag>> {
         match self {
             ScalarMaybeUndef::Scalar(scalar) => Ok(scalar),
             ScalarMaybeUndef::Undef => err!(ReadUndefBytes(Size::from_bytes(0))),
         }
     }

     #[inline(always)]
     pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
         self.not_undef()?.to_ptr()
     }

     #[inline(always)]
     pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
         self.not_undef()?.to_bits(target_size)
     }

     #[inline(always)]
     pub fn to_bool(self) -> EvalResult<'tcx, bool> {
         self.not_undef()?.to_bool()
     }

     #[inline(always)]
     pub fn to_char(self) -> EvalResult<'tcx, char> {
         self.not_undef()?.to_char()
     }

     #[inline(always)]
     pub fn to_f32(self) -> EvalResult<'tcx, f32> {
         self.not_undef()?.to_f32()
     }

     #[inline(always)]
     pub fn to_f64(self) -> EvalResult<'tcx, f64> {
         self.not_undef()?.to_f64()
     }

     #[inline(always)]
     pub fn to_u8(self) -> EvalResult<'tcx, u8> {
         self.not_undef()?.to_u8()
     }

     #[inline(always)]
     pub fn to_u32(self) -> EvalResult<'tcx, u32> {
         self.not_undef()?.to_u32()
     }

     #[inline(always)]
     pub fn to_u64(self) -> EvalResult<'tcx, u64> {
         self.not_undef()?.to_u64()
     }

     #[inline(always)]
     pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, u64> {
         self.not_undef()?.to_usize(cx)
     }

     #[inline(always)]
     pub fn to_i8(self) -> EvalResult<'tcx, i8> {
         self.not_undef()?.to_i8()
     }

     #[inline(always)]
     pub fn to_i32(self) -> EvalResult<'tcx, i32> {
         self.not_undef()?.to_i32()
     }

     #[inline(always)]
     pub fn to_i64(self) -> EvalResult<'tcx, i64> {
         self.not_undef()?.to_i64()
     }

     #[inline(always)]
     pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, i64> {
         self.not_undef()?.to_isize(cx)
     }
 }

 impl_stable_hash_for!(enum crate::mir::interpret::ScalarMaybeUndef {
     Scalar(v),
     Undef
 });
	use std::fmt;
	use rustc_macros::HashStable;

	use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}, subst::SubstsRef};
	use crate::hir::def_id::DefId;

	use super::{EvalResult, Pointer, PointerArithmetic, Allocation, AllocId, sign_extend, truncate};

	/// Represents the result of a raw const operation, pre-validation.
	#[derive(Copy, Clone, Debug, Eq, PartialEq, RustcEncodable, RustcDecodable, Hash, HashStable)]
	pub struct RawConst<'tcx> {
	// the value lives here, at offset 0, and that allocation definitely is a `AllocKind::Memory`
	// (so you can use `AllocMap::unwrap_memory`).
	pub alloc_id: AllocId,
	pub ty: Ty<'tcx>,
	}

	/// Represents a constant value in Rust. `Scalar` and `ScalarPair` are optimizations that
	/// match the `LocalState` optimizations for easy conversions between `Value` and `ConstValue`.
	#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord,
	RustcEncodable, RustcDecodable, Hash, HashStable)]
	pub enum ConstValue<'tcx> {
	/// A const generic parameter.
	Param(ParamConst),

	/// Infer the value of the const.
	Infer(InferConst<'tcx>),

	/// Used only for types with `layout::abi::Scalar` ABI and ZSTs.
	///
	/// Not using the enum `Value` to encode that this must not be `Undef`.
	Scalar(Scalar),

	/// Used only for slices and strings (`&[T]`, `&str`, `const [T]`, `mut str`, `Box<str>`,
	/// etc.).
	///
	/// Empty slices don't necessarily have an address backed by an `AllocId`, thus we also need to
	/// enable integer pointers. The `Scalar` type covers exactly those two cases. While we could
	/// create dummy-`AllocId`s, the additional code effort for the conversions doesn't seem worth
	/// it.
	Slice(Scalar, u64),

	/// An allocation together with a pointer into the allocation.
	/// Invariant: the pointer's `AllocId` resolves to the allocation.
	ByRef(Pointer, &'tcx Allocation),

	/// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other
	/// variants when the code is monomorphic enough for that.
	Unevaluated(DefId, SubstsRef<'tcx>),
	}

	#[cfg(target_arch = "x86_64")]
	static_assert!(CONST_SIZE: ::std::mem::size_of::<ConstValue<'static>>() == 40);

	impl<'tcx> ConstValue<'tcx> {
	#[inline]
	pub fn try_to_scalar(&self) -> Option<Scalar> {
	match *self {
	ConstValue::Param(_) \|
	ConstValue::Infer(_) \|
	ConstValue::ByRef(..) \|
	ConstValue::Unevaluated(..) \|
	ConstValue::Slice(..) => None,
	ConstValue::Scalar(val) => Some(val),
	}
	}

	#[inline]
	pub fn try_to_bits(&self, size: Size) -> Option<u128> {
	self.try_to_scalar()?.to_bits(size).ok()
	}

	#[inline]
	pub fn try_to_ptr(&self) -> Option<Pointer> {
	self.try_to_scalar()?.to_ptr().ok()
	}

	#[inline]
	pub fn new_slice(
	val: Scalar,
	len: u64,
	) -> Self {
	ConstValue::Slice(val, len)
	}
	}

	/// A `Scalar` represents an immediate, primitive value existing outside of a
	/// `memory::Allocation`. It is in many ways like a small chunk of a `Allocation`, up to 8 bytes in
	/// size. Like a range of bytes in an `Allocation`, a `Scalar` can either represent the raw bytes
	/// of a simple value or a pointer into another `Allocation`
	#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd,
	RustcEncodable, RustcDecodable, Hash, HashStable)]
	pub enum Scalar<Tag=(), Id=AllocId> {
	/// The raw bytes of a simple value.
	Bits {
	/// The first `size` bytes are the value.
	/// Do not try to read less or more bytes than that. The remaining bytes must be 0.
	size: u8,
	bits: u128,
	},

	/// A pointer into an `Allocation`. An `Allocation` in the `memory` module has a list of
	/// relocations, but a `Scalar` is only large enough to contain one, so we just represent the
	/// relocation and its associated offset together as a `Pointer` here.
	Ptr(Pointer<Tag, Id>),
	}

	#[cfg(target_arch = "x86_64")]
	static_assert!(SCALAR_SIZE: ::std::mem::size_of::<Scalar>() == 24);

	impl<Tag> fmt::Display for Scalar<Tag> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	match self {
	Scalar::Ptr(_) => write!(f, "a pointer"),
	Scalar::Bits { bits, .. } => write!(f, "{}", bits),
	}
	}
	}

	impl<'tcx> Scalar<()> {
	#[inline]
	pub fn with_default_tag<Tag>(self) -> Scalar<Tag>
	where Tag: Default
	{
	match self {
	Scalar::Ptr(ptr) => Scalar::Ptr(ptr.with_default_tag()),
	Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
	}
	}
	}

	impl<'tcx, Tag> Scalar<Tag> {
	#[inline]
	pub fn erase_tag(self) -> Scalar {
	match self {
	Scalar::Ptr(ptr) => Scalar::Ptr(ptr.erase_tag()),
	Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
	}
	}

	#[inline]
	pub fn with_tag(self, new_tag: Tag) -> Self {
	match self {
	Scalar::Ptr(ptr) => Scalar::Ptr(Pointer { tag: new_tag, ..ptr }),
	Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
	}
	}

	#[inline]
	pub fn ptr_null(cx: &impl HasDataLayout) -> Self {
	Scalar::Bits {
	bits: 0,
	size: cx.data_layout().pointer_size.bytes() as u8,
	}
	}

	#[inline]
	pub fn zst() -> Self {
	Scalar::Bits { bits: 0, size: 0 }
	}

	#[inline]
	pub fn ptr_offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
	let dl = cx.data_layout();
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, dl.pointer_size.bytes());
	Ok(Scalar::Bits {
	bits: dl.offset(bits as u64, i.bytes())? as u128,
	size,
	})
	}
	Scalar::Ptr(ptr) => ptr.offset(i, dl).map(Scalar::Ptr),
	}
	}

	#[inline]
	pub fn ptr_wrapping_offset(self, i: Size, cx: &impl HasDataLayout) -> Self {
	let dl = cx.data_layout();
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, dl.pointer_size.bytes());
	Scalar::Bits {
	bits: dl.overflowing_offset(bits as u64, i.bytes()).0 as u128,
	size,
	}
	}
	Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_offset(i, dl)),
	}
	}

	#[inline]
	pub fn ptr_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
	let dl = cx.data_layout();
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, dl.pointer_size().bytes());
	Ok(Scalar::Bits {
	bits: dl.signed_offset(bits as u64, i)? as u128,
	size,
	})
	}
	Scalar::Ptr(ptr) => ptr.signed_offset(i, dl).map(Scalar::Ptr),
	}
	}

	#[inline]
	pub fn ptr_wrapping_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> Self {
	let dl = cx.data_layout();
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, dl.pointer_size.bytes());
	Scalar::Bits {
	bits: dl.overflowing_signed_offset(bits as u64, i128::from(i)).0 as u128,
	size,
	}
	}
	Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_signed_offset(i, dl)),
	}
	}

	/// Returns this pointers offset from the allocation base, or from NULL (for
	/// integer pointers).
	#[inline]
	pub fn get_ptr_offset(self, cx: &impl HasDataLayout) -> Size {
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, cx.pointer_size().bytes());
	Size::from_bytes(bits as u64)
	}
	Scalar::Ptr(ptr) => ptr.offset,
	}
	}

	#[inline]
	pub fn is_null_ptr(self, cx: &impl HasDataLayout) -> bool {
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(size as u64, cx.data_layout().pointer_size.bytes());
	bits == 0
	},
	Scalar::Ptr(_) => false,
	}
	}

	#[inline]
	pub fn from_bool(b: bool) -> Self {
	Scalar::Bits { bits: b as u128, size: 1 }
	}

	#[inline]
	pub fn from_char(c: char) -> Self {
	Scalar::Bits { bits: c as u128, size: 4 }
	}

	#[inline]
	pub fn from_uint(i: impl Into<u128>, size: Size) -> Self {
	let i = i.into();
	debug_assert_eq!(truncate(i, size), i,
	"Unsigned value {} does not fit in {} bits", i, size.bits());
	Scalar::Bits { bits: i, size: size.bytes() as u8 }
	}

	#[inline]
	pub fn from_int(i: impl Into<i128>, size: Size) -> Self {
	let i = i.into();
	// `into` performed sign extension, we have to truncate
	let truncated = truncate(i as u128, size);
	debug_assert_eq!(sign_extend(truncated, size) as i128, i,
	"Signed value {} does not fit in {} bits", i, size.bits());
	Scalar::Bits { bits: truncated, size: size.bytes() as u8 }
	}

	#[inline]
	pub fn from_f32(f: f32) -> Self {
	Scalar::Bits { bits: f.to_bits() as u128, size: 4 }
	}

	#[inline]
	pub fn from_f64(f: f64) -> Self {
	Scalar::Bits { bits: f.to_bits() as u128, size: 8 }
	}

	#[inline]
	pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
	match self {
	Scalar::Bits { bits, size } => {
	assert_eq!(target_size.bytes(), size as u64);
	assert_ne!(size, 0, "to_bits cannot be used with zsts");
	Ok(bits)
	}
	Scalar::Ptr(_) => err!(ReadPointerAsBytes),
	}
	}

	#[inline]
	pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
	match self {
	Scalar::Bits { bits: 0, .. } => err!(InvalidNullPointerUsage),
	Scalar::Bits { .. } => err!(ReadBytesAsPointer),
	Scalar::Ptr(p) => Ok(p),
	}
	}

	#[inline]
	pub fn is_bits(self) -> bool {
	match self {
	Scalar::Bits { .. } => true,
	_ => false,
	}
	}

	#[inline]
	pub fn is_ptr(self) -> bool {
	match self {
	Scalar::Ptr(_) => true,
	_ => false,
	}
	}

	pub fn to_bool(self) -> EvalResult<'tcx, bool> {
	match self {
	Scalar::Bits { bits: 0, size: 1 } => Ok(false),
	Scalar::Bits { bits: 1, size: 1 } => Ok(true),
	_ => err!(InvalidBool),
	}
	}

	pub fn to_char(self) -> EvalResult<'tcx, char> {
	let val = self.to_u32()?;
	match ::std::char::from_u32(val) {
	Some(c) => Ok(c),
	None => err!(InvalidChar(val as u128)),
	}
	}

	pub fn to_u8(self) -> EvalResult<'static, u8> {
	let sz = Size::from_bits(8);
	let b = self.to_bits(sz)?;
	assert_eq!(b as u8 as u128, b);
	Ok(b as u8)
	}

	pub fn to_u32(self) -> EvalResult<'static, u32> {
	let sz = Size::from_bits(32);
	let b = self.to_bits(sz)?;
	assert_eq!(b as u32 as u128, b);
	Ok(b as u32)
	}

	pub fn to_u64(self) -> EvalResult<'static, u64> {
	let sz = Size::from_bits(64);
	let b = self.to_bits(sz)?;
	assert_eq!(b as u64 as u128, b);
	Ok(b as u64)
	}

	pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'static, u64> {
	let b = self.to_bits(cx.data_layout().pointer_size)?;
	assert_eq!(b as u64 as u128, b);
	Ok(b as u64)
	}

	pub fn to_i8(self) -> EvalResult<'static, i8> {
	let sz = Size::from_bits(8);
	let b = self.to_bits(sz)?;
	let b = sign_extend(b, sz) as i128;
	assert_eq!(b as i8 as i128, b);
	Ok(b as i8)
	}

	pub fn to_i32(self) -> EvalResult<'static, i32> {
	let sz = Size::from_bits(32);
	let b = self.to_bits(sz)?;
	let b = sign_extend(b, sz) as i128;
	assert_eq!(b as i32 as i128, b);
	Ok(b as i32)
	}

	pub fn to_i64(self) -> EvalResult<'static, i64> {
	let sz = Size::from_bits(64);
	let b = self.to_bits(sz)?;
	let b = sign_extend(b, sz) as i128;
	assert_eq!(b as i64 as i128, b);
	Ok(b as i64)
	}

	pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'static, i64> {
	let b = self.to_bits(cx.data_layout().pointer_size)?;
	let b = sign_extend(b, cx.data_layout().pointer_size) as i128;
	assert_eq!(b as i64 as i128, b);
	Ok(b as i64)
	}

	#[inline]
	pub fn to_f32(self) -> EvalResult<'static, f32> {
	Ok(f32::from_bits(self.to_u32()?))
	}

	#[inline]
	pub fn to_f64(self) -> EvalResult<'static, f64> {
	Ok(f64::from_bits(self.to_u64()?))
	}
	}

	impl<Tag> From<Pointer<Tag>> for Scalar<Tag> {
	#[inline(always)]
	fn from(ptr: Pointer<Tag>) -> Self {
	Scalar::Ptr(ptr)
	}
	}

	#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
	pub enum ScalarMaybeUndef<Tag=(), Id=AllocId> {
	Scalar(Scalar<Tag, Id>),
	Undef,
	}

	impl<Tag> From<Scalar<Tag>> for ScalarMaybeUndef<Tag> {
	#[inline(always)]
	fn from(s: Scalar<Tag>) -> Self {
	ScalarMaybeUndef::Scalar(s)
	}
	}

	impl<Tag> fmt::Display for ScalarMaybeUndef<Tag> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	match self {
	ScalarMaybeUndef::Undef => write!(f, "uninitialized bytes"),
	ScalarMaybeUndef::Scalar(s) => write!(f, "{}", s),
	}
	}
	}

	impl<'tcx> ScalarMaybeUndef<()> {
	#[inline]
	pub fn with_default_tag<Tag>(self) -> ScalarMaybeUndef<Tag>
	where Tag: Default
	{
	match self {
	ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.with_default_tag()),
	ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
	}
	}
	}

	impl<'tcx, Tag> ScalarMaybeUndef<Tag> {
	#[inline]
	pub fn erase_tag(self) -> ScalarMaybeUndef
	{
	match self {
	ScalarMaybeUndef::Scalar(s) => ScalarMaybeUndef::Scalar(s.erase_tag()),
	ScalarMaybeUndef::Undef => ScalarMaybeUndef::Undef,
	}
	}

	#[inline]
	pub fn not_undef(self) -> EvalResult<'static, Scalar<Tag>> {
	match self {
	ScalarMaybeUndef::Scalar(scalar) => Ok(scalar),
	ScalarMaybeUndef::Undef => err!(ReadUndefBytes(Size::from_bytes(0))),
	}
	}

	#[inline(always)]
	pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
	self.not_undef()?.to_ptr()
	}

	#[inline(always)]
	pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
	self.not_undef()?.to_bits(target_size)
	}

	#[inline(always)]
	pub fn to_bool(self) -> EvalResult<'tcx, bool> {
	self.not_undef()?.to_bool()
	}

	#[inline(always)]
	pub fn to_char(self) -> EvalResult<'tcx, char> {
	self.not_undef()?.to_char()
	}

	#[inline(always)]
	pub fn to_f32(self) -> EvalResult<'tcx, f32> {
	self.not_undef()?.to_f32()
	}

	#[inline(always)]
	pub fn to_f64(self) -> EvalResult<'tcx, f64> {
	self.not_undef()?.to_f64()
	}

	#[inline(always)]
	pub fn to_u8(self) -> EvalResult<'tcx, u8> {
	self.not_undef()?.to_u8()
	}

	#[inline(always)]
	pub fn to_u32(self) -> EvalResult<'tcx, u32> {
	self.not_undef()?.to_u32()
	}

	#[inline(always)]
	pub fn to_u64(self) -> EvalResult<'tcx, u64> {
	self.not_undef()?.to_u64()
	}

	#[inline(always)]
	pub fn to_usize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, u64> {
	self.not_undef()?.to_usize(cx)
	}

	#[inline(always)]
	pub fn to_i8(self) -> EvalResult<'tcx, i8> {
	self.not_undef()?.to_i8()
	}

	#[inline(always)]
	pub fn to_i32(self) -> EvalResult<'tcx, i32> {
	self.not_undef()?.to_i32()
	}

	#[inline(always)]
	pub fn to_i64(self) -> EvalResult<'tcx, i64> {
	self.not_undef()?.to_i64()
	}

	#[inline(always)]
	pub fn to_isize(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, i64> {
	self.not_undef()?.to_isize(cx)
	}
	}

	impl_stable_hash_for!(enum crate::mir::interpret::ScalarMaybeUndef {
	Scalar(v),
	Undef
	});