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Diffstat (limited to 'compiler/rustc_target/src/abi/mod.rs')
| -rw-r--r-- | compiler/rustc_target/src/abi/mod.rs | 1150 |
1 files changed, 1150 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs new file mode 100644 index 00000000000..4b565dd246f --- /dev/null +++ b/compiler/rustc_target/src/abi/mod.rs @@ -0,0 +1,1150 @@ +pub use Integer::*; +pub use Primitive::*; + +use crate::spec::Target; + +use std::convert::{TryFrom, TryInto}; +use std::num::NonZeroUsize; +use std::ops::{Add, AddAssign, Deref, Mul, Range, RangeInclusive, Sub}; + +use rustc_index::vec::{Idx, IndexVec}; +use rustc_macros::HashStable_Generic; +use rustc_span::Span; + +pub mod call; + +/// Parsed [Data layout](http://llvm.org/docs/LangRef.html#data-layout) +/// for a target, which contains everything needed to compute layouts. +pub struct TargetDataLayout { + pub endian: Endian, + pub i1_align: AbiAndPrefAlign, + pub i8_align: AbiAndPrefAlign, + pub i16_align: AbiAndPrefAlign, + pub i32_align: AbiAndPrefAlign, + pub i64_align: AbiAndPrefAlign, + pub i128_align: AbiAndPrefAlign, + pub f32_align: AbiAndPrefAlign, + pub f64_align: AbiAndPrefAlign, + pub pointer_size: Size, + pub pointer_align: AbiAndPrefAlign, + pub aggregate_align: AbiAndPrefAlign, + + /// Alignments for vector types. + pub vector_align: Vec<(Size, AbiAndPrefAlign)>, + + pub instruction_address_space: AddressSpace, +} + +impl Default for TargetDataLayout { + /// Creates an instance of `TargetDataLayout`. + fn default() -> TargetDataLayout { + let align = |bits| Align::from_bits(bits).unwrap(); + TargetDataLayout { + endian: Endian::Big, + i1_align: AbiAndPrefAlign::new(align(8)), + i8_align: AbiAndPrefAlign::new(align(8)), + i16_align: AbiAndPrefAlign::new(align(16)), + i32_align: AbiAndPrefAlign::new(align(32)), + i64_align: AbiAndPrefAlign { abi: align(32), pref: align(64) }, + i128_align: AbiAndPrefAlign { abi: align(32), pref: align(64) }, + f32_align: AbiAndPrefAlign::new(align(32)), + f64_align: AbiAndPrefAlign::new(align(64)), + pointer_size: Size::from_bits(64), + pointer_align: AbiAndPrefAlign::new(align(64)), + aggregate_align: AbiAndPrefAlign { abi: align(0), pref: align(64) }, + vector_align: vec![ + (Size::from_bits(64), AbiAndPrefAlign::new(align(64))), + (Size::from_bits(128), AbiAndPrefAlign::new(align(128))), + ], + instruction_address_space: AddressSpace::DATA, + } + } +} + +impl TargetDataLayout { + pub fn parse(target: &Target) -> Result<TargetDataLayout, String> { + // Parse an address space index from a string. + let parse_address_space = |s: &str, cause: &str| { + s.parse::<u32>().map(AddressSpace).map_err(|err| { + format!("invalid address space `{}` for `{}` in \"data-layout\": {}", s, cause, err) + }) + }; + + // Parse a bit count from a string. + let parse_bits = |s: &str, kind: &str, cause: &str| { + s.parse::<u64>().map_err(|err| { + format!("invalid {} `{}` for `{}` in \"data-layout\": {}", kind, s, cause, err) + }) + }; + + // Parse a size string. + let size = |s: &str, cause: &str| parse_bits(s, "size", cause).map(Size::from_bits); + + // Parse an alignment string. + let align = |s: &[&str], cause: &str| { + if s.is_empty() { + return Err(format!("missing alignment for `{}` in \"data-layout\"", cause)); + } + let align_from_bits = |bits| { + Align::from_bits(bits).map_err(|err| { + format!("invalid alignment for `{}` in \"data-layout\": {}", cause, err) + }) + }; + let abi = parse_bits(s[0], "alignment", cause)?; + let pref = s.get(1).map_or(Ok(abi), |pref| parse_bits(pref, "alignment", cause))?; + Ok(AbiAndPrefAlign { abi: align_from_bits(abi)?, pref: align_from_bits(pref)? }) + }; + + let mut dl = TargetDataLayout::default(); + let mut i128_align_src = 64; + for spec in target.data_layout.split('-') { + let spec_parts = spec.split(':').collect::<Vec<_>>(); + + match &*spec_parts { + ["e"] => dl.endian = Endian::Little, + ["E"] => dl.endian = Endian::Big, + [p] if p.starts_with('P') => { + dl.instruction_address_space = parse_address_space(&p[1..], "P")? + } + ["a", ref a @ ..] => dl.aggregate_align = align(a, "a")?, + ["f32", ref a @ ..] => dl.f32_align = align(a, "f32")?, + ["f64", ref a @ ..] => dl.f64_align = align(a, "f64")?, + [p @ "p", s, ref a @ ..] | [p @ "p0", s, ref a @ ..] => { + dl.pointer_size = size(s, p)?; + dl.pointer_align = align(a, p)?; + } + [s, ref a @ ..] if s.starts_with('i') => { + let bits = match s[1..].parse::<u64>() { + Ok(bits) => bits, + Err(_) => { + size(&s[1..], "i")?; // For the user error. + continue; + } + }; + let a = align(a, s)?; + match bits { + 1 => dl.i1_align = a, + 8 => dl.i8_align = a, + 16 => dl.i16_align = a, + 32 => dl.i32_align = a, + 64 => dl.i64_align = a, + _ => {} + } + if bits >= i128_align_src && bits <= 128 { + // Default alignment for i128 is decided by taking the alignment of + // largest-sized i{64..=128}. + i128_align_src = bits; + dl.i128_align = a; + } + } + [s, ref a @ ..] if s.starts_with('v') => { + let v_size = size(&s[1..], "v")?; + let a = align(a, s)?; + if let Some(v) = dl.vector_align.iter_mut().find(|v| v.0 == v_size) { + v.1 = a; + continue; + } + // No existing entry, add a new one. + dl.vector_align.push((v_size, a)); + } + _ => {} // Ignore everything else. + } + } + + // Perform consistency checks against the Target information. + let endian_str = match dl.endian { + Endian::Little => "little", + Endian::Big => "big", + }; + if endian_str != target.target_endian { + return Err(format!( + "inconsistent target specification: \"data-layout\" claims \ + architecture is {}-endian, while \"target-endian\" is `{}`", + endian_str, target.target_endian + )); + } + + if dl.pointer_size.bits().to_string() != target.target_pointer_width { + return Err(format!( + "inconsistent target specification: \"data-layout\" claims \ + pointers are {}-bit, while \"target-pointer-width\" is `{}`", + dl.pointer_size.bits(), + target.target_pointer_width + )); + } + + Ok(dl) + } + + /// Returns exclusive upper bound on object size. + /// + /// The theoretical maximum object size is defined as the maximum positive `isize` value. + /// This ensures that the `offset` semantics remain well-defined by allowing it to correctly + /// index every address within an object along with one byte past the end, along with allowing + /// `isize` to store the difference between any two pointers into an object. + /// + /// The upper bound on 64-bit currently needs to be lower because LLVM uses a 64-bit integer + /// to represent object size in bits. It would need to be 1 << 61 to account for this, but is + /// currently conservatively bounded to 1 << 47 as that is enough to cover the current usable + /// address space on 64-bit ARMv8 and x86_64. + pub fn obj_size_bound(&self) -> u64 { + match self.pointer_size.bits() { + 16 => 1 << 15, + 32 => 1 << 31, + 64 => 1 << 47, + bits => panic!("obj_size_bound: unknown pointer bit size {}", bits), + } + } + + pub fn ptr_sized_integer(&self) -> Integer { + match self.pointer_size.bits() { + 16 => I16, + 32 => I32, + 64 => I64, + bits => panic!("ptr_sized_integer: unknown pointer bit size {}", bits), + } + } + + pub fn vector_align(&self, vec_size: Size) -> AbiAndPrefAlign { + for &(size, align) in &self.vector_align { + if size == vec_size { + return align; + } + } + // Default to natural alignment, which is what LLVM does. + // That is, use the size, rounded up to a power of 2. + AbiAndPrefAlign::new(Align::from_bytes(vec_size.bytes().next_power_of_two()).unwrap()) + } +} + +pub trait HasDataLayout { + fn data_layout(&self) -> &TargetDataLayout; +} + +impl HasDataLayout for TargetDataLayout { + fn data_layout(&self) -> &TargetDataLayout { + self + } +} + +/// Endianness of the target, which must match cfg(target-endian). +#[derive(Copy, Clone, PartialEq)] +pub enum Endian { + Little, + Big, +} + +/// Size of a type in bytes. +#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)] +#[derive(HashStable_Generic)] +pub struct Size { + raw: u64, +} + +impl Size { + pub const ZERO: Size = Size { raw: 0 }; + + #[inline] + pub fn from_bits(bits: impl TryInto<u64>) -> Size { + let bits = bits.try_into().ok().unwrap(); + // Avoid potential overflow from `bits + 7`. + Size::from_bytes(bits / 8 + ((bits % 8) + 7) / 8) + } + + #[inline] + pub fn from_bytes(bytes: impl TryInto<u64>) -> Size { + Size { raw: bytes.try_into().ok().unwrap() } + } + + #[inline] + pub fn bytes(self) -> u64 { + self.raw + } + + #[inline] + pub fn bytes_usize(self) -> usize { + self.bytes().try_into().unwrap() + } + + #[inline] + pub fn bits(self) -> u64 { + self.bytes().checked_mul(8).unwrap_or_else(|| { + panic!("Size::bits: {} bytes in bits doesn't fit in u64", self.bytes()) + }) + } + + #[inline] + pub fn bits_usize(self) -> usize { + self.bits().try_into().unwrap() + } + + #[inline] + pub fn align_to(self, align: Align) -> Size { + let mask = align.bytes() - 1; + Size::from_bytes((self.bytes() + mask) & !mask) + } + + #[inline] + pub fn is_aligned(self, align: Align) -> bool { + let mask = align.bytes() - 1; + self.bytes() & mask == 0 + } + + #[inline] + pub fn checked_add<C: HasDataLayout>(self, offset: Size, cx: &C) -> Option<Size> { + let dl = cx.data_layout(); + + let bytes = self.bytes().checked_add(offset.bytes())?; + + if bytes < dl.obj_size_bound() { Some(Size::from_bytes(bytes)) } else { None } + } + + #[inline] + pub fn checked_mul<C: HasDataLayout>(self, count: u64, cx: &C) -> Option<Size> { + let dl = cx.data_layout(); + + let bytes = self.bytes().checked_mul(count)?; + if bytes < dl.obj_size_bound() { Some(Size::from_bytes(bytes)) } else { None } + } +} + +// Panicking addition, subtraction and multiplication for convenience. +// Avoid during layout computation, return `LayoutError` instead. + +impl Add for Size { + type Output = Size; + #[inline] + fn add(self, other: Size) -> Size { + Size::from_bytes(self.bytes().checked_add(other.bytes()).unwrap_or_else(|| { + panic!("Size::add: {} + {} doesn't fit in u64", self.bytes(), other.bytes()) + })) + } +} + +impl Sub for Size { + type Output = Size; + #[inline] + fn sub(self, other: Size) -> Size { + Size::from_bytes(self.bytes().checked_sub(other.bytes()).unwrap_or_else(|| { + panic!("Size::sub: {} - {} would result in negative size", self.bytes(), other.bytes()) + })) + } +} + +impl Mul<Size> for u64 { + type Output = Size; + #[inline] + fn mul(self, size: Size) -> Size { + size * self + } +} + +impl Mul<u64> for Size { + type Output = Size; + #[inline] + fn mul(self, count: u64) -> Size { + match self.bytes().checked_mul(count) { + Some(bytes) => Size::from_bytes(bytes), + None => panic!("Size::mul: {} * {} doesn't fit in u64", self.bytes(), count), + } + } +} + +impl AddAssign for Size { + #[inline] + fn add_assign(&mut self, other: Size) { + *self = *self + other; + } +} + +/// Alignment of a type in bytes (always a power of two). +#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)] +#[derive(HashStable_Generic)] +pub struct Align { + pow2: u8, +} + +impl Align { + pub fn from_bits(bits: u64) -> Result<Align, String> { + Align::from_bytes(Size::from_bits(bits).bytes()) + } + + pub fn from_bytes(align: u64) -> Result<Align, String> { + // Treat an alignment of 0 bytes like 1-byte alignment. + if align == 0 { + return Ok(Align { pow2: 0 }); + } + + let mut bytes = align; + let mut pow2: u8 = 0; + while (bytes & 1) == 0 { + pow2 += 1; + bytes >>= 1; + } + if bytes != 1 { + return Err(format!("`{}` is not a power of 2", align)); + } + if pow2 > 29 { + return Err(format!("`{}` is too large", align)); + } + + Ok(Align { pow2 }) + } + + pub fn bytes(self) -> u64 { + 1 << self.pow2 + } + + pub fn bits(self) -> u64 { + self.bytes() * 8 + } + + /// Computes the best alignment possible for the given offset + /// (the largest power of two that the offset is a multiple of). + /// + /// N.B., for an offset of `0`, this happens to return `2^64`. + pub fn max_for_offset(offset: Size) -> Align { + Align { pow2: offset.bytes().trailing_zeros() as u8 } + } + + /// Lower the alignment, if necessary, such that the given offset + /// is aligned to it (the offset is a multiple of the alignment). + pub fn restrict_for_offset(self, offset: Size) -> Align { + self.min(Align::max_for_offset(offset)) + } +} + +/// A pair of alignments, ABI-mandated and preferred. +#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Encodable, Decodable)] +#[derive(HashStable_Generic)] +pub struct AbiAndPrefAlign { + pub abi: Align, + pub pref: Align, +} + +impl AbiAndPrefAlign { + pub fn new(align: Align) -> AbiAndPrefAlign { + AbiAndPrefAlign { abi: align, pref: align } + } + + pub fn min(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign { + AbiAndPrefAlign { abi: self.abi.min(other.abi), pref: self.pref.min(other.pref) } + } + + pub fn max(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign { + AbiAndPrefAlign { abi: self.abi.max(other.abi), pref: self.pref.max(other.pref) } + } +} + +/// Integers, also used for enum discriminants. +#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, HashStable_Generic)] +pub enum Integer { + I8, + I16, + I32, + I64, + I128, +} + +impl Integer { + pub fn size(self) -> Size { + match self { + I8 => Size::from_bytes(1), + I16 => Size::from_bytes(2), + I32 => Size::from_bytes(4), + I64 => Size::from_bytes(8), + I128 => Size::from_bytes(16), + } + } + + pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign { + let dl = cx.data_layout(); + + match self { + I8 => dl.i8_align, + I16 => dl.i16_align, + I32 => dl.i32_align, + I64 => dl.i64_align, + I128 => dl.i128_align, + } + } + + /// Finds the smallest Integer type which can represent the signed value. + pub fn fit_signed(x: i128) -> Integer { + match x { + -0x0000_0000_0000_0080..=0x0000_0000_0000_007f => I8, + -0x0000_0000_0000_8000..=0x0000_0000_0000_7fff => I16, + -0x0000_0000_8000_0000..=0x0000_0000_7fff_ffff => I32, + -0x8000_0000_0000_0000..=0x7fff_ffff_ffff_ffff => I64, + _ => I128, + } + } + + /// Finds the smallest Integer type which can represent the unsigned value. + pub fn fit_unsigned(x: u128) -> Integer { + match x { + 0..=0x0000_0000_0000_00ff => I8, + 0..=0x0000_0000_0000_ffff => I16, + 0..=0x0000_0000_ffff_ffff => I32, + 0..=0xffff_ffff_ffff_ffff => I64, + _ => I128, + } + } + + /// Finds the smallest integer with the given alignment. + pub fn for_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Option<Integer> { + let dl = cx.data_layout(); + + for &candidate in &[I8, I16, I32, I64, I128] { + if wanted == candidate.align(dl).abi && wanted.bytes() == candidate.size().bytes() { + return Some(candidate); + } + } + None + } + + /// Find the largest integer with the given alignment or less. + pub fn approximate_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Integer { + let dl = cx.data_layout(); + + // FIXME(eddyb) maybe include I128 in the future, when it works everywhere. + for &candidate in &[I64, I32, I16] { + if wanted >= candidate.align(dl).abi && wanted.bytes() >= candidate.size().bytes() { + return candidate; + } + } + I8 + } +} + +/// Fundamental unit of memory access and layout. +#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub enum Primitive { + /// The `bool` is the signedness of the `Integer` type. + /// + /// One would think we would not care about such details this low down, + /// but some ABIs are described in terms of C types and ISAs where the + /// integer arithmetic is done on {sign,zero}-extended registers, e.g. + /// a negative integer passed by zero-extension will appear positive in + /// the callee, and most operations on it will produce the wrong values. + Int(Integer, bool), + F32, + F64, + Pointer, +} + +impl Primitive { + pub fn size<C: HasDataLayout>(self, cx: &C) -> Size { + let dl = cx.data_layout(); + + match self { + Int(i, _) => i.size(), + F32 => Size::from_bits(32), + F64 => Size::from_bits(64), + Pointer => dl.pointer_size, + } + } + + pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign { + let dl = cx.data_layout(); + + match self { + Int(i, _) => i.align(dl), + F32 => dl.f32_align, + F64 => dl.f64_align, + Pointer => dl.pointer_align, + } + } + + pub fn is_float(self) -> bool { + match self { + F32 | F64 => true, + _ => false, + } + } + + pub fn is_int(self) -> bool { + match self { + Int(..) => true, + _ => false, + } + } +} + +/// Information about one scalar component of a Rust type. +#[derive(Clone, PartialEq, Eq, Hash, Debug)] +#[derive(HashStable_Generic)] +pub struct Scalar { + pub value: Primitive, + + /// Inclusive wrap-around range of valid values, that is, if + /// start > end, it represents `start..=MAX`, + /// followed by `0..=end`. + /// + /// That is, for an i8 primitive, a range of `254..=2` means following + /// sequence: + /// + /// 254 (-2), 255 (-1), 0, 1, 2 + /// + /// This is intended specifically to mirror LLVM’s `!range` metadata, + /// semantics. + // FIXME(eddyb) always use the shortest range, e.g., by finding + // the largest space between two consecutive valid values and + // taking everything else as the (shortest) valid range. + pub valid_range: RangeInclusive<u128>, +} + +impl Scalar { + pub fn is_bool(&self) -> bool { + if let Int(I8, _) = self.value { self.valid_range == (0..=1) } else { false } + } + + /// Returns the valid range as a `x..y` range. + /// + /// If `x` and `y` are equal, the range is full, not empty. + pub fn valid_range_exclusive<C: HasDataLayout>(&self, cx: &C) -> Range<u128> { + // For a (max) value of -1, max will be `-1 as usize`, which overflows. + // However, that is fine here (it would still represent the full range), + // i.e., if the range is everything. + let bits = self.value.size(cx).bits(); + assert!(bits <= 128); + let mask = !0u128 >> (128 - bits); + let start = *self.valid_range.start(); + let end = *self.valid_range.end(); + assert_eq!(start, start & mask); + assert_eq!(end, end & mask); + start..(end.wrapping_add(1) & mask) + } +} + +/// Describes how the fields of a type are located in memory. +#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub enum FieldsShape { + /// Scalar primitives and `!`, which never have fields. + Primitive, + + /// All fields start at no offset. The `usize` is the field count. + Union(NonZeroUsize), + + /// Array/vector-like placement, with all fields of identical types. + Array { stride: Size, count: u64 }, + + /// Struct-like placement, with precomputed offsets. + /// + /// Fields are guaranteed to not overlap, but note that gaps + /// before, between and after all the fields are NOT always + /// padding, and as such their contents may not be discarded. + /// For example, enum variants leave a gap at the start, + /// where the discriminant field in the enum layout goes. + Arbitrary { + /// Offsets for the first byte of each field, + /// ordered to match the source definition order. + /// This vector does not go in increasing order. + // FIXME(eddyb) use small vector optimization for the common case. + offsets: Vec<Size>, + + /// Maps source order field indices to memory order indices, + /// depending on how the fields were reordered (if at all). + /// This is a permutation, with both the source order and the + /// memory order using the same (0..n) index ranges. + /// + /// Note that during computation of `memory_index`, sometimes + /// it is easier to operate on the inverse mapping (that is, + /// from memory order to source order), and that is usually + /// named `inverse_memory_index`. + /// + // FIXME(eddyb) build a better abstraction for permutations, if possible. + // FIXME(camlorn) also consider small vector optimization here. + memory_index: Vec<u32>, + }, +} + +impl FieldsShape { + pub fn count(&self) -> usize { + match *self { + FieldsShape::Primitive => 0, + FieldsShape::Union(count) => count.get(), + FieldsShape::Array { count, .. } => { + let usize_count = count as usize; + assert_eq!(usize_count as u64, count); + usize_count + } + FieldsShape::Arbitrary { ref offsets, .. } => offsets.len(), + } + } + + pub fn offset(&self, i: usize) -> Size { + match *self { + FieldsShape::Primitive => { + unreachable!("FieldsShape::offset: `Primitive`s have no fields") + } + FieldsShape::Union(count) => { + assert!( + i < count.get(), + "tried to access field {} of union with {} fields", + i, + count + ); + Size::ZERO + } + FieldsShape::Array { stride, count } => { + let i = u64::try_from(i).unwrap(); + assert!(i < count); + stride * i + } + FieldsShape::Arbitrary { ref offsets, .. } => offsets[i], + } + } + + pub fn memory_index(&self, i: usize) -> usize { + match *self { + FieldsShape::Primitive => { + unreachable!("FieldsShape::memory_index: `Primitive`s have no fields") + } + FieldsShape::Union(_) | FieldsShape::Array { .. } => i, + FieldsShape::Arbitrary { ref memory_index, .. } => { + let r = memory_index[i]; + assert_eq!(r as usize as u32, r); + r as usize + } + } + } + + /// Gets source indices of the fields by increasing offsets. + #[inline] + pub fn index_by_increasing_offset<'a>(&'a self) -> impl Iterator<Item = usize> + 'a { + let mut inverse_small = [0u8; 64]; + let mut inverse_big = vec![]; + let use_small = self.count() <= inverse_small.len(); + + // We have to write this logic twice in order to keep the array small. + if let FieldsShape::Arbitrary { ref memory_index, .. } = *self { + if use_small { + for i in 0..self.count() { + inverse_small[memory_index[i] as usize] = i as u8; + } + } else { + inverse_big = vec![0; self.count()]; + for i in 0..self.count() { + inverse_big[memory_index[i] as usize] = i as u32; + } + } + } + + (0..self.count()).map(move |i| match *self { + FieldsShape::Primitive | FieldsShape::Union(_) | FieldsShape::Array { .. } => i, + FieldsShape::Arbitrary { .. } => { + if use_small { + inverse_small[i] as usize + } else { + inverse_big[i] as usize + } + } + }) + } +} + +/// An identifier that specifies the address space that some operation +/// should operate on. Special address spaces have an effect on code generation, +/// depending on the target and the address spaces it implements. +#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)] +pub struct AddressSpace(pub u32); + +impl AddressSpace { + /// The default address space, corresponding to data space. + pub const DATA: Self = AddressSpace(0); +} + +/// Describes how values of the type are passed by target ABIs, +/// in terms of categories of C types there are ABI rules for. +#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub enum Abi { + Uninhabited, + Scalar(Scalar), + ScalarPair(Scalar, Scalar), + Vector { + element: Scalar, + count: u64, + }, + Aggregate { + /// If true, the size is exact, otherwise it's only a lower bound. + sized: bool, + }, +} + +impl Abi { + /// Returns `true` if the layout corresponds to an unsized type. + pub fn is_unsized(&self) -> bool { + match *self { + Abi::Uninhabited | Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } => false, + Abi::Aggregate { sized } => !sized, + } + } + + /// Returns `true` if this is a single signed integer scalar + pub fn is_signed(&self) -> bool { + match *self { + Abi::Scalar(ref scal) => match scal.value { + Primitive::Int(_, signed) => signed, + _ => false, + }, + _ => panic!("`is_signed` on non-scalar ABI {:?}", self), + } + } + + /// Returns `true` if this is an uninhabited type + pub fn is_uninhabited(&self) -> bool { + match *self { + Abi::Uninhabited => true, + _ => false, + } + } + + /// Returns `true` is this is a scalar type + pub fn is_scalar(&self) -> bool { + match *self { + Abi::Scalar(_) => true, + _ => false, + } + } +} + +rustc_index::newtype_index! { + pub struct VariantIdx { + derive [HashStable_Generic] + } +} + +#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub enum Variants { + /// Single enum variants, structs/tuples, unions, and all non-ADTs. + Single { index: VariantIdx }, + + /// Enum-likes with more than one inhabited variant: each variant comes with + /// a *discriminant* (usually the same as the variant index but the user can + /// assign explicit discriminant values). That discriminant is encoded + /// as a *tag* on the machine. The layout of each variant is + /// a struct, and they all have space reserved for the tag. + /// For enums, the tag is the sole field of the layout. + Multiple { + tag: Scalar, + tag_encoding: TagEncoding, + tag_field: usize, + variants: IndexVec<VariantIdx, Layout>, + }, +} + +#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub enum TagEncoding { + /// The tag directly stores the discriminant, but possibly with a smaller layout + /// (so converting the tag to the discriminant can require sign extension). + Direct, + + /// Niche (values invalid for a type) encoding the discriminant: + /// Discriminant and variant index coincide. + /// The variant `dataful_variant` contains a niche at an arbitrary + /// offset (field `tag_field` of the enum), which for a variant with + /// discriminant `d` is set to + /// `(d - niche_variants.start).wrapping_add(niche_start)`. + /// + /// For example, `Option<(usize, &T)>` is represented such that + /// `None` has a null pointer for the second tuple field, and + /// `Some` is the identity function (with a non-null reference). + Niche { + dataful_variant: VariantIdx, + niche_variants: RangeInclusive<VariantIdx>, + niche_start: u128, + }, +} + +#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub struct Niche { + pub offset: Size, + pub scalar: Scalar, +} + +impl Niche { + pub fn from_scalar<C: HasDataLayout>(cx: &C, offset: Size, scalar: Scalar) -> Option<Self> { + let niche = Niche { offset, scalar }; + if niche.available(cx) > 0 { Some(niche) } else { None } + } + + pub fn available<C: HasDataLayout>(&self, cx: &C) -> u128 { + let Scalar { value, valid_range: ref v } = self.scalar; + let bits = value.size(cx).bits(); + assert!(bits <= 128); + let max_value = !0u128 >> (128 - bits); + + // Find out how many values are outside the valid range. + let niche = v.end().wrapping_add(1)..*v.start(); + niche.end.wrapping_sub(niche.start) & max_value + } + + pub fn reserve<C: HasDataLayout>(&self, cx: &C, count: u128) -> Option<(u128, Scalar)> { + assert!(count > 0); + + let Scalar { value, valid_range: ref v } = self.scalar; + let bits = value.size(cx).bits(); + assert!(bits <= 128); + let max_value = !0u128 >> (128 - bits); + + if count > max_value { + return None; + } + + // Compute the range of invalid values being reserved. + let start = v.end().wrapping_add(1) & max_value; + let end = v.end().wrapping_add(count) & max_value; + + // If the `end` of our range is inside the valid range, + // then we ran out of invalid values. + // FIXME(eddyb) abstract this with a wraparound range type. + let valid_range_contains = |x| { + if v.start() <= v.end() { + *v.start() <= x && x <= *v.end() + } else { + *v.start() <= x || x <= *v.end() + } + }; + if valid_range_contains(end) { + return None; + } + + Some((start, Scalar { value, valid_range: *v.start()..=end })) + } +} + +#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)] +pub struct Layout { + /// Says where the fields are located within the layout. + pub fields: FieldsShape, + + /// Encodes information about multi-variant layouts. + /// Even with `Multiple` variants, a layout still has its own fields! Those are then + /// shared between all variants. One of them will be the discriminant, + /// but e.g. generators can have more. + /// + /// To access all fields of this layout, both `fields` and the fields of the active variant + /// must be taken into account. + pub variants: Variants, + + /// The `abi` defines how this data is passed between functions, and it defines + /// value restrictions via `valid_range`. + /// + /// Note that this is entirely orthogonal to the recursive structure defined by + /// `variants` and `fields`; for example, `ManuallyDrop<Result<isize, isize>>` has + /// `Abi::ScalarPair`! So, even with non-`Aggregate` `abi`, `fields` and `variants` + /// have to be taken into account to find all fields of this layout. + pub abi: Abi, + + /// The leaf scalar with the largest number of invalid values + /// (i.e. outside of its `valid_range`), if it exists. + pub largest_niche: Option<Niche>, + + pub align: AbiAndPrefAlign, + pub size: Size, +} + +impl Layout { + pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self { + let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar.clone()); + let size = scalar.value.size(cx); + let align = scalar.value.align(cx); + Layout { + variants: Variants::Single { index: VariantIdx::new(0) }, + fields: FieldsShape::Primitive, + abi: Abi::Scalar(scalar), + largest_niche, + size, + align, + } + } +} + +/// The layout of a type, alongside the type itself. +/// Provides various type traversal APIs (e.g., recursing into fields). +/// +/// Note that the layout is NOT guaranteed to always be identical +/// to that obtained from `layout_of(ty)`, as we need to produce +/// layouts for which Rust types do not exist, such as enum variants +/// or synthetic fields of enums (i.e., discriminants) and fat pointers. +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +pub struct TyAndLayout<'a, Ty> { + pub ty: Ty, + pub layout: &'a Layout, +} + +impl<'a, Ty> Deref for TyAndLayout<'a, Ty> { + type Target = &'a Layout; + fn deref(&self) -> &&'a Layout { + &self.layout + } +} + +/// Trait for context types that can compute layouts of things. +pub trait LayoutOf { + type Ty; + type TyAndLayout; + + fn layout_of(&self, ty: Self::Ty) -> Self::TyAndLayout; + fn spanned_layout_of(&self, ty: Self::Ty, _span: Span) -> Self::TyAndLayout { + self.layout_of(ty) + } +} + +/// The `TyAndLayout` above will always be a `MaybeResult<TyAndLayout<'_, Self>>`. +/// We can't add the bound due to the lifetime, but this trait is still useful when +/// writing code that's generic over the `LayoutOf` impl. +pub trait MaybeResult<T> { + type Error; + + fn from(x: Result<T, Self::Error>) -> Self; + fn to_result(self) -> Result<T, Self::Error>; +} + +impl<T> MaybeResult<T> for T { + type Error = !; + + fn from(Ok(x): Result<T, Self::Error>) -> Self { + x + } + fn to_result(self) -> Result<T, Self::Error> { + Ok(self) + } +} + +impl<T, E> MaybeResult<T> for Result<T, E> { + type Error = E; + + fn from(x: Result<T, Self::Error>) -> Self { + x + } + fn to_result(self) -> Result<T, Self::Error> { + self + } +} + +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +pub enum PointerKind { + /// Most general case, we know no restrictions to tell LLVM. + Shared, + + /// `&T` where `T` contains no `UnsafeCell`, is `noalias` and `readonly`. + Frozen, + + /// `&mut T`, when we know `noalias` is safe for LLVM. + UniqueBorrowed, + + /// `Box<T>`, unlike `UniqueBorrowed`, it also has `noalias` on returns. + UniqueOwned, +} + +#[derive(Copy, Clone, Debug)] +pub struct PointeeInfo { + pub size: Size, + pub align: Align, + pub safe: Option<PointerKind>, + pub address_space: AddressSpace, +} + +pub trait TyAndLayoutMethods<'a, C: LayoutOf<Ty = Self>>: Sized { + fn for_variant( + this: TyAndLayout<'a, Self>, + cx: &C, + variant_index: VariantIdx, + ) -> TyAndLayout<'a, Self>; + fn field(this: TyAndLayout<'a, Self>, cx: &C, i: usize) -> C::TyAndLayout; + fn pointee_info_at(this: TyAndLayout<'a, Self>, cx: &C, offset: Size) -> Option<PointeeInfo>; +} + +impl<'a, Ty> TyAndLayout<'a, Ty> { + pub fn for_variant<C>(self, cx: &C, variant_index: VariantIdx) -> Self + where + Ty: TyAndLayoutMethods<'a, C>, + C: LayoutOf<Ty = Ty>, + { + Ty::for_variant(self, cx, variant_index) + } + + /// Callers might want to use `C: LayoutOf<Ty=Ty, TyAndLayout: MaybeResult<Self>>` + /// to allow recursion (see `might_permit_zero_init` below for an example). + pub fn field<C>(self, cx: &C, i: usize) -> C::TyAndLayout + where + Ty: TyAndLayoutMethods<'a, C>, + C: LayoutOf<Ty = Ty>, + { + Ty::field(self, cx, i) + } + + pub fn pointee_info_at<C>(self, cx: &C, offset: Size) -> Option<PointeeInfo> + where + Ty: TyAndLayoutMethods<'a, C>, + C: LayoutOf<Ty = Ty>, + { + Ty::pointee_info_at(self, cx, offset) + } +} + +impl<'a, Ty> TyAndLayout<'a, Ty> { + /// Returns `true` if the layout corresponds to an unsized type. + pub fn is_unsized(&self) -> bool { + self.abi.is_unsized() + } + + /// Returns `true` if the type is a ZST and not unsized. + pub fn is_zst(&self) -> bool { + match self.abi { + Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } => false, + Abi::Uninhabited => self.size.bytes() == 0, + Abi::Aggregate { sized } => sized && self.size.bytes() == 0, + } + } + + /// Determines if this type permits "raw" initialization by just transmuting some + /// memory into an instance of `T`. + /// `zero` indicates if the memory is zero-initialized, or alternatively + /// left entirely uninitialized. + /// This is conservative: in doubt, it will answer `true`. + /// + /// FIXME: Once we removed all the conservatism, we could alternatively + /// create an all-0/all-undef constant and run the const value validator to see if + /// this is a valid value for the given type. + pub fn might_permit_raw_init<C, E>(self, cx: &C, zero: bool) -> Result<bool, E> + where + Self: Copy, + Ty: TyAndLayoutMethods<'a, C>, + C: LayoutOf<Ty = Ty, TyAndLayout: MaybeResult<Self, Error = E>> + HasDataLayout, + { + let scalar_allows_raw_init = move |s: &Scalar| -> bool { + if zero { + let range = &s.valid_range; + // The range must contain 0. + range.contains(&0) || (*range.start() > *range.end()) // wrap-around allows 0 + } else { + // The range must include all values. `valid_range_exclusive` handles + // the wrap-around using target arithmetic; with wrap-around then the full + // range is one where `start == end`. + let range = s.valid_range_exclusive(cx); + range.start == range.end + } + }; + + // Check the ABI. + let valid = match &self.abi { + Abi::Uninhabited => false, // definitely UB + Abi::Scalar(s) => scalar_allows_raw_init(s), + Abi::ScalarPair(s1, s2) => scalar_allows_raw_init(s1) && scalar_allows_raw_init(s2), + Abi::Vector { element: s, count } => *count == 0 || scalar_allows_raw_init(s), + Abi::Aggregate { .. } => true, // Cannot be excluded *right now*. + }; + if !valid { + // This is definitely not okay. + trace!("might_permit_raw_init({:?}, zero={}): not valid", self.layout, zero); + return Ok(false); + } + + // If we have not found an error yet, we need to recursively descend. + // FIXME(#66151): For now, we are conservative and do not do this. + Ok(true) + } +} |