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rust/compiler/rustc_abi/src/lib.rs

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// tidy-alphabetical-start
#![cfg_attr(feature = "nightly", allow(internal_features))]
#![cfg_attr(feature = "nightly", doc(rust_logo))]
#![cfg_attr(feature = "nightly", feature(rustdoc_internals))]
#![cfg_attr(feature = "nightly", feature(step_trait))]
#![warn(unreachable_pub)]
// tidy-alphabetical-end
use std::fmt;
#[cfg(feature = "nightly")]
use std::iter::Step;
use std::num::{NonZeroUsize, ParseIntError};
use std::ops::{Add, AddAssign, Mul, RangeInclusive, Sub};
use std::str::FromStr;
use bitflags::bitflags;
#[cfg(feature = "nightly")]
use rustc_data_structures::stable_hasher::StableOrd;
use rustc_index::{Idx, IndexSlice, IndexVec};
#[cfg(feature = "nightly")]
use rustc_macros::HashStable_Generic;
#[cfg(feature = "nightly")]
use rustc_macros::{Decodable_Generic, Encodable_Generic};
mod layout;
#[cfg(test)]
mod tests;
pub use layout::{LayoutCalculator, LayoutCalculatorError};
/// Requirements for a `StableHashingContext` to be used in this crate.
/// This is a hack to allow using the `HashStable_Generic` derive macro
/// instead of implementing everything in `rustc_middle`.
pub trait HashStableContext {}
#[derive(Clone, Copy, PartialEq, Eq, Default)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub struct ReprFlags(u8);
bitflags! {
impl ReprFlags: u8 {
const IS_C = 1 << 0;
const IS_SIMD = 1 << 1;
const IS_TRANSPARENT = 1 << 2;
// Internal only for now. If true, don't reorder fields.
// On its own it does not prevent ABI optimizations.
const IS_LINEAR = 1 << 3;
// If true, the type's crate has opted into layout randomization.
// Other flags can still inhibit reordering and thus randomization.
// The seed stored in `ReprOptions.field_shuffle_seed`.
const RANDOMIZE_LAYOUT = 1 << 4;
// Any of these flags being set prevent field reordering optimisation.
const FIELD_ORDER_UNOPTIMIZABLE = ReprFlags::IS_C.bits()
| ReprFlags::IS_SIMD.bits()
| ReprFlags::IS_LINEAR.bits();
const ABI_UNOPTIMIZABLE = ReprFlags::IS_C.bits() | ReprFlags::IS_SIMD.bits();
}
}
// This is the same as `rustc_data_structures::external_bitflags_debug` but without the
// `rustc_data_structures` to make it build on stable.
impl std::fmt::Debug for ReprFlags {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
bitflags::parser::to_writer(self, f)
}
}
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub enum IntegerType {
/// Pointer-sized integer type, i.e. `isize` and `usize`. The field shows signedness, e.g.
/// `Pointer(true)` means `isize`.
Pointer(bool),
/// Fixed-sized integer type, e.g. `i8`, `u32`, `i128`. The bool field shows signedness, e.g.
/// `Fixed(I8, false)` means `u8`.
Fixed(Integer, bool),
}
impl IntegerType {
pub fn is_signed(&self) -> bool {
match self {
IntegerType::Pointer(b) => *b,
IntegerType::Fixed(_, b) => *b,
}
}
}
/// Represents the repr options provided by the user.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub struct ReprOptions {
pub int: Option<IntegerType>,
pub align: Option<Align>,
pub pack: Option<Align>,
pub flags: ReprFlags,
/// The seed to be used for randomizing a type's layout
///
/// Note: This could technically be a `u128` which would
/// be the "most accurate" hash as it'd encompass the item and crate
/// hash without loss, but it does pay the price of being larger.
/// Everything's a tradeoff, a 64-bit seed should be sufficient for our
/// purposes (primarily `-Z randomize-layout`)
pub field_shuffle_seed: u64,
}
impl ReprOptions {
#[inline]
pub fn simd(&self) -> bool {
self.flags.contains(ReprFlags::IS_SIMD)
}
#[inline]
pub fn c(&self) -> bool {
self.flags.contains(ReprFlags::IS_C)
}
#[inline]
pub fn packed(&self) -> bool {
self.pack.is_some()
}
#[inline]
pub fn transparent(&self) -> bool {
self.flags.contains(ReprFlags::IS_TRANSPARENT)
}
#[inline]
pub fn linear(&self) -> bool {
self.flags.contains(ReprFlags::IS_LINEAR)
}
/// Returns the discriminant type, given these `repr` options.
/// This must only be called on enums!
pub fn discr_type(&self) -> IntegerType {
self.int.unwrap_or(IntegerType::Pointer(true))
}
/// Returns `true` if this `#[repr()]` should inhabit "smart enum
/// layout" optimizations, such as representing `Foo<&T>` as a
/// single pointer.
pub fn inhibit_enum_layout_opt(&self) -> bool {
self.c() || self.int.is_some()
}
pub fn inhibit_newtype_abi_optimization(&self) -> bool {
self.flags.intersects(ReprFlags::ABI_UNOPTIMIZABLE)
}
/// Returns `true` if this `#[repr()]` guarantees a fixed field order,
/// e.g. `repr(C)` or `repr(<int>)`.
pub fn inhibit_struct_field_reordering(&self) -> bool {
self.flags.intersects(ReprFlags::FIELD_ORDER_UNOPTIMIZABLE) || self.int.is_some()
}
/// Returns `true` if this type is valid for reordering and `-Z randomize-layout`
/// was enabled for its declaration crate.
pub fn can_randomize_type_layout(&self) -> bool {
!self.inhibit_struct_field_reordering() && self.flags.contains(ReprFlags::RANDOMIZE_LAYOUT)
}
/// Returns `true` if this `#[repr()]` should inhibit union ABI optimisations.
pub fn inhibits_union_abi_opt(&self) -> bool {
self.c()
}
}
/// Parsed [Data layout](https://llvm.org/docs/LangRef.html#data-layout)
/// for a target, which contains everything needed to compute layouts.
#[derive(Debug, PartialEq, Eq)]
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 f16_align: AbiAndPrefAlign,
pub f32_align: AbiAndPrefAlign,
pub f64_align: AbiAndPrefAlign,
pub f128_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,
/// Minimum size of #[repr(C)] enums (default c_int::BITS, usually 32)
/// Note: This isn't in LLVM's data layout string, it is `short_enum`
/// so the only valid spec for LLVM is c_int::BITS or 8
pub c_enum_min_size: Integer,
}
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) },
f16_align: AbiAndPrefAlign::new(align(16)),
f32_align: AbiAndPrefAlign::new(align(32)),
f64_align: AbiAndPrefAlign::new(align(64)),
f128_align: AbiAndPrefAlign::new(align(128)),
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,
c_enum_min_size: Integer::I32,
}
}
}
pub enum TargetDataLayoutErrors<'a> {
InvalidAddressSpace { addr_space: &'a str, cause: &'a str, err: ParseIntError },
InvalidBits { kind: &'a str, bit: &'a str, cause: &'a str, err: ParseIntError },
MissingAlignment { cause: &'a str },
InvalidAlignment { cause: &'a str, err: AlignFromBytesError },
InconsistentTargetArchitecture { dl: &'a str, target: &'a str },
InconsistentTargetPointerWidth { pointer_size: u64, target: u32 },
InvalidBitsSize { err: String },
}
impl TargetDataLayout {
/// Parse data layout from an
/// [llvm data layout string](https://llvm.org/docs/LangRef.html#data-layout)
///
/// This function doesn't fill `c_enum_min_size` and it will always be `I32` since it can not be
/// determined from llvm string.
pub fn parse_from_llvm_datalayout_string<'a>(
input: &'a str,
) -> Result<TargetDataLayout, TargetDataLayoutErrors<'a>> {
// Parse an address space index from a string.
let parse_address_space = |s: &'a str, cause: &'a str| {
s.parse::<u32>().map(AddressSpace).map_err(|err| {
TargetDataLayoutErrors::InvalidAddressSpace { addr_space: s, cause, err }
})
};
// Parse a bit count from a string.
let parse_bits = |s: &'a str, kind: &'a str, cause: &'a str| {
s.parse::<u64>().map_err(|err| TargetDataLayoutErrors::InvalidBits {
kind,
bit: s,
cause,
err,
})
};
// Parse a size string.
let parse_size =
|s: &'a str, cause: &'a str| parse_bits(s, "size", cause).map(Size::from_bits);
// Parse an alignment string.
let parse_align = |s: &[&'a str], cause: &'a str| {
if s.is_empty() {
return Err(TargetDataLayoutErrors::MissingAlignment { cause });
}
let align_from_bits = |bits| {
Align::from_bits(bits)
.map_err(|err| TargetDataLayoutErrors::InvalidAlignment { 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 input.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 = parse_align(a, "a")?,
["f16", ref a @ ..] => dl.f16_align = parse_align(a, "f16")?,
["f32", ref a @ ..] => dl.f32_align = parse_align(a, "f32")?,
["f64", ref a @ ..] => dl.f64_align = parse_align(a, "f64")?,
["f128", ref a @ ..] => dl.f128_align = parse_align(a, "f128")?,
// FIXME(erikdesjardins): we should be parsing nonzero address spaces
// this will require replacing TargetDataLayout::{pointer_size,pointer_align}
// with e.g. `fn pointer_size_in(AddressSpace)`
[p @ "p", s, ref a @ ..] | [p @ "p0", s, ref a @ ..] => {
dl.pointer_size = parse_size(s, p)?;
dl.pointer_align = parse_align(a, p)?;
}
[s, ref a @ ..] if s.starts_with('i') => {
let Ok(bits) = s[1..].parse::<u64>() else {
parse_size(&s[1..], "i")?; // For the user error.
continue;
};
let a = parse_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 = parse_size(&s[1..], "v")?;
let a = parse_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.
}
}
Ok(dl)
}
/// Returns **exclusive** upper bound on object size in bytes.
///
/// 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.
///
/// LLVM uses a 64-bit integer to represent object size in *bits*, but we care only for bytes,
/// so we adopt such a more-constrained size bound due to its technical limitations.
#[inline]
pub fn obj_size_bound(&self) -> u64 {
match self.pointer_size.bits() {
16 => 1 << 15,
32 => 1 << 31,
64 => 1 << 61,
bits => panic!("obj_size_bound: unknown pointer bit size {bits}"),
}
}
#[inline]
pub fn ptr_sized_integer(&self) -> Integer {
use Integer::*;
match self.pointer_size.bits() {
16 => I16,
32 => I32,
64 => I64,
bits => panic!("ptr_sized_integer: unknown pointer bit size {bits}"),
}
}
#[inline]
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 {
#[inline]
fn data_layout(&self) -> &TargetDataLayout {
self
}
}
// used by rust-analyzer
impl HasDataLayout for &TargetDataLayout {
#[inline]
fn data_layout(&self) -> &TargetDataLayout {
(**self).data_layout()
}
}
/// Endianness of the target, which must match cfg(target-endian).
#[derive(Copy, Clone, PartialEq, Eq)]
pub enum Endian {
Little,
Big,
}
impl Endian {
pub fn as_str(&self) -> &'static str {
match self {
Self::Little => "little",
Self::Big => "big",
}
}
}
impl fmt::Debug for Endian {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str(self.as_str())
}
}
impl FromStr for Endian {
type Err = String;
fn from_str(s: &str) -> Result<Self, Self::Err> {
match s {
"little" => Ok(Self::Little),
"big" => Ok(Self::Big),
_ => Err(format!(r#"unknown endian: "{s}""#)),
}
}
}
/// Size of a type in bytes.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub struct Size {
raw: u64,
}
#[cfg(feature = "nightly")]
impl StableOrd for Size {
const CAN_USE_UNSTABLE_SORT: bool = true;
// `Ord` is implemented as just comparing numerical values and numerical values
// are not changed by (de-)serialization.
const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}
// This is debug-printed a lot in larger structs, don't waste too much space there
impl fmt::Debug for Size {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Size({} bytes)", self.bytes())
}
}
impl Size {
pub const ZERO: Size = Size { raw: 0 };
/// Rounds `bits` up to the next-higher byte boundary, if `bits` is
/// not a multiple of 8.
pub fn from_bits(bits: impl TryInto<u64>) -> Size {
let bits = bits.try_into().ok().unwrap();
// Avoid potential overflow from `bits + 7`.
Size { raw: bits / 8 + ((bits % 8) + 7) / 8 }
}
#[inline]
pub fn from_bytes(bytes: impl TryInto<u64>) -> Size {
let bytes: u64 = bytes.try_into().ok().unwrap();
Size { raw: bytes }
}
#[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 {
#[cold]
fn overflow(bytes: u64) -> ! {
panic!("Size::bits: {bytes} bytes in bits doesn't fit in u64")
}
self.bytes().checked_mul(8).unwrap_or_else(|| overflow(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 }
}
/// Truncates `value` to `self` bits and then sign-extends it to 128 bits
/// (i.e., if it is negative, fill with 1's on the left).
#[inline]
pub fn sign_extend(self, value: u128) -> i128 {
let size = self.bits();
if size == 0 {
// Truncated until nothing is left.
return 0;
}
// Sign-extend it.
let shift = 128 - size;
// Shift the unsigned value to the left, then shift back to the right as signed
// (essentially fills with sign bit on the left).
((value << shift) as i128) >> shift
}
/// Truncates `value` to `self` bits.
#[inline]
pub fn truncate(self, value: u128) -> u128 {
let size = self.bits();
if size == 0 {
// Truncated until nothing is left.
return 0;
}
let shift = 128 - size;
// Truncate (shift left to drop out leftover values, shift right to fill with zeroes).
(value << shift) >> shift
}
#[inline]
pub fn signed_int_min(&self) -> i128 {
self.sign_extend(1_u128 << (self.bits() - 1))
}
#[inline]
pub fn signed_int_max(&self) -> i128 {
i128::MAX >> (128 - self.bits())
}
#[inline]
pub fn unsigned_int_max(&self) -> u128 {
u128::MAX >> (128 - self.bits())
}
}
// 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;
}
}
#[cfg(feature = "nightly")]
impl Step for Size {
#[inline]
fn steps_between(start: &Self, end: &Self) -> (usize, Option<usize>) {
u64::steps_between(&start.bytes(), &end.bytes())
}
#[inline]
fn forward_checked(start: Self, count: usize) -> Option<Self> {
u64::forward_checked(start.bytes(), count).map(Self::from_bytes)
}
#[inline]
fn forward(start: Self, count: usize) -> Self {
Self::from_bytes(u64::forward(start.bytes(), count))
}
#[inline]
unsafe fn forward_unchecked(start: Self, count: usize) -> Self {
Self::from_bytes(unsafe { u64::forward_unchecked(start.bytes(), count) })
}
#[inline]
fn backward_checked(start: Self, count: usize) -> Option<Self> {
u64::backward_checked(start.bytes(), count).map(Self::from_bytes)
}
#[inline]
fn backward(start: Self, count: usize) -> Self {
Self::from_bytes(u64::backward(start.bytes(), count))
}
#[inline]
unsafe fn backward_unchecked(start: Self, count: usize) -> Self {
Self::from_bytes(unsafe { u64::backward_unchecked(start.bytes(), count) })
}
}
/// Alignment of a type in bytes (always a power of two).
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub struct Align {
pow2: u8,
}
// This is debug-printed a lot in larger structs, don't waste too much space there
impl fmt::Debug for Align {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Align({} bytes)", self.bytes())
}
}
#[derive(Clone, Copy)]
pub enum AlignFromBytesError {
NotPowerOfTwo(u64),
TooLarge(u64),
}
impl AlignFromBytesError {
pub fn diag_ident(self) -> &'static str {
match self {
Self::NotPowerOfTwo(_) => "not_power_of_two",
Self::TooLarge(_) => "too_large",
}
}
pub fn align(self) -> u64 {
let (Self::NotPowerOfTwo(align) | Self::TooLarge(align)) = self;
align
}
}
impl fmt::Debug for AlignFromBytesError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(self, f)
}
}
impl fmt::Display for AlignFromBytesError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
AlignFromBytesError::NotPowerOfTwo(align) => write!(f, "`{align}` is not a power of 2"),
AlignFromBytesError::TooLarge(align) => write!(f, "`{align}` is too large"),
}
}
}
impl Align {
pub const ONE: Align = Align { pow2: 0 };
pub const EIGHT: Align = Align { pow2: 3 };
// LLVM has a maximal supported alignment of 2^29, we inherit that.
pub const MAX: Align = Align { pow2: 29 };
#[inline]
pub fn from_bits(bits: u64) -> Result<Align, AlignFromBytesError> {
Align::from_bytes(Size::from_bits(bits).bytes())
}
#[inline]
pub const fn from_bytes(align: u64) -> Result<Align, AlignFromBytesError> {
// Treat an alignment of 0 bytes like 1-byte alignment.
if align == 0 {
return Ok(Align::ONE);
}
#[cold]
const fn not_power_of_2(align: u64) -> AlignFromBytesError {
AlignFromBytesError::NotPowerOfTwo(align)
}
#[cold]
const fn too_large(align: u64) -> AlignFromBytesError {
AlignFromBytesError::TooLarge(align)
}
let tz = align.trailing_zeros();
if align != (1 << tz) {
return Err(not_power_of_2(align));
}
let pow2 = tz as u8;
if pow2 > Self::MAX.pow2 {
return Err(too_large(align));
}
Ok(Align { pow2 })
}
#[inline]
pub fn bytes(self) -> u64 {
1 << self.pow2
}
#[inline]
pub fn bytes_usize(self) -> usize {
self.bytes().try_into().unwrap()
}
#[inline]
pub fn bits(self) -> u64 {
self.bytes() * 8
}
#[inline]
pub fn bits_usize(self) -> usize {
self.bits().try_into().unwrap()
}
/// 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`.
#[inline]
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).
#[inline]
pub fn restrict_for_offset(self, offset: Size) -> Align {
self.min(Align::max_for_offset(offset))
}
}
/// A pair of alignments, ABI-mandated and preferred.
///
/// The "preferred" alignment is an LLVM concept that is virtually meaningless to Rust code:
/// it is not exposed semantically to programmers nor can they meaningfully affect it.
/// The only concern for us is that preferred alignment must not be less than the mandated alignment
/// and thus in practice the two values are almost always identical.
///
/// An example of a rare thing actually affected by preferred alignment is aligning of statics.
/// It is of effectively no consequence for layout in structs and on the stack.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub struct AbiAndPrefAlign {
pub abi: Align,
pub pref: Align,
}
impl AbiAndPrefAlign {
#[inline]
pub fn new(align: Align) -> AbiAndPrefAlign {
AbiAndPrefAlign { abi: align, pref: align }
}
#[inline]
pub fn min(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
AbiAndPrefAlign { abi: self.abi.min(other.abi), pref: self.pref.min(other.pref) }
}
#[inline]
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)]
#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
pub enum Integer {
I8,
I16,
I32,
I64,
I128,
}
impl Integer {
pub fn int_ty_str(self) -> &'static str {
use Integer::*;
match self {
I8 => "i8",
I16 => "i16",
I32 => "i32",
I64 => "i64",
I128 => "i128",
}
}
pub fn uint_ty_str(self) -> &'static str {
use Integer::*;
match self {
I8 => "u8",
I16 => "u16",
I32 => "u32",
I64 => "u64",
I128 => "u128",
}
}
#[inline]
pub fn size(self) -> Size {
use Integer::*;
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),
}
}
/// Gets the Integer type from an IntegerType.
pub fn from_attr<C: HasDataLayout>(cx: &C, ity: IntegerType) -> Integer {
let dl = cx.data_layout();
match ity {
IntegerType::Pointer(_) => dl.ptr_sized_integer(),
IntegerType::Fixed(x, _) => x,
}
}
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
use Integer::*;
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,
}
}
/// Returns the largest signed value that can be represented by this Integer.
#[inline]
pub fn signed_max(self) -> i128 {
use Integer::*;
match self {
I8 => i8::MAX as i128,
I16 => i16::MAX as i128,
I32 => i32::MAX as i128,
I64 => i64::MAX as i128,
I128 => i128::MAX,
}
}
/// Finds the smallest Integer type which can represent the signed value.
#[inline]
pub fn fit_signed(x: i128) -> Integer {
use 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.
#[inline]
pub fn fit_unsigned(x: u128) -> Integer {
use 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> {
use Integer::*;
let dl = cx.data_layout();
[I8, I16, I32, I64, I128].into_iter().find(|&candidate| {
wanted == candidate.align(dl).abi && wanted.bytes() == candidate.size().bytes()
})
}
/// Find the largest integer with the given alignment or less.
pub fn approximate_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Integer {
use 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
}
// FIXME(eddyb) consolidate this and other methods that find the appropriate
// `Integer` given some requirements.
#[inline]
pub fn from_size(size: Size) -> Result<Self, String> {
match size.bits() {
8 => Ok(Integer::I8),
16 => Ok(Integer::I16),
32 => Ok(Integer::I32),
64 => Ok(Integer::I64),
128 => Ok(Integer::I128),
_ => Err(format!("rust does not support integers with {} bits", size.bits())),
}
}
}
/// Floating-point types.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum Float {
F16,
F32,
F64,
F128,
}
impl Float {
pub fn size(self) -> Size {
use Float::*;
match self {
F16 => Size::from_bits(16),
F32 => Size::from_bits(32),
F64 => Size::from_bits(64),
F128 => Size::from_bits(128),
}
}
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
use Float::*;
let dl = cx.data_layout();
match self {
F16 => dl.f16_align,
F32 => dl.f32_align,
F64 => dl.f64_align,
F128 => dl.f128_align,
}
}
}
/// Fundamental unit of memory access and layout.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(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),
Float(Float),
Pointer(AddressSpace),
}
impl Primitive {
pub fn size<C: HasDataLayout>(self, cx: &C) -> Size {
use Primitive::*;
let dl = cx.data_layout();
match self {
Int(i, _) => i.size(),
Float(f) => f.size(),
// FIXME(erikdesjardins): ignoring address space is technically wrong, pointers in
// different address spaces can have different sizes
// (but TargetDataLayout doesn't currently parse that part of the DL string)
Pointer(_) => dl.pointer_size,
}
}
pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
use Primitive::*;
let dl = cx.data_layout();
match self {
Int(i, _) => i.align(dl),
Float(f) => f.align(dl),
// FIXME(erikdesjardins): ignoring address space is technically wrong, pointers in
// different address spaces can have different alignments
// (but TargetDataLayout doesn't currently parse that part of the DL string)
Pointer(_) => dl.pointer_align,
}
}
}
/// 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.
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub struct WrappingRange {
pub start: u128,
pub end: u128,
}
impl WrappingRange {
pub fn full(size: Size) -> Self {
Self { start: 0, end: size.unsigned_int_max() }
}
/// Returns `true` if `v` is contained in the range.
#[inline(always)]
pub fn contains(&self, v: u128) -> bool {
if self.start <= self.end {
self.start <= v && v <= self.end
} else {
self.start <= v || v <= self.end
}
}
/// Returns `self` with replaced `start`
#[inline(always)]
fn with_start(mut self, start: u128) -> Self {
self.start = start;
self
}
/// Returns `self` with replaced `end`
#[inline(always)]
fn with_end(mut self, end: u128) -> Self {
self.end = end;
self
}
/// Returns `true` if `size` completely fills the range.
#[inline]
fn is_full_for(&self, size: Size) -> bool {
let max_value = size.unsigned_int_max();
debug_assert!(self.start <= max_value && self.end <= max_value);
self.start == (self.end.wrapping_add(1) & max_value)
}
}
impl fmt::Debug for WrappingRange {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
if self.start > self.end {
write!(fmt, "(..={}) | ({}..)", self.end, self.start)?;
} else {
write!(fmt, "{}..={}", self.start, self.end)?;
}
Ok(())
}
}
/// Information about one scalar component of a Rust type.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum Scalar {
Initialized {
value: Primitive,
// 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.
valid_range: WrappingRange,
},
Union {
/// Even for unions, we need to use the correct registers for the kind of
/// values inside the union, so we keep the `Primitive` type around. We
/// also use it to compute the size of the scalar.
/// However, unions never have niches and even allow undef,
/// so there is no `valid_range`.
value: Primitive,
},
}
impl Scalar {
#[inline]
pub fn is_bool(&self) -> bool {
use Integer::*;
matches!(self, Scalar::Initialized {
value: Primitive::Int(I8, false),
valid_range: WrappingRange { start: 0, end: 1 }
})
}
/// Get the primitive representation of this type, ignoring the valid range and whether the
/// value is allowed to be undefined (due to being a union).
pub fn primitive(&self) -> Primitive {
match *self {
Scalar::Initialized { value, .. } | Scalar::Union { value } => value,
}
}
pub fn align(self, cx: &impl HasDataLayout) -> AbiAndPrefAlign {
self.primitive().align(cx)
}
pub fn size(self, cx: &impl HasDataLayout) -> Size {
self.primitive().size(cx)
}
#[inline]
pub fn to_union(&self) -> Self {
Self::Union { value: self.primitive() }
}
#[inline]
pub fn valid_range(&self, cx: &impl HasDataLayout) -> WrappingRange {
match *self {
Scalar::Initialized { valid_range, .. } => valid_range,
Scalar::Union { value } => WrappingRange::full(value.size(cx)),
}
}
#[inline]
/// Allows the caller to mutate the valid range. This operation will panic if attempted on a
/// union.
pub fn valid_range_mut(&mut self) -> &mut WrappingRange {
match self {
Scalar::Initialized { valid_range, .. } => valid_range,
Scalar::Union { .. } => panic!("cannot change the valid range of a union"),
}
}
/// Returns `true` if all possible numbers are valid, i.e `valid_range` covers the whole
/// layout.
#[inline]
pub fn is_always_valid<C: HasDataLayout>(&self, cx: &C) -> bool {
match *self {
Scalar::Initialized { valid_range, .. } => valid_range.is_full_for(self.size(cx)),
Scalar::Union { .. } => true,
}
}
/// Returns `true` if this type can be left uninit.
#[inline]
pub fn is_uninit_valid(&self) -> bool {
match *self {
Scalar::Initialized { .. } => false,
Scalar::Union { .. } => true,
}
}
}
// NOTE: This struct is generic over the FieldIdx for rust-analyzer usage.
/// Describes how the fields of a type are located in memory.
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum FieldsShape<FieldIdx: Idx> {
/// 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: IndexVec<FieldIdx, 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: IndexVec<FieldIdx, u32>,
},
}
impl<FieldIdx: Idx> FieldsShape<FieldIdx> {
#[inline]
pub fn count(&self) -> usize {
match *self {
FieldsShape::Primitive => 0,
FieldsShape::Union(count) => count.get(),
FieldsShape::Array { count, .. } => count.try_into().unwrap(),
FieldsShape::Arbitrary { ref offsets, .. } => offsets.len(),
}
}
#[inline]
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 {i} of union with {count} fields");
Size::ZERO
}
FieldsShape::Array { stride, count } => {
let i = u64::try_from(i).unwrap();
assert!(i < count, "tried to access field {i} of array with {count} fields");
stride * i
}
FieldsShape::Arbitrary { ref offsets, .. } => offsets[FieldIdx::new(i)],
}
}
#[inline]
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, .. } => {
memory_index[FieldIdx::new(i)].try_into().unwrap()
}
}
}
/// Gets source indices of the fields by increasing offsets.
#[inline]
pub fn index_by_increasing_offset(&self) -> impl ExactSizeIterator<Item = usize> + '_ {
let mut inverse_small = [0u8; 64];
let mut inverse_big = IndexVec::new();
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 (field_idx, &mem_idx) in memory_index.iter_enumerated() {
inverse_small[mem_idx as usize] = field_idx.index() as u8;
}
} else {
inverse_big = memory_index.invert_bijective_mapping();
}
}
// Primitives don't really have fields in the way that structs do,
// but having this return an empty iterator for them is unhelpful
// since that makes them look kinda like ZSTs, which they're not.
let pseudofield_count = if let FieldsShape::Primitive = self { 1 } else { self.count() };
(0..pseudofield_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 u32].index()
}
}
})
}
}
/// 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, Hash)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
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, Copy, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(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.
#[inline]
pub fn is_unsized(&self) -> bool {
match *self {
Abi::Uninhabited | Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } => false,
Abi::Aggregate { sized } => !sized,
}
}
#[inline]
pub fn is_sized(&self) -> bool {
!self.is_unsized()
}
/// Returns `true` if this is a single signed integer scalar
#[inline]
pub fn is_signed(&self) -> bool {
match self {
Abi::Scalar(scal) => match scal.primitive() {
Primitive::Int(_, signed) => signed,
_ => false,
},
_ => panic!("`is_signed` on non-scalar ABI {self:?}"),
}
}
/// Returns `true` if this is an uninhabited type
#[inline]
pub fn is_uninhabited(&self) -> bool {
matches!(*self, Abi::Uninhabited)
}
/// Returns `true` if this is a scalar type
#[inline]
pub fn is_scalar(&self) -> bool {
matches!(*self, Abi::Scalar(_))
}
/// Returns `true` if this is a bool
#[inline]
pub fn is_bool(&self) -> bool {
matches!(*self, Abi::Scalar(s) if s.is_bool())
}
/// Returns the fixed alignment of this ABI, if any is mandated.
pub fn inherent_align<C: HasDataLayout>(&self, cx: &C) -> Option<AbiAndPrefAlign> {
Some(match *self {
Abi::Scalar(s) => s.align(cx),
Abi::ScalarPair(s1, s2) => s1.align(cx).max(s2.align(cx)),
Abi::Vector { element, count } => {
cx.data_layout().vector_align(element.size(cx) * count)
}
Abi::Uninhabited | Abi::Aggregate { .. } => return None,
})
}
/// Returns the fixed size of this ABI, if any is mandated.
pub fn inherent_size<C: HasDataLayout>(&self, cx: &C) -> Option<Size> {
Some(match *self {
Abi::Scalar(s) => {
// No padding in scalars.
s.size(cx)
}
Abi::ScalarPair(s1, s2) => {
// May have some padding between the pair.
let field2_offset = s1.size(cx).align_to(s2.align(cx).abi);
(field2_offset + s2.size(cx)).align_to(self.inherent_align(cx)?.abi)
}
Abi::Vector { element, count } => {
// No padding in vectors, except possibly for trailing padding
// to make the size a multiple of align (e.g. for vectors of size 3).
(element.size(cx) * count).align_to(self.inherent_align(cx)?.abi)
}
Abi::Uninhabited | Abi::Aggregate { .. } => return None,
})
}
/// Discard validity range information and allow undef.
pub fn to_union(&self) -> Self {
match *self {
Abi::Scalar(s) => Abi::Scalar(s.to_union()),
Abi::ScalarPair(s1, s2) => Abi::ScalarPair(s1.to_union(), s2.to_union()),
Abi::Vector { element, count } => Abi::Vector { element: element.to_union(), count },
Abi::Uninhabited | Abi::Aggregate { .. } => Abi::Aggregate { sized: true },
}
}
pub fn eq_up_to_validity(&self, other: &Self) -> bool {
match (self, other) {
// Scalar, Vector, ScalarPair have `Scalar` in them where we ignore validity ranges.
// We do *not* ignore the sign since it matters for some ABIs (e.g. s390x).
(Abi::Scalar(l), Abi::Scalar(r)) => l.primitive() == r.primitive(),
(
Abi::Vector { element: element_l, count: count_l },
Abi::Vector { element: element_r, count: count_r },
) => element_l.primitive() == element_r.primitive() && count_l == count_r,
(Abi::ScalarPair(l1, l2), Abi::ScalarPair(r1, r2)) => {
l1.primitive() == r1.primitive() && l2.primitive() == r2.primitive()
}
// Everything else must be strictly identical.
_ => self == other,
}
}
}
// NOTE: This struct is generic over the FieldIdx and VariantIdx for rust-analyzer usage.
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum Variants<FieldIdx: Idx, VariantIdx: Idx> {
/// Single enum variants, structs/tuples, unions, and all non-ADTs.
Single { index: VariantIdx },
/// Enum-likes with more than one 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<VariantIdx>,
tag_field: usize,
variants: IndexVec<VariantIdx, LayoutS<FieldIdx, VariantIdx>>,
},
}
// NOTE: This struct is generic over the VariantIdx for rust-analyzer usage.
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum TagEncoding<VariantIdx: Idx> {
/// 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 `untagged_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 {
untagged_variant: VariantIdx,
niche_variants: RangeInclusive<VariantIdx>,
niche_start: u128,
},
}
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub struct Niche {
pub offset: Size,
pub value: Primitive,
pub valid_range: WrappingRange,
}
impl Niche {
pub fn from_scalar<C: HasDataLayout>(cx: &C, offset: Size, scalar: Scalar) -> Option<Self> {
let Scalar::Initialized { value, valid_range } = scalar else { return None };
let niche = Niche { offset, value, valid_range };
if niche.available(cx) > 0 { Some(niche) } else { None }
}
pub fn available<C: HasDataLayout>(&self, cx: &C) -> u128 {
let Self { value, valid_range: v, .. } = *self;
let size = value.size(cx);
assert!(size.bits() <= 128);
let max_value = size.unsigned_int_max();
// 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 Self { value, valid_range: v, .. } = *self;
let size = value.size(cx);
assert!(size.bits() <= 128);
let max_value = size.unsigned_int_max();
let niche = v.end.wrapping_add(1)..v.start;
let available = niche.end.wrapping_sub(niche.start) & max_value;
if count > available {
return None;
}
// Extend the range of valid values being reserved by moving either `v.start` or `v.end`
// bound. Given an eventual `Option<T>`, we try to maximize the chance for `None` to occupy
// the niche of zero. This is accomplished by preferring enums with 2 variants(`count==1`)
// and always taking the shortest path to niche zero. Having `None` in niche zero can
// enable some special optimizations.
//
// Bound selection criteria:
// 1. Select closest to zero given wrapping semantics.
// 2. Avoid moving past zero if possible.
//
// In practice this means that enums with `count > 1` are unlikely to claim niche zero,
// since they have to fit perfectly. If niche zero is already reserved, the selection of
// bounds are of little interest.
let move_start = |v: WrappingRange| {
let start = v.start.wrapping_sub(count) & max_value;
Some((start, Scalar::Initialized { value, valid_range: v.with_start(start) }))
};
let move_end = |v: WrappingRange| {
let start = v.end.wrapping_add(1) & max_value;
let end = v.end.wrapping_add(count) & max_value;
Some((start, Scalar::Initialized { value, valid_range: v.with_end(end) }))
};
let distance_end_zero = max_value - v.end;
if v.start > v.end {
// zero is unavailable because wrapping occurs
move_end(v)
} else if v.start <= distance_end_zero {
if count <= v.start {
move_start(v)
} else {
// moved past zero, use other bound
move_end(v)
}
} else {
let end = v.end.wrapping_add(count) & max_value;
let overshot_zero = (1..=v.end).contains(&end);
if overshot_zero {
// moved past zero, use other bound
move_start(v)
} else {
move_end(v)
}
}
}
}
// NOTE: This struct is generic over the FieldIdx and VariantIdx for rust-analyzer usage.
#[derive(PartialEq, Eq, Hash, Clone)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub struct LayoutS<FieldIdx: Idx, VariantIdx: Idx> {
/// Says where the fields are located within the layout.
pub fields: FieldsShape<FieldIdx>,
/// 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. coroutines 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<FieldIdx, VariantIdx>,
/// 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,
/// The largest alignment explicitly requested with `repr(align)` on this type or any field.
/// Only used on i686-windows, where the argument passing ABI is different when alignment is
/// requested, even if the requested alignment is equal to the natural alignment.
pub max_repr_align: Option<Align>,
/// The alignment the type would have, ignoring any `repr(align)` but including `repr(packed)`.
/// Only used on aarch64-linux, where the argument passing ABI ignores the requested alignment
/// in some cases.
pub unadjusted_abi_align: Align,
}
impl<FieldIdx: Idx, VariantIdx: Idx> LayoutS<FieldIdx, VariantIdx> {
pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {
let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar);
let size = scalar.size(cx);
let align = scalar.align(cx);
LayoutS {
variants: Variants::Single { index: VariantIdx::new(0) },
fields: FieldsShape::Primitive,
abi: Abi::Scalar(scalar),
largest_niche,
size,
align,
max_repr_align: None,
unadjusted_abi_align: align.abi,
}
}
}
impl<FieldIdx: Idx, VariantIdx: Idx> fmt::Debug for LayoutS<FieldIdx, VariantIdx>
where
FieldsShape<FieldIdx>: fmt::Debug,
Variants<FieldIdx, VariantIdx>: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// This is how `Layout` used to print before it become
// `Interned<LayoutS>`. We print it like this to avoid having to update
// expected output in a lot of tests.
let LayoutS {
size,
align,
abi,
fields,
largest_niche,
variants,
max_repr_align,
unadjusted_abi_align,
} = self;
f.debug_struct("Layout")
.field("size", size)
.field("align", align)
.field("abi", abi)
.field("fields", fields)
.field("largest_niche", largest_niche)
.field("variants", variants)
.field("max_repr_align", max_repr_align)
.field("unadjusted_abi_align", unadjusted_abi_align)
.finish()
}
}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum PointerKind {
/// Shared reference. `frozen` indicates the absence of any `UnsafeCell`.
SharedRef { frozen: bool },
/// Mutable reference. `unpin` indicates the absence of any pinned data.
MutableRef { unpin: bool },
/// Box. `unpin` indicates the absence of any pinned data. `global` indicates whether this box
/// uses the global allocator or a custom one.
Box { unpin: bool, global: bool },
}
/// Note that this information is advisory only, and backends are free to ignore it.
/// It can only be used to encode potential optimizations, but no critical information.
#[derive(Copy, Clone, Debug)]
pub struct PointeeInfo {
pub size: Size,
pub align: Align,
/// If this is `None`, then this is a raw pointer, so size and alignment are not guaranteed to
/// be reliable.
pub safe: Option<PointerKind>,
}
impl<FieldIdx: Idx, VariantIdx: Idx> LayoutS<FieldIdx, VariantIdx> {
/// Returns `true` if the layout corresponds to an unsized type.
#[inline]
pub fn is_unsized(&self) -> bool {
self.abi.is_unsized()
}
#[inline]
pub fn is_sized(&self) -> bool {
self.abi.is_sized()
}
/// Returns `true` if the type is sized and a 1-ZST (meaning it has size 0 and alignment 1).
pub fn is_1zst(&self) -> bool {
self.is_sized() && self.size.bytes() == 0 && self.align.abi.bytes() == 1
}
/// Returns `true` if the type is a ZST and not unsized.
///
/// Note that this does *not* imply that the type is irrelevant for layout! It can still have
/// non-trivial alignment constraints. You probably want to use `is_1zst` instead.
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,
}
}
/// Checks if these two `Layout` are equal enough to be considered "the same for all function
/// call ABIs". Note however that real ABIs depend on more details that are not reflected in the
/// `Layout`; the `PassMode` need to be compared as well. Also note that we assume
/// aggregates are passed via `PassMode::Indirect` or `PassMode::Cast`; more strict
/// checks would otherwise be required.
pub fn eq_abi(&self, other: &Self) -> bool {
// The one thing that we are not capturing here is that for unsized types, the metadata must
// also have the same ABI, and moreover that the same metadata leads to the same size. The
// 2nd point is quite hard to check though.
self.size == other.size
&& self.is_sized() == other.is_sized()
&& self.abi.eq_up_to_validity(&other.abi)
&& self.abi.is_bool() == other.abi.is_bool()
&& self.align.abi == other.align.abi
&& self.max_repr_align == other.max_repr_align
&& self.unadjusted_abi_align == other.unadjusted_abi_align
}
}
#[derive(Copy, Clone, Debug)]
pub enum StructKind {
/// A tuple, closure, or univariant which cannot be coerced to unsized.
AlwaysSized,
/// A univariant, the last field of which may be coerced to unsized.
MaybeUnsized,
/// A univariant, but with a prefix of an arbitrary size & alignment (e.g., enum tag).
Prefixed(Size, Align),
}
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