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use std::num::NonZero;
use rustc_hashes::Hash64;
use rustc_index::{Idx, IndexVec};
use crate::{
BackendRepr, FieldsShape, HasDataLayout, LayoutData, Niche, Primitive, Scalar, Size, Variants,
};
/// "Simple" layout constructors that cannot fail.
impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
pub fn unit<C: HasDataLayout>(cx: &C, sized: bool) -> Self {
let dl = cx.data_layout();
LayoutData {
variants: Variants::Single { index: VariantIdx::new(0) },
fields: FieldsShape::Arbitrary {
offsets: IndexVec::new(),
memory_index: IndexVec::new(),
},
backend_repr: BackendRepr::Memory { sized },
largest_niche: None,
uninhabited: false,
align: dl.i8_align,
size: Size::ZERO,
max_repr_align: None,
unadjusted_abi_align: dl.i8_align.abi,
randomization_seed: Hash64::new(0),
}
}
pub fn never_type<C: HasDataLayout>(cx: &C) -> Self {
let dl = cx.data_layout();
// This is also used for uninhabited enums, so we use `Variants::Empty`.
LayoutData {
variants: Variants::Empty,
fields: FieldsShape::Primitive,
backend_repr: BackendRepr::Memory { sized: true },
largest_niche: None,
uninhabited: true,
align: dl.i8_align,
size: Size::ZERO,
max_repr_align: None,
unadjusted_abi_align: dl.i8_align.abi,
randomization_seed: Hash64::ZERO,
}
}
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);
let range = scalar.valid_range(cx);
// All primitive types for which we don't have subtype coercions should get a distinct seed,
// so that types wrapping them can use randomization to arrive at distinct layouts.
//
// Some type information is already lost at this point, so as an approximation we derive
// the seed from what remains. For example on 64-bit targets usize and u64 can no longer
// be distinguished.
let randomization_seed = size
.bytes()
.wrapping_add(
match scalar.primitive() {
Primitive::Int(_, true) => 1,
Primitive::Int(_, false) => 2,
Primitive::Float(_) => 3,
Primitive::Pointer(_) => 4,
} << 32,
)
// distinguishes references from pointers
.wrapping_add((range.start as u64).rotate_right(16))
// distinguishes char from u32 and bool from u8
.wrapping_add((range.end as u64).rotate_right(16));
LayoutData {
variants: Variants::Single { index: VariantIdx::new(0) },
fields: FieldsShape::Primitive,
backend_repr: BackendRepr::Scalar(scalar),
largest_niche,
uninhabited: false,
size,
align,
max_repr_align: None,
unadjusted_abi_align: align.abi,
randomization_seed: Hash64::new(randomization_seed),
}
}
pub fn scalar_pair<C: HasDataLayout>(cx: &C, a: Scalar, b: Scalar) -> Self {
let dl = cx.data_layout();
let b_align = b.align(dl);
let align = a.align(dl).max(b_align).max(dl.aggregate_align);
let b_offset = a.size(dl).align_to(b_align.abi);
let size = (b_offset + b.size(dl)).align_to(align.abi);
// HACK(nox): We iter on `b` and then `a` because `max_by_key`
// returns the last maximum.
let largest_niche = Niche::from_scalar(dl, b_offset, b)
.into_iter()
.chain(Niche::from_scalar(dl, Size::ZERO, a))
.max_by_key(|niche| niche.available(dl));
let combined_seed = a.size(dl).bytes().wrapping_add(b.size(dl).bytes());
LayoutData {
variants: Variants::Single { index: VariantIdx::new(0) },
fields: FieldsShape::Arbitrary {
offsets: [Size::ZERO, b_offset].into(),
memory_index: [0, 1].into(),
},
backend_repr: BackendRepr::ScalarPair(a, b),
largest_niche,
uninhabited: false,
align,
size,
max_repr_align: None,
unadjusted_abi_align: align.abi,
randomization_seed: Hash64::new(combined_seed),
}
}
/// Returns a dummy layout for an uninhabited variant.
///
/// Uninhabited variants get pruned as part of the layout calculation,
/// so this can be used after the fact to reconstitute a layout.
pub fn uninhabited_variant<C: HasDataLayout>(cx: &C, index: VariantIdx, fields: usize) -> Self {
let dl = cx.data_layout();
LayoutData {
variants: Variants::Single { index },
fields: match NonZero::new(fields) {
Some(fields) => FieldsShape::Union(fields),
None => FieldsShape::Arbitrary {
offsets: IndexVec::new(),
memory_index: IndexVec::new(),
},
},
backend_repr: BackendRepr::Memory { sized: true },
largest_niche: None,
uninhabited: true,
align: dl.i8_align,
size: Size::ZERO,
max_repr_align: None,
unadjusted_abi_align: dl.i8_align.abi,
randomization_seed: Hash64::ZERO,
}
}
}
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