bjoernager/rust
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Refactor: VariantIdx::from_u32(0) -> FIRST_VARIANT

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Since structs are always `VariantIdx(0)`, there's a bunch of files where the only reason they had `VariantIdx` or `vec::Idx` imported at all was to get the first variant.

So this uses a constant for that, and adds some doc-comments to `VariantIdx` while I'm there, since it doesn't have any today.
This commit is contained in:
Scott McMurray 2023-03-25 18:43:03 -07:00
parent 96bd50dd47
commit 0439d13176
25 changed files with 80 additions and 78 deletions
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18
compiler/rustc_abi/src/layout.rs
View file

@ -43,7 +43,7 @@ pub trait LayoutCalculator {
.max_by_key(|niche| niche.available(dl));
LayoutS {
variants: Variants::Single { index: VariantIdx::new(0) },
variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Arbitrary {
offsets: vec![Size::ZERO, b_offset],
memory_index: vec![0, 1],
@ -264,7 +264,7 @@ pub trait LayoutCalculator {
abi = Abi::Uninhabited;
}
Some(LayoutS {
variants: Variants::Single { index: VariantIdx::new(0) },
variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Arbitrary { offsets, memory_index },
abi,
largest_niche,
@ -277,7 +277,7 @@ pub trait LayoutCalculator {
let dl = self.current_data_layout();
let dl = dl.borrow();
LayoutS {
variants: Variants::Single { index: VariantIdx::new(0) },
variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Primitive,
abi: Abi::Uninhabited,
largest_niche: None,
@ -331,7 +331,7 @@ pub trait LayoutCalculator {
}
// If it's a struct, still compute a layout so that we can still compute the
// field offsets.
None => VariantIdx::new(0),
None => FIRST_VARIANT,
};
let is_struct = !is_enum ||
@ -467,7 +467,7 @@ pub trait LayoutCalculator {
.max_by_key(|(_i, layout)| layout.size.bytes())
.map(|(i, _layout)| i)?;
let all_indices = (0..=variants.len() - 1).map(VariantIdx::new);
let all_indices = variants.indices();
let needs_disc =
|index: VariantIdx| index != largest_variant_index && !absent(&variants[index]);
let niche_variants = all_indices.clone().find(|v| needs_disc(*v)).unwrap().index()
@ -896,8 +896,8 @@ pub trait LayoutCalculator {
let optimize = !repr.inhibit_union_abi_opt();
let mut size = Size::ZERO;
let mut abi = Abi::Aggregate { sized: true };
let index = VariantIdx::new(0);
for field in &variants[index] {
let only_variant = &variants[FIRST_VARIANT];
for field in only_variant {
assert!(field.0.is_sized());
align = align.max(field.align());
@ -930,8 +930,8 @@ pub trait LayoutCalculator {
}
Some(LayoutS {
variants: Variants::Single { index },
fields: FieldsShape::Union(NonZeroUsize::new(variants[index].len())?),
variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Union(NonZeroUsize::new(only_variant.len())?),
abi,
largest_niche: None,
align,

17
compiler/rustc_abi/src/lib.rs
View file

@ -1380,8 +1380,21 @@ impl Niche {
}
rustc_index::newtype_index! {
/// The *source-order* index of a variant in a type.
///
/// For enums, these are always `0..variant_count`, regardless of any
/// custom discriminants that may have been defined, and including any
/// variants that may end up uninhabited due to field types. (Some of the
/// variants may not be present in a monomorphized ABI [`Variants`], but
/// those skipped variants are always counted when determining the *index*.)
///
/// `struct`s, `tuples`, and `unions`s are considered to have a single variant
/// with variant index zero, aka [`FIRST_VARIANT`].
#[derive(HashStable_Generic)]
pub struct VariantIdx {}
pub struct VariantIdx {
/// Equivalent to `VariantIdx(0)`.
const FIRST_VARIANT = 0;
}
}
#[derive(PartialEq, Eq, Hash, Clone)]
@ -1422,7 +1435,7 @@ impl LayoutS {
let size = scalar.size(cx);
let align = scalar.align(cx);
LayoutS {
variants: Variants::Single { index: VariantIdx::new(0) },
variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Primitive,
abi: Abi::Scalar(scalar),
largest_niche,