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Rollup merge of #145387 - zachs18:remove-tmplayout, r=cjgillot

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Remove TmpLayout in layout_of_enum

09a3846 from <https://github.com/rust-lang/rust/pull/103693> made LayoutData be owned instead of interned in `Variants::Multiple::variants`[^1], so there's no need for `TmpLayout` in layout_of_enum anymore, and we can just store the variants' layouts directly in the prospective `LayoutData`s' `variants` fields.

This should have no effect on semantics or layout.

(written as part of rust-lang/rust#145337 but not related to the layout optimizations in that PR)

[^1]: see line 1154 of `compiler/rustc_target/src/abi/mod.rs` in the linked commit; `Variants::Multiple::variants` effectively changed from `IndexVec<.., Layout<'tcx>>` to `IndexVec<.., LayoutData>`  where the `LayoutData`s are not interned as `Layout`s (`LayoutData` was at the time called `LayoutS`)
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Stuart Cook 2025-08-29 12:54:10 +10:00 • committed by GitHub
commit dd03ce8cba
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1 changed files with 9 additions and 30 deletions
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39
compiler/rustc_abi/src/layout.rs
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@ -594,23 +594,13 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
discr_range_of_repr: impl Fn(i128, i128) -> (Integer, bool),
discriminants: impl Iterator<Item = (VariantIdx, i128)>,
) -> LayoutCalculatorResult<FieldIdx, VariantIdx, F> {
// Until we've decided whether to use the tagged or
// niche filling LayoutData, we don't want to intern the
// variant layouts, so we can't store them in the
// overall LayoutData. Store the overall LayoutData
// and the variant LayoutDatas here until then.
struct TmpLayout<FieldIdx: Idx, VariantIdx: Idx> {
layout: LayoutData<FieldIdx, VariantIdx>,
variants: IndexVec<VariantIdx, LayoutData<FieldIdx, VariantIdx>>,
}
let dl = self.cx.data_layout();
// bail if the enum has an incoherent repr that cannot be computed
if repr.packed() {
return Err(LayoutCalculatorError::ReprConflict);
}
let calculate_niche_filling_layout = || -> Option<TmpLayout<FieldIdx, VariantIdx>> {
let calculate_niche_filling_layout = || -> Option<LayoutData<FieldIdx, VariantIdx>> {
if repr.inhibit_enum_layout_opt() {
return None;
}
@ -746,7 +736,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
niche_start,
},
tag_field: FieldIdx::new(0),
variants: IndexVec::new(),
variants: variant_layouts,
},
fields: FieldsShape::Arbitrary {
offsets: [niche_offset].into(),
@ -762,7 +752,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
randomization_seed: combined_seed,
};
Some(TmpLayout { layout, variants: variant_layouts })
Some(layout)
};
let niche_filling_layout = calculate_niche_filling_layout();
@ -1093,7 +1083,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
tag,
tag_encoding: TagEncoding::Direct,
tag_field: FieldIdx::new(0),
variants: IndexVec::new(),
variants: layout_variants,
},
fields: FieldsShape::Arbitrary {
offsets: [Size::ZERO].into(),
@ -1109,18 +1099,16 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
randomization_seed: combined_seed,
};
let tagged_layout = TmpLayout { layout: tagged_layout, variants: layout_variants };
let mut best_layout = match (tagged_layout, niche_filling_layout) {
let best_layout = match (tagged_layout, niche_filling_layout) {
(tl, Some(nl)) => {
// Pick the smaller layout; otherwise,
// pick the layout with the larger niche; otherwise,
// pick tagged as it has simpler codegen.
use cmp::Ordering::*;
let niche_size = |tmp_l: &TmpLayout<FieldIdx, VariantIdx>| {
tmp_l.layout.largest_niche.map_or(0, |n| n.available(dl))
let niche_size = |l: &LayoutData<FieldIdx, VariantIdx>| {
l.largest_niche.map_or(0, |n| n.available(dl))
};
match (tl.layout.size.cmp(&nl.layout.size), niche_size(&tl).cmp(&niche_size(&nl))) {
match (tl.size.cmp(&nl.size), niche_size(&tl).cmp(&niche_size(&nl))) {
(Greater, _) => nl,
(Equal, Less) => nl,
_ => tl,
@ -1129,16 +1117,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
(tl, None) => tl,
};
// Now we can intern the variant layouts and store them in the enum layout.
best_layout.layout.variants = match best_layout.layout.variants {
Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
Variants::Multiple { tag, tag_encoding, tag_field, variants: best_layout.variants }
}
Variants::Single { .. } | Variants::Empty => {
panic!("encountered a single-variant or empty enum during multi-variant layout")
}
};
Ok(best_layout.layout)
Ok(best_layout)
}
fn univariant_biased<