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[experiment] ty/layout: compute both niche-filling and tagged layouts for enums. #71045

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[experiment] ty/layout: compute both niche-filling and tagged layouts for enums. #71045

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12 changes: 8 additions & 4 deletions src/librustc_middle/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -871,6 +871,8 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
.iter_enumerated()
.all(|(i, v)| v.discr == ty::VariantDiscr::Relative(i.as_u32()));

let mut niche_filling_layout = None;

// Niche-filling enum optimization.
if !def.repr.inhibit_enum_layout_opt() && no_explicit_discriminants {
let mut dataful_variant = None;
Expand Down Expand Up @@ -967,7 +969,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let largest_niche =
Niche::from_scalar(dl, offset, niche_scalar.clone());

return Ok(tcx.intern_layout(Layout {
niche_filling_layout = Some(Layout {
variants: Variants::Multiple {
discr: niche_scalar,
discr_kind: DiscriminantKind::Niche {
Expand All @@ -986,7 +988,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
largest_niche,
size,
align,
}));
});
}
}
}
Expand Down Expand Up @@ -1209,7 +1211,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {

let largest_niche = Niche::from_scalar(dl, Size::ZERO, tag.clone());

tcx.intern_layout(Layout {
let tagged_layout = Layout {
variants: Variants::Multiple {
discr: tag,
discr_kind: DiscriminantKind::Tag,
Expand All @@ -1224,7 +1226,9 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
abi,
align,
size,
})
};

tcx.intern_layout(niche_filling_layout.unwrap_or(tagged_layout))
}

// Types with no meaningful known layout.
Expand Down