bjoernager/rust
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Incorporate review feedback from 103926.

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This commit is contained in:
Luqman Aden 2022-11-30 23:12:04 -08:00
parent a3800535b1
commit 4f4f22b11c
1 changed files with 35 additions and 40 deletions
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71
compiler/rustc_abi/src/layout.rs
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@ -729,39 +729,34 @@ pub trait LayoutCalculator {
align = align.max(AbiAndPrefAlign::new(repr_align)); align = align.max(AbiAndPrefAlign::new(repr_align));
} }
let optimize = !repr.inhibit_union_abi_opt(); let mut optimize = !repr.inhibit_union_abi_opt();
let mut size = Size::ZERO; let mut size = Size::ZERO;
let mut abi = None; let mut common_non_zst_abi_and_align: Option<(Abi, AbiAndPrefAlign)> = None;
let mut biggest_zst_align = align;
let mut biggest_non_zst_align = align;
let only_variant = &variants[FIRST_VARIANT]; let only_variant = &variants[FIRST_VARIANT];
for field in only_variant { for field in only_variant {
assert!(!field.0.is_unsized()); assert!(field.0.is_sized());
if optimize { if !field.0.is_zst() && optimize {
// If all non-ZST fields have the same ABI, forward this ABI
if field.0.is_zst() {
biggest_zst_align = biggest_zst_align.max(field.align());
} else {
biggest_non_zst_align = biggest_non_zst_align.max(field.align());
// Discard valid range information and allow undef // Discard valid range information and allow undef
let field_abi = match field.abi() { let field_abi = field.abi().to_union();
Abi::Scalar(x) => Abi::Scalar(x.to_union()),
Abi::ScalarPair(x, y) => Abi::ScalarPair(x.to_union(), y.to_union()),
Abi::Vector { element: x, count } => {
Abi::Vector { element: x.to_union(), count }
}
Abi::Uninhabited | Abi::Aggregate { .. } => Abi::Aggregate { sized: true },
};
if let Some(abi) = &mut abi { if let Some((abi, align)) = &mut common_non_zst_abi_and_align {
if *abi != field_abi { if *abi != field_abi {
// different fields have different ABI: reset to Aggregate // Different fields have different ABI: disable opt
*abi = Abi::Aggregate { sized: true }; optimize = false;
} else {
// Fields with the same non-Aggregate ABI should also
// have the same alignment
if !matches!(abi, Abi::Aggregate { .. }) {
assert_eq!(
align.abi,
field.align().abi,
"non-Aggregate field with matching ABI but differing alignment"
);
}
} }
} else { } else {
abi = Some(field_abi); common_non_zst_abi_and_align = Some((field_abi, field.align()));
}
} }
} }
@ -769,24 +764,24 @@ pub trait LayoutCalculator {
size = cmp::max(size, field.size()); size = cmp::max(size, field.size());
} }
let abi = match abi {
None => Abi::Aggregate { sized: true },
Some(non_zst_abi) => {
if biggest_zst_align.abi > biggest_non_zst_align.abi {
// If a zst has a bigger alignment than the non-zst fields,
// we cannot use scalar layout, because scalar(pair)s can't be
// more aligned than their primitive.
Abi::Aggregate { sized: true }
} else {
non_zst_abi
}
}
};
if let Some(pack) = repr.pack { if let Some(pack) = repr.pack {
align = align.min(AbiAndPrefAlign::new(pack)); align = align.min(AbiAndPrefAlign::new(pack));
} }
// If all non-ZST fields have the same ABI, we may forward that ABI
// for the union as a whole, unless otherwise inhibited.
let abi = match (optimize, common_non_zst_abi_and_align) {
(false, _) | (_, None) => Abi::Aggregate { sized: true },
(true, Some((abi, _))) => {
if abi.inherent_align(dl).map(|a| a.abi) != Some(align.abi) {
// Mismatched alignment: disable opt
Abi::Aggregate { sized: true }
} else {
abi
}
}
};
Some(LayoutS { Some(LayoutS {
variants: Variants::Single { index: FIRST_VARIANT }, variants: Variants::Single { index: FIRST_VARIANT },
fields: FieldsShape::Union(NonZeroUsize::new(only_variant.len())?), fields: FieldsShape::Union(NonZeroUsize::new(only_variant.len())?),