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This commit is contained in:
Luqman Aden 2023-02-19 16:25:07 -08:00
parent c63a204e23
commit 012f9a333b
2 changed files with 23 additions and 14 deletions
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35
compiler/rustc_abi/src/layout.rs
View File

@ -729,34 +729,43 @@ pub trait LayoutCalculator {
align = align.max(AbiAndPrefAlign::new(repr_align));
}
let mut optimize = !repr.inhibit_union_abi_opt();
// If all the non-ZST fields have the same ABI and union ABI optimizations aren't
// disabled, we can use that common ABI for the union as a whole.
struct AbiMismatch;
let mut common_non_zst_abi_and_align = if repr.inhibit_union_abi_opt() {
// Can't optimize
Err(AbiMismatch)
} else {
Ok(None)
};
let mut size = Size::ZERO;
let mut common_non_zst_abi_and_align: Option<(Abi, AbiAndPrefAlign)> = None;
let only_variant = &variants[FIRST_VARIANT];
for field in only_variant {
assert!(field.0.is_sized());
if !field.0.is_zst() && optimize {
if !field.0.is_zst() && !common_non_zst_abi_and_align.is_err() {
// Discard valid range information and allow undef
let field_abi = field.abi().to_union();
if let Some((abi, align)) = &mut common_non_zst_abi_and_align {
if *abi != field_abi {
if let Ok(Some((common_abi, common_align))) = &mut common_non_zst_abi_and_align {
if *common_abi != field_abi {
// Different fields have different ABI: disable opt
optimize = false;
common_non_zst_abi_and_align = Err(AbiMismatch);
} else {
// Fields with the same non-Aggregate ABI should also
// have the same alignment
if !matches!(abi, Abi::Aggregate { .. }) {
if !matches!(common_abi, Abi::Aggregate { .. }) {
assert_eq!(
align.abi,
*common_align,
field.align().abi,
"non-Aggregate field with matching ABI but differing alignment"
);
}
}
} else {
common_non_zst_abi_and_align = Some((field_abi, field.align()));
// First non-ZST field: record its ABI and alignment
common_non_zst_abi_and_align = Ok(Some((field_abi, field.align().abi)));
}
}
@ -770,11 +779,11 @@ pub trait LayoutCalculator {
// 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, _))) => {
let abi = match common_non_zst_abi_and_align {
Err(AbiMismatch) | Ok(None) => Abi::Aggregate { sized: true },
Ok(Some((abi, _))) => {
if abi.inherent_align(dl).map(|a| a.abi) != Some(align.abi) {
// Mismatched alignment: disable opt
// Mismatched alignment (e.g. union is #[repr(packed)]): disable opt
Abi::Aggregate { sized: true }
} else {
abi

2
compiler/rustc_abi/src/lib.rs
View File

@ -1306,7 +1306,7 @@ impl Abi {
})
}
/// Discard valid range information and allow undef
/// Discard validity range information and allow undef.
pub fn to_union(&self) -> Self {
assert!(self.is_sized());
match *self {