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Do not use scalar layout if there are ZSTs with alignment > 1

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This commit is contained in:
Oli Scherer 2022-11-03 14:45:42 +00:00 committed by Luqman Aden
parent 4b94c23219
commit 23d09aebc8
3 changed files with 157 additions and 21 deletions
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62
compiler/rustc_abi/src/layout.rs
View File

@ -731,36 +731,58 @@ pub trait LayoutCalculator {
let optimize = !repr.inhibit_union_abi_opt();
let mut size = Size::ZERO;
let mut abi = Abi::Aggregate { sized: true };
let mut abi = None;
let mut biggest_zst_align = align;
let mut biggest_non_zst_align = align;
let only_variant = &variants[FIRST_VARIANT];
for field in only_variant {
assert!(field.0.is_sized());
align = align.max(field.align());
assert!(!field.0.is_unsized());
// If all non-ZST fields have the same ABI, forward this ABI
if optimize && !field.0.is_zst() {
// Discard valid range information and allow undef
let field_abi = match field.abi() {
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 }
if 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
let field_abi = match field.abi() {
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 *abi != field_abi {
// different fields have different ABI: reset to Aggregate
*abi = Abi::Aggregate { sized: true };
}
} else {
abi = Some(field_abi);
}
Abi::Uninhabited | Abi::Aggregate { .. } => Abi::Aggregate { sized: true },
};
if size == Size::ZERO {
// first non ZST: initialize 'abi'
abi = field_abi;
} else if abi != field_abi {
// different fields have different ABI: reset to Aggregate
abi = Abi::Aggregate { sized: true };
}
}
align = align.max(field.align());
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 {
align = align.min(AbiAndPrefAlign::new(pack));
}

21
tests/ui/layout/debug.rs
View File

@ -17,6 +17,27 @@ type Test = Result<i32, i32>; //~ ERROR: layout_of
#[rustc_layout(debug)]
type T = impl std::fmt::Debug; //~ ERROR: layout_of
#[rustc_layout(debug)]
pub union V { //~ ERROR: layout_of
a: [u16; 0],
b: u8,
}
#[rustc_layout(debug)]
pub union W { //~ ERROR: layout_of
b: u8,
a: [u16; 0],
}
#[rustc_layout(debug)]
pub union Y { //~ ERROR: layout_of
b: [u8; 0],
a: [u16; 0],
}
#[rustc_layout(debug)]
type X = std::mem::MaybeUninit<u8>; //~ ERROR: layout_of
fn f() -> T {
0i32
}

95
tests/ui/layout/debug.stderr
View File

@ -307,5 +307,98 @@ error: layout_of(i32) = Layout {
LL | type T = impl std::fmt::Debug;
| ^^^^^^
error: aborting due to 5 previous errors
error: layout_of(V) = Layout {
size: Size(2 bytes),
align: AbiAndPrefAlign {
abi: Align(2 bytes),
pref: $PREF_ALIGN,
},
abi: Aggregate {
sized: true,
},
fields: Union(
2,
),
largest_niche: None,
variants: Single {
index: 0,
},
}
--> $DIR/debug.rs:21:1
|
LL | pub union V {
| ^^^^^^^^^^^
error: layout_of(W) = Layout {
size: Size(2 bytes),
align: AbiAndPrefAlign {
abi: Align(2 bytes),
pref: $PREF_ALIGN,
},
abi: Aggregate {
sized: true,
},
fields: Union(
2,
),
largest_niche: None,
variants: Single {
index: 0,
},
}
--> $DIR/debug.rs:27:1
|
LL | pub union W {
| ^^^^^^^^^^^
error: layout_of(Y) = Layout {
size: Size(0 bytes),
align: AbiAndPrefAlign {
abi: Align(2 bytes),
pref: $PREF_ALIGN,
},
abi: Aggregate {
sized: true,
},
fields: Union(
2,
),
largest_niche: None,
variants: Single {
index: 0,
},
}
--> $DIR/debug.rs:33:1
|
LL | pub union Y {
| ^^^^^^^^^^^
error: layout_of(std::mem::MaybeUninit<u8>) = Layout {
size: Size(1 bytes),
align: AbiAndPrefAlign {
abi: Align(1 bytes),
pref: $PREF_ALIGN,
},
abi: Scalar(
Union {
value: Int(
I8,
false,
),
},
),
fields: Union(
2,
),
largest_niche: None,
variants: Single {
index: 0,
},
}
--> $DIR/debug.rs:39:1
|
LL | type X = std::mem::MaybeUninit<u8>;
| ^^^^^^
error: aborting due to 9 previous errors