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there seems to be no reason to treat ZST specially in these cases

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This commit is contained in:
Ralf Jung 2023-08-27 18:06:59 +02:00
parent 0da9409e08
commit bf91321e0f
3 changed files with 9 additions and 19 deletions
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12
compiler/rustc_abi/src/layout.rs
View File

@ -359,13 +359,8 @@ struct TmpLayout {
// It'll fit, but we need to make some adjustments.
match layout.fields {
FieldsShape::Arbitrary { ref mut offsets, .. } => {
for (j, offset) in offsets.iter_enumerated_mut() {
// keep ZST at offset 0 to simplify Scalar/ScalarPair layout
if !variants[i][j].0.is_zst() {
for offset in offsets.iter_mut() {
*offset += this_offset;
} else {
debug_assert_eq!(offset.bytes(), 0);
}
}
}
_ => {
@ -962,11 +957,6 @@ fn univariant(
};
(
// Place ZSTs first to avoid "interesting offsets", especially with only
// one or two non-ZST fields. This helps Scalar/ScalarPair layouts. Note
// that these can ignore even some aligned ZST as long as the alignment
// is less than that of the scalar, hence we treat *all* ZST like that.
!f.0.is_zst(),
// Then place largest alignments first.
cmp::Reverse(alignment_group_key(f)),
// Then prioritize niche placement within alignment group according to

4
tests/ui/layout/debug.stderr
View File

@ -117,13 +117,13 @@ error: layout_of(S) = Layout {
fields: Arbitrary {
offsets: [
Size(0 bytes),
Size(0 bytes),
Size(8 bytes),
Size(4 bytes),
],
memory_index: [
1,
0,
2,
1,
],
},
largest_niche: None,

10
tests/ui/print_type_sizes/zero-sized-fields.stdout
View File

@ -1,16 +1,16 @@
print-type-size type: `S5<(), Empty>`: 16 bytes, alignment: 4 bytes
print-type-size field `.w`: 4 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
print-type-size field `.z`: 4 bytes
print-type-size field `.tagw`: 0 bytes
print-type-size field `.unit`: 0 bytes
print-type-size field `.void`: 0 bytes
print-type-size field `.empty`: 0 bytes
print-type-size field `.tagz`: 0 bytes
print-type-size field `.w`: 4 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
print-type-size field `.z`: 4 bytes
print-type-size type: `S1`: 8 bytes, alignment: 4 bytes
print-type-size field `.tag`: 0 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
print-type-size field `.tag`: 0 bytes
print-type-size type: `Empty`: 0 bytes, alignment: 1 bytes
print-type-size type: `Void`: 0 bytes, alignment: 1 bytes