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don't inhibit random field reordering on repr(packed(1))

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This commit is contained in:
Ralf Jung
2024-05-21 14:07:02 +02:00
parent e875391458
commit 37aeb75eb6
6 changed files with 14 additions and 19 deletions
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10
compiler/rustc_abi/src/layout.rs
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@@ -970,7 +970,7 @@ fn univariant<
let mut align = if pack.is_some() { dl.i8_align } else { dl.aggregate_align };
let mut max_repr_align = repr.align;
let mut inverse_memory_index: IndexVec<u32, FieldIdx> = fields.indices().collect();
let optimize = !repr.inhibit_struct_field_reordering_opt();
let optimize = !repr.inhibit_struct_field_reordering();
if optimize && fields.len() > 1 {
let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
let optimizing = &mut inverse_memory_index.raw[..end];
@@ -1007,13 +1007,15 @@ fn univariant<
// Calculates a sort key to group fields by their alignment or possibly some
// size-derived pseudo-alignment.
let alignment_group_key = |layout: &F| {
// The two branches here return values that cannot be meaningfully compared with
// each other. However, we know that consistently for all executions of
// `alignment_group_key`, one or the other branch will be taken, so this is okay.
if let Some(pack) = pack {
// Return the packed alignment in bytes.
layout.align.abi.min(pack).bytes()
} else {
// Returns `log2(effective-align)`. This is ok since `pack` applies to all
// fields equally. The calculation assumes that size is an integer multiple of
// align, except for ZSTs.
// Returns `log2(effective-align)`. The calculation assumes that size is an
// integer multiple of align, except for ZSTs.
let align = layout.align.abi.bytes();
let size = layout.size.bytes();
let niche_size = layout.largest_niche.map(|n| n.available(dl)).unwrap_or(0);