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don't inhibit random field reordering on repr(packed(1))
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RalfJung committed May 21, 2024
1 parent e875391 commit a53f3ed
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Showing 3 changed files with 6 additions and 13 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_abi/src/layout.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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];
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15 changes: 4 additions & 11 deletions compiler/rustc_abi/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -137,23 +137,16 @@ impl ReprOptions {
self.c() || self.int.is_some()
}

/// Returns `true` if this `#[repr()]` should inhibit struct field reordering
/// optimizations, such as with `repr(C)`, `repr(packed(1))`, or `repr(<int>)`.
pub fn inhibit_struct_field_reordering_opt(&self) -> bool {
if let Some(pack) = self.pack {
if pack.bytes() == 1 {
return true;
}
}

/// Returns `true` if this `#[repr()]` guarantees a fixed field order,
/// e.g. `repr(C)` or `repr(<int>)`.
pub fn inhibit_struct_field_reordering(&self) -> bool {
self.flags.intersects(ReprFlags::IS_UNOPTIMISABLE) || self.int.is_some()
}

/// Returns `true` if this type is valid for reordering and `-Z randomize-layout`
/// was enabled for its declaration crate.
pub fn can_randomize_type_layout(&self) -> bool {
!self.inhibit_struct_field_reordering_opt()
&& self.flags.contains(ReprFlags::RANDOMIZE_LAYOUT)
!self.inhibit_struct_field_reordering() && self.flags.contains(ReprFlags::RANDOMIZE_LAYOUT)
}

/// Returns `true` if this `#[repr()]` should inhibit union ABI optimisations.
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Original file line number Diff line number Diff line change
Expand Up @@ -278,7 +278,7 @@ fn reduce_ty<'tcx>(cx: &LateContext<'tcx>, mut ty: Ty<'tcx>) -> ReducedTy<'tcx>
ty = sized_ty;
continue;
}
if def.repr().inhibit_struct_field_reordering_opt() {
if def.repr().inhibit_struct_field_reordering() {
ReducedTy::OrderedFields(Some(sized_ty))
} else {
ReducedTy::UnorderedFields(ty)
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