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[RFC, V2] exclude packed attr for types that contain aligned types when possible #2770

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[RFC, V2] exclude packed attr for types that contain aligned types when possible #2770

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126 changes: 126 additions & 0 deletions bindgen-tests/tests/expectations/tests/packed_embeds_aligned.rs
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19 changes: 19 additions & 0 deletions bindgen-tests/tests/headers/packed_embeds_aligned.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
struct inner1 {
char a;
char b;
} __attribute__((aligned(2)));

struct inner2 {
struct inner1 a;
struct inner1 b;
} __attribute__((aligned(2)));

struct outer1 {
short a;
struct inner1 b;
} __attribute__((packed, aligned(2)));

struct outer2 {
short a;
struct inner2 b;
} __attribute__((packed, aligned(2)));
8 changes: 4 additions & 4 deletions bindgen/codegen/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2124,7 +2124,7 @@ impl CodeGenerator for CompInfo {
}

if let Some(layout) = layout {
if struct_layout.requires_explicit_align(layout) {
if self.needs_explicit_align() {
if layout.align == 1 {
packed = true;
} else {
Expand All @@ -2145,7 +2145,7 @@ impl CodeGenerator for CompInfo {
// TODO(emilio): It'd be nice to unify this with the struct path
// above somehow.
let layout = layout.expect("Unable to get layout information?");
if struct_layout.requires_explicit_align(layout) {
if self.needs_explicit_align() {
explicit_align = Some(layout.align);
}

Expand Down Expand Up @@ -2202,8 +2202,8 @@ impl CodeGenerator for CompInfo {
// "packed" attr is redundant, and do not include it if so.
if packed &&
!is_opaque &&
!(explicit_align.is_some() &&
self.already_packed(ctx).unwrap_or(false))
!((explicit_align.is_some() || self.contains_aligned_type(ctx)) &&
self.already_packed(ctx, layout).unwrap_or(false))
{
let n = layout.map_or(1, |l| l.align);
assert!(ctx.options().rust_features().repr_packed_n || n == 1);
Expand Down
29 changes: 0 additions & 29 deletions bindgen/codegen/struct_layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,6 @@ pub(crate) struct StructLayoutTracker<'a> {
latest_offset: usize,
padding_count: usize,
latest_field_layout: Option<Layout>,
max_field_align: usize,
last_field_was_bitfield: bool,
visibility: FieldVisibilityKind,
}
Expand Down Expand Up @@ -108,7 +107,6 @@ impl<'a> StructLayoutTracker<'a> {
latest_offset: 0,
padding_count: 0,
latest_field_layout: None,
max_field_align: 0,
last_field_was_bitfield: false,
}
}
Expand All @@ -127,7 +125,6 @@ impl<'a> StructLayoutTracker<'a> {
let ptr_size = self.ctx.target_pointer_size();
self.latest_offset += ptr_size;
self.latest_field_layout = Some(Layout::new(ptr_size, ptr_size));
self.max_field_align = ptr_size;
}

pub(crate) fn saw_base(&mut self, base_ty: &Type) {
Expand All @@ -137,7 +134,6 @@ impl<'a> StructLayoutTracker<'a> {

self.latest_offset += self.padding_bytes(layout) + layout.size;
self.latest_field_layout = Some(layout);
self.max_field_align = cmp::max(self.max_field_align, layout.align);
}
}

Expand All @@ -156,7 +152,6 @@ impl<'a> StructLayoutTracker<'a> {

self.latest_field_layout = Some(layout);
self.last_field_was_bitfield = true;
self.max_field_align = cmp::max(self.max_field_align, layout.align);
}

/// Returns a padding field if necessary for a given new field _before_
Expand Down Expand Up @@ -265,8 +260,6 @@ impl<'a> StructLayoutTracker<'a> {

self.latest_offset += field_layout.size;
self.latest_field_layout = Some(field_layout);
self.max_field_align =
cmp::max(self.max_field_align, field_layout.align);
self.last_field_was_bitfield = false;

debug!(
Expand Down Expand Up @@ -365,26 +358,6 @@ impl<'a> StructLayoutTracker<'a> {
}
}

pub(crate) fn requires_explicit_align(&self, layout: Layout) -> bool {
let repr_align = self.ctx.options().rust_features().repr_align;

// Always force explicit repr(align) for stuff more than 16-byte aligned
// to work-around https://github.com/rust-lang/rust/issues/54341.
//
// Worst-case this just generates redundant alignment attributes.
if repr_align && self.max_field_align >= 16 {
return true;
}

if self.max_field_align >= layout.align {
return false;
}

// We can only generate up-to a 8-bytes of alignment unless we support
// repr(align).
repr_align || layout.align <= MAX_GUARANTEED_ALIGN
}

fn padding_bytes(&self, layout: Layout) -> usize {
align_to(self.latest_offset, layout.align) - self.latest_offset
}
Expand All @@ -400,8 +373,6 @@ impl<'a> StructLayoutTracker<'a> {
Span::call_site(),
);

self.max_field_align = cmp::max(self.max_field_align, layout.align);

let vis = super::access_specifier(self.visibility);

quote! {
Expand Down
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