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Implement the special repr(C)-non-clike-enum layout

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This commit is contained in:
Alexis Beingessner 2017-11-20 12:26:13 -05:00
parent f50fd075c2
commit 8293fe9fdf
1 changed files with 26 additions and 16 deletions
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42
src/librustc/ty/layout.rs
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@ -942,8 +942,8 @@ impl<'a, 'tcx> LayoutDetails {
AlwaysSized,
/// A univariant, the last field of which may be coerced to unsized.
MaybeUnsized,
/// A univariant, but part of an enum.
EnumVariant(Integer),
/// A univariant, but with a prefix of an arbitrary size & alignment (e.g. enum tag).
Prefixed(Size, Align),
}
let univariant_uninterned = |fields: &[TyLayout], repr: &ReprOptions, kind| {
let packed = repr.packed();
@ -962,14 +962,11 @@ impl<'a, 'tcx> LayoutDetails {
let mut inverse_memory_index: Vec<u32> = (0..fields.len() as u32).collect();
// Anything with repr(C) or repr(packed) doesn't optimize.
let optimize = match kind {
StructKind::AlwaysSized |
StructKind::MaybeUnsized |
StructKind::EnumVariant(I8) => {
(repr.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty()
}
StructKind::EnumVariant(_) => false
};
let mut optimize = (repr.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty();
if let StructKind::Prefixed(_, align) = kind {
optimize &= align.abi() == 1;
}
if optimize {
let end = if let StructKind::MaybeUnsized = kind {
fields.len() - 1
@ -987,7 +984,7 @@ impl<'a, 'tcx> LayoutDetails {
(!f.is_zst(), cmp::Reverse(f.align.abi()))
})
}
StructKind::EnumVariant(_) => {
StructKind::Prefixed(..) => {
optimizing.sort_by_key(|&x| fields[x as usize].align.abi());
}
}
@ -1001,12 +998,11 @@ impl<'a, 'tcx> LayoutDetails {
let mut offset = Size::from_bytes(0);
if let StructKind::EnumVariant(discr) = kind {
offset = discr.size();
if let StructKind::Prefixed(prefix_size, prefix_align) = kind {
if !packed {
let discr_align = discr.align(dl);
align = align.max(discr_align);
align = align.max(prefix_align);
}
offset = prefix_size.abi_align(prefix_align);
}
for &i in &inverse_memory_index {
@ -1558,10 +1554,24 @@ impl<'a, 'tcx> LayoutDetails {
let mut start_align = Align::from_bytes(256, 256).unwrap();
assert_eq!(Integer::for_abi_align(dl, start_align), None);
// repr(C) on an enum tells us to make a (tag, union) layout,
// so we need to grow the prefix alignment to be at least
// the alignment of the union. (This value is used both for
// determining the alignment of the overall enum, and the
// determining the alignment of the payload after the tag.)
let mut prefix_align = min_ity.align(dl);
if def.repr.c() {
for fields in &variants {
for field in fields {
prefix_align = prefix_align.max(field.align);
}
}
}
// Create the set of structs that represent each variant.
let mut variants = variants.into_iter().enumerate().map(|(i, field_layouts)| {
let mut st = univariant_uninterned(&field_layouts,
&def.repr, StructKind::EnumVariant(min_ity))?;
&def.repr, StructKind::Prefixed(min_ity.size(), prefix_align))?;
st.variants = Variants::Single { index: i };
// Find the first field we can't move later
// to make room for a larger discriminant.