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rustc: use layout::Abi::ScalarPair for structs in more cases.

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This commit is contained in:
Eduard-Mihai Burtescu 2017-10-10 23:38:07 +03:00
parent 801a1a0fc1
commit d893285b65
1 changed files with 55 additions and 43 deletions
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98
src/librustc/ty/layout.rs
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@ -1078,19 +1078,28 @@ impl<'a, 'tcx> CachedLayout {
packed
};
// Unpack newtype ABIs.
if sized && optimize && size.bytes() > 0 {
// All but one field must be ZSTs, and so they all start at 0.
if offsets.iter().all(|o| o.bytes() == 0) {
let mut non_zst_fields = fields.iter().filter(|f| !f.is_zst());
// Unpack newtype ABIs and find scalar pairs.
if sized && size.bytes() > 0 {
// All other fields must be ZSTs, and we need them to all start at 0.
let mut zst_offsets =
offsets.iter().enumerate().filter(|&(i, _)| fields[i].is_zst());
if zst_offsets.all(|(_, o)| o.bytes() == 0) {
let mut non_zst_fields =
fields.iter().enumerate().filter(|&(_, f)| !f.is_zst());
// We have exactly one non-ZST field.
match (non_zst_fields.next(), non_zst_fields.next()) {
(Some(field), None) => {
// Field size matches and it has a scalar or scalar pair ABI.
if size == field.size {
match (non_zst_fields.next(), non_zst_fields.next(), non_zst_fields.next()) {
// We have exactly one non-ZST field.
(Some((i, field)), None, None) => {
// Field fills the struct and it has a scalar or scalar pair ABI.
if offsets[i].bytes() == 0 && size == field.size {
match field.abi {
Abi::Scalar(_) |
// For plain scalars we can't unpack newtypes
// for `#[repr(C)]`, as that affects C ABIs.
Abi::Scalar(_) if optimize => {
abi = field.abi.clone();
}
// But scalar pairs are Rust-specific and get
// treated as aggregates by C ABIs anyway.
Abi::ScalarPair(..) => {
abi = field.abi.clone();
}
@ -1098,43 +1107,46 @@ impl<'a, 'tcx> CachedLayout {
}
}
}
// Two non-ZST fields, and they're both scalars.
(Some((i, &TyLayout {
cached: &CachedLayout { abi: Abi::Scalar(ref a), .. }, ..
})), Some((j, &TyLayout {
cached: &CachedLayout { abi: Abi::Scalar(ref b), .. }, ..
})), None) => {
// Order by the memory placement, not source order.
let ((i, a), (j, b)) = if offsets[i] < offsets[j] {
((i, a), (j, b))
} else {
((j, b), (i, a))
};
let pair = scalar_pair(a.clone(), b.clone());
let pair_offsets = match pair.fields {
FieldPlacement::Arbitrary {
ref offsets,
ref memory_index
} => {
assert_eq!(memory_index, &[0, 1]);
offsets
}
_ => bug!()
};
if offsets[i] == pair_offsets[0] &&
offsets[j] == pair_offsets[1] &&
align == pair.align &&
primitive_align == pair.primitive_align &&
size == pair.size {
// We can use `ScalarPair` only when it matches our
// already computed layout (including `#[repr(C)]`).
abi = pair.abi;
}
}
_ => {}
}
}
}
// Look for a scalar pair, as an ABI optimization.
// FIXME(eddyb) ignore extra ZST fields and field ordering.
if sized && !packed && fields.len() == 2 {
match (&fields[0].abi, &fields[1].abi) {
(&Abi::Scalar(ref a), &Abi::Scalar(ref b)) => {
let pair = scalar_pair(a.clone(), b.clone());
let pair_offsets = match pair.fields {
FieldPlacement::Arbitrary {
ref offsets,
ref memory_index
} => {
assert_eq!(memory_index, &[0, 1]);
offsets
}
_ => bug!()
};
if offsets[0] == pair_offsets[0] &&
offsets[1] == pair_offsets[1] &&
memory_index[0] == 0 &&
memory_index[1] == 1 &&
align == pair.align &&
primitive_align == pair.primitive_align &&
size == pair.size {
// We can use `ScalarPair` only when it matches our
// already computed layout (including `#[repr(C)]`).
abi = pair.abi;
}
}
_ => {}
}
}
Ok(CachedLayout {
variants: Variants::Single { index: 0 },
fields: FieldPlacement::Arbitrary {