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rustc: unpack scalar newtype layout ABIs.

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This commit is contained in:
Eduard-Mihai Burtescu 2017-10-09 02:31:06 +03:00
parent 0b8697241f
commit 37a7521ef9
7 changed files with 129 additions and 50 deletions
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50
src/librustc/ty/layout.rs
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@ -1078,6 +1078,30 @@ 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());
// We have exactly one non-ZST field.
match (non_zst_fields.next(), non_zst_fields.next()) {
(Some(field), None) => {
// Field size match and it has a scalar ABI.
if size == field.size {
match field.abi {
Abi::Scalar(_) => {
abi = field.abi.clone();
}
_ => {}
}
}
}
_ => {}
}
}
}
// Look for a scalar pair, as an ABI optimization.
// FIXME(eddyb) ignore extra ZST fields and field ordering.
if sized && !packed && fields.len() == 2 {
@ -1424,6 +1448,18 @@ impl<'a, 'tcx> CachedLayout {
let mut st = univariant_uninterned(&variants[v], &def.repr, kind)?;
st.variants = Variants::Single { index: v };
// Exclude 0 from the range of a newtype ABI NonZero<T>.
if Some(def.did) == cx.tcx().lang_items().non_zero() {
match st.abi {
Abi::Scalar(ref mut scalar) |
Abi::ScalarPair(ref mut scalar, _) => {
if scalar.valid_range.start == 0 {
scalar.valid_range.start = 1;
}
}
_ => {}
}
}
return Ok(tcx.intern_layout(st));
}
@ -2284,20 +2320,6 @@ impl<'a, 'tcx> TyLayout<'tcx> {
};
}
// Is this the NonZero lang item wrapping a pointer or integer type?
if let ty::TyAdt(def, _) = self.ty.sty {
if Some(def.did) == cx.tcx().lang_items().non_zero() {
let field = self.field(cx, 0)?;
let offset = self.fields.offset(0);
if let Abi::Scalar(Scalar { value, ref valid_range }) = field.abi {
return Ok(Some((offset, Scalar {
value,
valid_range: 0..=valid_range.end
}, 0)));
}
}
}
// Perhaps one of the fields is non-zero, let's recurse and find out.
if let FieldPlacement::Union(_) = self.fields {
// Only Rust enums have safe-to-inspect fields