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Allow niche-filling dataful variants to be represented as a ScalarPair #49383

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Mar 28, 2018
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Allow niche-filling dataful variants to be represented as a ScalarPair #49383

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19 changes: 15 additions & 4 deletions src/librustc/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1517,10 +1517,21 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
let offset = st[i].fields.offset(field_index) + offset;
let size = st[i].size;

let abi = if offset.bytes() == 0 && niche.value.size(dl) == size {
Abi::Scalar(niche.clone())
} else {
Abi::Aggregate { sized: true }
let abi = match st[i].abi {
Abi::Scalar(_) => Abi::Scalar(niche.clone()),
Abi::ScalarPair(ref first, ref second) => {
// We need to use scalar_unit to reset the
// valid range to the maximal one for that
// primitive, because only the niche is
// guaranteed to be initialised, not the
// other primitive.
if offset.bytes() == 0 {
Abi::ScalarPair(niche.clone(), scalar_unit(second.value))
} else {
Abi::ScalarPair(scalar_unit(first.value), niche.clone())
}
}
_ => Abi::Aggregate { sized: true },
};

return Ok(tcx.intern_layout(LayoutDetails {
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6 changes: 6 additions & 0 deletions src/test/codegen/function-arguments.rs
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Expand Up @@ -133,6 +133,12 @@ pub fn trait_borrow(_: &Drop) {
pub fn trait_box(_: Box<Drop>) {
}

// CHECK: { i8*, i8* } @trait_option(i8* noalias %x.0, i8* %x.1)
#[no_mangle]
pub fn trait_option(x: Option<Box<Drop>>) -> Option<Box<Drop>> {
x
}

// CHECK: { [0 x i16]*, [[USIZE]] } @return_slice([0 x i16]* noalias nonnull readonly %x.0, [[USIZE]] %x.1)
#[no_mangle]
pub fn return_slice(x: &[u16]) -> &[u16] {
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