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Auto merge of #96197 - erikdesjardins:scalarpairenum, r=oli-obk

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Mark payload fields of ScalarPair enums as Scalar::Union when they're not always initialized

Fixes #96158

r? `@RalfJung`
This commit is contained in:
bors 2022-04-22 10:50:23 +00:00
commit a8272f23cc
3 changed files with 795 additions and 16 deletions
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37
compiler/rustc_middle/src/ty/layout.rs
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@ -1120,21 +1120,12 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
match st[i].abi() {
Abi::Scalar(_) => Abi::Scalar(niche_scalar),
Abi::ScalarPair(first, 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.
// Only the niche is guaranteed to be initialised,
// so use union layout for the other primitive.
if offset.bytes() == 0 {
Abi::ScalarPair(
niche_scalar,
scalar_unit(second.primitive()),
)
Abi::ScalarPair(niche_scalar, second.to_union())
} else {
Abi::ScalarPair(
scalar_unit(first.primitive()),
niche_scalar,
)
Abi::ScalarPair(first.to_union(), niche_scalar)
}
}
_ => Abi::Aggregate { sized: true },
@ -1329,6 +1320,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
} else {
// Try to use a ScalarPair for all tagged enums.
let mut common_prim = None;
let mut common_prim_initialized_in_all_variants = true;
for (field_layouts, layout_variant) in iter::zip(&variants, &layout_variants) {
let FieldsShape::Arbitrary { ref offsets, .. } = layout_variant.fields else {
bug!();
@ -1336,7 +1328,10 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let mut fields =
iter::zip(field_layouts, offsets).filter(|p| !p.0.is_zst());
let (field, offset) = match (fields.next(), fields.next()) {
(None, None) => continue,
(None, None) => {
common_prim_initialized_in_all_variants = false;
continue;
}
(Some(pair), None) => pair,
_ => {
common_prim = None;
@ -1344,7 +1339,11 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
}
};
let prim = match field.abi {
Abi::Scalar(scalar) => scalar.primitive(),
Abi::Scalar(scalar) => {
common_prim_initialized_in_all_variants &=
matches!(scalar, Scalar::Initialized { .. });
scalar.primitive()
}
_ => {
common_prim = None;
break;
@ -1364,7 +1363,13 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
}
}
if let Some((prim, offset)) = common_prim {
let pair = self.scalar_pair(tag, scalar_unit(prim));
let prim_scalar = if common_prim_initialized_in_all_variants {
scalar_unit(prim)
} else {
// Common prim might be uninit.
Scalar::Union { value: prim }
};
let pair = self.scalar_pair(tag, prim_scalar);
let pair_offsets = match pair.fields {
FieldsShape::Arbitrary { ref offsets, ref memory_index } => {
assert_eq!(memory_index, &[0, 1]);