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avoid double-cast in mplace_field

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This commit is contained in:
Ralf Jung 2020-03-21 16:28:34 +01:00
parent 9de600892d
commit cd15b659c7
1 changed files with 8 additions and 8 deletions
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16
src/librustc_mir/interpret/place.rs
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@ -396,9 +396,10 @@ where
field: u64,
) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
// Not using the layout method because we want to compute on u64
let offset = match base.layout.fields {
let (offset, field_layout) = match base.layout.fields {
layout::FieldPlacement::Arbitrary { ref offsets, .. } => {
offsets[usize::try_from(field).unwrap()]
let field = usize::try_from(field).unwrap();
(offsets[field], base.layout.field(self, field)?)
}
layout::FieldPlacement::Array { stride, .. } => {
let len = base.len(self)?;
@ -406,23 +407,22 @@ where
// This can only be reached in ConstProp and non-rustc-MIR.
throw_ub!(BoundsCheckFailed { len, index: field });
}
Size::mul(stride, field) // `Size` multiplication is checked
// All fields have the same layout.
(Size::mul(stride, field), base.layout.field(self, 9)?)
}
layout::FieldPlacement::Union(count) => {
let field = usize::try_from(field).unwrap();
assert!(
field < u64::try_from(count).unwrap(),
field < count,
"Tried to access field {} of union {:#?} with {} fields",
field,
base.layout,
count
);
// Offset is always 0
Size::from_bytes(0)
(Size::from_bytes(0), base.layout.field(self, field)?)
}
};
// the only way conversion can fail if is this is an array (otherwise we already panicked
// above). In that case, all fields have the same layout.
let field_layout = base.layout.field(self, usize::try_from(field).unwrap_or(0))?;
// Offset may need adjustment for unsized fields.
let (meta, offset) = if field_layout.is_unsized() {