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Untangle ZST validation from integer validation and generalize it to all zsts #68219

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Merged
merged 2 commits into from
Jan 15, 2020
Merged

Untangle ZST validation from integer validation and generalize it to all zsts #68219

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Untangle ZST validation from integer validation and generalize it to …
oli-obk Jan 13, 2020
0e14b9f
Add tests
oli-obk Jan 15, 2020
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18 changes: 7 additions & 11 deletions src/librustc_mir/interpret/validity.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -587,12 +587,6 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
// padding.
match tys.kind {
ty::Int(..) | ty::Uint(..) | ty::Float(..) => true,
ty::Tuple(tys) if tys.len() == 0 => true,
ty::Adt(adt_def, _)
if adt_def.is_struct() && adt_def.all_fields().next().is_none() =>
{
true
}
_ => false,
}
} =>
Expand All @@ -609,11 +603,6 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
}
// This is the element type size.
let layout = self.ecx.layout_of(tys)?;
// Empty tuples and fieldless structs (the only ZSTs that allow reaching this code)
// have no data to be checked.
if layout.is_zst() {
return Ok(());
}
// This is the size in bytes of the whole array.
let size = layout.size * len;
// Size is not 0, get a pointer.
Expand Down Expand Up @@ -656,6 +645,13 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
}
}
}
// Fast path for arrays and slices of ZSTs. We only need to check a single ZST element
// of an array and not all of them, because there's only a single value of a specific
// ZST type, so either validation fails for all elements or none.
ty::Array(tys, ..) | ty::Slice(tys) if self.ecx.layout_of(tys)?.is_zst() => {
// Validate just the first element
self.walk_aggregate(op, fields.take(1))?
}
_ => {
self.walk_aggregate(op, fields)? // default handler
}
Expand Down