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Mark scalar layout unions so that backends that do not support partially initialized scalars can special case them.

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This commit is contained in:
Oli Scherer
2022-03-03 12:02:12 +00:00
parent 2ed6786404
commit d32ce37a17
37 changed files with 356 additions and 288 deletions
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8
compiler/rustc_const_eval/src/interpret/operand.rs
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@@ -265,6 +265,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}));
};
// It may seem like all types with `Scalar` or `ScalarPair` ABI are fair game at this point.
// However, `MaybeUninit<u64>` is considered a `Scalar` as far as its layout is concerned --
// and yet cannot be represented by an interpreter `Scalar`, since we have to handle the
// case where some of the bytes are initialized and others are not. So, we only permit
// reads from `Scalar`s and `ScalarPair`s that cannot be uninitialized.
match mplace.layout.abi {
Abi::Scalar(..) => {
let scalar = alloc.read_scalar(alloc_range(Size::ZERO, mplace.layout.size))?;
@@ -274,7 +279,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// We checked `ptr_align` above, so all fields will have the alignment they need.
// We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
// which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
let (a, b) = (a.value, b.value);
let (a_size, b_size) = (a.size(self), b.size(self));
let b_offset = a_size.align_to(b.align(self).abi);
assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
@@ -676,7 +680,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// may be a pointer. This is `tag_val.layout`; we just use it for sanity checks.
// Get layout for tag.
let tag_layout = self.layout_of(tag_scalar_layout.value.to_int_ty(*self.tcx))?;
let tag_layout = self.layout_of(tag_scalar_layout.primitive().to_int_ty(*self.tcx))?;
// Read tag and sanity-check `tag_layout`.
let tag_val = self.read_immediate(&self.operand_field(op, tag_field)?)?;