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37 lines
1.5 KiB
Rust
37 lines
1.5 KiB
Rust
//@ run-pass
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#[repr(packed)]
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struct Packed<T: Copy>(#[allow(dead_code)] T);
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impl<T: Copy> Copy for Packed<T> {}
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impl<T: Copy> Clone for Packed<T> {
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fn clone(&self) -> Self { *self }
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}
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fn sanity_check_size<T: Copy>(one: T) {
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let two = [one, one];
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let stride = (&two[1] as *const _ as usize) - (&two[0] as *const _ as usize);
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let (size, align) = (std::mem::size_of::<T>(), std::mem::align_of::<T>());
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assert_eq!(stride, size);
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assert_eq!(size % align, 0);
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}
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fn main() {
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// This can fail if rustc and LLVM disagree on the size of a type.
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// In this case, `Option<Packed<(&(), u32)>>` was erroneously not
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// marked as packed despite needing alignment `1` and containing
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// its `&()` discriminant, which has alignment larger than `1`.
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sanity_check_size((Some(Packed((&(), 0))), true));
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// In #46769, `Option<(Packed<&()>, bool)>` was found to have
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// pointer alignment, without actually being aligned in size.
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// e.g., on 64-bit platforms, it had alignment `8` but size `9`.
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type PackedRefAndBool<'a> = (Packed<&'a ()>, bool);
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sanity_check_size::<Option<PackedRefAndBool>>(Some((Packed(&()), true)));
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// Make sure we don't pay for the enum optimization in size,
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// e.g., we shouldn't need extra padding after the packed data.
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assert_eq!(std::mem::align_of::<Option<PackedRefAndBool>>(), 1);
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assert_eq!(std::mem::size_of::<Option<PackedRefAndBool>>(),
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std::mem::size_of::<PackedRefAndBool>());
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}
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