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Support arrays of zeros in Vec's __rust_alloc_zeroed optimization #95362

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merged 1 commit into from
May 1, 2022
Merged

Support arrays of zeros in Vec's __rust_alloc_zeroed optimization #95362

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9 changes: 8 additions & 1 deletion library/alloc/src/vec/is_zero.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ use crate::boxed::Box;

#[rustc_specialization_trait]
pub(super) unsafe trait IsZero {
/// Whether this value is zero
/// Whether this value's representation is all zeros
fn is_zero(&self) -> bool;
}

Expand Down Expand Up @@ -49,6 +49,13 @@ unsafe impl<T> IsZero for *mut T {
}
}

unsafe impl<T: IsZero, const N: usize> IsZero for [T; N] {
#[inline]
fn is_zero(&self) -> bool {
self.iter().all(IsZero::is_zero)
}
}

// `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
// For fat pointers, the bytes that would be the pointer metadata in the `Some`
// variant are padding in the `None` variant, so ignoring them and
Expand Down