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const_intrinsic_copy - Add Reference to tracking issue #80699

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Merged
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Jan 5, 2021
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const_intrinsic_copy - Add Reference to tracking issue #80699

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5 changes: 2 additions & 3 deletions library/core/src/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1845,7 +1845,7 @@ pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -
/// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
#[doc(alias = "memcpy")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "none")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[inline]
pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
extern "rust-intrinsic" {
Expand Down Expand Up @@ -1929,11 +1929,10 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
/// ```
#[doc(alias = "memmove")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "none")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[inline]
pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
extern "rust-intrinsic" {
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "none")]
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This is not needed, right?

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I would have thought it is, otherwise you should not be able to call it below, looks like we have a hole in our analysis somewhere. The rustc_const_unstable attribute is what makes the intrinsic const, since we cannot have const fn intrinsics since the syntax doesn't allow this.

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uff.. I just checked, we have no unit tests ensuring that this actually works, so it must've regressed.

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The reason I noticed it was because I did not see the corresponding line for copy_nonoverlapping

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I believe I got the error before the rebase(the reason the attribute was on copy at all)

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@usbalbin usbalbin Jan 4, 2021 •
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As far as I can tell, only looking at #79684, the error probably disappeared somewhere between the 4th and 21th of December. Quite a large span, but perhaps somewhere to start...

I might be completely wrong

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I... have an inlkling. I'm waiting for a rebuild with some more trace! instructions, now that I am able to reproduce. I think the issue may be that the copy intrinsic is declare inside a function with rustc_const_unstable and inherits that

fn copy<T>(src: *const T, dst: *mut T, count: usize);
}

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