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Rollup merge of #50837 - steveklabnik:revert-49767, r=QuietMisdreavus
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Revert #49767

There was [some confusion](#49767 (comment)) and I accidentally merged a PR that wasn't ready.
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@Mark-Simulacrum
Mark-Simulacrum authored May 17, 2018
2 parents 54df1bf + eac94d1 commit 53ea73a
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161 changes: 31 additions & 130 deletions src/libcore/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -962,122 +962,59 @@ extern "rust-intrinsic" {
/// value is not necessarily valid to be used to actually access memory.
pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;

/// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
/// and destination must *not* overlap.
/// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
/// and destination may *not* overlap.
///
/// For regions of memory which might overlap, use [`copy`] instead.
///
/// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`].
///
/// [`copy`]: ./fn.copy.html
/// [`memcpy`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memcpy
/// `copy_nonoverlapping` is semantically equivalent to C's `memcpy`.
///
/// # Safety
///
/// Behavior is undefined if any of the following conditions are violated:
///
/// * The region of memory which begins at `src` and has a length of
/// `count * size_of::<T>()` bytes must be *both* valid and initialized.
///
/// * The region of memory which begins at `dst` and has a length of
/// `count * size_of::<T>()` bytes must be valid (but may or may not be
/// initialized).
///
/// * The two regions of memory must *not* overlap.
///
/// * `src` must be properly aligned.
///
/// * `dst` must be properly aligned.
///
/// Additionally, if `T` is not [`Copy`], only the region at `src` *or* the
/// region at `dst` can be used or dropped after calling
/// `copy_nonoverlapping`. `copy_nonoverlapping` creates bitwise copies of
/// `T`, regardless of whether `T: Copy`, which can result in undefined
/// behavior if both copies are used.
///
/// [`Copy`]: ../marker/trait.Copy.html
/// Beyond requiring that the program must be allowed to access both regions
/// of memory, it is Undefined Behavior for source and destination to
/// overlap. Care must also be taken with the ownership of `src` and
/// `dst`. This method semantically moves the values of `src` into `dst`.
/// However it does not drop the contents of `dst`, or prevent the contents
/// of `src` from being dropped or used.
///
/// # Examples
///
/// Manually implement [`Vec::append`]:
/// A safe swap function:
///
/// ```
/// use std::mem;
/// use std::ptr;
///
/// /// Moves all the elements of `src` into `dst`, leaving `src` empty.
/// fn append<T>(dst: &mut Vec<T>, src: &mut Vec<T>) {
/// let src_len = src.len();
/// let dst_len = dst.len();
///
/// // Ensure that `dst` has enough capacity to hold all of `src`.
/// dst.reserve(src_len);
///
/// # #[allow(dead_code)]
/// fn swap<T>(x: &mut T, y: &mut T) {
/// unsafe {
/// // The call to offset is always safe because `Vec` will never
/// // allocate more than `isize::MAX` bytes.
/// let dst = dst.as_mut_ptr().offset(dst_len as isize);
/// let src = src.as_ptr();
///
/// // The two regions cannot overlap becuase mutable references do
/// // not alias, and two different vectors cannot own the same
/// // memory.
/// ptr::copy_nonoverlapping(src, dst, src_len);
/// }
/// // Give ourselves some scratch space to work with
/// let mut t: T = mem::uninitialized();
///
/// unsafe {
/// // Truncate `src` without dropping its contents.
/// src.set_len(0);
/// // Perform the swap, `&mut` pointers never alias
/// ptr::copy_nonoverlapping(x, &mut t, 1);
/// ptr::copy_nonoverlapping(y, x, 1);
/// ptr::copy_nonoverlapping(&t, y, 1);
///
/// // Notify `dst` that it now holds the contents of `src`.
/// dst.set_len(dst_len + src_len);
/// // y and t now point to the same thing, but we need to completely forget `t`
/// // because it's no longer relevant.
/// mem::forget(t);
/// }
/// }
///
/// let mut a = vec!['r'];
/// let mut b = vec!['u', 's', 't'];
///
/// append(&mut a, &mut b);
///
/// assert_eq!(a, &['r', 'u', 's', 't']);
/// assert!(b.is_empty());
/// ```
///
/// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);

/// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
/// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
/// and destination may overlap.
///
/// If the source and destination will *never* overlap,
/// [`copy_nonoverlapping`] can be used instead.
///
/// `copy` is semantically equivalent to C's [`memmove`].
///
/// [`copy_nonoverlapping`]: ./fn.copy_nonoverlapping.html
/// [`memmove`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memmove
/// `copy` is semantically equivalent to C's `memmove`.
///
/// # Safety
///
/// Behavior is undefined if any of the following conditions are violated:
///
/// * The region of memory which begins at `src` and has a length of
/// `count * size_of::<T>()` bytes must be *both* valid and initialized.
///
/// * The region of memory which begins at `dst` and has a length of
/// `count * size_of::<T>()` bytes must be valid (but may or may not be
/// initialized).
///
/// * `src` must be properly aligned.
///
/// * `dst` must be properly aligned.
///
/// Additionally, if `T` is not [`Copy`], only the region at `src` *or* the
/// region at `dst` can be used or dropped after calling `copy`. `copy`
/// creates bitwise copies of `T`, regardless of whether `T: Copy`, which
/// can result in undefined behavior if both copies are used.
///
/// [`Copy`]: ../marker/trait.Copy.html
/// Care must be taken with the ownership of `src` and `dst`.
/// This method semantically moves the values of `src` into `dst`.
/// However it does not drop the contents of `dst`, or prevent the contents of `src`
/// from being dropped or used.
///
/// # Examples
///
Expand All @@ -1094,34 +1031,15 @@ extern "rust-intrinsic" {
/// dst
/// }
/// ```
///
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<T>(src: *const T, dst: *mut T, count: usize);

/// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
/// `val`.
///
/// `write_bytes` is semantically equivalent to C's [`memset`].
///
/// [`memset`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memset
///
/// # Safety
///
/// Behavior is undefined if any of the following conditions are violated:
///
/// * The region of memory which begins at `dst` and has a length of
/// `count` bytes must be valid.
///
/// * `dst` must be properly aligned.
///
/// Additionally, the caller must ensure that writing `count` bytes to the
/// given region of memory results in a valid value of `T`. Creating an
/// invalid value of `T` can result in undefined behavior. An example is
/// provided below.
/// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
/// bytes of memory starting at `dst` to `val`.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::ptr;
///
Expand All @@ -1132,23 +1050,6 @@ extern "rust-intrinsic" {
/// }
/// assert_eq!(vec, [b'a', b'a', 0, 0]);
/// ```
///
/// Creating an invalid value:
///
/// ```no_run
/// use std::{mem, ptr};
///
/// let mut v = Box::new(0i32);
///
/// unsafe {
/// // Leaks the previously held value by overwriting the `Box<T>` with
/// // a null pointer.
/// ptr::write_bytes(&mut v, 0, mem::size_of::<Box<i32>>());
/// }
///
/// // At this point, using or dropping `v` results in undefined behavior.
/// // v = Box::new(0i32); // ERROR
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);

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