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Rollup merge of #99113 - WaffleLapkin:arc_simplify, r=Mark-Simulacrum
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Simplify [a]rc code a little

Nothing interesting, just make [a]rc code a little nicer by using `byte_sub` and `let`-`else`.
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Dylan-DPC authored Jul 15, 2022
2 parents 30243dd + 69f8eb1 commit 99f3132
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Showing 3 changed files with 11 additions and 12 deletions.
1 change: 1 addition & 0 deletions library/alloc/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,7 @@
#![cfg_attr(test, feature(new_uninit))]
#![feature(nonnull_slice_from_raw_parts)]
#![feature(pattern)]
#![feature(pointer_byte_offsets)]
#![feature(ptr_internals)]
#![feature(ptr_metadata)]
#![feature(ptr_sub_ptr)]
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11 changes: 5 additions & 6 deletions library/alloc/src/rc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -907,8 +907,7 @@ impl<T: ?Sized> Rc<T> {
let offset = unsafe { data_offset(ptr) };

// Reverse the offset to find the original RcBox.
let rc_ptr =
unsafe { (ptr as *mut u8).offset(-offset).with_metadata_of(ptr as *mut RcBox<T>) };
let rc_ptr = unsafe { ptr.byte_sub(offset) as *mut RcBox<T> };

unsafe { Self::from_ptr(rc_ptr) }
}
Expand Down Expand Up @@ -2331,7 +2330,7 @@ impl<T: ?Sized> Weak<T> {
let offset = unsafe { data_offset(ptr) };
// Thus, we reverse the offset to get the whole RcBox.
// SAFETY: the pointer originated from a Weak, so this offset is safe.
unsafe { (ptr as *mut u8).offset(-offset).with_metadata_of(ptr as *mut RcBox<T>) }
unsafe { ptr.byte_sub(offset) as *mut RcBox<T> }
};

// SAFETY: we now have recovered the original Weak pointer, so can create the Weak.
Expand Down Expand Up @@ -2684,7 +2683,7 @@ impl<T: ?Sized> Unpin for Rc<T> {}
///
/// The pointer must point to (and have valid metadata for) a previously
/// valid instance of T, but the T is allowed to be dropped.
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> usize {
// Align the unsized value to the end of the RcBox.
// Because RcBox is repr(C), it will always be the last field in memory.
// SAFETY: since the only unsized types possible are slices, trait objects,
Expand All @@ -2695,7 +2694,7 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
}

#[inline]
fn data_offset_align(align: usize) -> isize {
fn data_offset_align(align: usize) -> usize {
let layout = Layout::new::<RcBox<()>>();
(layout.size() + layout.padding_needed_for(align)) as isize
layout.size() + layout.padding_needed_for(align)
}
11 changes: 5 additions & 6 deletions library/alloc/src/sync.rs
Original file line number Diff line number Diff line change
Expand Up @@ -908,8 +908,7 @@ impl<T: ?Sized> Arc<T> {
let offset = data_offset(ptr);

// Reverse the offset to find the original ArcInner.
let arc_ptr =
(ptr as *mut u8).offset(-offset).with_metadata_of(ptr as *mut ArcInner<T>);
let arc_ptr = ptr.byte_sub(offset) as *mut ArcInner<T>;

Self::from_ptr(arc_ptr)
}
Expand Down Expand Up @@ -1942,7 +1941,7 @@ impl<T: ?Sized> Weak<T> {
let offset = unsafe { data_offset(ptr) };
// Thus, we reverse the offset to get the whole RcBox.
// SAFETY: the pointer originated from a Weak, so this offset is safe.
unsafe { (ptr as *mut u8).offset(-offset).with_metadata_of(ptr as *mut ArcInner<T>) }
unsafe { ptr.byte_sub(offset) as *mut ArcInner<T> }
};

// SAFETY: we now have recovered the original Weak pointer, so can create the Weak.
Expand Down Expand Up @@ -2749,7 +2748,7 @@ impl<T: ?Sized> Unpin for Arc<T> {}
///
/// The pointer must point to (and have valid metadata for) a previously
/// valid instance of T, but the T is allowed to be dropped.
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> usize {
// Align the unsized value to the end of the ArcInner.
// Because RcBox is repr(C), it will always be the last field in memory.
// SAFETY: since the only unsized types possible are slices, trait objects,
Expand All @@ -2760,7 +2759,7 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
}

#[inline]
fn data_offset_align(align: usize) -> isize {
fn data_offset_align(align: usize) -> usize {
let layout = Layout::new::<ArcInner<()>>();
(layout.size() + layout.padding_needed_for(align)) as isize
layout.size() + layout.padding_needed_for(align)
}

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