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Stylo: replace uses of mem::uninitialized with MaybeUninit

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MozReview-Commit-ID: KGhYL6DJRaR
This commit is contained in:
Simon Sapin 2019-07-06 18:16:30 +02:00
parent 00b3fb49c4
commit 17ec774a49
9 changed files with 60 additions and 68 deletions
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29
components/servo_arc/lib.rs
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@ -52,25 +52,6 @@ use std::sync::atomic;
use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};
use std::{isize, usize};
// Private macro to get the offset of a struct field in bytes from the address of the struct.
macro_rules! offset_of {
($container:path, $field:ident) => {{
// Make sure the field actually exists. This line ensures that a compile-time error is
// generated if $field is accessed through a Deref impl.
let $container { $field: _, .. };
// Create an (invalid) instance of the container and calculate the offset to its
// field. Using a null pointer might be UB if `&(*(0 as *const T)).field` is interpreted to
// be nullptr deref.
let invalid: $container = ::std::mem::uninitialized();
let offset = &invalid.$field as *const _ as usize - &invalid as *const _ as usize;
// Do not run destructors on the made up invalid instance.
::std::mem::forget(invalid);
offset as isize
}};
}
/// A soft limit on the amount of references that may be made to an `Arc`.
///
/// Going above this limit will abort your program (although not
@ -196,6 +177,14 @@ struct ArcInner<T: ?Sized> {
unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
/// Computes the offset of the data field within ArcInner.
fn data_offset<T>() -> usize {
let size = size_of::<ArcInner<()>>();
let align = align_of::<T>();
// https://github.com/rust-lang/rust/blob/1.36.0/src/libcore/alloc.rs#L187-L207
size.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1)
}
impl<T> Arc<T> {
/// Construct an `Arc<T>`
#[inline]
@ -251,7 +240,7 @@ impl<T> Arc<T> {
unsafe fn from_raw(ptr: *const T) -> Self {
// To find the corresponding pointer to the `ArcInner` we need
// to subtract the offset of the `data` field from the pointer.
let ptr = (ptr as *const u8).offset(-offset_of!(ArcInner<T>, data));
let ptr = (ptr as *const u8).sub(data_offset::<T>());
Arc {
p: ptr::NonNull::new_unchecked(ptr as *mut ArcInner<T>),
phantom: PhantomData,