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Auto merge of #54668 - RalfJung:use-maybe-uninit, r=SimonSapin
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Use MaybeUninit in libcore

All code by @japaric. This re-submits the second half of #53508 (the first half is at #54667). This is likely the one containing the perf regression.
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@bors
bors committed Nov 26, 2018
2 parents 6bfb46e + 59786b0 commit 75d937c
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Showing 5 changed files with 53 additions and 52 deletions.
27 changes: 14 additions & 13 deletions src/libcore/fmt/float.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
// except according to those terms.

use fmt::{Formatter, Result, LowerExp, UpperExp, Display, Debug};
use mem;
use mem::MaybeUninit;
use num::flt2dec;

// Don't inline this so callers don't use the stack space this function
Expand All @@ -20,11 +20,11 @@ fn float_to_decimal_common_exact<T>(fmt: &mut Formatter, num: &T,
where T: flt2dec::DecodableFloat
{
unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 4] = mem::uninitialized();
let mut buf = MaybeUninit::<[u8; 1024]>::uninitialized(); // enough for f32 and f64
let mut parts = MaybeUninit::<[flt2dec::Part; 4]>::uninitialized();
let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
false, &mut buf, &mut parts);
false, buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted)
}
}
Expand All @@ -38,10 +38,11 @@ fn float_to_decimal_common_shortest<T>(fmt: &mut Formatter, num: &T,
{
unsafe {
// enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
let mut parts: [flt2dec::Part; 4] = mem::uninitialized();
let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninitialized();
let mut parts = MaybeUninit::<[flt2dec::Part; 4]>::uninitialized();
let formatted = flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num,
sign, precision, false, &mut buf, &mut parts);
sign, precision, false, buf.get_mut(),
parts.get_mut());
fmt.pad_formatted_parts(&formatted)
}
}
Expand Down Expand Up @@ -75,11 +76,11 @@ fn float_to_exponential_common_exact<T>(fmt: &mut Formatter, num: &T,
where T: flt2dec::DecodableFloat
{
unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 6] = mem::uninitialized();
let mut buf = MaybeUninit::<[u8; 1024]>::uninitialized(); // enough for f32 and f64
let mut parts = MaybeUninit::<[flt2dec::Part; 6]>::uninitialized();
let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
upper, &mut buf, &mut parts);
upper, buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted)
}
}
Expand All @@ -94,11 +95,11 @@ fn float_to_exponential_common_shortest<T>(fmt: &mut Formatter,
{
unsafe {
// enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
let mut parts: [flt2dec::Part; 6] = mem::uninitialized();
let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninitialized();
let mut parts = MaybeUninit::<[flt2dec::Part; 6]>::uninitialized();
let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest,
*num, sign, (0, 0), upper,
&mut buf, &mut parts);
buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted)
}
}
Expand Down
17 changes: 13 additions & 4 deletions src/libcore/mem.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -950,7 +950,7 @@ impl<T> ManuallyDrop<T> {
/// ManuallyDrop::new(Box::new(()));
/// ```
#[stable(feature = "manually_drop", since = "1.20.0")]
#[inline]
#[inline(always)]
pub const fn new(value: T) -> ManuallyDrop<T> {
ManuallyDrop { value }
}
Expand All @@ -967,7 +967,7 @@ impl<T> ManuallyDrop<T> {
/// let _: Box<()> = ManuallyDrop::into_inner(x); // This drops the `Box`.
/// ```
#[stable(feature = "manually_drop", since = "1.20.0")]
#[inline]
#[inline(always)]
pub const fn into_inner(slot: ManuallyDrop<T>) -> T {
slot.value
}
Expand Down Expand Up @@ -1015,15 +1015,15 @@ impl<T: ?Sized> ManuallyDrop<T> {
#[stable(feature = "manually_drop", since = "1.20.0")]
impl<T: ?Sized> Deref for ManuallyDrop<T> {
type Target = T;
#[inline]
#[inline(always)]
fn deref(&self) -> &T {
&self.value
}
}

#[stable(feature = "manually_drop", since = "1.20.0")]
impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
#[inline]
#[inline(always)]
fn deref_mut(&mut self) -> &mut T {
&mut self.value
}
Expand All @@ -1044,6 +1044,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code.
/// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub const fn new(val: T) -> MaybeUninit<T> {
MaybeUninit { value: ManuallyDrop::new(val) }
}
Expand All @@ -1053,6 +1054,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code.
/// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub const fn uninitialized() -> MaybeUninit<T> {
MaybeUninit { uninit: () }
}
Expand All @@ -1066,6 +1068,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code.
/// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline]
pub fn zeroed() -> MaybeUninit<T> {
let mut u = MaybeUninit::<T>::uninitialized();
unsafe {
Expand All @@ -1076,6 +1079,7 @@ impl<T> MaybeUninit<T> {

/// Set the value of the `MaybeUninit`. This overwrites any previous value without dropping it.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn set(&mut self, val: T) {
unsafe {
self.value = ManuallyDrop::new(val);
Expand All @@ -1091,6 +1095,7 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn into_inner(self) -> T {
ManuallyDrop::into_inner(self.value)
}
Expand All @@ -1102,6 +1107,7 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn get_ref(&self) -> &T {
&*self.value
}
Expand All @@ -1113,20 +1119,23 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn get_mut(&mut self) -> &mut T {
&mut *self.value
}

/// Get a pointer to the contained value. Reading from this pointer will be undefined
/// behavior unless the `MaybeUninit` is initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn as_ptr(&self) -> *const T {
unsafe { &*self.value as *const T }
}

/// Get a mutable pointer to the contained value. Reading from this pointer will be undefined
/// behavior unless the `MaybeUninit` is initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn as_mut_ptr(&mut self) -> *mut T {
unsafe { &mut *self.value as *mut T }
}
Expand Down
35 changes: 16 additions & 19 deletions src/libcore/ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -79,7 +79,7 @@ use ops::{CoerceUnsized, DispatchFromDyn};
use fmt;
use hash;
use marker::{PhantomData, Unsize};
use mem;
use mem::{self, MaybeUninit};
use nonzero::NonZero;

use cmp::Ordering::{self, Less, Equal, Greater};
Expand Down Expand Up @@ -295,17 +295,14 @@ pub const fn null_mut<T>() -> *mut T { 0 as *mut T }
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
// Give ourselves some scratch space to work with
let mut tmp: T = mem::uninitialized();
// Give ourselves some scratch space to work with.
// We do not have to worry about drops: `MaybeUninit` does nothing when dropped.
let mut tmp = MaybeUninit::<T>::uninitialized();

// Perform the swap
copy_nonoverlapping(x, &mut tmp, 1);
copy_nonoverlapping(x, tmp.as_mut_ptr(), 1);
copy(y, x, 1); // `x` and `y` may overlap
copy_nonoverlapping(&tmp, y, 1);

// y and t now point to the same thing, but we need to completely forget `tmp`
// because it's no longer relevant.
mem::forget(tmp);
copy_nonoverlapping(tmp.get_ref(), y, 1);
}

/// Swaps `count * size_of::<T>()` bytes between the two regions of memory
Expand Down Expand Up @@ -392,8 +389,8 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {
while i + block_size <= len {
// Create some uninitialized memory as scratch space
// Declaring `t` here avoids aligning the stack when this loop is unused
let mut t: Block = mem::uninitialized();
let t = &mut t as *mut _ as *mut u8;
let mut t = mem::MaybeUninit::<Block>::uninitialized();
let t = t.as_mut_ptr() as *mut u8;
let x = x.add(i);
let y = y.add(i);

Expand All @@ -407,10 +404,10 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {

if i < len {
// Swap any remaining bytes
let mut t: UnalignedBlock = mem::uninitialized();
let mut t = mem::MaybeUninit::<UnalignedBlock>::uninitialized();
let rem = len - i;

let t = &mut t as *mut _ as *mut u8;
let t = t.as_mut_ptr() as *mut u8;
let x = x.add(i);
let y = y.add(i);

Expand Down Expand Up @@ -575,9 +572,9 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn read<T>(src: *const T) -> T {
let mut tmp: T = mem::uninitialized();
copy_nonoverlapping(src, &mut tmp, 1);
tmp
let mut tmp = MaybeUninit::<T>::uninitialized();
copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
tmp.into_inner()
}

/// Reads the value from `src` without moving it. This leaves the
Expand Down Expand Up @@ -642,11 +639,11 @@ pub unsafe fn read<T>(src: *const T) -> T {
#[inline]
#[stable(feature = "ptr_unaligned", since = "1.17.0")]
pub unsafe fn read_unaligned<T>(src: *const T) -> T {
let mut tmp: T = mem::uninitialized();
let mut tmp = MaybeUninit::<T>::uninitialized();
copy_nonoverlapping(src as *const u8,
&mut tmp as *mut T as *mut u8,
tmp.as_mut_ptr() as *mut u8,
mem::size_of::<T>());
tmp
tmp.into_inner()
}

/// Overwrites a memory location with the given value without reading or
Expand Down
12 changes: 3 additions & 9 deletions src/libcore/slice/rotate.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
// except according to those terms.

use cmp;
use mem;
use mem::{self, MaybeUninit};
use ptr;

/// Rotation is much faster if it has access to a little bit of memory. This
Expand All @@ -26,12 +26,6 @@ union RawArray<T> {
}

impl<T> RawArray<T> {
fn new() -> Self {
unsafe { mem::uninitialized() }
}
fn ptr(&self) -> *mut T {
unsafe { &self.typed as *const T as *mut T }
}
fn cap() -> usize {
if mem::size_of::<T>() == 0 {
usize::max_value()
Expand Down Expand Up @@ -88,8 +82,8 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mid: *mut T, mut right: usize) {
}
}

let rawarray = RawArray::new();
let buf = rawarray.ptr();
let mut rawarray = MaybeUninit::<RawArray<T>>::uninitialized();
let buf = &mut (*rawarray.as_mut_ptr()).typed as *mut [T; 2] as *mut T;

let dim = mid.sub(left).add(right);
if left <= right {
Expand Down
14 changes: 7 additions & 7 deletions src/libcore/slice/sort.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@
//! stable sorting implementation.

use cmp;
use mem;
use mem::{self, MaybeUninit};
use ptr;

/// When dropped, copies from `src` into `dest`.
Expand Down Expand Up @@ -226,14 +226,14 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
let mut block_l = BLOCK;
let mut start_l = ptr::null_mut();
let mut end_l = ptr::null_mut();
let mut offsets_l: [u8; BLOCK] = unsafe { mem::uninitialized() };
let mut offsets_l = MaybeUninit::<[u8; BLOCK]>::uninitialized();

// The current block on the right side (from `r.sub(block_r)` to `r`).
let mut r = unsafe { l.add(v.len()) };
let mut block_r = BLOCK;
let mut start_r = ptr::null_mut();
let mut end_r = ptr::null_mut();
let mut offsets_r: [u8; BLOCK] = unsafe { mem::uninitialized() };
let mut offsets_r = MaybeUninit::<[u8; BLOCK]>::uninitialized();

// FIXME: When we get VLAs, try creating one array of length `min(v.len(), 2 * BLOCK)` rather
// than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.
Expand Down Expand Up @@ -272,8 +272,8 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize

if start_l == end_l {
// Trace `block_l` elements from the left side.
start_l = offsets_l.as_mut_ptr();
end_l = offsets_l.as_mut_ptr();
start_l = offsets_l.as_mut_ptr() as *mut u8;
end_l = offsets_l.as_mut_ptr() as *mut u8;
let mut elem = l;

for i in 0..block_l {
Expand All @@ -288,8 +288,8 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize

if start_r == end_r {
// Trace `block_r` elements from the right side.
start_r = offsets_r.as_mut_ptr();
end_r = offsets_r.as_mut_ptr();
start_r = offsets_r.as_mut_ptr() as *mut u8;
end_r = offsets_r.as_mut_ptr() as *mut u8;
let mut elem = r;

for i in 0..block_r {
Expand Down

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