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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 https://github.com/rust-lang/rust/pull/53508 (the first half is at https://github.com/rust-lang/rust/pull/54667). This is likely the one containing the perf regression.
This commit is contained in:
bors 2018-11-26 22:20:20 +00:00
commit 75d937c49b
5 changed files with 53 additions and 52 deletions
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27
src/libcore/fmt/float.rs
View File

@ -9,7 +9,7 @@
// except according to those terms. // except according to those terms.
use fmt::{Formatter, Result, LowerExp, UpperExp, Display, Debug}; use fmt::{Formatter, Result, LowerExp, UpperExp, Display, Debug};
use mem; use mem::MaybeUninit;
use num::flt2dec; use num::flt2dec;
// Don't inline this so callers don't use the stack space this function // Don't inline this so callers don't use the stack space this function
@ -20,11 +20,11 @@ fn float_to_decimal_common_exact<T>(fmt: &mut Formatter, num: &T,
where T: flt2dec::DecodableFloat where T: flt2dec::DecodableFloat
{ {
unsafe { unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64 let mut buf = MaybeUninit::<[u8; 1024]>::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 4] = mem::uninitialized(); let mut parts = MaybeUninit::<[flt2dec::Part; 4]>::uninitialized();
let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact, let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision, *num, sign, precision,
false, &mut buf, &mut parts); false, buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted) fmt.pad_formatted_parts(&formatted)
} }
} }
@ -38,10 +38,11 @@ fn float_to_decimal_common_shortest<T>(fmt: &mut Formatter, num: &T,
{ {
unsafe { unsafe {
// enough for f32 and f64 // enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized(); let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninitialized();
let mut parts: [flt2dec::Part; 4] = mem::uninitialized(); let mut parts = MaybeUninit::<[flt2dec::Part; 4]>::uninitialized();
let formatted = flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num, 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) fmt.pad_formatted_parts(&formatted)
} }
} }
@ -75,11 +76,11 @@ fn float_to_exponential_common_exact<T>(fmt: &mut Formatter, num: &T,
where T: flt2dec::DecodableFloat where T: flt2dec::DecodableFloat
{ {
unsafe { unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64 let mut buf = MaybeUninit::<[u8; 1024]>::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 6] = mem::uninitialized(); let mut parts = MaybeUninit::<[flt2dec::Part; 6]>::uninitialized();
let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact, let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision, *num, sign, precision,
upper, &mut buf, &mut parts); upper, buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted) fmt.pad_formatted_parts(&formatted)
} }
} }
@ -94,11 +95,11 @@ fn float_to_exponential_common_shortest<T>(fmt: &mut Formatter,
{ {
unsafe { unsafe {
// enough for f32 and f64 // enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized(); let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninitialized();
let mut parts: [flt2dec::Part; 6] = mem::uninitialized(); let mut parts = MaybeUninit::<[flt2dec::Part; 6]>::uninitialized();
let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest,
*num, sign, (0, 0), upper, *num, sign, (0, 0), upper,
&mut buf, &mut parts); buf.get_mut(), parts.get_mut());
fmt.pad_formatted_parts(&formatted) fmt.pad_formatted_parts(&formatted)
} }
} }

17
src/libcore/mem.rs
View File

@ -950,7 +950,7 @@ impl<T> ManuallyDrop<T> {
/// ManuallyDrop::new(Box::new(())); /// ManuallyDrop::new(Box::new(()));
/// ``` /// ```
#[stable(feature = "manually_drop", since = "1.20.0")] #[stable(feature = "manually_drop", since = "1.20.0")]
#[inline] #[inline(always)]
pub const fn new(value: T) -> ManuallyDrop<T> { pub const fn new(value: T) -> ManuallyDrop<T> {
ManuallyDrop { value } ManuallyDrop { value }
} }
@ -967,7 +967,7 @@ impl<T> ManuallyDrop<T> {
/// let _: Box<()> = ManuallyDrop::into_inner(x); // This drops the `Box`. /// let _: Box<()> = ManuallyDrop::into_inner(x); // This drops the `Box`.
/// ``` /// ```
#[stable(feature = "manually_drop", since = "1.20.0")] #[stable(feature = "manually_drop", since = "1.20.0")]
#[inline] #[inline(always)]
pub const fn into_inner(slot: ManuallyDrop<T>) -> T { pub const fn into_inner(slot: ManuallyDrop<T>) -> T {
slot.value slot.value
} }
@ -1015,7 +1015,7 @@ impl<T: ?Sized> ManuallyDrop<T> {
#[stable(feature = "manually_drop", since = "1.20.0")] #[stable(feature = "manually_drop", since = "1.20.0")]
impl<T: ?Sized> Deref for ManuallyDrop<T> { impl<T: ?Sized> Deref for ManuallyDrop<T> {
type Target = T; type Target = T;
#[inline] #[inline(always)]
fn deref(&self) -> &T { fn deref(&self) -> &T {
&self.value &self.value
} }
@ -1023,7 +1023,7 @@ impl<T: ?Sized> Deref for ManuallyDrop<T> {
#[stable(feature = "manually_drop", since = "1.20.0")] #[stable(feature = "manually_drop", since = "1.20.0")]
impl<T: ?Sized> DerefMut for ManuallyDrop<T> { impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
#[inline] #[inline(always)]
fn deref_mut(&mut self) -> &mut T { fn deref_mut(&mut self) -> &mut T {
&mut self.value &mut self.value
} }
@ -1044,6 +1044,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code. /// 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. /// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub const fn new(val: T) -> MaybeUninit<T> { pub const fn new(val: T) -> MaybeUninit<T> {
MaybeUninit { value: ManuallyDrop::new(val) } MaybeUninit { value: ManuallyDrop::new(val) }
} }
@ -1053,6 +1054,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code. /// 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. /// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub const fn uninitialized() -> MaybeUninit<T> { pub const fn uninitialized() -> MaybeUninit<T> {
MaybeUninit { uninit: () } MaybeUninit { uninit: () }
} }
@ -1066,6 +1068,7 @@ impl<T> MaybeUninit<T> {
/// Note that dropping a `MaybeUninit` will never call `T`'s drop code. /// 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. /// It is your responsibility to make sure `T` gets dropped if it got initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline]
pub fn zeroed() -> MaybeUninit<T> { pub fn zeroed() -> MaybeUninit<T> {
let mut u = MaybeUninit::<T>::uninitialized(); let mut u = MaybeUninit::<T>::uninitialized();
unsafe { unsafe {
@ -1076,6 +1079,7 @@ impl<T> MaybeUninit<T> {
/// Set the value of the `MaybeUninit`. This overwrites any previous value without dropping it. /// Set the value of the `MaybeUninit`. This overwrites any previous value without dropping it.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn set(&mut self, val: T) { pub fn set(&mut self, val: T) {
unsafe { unsafe {
self.value = ManuallyDrop::new(val); self.value = ManuallyDrop::new(val);
@ -1091,6 +1095,7 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized /// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior. /// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn into_inner(self) -> T { pub unsafe fn into_inner(self) -> T {
ManuallyDrop::into_inner(self.value) ManuallyDrop::into_inner(self.value)
} }
@ -1102,6 +1107,7 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized /// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior. /// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn get_ref(&self) -> &T { pub unsafe fn get_ref(&self) -> &T {
&*self.value &*self.value
} }
@ -1113,6 +1119,7 @@ impl<T> MaybeUninit<T> {
/// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized /// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
/// state, otherwise this will immediately cause undefined behavior. /// state, otherwise this will immediately cause undefined behavior.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub unsafe fn get_mut(&mut self) -> &mut T { pub unsafe fn get_mut(&mut self) -> &mut T {
&mut *self.value &mut *self.value
} }
@ -1120,6 +1127,7 @@ impl<T> MaybeUninit<T> {
/// Get a pointer to the contained value. Reading from this pointer will be undefined /// Get a pointer to the contained value. Reading from this pointer will be undefined
/// behavior unless the `MaybeUninit` is initialized. /// behavior unless the `MaybeUninit` is initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn as_ptr(&self) -> *const T { pub fn as_ptr(&self) -> *const T {
unsafe { &*self.value as *const T } unsafe { &*self.value as *const T }
} }
@ -1127,6 +1135,7 @@ impl<T> MaybeUninit<T> {
/// Get a mutable pointer to the contained value. Reading from this pointer will be undefined /// Get a mutable pointer to the contained value. Reading from this pointer will be undefined
/// behavior unless the `MaybeUninit` is initialized. /// behavior unless the `MaybeUninit` is initialized.
#[unstable(feature = "maybe_uninit", issue = "53491")] #[unstable(feature = "maybe_uninit", issue = "53491")]
#[inline(always)]
pub fn as_mut_ptr(&mut self) -> *mut T { pub fn as_mut_ptr(&mut self) -> *mut T {
unsafe { &mut *self.value as *mut T } unsafe { &mut *self.value as *mut T }
} }

35
src/libcore/ptr.rs
View File

@ -79,7 +79,7 @@ use ops::{CoerceUnsized, DispatchFromDyn};
use fmt; use fmt;
use hash; use hash;
use marker::{PhantomData, Unsize}; use marker::{PhantomData, Unsize};
use mem; use mem::{self, MaybeUninit};
use nonzero::NonZero; use nonzero::NonZero;
use cmp::Ordering::{self, Less, Equal, Greater}; use cmp::Ordering::{self, Less, Equal, Greater};
@ -295,17 +295,14 @@ pub const fn null_mut<T>() -> *mut T { 0 as *mut T }
#[inline] #[inline]
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn swap<T>(x: *mut T, y: *mut T) { pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
// Give ourselves some scratch space to work with // Give ourselves some scratch space to work with.
let mut tmp: T = mem::uninitialized(); // We do not have to worry about drops: `MaybeUninit` does nothing when dropped.
let mut tmp = MaybeUninit::<T>::uninitialized();
// Perform the swap // 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(y, x, 1); // `x` and `y` may overlap
copy_nonoverlapping(&tmp, y, 1); copy_nonoverlapping(tmp.get_ref(), 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);
} }
/// Swaps `count * size_of::<T>()` bytes between the two regions of memory /// Swaps `count * size_of::<T>()` bytes between the two regions of memory
@ -392,8 +389,8 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {
while i + block_size <= len { while i + block_size <= len {
// Create some uninitialized memory as scratch space // Create some uninitialized memory as scratch space
// Declaring `t` here avoids aligning the stack when this loop is unused // Declaring `t` here avoids aligning the stack when this loop is unused
let mut t: Block = mem::uninitialized(); let mut t = mem::MaybeUninit::<Block>::uninitialized();
let t = &mut t as *mut _ as *mut u8; let t = t.as_mut_ptr() as *mut u8;
let x = x.add(i); let x = x.add(i);
let y = y.add(i); let y = y.add(i);
@ -407,10 +404,10 @@ unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) {
if i < len { if i < len {
// Swap any remaining bytes // Swap any remaining bytes
let mut t: UnalignedBlock = mem::uninitialized(); let mut t = mem::MaybeUninit::<UnalignedBlock>::uninitialized();
let rem = len - i; 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 x = x.add(i);
let y = y.add(i); let y = y.add(i);
@ -575,9 +572,9 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
#[inline] #[inline]
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn read<T>(src: *const T) -> T { pub unsafe fn read<T>(src: *const T) -> T {
let mut tmp: T = mem::uninitialized(); let mut tmp = MaybeUninit::<T>::uninitialized();
copy_nonoverlapping(src, &mut tmp, 1); copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
tmp tmp.into_inner()
} }
/// Reads the value from `src` without moving it. This leaves the /// Reads the value from `src` without moving it. This leaves the
@ -642,11 +639,11 @@ pub unsafe fn read<T>(src: *const T) -> T {
#[inline] #[inline]
#[stable(feature = "ptr_unaligned", since = "1.17.0")] #[stable(feature = "ptr_unaligned", since = "1.17.0")]
pub unsafe fn read_unaligned<T>(src: *const T) -> T { 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, 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>()); mem::size_of::<T>());
tmp tmp.into_inner()
} }
/// Overwrites a memory location with the given value without reading or /// Overwrites a memory location with the given value without reading or

12
src/libcore/slice/rotate.rs
View File

@ -9,7 +9,7 @@
// except according to those terms. // except according to those terms.
use cmp; use cmp;
use mem; use mem::{self, MaybeUninit};
use ptr; use ptr;
/// Rotation is much faster if it has access to a little bit of memory. This /// Rotation is much faster if it has access to a little bit of memory. This
@ -26,12 +26,6 @@ union RawArray<T> {
} }
impl<T> 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 { fn cap() -> usize {
if mem::size_of::<T>() == 0 { if mem::size_of::<T>() == 0 {
usize::max_value() usize::max_value()
@ -88,8 +82,8 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mid: *mut T, mut right: usize) {
} }
} }
let rawarray = RawArray::new(); let mut rawarray = MaybeUninit::<RawArray<T>>::uninitialized();
let buf = rawarray.ptr(); let buf = &mut (*rawarray.as_mut_ptr()).typed as *mut [T; 2] as *mut T;
let dim = mid.sub(left).add(right); let dim = mid.sub(left).add(right);
if left <= right { if left <= right {

14
src/libcore/slice/sort.rs
View File

@ -17,7 +17,7 @@
//! stable sorting implementation. //! stable sorting implementation.
use cmp; use cmp;
use mem; use mem::{self, MaybeUninit};
use ptr; use ptr;
/// When dropped, copies from `src` into `dest`. /// When dropped, copies from `src` into `dest`.
@ -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 block_l = BLOCK;
let mut start_l = ptr::null_mut(); let mut start_l = ptr::null_mut();
let mut end_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`). // The current block on the right side (from `r.sub(block_r)` to `r`).
let mut r = unsafe { l.add(v.len()) }; let mut r = unsafe { l.add(v.len()) };
let mut block_r = BLOCK; let mut block_r = BLOCK;
let mut start_r = ptr::null_mut(); let mut start_r = ptr::null_mut();
let mut end_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 // 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. // than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.
@ -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 { if start_l == end_l {
// Trace `block_l` elements from the left side. // Trace `block_l` elements from the left side.
start_l = offsets_l.as_mut_ptr(); start_l = offsets_l.as_mut_ptr() as *mut u8;
end_l = offsets_l.as_mut_ptr(); end_l = offsets_l.as_mut_ptr() as *mut u8;
let mut elem = l; let mut elem = l;
for i in 0..block_l { for i in 0..block_l {
@ -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 { if start_r == end_r {
// Trace `block_r` elements from the right side. // Trace `block_r` elements from the right side.
start_r = offsets_r.as_mut_ptr(); start_r = offsets_r.as_mut_ptr() as *mut u8;
end_r = offsets_r.as_mut_ptr(); end_r = offsets_r.as_mut_ptr() as *mut u8;
let mut elem = r; let mut elem = r;
for i in 0..block_r { for i in 0..block_r {