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Overhaul of the AllocRef trait to match allocator-wg's latest consens #69889

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111 changes: 78 additions & 33 deletions src/liballoc/alloc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

#![stable(feature = "alloc_module", since = "1.28.0")]

use core::intrinsics::{min_align_of_val, size_of_val};
use core::intrinsics::{self, min_align_of_val, size_of_val};
use core::ptr::{NonNull, Unique};
use core::usize;

Expand Down Expand Up @@ -165,11 +165,19 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
#[unstable(feature = "allocator_api", issue = "32838")]
unsafe impl AllocRef for Global {
#[inline]
fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
fn alloc(&mut self, layout: Layout, init: AllocInit) -> Result<(NonNull<u8>, usize), AllocErr> {
let new_size = layout.size();
if new_size == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe { NonNull::new(alloc(layout)).ok_or(AllocErr).map(|p| (p, layout.size())) }
unsafe {
let raw_ptr = match init {
AllocInit::Uninitialized => alloc(layout),
AllocInit::Zeroed => alloc_zeroed(layout),
};
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok((ptr, new_size))
}
}
}

Expand All @@ -181,33 +189,77 @@ unsafe impl AllocRef for Global {
}

#[inline]
unsafe fn realloc(
unsafe fn grow(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
placement: ReallocPlacement,
init: AllocInit,
) -> Result<(NonNull<u8>, usize), AllocErr> {
match (layout.size(), new_size) {
(0, 0) => Ok((layout.dangling(), 0)),
(0, _) => self.alloc(Layout::from_size_align_unchecked(new_size, layout.align())),
(_, 0) => {
self.dealloc(ptr, layout);
Ok((layout.dangling(), 0))
let old_size = layout.size();
debug_assert!(
new_size >= old_size,
"`new_size` must be greater than or equal to `layout.size()`"
);

if old_size == new_size {
return Ok((ptr, new_size));
}

match placement {
ReallocPlacement::MayMove => {
if old_size == 0 {
self.alloc(Layout::from_size_align_unchecked(new_size, layout.align()), init)
} else {
// `realloc` probably checks for `new_size > old_size` or something similar.
// `new_size` must be greater than or equal to `old_size` due to the safety constraint,
// and `new_size` == `old_size` was caught before
intrinsics::assume(new_size > old_size);
let ptr =
NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)?;
let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
init.initialize_offset(ptr, new_layout, old_size);
Ok((ptr, new_size))
}
}
(_, _) => NonNull::new(realloc(ptr.as_ptr(), layout, new_size))
.ok_or(AllocErr)
.map(|p| (p, new_size)),
ReallocPlacement::InPlace => Err(AllocErr),
}
}

#[inline]
fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe {
NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
unsafe fn shrink(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
placement: ReallocPlacement,
) -> Result<(NonNull<u8>, usize), AllocErr> {
let old_size = layout.size();
debug_assert!(
new_size <= old_size,
"`new_size` must be smaller than or equal to `layout.size()`"
);

if old_size == new_size {
return Ok((ptr, new_size));
}

match placement {
ReallocPlacement::MayMove => {
let ptr = if new_size == 0 {
self.dealloc(ptr, layout);
layout.dangling()
} else {
// `realloc` probably checks for `new_size > old_size` or something similar.
// `new_size` must be smaller than or equal to `old_size` due to the safety constraint,
// and `new_size` == `old_size` was caught before
intrinsics::assume(new_size < old_size);
NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)?
};
Ok((ptr, new_size))
}
ReallocPlacement::InPlace => Err(AllocErr),
}
}
}
Expand All @@ -218,14 +270,10 @@ unsafe impl AllocRef for Global {
#[lang = "exchange_malloc"]
#[inline]
unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
if size == 0 {
align as *mut u8
} else {
let layout = Layout::from_size_align_unchecked(size, align);
match Global.alloc(layout) {
Ok((ptr, _)) => ptr.as_ptr(),
Err(_) => handle_alloc_error(layout),
}
let layout = Layout::from_size_align_unchecked(size, align);
match Global.alloc(layout, AllocInit::Uninitialized) {
Ok((ptr, _)) => ptr.as_ptr(),
Err(_) => handle_alloc_error(layout),
}
}

Expand All @@ -239,11 +287,8 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
let size = size_of_val(ptr.as_ref());
let align = min_align_of_val(ptr.as_ref());
// We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
if size != 0 {
let layout = Layout::from_size_align_unchecked(size, align);
Global.dealloc(ptr.cast().into(), layout);
}
let layout = Layout::from_size_align_unchecked(size, align);
Global.dealloc(ptr.cast().into(), layout)
}

/// Abort on memory allocation error or failure.
Expand Down
5 changes: 3 additions & 2 deletions src/liballoc/alloc/tests.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,9 @@ use test::Bencher;
fn allocate_zeroed() {
unsafe {
let layout = Layout::from_size_align(1024, 1).unwrap();
let (ptr, _) =
Global.alloc_zeroed(layout.clone()).unwrap_or_else(|_| handle_alloc_error(layout));
let (ptr, _) = Global
.alloc(layout.clone(), AllocInit::Zeroed)
.unwrap_or_else(|_| handle_alloc_error(layout));

let mut i = ptr.cast::<u8>().as_ptr();
let end = i.add(layout.size());
Expand Down
44 changes: 21 additions & 23 deletions src/liballoc/boxed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -146,7 +146,7 @@ use core::ptr::{self, NonNull, Unique};
use core::slice;
use core::task::{Context, Poll};

use crate::alloc::{self, AllocRef, Global};
use crate::alloc::{self, AllocInit, AllocRef, Global};
use crate::raw_vec::RawVec;
use crate::str::from_boxed_utf8_unchecked;
use crate::vec::Vec;
Expand Down Expand Up @@ -196,14 +196,12 @@ impl<T> Box<T> {
#[unstable(feature = "new_uninit", issue = "63291")]
pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
let layout = alloc::Layout::new::<mem::MaybeUninit<T>>();
unsafe {
let ptr = if layout.size() == 0 {
NonNull::dangling()
} else {
Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).0.cast()
};
Box::from_raw(ptr.as_ptr())
}
let ptr = Global
.alloc(layout, AllocInit::Uninitialized)
.unwrap_or_else(|_| alloc::handle_alloc_error(layout))
.0
.cast();
unsafe { Box::from_raw(ptr.as_ptr()) }
}

/// Constructs a new `Box` with uninitialized contents, with the memory
Expand All @@ -226,11 +224,13 @@ impl<T> Box<T> {
/// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed
#[unstable(feature = "new_uninit", issue = "63291")]
pub fn new_zeroed() -> Box<mem::MaybeUninit<T>> {
unsafe {
let mut uninit = Self::new_uninit();
ptr::write_bytes::<T>(uninit.as_mut_ptr(), 0, 1);
uninit
}
let layout = alloc::Layout::new::<mem::MaybeUninit<T>>();
let ptr = Global
.alloc(layout, AllocInit::Zeroed)
.unwrap_or_else(|_| alloc::handle_alloc_error(layout))
.0
.cast();
unsafe { Box::from_raw(ptr.as_ptr()) }
}

/// Constructs a new `Pin<Box<T>>`. If `T` does not implement `Unpin`, then
Expand Down Expand Up @@ -266,14 +266,12 @@ impl<T> Box<[T]> {
#[unstable(feature = "new_uninit", issue = "63291")]
pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
let layout = alloc::Layout::array::<mem::MaybeUninit<T>>(len).unwrap();
unsafe {
let ptr = if layout.size() == 0 {
NonNull::dangling()
} else {
Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).0.cast()
};
Box::from_raw(slice::from_raw_parts_mut(ptr.as_ptr(), len))
}
let ptr = Global
.alloc(layout, AllocInit::Uninitialized)
.unwrap_or_else(|_| alloc::handle_alloc_error(layout))
.0
.cast();
unsafe { Box::from_raw(slice::from_raw_parts_mut(ptr.as_ptr(), len)) }
}
}

Expand Down Expand Up @@ -778,7 +776,7 @@ impl<T: Copy> From<&[T]> for Box<[T]> {
let buf = RawVec::with_capacity(len);
unsafe {
ptr::copy_nonoverlapping(slice.as_ptr(), buf.ptr(), len);
buf.into_box()
buf.into_box().assume_init()
}
}
}
Expand Down
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