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Auto merge of #75657 - TimDiekmann:allocref-cleanup, r=Amanieu
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Clean up AllocRef implementation and documentation

r? @Amanieu
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@bors
bors committed Aug 18, 2020
2 parents b287b56 + 63d241a commit be97d13
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Showing 3 changed files with 183 additions and 178 deletions.
148 changes: 74 additions & 74 deletions library/alloc/src/alloc.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -161,30 +161,69 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
}

impl Global {
#[inline]
fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
match layout.size() {
0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
// SAFETY: `layout` is non-zero in size,
size => unsafe {
let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok(NonNull::slice_from_raw_parts(ptr, size))
},
}
}

// Safety: Same as `AllocRef::grow`
#[inline]
unsafe fn grow_impl(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
zeroed: bool,
) -> Result<NonNull<[u8]>, AllocErr> {
debug_assert!(
new_size >= layout.size(),
"`new_size` must be greater than or equal to `layout.size()`"
);

match layout.size() {
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
0 => unsafe {
let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
self.alloc_impl(new_layout, zeroed)
},

// SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
// as required by safety conditions. Other conditions must be upheld by the caller
old_size => unsafe {
// `realloc` probably checks for `new_size >= size` or something similar.
intrinsics::assume(new_size >= layout.size());

let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
if zeroed {
raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
}
Ok(NonNull::slice_from_raw_parts(ptr, new_size))
},
}
}
}

#[unstable(feature = "allocator_api", issue = "32838")]
unsafe impl AllocRef for Global {
#[inline]
fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
let size = layout.size();
let ptr = if size == 0 {
layout.dangling()
} else {
// SAFETY: `layout` is non-zero in size,
unsafe { NonNull::new(alloc(layout)).ok_or(AllocErr)? }
};
Ok(NonNull::slice_from_raw_parts(ptr, size))
self.alloc_impl(layout, false)
}

#[inline]
fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
let size = layout.size();
let ptr = if size == 0 {
layout.dangling()
} else {
// SAFETY: `layout` is non-zero in size,
unsafe { NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr)? }
};
Ok(NonNull::slice_from_raw_parts(ptr, size))
self.alloc_impl(layout, true)
}

#[inline]
Expand All @@ -203,26 +242,8 @@ unsafe impl AllocRef for Global {
layout: Layout,
new_size: usize,
) -> Result<NonNull<[u8]>, AllocErr> {
debug_assert!(
new_size >= layout.size(),
"`new_size` must be greater than or equal to `layout.size()`"
);

// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, then `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
0 => self.alloc(Layout::from_size_align_unchecked(new_size, layout.align())),
old_size => {
// `realloc` probably checks for `new_size >= size` or something similar.
intrinsics::assume(new_size >= old_size);
let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok(NonNull::slice_from_raw_parts(ptr, new_size))
}
}
}
// SAFETY: all conditions must be upheld by the caller
unsafe { self.grow_impl(ptr, layout, new_size, false) }
}

#[inline]
Expand All @@ -232,27 +253,8 @@ unsafe impl AllocRef for Global {
layout: Layout,
new_size: usize,
) -> Result<NonNull<[u8]>, AllocErr> {
debug_assert!(
new_size >= layout.size(),
"`new_size` must be greater than or equal to `layout.size()`"
);

// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, then `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
0 => self.alloc_zeroed(Layout::from_size_align_unchecked(new_size, layout.align())),
old_size => {
// `realloc` probably checks for `new_size >= size` or something similar.
intrinsics::assume(new_size >= old_size);
let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok(NonNull::slice_from_raw_parts(ptr, new_size))
}
}
}
// SAFETY: all conditions must be upheld by the caller
unsafe { self.grow_impl(ptr, layout, new_size, true) }
}

#[inline]
Expand All @@ -262,30 +264,28 @@ unsafe impl AllocRef for Global {
layout: Layout,
new_size: usize,
) -> Result<NonNull<[u8]>, AllocErr> {
let old_size = layout.size();
debug_assert!(
new_size <= old_size,
new_size <= layout.size(),
"`new_size` must be smaller than or equal to `layout.size()`"
);

let ptr = if new_size == 0 {
match new_size {
// SAFETY: conditions must be upheld by the caller
unsafe {
0 => unsafe {
self.dealloc(ptr, layout);
}
layout.dangling()
} else {
// SAFETY: new_size is not zero,
// Other conditions must be upheld by the caller
let raw_ptr = unsafe {
// `realloc` probably checks for `new_size <= old_size` or something similar.
intrinsics::assume(new_size <= old_size);
realloc(ptr.as_ptr(), layout, new_size)
};
NonNull::new(raw_ptr).ok_or(AllocErr)?
};
Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0))
},

Ok(NonNull::slice_from_raw_parts(ptr, new_size))
// SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
new_size => unsafe {
// `realloc` probably checks for `new_size <= size` or something similar.
intrinsics::assume(new_size <= layout.size());

let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok(NonNull::slice_from_raw_parts(ptr, new_size))
},
}
}
}

Expand Down
58 changes: 29 additions & 29 deletions library/core/src/alloc/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,11 @@ pub unsafe trait AllocRef {
/// alignment and a size given by `new_size`. To accomplish this, the allocator may extend the
/// allocation referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. The memory may or may not have been freed, and should be
/// considered unusable unless it was transferred back to the caller again via the return value
/// of this method.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.
///
Expand Down Expand Up @@ -192,12 +197,9 @@ pub unsafe trait AllocRef {
"`new_size` must be greater than or equal to `layout.size()`"
);

let new_layout =
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
// The caller must ensure that `new_size` is greater than or equal to zero. If it's equal
// to zero, it's catched beforehand.
unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
let new_ptr = self.alloc(new_layout)?;

// SAFETY: because `new_size` must be greater than or equal to `size`, both the old and new
Expand All @@ -206,10 +208,11 @@ pub unsafe trait AllocRef {
// `copy_nonoverlapping` is safe.
// The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_non_null_ptr().as_ptr(), size);
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), size);
self.dealloc(ptr, layout);
Ok(new_ptr)
}

Ok(new_ptr)
}

/// Behaves like `grow`, but also ensures that the new contents are set to zero before being
Expand All @@ -218,12 +221,12 @@ pub unsafe trait AllocRef {
/// The memory block will contain the following contents after a successful call to
/// `grow_zeroed`:
/// * Bytes `0..layout.size()` are preserved from the original allocation.
/// * Bytes `layout.size()..old_size` will either be preserved or zeroed,
/// depending on the allocator implementation. `old_size` refers to the size of
/// the `MemoryBlock` prior to the `grow_zeroed` call, which may be larger than the size
/// that was originally requested when it was allocated.
/// * Bytes `old_size..new_size` are zeroed. `new_size` refers to
/// the size of the `MemoryBlock` returned by the `grow` call.
/// * Bytes `layout.size()..old_size` will either be preserved or zeroed, depending on the
/// allocator implementation. `old_size` refers to the size of the memory block prior to
/// the `grow_zeroed` call, which may be larger than the size that was originally requested
/// when it was allocated.
/// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory
/// block returned by the `grow` call.
///
/// # Safety
///
Expand Down Expand Up @@ -261,12 +264,9 @@ pub unsafe trait AllocRef {
"`new_size` must be greater than or equal to `layout.size()`"
);

let new_layout =
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
// The caller must ensure that `new_size` is greater than or equal to zero. If it's equal
// to zero, it's caught beforehand.
unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
let new_ptr = self.alloc_zeroed(new_layout)?;

// SAFETY: because `new_size` must be greater than or equal to `size`, both the old and new
Expand All @@ -275,10 +275,11 @@ pub unsafe trait AllocRef {
// `copy_nonoverlapping` is safe.
// The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_non_null_ptr().as_ptr(), size);
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), size);
self.dealloc(ptr, layout);
Ok(new_ptr)
}

Ok(new_ptr)
}

/// Attempts to shrink the memory block.
Expand All @@ -290,8 +291,8 @@ pub unsafe trait AllocRef {
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. The memory may or may not have been freed, and should be
/// considered unusable unless it was transferred back to the caller again via the
/// return value of this method.
/// considered unusable unless it was transferred back to the caller again via the return value
/// of this method.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.
Expand Down Expand Up @@ -332,11 +333,9 @@ pub unsafe trait AllocRef {
"`new_size` must be smaller than or equal to `layout.size()`"
);

let new_layout =
// SAFETY: the caller must ensure that the `new_size` does not overflow.
// `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
// The caller must ensure that `new_size` is greater than zero.
unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
let new_ptr = self.alloc(new_layout)?;

// SAFETY: because `new_size` must be lower than or equal to `size`, both the old and new
Expand All @@ -345,10 +344,11 @@ pub unsafe trait AllocRef {
// `copy_nonoverlapping` is safe.
// The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_non_null_ptr().as_ptr(), size);
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), size);
self.dealloc(ptr, layout);
Ok(new_ptr)
}

Ok(new_ptr)
}

/// Creates a "by reference" adaptor for this instance of `AllocRef`.
Expand Down
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