bjoernager/rust
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Remove fast path in reallocation for same layout sizes

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This commit is contained in:
Tim Diekmann 2020-08-17 13:23:38 +02:00
parent 67e7b9b8cf
commit c619b36975
3 changed files with 20 additions and 52 deletions
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27
library/alloc/src/alloc.rs
View file

@ -209,16 +209,14 @@ unsafe impl AllocRef for Global {
);
// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, than `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
old_size if old_size == new_size => {
Ok(NonNull::slice_from_raw_parts(ptr, new_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);
// `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))
@ -240,16 +238,14 @@ unsafe impl AllocRef for Global {
);
// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, than `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
old_size if old_size == new_size => {
Ok(NonNull::slice_from_raw_parts(ptr, new_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);
// `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)?;
@ -272,11 +268,8 @@ unsafe impl AllocRef for Global {
"`new_size` must be smaller than or equal to `layout.size()`"
);
let ptr = if new_size == old_size {
ptr
} else if new_size == 0 {
// SAFETY: `layout` is non-zero in size as `old_size` != `new_size`
// Other conditions must be upheld by the caller
let ptr = if new_size == 0 {
// SAFETY: conditions must be upheld by the caller
unsafe {
self.dealloc(ptr, layout);
}
@ -285,8 +278,8 @@ unsafe impl AllocRef for Global {
// 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` 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)?

18
library/core/src/alloc/mod.rs
View file

@ -163,8 +163,6 @@ pub unsafe trait AllocRef {
/// * `new_size` must be greater than or equal to `layout.size()`, and
/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`, must not overflow
/// (i.e., the rounded value must be less than or equal to `usize::MAX`).
// Note: We can't require that `new_size` is strictly greater than `layout.size()` because of ZSTs.
// alternative: `new_size` must be strictly greater than `layout.size()` or both are zero
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
@ -194,10 +192,6 @@ pub unsafe trait AllocRef {
"`new_size` must be greater than or equal to `layout.size()`"
);
if size == new_size {
return Ok(NonNull::slice_from_raw_parts(ptr, 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.
@ -238,8 +232,6 @@ pub unsafe trait AllocRef {
/// * `new_size` must be greater than or equal to `layout.size()`, and
/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`, must not overflow
/// (i.e., the rounded value must be less than or equal to `usize::MAX`).
// Note: We can't require that `new_size` is strictly greater than `layout.size()` because of ZSTs.
// alternative: `new_size` must be strictly greater than `layout.size()` or both are zero
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
@ -269,10 +261,6 @@ pub unsafe trait AllocRef {
"`new_size` must be greater than or equal to `layout.size()`"
);
if size == new_size {
return Ok(NonNull::slice_from_raw_parts(ptr, 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.
@ -315,8 +303,6 @@ pub unsafe trait AllocRef {
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator,
/// * `layout` must [*fit*] that block of memory (The `new_size` argument need not fit it.), and
/// * `new_size` must be smaller than or equal to `layout.size()`.
// Note: We can't require that `new_size` is strictly smaller than `layout.size()` because of ZSTs.
// alternative: `new_size` must be smaller than `layout.size()` or both are zero
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
@ -346,10 +332,6 @@ pub unsafe trait AllocRef {
"`new_size` must be smaller than or equal to `layout.size()`"
);
if size == new_size {
return Ok(NonNull::slice_from_raw_parts(ptr, 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.

27
library/std/src/alloc.rs
View file

@ -185,16 +185,14 @@ unsafe impl AllocRef for System {
);
// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, than `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
old_size if old_size == new_size => {
Ok(NonNull::slice_from_raw_parts(ptr, new_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);
// `realloc` probably checks for `new_size >= size` or something similar.
intrinsics::assume(new_size >= old_size);
let raw_ptr = GlobalAlloc::realloc(&System, ptr.as_ptr(), layout, new_size);
let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
Ok(NonNull::slice_from_raw_parts(ptr, new_size))
@ -216,16 +214,14 @@ unsafe impl AllocRef for System {
);
// SAFETY: `new_size` must be non-zero, which is checked in the match expression.
// If `new_size` is zero, than `old_size` has to be zero as well.
// Other conditions must be upheld by the caller
unsafe {
match layout.size() {
old_size if old_size == new_size => {
Ok(NonNull::slice_from_raw_parts(ptr, new_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);
// `realloc` probably checks for `new_size >= size` or something similar.
intrinsics::assume(new_size >= old_size);
let raw_ptr = GlobalAlloc::realloc(&System, 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)?;
@ -248,11 +244,8 @@ unsafe impl AllocRef for System {
"`new_size` must be smaller than or equal to `layout.size()`"
);
let ptr = if new_size == old_size {
ptr
} else if new_size == 0 {
// SAFETY: `layout` is non-zero in size as `old_size` != `new_size`
// Other conditions must be upheld by the caller
let ptr = if new_size == 0 {
// SAFETY: conditions must be upheld by the caller
unsafe {
self.dealloc(ptr, layout);
}
@ -261,8 +254,8 @@ unsafe impl AllocRef for System {
// 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` probably checks for `new_size <= old_size` or something similar.
intrinsics::assume(new_size <= old_size);
GlobalAlloc::realloc(&System, ptr.as_ptr(), layout, new_size)
};
NonNull::new(raw_ptr).ok_or(AllocErr)?