nordic-dev.net/rust
nordic-dev.net/rust
2
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-05-14 02:49:40 +00:00
Code Issues Packages Projects Releases Wiki Activity

make ptr::rotate smaller when using optimize_for_size

Browse Source 
code to reproduce https://github.com/folkertdev/optimize_for_size-slice-rotate

In the example the size of `.text` goes down from 1624 to 276 bytes.
This commit is contained in:
Folkert 2024-05-29 13:38:00 +02:00
parent 5870f1ccbb
commit 14c1f740f2
No known key found for this signature in database
GPG Key ID: 1F17F6FFD112B97C
1 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
library/core/src/slice/rotate.rs
View File

@ -71,7 +71,9 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize)
if (right == 0) || (left == 0) {
return;
}
if (left + right < 24) || (mem::size_of::<T>() > mem::size_of::<[usize; 4]>()) {
if !cfg!(feature = "optimize_for_size")
&& ((left + right < 24) || (mem::size_of::<T>() > mem::size_of::<[usize; 4]>()))
{
// Algorithm 1
// Microbenchmarks indicate that the average performance for random shifts is better all
// the way until about `left + right == 32`, but the worst case performance breaks even
@ -158,7 +160,9 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize)
}
return;
// `T` is not a zero-sized type, so it's okay to divide by its size.
} else if cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>() {
} else if !cfg!(feature = "optimize_for_size")
&& cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>()
{
// Algorithm 2
// The `[T; 0]` here is to ensure this is appropriately aligned for T
let mut rawarray = MaybeUninit::<(BufType, [T; 0])>::uninit();