Commit4aa43c7

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Auto merge ofrust-lang#125720 - folkertdev:optimize_for_size-ptr-rotate, r=Amanieu

make `ptr::rotate` smaller when using `optimize_for_size`code to reproducehttps://github.com/folkertdev/optimize_for_size-slice-rotateIn the example the size of `.text` goes down from 1624 to 276 bytes.```> cargo size --release --features "left-std" -- -Aslice-rotate :section size addr.vector_table 1024 0x0.text 1624 0x400.rodata 0 0xa58.data 0 0x20000000.gnu.sgstubs 0 0xa60.bss 0 0x20000000.uninit 0 0x20000000.debug_loc 591 0x0.debug_abbrev 1452 0x0.debug_info 10634 0x0.debug_aranges 480 0x0.debug_ranges 1504 0x0.debug_str 11716 0x0.comment 72 0x0.ARM.attributes 56 0x0.debug_frame 1036 0x0.debug_line 5837 0x0Total 36026> cargo size --release --features "left-size" -- -Aslice-rotate :section size addr.vector_table 1024 0x0.text 276 0x400.rodata 0 0x514.data 0 0x20000000.gnu.sgstubs 0 0x520.bss 0 0x20000000.uninit 0 0x20000000.debug_loc 347 0x0.debug_abbrev 965 0x0.debug_info 4216 0x0.debug_aranges 168 0x0.debug_ranges 216 0x0.debug_str 3615 0x0.comment 72 0x0.ARM.attributes 56 0x0.debug_frame 232 0x0.debug_line 723 0x0Total 11910```tracking issue:rust-lang#125612

2 parents89b5784 +1265244 commit4aa43c7Copy full SHA for 4aa43c7

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core/src/slice
- rotate.rs

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`‎core/src/slice/rotate.rs‎`

Lines changed: 6 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -71,7 +71,9 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize)`
`71`	`71`	`if(right ==0) \|\|(left ==0){`
`72`	`72`	`return;`
`73`	`73`	`}`
`74`		`-if(left + right <24) \|\|(mem::size_of::<T>() > mem::size_of::<[usize;4]>()){`
	`74`	`+if !cfg!(feature ="optimize_for_size")`
	`75`	`+ &&((left + right <24) \|\|(mem::size_of::<T>() > mem::size_of::<[usize;4]>()))`
	`76`	`+{`
`75`	`77`	`// Algorithm 1`
`76`	`78`	`// Microbenchmarks indicate that the average performance for random shifts is better all`
`77`	`79`	// 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)`
`158`	`160`	`}`
`159`	`161`	`return;`
`160`	`162`	// `T` is not a zero-sized type, so it's okay to divide by its size.
`161`		`-}elseif cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>(){`
	`163`	`+}elseif !cfg!(feature ="optimize_for_size")`
	`164`	`+ && cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>()`
	`165`	`+{`
`162`	`166`	`// Algorithm 2`
`163`	`167`	// The `[T; 0]` here is to ensure this is appropriately aligned for T
`164`	`168`	`letmut rawarray =MaybeUninit::<(BufType,[T;0])>::uninit();`

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Commit4aa43c7

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`‎core/src/slice/rotate.rs‎`

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