Reuse the mem::swap optimizations to speed up slice::rotate #42819
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Exposes the swapping logic from PR 40454 as `pub unsafe fn ptr::swap_nonoverlapping` under feature swap_nonoverlapping This is most helpful for compound types where LLVM didn't vectorize the loop. Highlight: bench slice::rotate_medium_by727_strings gets 38% faster.
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r? @sfackler (rust_highfive has picked a reviewer for you, use r? to override) |
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friendly ping @sfackler, pinging you on IRC too! |
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@bors r+ |
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📌 Commit 47fa016 has been approved by |
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⌛ Testing commit 47fa016 with merge 240dcc4d98ed5e20f3d3177ac77debc65aa131e9... |
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💔 Test failed - status-travis |
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@bors: retry
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arielb1
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Reuse the mem::swap optimizations to speed up slice::rotate This is most helpful for compound types where LLVM didn't vectorize the loop. Highlight: bench slice::rotate_medium_by727_strings gets 38% faster. Exposes the swapping logic from PR #40454 as `pub unsafe fn ptr::swap_nonoverlapping` under library feature `swap_nonoverlapping` #42818. (The new method seemed plausible, and was the simplest way to share the logic. I'm not attached to it, though, so let me know if a different way would be better.)
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☀️ Test successful - status-appveyor, status-travis |
SimonSapin
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Jul 5, 2017
| pub unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) { | ||
| let x = x as *mut u8; | ||
| let y = y as *mut u8; | ||
| let len = mem::size_of::<T>() * count; |
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Should this use .checked_mul(count).unwrap()?
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I don't think that's necessary, because of the safety requirement that the arguments refer to valid ranges of memory -- if it's valid, its length must fit in a usize.
cuviper
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Jul 11, 2017
This is a workaround for rust-lang#42778, which was git-bisected to rust-lang#40454's optimizations to `mem::swap`, later moved to `ptr` in rust-lang#42819. Natively compiled rustc couldn't even compile stage1 libcore on powerpc64 and s390x, but they work fine without this `repr(simd)`. Since powerpc64le works OK, it seems probably related to being big-endian. The underlying problem is not yet known, but this at least makes those architectures functional again in the meantime. cc @arielb1
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Jul 15, 2017
Disable big-endian simd in swap_nonoverlapping_bytes This is a workaround for rust-lang#42778, which was git-bisected to rust-lang#40454's optimizations to `mem::swap`, later moved to `ptr` in rust-lang#42819. Natively compiled rustc couldn't even compile stage1 libcore on powerpc64 and s390x, but they work fine without this `repr(simd)`. Since powerpc64le works OK, it seems probably related to being big-endian. The underlying problem is not yet known, but this at least makes those architectures functional again in the meantime. cc @arielb1
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This is most helpful for compound types where LLVM didn't vectorize the loop. Highlight: bench slice::rotate_medium_by727_strings gets 38% faster.
Exposes the swapping logic from PR #40454 as
pub unsafe fn ptr::swap_nonoverlappingunder library featureswap_nonoverlapping#42818.(The new method seemed plausible, and was the simplest way to share the logic. I'm not attached to it, though, so let me know if a different way would be better.)