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Removes alignment requirement in st3,ld3 #2143

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Merged
folkertdev merged 4 commits into from
May 31, 2026
+18 −17
Merged

Removes alignment requirement in st3,ld3 #2143

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281d640
Removes alignment requirement in st3
awxkee May 30, 2026
b9a40e5
Update crates/core_arch/src/macros.rs
awxkee May 31, 2026
3fdc05a
Removes alignment requirement in st3
awxkee May 31, 2026
fc7a454
Removes alignment requirement in st3
awxkee May 31, 2026
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35 changes: 18 additions & 17 deletions crates/core_arch/src/macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -266,23 +266,22 @@ macro_rules! deinterleaving_load {
transmute((v0, v1))
}};

// N = 3
($elem:ty, $lanes:literal, 3, $ptr:expr) => {{
use $crate::core_arch::macros::deinterleave_mask;
use $crate::core_arch::simd::Simd;
use $crate::mem::{MaybeUninit, transmute};
use $crate::mem::transmute;

type V = Simd<$elem, $lanes>;
type W = Simd<$elem, { $lanes * 3 }>;
type Arr = [$elem; { $lanes * 3 }];

// NOTE: copy_nonoverlapping requires both pointers to be aligned to at least align_of::<$elem>(),
// passing a pointer that is not sufficiently aligned is an UB.
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let arr: Arr = $crate::ptr::read_unaligned($ptr as *const [$elem; { $lanes * 3 }]);
// NOTE: repr(simd) adds padding to make the total size a power of two.
// Hence reading W from ptr might read out of bounds.
let mut mem = MaybeUninit::<W>::uninit();
$crate::ptr::copy_nonoverlapping(
$ptr.cast::<$elem>(),
mem.as_mut_ptr().cast::<$elem>(),
$lanes * 3,
);
let w = mem.assume_init();
// Hence reading a W from ptr might read out of bounds.
type W = Simd<$elem, { $lanes * 3 }>;
let w: W = W::from_array(arr);

let v0: V = simd_shuffle!(w, w, deinterleave_mask::<$lanes, 3, 0>());
let v1: V = simd_shuffle!(w, w, deinterleave_mask::<$lanes, 3, 1>());
Expand All @@ -291,6 +290,7 @@ macro_rules! deinterleaving_load {
transmute((v0, v1, v2))
}};

// N = 4
($elem:ty, $lanes:literal, 4, $ptr:expr) => {{
use $crate::core_arch::macros::deinterleave_mask;
use $crate::core_arch::simd::Simd;
Expand Down Expand Up @@ -345,16 +345,17 @@ macro_rules! interleaving_store {
let v2v2: Simd<$elem, { $lanes * 2 }> =
simd_shuffle!($v.2, $v.2, identity::<{ $lanes * 2 }>());

type W = Simd<$elem, { $lanes * 3 }>;

// NOTE: repr(simd) adds padding to make the total size a power of two.
// Hence writing W to ptr might write out of bounds.
type W = Simd<$elem, { $lanes * 3 }>;
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let w: W = simd_shuffle!(v0v1, v2v2, interleave_mask::<{ $lanes * 3 }, $lanes, 3>());
$crate::ptr::copy_nonoverlapping(
(&w as *const W).cast::<$elem>(),
$ptr.cast::<$elem>(),
$lanes * 3,
);

let arr: [$elem; { $lanes * 3 }] = $crate::mem::transmute_copy(&w);

// NOTE: copy_nonoverlapping requires both pointers to be aligned to at least align_of::<$elem>(),
// passing a pointer that is not sufficiently aligned is an UB.
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$ptr.cast::<[$elem; { $lanes * 3 }]>().write_unaligned(arr);
}};

// N = 4
Expand Down
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