aarch64: use intrinsics::simd for horizontal add and abs#1872
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Amanieu merged 2 commits intorust-lang:masterfrom Jul 15, 2025
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aarch64: use intrinsics::simd for horizontal add and abs#1872Amanieu merged 2 commits intorust-lang:masterfrom
aarch64: use intrinsics::simd for horizontal add and abs#1872Amanieu merged 2 commits intorust-lang:masterfrom
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folkertdev
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aarch64: use intrinsics::simd for horizontal add and abs
folkertdev
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Jul 12, 2025
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| unsafe extern "unadjusted" { | ||
| #[cfg_attr( | ||
| any(target_arch = "aarch64", target_arch = "arm64ec"), | ||
| link_name = "llvm.aarch64.neon.abs.v1i64" | ||
| )] | ||
| fn _vabs_s64(a: int64x1_t) -> int64x1_t; | ||
| unsafe { | ||
| let neg: int64x1_t = simd_neg(a); | ||
| let mask: int64x1_t = simd_ge(a, neg); | ||
| simd_select(mask, a, neg) | ||
| } | ||
| unsafe { _vabs_s64(a) } | ||
| } | ||
| #[doc = "Absolute Value (wrapping)."] | ||
| #[doc = "[Arm's documentation](https://developer.arm.com/architectures/instruction-sets/intrinsics/vabsd_s64)"] | ||
| #[doc = "[Arm's documentation](https://developer.arm.com/architectures/instruction-sets/intrinsics/vabsq_s64)"] |
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the diff here is wonky because the order of the definitions changed.
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| # FIXME(llvm): this should be `i64::wrapping_abs` but it optimizes differently. | ||
| # See https://github.com/llvm/llvm-project/issues/148388. | ||
| - LLVMLink: | ||
| name: "vabsd_s64" | ||
| links: | ||
| - link: "llvm.aarch64.neon.abs.i64" | ||
| arch: aarch64,arm64ec |
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Just kept this as-is for now, but from what I can tell i64::wrapping_abs would be equivalent.
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The LLVM issue is closed, is this comment still relevant?
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I updated the comment. it's kind of subtle, but the intrinsic keeps the value in a simd register, while the scalar version uses GPRs.
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