Improve SVE2 optimizations of SimdSynetConvert32fTo8u - #896
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Replace gather/scatter in the NHWC channels==3 path with sequential vector loads and stores using a repeating per-channel scale/shift pattern. Co-authored-by: igor.ermolaev <igor.ermolaev@altezza.org>
ermig1979
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August 20, 2026 09:20
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The SVE2 NHWC
channels == 3path ofSimdSynetConvert32fTo8uused gather/scatter, which is slower than the NEON implementation that processes interleaved RGB with sequential vector loads.This change matches the NEON/AVX512 approach:
[s0,s1,s2,s0,...]withsvtblfloat32lanes and store consecutive bytes (svld1/svst1b)Release notes for 7.2.165 list the improvement.
Correctness was checked by cross-compiling for AArch64 and running under QEMU SVE2 at VL=128 (
svcntw=4) and VL=512 (svcntw=16):Simd::Sve2::SynetConvert32fTo8u: 228 cases, 0 failures (NHWC c=3 including tails, plus NCHW / other channel counts)Test::SynetConvert32fTo8uAutoTest: all tests finished successfully