Choosing between fixed-width NEON and length-agnostic SVE for portable AArch64 SIMD
Goal: create a single AArch64 binary that runs on every ARMv8‑A CPU, using NEON when SVE is absent and automatically exploiting longer vectors on SVE‑capable cores without maintaining separate builds. Constraints: GCC and Clang’s auto‑vectorizer may choose NEON, SVE, or a mixture depending on -march, -mtune, optimization level, data alignment, or OpenMP SIMD