Function svclasta_s64 

pub fn svclasta_s64(
    pg: svbool_t,
    fallback: svint64_t,
    data: svint64_t,
) -> svint64_t

🔬This is a nightly-only experimental API. (stdarch_aarch64_sve #145052)

Available on (AArch64 or ARM64EC) and target feature sve only.

Conditionally extract element after last Arm’s documentation