pub fn backend() -> BackendExpand description
The backend these kernels use, resolved once per process.
Runs simdispatch::Selection over FGF_TIERS — every tier this crate implements
kernels for, or Backend::Scalar when SIMD is compiled out — then
adjusted by the downgrade-only SIMD_BACKEND override. May be downgraded
at startup via SIMD_BACKEND (v4x, v3_gfni_crypto, v3, v2,
scalar); requests for a backend the host
cannot run are ignored. v4x resolves only with the simd512 feature on
an AVX-512+GFNI host; SIMD_BACKEND=v4 is not a selected tier and behaves
like any unsupported request. Detection itself is simdispatch’s
archmage summon() probe — the one probe in the stack.