pub fn select_tier(m: u32, present: [bool; 5], exact_m: bool) -> Option<usize>Expand description
2026-09-25: Pure tier decision: index into W4A16_BATCHM_WIDTHS of the
narrowest tier that covers m rows and is present in the loaded target,
or None when no such tier exists (or m is 0).
present[i] is whether W4A16_BATCHM_WIDTHS[i] resolved. exact_m is
exact_m_tiers_enabled, passed in so both values are testable without
the process environment or the latched OnceLock.
Narrowest-that-covers, not exact-only: a target missing a tier still dispatches on the next wider one.