[joshuaswarren]

AGX correctness series — fast-track for upstream submission

Six patches, stock-main only, no perf-only changes, no internal receipts: the correctness subset of the [Honeykrisp integration PR](PR # (integration branch, opened alongside)) that Dj asked to have upstreamed, prepared per the agreed sequencing ("send the ubfe mod-32 correctness fix first; hold cooperative-matrix commits until the correctness work is through").

1. agx: keep the mod-32 shift count when fusing ushr+iand into ubfe — wrong-results fix
2. agx: represent the fused shift-then-mask as ubfe, not ubitfield_extract
3. agx: correctly rounded fdiv/frcp, faithful log/log2, exact sin/cos reduction
4. agx: lower the fdiv that int64 lowering and the perspective divide emit late
5. agx: handle flush-to-zero in precise fp32 division, log and sine
6. nir: pass FP_MATH_CTRL to the builder generator — affects every Mesa driver, not just AGX: the builder generator dropped FP_MATH_CTRL, so any driver using it compiled with wrong fast-math settings

Intended flow: merge or cherry-pick to freedesktop mesa/main (an MR-ready format-patch series is at joshuaswarren/mesa:upstream/correctness). The full Honeykrisp integration PR will rebase after this lands.

All six verified on Apple M1 hardware (t8103) against the mlx-omarchy regression battery — the same commits that carry the pinned-inference results the team publishes.