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[CK_TILE][FMHA] Fix sink un-mask under right-window and emit fp8bf16 batch_prefill sink kernels (#6914) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Summary Two related fixes to `ck_tile` FMHA so that StreamLLM-sink + sliding-window batch-prefill works correctly for fp8 KV / bf16 compute. Review the commits in this order: 1. `fmha: emit sink kernels for fp8bf16 batch_prefill` Extends `example/ck_tile/01_fmha/codegen/ops/fmha_batch_prefill.py` so the fp8(KV) / bf16(QO) batch-prefill codegen also emits the `mask=mask_enum::generic_with_sink` variant. Without this the runtime could not dispatch to a sink-aware kernel for the fp8bf16 path. 2. `fmha: respect right-window in IsOutOfSinkBound` The sink un-mask in `GenericAttentionMask::IsOutOfSinkBound` (local-mask branch) used `(i_y + x) > 1` as the gate, which conditioned on the row index instead of the column index. As a result, queries `1..sink-1` could attend to *future* sink positions (violating causal / right-window), while query `0` fell back to the plain causal mask. The fix replaces the guard with `i_x < i_y + x` so every query only sees sink columns up to its own right-window boundary. 3. `fmha: clarify IsOutOfSinkBound predicate comment` Doc-only follow-up that rewrites the comment above the predicate as a clause-by-clause explanation (`i_x < sink`, `i_x < i_y + x`, `y < y_total`, `i_y < x_total`). ## Test plan - [x] Repro on aiter `op_tests/test_batch_prefill.py` (fp8 + bf16_dequant modes with `sink=4`, `win_left=1023`, `softcap=0.0`, `sal=True`) now passes for all parametrized shapes. - [x] Existing fp16/bf16 batch-prefill paths (no sink) unchanged — codegen diff only adds the `generic_with_sink` variant for fp8bf16; existing kernel object lists unaffected. ## Submission Checklist - [x] Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.