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[CK_TILE] Fix typo in fmha_fwd_kernel K-dram unmerge tuple sizes (#7141) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Summary The qr_async_trload K-dram lambda's `else (XorLengthFold == 1)` branch in `fmha_fwd_kernel.hpp` writes the outer-tile dim of its 3-tuple unmerge/xor/merge as ```cpp number<FmhaPipeline::kQKHeaddim / kDramTileK / FmhaPipeline::kAlignmentK>{} ``` which divides one extra time. For every fp16/bf16 hdim=128 configuration the outer length collapses to **0**, e.g. `128 / 128 / 8 == 0`. The 3-tuple product no longer equals `kQKHeaddim`, so unmerge → xor → merge stops round-tripping the head dimension. This bug was masked by the async-load path: it only walks the descriptor via stride and silently absorbs a length=0 outer dim. Any consumer that actually traverses the descriptor (e.g. the TDM path on gfx1250) immediately faults on the resulting `tuple<int, constant<0>>`. The fix drops the extra `/ kAlignmentK` in all three call sites in the same lambda so the outer dim becomes `kQKHeaddim / kDramTileK` and the product is restored to `kQKHeaddim`. Strides are unaffected, so the async path is bit-identical. | Config (fp16/bf16) | hdim | kDramTileK | kAlignmentK | a (typo) | a (fixed) | product (typo) | product (fixed) | |---|---|---|---|---|---|---|---| | hdim128, kKLoadOnce | 128 | 128 | 8 | 0 | 1 | **0** | **128** | | hdim128, kK0=32 | 128 | 32 | 8 | 0 | 4 | **0** | **128** | | hdim64, kKLoadOnce | 64 | 64 | 8 | 0 | 1 | **0** | **64** | | hdim256, kK0=32 | 256 | 32 | 8 | 1 | 8 | **32** | **256** | Bug introduced in 2cc0af6a815a (PR #2888 \"[CK_TILE] FMHA FWD bug fix\"), where the original 2-tuple unmerge was generalized to a 3-tuple and the typo slipped in. ## Test plan - [x] Built `test_ck_tile_fmha_fwd` (umbrella, 5 gtest binaries) on gfx950 native at develop b3bdc63a509 with `dev-gfx950` preset (clang 22, ROCm 7.2.2). Compiles cleanly with `-Werror -Weverything`. - [x] Ran `ctest -R test_ck_tile_fmha_fwd` on gfx950 native, baseline vs patched: identical pass/fail (3 pass / 2 fail), identical failing case set (114 gtest fails + 2 GPU memory access faults, all in pre-existing fp16/bf16 group-mode `Alibi`/`Dropout` cases that reproduce on develop without this patch). Total wall time 403s → 393s. Per-case latency drift ±8% (noise). - [x] CI to verify on other gfx9 / gfx11 architectures.