bump aiter to 859e56f98 for gfx1201/gfx1200 FP8 support

[johnodin99]

Motivation

This PR addresses the FP8 architecture gate for RDNA4 (gfx1200 / gfx1201) in the AMD Triton flash-attention path.

Currently, FP8 support can be blocked by the architecture support table even when running on an FP8-capable RDNA4 platform. This PR updates the bundled aiter submodule to a newer revision that includes RDNA4 FP8 architecture support.

Related issue:

• [Issue]: arch_supports_fp8() for gfx950 and gfx1201? #146

Technical Details

This PR bumps the third_party/aiter submodule:

third_party/aiter: 428e8e761 -> 859e56f98

The newer aiter revision includes RDNA4 FP8 support for gfx1200 / gfx1201, including updates to the FP8 architecture capability checks used by the AMD Triton flash-attention path.

The nested CK submodule under aiter is also updated through the aiter submodule state:

third_party/aiter/3rdparty/composable_kernel: 020b6f435e787b6f7f40aabf638a3ef9ab6a9002

This PR is intentionally limited to the aiter submodule bump. It does not directly modify flash-attention kernels or change the AMD Triton FA2 direct-FP8 tensor path.

Note:

Direct FP8 tensors through flash_attn_func currently hit the AMD Triton FA2 interface, which raises NotImplementedError for FP8 tensors. The validated FP8 path in this PR is the AITER FA3 FP8 path.

Test Plan

Tested locally on gfx1201 with:

ROCm: 7.2
PyTorch: 2.11.0+rocm7.2
FLASH_ATTENTION_TRITON_AMD_ENABLE=TRUE
GPU_ARCHS=gfx1201

The following checks were run:

1. Build flash-attention with the updated aiter submodule.

2. Verify the FP8 architecture gate:

arch: gfx1201
supports_fp8: True
PR-A gate check: PASS

3. Run FP16 forward smoke test using flash_attn_func.

4. Run FP16 backward smoke test using flash_attn_func.

5. Run AITER FA3 FP8 forward numerical correctness check against an FP32 reference attention implementation.

The FP8 numerical check covers:

causal=False, head_dim=128
causal=False, head_dim=64
causal=True,  head_dim=128
causal=True,  head_dim=64

Test Result

All local validation checks passed on gfx1201.

Summary:

FP8 arch gate:
  arch=gfx1201
  supports_fp8=True
  PASS

FP16 forward smoke test:
  PASS

FP16 backward smoke test:
  PASS

AITER FA3 FP8 forward numerical check:
  ALL FP8 FWD NUMERICAL CHECKS PASS

FP8 numerical accuracy versus FP32 reference:

causal=False, head_dim=128:
  rel_fro=5.1931e-02
  cosine=0.998652
  PASS

causal=False, head_dim=64:
  rel_fro=5.4826e-02
  cosine=0.998498
  PASS

causal=True, head_dim=128:
  rel_fro=4.6094e-02
  cosine=0.998937
  PASS

causal=True, head_dim=64:
  rel_fro=4.8156e-02
  cosine=0.998840
  PASS

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[johnodin99]

check record

check_record.txt