[arai713]

Motivation

Padding-mask support on the SDPA path for gfx942/gfx950. The kernel-side masking has to land inside the stride shell, which doesn't exist yet, and the arbitrary-length buffer clipping it rides on is a separate ticket. This PR lands the host-side, non-blocked foundation so the kernel masking is a mechanical drop-in when the shell arrives: the oracle can express padding, the hipDNN length tensors are validated and normalized, and the exact mask the kernel must emit is specified and cross-checked.

Technical Details

• dense_attention_reference gains optional seqlen_q / seqlen_kv. None keeps the exact unpadded arithmetic. When set, keys past seqlen_kv are masked, a row with no valid key yields O = 0, and padded query rows are zeroed.
• _sdpa_seqlen.py: host adapter validating hipDNN SEQ_LEN_Q/KV at the boundary (integer dtype, per-batch count, 0 <= len <= S_max) and returning the flat per-batch int32 arrays the shell reads. The call signature is provisional until the shell kernargs freeze.
• _sdpa_padding_mask.py: host specification of the kernel-side mask, keep_key and row_is_valid (the epilogue's padded-row zeroing). The live IR emitter is deferred to the shell, where it carries its byte-identity C++ mirror. This module is the host reference it must match.

Test Plan

• Oracle padding tests (tests/test_numeric_references.py)
• Adapter tests (library/tests/test_sdpa_seqlen.py)
• Mask-spec tests incl. composition against the oracle (library/tests/test_sdpa_padding_mask.py)
• Library layering guard (new kernel-layer files import downward only)
• Byte-identity: N/A, no emission change

Test Result

• 24 passed across the four suites above, no GPU and no torch. The mask spec's predicates are proven to reproduce dense_attention_reference's padded output exactly.

Related

JIRA ID: AICK-2518

Submission Checklist

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

[therock-pr-bot]

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[arai713]

Moved to this PR: #13953