Eliminate Legacy MHA Unfused path from ONNX Attention; unify on 3-tier dispatch with causal alignment fix#27992

Merged

titaiwangms merged 6 commits into

microsoft:mainfrom

titaiwangms:feature/mea-decode-support-v2

May 4, 2026

Commits on May 4, 2026

Eliminate Legacy MHA Unfused path from ONNX Attention; unify on 3-tier dispatch

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Address Copilot review: SafeInt for scratch sizes, clarify MEA test naming

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Address review findings: document output_qk padding, extract MEA predicate, readability fixes

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Reject is_causal + TensorScatter + S_q!=S_kv at dispatch with NOT_IMPLEMENTED

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Enable CPU EP for causal alignment tests

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Fix lintrunner formatting in attention.cc

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