ADR 0041: A2/A3 MX CUBE profile applicability

Decision scope

This decision is a bounded negative applicability checkpoint. Parent ADR 0086, cube-matrix, and S5-T2 remain open.

Context

S5-T2-A separates profile applicability from numeric result semantics. The accepted profile identities from ADR 0037 allow target profiles such as pto-a2a3-numeric-v1, but a profile identity does not imply that every operation/type tuple is supported by that target.

Target-specific support restrictions must be explicit in PTO. This decision defines a bounded A2/A3 support exclusion for the six MX CUBE selectors. It is a support-boundary decision only and supplies no CUBE payload arithmetic.

Decision

For pto-a2a3-numeric-v1, the following direct CUBE operation selectors are unsupported for every one of the 25 architectural TileDataType identities:

Operation key	Function
tile:CUBE:TMATMUL_MX	4
tile:CUBE:TMATMUL_MX_BIAS	5
tile:CUBE:TMATMUL_MX_ACC	6
tile:CUBE:TGEMV_MX	20
tile:CUBE:TGEMV_MX_BIAS	21
tile:CUBE:TGEMV_MX_ACC	22

Each tuple rejects as IllegalInstruction before operand legality checks, semantic-handler dispatch, destination writes, memory effects, or result-rule selection. result_rule_id is therefore null for all 150 tuples.

The ASL represents this bounded decision with NumericApplicabilityRules_A2A3MxRejection, an accepted negative-rule set, not with a complete executable A2/A3 profile. NumericApplicabilityRules_None means that no accepted negative rule is being applied; it does not claim that an operation is supported by A2/A3 or A5. The public PTO-v0 execution entry points continue to use that None rule set and retain their Stage 4 raw-carrier behavior.

The generated spec/evidence/numeric-profile-applicability-closure.json ledger is the machine-readable acceptance package. Its source catalog is spec/catalog/numeric-profile-applicability.json.

Consequences

• A2/A3 MX support is now fail-closed instead of inferred from the portable CUBE operation inventory.
• The six MX selectors remain accepted PTO direct tile operation identities in the portable catalog; this ADR only constrains the A2/A3 numeric profile.
• Absence from this bounded rejection catalog is not positive support evidence; the remaining A2/A3 and A5 operation/type matrices stay fail-closed review obligations.
• No MX numeric result semantics, FP8/FP4 scale behavior, accumulation order, rounding, saturation, or exceptional-value rule is accepted here.
• ADR 0086, the cube-matrix domain, and S5-T2 remain open until every profile applicability and result rule is complete and independently verified.