ADR 0100: Cooperative Group-M Distribution and Inactive PE Semantics

Context

Cooperative TMATMUL needs one Core-total row count while Local descriptors, capacity, dependencies, subviews, and destination generations remain private to one PE. Earlier decisions treated LB0 as a uniform per-PE M and permitted arbitrary nonzero masks. That cannot represent tail groups with zero-row PEs without observing invalid compute-only Local values.

Decision

For Local-A/Shared-B and Shared-A/Shared-B TMATMUL ordinary, ACC, BIAS, MX, MX+ACC, and MX+BIAS forms, LB0 is group_M, the Core-total valid output-row count in 1 through 128. LB1 remains N and LB2 remains K. Every executing form uses encoded PE_MASK=1111; every sparse nonzero mask raises Fault_TileLegality before effects. PE_MASK=0000 retains the existing strict no-op. All-Local TMATMUL keeps per-PE M and TGEMV remains Local-only.

The fixed distribution is:

M_per_PE = 16, when 1 <= group_M <= 64
M_per_PE = 32, when 65 <= group_M <= 128
valid_M[i] = clamp(group_M - i*M_per_PE, 0, M_per_PE)

Shared A has shape [group_M,K]; Shared B has shape [K,N]. Active PE i consumes Shared-A rows beginning at i*M_per_PE, or its own Local A fragment, and publishes one Local [valid_M[i],N] fragment. The formal single-PE execution view charges only that current PE's Local pool.

All four PEs retain decode, raw binder/schema completeness, dimensions, topology, mask, rendezvous, every Shared descriptor/view/readiness/capacity check, common fault selection, and atomic collective completion. When valid_M[i]=0, PE i does not resolve or inspect compute-only Local mappings, descriptors, payloads, dependencies, subviews, aliases, allocation, generation, parameters, reductions, or outputs. Required encoded roles remain present and raw-legal. Invalid Shared state still rejects the collective.

Group-level and Shared preflight therefore precedes generic Local Stage2 work. For an active PE, the accepted B.SUBVIEW/B.ASSEMBLE dependency, generation, rollback, and publication rules apply unchanged to the derived valid_M fragment. For an inactive PE, those Local mechanisms are not entered.

Partial supersession

This decision supersedes only the cooperative M and nonzero-mask clauses of ADR-0072 and ADR-0097. Their independent 256 KiB Local pools, one 256 KiB Core-wide Shared pool, fixed PE identities, SizeCode and SharedTileID rules, Shared persistence/readiness, transpose, precise fault, rollback, and atomic publication decisions remain accepted. ADR-0098 active-role range and generation semantics remain protected.

Verification

Independent decoded AVS points prove group sizes 1, 17, 64, 65, and 128; exact sparse-mask rejection; strict zero-mask no-effect; current-PE Shared-A row selection; active-fragment allocation; inactive unallocated Local source/subview/assemble suppression; structural-negative rejection; and Shared-negative rejection without Local effects.

Release impact

This is an architecture-visible interpretation and mask change for the 0.58.4 candidate. It does not regenerate the 0.58.3 release or authorize 0.58.4 validation, tagging, or publication.