ADR 0055: Complete-Bundle B.IOR Schema and Defaults

Superseded in part by ADR 0074: TLOAD/TSTORE B.IOR.RegSrc1 and its dense omission default are byte quantities. Encoding, schema resolution, and the omission-versus-encoded-zero distinction below remain in force.

Historical-evidence note: verification paths named below record the evidence used when this ADR was accepted; deleted aggregate checks are not active architecture or release owners. Current ownership is the four-surface ASL tree, with per-ID AVS coverage projected into spec/evidence/release-traceability-readiness.json.

• Date: 2026-08-07
• Deciders: PTO ISA maintainers
• Tracks: issue #51

Current release inventory is governed by ASL and generated projections; numeric inventories below are acceptance-time history, not the current active decoder set.

Context

The reissued PTO ISA 0.58 catalog encodes B.IOR with four five-bit fields, but older prose treated selector zero as absence, rejected aliases, and rendered all raw fields before the operation's final operand schema was known. That model cannot distinguish three separate facts: whether a B.IOR word exists, whether the completed bundle schema consumes a field, and which architectural register a consumed field selects.

The mismatch is visible when other headers contribute to the schema. In particular, Matrix PostProcessConfig is known only after B.FPATR and related attributes are composed with BSTART. A disassembler that renders B.IOR from the word alone can therefore guess the wrong arity. The same ambiguity made an omitted instruction indistinguishable from an encoded selector zero.

Decision

PTO direct-operation bundles allow zero or one encoded B.IOR. The active operand schema is resolved after the complete bundle is collected from BSTART, B.FPATR/PostProcessConfig, and every other schema-contributing header. Each header defines the default contribution used when the header or an optional operand is omitted.

The same completed-schema rule applies to the full direct-operation operand record. Ordered B.IOT entries provide every required tile destination/source; B.IOR provides consumed GPR inputs; B.DIM, B.DATR, and related headers provide their named controls; remaining optional fields retain the selected operation's explicit default. Consequently all 109 accepted direct tile operations are schema-representable, while malformed or surplus bindings remain fail-closed.

Encoded-instruction presence, schema operand presence, and selector value are separate architectural concepts. If B.IOR is omitted, every consumed register operand defaults to R0/zero unless its operation explicitly defines another default. If B.IOR is present, selector zero is the real architectural zero register. Fields not consumed by the resolved schema must be encoded as zero, and execution reads only consumed fields.

For the current executable direct-operation catalog, register inputs bind to RegSrc0 and RegSrc1 in architectural operand order. An address, when present, is the first input; otherwise scalar0 is first. No current direct operation consumes RegSrc2 or RegDst; adding such a consumer requires an explicit catalog/schema change and executable evidence. ADR 0058 refines this consumer statement for the complete ordered GPR schema and records the operation-specific control decoding for diagonal and flag0.

TLOAD and TSTORE keep their existing instruction encoding, B.IOR layout, opcode, selector, and instruction length. RegSrc0 supplies the base address; RegSrc1 supplies row stride in elements. A two-dimensional access uses base + (row * row_stride + column) * element_size, with packed four-bit types selecting the byte and nibble from that same logical index. If B.IOR is omitted, base defaults to zero and row stride defaults to resolved LB2/Col for dense rows. If B.IOR is encoded with RegSrc1=zero, the stride is the real zero-register value; the omission default does not apply.

All four B.IOR fields use absolute GPR selectors 0..23. Values 24..31 are reserved in this instruction even where the generic scalar selector namespace assigns them another meaning. They reject during decoded operand legality, before B.IOR state changes. Repeated inputs and source/destination aliases are legal. A second B.IOR is a bundle-control fault and does not overwrite the first binding.

Canonical text uses zero/sp/a0..a7/ra/s0..s8/x0..x3; an assembler may also accept R0..R23. Numeric zero placeholders and relative register spellings are not canonical B.IOR operands. Disassembly collects the full bundle before rendering a schema-shaped operand list. No encoded word produces no line; encoded all-zero produces a B.IOR line with the consumed zero operands. A standalone decoder without bundle context emits a raw/unknown representation.

PTO does not define a decoupled programmable-body B.IOR declaration stream. Multiple declaration records and relative dependency-register semantics are outside the PTO instruction contract.

PE_MASK=0000 remains a strict no-effect case. Schema defaults may be resolved, but no register read, memory access, allocation, rename, fault, consume, descriptor update, or lifetime update occurs.

Consequences

• PTO v0.58 keeps the same B.IOR bit layout and form identity; only legality, schema resolution, canonical text, and dynamic defaulting change.
• Selector-range constraints become machine-readable command-catalog data and are inherited by generated decoders and downstream PTO projections.
• Because the binary-closure fingerprint includes decoded legality constraints, the reviewed 573-form envelope is rebound from 9155a78499c4908e0fdc7ac2a48159eacb5c1dfc78ea724dbedf689369430993 to 5f2855a4a9d8fe8fc2908a3940b9d9153f7232222fdd486a675217106142b4a3. The B.IOR field positions, masks, matches, length, and TLOAD/TSTORE mode/function selectors do not change.
• The ASL bridge no longer requires an encoded B.IOR merely because an operation consumes a scalar/address operand.
• Shared TLOAD/TSTORE use the same unchanged base/row-stride B.IOR fields and omission defaults; an encoded Shared B.IOR still requires every unconsumed field to be zero.
• Historical documents remain evidence of the superseded design; current instruction and assembly pages use semantic sizes and schema-shaped GPR text.

Supersession

This decision supersedes ADR 0032's and ADR 0036's narrow three-field bundle bridge, and ADR 0052/ADR 0054 where they describe B.IOR absence, raw-field assembly, duplicate-register legality, or mandatory scalar binding. ADR 0058 narrowly supersedes the complete-bundle consumer-resolution paragraph above; the B.IOR encoding, omission-versus-zero distinction, and all other retained decisions remain in force.

Verification

The independent points under tests/asl/block/operands/B.IOR/ cover selector range, omission/defaults, encoded-zero semantics, unused nonzero rejection, repeated selectors, second- B.IOR preservation, and zero-mask no effects. scripts/generate-asl-decoders projects the catalog constraints into the executable decoder; scripts/check-catalogs, scripts/check-binary-closure, repository checks, and the release manifest bind the decision to PTO 0.58 artifacts.