ADR 0057: Tile Classification and Execution-Engine Aliases

• Date: 2026-08-09
• Deciders: PTO ISA maintainers

Context

The active Tile tree used migration-era categories such as tile-tile-elementwise, reduction, and complex-layout, while the PTO programming surface already defines eight stable instruction classes. The binary carrier name TEPL also mixed an encoding identity with an execution-engine classification. That made navigation, engine ownership, and downstream assembly terminology drift even though the Mode/Function encoding itself remained valid.

Decision

The normative owners are the mnemonic ASL records below asl/tile/ and the engine/alias clauses in asl/arch/overview/. This ADR records rationale only.

PTO uses these instruction classes: Sync and Config; Elementwise Tile-Tile; Tile-Scalar and Immediate; Reduce and Expand; Memory and Data Movement; Matrix and Matrix-Vector; Layout and Rearrangement; and Irregular and Complex. Direct Tile operations currently occupy the latter seven classes. Classification is semantic and remains independent of execution-engine selection.

Every direct Tile operation names exactly one engine: VEC, TLSU, CUBE, or SFU. VEC is restricted to elementwise operations. Operations requiring specialized or complex hardware use SFU; memory/data-transfer operations use TLSU; matrix operations use CUBE. A semantic class does not imply an engine: for example, a data-rearrangement operation may use TLSU, while a complex elementwise operation may use SFU.

The existing TEPL Mode/Function bit encoding is unchanged. BSTART.VEC and BSTART.SFU are accepted assembly aliases constrained by the selected Tile operation's engine. BSTART.TEPL remains an accepted compatibility spelling. Canonical assembly and disassembly render BSTART.VEC or BSTART.SFU, never BSTART.TEPL. Alias selection cannot create a new encoding, change selector ownership, or change instruction semantics.

Consequences

• ASL paths, mirrored Markdown, and mirrored independent tests use the PTO instruction classes rather than encoding-family directories.
• Catalog projections expose both semantic class and execution engine while retaining Mode, Function, selector, mask, and match unchanged.
• Downstream assemblers may accept the TEPL compatibility spelling, but all new generated text and disassembly use the engine-specific canonical spelling.
• TEPL remains only the unchanged binary carrier and compatibility spelling; it is not an execution-engine classification.