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ADR 0053: PTO ISA 0.58.0 Tile Operation Cleanup

  • Date: 2026-08-05
  • Deciders: PTO ISA maintainers

Context​

The 0.58.0 release performed a tile operation cleanup. This ADR records four decisions that refine the operation set before release closure.

Decisions​

D1: Remove TRANDOM​

TRANDOM (hardware random number generation) is removed. It can be adequately simulated in software via a scalar PRNG seeded from a cycle counter or system entropy source. A dedicated tile instruction for random number generation does not justify the encoding space and implementation complexity at this maturity level.

D2: Keep TSORT name, make sort width a parameter​

TSORT32 is renamed back to TSORT. The sort width (previously hard-coded as 32 in the name) becomes an instruction parameter (sort_width), allowing the same mnemonic to cover multiple sort widths in future profiles without renaming.

D3: Restore THISTOGRAM, MGATHER_MASK, MSCATTER_MASK, MGATHER_CAS​

These four operations were removed in the initial 0.58.0 catalog but are restored:

  • THISTOGRAM — tile histogram computation is performance-critical for ML training profiling and cannot be efficiently emulated.
  • MGATHER_MASK, MSCATTER_MASK — masked gather/scatter are required for sparse tensor operations.
  • MGATHER_CAS — atomic compare-and-swap gather is required for lock-free data structure operations on global memory.

D4: Rename TMA family to TLSU​

The "Tile Memory Accelerator" (TMA) family is renamed to "Tile Load-Store Unit" (TLSU). This name more accurately describes the family's role (tile ↔ global memory data movement) and avoids confusion with the hardware TMA unit naming.

All "family": "TMA" references in catalogs, ASL sources, and tests are renamed to "family": "TLSU". BSTART.TLSU is the family notation used by explanatory assembly sequences; the accepted binary command forms remain the exact named BSTART.* instructions. In particular, the restored selectors use BSTART.MGATHER.MASK, BSTART.MSCATTER.MASK, and BSTART.MGATHER.CAS; a generic BSTART.TLSU encoded form is not introduced.

Consequences​

  • Operation count changes: 106 → 109 (remove TRANDOM: −1, restore THISTOGRAM: +1, restore MGATHER_MASK/MSCATTER_MASK/MGATHER_CAS: +3)
  • Encoding ABI: TSORT selector unchanged, sort width becomes a parameter. The retained masked/CAS selectors keep Functions 6–8. To avoid an encoding collision, the newer Shared-TLSU variants use Functions 9–12 for TMOV and Function 14 for TSTORE.SPART; Function 13 remains GMOV.
  • Command-form count changes from 96 to 99 by restoring the three exact masked/CAS bundle-start forms.
  • Generated evidence files must be regenerated to reflect the new family name and operation/command counts.
Last updated on by Kevin Zhou