6. PTO assembly (PTO-AS)¶

6.1 Scope¶

This chapter defines the Virtual ISA contract of PTO-AS as the textual form of PTO programs. The normative grammar remains:

• docs/assembly/PTO-AS.md
• docs/assembly/PTO-AS.bnf

6.2 Core form¶

PTO-AS uses an instruction-centric SSA-like textual form. A typical statement shape is:

%dst = tadd %src0, %src1 : (!pto.tile<...>, !pto.tile<...>) -> !pto.tile<...>;

The textual form SHOULD remain deterministic under round-trip tooling.

6.3 Operand classes¶

PTO-AS operands include:

• tile operands
• memory/global operands
• scalar/immediate operands
• event/dependency operands (where applicable)
• attributes/modifiers expressed by dictionary form

Each instruction family MUST define required operand classes and positional constraints.

6.4 Attribute and modifier contract¶

Attributes MUST define:

• name and type
• allowed value domain
• default value policy (if any)
• semantic impact
• diagnostics behavior for invalid values

6.5 Structural validity rules¶

A structurally valid PTO-AS program MUST satisfy:

• operand/result arity consistency
• type-class compatibility per operation contract
• required attribute presence
• parseable and schema-valid statement forms

6.6 Diagnostics contract¶

PTO-AS diagnostics MUST be:

• location-aware for parse and structural errors
• deterministic for equivalent inputs
• actionable with expected-vs-actual constraints

6.7 Compatibility and evolution¶

PTO-AS evolution SHOULD be additive. Breaking textual-syntax changes MUST be versioned and accompanied by migration guidance. Toolchains MUST reject unsupported syntax with deterministic diagnostics.