hakorune/docs/development/current/main/phases/phase-279/README.md

Phase 279 P0: Type propagation pipeline SSOT unification

Status: ✅ completed (2025-12-22)

Goal: eliminate “two compiler pipelines” by making type propagation run through one SSOT entry with a fixed order across routes, so the same fixture cannot pass in one route and fail in another purely due to ordering drift.

Background trigger:

• A real incident occurred where PHI type resolution ran before BinOp re-propagation in one route, but after it in another, producing LLVM parity breakage. This is effectively “two compilers”.

Scope:

• Define a single type propagation pipeline entry (SSOT).
• Make every route that emits MIR/LLVM metadata call that SSOT entry.
• Add fail-fast guards that make order drift impossible to miss.

SSOT references:

• Current status log: docs/development/current/main/10-Now.md
• Backlog entry: docs/development/current/main/30-Backlog.md

Implementation guide:

• docs/development/current/main/phases/phase-279/P0-INSTRUCTIONS.md
• Claude Code instructions:
  • docs/development/current/main/phases/phase-279/P0-CLAUDE.md

Non-goals:

• new language features (no Union/Any)
• broad optimizer rewrite
• adding new environment variables

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SSOT Entry Point

File: src/mir/type_propagation/pipeline.rs

This is the single source of truth for type propagation. All routes MUST call this pipeline.

Main Entry

• TypePropagationPipeline::run(function, value_types) - SSOT entry point

Pipeline Steps (fixed order)

1. Copy propagation (initial) - Propagate types through Copy chains
2. BinOp re-propagation - Numeric promotion (Int+Float→Float, String+String→StringBox)
3. Copy propagation (after promotion) - Propagate promoted types
4. PHI type inference (private step) - Resolve PHI node types

Callers (exhaustive list)

• src/mir/builder/lifecycle.rs::finalize_module() - Builder lifecycle route (AST → MIR)
• src/mir/join_ir_vm_bridge/joinir_function_converter.rs::propagate_types() - JoinIR bridge route (JoinIR → MIR)

Consumer (read-only)

• LLVM harness (Python llvm_py/) - Consumer only, no type propagation logic (best-effort forbidden)

Fail-Fast Guards

Structural guarantee (Phase 279 P0):

• PHI type inference is a private step inside TypePropagationPipeline
• lifecycle.rs and joinir_function_converter.rs cannot call PhiTypeResolver directly
• Only public API: TypePropagationPipeline::run()
• Order drift is structurally impossible (private encapsulation)

Environment variables (existing, reused):

• NYASH_PHI_GLOBAL_DEBUG=1 - PHI type inference debug output
• NYASH_BINOP_REPROP_DEBUG=1 - BinOp re-propagation debug output

No new environment variables (Phase 279 P0 policy: prevent env var sprawl)

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Implementation Summary

Files changed (6 total):

• New: src/mir/type_propagation/mod.rs - Module definition
• New: src/mir/type_propagation/pipeline.rs - SSOT pipeline implementation (~300 lines)
• Modified: src/mir/mod.rs - Add type_propagation module export
• Modified: src/mir/builder/lifecycle.rs - Replace with SSOT call (~400 lines removed)
• Modified: src/mir/join_ir_vm_bridge/joinir_function_converter.rs - Replace with SSOT call (~100 lines removed)
• Modified: docs/development/current/main/phases/phase-279/README.md - Document SSOT entry

Code reduction:

• Removed ~500 lines of duplicate BinOp re-propagation logic
• Consolidated 2 implementations into 1 SSOT

Completion:

• docs/development/current/main/phases/phase-279/P0-COMPLETION.md - Completion record