- Delete legacy jump_args/jump_args_layout fields from BasicBlock
- Add return_env/return_env_layout for Return-specific metadata
- Rename set_return_edge_args() → set_return_env() (clearer semantics)
- Remove 8 legacy helper methods (has/get/set/clear legacy_jump_args)
- Simplify set_jump/branch_with_edge_args (remove legacy sync, keep API)
- Update edge_args_from_terminator() to terminator-only (no fallback)
- Update 10+ JoinIR handler/test sites to use new API
This completes Phase 260 P0 → P2 migration: edge-args are now
exclusively in terminator operands (Jump/Branch) or Return-specific
metadata (renamed from legacy terminology).
BREAKING: BasicBlock.jump_args field removed. Use terminator edge-args
or block.return_env() for Return blocks.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
tomoaki
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