Root Cause:
- Else blocks were not propagating variable assignments to outer scope
- Bug 1 (if_form.rs): PHI materialization happened before variable_map reset,
causing PHI nodes to be lost
- Bug 2 (phi.rs): Variable merge didn't check if else branch modified variables
Changes:
- src/mir/builder/if_form.rs:93-127
- Reordered: reset variable_map BEFORE materializing PHI nodes
- Now matches then-branch pattern (reset → materialize → execute)
- Applied to both "else" and "no else" branches for consistency
- src/mir/builder/phi.rs:137-154
- Added else_modified_var check to detect variable modifications
- Use modified value from else_var_map_end_opt when available
- Fall back to pre-if value only when truly not modified
Test Results:
✅ Simple block: { x=42 } → 42
✅ If block: if 1 { x=42 } → 42
✅ Else block: if 0 { x=99 } else { x=42 } → 42 (FIXED!)
✅ Stage-B body extraction: "return 42" correctly extracted (was null)
Impact:
- Else block variable assignments now work correctly
- Stage-B compiler body extraction restored
- Selfhost builder path can now function
- Foundation for Phase 21.x progress
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
