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fix(mir): fix else block scope bug - PHI materialization order

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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>
This commit is contained in:
nyash-codex
2025-11-13 20:16:20 +09:00
parent 801833df8d
commit 8b44c5009f
19 changed files with 309 additions and 205 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
src/mir/builder/if_form.rs
View File

@ -93,22 +93,35 @@ impl MirBuilder {
self.debug_push_region(format!("join#{}", join_id) + "/else");
// Scope enter for else-branch
self.hint_scope_enter(0);
// Materialize all variables at block entry via single-pred Phi (correctness-first)
for (name, &pre_v) in pre_if_var_map.iter() {
let phi_val = self.insert_phi_single(pre_branch_bb, pre_v)?;
self.variable_map.insert(name.clone(), phi_val);
if trace_if {
eprintln!(
"[if-trace] else-entry phi var={} pre={:?} -> dst={:?}",
name, pre_v, phi_val
);
}
}
let (else_value_raw, else_ast_for_analysis, else_var_map_end_opt) = if let Some(else_ast) = else_branch {
// Reset variable_map BEFORE materializing PHI nodes (same pattern as then-branch)
self.variable_map = pre_if_var_map.clone();
// Materialize all variables at block entry via single-pred Phi (correctness-first)
for (name, &pre_v) in pre_if_var_map.iter() {
let phi_val = self.insert_phi_single(pre_branch_bb, pre_v)?;
self.variable_map.insert(name.clone(), phi_val);
if trace_if {
eprintln!(
"[if-trace] else-entry phi var={} pre={:?} -> dst={:?}",
name, pre_v, phi_val
);
}
}
let val = self.build_expression(else_ast.clone())?;
(val, Some(else_ast), Some(self.variable_map.clone()))
} else {
// No else branch: materialize PHI nodes for the empty else block
self.variable_map = pre_if_var_map.clone();
for (name, &pre_v) in pre_if_var_map.iter() {
let phi_val = self.insert_phi_single(pre_branch_bb, pre_v)?;
self.variable_map.insert(name.clone(), phi_val);
if trace_if {
eprintln!(
"[if-trace] else-entry phi var={} pre={:?} -> dst={:?}",
name, pre_v, phi_val
);
}
}
let void_val = crate::mir::builder::emission::constant::emit_void(self);
(void_val, None, None)
};