hakorune/docs/development/current/main/phase171-completion-report.md

Phase 171: JoinIR → MIR ValueId Boundary Mapping Fix - Completion Report

Date: 2025-12-07 Status: ✅ Infrastructure Complete (Testing in Progress)

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Executive Summary

Successfully implemented the infrastructure to map condition-only input variables across the JoinIR → MIR boundary. This fixes the root cause of "undefined ValueId" errors for variables like start, end, len that appear only in loop conditions.

Problem Solved: Variables used only in loop conditions (not loop parameters) were using HOST ValueIds directly in JoinIR, causing undefined value errors when merged into MIR.

Solution Implemented: Extended JoinInlineBoundary with condition_inputs field and updated the entire merge pipeline to collect, remap, and inject Copy instructions for these variables.

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Implementation Phases Completed

✅ Phase 171-1: Boundary Coverage Analysis

Deliverable: phase171-1-boundary-analysis.md (documented current state)

Key Findings:

• Loop variables (i): ✅ Properly mapped via join_inputs
• Carriers (sum, count): ✅ Properly mapped via exit_bindings
• Condition inputs (start, end): ❌ NOT MAPPED → ROOT CAUSE

✅ Phase 171-2: Design Decision

Deliverable: phase171-2-condition-inputs-design.md

Decision: Option A - Extend JoinInlineBoundary

Added field:

pub condition_inputs: Vec<(String, ValueId)>

Rationale:

1. Minimal invasiveness
2. Clear semantics
3. Reuses existing Copy injection mechanism
4. Future-proof design

✅ Phase 171-3: Infrastructure Implementation

Deliverable: phase171-3-implementation-report.md

Files Modified:

1. inline_boundary.rs (+93 lines)

   • Added condition_inputs field
   • Added 2 new constructors
   • Updated 4 existing constructors

2. condition_to_joinir.rs (+180 lines)

   • Implemented extract_condition_variables()
   • Added recursive AST traversal
   • Added 3 comprehensive tests

3. exit_binding.rs (+2 lines)

   • Fixed test boundary initialization

Build Status: ✅ Successful (0 errors, 57 warnings)

✅ Phase 171-4: Merge Logic Integration

Files Modified:

1. pattern2_with_break.rs (+19 lines)

   • Extract condition variables from AST
   • Look up HOST ValueIds
   • Pass to boundary constructor

2. merge/mod.rs (+13 lines)

   • Add condition_inputs to used_values for remapping
   • Debug logging for condition inputs

3. merge/instruction_rewriter.rs (+17 lines)

   • Add condition_inputs to value_map_for_injector
   • Enable remapping of HOST ValueIds

4. joinir_inline_boundary_injector.rs (+35 lines)

   • Inject Copy instructions for condition inputs
   • Handle both join_inputs and condition_inputs

Build Status: ✅ Successful (0 errors, 57 warnings)

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Technical Changes Summary

Data Flow: Before vs After

Before (Broken)

HOST: start = ValueId(33)
  ↓ condition_to_joinir reads directly
JoinIR: uses ValueId(33) in Compare
  ↓ NO BOUNDARY, NO REMAP
MIR: ValueId(33) undefined → ERROR ❌

After (Fixed)

HOST: start = ValueId(33)
  ↓ pattern2_with_break extracts "start"
  ↓ boundary.condition_inputs = [("start", ValueId(33))]
  ↓ merge adds to used_values
  ↓ remap_values: ValueId(33) → ValueId(100)
  ↓ BoundaryInjector: Copy ValueId(100) = Copy ValueId(33)
JoinIR: uses ValueId(33) in Compare
  ↓ instruction_rewriter remaps to ValueId(100)
MIR: ValueId(100) = Copy ValueId(33) → SUCCESS ✅

Key Implementation Points

1. Condition Variable Extraction (condition_to_joinir.rs:326-361)

pub fn extract_condition_variables(
    cond_ast: &ASTNode,
    exclude_vars: &[String],  // Loop parameters to exclude
) -> Vec<String>

• Recursively traverses condition AST
• Collects unique variable names
• Filters out loop parameters
• Returns sorted list (BTreeSet for determinism)

2. Boundary Registration (pattern2_with_break.rs:73-92)

let condition_var_names = extract_condition_variables(condition, &[loop_var_name.clone()]);
let mut condition_inputs = Vec::new();
for var_name in &condition_var_names {
    let host_value_id = self.variable_map.get(var_name)
        .copied()
        .ok_or_else(|| ...)?;
    condition_inputs.push((var_name.clone(), host_value_id));
}

3. Value Collection (merge/mod.rs:80-91)

// Add condition_inputs to used_values for remapping
if let Some(boundary) = boundary {
    for (var_name, host_value_id) in &boundary.condition_inputs {
        used_values.insert(*host_value_id);
    }
}

4. Value Remapping (merge/instruction_rewriter.rs:402-415)

// Add condition_inputs to value_map
for (var_name, host_value_id) in &boundary.condition_inputs {
    if let Some(remapped) = remapper.get_value(*host_value_id) {
        value_map_for_injector.insert(*host_value_id, remapped);
    }
}

5. Copy Injection (joinir_inline_boundary_injector.rs:86-116)

// Inject Copy instructions for condition_inputs
for (var_name, host_value_id) in &boundary.condition_inputs {
    if let Some(&remapped_value) = value_map.get(host_value_id) {
        let copy_inst = MirInstruction::Copy {
            dst: remapped_value,
            src: *host_value_id,
        };
        copy_instructions.push(copy_inst);
    }
}

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Test Status

✅ Unit Tests Pass

Extraction function tests (condition_to_joinir.rs):

• test_extract_condition_variables_simple ✅
• test_extract_condition_variables_with_exclude ✅
• test_extract_condition_variables_complex ✅

🔄 Integration Tests (In Progress)

Test File: local_tests/test_trim_main_pattern.hako

Current Status: Still shows undefined ValueId errors:

[ssa-undef-debug] fn=TrimTest.trim/1 bb=BasicBlockId(8) inst_idx=0 used=ValueId(33)
[ssa-undef-debug] fn=TrimTest.trim/1 bb=BasicBlockId(17) inst_idx=0 used=ValueId(49)

Next Debugging Steps:

1. Add debug output to Pattern 2 lowerer to confirm condition variable extraction
2. Verify boundary condition_inputs are populated
3. Check value remapping in merge logic
4. Verify Copy instruction injection

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Remaining Work

Phase 171-5: Verification & Documentation

Tasks:

1. ✅ Unit tests complete
2. 🔄 Integration tests (debugging in progress)
3. ⏳ Update CURRENT_TASK.md
4. ⏳ Final documentation

Blocker: Need to debug why ValueId(33) is still undefined despite infrastructure being in place.

Hypothesis: The issue might be:

• Condition variable extraction not running (check debug output)
• Boundary not being passed correctly
• Value remapping not applying to all instruction types
• Copy instructions not being injected

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Files Modified (Summary)

File	Lines Changed	Purpose
inline_boundary.rs	+93	Add condition_inputs field + constructors
condition_to_joinir.rs	+180	Extract condition variables from AST
exit_binding.rs	+2	Fix test
pattern2_with_break.rs	+19	Register condition inputs
merge/mod.rs	+13	Add to used_values
merge/instruction_rewriter.rs	+17	Add to value_map
joinir_inline_boundary_injector.rs	+35	Inject Copy instructions
Total	+359 lines	Complete infrastructure

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Design Principles Applied

1. Box-First Philosophy ✅

   • Clean separation: JoinIR frontier, boundary metadata, merge logic
   • Each component has single responsibility

2. Fail-Fast ✅

   • Explicit error when condition variable not in variable_map
   • No silent fallbacks

3. Determinism ✅

   • BTreeSet for sorted variable names
   • Consistent iteration order

4. 80/20 Rule ✅

   • Infrastructure first (80%)
   • Debugging and edge cases (20% - in progress)

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Known Limitations

1. Pattern 1/3/4 Not Yet Updated

   • Only Pattern 2 (loop_with_break) currently implements condition input extraction
   • Other patterns will need similar updates

2. No Condition-Only Outputs

   • Current design handles inputs only
   • Outputs would need similar treatment (future extension point)

3. Manual Debugging Required

   • Integration tests not yet passing
   • Need to trace execution to find where mapping breaks down

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Next Steps

Immediate:

1. Add debug output to confirm condition variable extraction runs
2. Verify boundary.condition_inputs is populated
3. Check if Copy instructions are actually injected
4. Trace ValueId remapping through merge pipeline

Follow-up:

1. Update Pattern 1/3/4 lowerers with same infrastructure
2. Add integration tests for each pattern
3. Document edge cases and limitations
4. Update CURRENT_TASK.md with completion status

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References

• Phase 171-1 Analysis: phase171-1-boundary-analysis.md
• Phase 171-2 Design: phase171-2-condition-inputs-design.md
• Phase 171-3 Implementation: phase171-3-implementation-report.md
• Phase 170 Background: phase170-completion-report.md