hakorune/docs/development/current/main/phases/phase-114

Phase 114: if-only return+post parity

Status: DONE

Background

Phase 114 extends if-only JoinIR lowering to support cases where:

• The if-only branch contains an early return
• Post-if statements exist after the if block
• The function eventually returns a value from the post-if path

This pattern is common in early-exit optimization code where certain conditions trigger an immediate return, while the normal flow continues with additional processing.

Test Fixture

File: apps/tests/phase114_if_only_return_then_post_min.hako

// Phase 114: if-only return+post parity
// Tests: early return in if-only with post-if statements

static box Main {
  f(flag) {
    local x = 1
    if flag == 1 { return 7 }
    x = x + 1
    return x
  }

  main() {
    print(f(1))
    print(f(0))
    return "OK"
  }
}

Expected Output:

7
2

Logic:

• f(1): condition true → early return 7
• f(0): condition false → x=1+1=2, return 2

Implementation

This pattern was already supported by the existing JoinIR if-only lowering infrastructure:

• If-select pattern recognition
• Early return handling via exit line routing
• Post-if statement processing in the else path

No new implementation was required - Phase 114 validates that this pattern works correctly in both VM and LLVM backends.

Testing

Smoke Tests

1. VM Backend: tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_vm.sh

   bash tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_vm.sh
   

2. LLVM EXE Backend: tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_llvm_exe.sh

   bash tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_llvm_exe.sh
   

Both tests run with:

• NYASH_DISABLE_PLUGINS=1 (core path only)
• HAKO_JOINIR_STRICT=1 (strict validation)

Regression Tests

Verified backward compatibility with:

• Phase 103: if-only early return (both branches return)
• Phase 113: if-only partial assign (one branch assigns)

All regression tests pass without modifications.

Verification Commands

# Quick VM test
bash tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_vm.sh

# Full LLVM EXE test (requires plugins)
bash tools/smokes/v2/profiles/integration/apps/phase114_if_only_return_then_post_llvm_exe.sh

# Regression verification
bash tools/smokes/v2/profiles/integration/apps/phase103_if_only_early_return_vm.sh
bash tools/smokes/v2/profiles/integration/apps/phase113_if_only_partial_assign_vm.sh
bash tools/smokes/v2/profiles/integration/apps/phase113_if_only_partial_assign_llvm_exe.sh

Architecture Notes

Pattern Coverage

Phase 114 completes the if-only pattern matrix:

Pattern	Phase	Description
Both branches return early	Phase 103	if flag { return A } else { return B }
One branch assigns, else implicit	Phase 113	if flag { x = value } (else preserves x)
One branch returns early, else continues	Phase 114	if flag { return A }; post-code; return B

Box Theory Alignment

This implementation follows Box Theory modularization principles:

• Single responsibility: If-only lowering handles one pattern variation
• Separation of concerns: Exit line routing is independent from assignment merging
• Reusability: Post-if statement processing reuses existing boundary SSA infrastructure
• Fail-Fast: No fallback paths - pattern either matches or explicitly fails

Exit Line Routing

The key to Phase 114 is proper exit line routing:

1. Early return: Creates an exit line directly to function return
2. Post-if path: Continues to post-if statements, then returns
3. No join point: The two paths never merge (one exits early)

This is handled by the existing ExitLineReconnector Box.

Related Documentation

• Phase 103: if-only early return
• Phase 113: if-only partial assign
• JoinIR Architecture Overview
• Exit Line Architecture