Combinational LEC: Key-Point Matching and Structural Normalization: Debug Playbook

Debug playbook

Debug Playbook for Combinational LEC: Key-Point Matching and Structural Normalization is anchored on non-vacuous closure rate, counterexample turnaround, and residual-risk trend by requirement class. Convert outcomes into assumption-aware, evidence-backed actions.

1. Freeze assumptions, RTL hash, and engine metadata.

2. Locate first divergence cycle and classify source.

3. Classify mechanism: model mismatch, weak property, setup issue, or RTL defect.

4. Apply one focused reproducer and one bounded fix.

5. Re-run sibling properties and critical covers before closure.

Review memo template

FORMAL REVIEW MEMO - Equivalence Checking (LEC/SEC) / Combinational LEC: Key-Point Matching and Structural Normalization

1. Symptom
   - Failing metric: non-vacuous closure rate, counterexample turnaround, and residual-risk trend by requirement class
   - Trigger context: <mode/reset/env assumptions>
   - First divergence boundary: <model/property/rtl>

2. Mechanism hypothesis
   - Candidate mechanism: Combinational LEC proves that two designs produce identical outputs for identical inputs in the same cycle, making it ideal for pure combinational logic transformations and synthesis-preserved cone rewrites.
   - Competing hypotheses: weak property, over-constraint, setup mismatch, rtl bug
   - Missing evidence: <trace, vacuity report, cover status>

3. Proposed action
   - Smallest reversible change: <assumption/property/rtl>
   - Expected movement: <closure quality, runtime, bug isolation>
   - Regression risk: hidden legal behavior, false pass, schedule churn

4. Signoff
   - Required artifact: closure packet for Combinational LEC: Key-Point Matching and Structural Normalization: assumptions audit, proof status matrix, and replay-ready divergence trace
   - Required owners: formal verification owner, rtl owner, Equivalence Checking (LEC/SEC) owner
   - Final decision: close, bounded closure, rollback, or escalate

Formal deep dive

Equivalence confidence comes from transformation-aware setup and rapid first-divergence diagnosis.

Concept diagram

EQUIVALENCE WORKFLOW

golden and revised design -> mapping and alignment -> mismatch triage -> closure evidence

Metric graph

LEC/SEC DEBUG SIGNALS

setup mismatches        █████
real behavioral deltas  ███
resolved divergences    ███████

Metrics and artifacts to collect

• compare-point match quality

• SEC latency-alignment success

• RTL-to-gate variant coverage

• ECO mismatch root-cause aging

Mini case study

A late ECO mismatch was traced to clock-gating setup, then closed with repeatable SEC alignment rules.

Debug branches

• Classify mismatch source before editing waiver sets.

• Use SEC when latency movement is intentional.

• Replay first divergence in simulation for cross-validation.

Senior review question

Ask: which requirement intent is proven, under which assumptions, and what residual risk remains?

Key takeaways

• Tie each proof claim to assumption boundaries and reachability evidence.

• Prefer minimal reversible fixes and preserve legal behavior visibility.

Common pitfalls

• Treating runtime reduction as proof-quality improvement without audits.

• Declaring closure while critical covers remain unreachable.

• Using broad waivers instead of first-divergence root-cause ownership.

Debug ladder

Sequence: reproduce -> classify -> isolate first divergence -> patch -> revalidate sibling properties.

Avoid mixing assumption and RTL fixes in the same experiment.