Synthesis & Logic Optimization · All levels
ECO Regression Discipline: Comparison Matrix
Comparison Matrix for ECO Regression Discipline.
Comparison matrix
Patch aggressiveness trades turnaround time against validation burden.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | stable | slower | new design spin |
| Balanced | practical | needs monitoring | normal closure |
| Aggressive | fast | higher risk | schedule crunch |
| Structural | durable | long loop | repeat offender |
+------------------+----------------+----------------+----------------+When to choose each approach
Select strategy by risk budget, not convenience.
Interview traps
Skipping manifest diff
No side-effect regression
Evidence comparison
SYNTHESIS EVIDENCE MATRIX — ECO Regression Discipline
+--------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+--------------------+------------------------+--------------------------+-------------------------+
| compile QoR report | metric movement | root-cause class | inspect transform logs |
| SDC diff | constraint drift | library quality | rerun with baseline SDC |
| library map diff | cell view changes | RTL intent quality | lock/validate lib set |
| topo vs logical QoR | physical correlation | final route signoff | PD trial correlation |
| regression matrix | closure stability | architecture optimality | decide merge/rollback |
+--------------------+------------------------+--------------------------+-------------------------+Synthesis deep dive
Incremental and ECO synthesis protect schedule only with strict regression discipline.
Concept diagram
INCREMENTAL ECO LOOP
identify delta -> localized compile -> patch -> regression -> releaseMetric graph
ECO CYCLE TIME
full compile ███████████
incremental █████Reports and artifacts
incremental reuse
ECO patch list
LEC status
regression matrix
Mini case study
Localized compile cut turnaround 40%, but skipped LEC caused rollback.
Debug branches
Reuse ratio is not enough
Patch locality check
Always include equivalence hooks
Senior review question
Ask: what evidence proves this QoR move is real and stable?
Key takeaways
State exact run context (RTL, SDC, libs, switches) with every QoR claim.
Re-run timing, area, and power regressions after each synthesis ECO.
Common pitfalls
Comparing runs with mismatched constraints or library views.
Timing-only fixes that violate power or area budgets.
Skipping equivalence checks after structural changes.
Principal synthesis review addendum
Regression discipline prevents late-stage surprises by enforcing setup/hold, power, and equivalence checks after every ECO wave.
Metric: post-ECO regressions caught, corner coverage, signoff approval latency