Synthesis & Logic Optimization · All levels
Datapath Inference: Comparison Matrix
Comparison Matrix for Datapath Inference.
Comparison matrix
Retiming and pipelining trade latency, verification cost, and QoR gains.
+------------------+----------------+----------------+----------------+
| 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 — Datapath Inference
+--------------------+------------------------+--------------------------+-------------------------+
| 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
Datapath and retiming gains are only real if formal and timing remain clean.
Concept diagram
DATAPATH + RETIME
operator inference -> stage balancing -> formal proof -> QoR validationMetric graph
FREQUENCY VS LATENCY
Fmax gain ████████
latency cost ████Reports and artifacts
retiming report
datapath inference log
equivalence status
latency impact sheet
Mini case study
Retiming met frequency target, but missing formal hooks delayed closure by two days.
Debug branches
Check retime blockers
Formal first for aggressive moves
Compare with pipeline option
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
Datapath-aware synthesis recognizes arithmetic patterns and maps them to optimized structures; RTL shape determines whether inference succeeds.
Metric: inferred arithmetic structure count, depth reduction, datapath area delta