ECO Regression Discipline: Design Space

Design space exploration

For ECO Regression Discipline, options trade QoR gain, risk, and schedule.

Option A — conservative

• Conservative constraints: helps predictability

• Risk: slower PPA gains

• Validate with: first-silicon safety

Option B — balanced

• Balanced QoR tuning: helps stable closure

• Risk: requires discipline

• Validate with: typical product mode

Option C — aggressive compile

• Aggressive compile push: helps fast timing recovery

• Risk: power/hold regressions

• Validate with: late schedule

Option D — structural change

• Structural RTL change: helps long-term fix

• Risk: schedule impact

• Validate with: recurring bottleneck

DESIGN SPACE — ECO Regression Discipline
QoR gain <-> regression risk <-> schedule pressure

Design pitfalls

• Single-metric optimization

• No rollback path

• Weak run comparability

Tradeoff curve

BEFORE / AFTER QOR — ECO Regression Discipline

QoR score
  0 |                     --- target zone
 -1 |        ● regression
 -2 |             ● baseline
 -0.5|                  ● after fix
    +----------------------------------> iteration

Validate timing + area + power, not one number.

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 -> release

Metric 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