Incremental Compile: Expanded Case Study

Extended case study

Closure review: reuse ratio, localized QoR delta, compile turnaround time regressed after a change touching Incremental Compile.

Background

Team previously had stable baseline across weekly compile runs and agreed guardbands.

Symptoms observed

• reuse ratio, localized QoR delta, compile turnaround time moved beyond threshold

• Mismatch between local and CI runs

• Owner disagreement on first fix

Investigation timeline

1. Hour 0: freeze manifests and compare run metadata

2. Hour 1: isolate section/topic-specific failure pattern

3. Hour 2: verify constraints and library view consistency

4. Hour 3: inspect transform and mapping deltas

5. Hour 4: choose one reversible fix

6. Hour 5: execute full regression matrix

7. Hour 6: publish closure memo and next actions

Root cause

Root cause centered on Incremental Compile: Incremental compile reuses stable optimization regions while targeting changed cones, reducing churn and iteration cost.

Fix and validation

• Targeted synthesis tweak with audit trail

• Re-run incremental reuse report, changed-cone map, QoR diff

• Update dashboard and handoff notes

Lessons learned

• Compare like-for-like runs only

• Assign clear owner before ECO

• Keep rollback ready

CASE STUDY — Incremental Compile
baseline / regression / recovery QoR snapshot

Sequence under stress

SYNTHESIS FLOW — Incremental Compile

RTL + constraints
      |
      v
elaboration + checks
      |
      v
mapping + optimization
      |
      v
QoR reports (timing/area/power)
      |
      v
incremental ECO + regression

Primary metric: reuse ratio, localized QoR delta, compile turnaround time

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

Incremental compile reuses stable optimization regions while targeting changed cones, reducing churn and iteration cost.

Metric: reuse ratio, localized QoR delta, compile turnaround time