Stage 1: Design Optimization - 2025.2 English - UG906

The Design Optimization stage runs in sequential steps, as shown in the following diagram.

Figure 1. Design Optimization Steps

In each step, multiple implementation commands such as opt_design, place_design, and route_design can run, and QoR suggestions can be generated. Each step has a target suggestion list. If any generated suggestions appear on this list, the design is reset to the required design stage so the suggestions can be successfully applied. If there are no suggestions on the target list for a step, that step is skipped.

The details of design optimization steps are as follows.

Clean Up XDC

Check the design for issues that cause implementation errors or timing failures that cannot be fixed. If an error is found, the flow exits. No suggestions are generated or applied in this step.

Clean Up Utilization

Look for suggestions that reduce utilization without impacting timing. Other non-utilization suggestions might also be applied if they can be detected and fixed early.

Clean Up Clocking

Run the design to place_design to generate accurate clock skew timing values. If clocking suggestions exist, reset the flow.

Note: If there are no suggestions in the Clean Up Utilization and Clean Up Clocking steps, the flow reports a special First Pass stage. This serves as a baseline reference for later stages. To save compile time, this stage is skipped if suggestions are found.

Clean Up Congestion

Run a limited portion of the router to identify congestion in the design, then generate congestion-related suggestions. Apply these suggestions if they exist.

Note: The log file might show that route_design failed during congestion analysis. This is expected because a full route is not intended at this point.

Clean Up Timing

Generate QoR suggestions based on failing timing paths from the preceding phase’s checkpoint, then rerun the placer.

At the end of the Design Optimization stage, the tool decides whether to exit or to advance the best run to Stage 2: Tool Option Exploration.

To review the modifications made during the IDR, use the QoR suggestion report to see which suggestions were GENERATED and APPLIED at each step. The design run directory also contains multiple checkpoints that you can access for further analysis.