Aspects of processing a circuit design include synthesizing the circuit design and placing elements of the synthesized circuit design. After placing and before routing, respective delay values and slacks are determined. A first path having a most negative slack is determined and a first group of candidate paths is selected. The first group of candidate paths is a subset of critical paths of the circuit design, and the first group of candidate paths have delay values within a threshold range of delay values from the delay value of the first path. The first group of candidate paths are modified to reduce the respective delay values and a second group of candidate paths is selected. The second group of candidate paths have circuit structures that match selected circuit structures and are modified to reduce the respective delay values. A critical path having a most negative slack is iteratively selected and modified to reduce the respective delay value.