In report_clock_power, what's the actual difference between a "segment" and a "subtree"?

Short Answer

A segment is the clock buffer tree from one ICG cell to the next ICG cells or sinks in its fanout -- a local slice. A subtree is the clock tree from an ICG cell all the way to the sinks -- the full downstream structure. report_clock_power -type per_segment gives you the local slice view; -type per_subtree gives you the full downstream view from that ICG onward.

Technical Explanation

• A segment is the clock buffer tree from one ICG cell to the next ICG cells or sinks in its fanout -- a local, bounded slice of the tree.
• A subtree is the clock tree from an ICG cell all the way to the sinks -- the full downstream structure from that point, not just the next hop.
• report_clock_power -type per_segment reports the local slice view; -type per_subtree reports the full downstream view -- choosing the wrong one gives you either too narrow or too broad a picture of where power is actually going.
• This distinction also respects the power.clock_network_include_clock_sink_pin_power setting, which affects whether sink pin power is folded into either view.

Follow-up Question & Model Response

"If you wanted to know the total power impact of disabling one specific ICG entirely, would you use per_segment or per_subtree, and why?"

Candidate Model Response: per_subtree, since disabling the ICG removes power consumption for everything downstream of it, not just the immediate next hop that per_segment would report.