Lost parasitic annotations because of dbNetwork details

[povik]

Describe the bug

This bug is with hierarchy enabled through -hier.

When creating a parasitic annotation in read_spef, we find the target net using Network::findNetRelative, which calls dbNetwork::findNet, which preferentially returns dbNet* as opposed to dbModNet*.

In the cases I studied, dbNet* is what the parasitic annotation is eventually registered under inside ConcreteParasitics.

When the parasitic is looked up through findParasiticNetwork(Pin*) which internally calls findParasiticNet, we use a dbModNet* to look up the parasitic network, which finds no annotation. This is because dbNetwork::net(Pin *) returns a dbModNet, and highestConnectedNet is a passthrough as defined on dbNetwork.

This makes us miss the annotation on 3777 driver pins on nangate45/bp_multi_top. The check I'm adding in The-OpenROAD-Project/OpenROAD-flow-scripts#3979 should make this visible.

Expected Behavior

No lost or ignored annotations

Environment

OR 02fc8ab5

To Reproduce

See above

Relevant log output

Screenshots

No response

Additional Context

No response

[povik]

One workaround I have found is to patch

 const Net* dbNetwork::highestConnectedNet(Net* net) const
 {
-  return net;
+  return findFlatNet(net);
 }

but perhaps that will cause new problems and we need to validate how dbNetwork exposes hierarchical netlists against the contracts of sta's Network interface. There's a TODO in dbNetwork::net(Pin *) saying that we should make it return the flat net, i.e. dbNet*.

[povik]

To your attention @maliberty @jhkim-pii @dsengupta0628

[dsengupta0628]

This is likely the reason why my latest CI (with the STA merge) shows garbage WNS/TNS on nangate45/bb_multi_top too thus blocking that merge- so I am working on this with higher priority

00:48:26 [ERROR] finish__timing__setup__ws fail test: -734556 >= -4.92
00:48:26 [ERROR] finish__timing__setup__tns fail test: -8042230 >= -373

 Slew   Delay    Time   Description
-----------------------------------------------------------------------------
 2941115.50    0.00   24.44 v rof1_0__core/place13449/A (BUF_X1)
.....
 67945.23    0.00 715271.75 v rof1_0__core/_12164_/S (MUX2_X1)