dcalc: CCS ReceiverModel accessors, converged-Ceff exposure, reportGateDelay crash fix, receiver-cap Ceff solve

[saurav-fermions]

Summary

Four CCS (Composite Current Source) delay-calc changes: three purely-additive read-only accessors, one Signal-11 crash fix, and one flag-gated (default-OFF) enhancement to the ccs_ceff effective-capacitance solve. With flags off / accessors not called, timing is byte-identical to upstream.

1. Read-only ReceiverModel capacitance accessors (TableModel.{hh,cc})

Adds hasCapacitanceModel() / capacitance() to evaluate the CCS receiver-capacitance tables OpenSTA already parses into capacitance_models_ but never consumes. Used only by an additive external diagnostic; the NLDM delay path does not call them → flag-off byte-identical.

2. Expose converged CCS effective capacitance (ArcDelayCalc.hh, CcsCeffDelayCalc.*)

Additive read-only effectiveCapacitance() on ArcDelayCalc (base returns a negative sentinel), overridden by CcsCeffDelayCalc to return the region-0 effective capacitance the most recent gateDelay() converged to (negative sentinel on NLDM fallback). Purely additive — no existing delay value changes.

3. reportGateDelay crash fix (CcsCeffDelayCalc.cc)

reportGateDelay() can be called directly (e.g. by report_dcalc) without a preceding gateDelay() for the same arc. It used the stale drvr_pin_ member and an unset parasitics_ member, dereferencing bad pointers and crashing (Signal 11). The fix resolves parasitics_ from the scene and uses the drvr_pin parameter, matching gateDelay().

4. Receiver capacitance in ccs_ceff Ceff solve (CcsCeffDelayCalc.*, flag-gated, default OFF)

When the receiver model is enabled, the per-region far-cap (c1) contribution of any load pin carrying a CCS receiver_capacitance model is swapped from its constant NLDM pin cap to the library's region-dependent receiver cap (Cr1 in the Miller/transition region below the receiver threshold, Cr2 in the settled region). Pins without a receiver model keep the constant NLDM contribution (graceful fallback). Default OFF → byte-identical to prior ccs_ceff.

Testing

• Full OpenSTA ctest suite: 6083/6084 pass. The single failure (tcl.power.vcd_detailed) is a pre-existing last-digit floating-point rounding diff in the power module that fails identically on unmodified master (unrelated to this change).
• set_ccs_delay_calc regressions pass; default-OFF behavior verified byte-identical on both the global-NLDM-default and ccs_ceff-receiver-off axes.

Notes

• dcalc/DelayCalc.i is a SWIG interface; clang-format intentionally not run on src/sta/* per project convention.
• Items 1–3 are additive/bug-fix; item 4 is default-off. No behavior change for existing users.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[gemini-code-assist]

Code Review

This pull request implements support for the CCS receiver-capacitance model in the Ceff delay calculations, introducing a process-global toggle, region-dependent receiver capacitance evaluations, and exposing the converged effective capacitance. The review feedback identifies three critical safety issues: an uninitialized member variable drvr_pin_ in gateDelay(), a potential null pointer dereference when accessing parasitics_ in reportGateDelay(), and a missing null check for the rf parameter in capacitanceModel().

[gemini-code-assist]

The member variable drvr_pin_ is never initialized or assigned in gateDelay(). However, it is subsequently used on line 161 (pinPvt(drvr_pin_, scene, min_max)) and in watchWaveform() (line 617). This results in undefined behavior or crashes due to dereferencing an uninitialized or stale pointer. Assign drvr_pin_ = drvr_pin; at the beginning of gateDelay() to resolve this.

  drvr_pin_ = drvr_pin;
  parasitics_ = scene->parasitics(min_max);
  parasitic_ = parasitic;
  output_waveforms_ = nullptr;
  last_ceff_ = -1.0;  // OpenROAD-fork: ccs-delay2 -- reset; set on CCS path.

[gemini-code-assist]

If scene->parasitics(min_max) returns nullptr (e.g., if parasitics are not defined or SPEF is not loaded for the current corner), dereferencing parasitics_ on lines 796, 799, and 804 will cause a crash (Signal 11). Add a null check for parasitics_ before accessing its members.

  parasitics_ = scene->parasitics(min_max);
  if (parasitics_ && parasitic && !parasitics_->isPiElmore(parasitic)) {
    // Use the drvr_pin PARAMETER, not the stale drvr_pin_ member.
    pi_elmore =
        parasitics_->reduceToPiElmore(parasitic, drvr_pin, rf, scene, min_max);
  }
  std::string report =
      table_dcalc_->reportGateDelay(drvr_pin, arc, in_slew, load_cap, pi_elmore,
                                    load_pin_index_map, scene, min_max, digits);
  if (parasitics_) {
    parasitics_->deleteDrvrReducedParasitics(drvr_pin);  // OpenROAD-fork: ccs-delay-path
  }

[gemini-code-assist]

If the rf parameter is passed as nullptr, calling rf->index() will dereference a null pointer and crash. Adding a defensive null check at the beginning of capacitanceModel() will safely protect this method and its callers (hasCapacitanceModel() and capacitance()).

{
  if (rf == nullptr)
    return nullptr;
  const size_t idx = segment * RiseFall::index_count + rf->index();

[saurav-fermions]

Thanks:

• reportGateDelay parasitics null (CcsCeffDelayCalc.cc:~800): added — if scene->parasitics(min_max) is null (parasitics not loaded for the corner) we skip the pi/Elmore reduction and cleanup instead of dereferencing.
• ReceiverModel::capacitanceModel null RiseFall (TableModel.cc): returns nullptr on a null rf instead of calling rf->index().

On the critical note about drvr_pin_ in the POCV block (CcsCeffDelayCalc.cc:~161): that pinPvt(drvr_pin_, …) usage is pre-existing code (it's on master, unchanged by this PR — see the same line there), not introduced here. This PR's crash fix is specifically the reportGateDelay() path, which previously used the stale drvr_pin_ member and an unset parasitics_; it now uses the drvr_pin parameter and resolves parasitics_ from the scene. If the pre-existing POCV drvr_pin_ path warrants hardening, that's worth a separate dedicated fix. ccs/dcalc suite passes (5/5).