mbff: Use getLibertyCell (now testCell) instead of libertyCell.

[Logikable]

dbNetwork::getLibertyCell (now testCell) returns the TestCell if available. After 89f47ff, certain parts of the MBFF code began to compare the TestCell against the base cell. This causes a crash in GetPinMapping() in certain PDKs.

[gemini-code-assist]

Code Review

This pull request replaces the private getLibertyCell method with a public testCell method in dbNetwork and updates its usages, including replacing libertyCell calls in src/gpl/src/mbff.cpp. Feedback focuses on several instances in mbff.cpp where the returned lib_cell pointer from testCell is dereferenced or used without a null check, which could lead to potential crashes or undefined behavior if the cell does not have a corresponding liberty cell.

[gemini-code-assist]

The network_->testCell(cell) call can return nullptr if the cell does not have a corresponding liberty cell (e.g., for physical-only cells). Dereferencing lib_cell directly on the following line without a null check will cause a crash. We should add a defensive null check and return a fallback value.

  const sta::LibertyCell* lib_cell = network_->testCell(cell);
  if (lib_cell == nullptr) {
    return d;
  }

[gemini-code-assist]

The network_->testCell(cell) call can return nullptr. Dereferencing lib_cell directly on the following line to access sequentials() will cause a crash. We should wrap the access in a null check.

  const sta::LibertyCell* lib_cell = network_->testCell(cell);
  if (lib_cell != nullptr) {
    const auto& seqs = lib_cell->sequentials();
    if (!seqs.empty()) {
      ret.func_idx = GetMatchingFunc(seqs.front().data(), inst, isTray);
    }
  }

[gemini-code-assist]

The network_->testCell(cell) call can return nullptr. Passing a null pointer to sta::LibertyCellPortIterator will cause undefined behavior or a crash. We should add a null check and return an empty map if lib_cell is null.

  const sta::LibertyCell* lib_cell = network_->testCell(cell);
  if (lib_cell == nullptr) {
    return {};
  }
  sta::LibertyCellPortIterator port_itr(lib_cell);

[maliberty]

Please add a unit test that would fail without this fix.

[Logikable]

Done, PTAL.