gpl: report HPWL after global placement

[minjukim55]

What

Global placement printed HPWL only inside its iteration table and wrote no wirelength metric, so neither the log nor a metrics file had a final global placement number. Now both:

[INFO GPL-1018] Final HPWL (um): 2597.56
"route__wirelength__estimated": 2597.56

void Replace::reportHpwlMetric()
{
  odb::dbBlock* block = db_->getChip()->getBlock();
  const int64_t hpwl = odb::WireLengthEvaluator(block).hpwl();
  log_->info(GPL, 1018, "Final HPWL (um): {:.2f}", block->dbuToMicrons(hpwl));
  log_->metric("route__wirelength__estimated", block->dbuToMicrons(hpwl));
}

Called at the end of Replace::doNesterovPlace(), after NesterovPlace::doNesterovPlace() has updated the db.

Why this name and this evaluator

route__wirelength__estimated measured with odb::WireLengthEvaluator is exactly what dpl reports (src/dpl/src/Opendp.cpp). Under ORFS metrics stages the two land as globalplace__route__wirelength__estimated and detailedplace__route__wirelength__estimated, measured the same way, so the gpl -> dpl HPWL delta is meaningful.

Testing

• ctest -L " gpl ": 75/75 pass. 35 golden logs updated, each with exactly the one new line and nothing else, so placement results are unchanged.
• openroad -metrics ... src/gpl/test/simple01.tcl writes "route__wirelength__estimated": 2597.56.

Note

global_placement -incremental runs nesterov up to twice, so the metric key can appear twice in one metrics file with the final value last (JSON readers keep the last). Same pattern grt already has with antenna_diodes_count.

[gemini-code-assist]

Code Review

This pull request introduces a new method reportHpwlMetric to calculate, log, and record the final Half-Parameter Wire Length (HPWL) metric after global placement, updating various test expectations to reflect this new log output. The review feedback recommends adding defensive null checks for db_, the chip, and the block within reportHpwlMetric to prevent potential segmentation faults.

[gemini-code-assist]

To prevent potential segmentation faults, add defensive null checks for db_, db_->getChip(), and the retrieved block before attempting to evaluate the wire length.

void Replace::reportHpwlMetric()
{
  if (!db_ || !db_->getChip() || !db_->getChip()->getBlock()) {
    return;
  }
  odb::dbBlock* block = db_->getChip()->getBlock();
  const int64_t hpwl = odb::WireLengthEvaluator(block).hpwl();
  log_->info(GPL, 1018, "Final HPWL (um): {:.2f}", block->dbuToMicrons(hpwl));
  log_->metric("route__wirelength__estimated", block->dbuToMicrons(hpwl));
}