dpl: negotiation dynamic window

[gudeh]

Summary

Makes the Negotiation Legalizer search window range adaptive instead of fixed X and Y dimensions.

We apply two extensions:

1. An extension is applied depending on instance size.
   • For Y direction we guarantee at least the cell height times the tunable constant (kRowSearchWindow, default 5).
     • We consider for at least kRowSearchWindow valid rows. Multi-height rows may require more rows included.
   • For the X direction we guarantee at least 1 full instance width on each side.
   • Both X and Y are clamped at the same max displacement used for Diamond Search.

Experiments showed far more problems on the Y direction with multi-height and hybrid row structures, requiring more extensions on such dimension.

2. A second extension may be applied if an instance is close to an off-core or macro border, we apply an extension to the search window on the opposite side overlapping the off-core or macro.
   • Experiments showed problems with instances close to borders and neighboring fixed instances.

Type of Change

• New feature

Impact

This solves convergence issues Negotiation Legalizer was having with multi-height cells designs. We were getting search windows too small, and a few instances never moving.

Verification

• I have verified that the local build succeeds (./etc/Build.sh).
• I have run the relevant tests and they pass.
• My code follows the repository's formatting guidelines.
• I have included tests to prevent regressions.
• I have signed my commits (DCO).

Related Issues

This is one of multiple PRs splitting up PR #10226 to make Negotiation the default algorithm at DPL.

This is the last PR to solve all known issues with Negotiation Legalizer. After this one I expect only to make cosmetic modifications and actually switching to the new default.

[gudeh]

The diffs here should be more clear after #10681 is merged.

[gemini-code-assist]

Code Review

This pull request enhances the detailed_placement command in OpenDP by introducing configurable search windows (-site_search_window, -row_search_window) and DRC penalties (-drc_penalty) for the NegotiationLegalizer. It also adds stuck-cell diagnostics, improves GUI debugging with a negotiation violations chart, and updates the observer to track current-iteration movers. Feedback is provided regarding a potential null pointer dereference when retrieving the master of an instance in Opendp::detailedPlacement, which should be guarded to prevent segmentation faults.

[gemini-code-assist]

In the calculation of total_inst_area, inst->getMaster() is called and dereferenced directly without checking if it is nullptr. While instances in a placed design typically have a master, it is safer to add a null check to prevent potential segmentation faults in edge cases or during intermediate database states.

    for (odb::dbInst* inst : block_->getInsts()) {
      odb::dbMaster* master = inst->getMaster();
      if (master != nullptr) {
        total_inst_area += static_cast<int64_t>(master->getWidth())
                           * static_cast<int64_t>(master->getHeight());
      }
    }