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());
      }
    }

[eder-matheus]

@codex review

[chatgpt-codex-connector]

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[gudeh]

@eder-matheus @osamahammad21 This one should be our priority considering DPL. With this PR merged we have solved all known issues with Negotiation legalizer.

[stefanottili]

@gudeh please give ispd15_mgc_superblue12 a try.
Last time tried with/without negotiation legalizer it failed because gpl placed a cell wider then the stdcell row width between two macros and then dpl was not able to move this cell.

[osamahammad21]

Instead of the per-side deficit-and-reallocate logic, model each axis as one budget of 2 * window positions explored by two pointers walking outward from the anchor. Each consumes from the shared budget until it runs out or hits a wall; when one side walls early, the other naturally absorbs the rest. No separate deficit computation, nothing explored past a wall, and the both-walls case falls out for free. disable_window_extension reduces to just the per-side cap (window vs max_displacement).

Also, Can we get a multi-height test here? All the negotiation tests are single-height gcd, so none of the new code paths actually run.

[osamahammad21]

what if both ends are hitting a wall? or what if the extended window itself is hitting a wall?

[gudeh]

I see an example with only a 2 row strip sandwiched by macros. The window fits nicely on the available space.

And if it were to overlap with the macro (as it did before) is a problem because before we accept any actual movement we check for site validity, even after the window extension.

[osamahammad21]

how do you plan to test this?