syn: Add gate remapping by Ashenhurst-Curtis decomposition with shared set

[povik]

Summary

[Describe your changes here]

Type of Change

• New feature

Impact

New syn::acd_resynth command for invoking timing-oriented ACD resynthesis. This has the form of an undocumented developer command in the interim before we get SDC propagation infrastructure which will allow us to fold this optimization step directly into synthesize.

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

[Link issues here]

[gemini-code-assist]

Code Review

This pull request introduces the Ashenhurst-Curtis decomposition (ACD) flow for gate-level resynthesis, adding new files for ACD synthesis, timing, and target indexing, while refactoring the combinational mapper to use the new target index. The review feedback highlights several critical issues and improvements: potential out-of-bounds memory accesses in ArrivalSet::atExit (when outputs exceed two) and outputArrival (when a port is not found), an unconditional overwrite of the budget parameter that ignores caller-specified limits, a redundant null check for sta in populateCutTiming, and a missing continue statement in buildIndex when handling tie cells with zero inputs.

[gemini-code-assist]

When inputs.empty() is true, tie cells are identified and stored in index.tie_low / index.tie_high. However, the loop does not continue afterward, meaning the code will proceed to evaluate fexprEval and npnSemiclassAllRepr with 0 inputs, which is buggy and redundant. Adding a continue avoids this.

Suggested change

	}
	}
	}
	index.tie_high = {cell, 0};
	}
	}
	continue;
	}

[maliberty]

not resolved?

[maliberty]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 138ac4b393

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[chatgpt-codex-connector]

Require per-output slack before accepting cuts

For a two-output cut, this accepts a replacement solely because the cut-wide worst slack improves. If the original roots have slacks like -100ps and -20ps, a candidate with -50ps and -80ps passes this check because the minimum improved from -100ps to -80ps, even though the second endpoint lost 60ps; the same can turn a previously positive side output negative. Since commit() rewires all roots of the substitution, the acceptance test should also enforce per-root no-regression/non-violation, not just WNS improvement.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Use unique remap instance names

When the input design already contains an instance named remap0/remapN (or a netlist from a previous run is reloaded), this raw dbInst::create returns nullptr on duplicate names in ODB, and the following inst->getITerm(...) dereferences it. Use ODB's uniquifying create/helper for generated remap objects so acd_resynth -apply cannot crash on ordinary name collisions.

Useful? React with 👍 / 👎.