opt -max_iter

[akashlevy]

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[greptile-apps]

Greptile Summary

This PR adds a -max_iter <number> option to the opt pass that caps the number of optimization loop iterations, defaulting to 20 (with 0 meaning unlimited). It also fixes a pre-existing bug where the finish log message always said "Finished fast OPT passes." regardless of mode.

• Behavioral change: max_iter now defaults to 20, whereas previously opt ran until convergence with no iteration limit. Designs that previously needed more than 20 iterations will now stop early with only a log-header notification and no hard warning or non-zero exit.
• atoi for argument parsing (line 165): invalid non-numeric input silently becomes 0 (unlimited) rather than producing an error message.
• Double blank line in the help block (lines 72–73): an extra log(\"\ \") produces an unnecessary gap in --help output.

Confidence Score: 3/5

The PR introduces a default iteration cap of 20 on a pass that previously ran until convergence, which is a silent behavioral change for existing users whose designs may need more iterations.

The default of 20 iterations changes the long-standing unconditional convergence behavior of opt. Any design that previously required more than 20 loop passes will now stop early; the only signal is a log header, with no hard warning or error. This could go unnoticed in automated flows and leave netlists in a less-optimised state without the user realising it.

passes/opt/opt.cc — specifically the default value of max_iter and the absence of a louder warning when the limit is reached.

Important Files Changed

Filename	Overview
passes/opt/opt.cc	Adds -max_iter option to the opt pass with a default of 20; introduces a breaking behavioral change (previously unlimited iterations), uses atoi without error checking, and contains a redundant opt_clean call in the fast_mode max-iter exit path.
docs/source/code_examples/macro_commands/opt.ys	Documentation example updated to reflect the new -max_iter loop-termination condition; change is accurate and consistent with the implementation.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[opt execute] --> B{fast_mode?}

    B -- yes --> FM_START[iter = 0]
    FM_START --> FM_LOOP[iter++\nopt_expr\nopt_merge\nscratchpad_unset\nopt_dff]
    FM_LOOP --> FM_CHK{did_something?}
    FM_CHK -- no --> FM_POST[opt_clean after loop]
    FM_CHK -- yes --> FM_CLEAN[opt_hier / opt_boundary\nopt_clean]
    FM_CLEAN --> FM_MAX{max_iter > 0\nand iter >= max_iter?}
    FM_MAX -- yes --> FM_REACHED[reached_max_iter = true]
    FM_REACHED --> FM_POST
    FM_MAX -- no --> FM_LOG[log Rerunning...]
    FM_LOG --> FM_LOOP
    FM_POST --> END

    B -- no --> NF_INIT[opt_expr\nopt_merge -nomux\niter = 0]
    NF_INIT --> NF_LOOP[iter++\nscratchpad_unset\nopt_muxtree/reduce/merge\nopt_share/dff/hier/boundary\nopt_clean\nopt_expr]
    NF_LOOP --> NF_CHK{did_something?}
    NF_CHK -- no --> END
    NF_CHK -- yes --> NF_MAX{max_iter > 0\nand iter >= max_iter?}
    NF_MAX -- yes --> NF_REACHED[reached_max_iter = true]
    NF_REACHED --> END
    NF_MAX -- no --> NF_LOG[log Rerunning...]
    NF_LOG --> NF_LOOP

    END[design.optimize/sort/check\nlog Finished OPT passes]

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