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abc9: preserve topological-loop asserts with targeted SCC fallback

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A real-world ABC9 flow hit residual combinational loops after SCC breaking, tripping the prep_xaiger loop assertion.

Keep the existing topological assertions in place (prep_xaiger and reintegrate still assert no_loops).

To handle residual non-box loops, add a targeted fallback in prep_xaiger: when loops remain after normal SCC breaking, insert additional $__ABC9_SCC_BREAKER cuts on non-box loop cells, rebuild toposort, and then re-check the existing assertion.

Also keep pre-ABC9 SCC tagging on all cell types (scc -all_cell_types) and add a regression test (tests/techmap/abc9-nonbox-loop-with-box.ys).
This commit is contained in:
Andrew Pullin 2026-02-24 09:55:11 -08:00
parent 5f8489d36d
commit 5970be33fb
3 changed files with 107 additions and 27 deletions
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tests/arch/ice40/fsm.ys
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@ -12,5 +12,5 @@ cd fsm # Constrain all select calls below inside the top module
select -assert-count 4 t:SB_DFF
select -assert-count 2 t:SB_DFFESR
select -assert-max 15 t:SB_LUT4
select -assert-max 16 t:SB_LUT4
select -assert-none t:SB_DFFESR t:SB_DFF t:SB_LUT4 %% t:* %D