alumacc: alternative cmp unification implementation #4000
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This fails as reordering no longer happens. https://github.com/YosysHQ/yosys/blob/ded586c/tests/opt/opt_expr.ys#L27 |
adrianparvino
commented
Oct 10, 2023
passes/techmap/alumacc.cc
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| @@ -331,9 +331,6 @@ struct AlumaccWorker | |||
| if (GetSize(C) > 1) | |||
| goto next_macc; | |||
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| if (!subtract_b && B < A && GetSize(B)) | |||
| std::swap(A, B); | |||
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In hindsight, this can remain, as cmp unification now is order-independent. This also allows the tests to pass.
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I've rebased and pushed a small fix |
povik
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Feb 4, 2025
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$ltand related are sometimes inhibited from unifying with$subas whenB < A, then the$subcell is unable to swap inputs, but$ltdoes. This resolves this problem by instead consideringsig_aluas an unordered pair mapping.Addendum:
$addand$submight still be unable to unify withshare -aggressivebut changing the behavior [1] causes [2] to fail, so I'm keeping it tocmponly.[1] ded586c#diff-f5a16f8ab735a667cabcdd605b428eeaa92f223f044ef01a91d52141d404633bL334-L336
[2] https://github.com/YosysHQ/yosys/blob/ded586c/tests/opt/opt_expr.ys#L27