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Ömer Sinan Ağacan authored
The type synonym expander was doing redundant work by looking at same types again and again. This patch fixes the loop code when both of the types can be expanded, to do `O(min(n, m))` comparisons and `O(n + m)` expansions, where `n` is expansions of the first type and `m` is expansions of the second type. Reported by sjcjoosten in T10547. Test Plan: Added a regression test that was taking several minutes to type check before this patch. Reviewers: bgamari, simonpj, austin, ezyang Reviewed By: bgamari, simonpj, austin, ezyang Subscribers: simonpj, thomie Differential Revision: https://phabricator.haskell.org/D2198 GHC Trac Issues: #10547
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