performance regressions

[Richard Eisenberg]

Hi devs,

Phab has shown up some performance regressions in my recent commits. See https://phabricator.haskell.org/harbormaster/build/2607/. The failures except for haddock.base are new, and evidently my fault. They didn't show up on Travis. Will look into it shortly, but I doubt over the weekend.

I don't think this should hold up the 7.10 fork, however. I have a suspicion as to what caused the problem -- the reimplementation of TcInteract.matchFam. That reimplementation was solely to reduce code repetition between TcInteract.matchFam and FamInstEnv.reduceTyFamApp_maybe. It can safely be rolled back -- just use the implementation of matchFam that existed before my commits.

I'll look into this Monday at the latest, but if a remedy is needed sooner, try the technique above.

Why would these failures show up on Phab but not on Travis?

Sorry about the bother!

Thanks,
Richard
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