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niteria authored
Before this change, for each constructor that we want to allocate a tag for we would traverse a list of all the constructors in a datatype to determine which tag a constructor should get. This is obviously quadratic and for datatypes with 10k constructors it actually makes a big difference. This change implements the plan outlined by @simonpj in https://mail.haskell.org/pipermail/ghc-devs/2017-October/014974.html which is basically about using a map and constructing it outside the loop. One place where things got a bit awkward was TysWiredIn.hs, it would have been possible to just assign the tags by hand, but that seemed error-prone to me, so I decided to go through a map there as well. Test Plan: ./validate On a file with 10k constructors Before: 8,130,522,344 bytes allocated in the heap Total time 3.682s ( 3.920s elapsed) After: 4,133,478,744 bytes allocated in the heap Total time 2.509s ( 2.750s elapsed) Reviewers: simonpj, bgamari Reviewed By: simonpj Subscribers: goldfire, rwbarton, thomie, simonmar, carter, simonpj GHC Trac Issues: #14657 Differential Revision: https://phabricator.haskell.org/D4289
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