#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: patch Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, Wiki Page: | Phab:D1268 -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"a5cb27f323a0c78f61db1a3c5338045b0981850b/ghc" a5cb27f3/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="a5cb27f323a0c78f61db1a3c5338045b0981850b" Make type-class dictionary let binds deterministic When generating dictionary let binds in dsTcEvBinds we may end up generating them in arbitrary order according to Unique order. Consider: ``` let $dEq = GHC.Classes.$fEqInt in let $$dNum = GHC.Num.$fNumInt in ... ``` vs ``` let $dNum = GHC.Num.$fNumInt in let $dEq = GHC.Classes.$fEqInt in ... ``` The way this change fixes it is by using `UniqDFM` - a type of deterministic finite maps of things keyed on `Unique`s. This way when you pull out evidence variables corresponding to type-class dictionaries they are in deterministic order. Currently it's the order of insertion and the way it's implemented is by tagging the values with the time of insertion. Test Plan: I've added a new test case to reproduce the issue. ./validate Reviewers: ezyang, simonmar, austin, simonpj, bgamari Reviewed By: simonmar, simonpj, bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1396 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:129> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler