#11163: New exhaustiveness checker breaks T5642 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: gkaracha Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2 Resolution: | Keywords: pattern | checker, PatternMatchWarnings Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gkaracha): After merging Phab:D1795, I checked again the situation with T5642: With the old pattern match checker the deviation (for bytes allocated) for #5642 was 196.8%. With the current HEAD it is 222.3%, yet this increase is not only due to the new checker. Disabling coverage checking for the test gives deviation 212.0%, which means that only 10.3% is due to the new checker. Concerning this 10.3%, the module uses the generics library and function `to :: Rep a x -> a` has 100 clauses, all with nested patterns. Most importantly, `Rep` is a type family, which means that the new checker goes the extra mile to ensure they are all well-typed. Hence, this 10.3% is quite reasonable (the old pattern match checker was --in most cases-- faster because it did not take into account types). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11163#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler