#12754: Adding an explicit export list halves compilation time. -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- A file only containing a 10000 constructor enumeration type compiles twice as fast with an explicit export list compare to having no export list. {{{ # print "module A where" print "module A (T ( .. ) ) where" print "\n" print "data T = C" for i in range(0,10000): print (" | C" + str(i)) }}} Without an export list: {{{ [1 of 1] Compiling A ( A.hs, A.o ) real 0m22.872s user 0m19.653s sys 0m0.868s }}} With the export list: {{{ [1 of 1] Compiling A ( A.hs, A.o ) real 0m11.249s user 0m10.428s sys 0m0.435s }}} The culprit here is `exports_from_avail`, in the case that no export list is provided, the things to export are gathered from the `GlobalRdrEnv`. Each constructor is placed in its own `Avail` which are then combined by `plusAvail` which is implemented using the expensive `unionLists`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12754 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler