#14936: GHC 8.4 performance regressions when using newtypes -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.4.2 Component: Compiler | Version: 8.4.1 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): bgamari, your suspicions have been confirmed: {{{ $ ghc2/inplace/bin/ghc-stage2 -O2 -fforce-recomp -DDEBUG Bug.hs [1 of 1] Compiling Bug2 ( Bug.hs, Bug.o ) WARNING: file compiler/specialise/SpecConstr.hs, line 2078 SpecConstr: bad covars: [sg_s2Ba] $wslowGo_s2A8 (-# ds_X2vv 1#) (wild_Xi `cast` (Sym (N:Foo[0] <(Int, Int)>_R) :: ((Int, Int) :: *) ~R# (Foo (Int, Int) :: *))) w_s2A3 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14936#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler