#9233: Compiler performance regression ---------------------------------+------------------------------------ Reporter: augustss | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Windows | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: ---------------------------------+------------------------------------ Comment (by rwbarton): The following patch reduces compile time for Lennart's program to 15s (compare 9s 7.6.3, 25s 7.8.1, 18s with my previous patch): {{{ diff --git a/compiler/types/Coercion.lhs b/compiler/types/Coercion.lhs index b33eae9..1417ad7 100644 --- a/compiler/types/Coercion.lhs +++ b/compiler/types/Coercion.lhs @@ -1033,6 +1033,7 @@ mkNthCo n (Refl r ty) = ASSERT( ok_tc_app ty n ) Refl r' (tyConAppArgN n ty) where tc = tyConAppTyCon ty r' = nthRole r tc n +mkNthCo n (TyConAppCo _ _ cos) = cos !! n mkNthCo n co = ASSERT( ok_tc_app _ty1 n && ok_tc_app _ty2 n ) NthCo n co where }}} Richard, does this look okay to you (modulo error handling—is it possible that `n >= length cos`?)? I am emboldened by this equation from !OptCoercion {{{ opt_co' env sym mrole (NthCo n (TyConAppCo _ _ cos)) = opt_co env sym mrole (getNth cos n) }}} but cautious due to the comment above it. The simplifier was somehow building up a hugely nested coercion `(Nth:1 (Nth:1 (Nth:1 (... (<String>_R -> <Bool>_R -> <Bool>_R -> ... -> <Bool>_R -> Sym (Identity.NTCo:Identity[0] <Options>_R))...))))`. After this patch, the slowdown from 7.6 to 7.8 on Lennart's program is in line with what I see on other modules. There is still a signification regression overall, but this program was particularly bad. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9233#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler