#16382: Lifting a function from where clause to top level causes compilation time to triple -------------------------------------+------------------------------------- Reporter: danidiaz | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.2 Keywords: | 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: -------------------------------------+------------------------------------- I have this program that depends on the library "red-black-record" version 2.0.2.2 on Hackage: {{{#!hs {-# LANGUAGE DataKinds, TypeApplications #-} module Main where import Data.RBR (FromList,Delete,Variant,I,injectI,winnowI,match) import GHC.TypeLits type Phase01 = FromList '[ '("ctor1",Int), '("ctor2",Bool), '("ctor4",Char), '("ctor3",Char), '("ctor6",Char), '("ctor5",Char), '("ctor10",Char), '("ctor11",Char), '("ctor13",Char), '("ctor14",Char), '("ctor39",Char), '("ctor46",Char), '("ctor47",Char), '("ctor44",Char), '("ctor43",Char), '("ctor7",Char), '("ctor9",Char), '("ctor20",Char), '("ctor45",Char), '("ctor21",Char), '("ctor48",Char), '("ctor49",Char), '("ctor50",Char), '("ctor41",Char), '("ctor33",Char), '("ctor32",Char), '("ctor42",Char), '("ctor22",Char), '("ctor23",Char), '("ctor8",Char), '("ctor40",Char), '("ctor29",Char), '("ctor24",Char), '("ctor38",Char), '("ctor25",Char), '("ctor26",Char), '("ctor27",Char), '("ctor28",Char), '("ctor36",Char), '("ctor52",Char), '("ctor51",Char), '("ctor53",Char), '("ctor12",Char), '("ctor54",Char), '("ctor15",Char), '("ctor31",Char), '("ctor30",Char), '("ctor34",Char), '("ctor35",Char), '("ctor17",Char), '("ctor16",Char), '("ctor18",Char), '("ctor19",Char), '("ctor37",Char) ] type Phase02 = Delete "ctor1" Int Phase01 main :: IO () main = print (match @"ctor17" (fromPhase1ToPhase2 (injectI @"ctor1" 2))) where fromPhase1ToPhase2 :: Variant I Phase01 -> Variant I Phase02 fromPhase1ToPhase2 v = case winnowI @"ctor1" @Int v of Right z -> injectI @"ctor2" False Left l -> l }}} "red-black-record" provides extensible variants; the code is basically removing a branch from a variant with 50-plus branches, and then trying to match another branch. It is type family-heavy code. The code as it is takes **~9 seconds** to compile on my machine. But when I move the `fromPhase1ToPhase2` function to the top level (including the signature) compilation time balloons to **~29 seconds**. Is there a reason it should be so? As another datapoint, moving the function to the top level but omitting the complex type-level map parameters (`Phase01`, `Phase02`) using partial type signatures (also requires a new type application) compiles in **~9 seconds** again. {{{#!hs {-# LANGUAGE PartialTypeSignatures #-} {-# OPTIONS_GHC -Wno-partial-type-signatures #-} -- ... type Phase02 = Delete "ctor1" Int Phase01 fromPhase1ToPhase2 :: Variant I _ -> Variant I _ fromPhase1ToPhase2 v = case winnowI @"ctor1" @Int @Phase01 v of Right z -> injectI @"ctor2" False Left l -> l main :: IO () main = print (match @"ctor17" (fromPhase1ToPhase2 (injectI @"ctor1" 2))) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16382 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler