Zubin pushed to branch wip/27845 at Glasgow Haskell Compiler / GHC Commits: 0689685b by Zubin Duggal at 2026-09-30T17:00:36+05:30 DmdAnal: Make AbsDmd neutral in maxDmd fixes #27845 - - - - - 9 changed files: - + changelog.d/27845 - compiler/GHC/Types/Demand.hs - + testsuite/tests/dmdanal/should_run/T27845.hs - + testsuite/tests/dmdanal/should_run/T27845.stdout - + testsuite/tests/dmdanal/should_run/T27845_Lib.hs - + testsuite/tests/dmdanal/should_run/T27845b.hs - + testsuite/tests/dmdanal/should_run/T27845b.stdout - + testsuite/tests/dmdanal/should_run/T27845b_Lib.hs - testsuite/tests/dmdanal/should_run/all.T Changes: ===================================== changelog.d/27845 ===================================== @@ -0,0 +1,5 @@ +section: compiler +synopsis: Fix a bug where an argument used lazily only by a function's stable + unfolding could be treated as strict in its fields. +mrs: !16746 +issues: #27845 ===================================== compiler/GHC/Types/Demand.hs ===================================== @@ -924,6 +924,8 @@ maxCard (Card a) (Card b) = Card ((a .&. b .&. 0b001) .|. ((a .|. b) .&. 0b110)) maxDmd :: Demand -> Demand -> Demand maxDmd BotDmd dmd2 = dmd2 maxDmd dmd1 BotDmd = dmd1 +maxDmd AbsDmd dmd2 = dmd2 +maxDmd dmd1 AbsDmd = dmd1 maxDmd (n1 :* sd1) (n2 :* sd2) = maxCard n1 n2 :* maxSubDmd sd1 sd2 ===================================== testsuite/tests/dmdanal/should_run/T27845.hs ===================================== @@ -0,0 +1,14 @@ +module Main where +import T27845_Lib (f) +import System.Environment (getArgs) + +{-# NOINLINE mkArg #-} +mkArg :: Int -> Int +mkArg n | n < 0 = n + | otherwise = error ("boom " ++ show n) + +main :: IO () +main = do + n <- length <$> getArgs + let x = mkArg n + print (length (f (x, x) n)) ===================================== testsuite/tests/dmdanal/should_run/T27845.stdout ===================================== @@ -0,0 +1 @@ +0 ===================================== testsuite/tests/dmdanal/should_run/T27845_Lib.hs ===================================== @@ -0,0 +1,11 @@ +module T27845_Lib where + +{-# INLINABLE [2] f #-} +f :: a -> Int -> [a] +f p x = lazyUse p x ++ lazyUse p (x + 1) ++ lazyUse p (x + 2) + +{-# NOINLINE lazyUse #-} +lazyUse :: a -> Int -> [a] +lazyUse p x = p `seq` replicate x p + +{-# RULES "lazyUse" [1] forall p x. lazyUse p x = [] #-} ===================================== testsuite/tests/dmdanal/should_run/T27845b.hs ===================================== @@ -0,0 +1,14 @@ +module Main where +import T27845b_Lib (outer) +import System.Environment (getArgs) + +{-# NOINLINE mkArg #-} +mkArg :: Int -> Int +mkArg n | n < 0 = n + | otherwise = error ("boom " ++ show n) + +main :: IO () +main = do + n <- length <$> getArgs + let x = mkArg n + print (length (outer (x, x) n)) ===================================== testsuite/tests/dmdanal/should_run/T27845b.stdout ===================================== @@ -0,0 +1 @@ +0 ===================================== testsuite/tests/dmdanal/should_run/T27845b_Lib.hs ===================================== @@ -0,0 +1,14 @@ +module T27845b_Lib where + +outer :: a -> Int -> [a] +outer a n = + let {-# INLINABLE [2] g #-} + g x = lazyUse a (x + 0) ++ lazyUse a (x + 1) ++ lazyUse a (x + 2) + in g n ++ g (n + 1) ++ g (n + 2) +{-# NOINLINE outer #-} + +{-# NOINLINE lazyUse #-} +lazyUse :: a -> Int -> [a] +lazyUse p x = p `seq` replicate x p + +{-# RULES "lazyUse" [1] forall p x. lazyUse p x = [] #-} ===================================== testsuite/tests/dmdanal/should_run/all.T ===================================== @@ -37,3 +37,5 @@ test('T25439', normal, compile_and_run, ['']) test('T26748', normal, compile_and_run, ['']) test('T26416', [extra_files(['M1.hs'])], multimod_compile_and_run, ['T26416','M1.hs']) test('T27626', [extra_files(['M2.hs'])], multimod_compile_and_run, ['T27626','M2.hs']) +test('T27845', [extra_files(['T27845_Lib.hs'])], multimod_compile_and_run, ['T27845','T27845_Lib.hs']) +test('T27845b', [extra_files(['T27845b_Lib.hs'])], multimod_compile_and_run, ['T27845b','T27845b_Lib.hs']) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/0689685b1903dc6bd4fbf10efae94ab6... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/0689685b1903dc6bd4fbf10efae94ab6... You're receiving this email because of your account on gitlab.haskell.org. Manage all notifications: https://gitlab.haskell.org/-/profile/notifications | Help: https://gitlab.haskell.org/help