#11131: Eta reduction/expansion loop -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- In the build log for HEAD today you'll see: {{{ WARNING: file compiler\simplCore\SimplCore.hs, line 604 Simplifier bailing out after 10 iterations [148, 4, 4, 4, 4, 4, 4, 4, 4, 4] Size = {terms: 290, types: 237, coercions: 56} }}} when compiling`Data/ByteString/Builder/Prim/Internal/Floating.hs`. There is a loop here: in each simplifier pass we get an eta-expansion and an eta reduction, which cancel each other out. This is bad. Here is the offending snippet of code {{{ ((bindIO @ () @ () ($fStorableDouble_$cpoke (castPtr @ Word8 @ Double op) x) ((\ (ds :: ()) -> (\ (eta_B1 :: State# RealWorld) -> (k `cast` (NTCo:IO[0] <()>_R :: IO () ~R# (State# RealWorld -> (# State# RealWorld, () #)))) eta_B1) `cast` (Sym (NTCo:IO[0] <()>_R) :: (State# RealWorld -> (# State# RealWorld, () #)) ~R# IO ())) `cast` (<()>_R -> NTCo:IO[0] <()>_R ; Sym (NTCo:IO[0] <()>_R) :: (() -> IO ()) ~R# (() -> IO ())))) `cast` (NTCo:IO[0] <()>_R :: IO () ~R# (State# RealWorld -> (# State# RealWorld, () #)))) }}} At this point `k` is in scope with arity 2. Actually its binding is {{{ k :: IO () k = bindIO @ Word64 @ () a_s2As a_s2Au }}} I'm not precisely sure why this goes wrong, but it's very clearly bogus, so I'm opening a ticket to keep track. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11131 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler