#12689: DataCon wrappers get in the way of rules -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- This is a spin-off of https://ghc.haskell.org/trac/ghc/ticket/12618#comment:25: Simon writes there: Actually this is already a problem today. It's just rendered more prominent now that even `(:)` has a wrapper. Consider {{{#!hs data T = MkT {-# UNPACK #-} !Int {-# RULES "fT" f MkT = True "gT" forall x. g (MkT x) = x #-} f :: (Int -> T) -> Bool {-# NOINLINE f #-} f x = True g :: T -> Int {-# NOINLINE g #-} g (MkT x) = x+1 }}} yields {{{ Foo.hs:9:1: warning: [-Winline-rule-shadowing] Rule "fT" may never fire because 'Foo.$WMkT' might inline first Probable fix: add an INLINE[n] or NOINLINE[n] pragma for 'Foo.$WMkT' Foo.hs:10:1: warning: [-Winline-rule-shadowing] Rule "gT" may never fire because 'Foo.$WMkT' might inline first Probable fix: add an INLINE[n] or NOINLINE[n] pragma for 'Foo.$WMkT' }}} What to do? If we are to match these rules, we really must delay inlining the wrapper for `MkT` (after inlining we get a mess of unboxing etc). So either we must allow you to add a `NOINLINE` pragma to `MkT`; or we must add one automatically (e.g. `NOINLINE [1]`). Delaying all consructor-wrapper inlining to phase 1 is potentially quite drastic, because case-of-known-constructor wouldn't happen until the wrappers are inlined. Maybe that's ok; I'm not sure. Worth trying I think. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12689 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler