#14626: No need to enter a scrutinised value -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: heisenbug Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: performance Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13861 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Yes, the whole point heisenbug's patch is to return `xs` without entering it. But we we are returning a badly-tagged pointer. If in the above code we return R1, that will be bad. Really we should un-tag it only if/when we enter it. For example if we had {{{ data MkS = MkS ![Int] f (MkT xs) = MkS xs }}} then when we build `MkS xs` we need a correctly tagged xs, not a de-tagged one. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14626#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler