#8668: SPECIALIZE silently fails to apply ----------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 (amd64) | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+------------------------------------- I have a small example where GHC refuses to specialize a call to `(+)`, compiling with -O2. The two files are Foo.hs (http://lpaste.net/98464) and Main.hs (http://lpaste.net/98342). There seem to be two problems: 1. The active `SPECIALIZE` pragma should be applied, but isn't. This can be seen by comparing the core and runtimes of `fcTest` (slow) vs `vtTest` (fast). I need this version of the pragma in my real code as the phantom type `m` is reified, so I need to specialize the vector code without specifying the phantom type. 2. I can get `fcTest` to run fast if I use the commented-out `SPECIALIZE` pragma instead. However, that pragma seems very straightforward to me (all types are concrete). The docs indicate that GHC should automatically specialize in most cases, why does it not specialize to the commented-out signature automatically? This problem is also posted here: http://stackoverflow.com/questions/21071706/specialization-with- constraints -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8668 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler