[GHC] #12659: Unactionable core lint warning due to floating out

[GHC]

#12659: Unactionable core lint warning due to floating out
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:  newcomer       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 I was looking through the build log to try and make it a bit less noisy by
 removing some warnings. There were quite a lot of core lint warnings which
 complain about INLINE progams on loop breakers. However,
 sometimes these bindings are not marked INLINE at the source level but by
 GHC itself.

 {{{
 cmmDebugLink :: [Label] -> [DebugBlock] -> [DebugBlock]
 cmmDebugLink labels blocks = map link blocks
   where blockPos :: LabelMap Int
         blockPos = mapFromList $ flip zip [0..] labels
         link block = block { dblPosition = mapLookup (dblLabel block)
 blockPos
                            , dblBlocks   = map link (dblBlocks block)
                            }
 }}}

 For example, in this function, `link` gets floated out to the top level
 and then marked as `INLINE` even though it is self-recursive. This causes
 the following warning:

 {{{
 *** Core Lint warnings : in result of CorePrep ***
 5170    <no location info>: warning:
 5171        [RHS of link_slxp :: DebugBlock -> DebugBlock]
 5172        INLINE binder is (non-rule) loop breaker: link_slxp
 5173
 }}}

 But because it's generated by the compiler, there isn't a sensible way to
 suppress the warning.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12659>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler