[GHC] #12632: Inline and Noinline pragmas ignored for instance functions

[GHC]

#12632: Inline and Noinline pragmas ignored for instance functions
-------------------------------------+-------------------------------------
        Reporter:  jeremy-list       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by jeremy-list):

 Compiling this code with "-O2 -ddump-rule-firings":

 {{{
 class Inv a where
   inv :: a -> a

 instance Inv Bool where
   {-# NOINLINE inv #-}
   inv = not

 {-# RULES "force-inline" forall (a :: Bool) . inv a = not a #-}

 main = print (inv True)
 }}}
 The output from GHC is:

 {{{
 [1 of 1] Compiling Main             ( sample1.hs, sample1.o )

 sample1.hs:8:11: warning: [-Winline-rule-shadowing]
     Rule "force-inline" may never fire because ‘inv’ might inline first
     Probable fix: add an INLINE[n] or NOINLINE[n] pragma for ‘inv’
 Rule fired: force-inline
 Rule fired: Class op show
 Linking sample1 ...
 }}}
 Here the warning is incorrect because it ignores the NOINLINE pragma, but
 the rule is fired because the function isn't actually inlined.

 If the NOINLINE pragma is changed to INLINE the output from GHC is
 identical: the warning is emitted and the rule is fired. This is incorrect
 because the rule shouldn't fire if the function is inlined.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12632#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler