[GHC] #14239: Let -fspecialise-aggressively respect NOINLINE (or NOSPECIALISABLE?)

[GHC]

#14239: Let -fspecialise-aggressively respect NOINLINE (or NOSPECIALISABLE?)
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        Reporter:  MikolajKonarski   |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 There is something odd here.   In comment:2 I proposed:
 * NOSPECIALISABLE: please do not specialise this function (even if it
 would otherwise be easy to do so)
 * NOINLINE: please do not inline or specialise this function (even if it
 would otherwise be easy to do so). That is, hide its implementation from
 the caller.

 But it seems odd to allow a function to be inlined, but not to allow it to
 be specialised, doesn't it?  After all, inlining is really just a drastic
 form of specialisation: once per call site!  You can think of
 specialisation as a way to economise on all these inlinings by sharing
 them among similar call sites.

 So I wonder whether we should reverse the semantics thus:

 * NOINLINE: please do not inline this function (even if it would otherwise
 be easy to do so). But GHC is free to specialise it.
 * NOSPECIALISABLE: please do not inline or specialise this function (even
 if it would otherwise be easy to do so).

 You could also argue for inlining and specialisation to be orthogonal, but
 that'd lead to strange cases where you (accidentally perhaps) say to
 inline but never specialise or some other odd combination.  I'm inclined
 to stick with four mutually-exclusive settings for now.

 Anyone else care to comment?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14239#comment:4>
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