[GHC] #14068: Turn tail-recursive functions into recursive jointpoints

[GHC]

#14068: Turn tail-recursive functions into recursive jointpoints
-------------------------------------+-------------------------------------
           Reporter:  nomeata        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The function
 {{{
 let f x y = case y of
               A -> f x' y'
               B -> e2
               C -> e3
 in g f
 }}}
 is not turned into a recursive join point, because the call to `f` is not
 in tail call position. But the recursive calls are, and these matter
 performance-wise! Hence, it would be beneficial to turn this into
 {{{
 let f x y = joinrec $j x y = case x y of
                               A -> $j x' y'
                               B -> e2
                               C -> e3
             in $j x y
 in g f
 }}}

 This has the additional effect that now `f` is no longer recursive and may
 get inlined.

 This came up in #13966, and might go well with #14067.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14068>
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