[GHC] #8326: Place heap checks common in case alternatives before the case

[GHC]

#8326: Place heap checks common in case alternatives before the case
-------------------------------------+-------------------------------------
        Reporter:  jstolarek         |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.7
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:  8317
 Related Tickets:  #1498             |  Differential Revisions:  Phab:D343
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Terrific.  Could you try the effect of re-enabling the fix in
 [ticket:8317#comment:2].  The code is still in `Simplify.hs`, just
 commented out.  Look for "Disabled until we fix #8326".

 If that works (no perf cost, no binary size increase), then the next step
 is to remove the special case `Note [case on bool]` in `StgCmmExpr`; it
 will never be used because the `Simplify` change will catch the case
 first.

 Might you try those two steps?  Thanks!

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8326#comment:35>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler