[GHC] #8275: Loopification breaks profiling

[GHC]

#8275: Loopification breaks profiling
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        Reporter:  jstolarek            |            Owner:
            Type:  bug                  |           Status:  patch
        Priority:  high                 |        Milestone:  7.8.1
       Component:  Profiling            |          Version:  7.7
      Resolution:                       |         Keywords:
Operating System:  Unknown/Multiple     |     Architecture:
 Type of failure:  Building GHC failed  |  Unknown/Multiple
       Test Case:                       |       Difficulty:  Unknown
        Blocking:                       |       Blocked By:  8456
                                        |  Related Tickets:
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Comment (by parcs):

 Replying to [comment:33 jstolarek]:
 > Thanks Patrick! Currently I'm without my main laptop so I can't verify
 your patch - I will do it in Wednesday, unless someone else can do it
 before.

 Okay, great.

 And here's an ugly PoC patch that moves the self-loop label below the
 stack check:

 {{{
 #!diff
 diff --git a/compiler/codeGen/StgCmmBind.hs
 b/compiler/codeGen/StgCmmBind.hs
 index 16477c8..029b8af 100644
 --- a/compiler/codeGen/StgCmmBind.hs
 +++ b/compiler/codeGen/StgCmmBind.hs
 @@ -481,7 +481,6 @@ closureCodeBody top_lvl bndr cl_info cc args arity
 body fv_details
                  -- of a self-recursive tail call. See Note
                  -- [Self-recursive tail calls] in StgCmmExpr
                  ; loop_header_id <- newLabelC
 -                ; emitLabel loop_header_id
                  -- Extend reader monad with information that
                  -- self-recursive tail calls can be optimized into local
                  -- jumps
 diff --git a/compiler/codeGen/StgCmmHeap.hs
 b/compiler/codeGen/StgCmmHeap.hs
 index 55ddfd4..f01d042 100644
 --- a/compiler/codeGen/StgCmmHeap.hs
 +++ b/compiler/codeGen/StgCmmHeap.hs
 @@ -615,6 +615,12 @@ do_checks mb_stk_hwm checkYield mb_alloc_lit do_gc =
 do
      Nothing -> return ()
      Just stk_hwm -> tickyStackCheck >> (emit =<< mkCmmIfGoto (sp_oflo
 stk_hwm) gc_id)

 +  self_loop_info <- getSelfLoop
 +  case self_loop_info of
 +    Just (_,loop_header_id,_)
 +        | checkYield && isJust mb_stk_hwm -> emitLabel loop_header_id
 +    _otherwise -> return ()
 +
    if (isJust mb_alloc_lit)
      then do
       tickyHeapCheck
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8275#comment:34>
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