[GHC] #6084: Add stg_ap_pnnv and related call patterns

[GHC]

#6084: Add stg_ap_pnnv and related call patterns
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        Reporter:  SimonMeier        |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Runtime System    |          Version:  7.4.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:  8313              |  Related Tickets:
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Changes (by int-e):

 * status:  closed => new
 * resolution:  fixed =>


Comment:

 This needs more work--currently the stage 2 compiler crashes occasionally.
 The obvious problem is that the new fast path in the code generated by
 {{{StgCmmLayout.slowCall}}} does not untag the pointer to the closure
 (this affects the arity test as well which makes it hard to trigger). I
 tried to fix this as follows:
 {{{
 --- a/compiler/codeGen/StgCmmLayout.hs
 +++ b/compiler/codeGen/StgCmmLayout.hs
 @@ -192,9 +192,12 @@ slowCall fun stg_args
          let n_args = length stg_args
          if n_args > arity && optLevel dflags >= 2
             then do
 +             funv <- (CmmReg . CmmLocal) `fmap` assignTemp fun
 +             let untaggedFunv = cmmOffset dflags funv (-1) -- is the tag
 always 1?
 +
               fast_code <- getCode $
                  emitCall (NativeNodeCall, NativeReturn)
 -                  (entryCode dflags (closureInfoPtr dflags fun))
 +                  (entryCode dflags (closureInfoPtr dflags untaggedFunv))
                    (nonVArgs ((P,Just fun):argsreps))

               slow_lbl <- newLabelC
 @@ -202,10 +205,9 @@ slowCall fun stg_args
               is_tagged_lbl <- newLabelC
               end_lbl <- newLabelC

 -             funv <- (CmmReg . CmmLocal) `fmap` assignTemp fun
 -
 -             let correct_arity = cmmEqWord dflags (funInfoArity dflags
 funv)
 -                                                  (mkIntExpr dflags
 n_args)
 +             let correct_arity = cmmEqWord dflags
 +                                 (funInfoArity dflags untaggedFunv)
 +                                 (mkIntExpr dflags n_args)

               pprTrace "fast call" (int n_args) $ return ()
 }}}
 But now I get
 {{{
 ghc-stage2: internal error: PAP object entered!
 }}}
 and indeed PAPs are treated specially in the {{{stg_ap_*}}} functions, and
 the fast path does not mirror that special treatment.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6084#comment:19>
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