Re: [GHC] #8335: Create more specialized entries to GC

6 Oct 2015

      #8335: Create more specialized entries to GC
-------------------------------------+-------------------------------------
        Reporter:  jstolarek         |                Owner:  bgamari
            Type:  task              |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.7
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
-------------------------------------+-------------------------------------
Changes (by bgamari):

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

Comment:

 I think this may be fixed (at least in the current state of `master`,
 a3c78abcbdfe5025dc704acdcd0a85c78cabbd6b).

 This program (taken from #8326),
 {{{#!hs
 {-# LANGUAGE MagicHash #-}
 module Test where

 import GHC.Prim
 import GHC.Types

 f :: Int# -> Int
 f x | isTrue# (x ># 0#) = I# x
     | otherwise         = -(I# x)
 }}}

 produces this Core,
 {{{#!hs
 f :: Int# -> Int
 f =
   \ (x_anw :: Int#) ->
     case tagToEnum# @ Bool (># x_anw 0#) of _ [Occ=Dead] {
       False -> I# (negateInt# x_anw);
       True -> I# x_anw
     }
 }}}

 which is ultimately lowered to this C--,
 {{{
  Test.f_entry() //  [R2]
          { info_tbl: [(cyv,
                        label: Test.f_info
                        rep:HeapRep static { Fun {arity: 1 fun_type:
 ArgSpec 4} })]
            stack_info: arg_space: 8 updfr_space: Just 8
          }
      {offset
        cyv:
            Hp = Hp + 16;
            if (Hp > HpLim) goto cyz; else goto cyy;
        cyz:
            HpAlloc = 16;
            R2 = R2;
            R1 = Test.f_closure;
            call (stg_gc_fun)(R2, R1) args: 8, res: 0, upd: 8;
        cyy:
            if (%MO_S_Gt_W64(R2, 0)) goto cyL; else goto cyI;
        cyL:
            I64[Hp - 8] = GHC.Types.I#_con_info;
            I64[Hp] = R2;
            R1 = Hp - 7;
            call (P64[Sp])(R1) args: 8, res: 0, upd: 8;
        cyI:
            I64[Hp - 8] = GHC.Types.I#_con_info;
            I64[Hp] = -R2;
            R1 = Hp - 7;
            call (P64[Sp])(R1) args: 8, res: 0, upd: 8;
      }
  }]
 }}}

 Jan, would you agree that all looks okay here?

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8335#comment:2
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler