StgRhsClosure freevar and argument name duplicates

[Csaba Hruska]

An example for the duplication please check the divModInteger
<https://github.com/ghc/ghc/blob/master/libraries/integer-simple/GHC/Integer/Type.hs#L373-L380>
function from integer-simple GHC.Integer.Type.
The STG (GHC 8.2.2) generated from *divModInteger **:: Integer -> Integer
-> (# Integer, Integer #) *contains duplications in a closure binder list.

Using my custom STG printer it looks like:
module GHC.Integer.Type where

using GHC.Prim
using GHC.Tuple
using GHC.Types

GHC.Integer.Type.divModInteger {-083-} =
  closure (F:) (B:
  n.s84123 {-s84123-}
  d.s84124 {-s84124-}) {
  case GHC.Integer.Type.quotRemInteger {-084-}
         n.s84123 {-s84123-}
         d.s84124 {-s84124-}
  of qr.s84125 {-s84125-} {
    GHC.Prim.(#,#) {-86-} ipv.s84126 {-s84126-} ipv1.s84127 {-s84127-} ->
      let $j.s84128 {-s84128-} =
            closure (F:
            d.s84124 {-s84124-}
*            ipv.s84126 {-s84126-}*
*            ipv1.s84127 {-s84127-}*
*            ipv.s84126 {-s84126-}*
            *ipv1.s84127 {-s84127-}*) (B:
            wild.s84129 {-s84129-}) {
            let $j1.s84130 {-s84130-} =
                  closure (F:
                  d.s84124 {-s84124-}
                  ipv.s84126 {-s84126-}
                  ipv1.s84127 {-s84127-}
                  ipv.s84126 {-s84126-}
                  ipv1.s84127 {-s84127-}
                  wild.s84129 {-s84129-}) (B:
                  wild1.s84131 {-s84131-}) {
                  case _stg_prim_negateInt#
                         wild.s84129 {-s84129-}
                  of sat.s84132 {-s84132-} {
                    DEFAULT ->
                      case _stg_prim_==#
                             wild1.s84131 {-s84131-}
                             sat.s84132 {-s84132-}
                      of sat.s84133 {-s84133-} {
                        DEFAULT ->
                          case _stg_prim_tagToEnum#
                                 sat.s84133 {-s84133-}
                          of wild2.s84134 {-s84134-} {
                            GHC.Types.False {-612-} ->
                              GHC.Prim.(#,#) {-86-}
                                ipv.s84126 {-s84126-}
                                ipv1.s84127 {-s84127-}
                            GHC.Types.True {-645-} ->
                              case GHC.Integer.Type.plusInteger {-066-}
                                     ipv1.s84127 {-s84127-}
                                     d.s84124 {-s84124-}
                              of r'.s84135 {-s84135-} {
                                DEFAULT ->
                                  case GHC.Integer.Type.plusInteger {-066-}
                                         ipv.s84126 {-s84126-}
                                         GHC.Integer.Type.lvl11 {-r50574-}
                                  of q'.s84136 {-s84136-} {
                                    DEFAULT ->
                                      GHC.Prim.(#,#) {-86-}
                                        q'.s84136 {-s84136-}
                                        r'.s84135 {-s84135-}
                                  }
                              }
                          }
                      }
                  }}

            in case ipv1.s84127 {-s84127-}
               of wild1.s84137 {-s84137-} {
                 GHC.Integer.Type.S# {-621-} i#.s84138 {-s84138-} ->
                   case _stg_prim_<#
                          i#.s84138 {-s84138-} 0#
                   of sat.s84140 {-s84140-} {
                     DEFAULT ->
                       case _stg_prim_>#
                              i#.s84138 {-s84138-} 0#
                       of sat.s84139 {-s84139-} {
                         DEFAULT ->
                           case _stg_prim_-#
                                  sat.s84139 {-s84139-}
                                  sat.s84140 {-s84140-}
                           of sat.s84141 {-s84141-} {
                             DEFAULT ->
                               $j1.s84130 {-s84130-}
                                 sat.s84141 {-s84141-}
                           }
                       }
                   }
                 GHC.Integer.Type.Jp# {-r5813-} dt.s84142 {-s84142-} ->
                   $j1.s84130 {-s84130-} 1#
                 GHC.Integer.Type.Jn# {-r5814-} dt.s84143 {-s84143-} ->
                   $j1.s84130 {-s84130-} -1#
               }}

      in case d.s84124 {-s84124-}
         of wild.s84144 {-s84144-} {
           GHC.Integer.Type.S# {-621-} i#.s84145 {-s84145-} ->
             case _stg_prim_<#
                    i#.s84145 {-s84145-} 0#
             of sat.s84147 {-s84147-} {
               DEFAULT ->
                 case _stg_prim_>#
                        i#.s84145 {-s84145-} 0#
                 of sat.s84146 {-s84146-} {
                   DEFAULT ->
                     case _stg_prim_-#
                            sat.s84146 {-s84146-}
                            sat.s84147 {-s84147-}
                     of sat.s84148 {-s84148-} {
                       DEFAULT ->
                         $j.s84128 {-s84128-}
                           sat.s84148 {-s84148-}
                     }
                 }
             }
           GHC.Integer.Type.Jp# {-r5813-} dt.s84149 {-s84149-} ->
             $j.s84128 {-s84128-} 1#
           GHC.Integer.Type.Jn# {-r5814-} dt.s84150 {-s84150-} ->
             $j.s84128 {-s84128-} -1#
         }
  }}


On Mon, Nov 5, 2018 at 2:08 PM Simon Peyton Jones <simonpj at microsoft.com>
wrote:

> I don’t think there should be duplicates in either. Do you have a test
> case that shows duplicates?
>
>
>
> Simon
>
>
>
> *From:* ghc-devs <ghc-devs-bounces at haskell.org> *On Behalf Of *Csaba
> Hruska
> *Sent:* 04 November 2018 11:22
> *To:* ghc-devs at haskell.org
> *Subject:* Re: StgRhsClosure freevar and argument name duplicates
>
>
>
> Is it possible that GHC generates STG with invalid binding semantics for
> certain cases that the Cmm codegen fix or ignore?
>
> This could explain my observations.
>
> I've checked the Stg linter source (StgLint.hs ; GHC 8.2.2 and github
> master) and it does not check StgRhsClosure free var and binder list at all.
>
> And the scope checker function (addInScopeVars) does not check for
> duplicates.
>
>
>
> Any thoughts?
>
>
>
> Cheers,
>
> Csaba
>
>
>
> On Sat, Nov 3, 2018 at 9:53 AM Csaba Hruska <csaba.hruska at gmail.com>
> wrote:
>
> Hi,
>
>
>
> Can StgRhsClosure's freevar list ([occ]) or argument list ([bndr]) contain
> duplicates?
>
>
>
> Cheers,
>
> Csaba
>
>
>
> data GenStgRhs bndr occ
>   = StgRhsClosure
>         CostCentreStack         -- CCS to be attached (default is
> CurrentCCS)
>         StgBinderInfo           -- Info about how this binder is used (see
> below)
>         *[occ]*                   -- non-global free vars; a list, rather
> than
>                                 -- a set, because order is important
>         !UpdateFlag             -- ReEntrant | Updatable | SingleEntry
>         *[bndr]*                  -- arguments; if empty, then not a
> function;
>                                 -- as above, order is important.
>         (GenStgExpr bndr occ)   -- body
>
>
>
>
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