scope invariants in core

[Ranjit Jhala]

Hi Simon -- Terrific, this seems to be the ticket...! Thanks a bunch! Ranjit.

On Mon, Mar 18, 2013 at 1:34 PM, Simon Peyton-Jones
<simonpj at microsoft.com> wrote:
> That does seem odd.
>
> Use -dppr-debug so you can see the actual unique on each Id, just to make sure the print-name isn't different from the underlying unique.
>
> In an older version of GHC (before March 2012; patch below) variables could not be bound to unboxed tuples, so if your fork is based on a sufficiently old version that might be a problem.
>
> Aha.  Before the patch below, I see this code in Core Lint
>
>      -- If the binder is an unboxed tuple type, don't put it in scope
>      ; let scope = if (isUnboxedTupleType (idType var)) then
>                        pass_var
>                    else lintAndScopeId var
>
> and indeed the patch below removes those lines.  So that's it.  You need to update. Whether you can do so for just this one patch is more than I can say!
>
> Simon
>
> commit 09987de4ece1fc634af6b2b37173b12ed46fdf3e
> Author: Max Bolingbroke <batterseapower at hotmail.com>
> Date:   Sun Mar 18 00:00:38 2012 +0000
>
>     Support code generation for unboxed-tuple function arguments
>
>     This is done by a 'unarisation' pre-pass at the STG level which
>     translates away all (live) binders binding something of unboxed
>     tuple type.
>
>     This has the following knock-on effects:
>       * The subkind hierarchy is vastly simplified (no UbxTupleKind or ArgKind)
>       * Various relaxed type checks in typechecker, 'foreign import prim' etc
>       * All case binders may be live at the Core level
>
>
> |  -----Original Message-----
> |  From: glasgow-haskell-users-bounces at haskell.org
> | [mailto:glasgow-haskell-users-  bounces at haskell.org] On Behalf Of
> | Ranjit Jhala
> |  Sent: 18 March 2013 18:06
> |  To: glasgow-haskell-users at haskell.org
> |  Subject: scope invariants in core
> |
> |  Hi all,
> |
> |  I have been manipulating CoreExpr to convert it to A-Normal Form.
> |  Mostly, things have been working fine, but I hit an error this
> | morning of the form:
> |
> |      lq_anf__d11u is out of scope
> |
> |  where lq_anf__d11u is a binder I have introduced in the transformed
> | expression
> |
> |      Data.ByteString.Internal.c_strlen =
> |     (\ (ds_d11l :: GHC.Ptr.Ptr Foreign.C.Types.CChar) ->
> |        case ds_d11l of lq_anf__d11t { GHC.Ptr.Ptr ds_d11n ->
> |        let {
> |          lq_anf__d11x
> |            :: GHC.Prim.State# GHC.Prim.RealWorld
> |               -> (# GHC.Prim.State# GHC.Prim.RealWorld, GHC.Word.Word32 #)
> |          [LclId]
> |          lq_anf__d11x =
> |            \ (ds_d11q :: GHC.Prim.State# GHC.Prim.RealWorld) ->
> |              case {__pkg_ccall main strlen GHC.Prim.Addr#
> |                           -> GHC.Prim.State# GHC.Prim.RealWorld
> |                           -> (# GHC.Prim.State# GHC.Prim.RealWorld,
> | GHC.Prim.Word# #)}
> |                     ds_d11n ds_d11q
> |              of lq_anf__d11u { __DEFAULT ->
> |              case lq_anf__d11u of lq_anf__d11v { (# ds_d11p, ds_d11o #) ->
> |              let {
> |                lq_anf__d11w :: GHC.Word.Word32
> |                [LclId]
> |                lq_anf__d11w = GHC.Word.W32# ds_d11o } in
> |              (# ds_d11p, lq_anf__d11w #)
> |              }
> |              } } in
> |        GHC.Types.IO @ GHC.Word.Word32 lq_anf__d11x
> |        })
> |
> |
> |  It would appear, that the variable IS in scope (as it is bound by
> | the case-expression just before it is used, but perhaps the binder  is
> | not added to the environment because of its type (# ... , ... #)?
> |  Or is there some other invariant I am breaking?
> |
> |  Can anyone familiar with the scoping invariants of CoreExpr/CoreSyn
> | give me a hint as to what might be happening?
> |
> |  Many thanks in advance!
> |
> |  Ranjit.
> |
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