Simon Peyton Jones simonpj at microsoft.com
Thu Mar 26 12:48:30 UTC 2015

Iavor, Richard, and others
We always thought it was the Right Thing to generate the runtime representation for a TyCon (used in Typeable type representations) at the definition site of the type, not "on the fly".  I thought I'd do this.
But it was a LOT harder than I expected.  I have spent a ridiculous amount of time on it over the last three weeks.  Sigh.
However (a) it's done, (b) I did a lot of other tidying up (as usual).  So I'm keen to use it.
Would you like to take a look?  It's on branch wip/T9858-typeable-spj.  Relevant log messages below.
Unsurprisingly, some perf/compiler tests get a bit slower (see below).
More surprisingly, there are two perf/should_run tests that get worse

   perf/should_run  T5205 [stat not good enough] (normal)

   perf/should_run  lazy-bs-alloc [stat not good enough] (normal)
This is much more surprising: neither seems to have anything much to do with Typeable.  But I can't investigate before I go on holiday. Would anyone else like to?
It's all up to date wrt HEAD.

commit fcd18c42b6ae2e73a9f4c67dbe6d994b0f8468c8

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Thu Mar 26 11:06:12 2015 +0000

    Remove a redndant 'return'

commit a6200759fd2f3f0e901cb2092e148bf31abb08b4

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Mon Mar 23 14:53:53 2015 +0000

    Error message wibbles

    These are associated with

     - new instance reporting

     - typeable changes in -ddump-simpl output

     - -ddump-types being a bit less verbose

     - some renaming of type variables in debugger output (no idea why this happens)

commit fe510d911b6cf61d6884b8b42d8771d4aea3229f

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Mon Mar 23 14:50:23 2015 +0000

    Generate Typeble info at definition sites

    This patch implements the idea floated in #9858, namely that we should

    generate type-representation information at the data type declaration

    site, rather than when solving a Typeable constraint.

    However, this turned out quite a bit harder than I expected.  I still

    think it's the right thing to do, and it's done now, but it was quite

    a struggle.

    See particularly

      * Note [Grand plan for Typeable] in TcTypeable (which is a new module)

      * Note [The overall promotion story] in DataCon (clarifies existing stuff)

    The most painful bit was that to generate Typeable instances (ie TyConRepName

    bindings) for every TyCon is tricky for types in ghc-prim etc:

      - we need to have enough data types around to *define* a TyCon

      - many of these types are wired-in

    Also, to minimise the code generated for each data type, I wanted to generate

    pure data, not CAFs with unpackCString# stuff floating about.



    Three perf/compiler tests start to allocate quite a bit more. This isn't surprising,

    because they all allocate zillions of data types, with practically no other code,

    esp T1969

       T1969:  GHC allocates 30% more

       T5642:  GHC allocates 14% more

       T9872d: GHC allocates  5% more

    I'm treating this as acceptable.  The payoff comes in Typeable-heavy code.

    Remaining to do


    * I think that "TyCon" and "Module" are over-generic names to use for

      the runtime type representations used in GHC.Typeable.  Better might

      be "TrTyCon" and "TrModule".  But I have not yet done this

    * Add more info the the "TyCon" e.g. source location where it was defined

    * Use the new "Module" type to help with Trac #10068

    * It would be possible to generate TyConRepName (ie Typeable instances)

      selectively rather than all the time.  We'd need to persist the information

      in interface files.  Lacking a motivating reason I have not done this, but

      it would not be difficult.



    As is so often the case, I ended up refactoring more than I intended.

    In particular

    * In TyCon,

          - a type *family* (whether type or data)

            is repesented by a FamilyTyCon

          - a algebraic data type (including data/newtype instances)

            is represented by AlgTyCon

      This wasn't true before; a data family was represented as

      an AlgTyCon.  There are some corresponding changes in IfaceSyn.

      Also get rid of the (unhelpfully named) tyConParent.

    * In TyCon define 'Promoted', isomorphic to Maybe, used when things

      are optionally promoted; and use it elsewhere in GHC.

    * Each TyCon, including promoted TyCons, contains its TyConRepName,

      if it has one.  This is, in effect, the name of its Typeable


    * I added PatSynId, DefMethId, and ReflectionId to the IdInfo.IdDetails

      type.  They are used for debugging only, namely to suppress excessive

      output in -ddump-types.

    * Tidy up the generation of PrelInfo.knownKeyNames

    * Move newImplicitBinder from IfaceEnv to BuildTyCl

    * PrelNames.conName renamed to dcQual for consistency with varQual, tcQual

    * Move mkDefaultMethodIds, mkRecSelBinds from TcTyClsDecls to TcTyDecls

commit 021e6f583a1159b0a3581ab1713d560cadc2bdf7

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Mon Mar 23 14:32:31 2015 +0000

    tcRnDeclsi can use tcRnSrcDecls

    I'm not sure why tcRnDeclsi didn't call tcRnSrcDecls before, but now it

    does.  About 20 lines of code vanish. Hooray.

commit 6473d110ab1aa22a5933e405b59e3f597562ce02

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Fri Mar 20 12:38:42 2015 +0000

    Implement lookupGlobal in TcEnv, and use it

    This localises the (revolting) initTcForLookup function, exposing

    instead the more civilised interface for lookupGlobal

commit 7078a11f50e3af9139dd5ceef032e89047677833

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Fri Mar 20 12:36:22 2015 +0000

   Comments and white space

commit 48512df5751a07fd503f0ba523e5504d09ee258d

Author: Simon Peyton Jones <simonpj at microsoft.com>

Date:   Fri Mar 20 12:27:59 2015 +0000

    Improve the error messages for class instance errors

    See Note [Displaying potential instances].

simonpj at cam-05-unx:~/code/HEAD-5$

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