Generate Typeable info at definition sites

This patch implements the idea floated in Trac #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.

Performance
~~~~~~~~~~~
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

 * T3294:   GHC allocates 110% more (filed #11030 to track this)
 * T1969:   GHC allocates 30% more
 * T4801:   GHC allocates 14% more
 * T5321FD: GHC allocates 13% more
 * T783:    GHC allocates 12% more
 * T9675:   GHC allocates 12% more
 * T5642:   GHC allocates 10% more
 * T9961:   GHC allocates 6% more

 * T9203:   Program allocates 54% less

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 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.

Refactoring
~~~~~~~~~~~
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.

 * Cleanup handling of knownKeyNames

 * Each TyCon, including promoted TyCons, contains its TyConRepName, if
   it has one. This is, in effect, the name of its Typeable instance.

Requires update of the haddock submodule.

Differential Revision: https://phabricator.haskell.org/D757

1 files changed, 17 insertions, 2 deletions

diff --git a/compiler/basicTypes/OccName.hs b/compiler/basicTypes/OccName.hs
index 67942df518..e2997096aa 100644
--- a/compiler/basicTypes/OccName.hs
+++ b/compiler/basicTypes/OccName.hs
@@ -72,6 +72,7 @@ module OccName (
         mkPReprTyConOcc,
         mkPADFunOcc,
         mkRecFldSelOcc,
+        mkTyConRepUserOcc, mkTyConRepSysOcc,
 
         -- ** Deconstruction
         occNameFS, occNameString, occNameSpace,
@@ -586,7 +587,8 @@ mkDataConWrapperOcc, mkWorkerOcc,
         mkGenR, mkGen1R, mkGenRCo,
         mkDataTOcc, mkDataCOcc, mkDataConWorkerOcc, mkNewTyCoOcc,
         mkInstTyCoOcc, mkEqPredCoOcc, mkClassOpAuxOcc,
-        mkCon2TagOcc, mkTag2ConOcc, mkMaxTagOcc
+        mkCon2TagOcc, mkTag2ConOcc, mkMaxTagOcc,
+        mkTyConRepUserOcc, mkTyConRepSysOcc
    :: OccName -> OccName
 
 -- These derived variables have a prefix that no Haskell value could have
@@ -609,11 +611,24 @@ mkNewTyCoOcc        = mk_simple_deriv tcName   "NTCo:"  -- Coercion for newtypes
 mkInstTyCoOcc       = mk_simple_deriv tcName   "TFCo:"   -- Coercion for type functions
 mkEqPredCoOcc       = mk_simple_deriv tcName   "$co"
 
--- used in derived instances
+-- Used in derived instances
 mkCon2TagOcc        = mk_simple_deriv varName  "$con2tag_"
 mkTag2ConOcc        = mk_simple_deriv varName  "$tag2con_"
 mkMaxTagOcc         = mk_simple_deriv varName  "$maxtag_"
 
+-- TyConRepName stuff; see Note [Grand plan for Typeable] in TcTypeable
+-- incluing the wrinkle about mkSpecialTyConRepName
+mkTyConRepSysOcc occ = mk_simple_deriv varName prefix occ
+  where
+    prefix | isDataOcc occ = "$tc'"
+           | otherwise     = "$tc"
+
+mkTyConRepUserOcc occ = mk_simple_deriv varName prefix occ
+  where
+    -- *User-writable* prefix, for types in gHC_TYPES
+    prefix | isDataOcc occ = "tc'"
+           | otherwise     = "tc"
+
 -- Generic deriving mechanism
 
 -- | Generate a module-unique name, to be used e.g. while generating new names