Typeable

Thu Mar 26 13:23:32 UTC 2015

I'll take a look in the next few days. I'm concerned about that performance regression -- we'll need to get a handle on it.

Enjoy your holiday!

Richard

On Mar 26, 2015, at 8:48 AM, Simon Peyton Jones <simonpj at microsoft.com> wrote:

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