GitLab

--------------------------------------
	Make Template Haskell into the HEAD
	--------------------------------------

This massive commit transfers to the HEAD all the stuff that
Simon and Tim have been doing on Template Haskell.  The
meta-haskell-branch is no more!

WARNING: make sure that you

  * Update your links if you are using link trees.
    Some modules have been added, some have gone away.

  * Do 'make clean' in all library trees.
    The interface file format has changed, and you can
    get strange panics (sadly) if GHC tries to read old interface files:
    e.g.  ghc-5.05: panic! (the `impossible' happened, GHC version 5.05):
	  Binary.get(TyClDecl): ForeignType

  * You need to recompile the rts too; Linker.c has changed


However the libraries are almost unaltered; just a tiny change in
Base, and to the exports in Prelude.


NOTE: so far as TH itself is concerned, expression splices work
fine, but declaration splices are not complete.


		---------------
		The main change
		---------------

The main structural change: renaming and typechecking have to be
interleaved, because we can't rename stuff after a declaration splice
until after we've typechecked the stuff before (and the splice
itself).

* Combine the renamer and typecheker monads into one
	(TcRnMonad, TcRnTypes)
  These two replace TcMonad and RnMonad

* Give them a single 'driver' (TcRnDriver).  This driver
  replaces TcModule.lhs and Rename.lhs

* The haskell-src library package has a module
	Language/Haskell/THSyntax
  which defines the Haskell data type seen by the TH programmer.

* New modules:
	hsSyn/Convert.hs 	converts THSyntax -> HsSyn
	deSugar/DsMeta.hs 	converts HsSyn -> THSyntax

* New module typecheck/TcSplice type-checks Template Haskell splices.

		-------------
		Linking stuff
		-------------

* ByteCodeLink has been split into
	ByteCodeLink	(which links)
	ByteCodeAsm	(which assembles)

* New module ghci/ObjLink is the object-code linker.

* compMan/CmLink is removed entirely (was out of place)
  Ditto CmTypes (which was tiny)

* Linker.c initialises the linker when it is first used (no need to call
  initLinker any more).  Template Haskell makes it harder to know when
  and whether to initialise the linker.


	-------------------------------------
	Gathering the LIE in the type checker
	-------------------------------------

* Instead of explicitly gathering constraints in the LIE
	tcExpr :: RenamedExpr -> TcM (TypecheckedExpr, LIE)
  we now dump the constraints into a mutable varabiable carried
  by the monad, so we get
	tcExpr :: RenamedExpr -> TcM TypecheckedExpr

  Much less clutter in the code, and more efficient too.
  (Originally suggested by Mark Shields.)


		-----------------
		Remove "SysNames"
		-----------------

Because the renamer and the type checker were entirely separate,
we had to carry some rather tiresome implicit binders (or "SysNames")
along inside some of the HsDecl data structures.  They were both
tiresome and fragile.

Now that the typechecker and renamer are more intimately coupled,
we can eliminate SysNames (well, mostly... default methods still
carry something similar).

		-------------
		Clean up HsPat
		-------------

One big clean up is this: instead of having two HsPat types (InPat and
OutPat), they are now combined into one.  This is more consistent with
the way that HsExpr etc is handled; there are some 'Out' constructors
for the type checker output.

So:
	HsPat.InPat	--> HsPat.Pat
	HsPat.OutPat	--> HsPat.Pat
	No 'pat' type parameter in HsExpr, HsBinds, etc

	Constructor patterns are nicer now: they use
		HsPat.HsConDetails
	for the three cases of constructor patterns:
		prefix, infix, and record-bindings

	The *same* data type HsConDetails is used in the type
	declaration of the data type (HsDecls.TyData)

Lots of associated clean-up operations here and there.  Less code.
Everything is wonderful.

PrimRep Cleanup

   - Remove all PrimReps which were just different flavours of
     PtrRep.  Now, everything which is a pointer to a closure of
     some kind is always a PtrRep.

   - Three of the deleted PrimReps, namely ArrayRep, ByteArrayRep,
     and ForeignObj rep, had a subtle reason for their existence:
     the abstract C pretty-printer(!) used them to decide whether
     to apply a shim to an outgoing C-call argument: a ByteArrayRep
     argument would be adjusted to point past the object header,
     for example.

     I've changed this to happen in a much more reasonable and
     obvious way: there are now explict macros in AbsCSyn to do the
     adjustment, and the code generator makes calls to these as
     necessary.  Slightly less hackery is necessary in the NCG as
     a result.

Implement a primitive failsafe mechanism for protecting against
linking inconsistent object files.  The idea is that if object files
which were compiled in the wrong order (non-dependency order) or
compiled in different ways (eg. profiled vs. non-profiled) are linked
together, a link error will result.

This is achieved by adding the module version and the way to the
module init label.  For example, previously the init label for a
module Foo was named

	__stginit_Foo

now it is named

	__stginit_Foo_<version>_<way>

where <version> is the module version of Foo (same as the version in
the interface file), and <way> is the current way (or empty).

We also have to have a way to refer to the old plain init label, for
using as the argument to shutdownHaskell() in a program using foreign
exports.  So the old label now points to a jump instruction which
transfers control to the new init code.

FastString cleanup, stage 1.

The FastString type is no longer a mixture of hashed strings and
literal strings, it contains hashed strings only with O(1) comparison
(except for UnicodeStr, but that will also go away in due course).  To
create a literal instance of FastString, use FSLIT("..").

By far the most common use of the old literal version of FastString
was in the pattern

	  ptext SLIT("...")

this combination still works, although it doesn't go via FastString
any more.  The next stage will be to remove the need to use this
special combination at all, using a RULE.

To convert a FastString into an SDoc, now use 'ftext' instead of
'ptext'.

I've also removed all the FAST_STRING related macros from HsVersions.h
except for SLIT and FSLIT, just use the relevant functions from
FastString instead.

Urk, code generator assumed reversed info tables
in its implementation of dataToTag# - broke a
compiler built unregisterised rather weirdly
(and only, none of the code in testsuite/ nor
nofib/ showed up this bug.)

This commit assumes that unregisterised==
info_tables_not_next_to_code & calls upon
a trusty old PrimOps.h macro to locate the tag
in the info table (the reasons for doing it
this way is explained in AbsCUtils.lhs
comments).

To help the poor sod who has to debug a break
like this sometime in the future, I'm trying to
come up with a repro case smaller than
ghc/compiler/ -- not yet successful.

Anyway, this concludes the fixes to the
unregisterised bits; I hereby claim that it
is now working again.

Clean up the AbsC -> AbsC translation of array operations.

* MachOps MO_ReadOSBI and MO_WriteOSBI, which previously did
  array indexing, are gone.  We translate now just to plain
  memory references and explicit address computations.  This
  has the happy side effect that all MachOps now return exactly
  one result (previously it was 0 or 1), cleaning up various
  bits of code.

  As a result the Abstract C structure now contains an unneccessary
  restriction, which is that the result of a MachOp can only be
  assigned to a temporary.  This made sense when MachOps had variable
  numbers of results (0, 1 or 2, originally), but is no longer needed.
  MachOps applied to args could now be allowed to appear as
  arbitrary nodes in expression trees, but so far they are not.

* Get rid of CAddrMode constructor CMem, since it is a special case of
  CVal with a RegRelative of CIndex.

AbstractC is inconsistent and non-orthogonal.  The StixStmt + StixExpr
combination expresses a large part of what AbstractC does in a cleaner
and simpler way, IMO.

- Implement a small GC optimisation: when a static constructor has
  been determined to have no (indirect) CAF references, we set its
  static link field to a non-zero value (currently 1).  This prevents
  the garbage collector from traversing this closure and transitively
  everything it points to, and thus should speed up GC a little.

- Omit the static link field from static constructors which have no
  pointer fields (i.e. they are CONSTR_NOCAF_STATIC).

- Add the padding words and the static link field for a static
  constructor at (AbsC) code generation time, rather than in the back
  ends.  This eliminates some duplication between PprAbsC and
  AbsCStixGen.

Get rid of multiple-result MachOps (MO_NatS_AddC, MO_NatS_SubC,
MO_NatS_MulC) which implement {add,sub,mul}IntC#.  Supporting gunk
in the NCG disappears as a result.

Instead:

* {add,sub}IntC# are translated out during abstract C simplification,
  turning into the xor-xor-invert-and-shift sequence previously defined
  in PrimOps.h.

* mulIntC# is more difficult to get rid of portably.  Instead we have
  a new single-result PrimOp, mulIntMayOflo, with corresponding MachOp
  MO_NatS_MulMayOflo.  This tells you whether a W x W -> W signed
  multiply might overflow, where W is the word size.  When W=32, is
  implemented by computing a 2W-long result.  When W=64, we use the
  previous approximation.

PrelNum.lhs' implementation of timesInteger changes slightly, to use
the new PrimOp.

Add constructor CBytesPerWord to (the wildly-misnamed) CAddrMode, and
use this in various places to remove word size dependencies in the
C -> C simplification pass.  Tart up the Stix constant folder a bit
so as to be able to fold out the shift/mask literal expressions.

--------------------------------------------
        Translate out PrimOps at the AbstractC level
        --------------------------------------------

This is the first in what might be a series of changes intended
to make GHC less dependent on its C back end.  The main change is
to translate PrimOps into vanilla abstract C inside the compiler,
rather than having to duplicate that work in each code generation
route.  The main changes are:

* A new type, MachOp, in compiler/absCSyn/MachOp.hs.  A MachOp
  is a primitive operation which we can reasonably expect the
  native code generators to implement.  The set is quite small
  and unlikely to change much, if at all.

* Translations from PrimOps to MachOps, at the end of
  absCSyn/AbsCUtils.  This should perhaps be moved to a different
  module, but it is hard to see how to do this without creating
  a circular dep between it and AbsCUtils.

* The x86 insn selector has been updated to track these changes.  The
  sparc insn selector remains to be done.

As a result of this, it is possible to compile much more code via the
NCG than before.  Almost all the Prelude can be compiled with it.
Currently it does not know how to do 64-bit code generation.  Once
this is fixed, the entire Prelude should be compilable that way.

I also took the opportunity to clean up the NCG infrastructure.
The old Stix data type has been split into StixStmt (statements)
and StixExpr (now denoting values only).  This removes a class
of impossible constructions and clarifies the NCG.

Still to do, in no particular order:

* String and literal lifting, currently done in the NCG at the top
  of nativeGen/MachCode, should be done in the AbstractC flattener,
  for the benefit of all targets.

* Further cleaning up of Stix assignments.

* Remove word-size dependency from Abstract C.  (should be easy).

* Translate out MagicIds in the AbsC -> Stix translation, not
  in the Stix constant folder. (!)

Testsuite failures caused by this:

* memo001 - fails (segfaults) for some unknown reason now.
* arith003 - wrong answer in gcdInt boundary cases.
* arith011 - wrong answer for shifts >= word size.
* cg044 - wrong answer for some FP boundary cases.

These should be fixed, but I don't think they are mission-critical for
anyone.

Fix a long-standing bug in the cost attribution of cost-center stacks.
The problem case is this:

	let z = _scc_ "z" f x
	in ... z ...

previously we were attributing the cost of allocating the closure 'z'
to the enclosing cost center stack (CCCS), when it should really be
attributed to "z":CCCS.  The effects are particularly visible with
retainer profiling, because the closure retaining 'f' and 'x' would
show up with the wrong CCS attached.

To fix this, we need a new form of CCS representation internally:
'PushCC CostCentre CostCentreStack' which subsumes (and therefore
replaces) SingletonCCS.  SingletonCCS is now represented by 'PushCC cc
NoCCS'.

The CCS argument to SET_HDR may now be an arbitrary expression, such
as PushCostCentre(CCCS,foo_cc), as may be the argument to CCS_ALLOC().
So we combine SET_HDR and CCS_ALLOC into a single macro, SET_HDR_, to
avoid repeated calls to PushCostCentre().

Updates to the native code generator following the changes to fix the
large block allocation bug, and changes to use the new
function-address cache in the register table to reduce code size.

Also: I changed the pretty-printing machinery for assembly code to use
Pretty rather than Outputable, since we don't make use of the styles
and it should improve performance.  Perhaps the same should be done
for abstract C.

-------------------------------
	Code generation and SRT hygiene
	-------------------------------

This is a big tidy up commit.  I don't think it breaks anything,
but it certainly makes the code clearer (to me).

I'm not certain that you can use it without sucking in my other
big commit... they come from the same tree.


Core-to-STG, live variables and Static Reference Tables (SRTs)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I did a big tidy-up of the live-variable computation in CoreToStg.
The key idea is that the live variables consist of two parts:
	dynamic live vars
	static live vars (CAFs)

These two always travel round together, but they were always
treated separately by the code until now. Now it's a new data type:

type LiveInfo = (StgLiveVars, 	-- Dynamic live variables;
				-- i.e. ones with a nested (non-top-level) binding
		 CafSet)	-- Static live variables;
				-- i.e. top-level variables that are CAFs or refer to them

There's lots of documentation in CoreToStg.

Code generation
~~~~~~~~~~~~~~~
Arising from this, I found that SRT labels were stored in
a LambdaFormInfo during code generation, whereas they *ought*
to be in the ClosureInfo (which in turn contains a LambdaFormInfo).

This led to lots of changes in ClosureInfo, and I took the opportunity
to make it into a labelled record.

Similarly, I made the data type in AbstractC a bit more explicit:

  -- C_SRT is what StgSyn.SRT gets translated to...
  -- we add a label for the table, and expect only the 'offset/length' form

data C_SRT = NoC_SRT
	   | C_SRT CLabel !Int{-offset-} !Int{-length-}

(Previously there were bottoms lying around.)

Removed 32-bit dependencies in the generation and handling of
liveness mask bitmaps.  We now support both 32-bit and 64-bit
machines with identical .hc files.  Support for >64-bit machines
would be easy to add.  Note that old .hc files are incompatible
with the changes made to ghc/include/InfoMacros.h!

-------------------------------------------
	Towards generalising 'foreign' declarations
	-------------------------------------------

This is a first step towards generalising 'foreign' declarations to
handle langauges other than C.  Quite a lot of files are touched,
but nothing has really changed.  Everything should work exactly as
before.

	But please be on your guard for ccall-related bugs.

Main things

Basic data types: ForeignCall.lhs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Remove absCSyn/CallConv.lhs

* Add prelude/ForeignCall.lhs.  This defines the ForeignCall
  type and its variants

* Define ForeignCall.Safety to say whether a call is unsafe
  or not (was just a boolean).  Lots of consequential chuffing.

* Remove all CCall stuff from PrimOp, and put it in ForeignCall


Take CCallOp out of the PrimOp type (where it was always a glitch)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Add IdInfo.FCallId variant to the type IdInfo.GlobalIdDetails,
	along with predicates Id.isFCallId, Id.isFCallId_maybe

* Add StgSyn.StgOp, to sum PrimOp with FCallOp, because it
  *is* useful to sum them together in Stg and AbsC land.  If
  nothing else, it minimises changes.


Also generally rename "CCall" stuff to "FCall" where it's generic
to all foreign calls.

FastInt fixes

Move FAST_INT and FAST_BOOL into their own module FastTypes, replacing
the macro definitions in HsVersions.h with real definitions.  Change
most of the names in the process.

Now we don't get bogus imports of GlaExts all over the place, and
-fwarn-unused-imports is less noisy.

Now Char, Char#, StgChar have 31 bits (physically 32).
"foo"# is still an array of bytes.

CharRep represents 32 bits (on a 64-bit arch too). There is also
Int8Rep, used in those places where bytes were originally meant.
readCharArray, indexCharOffAddr etc. still use bytes. Storable and
{I,M}Array use wide Chars.

In future perhaps all sized integers should be primitive types. Then
some usages of indexing primops scattered through the code could
be changed to then-available Int8 ones, and then Char variants of
primops could be made wide (other usages that handle text should use
conversion that will be provided later).

I/O and _ccall_ arguments assume ISO-8859-1. UTF-8 is internally used
for string literals (only).

Z-encoding is ready for Unicode identifiers.

Ranges of intlike and charlike closures are more easily configurable.

I've probably broken nativeGen/MachCode.lhs:chrCode for Alpha but I
don't know the Alpha assembler to fix it (what is zapnot?). Generally
I'm not sure if I've done the NCG changes right.

This commit breaks the binary compatibility (of course).

TODO:
* is* and to{Lower,Upper} in Char (in progress).
* Libraries for text conversion (in design / experiments),
  to be plugged to I/O and a higher level foreign library.
* PackedString.
* StringBuffer and accepting source in encodings other than ISO-8859-1.

Many fixes to DLLisation. These were previously covered up because code was
leaking into the import libraries for DLLs, so the fact that some symbols
were thought of as local rather than in another DLL wasn't a problem.

The main problems addressed by this commit are:

1. Fixes RTS symbols working properly when DLLised. They didn't before.
2. Uses NULL instead of stg_error_entry, because DLL entry points can't be
   used as static initialisers.
3. PrelGHC.hi-boot changed to be in package RTS, and export of PrelNum and
   PrelErr moved to PrelBase, so that references to primops & the like
   are cross-DLL as they should be.
4. Pass imports around as Modules rather than ModuleNames, so that
   ModuleInitLabels can be checked to see if they're in a DLL or not.

New form of literal: MachLabel, for addresses of labels.  Used by
foreign label instead of MachLitLit now.

Real lit-lits now cause the NCG to panic.

Also: removed CLitLit from AbsCSyn; it was only used in one place for
a purpose it shouldn't have been used for in the first place.

I lied earlier.  _ccall_GC_ should work now.

This utterly gigantic commit is what I've been up to in background
mode in the last couple of months.  Originally the main goal
was to get rid of Con (staturated constant applications)
in the CoreExpr type, but one thing led to another, and I kept
postponing actually committing.   Sorry.

	Simon, 23 March 2000


I've tested it pretty thoroughly, but doubtless things will break.

Here are the highlights

* Con is gone; the CoreExpr type is simpler
* NoRepLits have gone
* Better usage info in interface files => less recompilation
* Result type signatures work
* CCall primop is tidied up
* Constant folding now done by Rules
* Lots of hackery in the simplifier
* Improvements in CPR and strictness analysis

Many bug fixes including

* Sergey's DoCon compiles OK; no loop in the strictness analyser
* Volker Wysk's programs don't crash the CPR analyser

I have not done much on measuring compilation times and binary sizes;
they could have got worse.  I think performance has got significantly
better, though, in most cases.


Removing the Con form of Core expressions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The big thing is that

  For every constructor C there are now *two* Ids:

	C is the constructor's *wrapper*. It evaluates and unboxes arguments
	before calling $wC.  It has a perfectly ordinary top-level defn
	in the module defining the data type.

	$wC is the constructor's *worker*.  It is like a primop that simply
	allocates and builds the constructor value.  Its arguments are the
	actual representation arguments of the constructor.
	Its type may be different to C, because:
		- useless dict args are dropped
		- strict args may be flattened

  For every primop P there is *one* Id, its (curried) Id

  Neither contructor worker Id nor the primop Id have a defminition anywhere.
  Instead they are saturated during the core-to-STG pass, and the code generator
  generates code for them directly. The STG language still has saturated
  primops and constructor applications.

* The Const type disappears, along with Const.lhs.  The literal part
  of Const.lhs reappears as Literal.lhs.  Much tidying up in here,
  to bring all the range checking into this one module.

* I got rid of NoRep literals entirely.  They just seem to be too much trouble.

* Because Con's don't exist any more, the funny C { args } syntax
  disappears from inteface files.


Parsing
~~~~~~~
* Result type signatures now work
	f :: Int -> Int = \x -> x
	-- The Int->Int is the type of f

	g x y :: Int = x+y
	-- The Int is the type of the result of (g x y)


Recompilation checking and make
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* The .hi file for a modules is not touched if it doesn't change.  (It used to
  be touched regardless, forcing a chain of recompilations.)  The penalty for this
  is that we record exported things just as if they were mentioned in the body of
  the module.  And the penalty for that is that we may recompile a module when
  the only things that have changed are the things it is passing on without using.
  But it seems like a good trade.

* -recomp is on by default

Foreign declarations
~~~~~~~~~~~~~~~~~~~~
* If you say
	foreign export zoo :: Int -> IO Int
  then you get a C produre called 'zoo', not 'zzoo' as before.
  I've also added a check that complains if you export (or import) a C
  procedure whose name isn't legal C.


Code generation and labels
~~~~~~~~~~~~~~~~~~~~~~~~~~
* Now that constructor workers and wrappers have distinct names, there's
  no need to have a Foo_static_closure and a Foo_closure for constructor Foo.
  I nuked the entire StaticClosure story.  This has effects in some of
  the RTS headers (i.e. s/static_closure/closure/g)


Rules, constant folding
~~~~~~~~~~~~~~~~~~~~~~~
* Constant folding becomes just another rewrite rule, attached to the Id for the
  PrimOp.   To achieve this, there's a new form of Rule, a BuiltinRule (see CoreSyn.lhs).
  The prelude rules are in prelude/PrelRules.lhs, while simplCore/ConFold.lhs has gone.

* Appending of constant strings now works, using fold/build fusion, plus
  the rewrite rule
	unpack "foo" c (unpack "baz" c n)  =  unpack "foobaz" c n
  Implemented in PrelRules.lhs

* The CCall primop is tidied up quite a bit.  There is now a data type CCall,
  defined in PrimOp, that packages up the info needed for a particular CCall.
  There is a new Id for each new ccall, with an big "occurrence name"
	{__ccall "foo" gc Int# -> Int#}
  In interface files, this is parsed as a single Id, which is what it is, really.

Miscellaneous
~~~~~~~~~~~~~
* There were numerous places where the host compiler's
  minInt/maxInt was being used as the target machine's minInt/maxInt.
  I nuked all of these; everything is localised to inIntRange and inWordRange,
  in Literal.lhs

* Desugaring record updates was broken: it didn't generate correct matches when
  used withe records with fancy unboxing etc.  It now uses matchWrapper.

* Significant tidying up in codeGen/SMRep.lhs

* Add __word, __word64, __int64 terminals to signal the obvious types
  in interface files.  Add the ability to print word values in hex into
  C code.

* PrimOp.lhs is no longer part of a loop.  Remove PrimOp.hi-boot*


Types
~~~~~
* isProductTyCon no longer returns False for recursive products, nor
  for unboxed products; you have to test for these separately.
  There's no reason not to do CPR for recursive product types, for example.
  Ditto splitProductType_maybe.

Simplification
~~~~~~~~~~~~~~~
* New -fno-case-of-case flag for the simplifier.  We use this in the first run
  of the simplifier, where it helps to stop messing up expressions that
  the (subsequent) full laziness pass would otherwise find float out.
  It's much more effective than previous half-baked hacks in inlining.

  Actually, it turned out that there were three places in Simplify.lhs that
  needed to know use this flag.

* Make the float-in pass push duplicatable bindings into the branches of
  a case expression, in the hope that we never have to allocate them.
  (see FloatIn.sepBindsByDropPoint)

* Arrange that top-level bottoming Ids get a NOINLINE pragma
  This reduced gratuitous inlining of error messages.
  But arrange that such things still get w/w'd.

* Arrange that a strict argument position is regarded as an 'interesting'
  context, so that if we see
	foldr k z (g x)
  then we'll be inclined to inline g; this can expose a build.

* There was a missing case in CoreUtils.exprEtaExpandArity that meant
  we were missing some obvious cases for eta expansion
  Also improve the code when handling applications.

* Make record selectors (identifiable by their IdFlavour) into "cheap" operations.
	  [The change is a 2-liner in CoreUtils.exprIsCheap]
  This means that record selection may be inlined into function bodies, which
  greatly improves the arities of overloaded functions.

* Make a cleaner job of inlining "lone variables".  There was some distributed
  cunning, but I've centralised it all now in SimplUtils.analyseCont, which
  analyses the context of a call to decide whether it is "interesting".

* Don't specialise very small functions in Specialise.specDefn
  It's better to inline it.  Rather like the worker/wrapper case.

* Be just a little more aggressive when floating out of let rhss.
  See comments with Simplify.wantToExpose
  A small change with an occasional big effect.

* Make the inline-size computation think that
	case x of I# x -> ...
  is *free*.


CPR analysis
~~~~~~~~~~~~
* Fix what was essentially a bug in CPR analysis.  Consider

	letrec f x = let g y = let ... in f e1
		     in
		     if ... then (a,b) else g x

  g has the CPR property if f does; so when generating the final annotated
  RHS for f, we must use an envt in which f is bound to its final abstract
  value.  This wasn't happening.  Instead, f was given the CPR tag but g
  wasn't; but of course the w/w pass gives rotten results in that case!!
  (Because f's CPR-ness relied on g's.)

  On they way I tidied up the code in CprAnalyse.  It's quite a bit shorter.

  The fact that some data constructors return a constructed product shows
  up in their CPR info (MkId.mkDataConId) not in CprAnalyse.lhs



Strictness analysis and worker/wrapper
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* BIG THING: pass in the demand to StrictAnal.saExpr.  This affects situations
  like
	f (let x = e1 in (x,x))
  where f turns out to have strictness u(SS), say.  In this case we can
  mark x as demanded, and use a case expression for it.

  The situation before is that we didn't "know" that there is the u(SS)
  demand on the argument, so we simply computed that the body of the let
  expression is lazy in x, and marked x as lazily-demanded.  Then even after
  f was w/w'd we got

	let x = e1 in case (x,x) of (a,b) -> $wf a b

  and hence

	let x = e1 in $wf a b

  I found a much more complicated situation in spectral/sphere/Main.shade,
  which improved quite a bit with this change.

* Moved the StrictnessInfo type from IdInfo to Demand.  It's the logical
  place for it, and helps avoid module loops

* Do worker/wrapper for coerces even if the arity is zero.  Thus:
	stdout = coerce Handle (..blurg..)
  ==>
	wibble = (...blurg...)
	stdout = coerce Handle wibble
  This is good because I found places where we were saying
	case coerce t stdout of { MVar a ->
	...
	case coerce t stdout of { MVar b ->
	...
  and the redundant case wasn't getting eliminated because of the coerce.

Clean up the module initialisation stuff a bit, and add support for
module initialisation blocks in the native code generator.

- generalise the per-module initialisation stubs so that we use it
  in normal (non-profiled) code too.  The initialisation stubs are
  now called '__init_<module>' rather than '_reg<module>'.

- Register foreign exported functions as stable pointers in the
  initialisation code for the module.  This fixes the foreign export
  problems reported by several people.

- remove the concept of "module groups" from the profiling subsystem.

- change the profiling semantics slightly; it should be unnecessary
  to use '-caf-all' to get reasonable profiles now.

This commit adds in the current state of our SMP support.  Notably,
this allows the new way 's' to be built, providing support for running
multiple Haskell threads simultaneously on top of any pthreads
implementation, the idea being to take advantage of commodity SMP
boxes.

Don't expect to get much of a speedup yet; due to the excessive
locking required to synchronise access to mutable heap objects, you'll
see a slowdown in most cases, even on a UP machine.  The best I've
seen is a 1.6-1.7 speedup on an example that did no locking (two
optimised nfibs in parallel).

	- new RTS -N flag specifies how many pthreads to start.

	- new driver -smp flag, tells the driver to use way 's'.

	- new compiler -fsmp option (not for user comsumption)
	  tells the compiler not to generate direct jumps to
	  thunk entry code.

	- largely rewritten scheduler

	- _ccall_GC is now done by handing back a "token" to the
	  RTS before executing the ccall; it should now be possible
	  to execute blocking ccalls in the current thread while
	  allowing the RTS to continue running Haskell threads as
	  normal.

	- you can only call thread-safe C libraries from a way 's'
	  build, of course.

Pthread support is still incomplete, and weird things (including
deadlocks) are likely to happen.

To workaround gcc/egcs bugs re: handling of non-toplevel "extern" decls,
lift them out to the top. i.e., extend mechanism by which "typedefs"
are lifted out to the toplevel (for the same reasons) to also encompass
"extern"s.

Note: the default is not to emit an "extern" decl for every _ccall_,
as this runs the chance of (trivially) conflicting with header file
includes. So, to enable, use -optC-femit-extern-decls.

- Implement update-in-place in certain very specialised circumstances
- Clean up abstract C a bit
- Speed up pretty-printing absC a bit.

Support for "unregisterised" builds.  An unregisterised build doesn't
use the assembly mangler, doesn't do tail jumping (uses the
mini-interpreter), and doesn't use global register variables.

Plenty of cleanups and bugfixes in the process.

Add way 'u' to GhcLibWays to get unregisterised libs & RTS.

[ note: not *quite* working fully yet... there's still a bug or two
  lurking ]

- New Wired-in Id: getTag# :: a -> Int#
	for a data type, returns the tag of the constructor.
	for a function, returns a spurious number probably.
	dataToTag# is the name of the underlying primitive which
	pulls out the tag (its argument is assumed to be
	evaluated).

- Generate constructor tables for enumerated types, so we
  can do tagToEnum#.

- Remove hacks in CoreToStg for dataToTag#.

Save a few bytes by ommitting the static link field on closures with
an empty SRT.

Make a few things strict.

Another big commit from Simon.  Actually, the last one
didn't all go into the main trunk; because of a CVS glitch it
ended up in the wrong branch.

So this commit includes:

* Scoped type variables
* Warnings for unused variables should work now (they didn't before)
* Simplifier improvements:
	- Much better treatment of strict arguments
	- Better treatment of bottoming Ids
	- No need for w/w split for fns that are merely strict
	- Fewer iterations needed, I hope
* Less gratuitous renaming in interface files and abs C
* OccName is a separate module, and is an abstract data type

I think the whole Prelude and Exts libraries compile correctly.
Something isn't quite right about typechecking existentials though.

Move 4.01 onto the main trunk.

- added primops for read&writing StablePtrs to ByteArrays, Adds and FOs
- egcs crashes in odd ways when encountering the typedefs we need to
  produce when compiling 'foreign import dynamic's. To workaround the
  problem, kludgily add a CCallTypedef constructor to AbsCSyn.AbstractC
  which the flattener will produce (at the toplevel) when encountering
  CCallOps inside COptStmts.
- augmented PrimOp.CCallOp to carry a unique when it represents a
  'foreign import dynamic' call. The CoreToStg pass ensures that these
  uniques are exactly that. They're used to eventuall generate (unique)
  typedef names.

Added LongRegs to MagicIds

The Great Multi-Parameter Type Classes Merge.

Notes from Simon (abridged):

* Multi-parameter type classes are fully implemented.
* Error messages from the type checker should be noticeably improved
* Warnings for unused bindings (-fwarn-unused-names)
* many other minor bug fixes.

Internally there are the following changes

* Removal of Haskell 1.2 compatibility.
* Dramatic clean-up of the PprStyle stuff.
* The type Type has been substantially changed.
* The dictionary for each class is represented by a new
  data type for that purpose, rather than by a tuple.

imports changed

Don't include nativeGen/ bits if OMIT_NATIVE_CODEGEN is set

imports updated

2.04 changes