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Add constant-folding rules for Float# and Double#

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Fix *two* bugs in formatRealFloat:

The first one is in the Haskell 98 errata, namely that negative
exponents cause an infinite loop in the FFFixed case when no precision
is specified.  eg. `Numeric.showFFloat Nothing 0.02 ""'  I've modified
the code in the errata to properly handle the e == 0 case and to be
slightly more efficient when e > 0.

The second bug is this:

   Prelude> Numeric.showFFloat (Just 0) 0.02 ""
   "0."

* Add {intToInt,wordToWord}{8,16,32}# primops. WARNING: Not implemented
  in ncg for Alpha and Sparc. But -O -fasm is not going to go far anyway
  because of other omissions.

* Have full repertoire of 8,16,32-bit signed and unsigned MachMisc.Size
  values. Again only x86 is fully supported. They are used for
  {index,read,write}{Int,Word}{8,16,32}{OffAddr,Array}# and
  {intToInt,wordToWord}{8,16,32}# primops.

* Have full repertoire of
  {index,read,write}\
  {Char,WideChar,Int,Word,Addr,Float,Double,StablePtr,\
   {Int,Word}{8,16,32,64}}\
  {OffAddr,Array} primops and appropriate instances.
  There were various omissions in various places.

* Add {plus,minus,times}Word# primops to avoid so many Word# <-> Int#
  coercions.

* Rewrite modules PrelWord and PrelInt almost from scratch.

* Simplify fromInteger and realToFrac rules. For each of
  {Int,Word}{8,16,32} there is just a pair of fromInteger rules
  replacing the source or target type with Int or Word. For
  {Int,Word,Int64,Word64} there are rules from any to any.
  Don't include rules which are derivable from inlining anyway,
  e.g. those mentioning Integer. Old explicit coercions are simply
  defined as appropriately typed fromInteger.

* Various old coercion functions marked as deprecated.

* Add instance Bits Int, and
  instance {Show,Num,Real,Enum,Integral,Bounded,Ix,Read,Bits} Word.

* Coercions to sized integer types consistently behave as cutting the
  right amount of bits from the infinite two-complement representation.
  For example (fromIntegral (-1 :: Int8) :: Word64) == maxBound.

* ghc/tests/numeric/should_run/arith011 tests {Int,Word}64 and instance
  Bits Int, and does not try to use overflowing toEnum. arith011.stdout
  is not updated yet because of a problem I will tell about soon.

* Move fromInteger and realToFrac from Prelude to PrelReal.
  Move fromInt from PrelNum to PrelReal and define as fromInteger.
  Define toInt as fromInteger. fromInteger is the place to write
  integer conversion rules for.

* Remove ArrayBase.newInitialisedArray, use default definition of
  newArray instead.

* Bugs fixed:
  - {quot,rem}Word# primop attributes.
  - integerToInt64# for small negative values.
  - {min,max}Bound::Int on 64-bit platforms.
  - iShiftRL64#.
  - Various Bits instances.

* Polishing:
  - Use 'ppr' instead of 'pprPrimOp' and 'text . showPrimRep'.
  - PrimRep.{primRepString,showPrimRepToUser} removed.
  - MachMisc.sizeOf returns Int instead of Integer.
  - Some eta reduction, parens, spacing, and reordering cleanups -
    sorry, couldn't resist.

* Questions:
  - Should iShiftRL and iShiftRL64 be removed? IMHO they should,
    s/iShiftRA/iShiftR/, s/shiftRL/shiftR/. The behaviour on shifting
    is a property of the signedness of the type, not the operation!
    I haven't done this change.

fromInt

Remove fromInt from class Num, though it is retained
as an overloaded operation (with unchanged type) in PrelNum.

There are quite a few consequential changes in the Prelude.
I hope I got them all correct!

Also fix a bug that meant Integer (and its instances)
wasn't getting slurped in by the renamer, even though it
was needed for defaulting.

Remove redundant imports and dead code

- fix copyrights
- remove some unused imports
- comment formatting fixes

ieee-flpt.h is in ../../includes, not ../includes.

More RULES for coercions and truncate.

Removed -fcompiling-prelude flag (now removed from compiler)

Make it so that -fcompiling-prelude applies only
for Prelude modules (i.e. ones called Prelxxx).

I've done this with an {-# OPTIONS #-} line in each
such module (they all has -fno-implicit-prelude anyway)
but a less repetitive approach in the Makefile would
be welcome.

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.

Make Enum for Ratio behave like the Report says

This commit implements a substantial re-organisation of the Prelude
It also fixes a couple of small renamer bugs that were reported recently
	(notably, Sven pointed out that we weren't reporting
	unused imports properly)

My original goal was to get rid of all "orphan" modules (i.e. ones
with instance decls that don't belong either to a tycon or a class
defined in the same module).  This should reduce the number of
interface files that have to be read when compiling small Haskell
modules.

But like most expeditions into the Prelude Swamp, it spiraled out
of control.  The result is quite satisfactory, though.

	GONE AWAY:	PrelCCall, PrelNumExtra

	NEW:		PrelReal, PrelFloat, PrelByteArr, PrelNum.hi-boot

(The extra PrelNum.hi-boot is because of a tiresome thin-air Id, addr2Integer,
which used to be in PrelBase.)

Quite a lot of types have moved from one module to another,
which entails some changes to part of the compiler (PrelInfo, PrelMods) etc,
and there are a few places in the RTS includes and even in the driver
that know about these home modules (alas).

So the rough structure is as follows, in (linearised) dependency order
	[this list now appears in PrelBase.lhs]

PrelGHC		Has no implementation.  It defines built-in things, and
		by importing it you bring them into scope.
		The source file is PrelGHC.hi-boot, which is just
		copied to make PrelGHC.hi

		Classes: CCallable, CReturnable

PrelBase	Classes: Eq, Ord, Functor, Monad
		Types:   list, (), Int, Bool, Ordering, Char, String

PrelTup		Types: tuples, plus instances for PrelBase classes

PrelShow	Class: Show, plus instances for PrelBase/PrelTup types

PrelEnum	Class: Enum,  plus instances for PrelBase/PrelTup types

PrelMaybe	Type: Maybe, plus instances for PrelBase classes

PrelNum		Class: Num, plus instances for Int
		Type:  Integer, plus instances for all classes so far (Eq, Ord, Num, Show)

		Integer is needed here because it is mentioned in the signature
		of 'fromInteger' in class Num

PrelReal	Classes: Real, Integral, Fractional, RealFrac
			 plus instances for Int, Integer
		Types:  Ratio, Rational
			plus intances for classes so far

		Rational is needed here because it is mentioned in the signature
		of 'toRational' in class Real

Ix		Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples

PrelArr		Types: Array, MutableArray, MutableVar

		Does *not* contain any ByteArray stuff (see PrelByteArr)
		Arrays are used by a function in PrelFloat

PrelFloat	Classes: Floating, RealFloat
		Types:   Float, Double, plus instances of all classes so far

		This module contains everything to do with floating point.
		It is a big module (900 lines)
		With a bit of luck, many modules can be compiled without ever reading PrelFloat.hi

PrelByteArr	Types: ByteArray, MutableByteArray

		We want this one to be after PrelFloat, because it defines arrays
		of unboxed floats.


Other Prelude modules are much easier with fewer complex dependencies.

A regrettably-gigantic commit that puts in place what Simon PJ
has been up to for the last month or so, on and off.

The basic idea was to restore unfoldings to *occurrences* of
variables without introducing a space leak.  I wanted to make
sure things improved relative to 4.04, and that proved depressingly
hard.  On the way I discovered several quite serious bugs in the
simplifier.

Here's a summary of what's gone on.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* No commas between for-alls in RULES.  This makes the for-alls have
  the same syntax as in types.

* Arrange that simplConArgs works in one less pass than before.
  This exposed a bug: a bogus call to completeBeta.

* Add a top-level flag in CoreUnfolding, used in callSiteInline

* Extend w/w to use etaExpandArity, so it does eta/coerce expansion

* Implement inline phases.   The meaning of the inline pragmas is
  described in CoreUnfold.lhs.  You can say things like
	{#- INLINE 2 build #-}
  to mean "inline build in phase 2"

* Don't float anything out of an INLINE.
  Don't float things to top level unless they also escape a value lambda.
	[see comments with SetLevels.lvlMFE
  Without at least one of these changes, I found that
	{-# INLINE concat #-}
	concat = __inline (/\a -> foldr (++) [])
  was getting floated to
	concat = __inline( /\a -> lvl a )
	lvl = ...inlined version of foldr...

  Subsequently I found that not floating constants out of an INLINE
  gave really bad code like
	__inline (let x = e in \y -> ...)
  so I now let things float out of INLINE

* Implement the "reverse-mapping" idea for CSE; actually it turned out to be easier
  to implement it in SetLevels, and may benefit full laziness too.

* It's a good idea to inline inRange. Consider

	index (l,h) i = case inRange (l,h) i of
		  	  True ->  l+i
			  False -> error
  inRange itself isn't strict in h, but if it't inlined then 'index'
  *does* become strict in h.  Interesting!

* Big change to the way unfoldings and occurrence info is propagated in the simplifier
  The plan is described in Subst.lhs with the Subst type
  Occurrence info is now in a separate IdInfo field than user pragmas

* I found that
	(coerce T (coerce S (\x.e))) y
  didn't simplify in one round. First we get to
	(\x.e) y
  and only then do the beta. Solution: cancel the coerces in the continuation

* Amazingly, CoreUnfold wasn't counting the cost of a function an application.

* Disable rules in initial simplifier run.  Otherwise full laziness
  doesn't get a chance to lift out a MFE before a rule (e.g. fusion)
  zaps it.  queens is a case in point

* Improve float-out stuff significantly.  The big change is that if we have

	\x -> ... /\a -> ...let p = ..a.. in let q = ...p...

  where p's rhs doesn't x, we abstract a from p, so that we can get p past x.
  (We did that before.)  But we also substitute (p a) for p in q, and then
  we can do the same thing for q.  (We didn't do that, so q got stuck.)
  This is much better.  It involves doing a substitution "as we go" in SetLevels,
  though.

formatRealFloat: Fixed some e==0 confusion in the default case for FFExponent

Drop the use of _ccall_, _casm_ and lit-lits in std/, "foreign import" is
the future.

USE_REPORT_PRELUDE patches from Wolfram Kahl.

Add a few SPECIALISE/INLINE pragmas.

../compiler/msg_prel

wibble

Add two new operations to StgPrimFloat.c:

	__int_encodeFloat
	__int_encodeDouble

for encoding floats/doubles from small integers.  This avoids having
to convert small integers to large ones before an encodeFloat
operation, and fixes the two cases of slowdown in nofib after the
small integer changes.

Also:
	- remove encodeFloat and decodeFloat as primops
	- use foreign import for encode{Float,Double} and
	  the various isNaN etc. ccalls in PrelNumExtra.

Reinstate specialisations for fromIntegral and realToFrac

Fast Integers.  The rep. of Integers is now

	data Integer = S# Int#
		     | J# Int# ByteArray#

- several new primops added for overflow-detecting arithmetic
- negateInteger# removed; it can be done directly
- integer_0, integer_1 etc. removed.
- the compiler now uses S# where it previously used int2Integer.
- the compiler generates small integers for -2^32 .. 2^32-1, instead
  of -2^29 .. -2^29-1.

- PrelST.State datatype moved to LazyST (its only use).
- some library code (in Time.lhs) still needs cleaning up, it depends
  on the Integer rep.

Optimise take a little.

Fix two bugs in formatRealFloat.

H98 Prelude tweaks

Enum instances updated to comply with the behaviour that
Haskell 98 specifies. Notable changes,

  * [a..b] is not the empty list when a>b any longer.
  * [x..] and [x,y..] for Enum Int are now bounded lists.

The first change is might be worth bearing in mind when converting
1.4 code to Haskell 98; functions may have made use of the
old behaviour.

The Fight against needless use of (++) continues.

Changes to make the Prelude comply with Haskell 98.

I claim that this completes GHC's implementation of Haskell 98 (at
least feature-wise, but there's bound to be some bugs lurking..)

Move 4.01 onto the main trunk.

Removed commented-out Haskell-1.2 methods

tweaked Integral.Int.div to cope with overflows

floatToDigits bugfix

Add specialise pragmas (which don't work at the moment, due to an
unidentified bug in the specialiser/simplifier).

- Add NOINLINE pragmas to the unsafe things (unsafe*IO, unsafe*ST, runST etc.)
- Move unsafe function back into the proper modules
- Remove PrelUnsafe*.lhs

- one `quotRem` is faster than separate `quot` and `rem` on Integers.

jtos: leave Integer-land ASAP

Library re-organisation:

All libraries now live under ghc/lib, which has the following structure:

	ghc/lib/std    		--  all prelude files 		(libHS.a)
	ghc/lib/std/cbits

	ghc/lib/exts		-- standard Hugs/GHC extensions (libHSexts.a)
				-- available with '-fglasgow-exts'

	ghc/lib/posix		-- POSIX library                (libHSposix.a)
	ghc/lib/posix/cbits     -- available with '-syslib posix'

	ghc/lib/misc		-- used to be hslibs/ghc	(libHSmisc.a)
	ghc/lib/misc/cbits	-- available with '-syslib misc'

	ghc/lib/concurrent	-- Concurrent libraries		(libHSconc.a)
				-- available with '-concurrent'

Also, several non-standard prelude modules had their names changed to begin
with 'Prel' to reduce namespace pollution.

	Addr      ==> PrelAddr     (Addr interface available in 'exts')
	ArrBase   ==> PrelArr
	CCall     ==> PrelCCall    (CCall interface available in 'exts')
	ConcBase  ==> PrelConc
	GHCerr    ==> PrelErr
	Foreign   ==> PrelForeign  (Foreign interface available in 'exts')
	GHC       ==> PrelGHC
	IOHandle  ==> PrelHandle
	IOBase    ==> PrelIOBase
	GHCmain   ==> PrelMain
	STBase    ==> PrelST
	Unsafe    ==> PrelUnsafe
	UnsafeST  ==> PrelUnsafeST

* removed ghc/Error.{lhs,hi-boot}
* moved contents of Error to GHCerr + adjusted
  import lists of files that use old Error functionality.
* moved seqError from Prelude to GHCerr.