[project @ 2000-09-14 13:46:39 by simonpj]

[project @ 2000-09-14 13:46:39 by simonpj]
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	Simon's tuning changes: early Sept 2000
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Library changes
~~~~~~~~~~~~~~~
* Eta expand PrelShow.showLitChar.  It's impossible to compile this well,
  and it makes a big difference to some programs (e.g. gen_regexps)

* Make PrelList.concat into a good producer (in the foldr/build sense)

Flag changes
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* Add -ddump-hi-diffs to print out changes in interface files.  Useful
  when watching what the compiler is doing

* Add -funfolding-update-in-place to enable the experimental optimisation
  that makes the inliner a bit keener to inline if it's in the RHS of
  a thunk that might be updated in place.  Sometimes this is a bad idea
  (one example is in spectral/sphere; see notes in nofib/Simon-nofib-notes)

Tuning things
~~~~~~~~~~~~~
* Fix a bug in SetLevels.lvlMFE.  (change ctxt_lvl to dest_level)
  I don't think this has any performance effect, but it saves making
  a redundant let-binding that is later eliminated.

* Desugar.dsProgram and DsForeign
  Glom together all the bindings into a single Rec.  Previously the
  bindings generated by 'foreign' declarations were not glommed together, but
  this led to an infelicity (i.e. poorer code than necessary) in the modules
  that actually declare Float and Double (explained a bit more in Desugar.dsProgram)

* OccurAnal.shortMeOut and IdInfo.shortableIdInfo
  Don't do the occurrence analyser's shorting out stuff for things which
  have rules.  Comments near IdInfo.shortableIdInfo.
  This is deeply boring, and mainly to do with making rules work well.
  Maybe rules should have phases attached too....

* CprAnalyse.addIdCprInfo
  Be a bit more willing to add CPR information to thunks;
  in particular, if the strictness analyser has just discovered that this
  is a strict let, then the let-to-case transform will happen, and CPR is fine.
  This made a big difference to PrelBase.modInt, which had something like
	modInt = \ x -> let r = ... -> I# v in
			...body strict in r...
  r's RHS isn't a value yet; but modInt returns r in various branches, so
  if r doesn't have the CPR property then neither does modInt

* MkId.mkDataConWrapId
  Arrange that vanilla constructors, like (:) and I#, get unfoldings that are
  just a simple variable $w:, $wI#.  This ensures they'll be inlined even into
  rules etc, which makes matching a bit more reliable.  The downside is that in
  situations like (map (:) xs), we'll end up with (map (\y ys. $w: y ys) xs.
  Which is tiresome but it doesn't happen much.

* SaAbsInt.findStrictness
  Deal with the case where a thing with no arguments is bottom.  This is Good.
  E.g.   module M where { foo = error "help" }
  Suppose we have in another module
	case M.foo of ...
  Then we'd like to do the case-of-error transform, without inlining foo.

Tidying up things
~~~~~~~~~~~~~~~~~
* Reorganised Simplify.completeBinding (again).

* Removed the is_bot field in CoreUnfolding (is_cheap is true if is_bot is!)
  This is just a tidy up

* HsDecls and others
  Remove the NewCon constructor from ConDecl.  It just added code, and nothing else.
  And it led to a bug in MkIface, which though that a newtype decl was always changing!

* IdInfo and many others
  Remove all vestiges of UpdateInfo (hasn't been used for years)