1. 14 Dec, 2009 1 commit
    • simonpj@microsoft.com's avatar
      Tidy up computation of result discounts in CoreUnfold · aff23274
      simonpj@microsoft.com authored
      Mostly this patch is a tidy-up, but it did reveal one inconsistency
      that I fixed.  When computing result discounts for case expressions,
      we were *adding* result-discounts for cases on non-arguments, but
      *picking the one for the max-size branch* for arguments. I think you
      could argue the toss, but it seems neater (and the code is nicer)
      to be consistent (ie always add).  See Note [addAltSize result discounts].
      
      The nofib results seem fine
      
              Program           Size    Allocs   Runtime   Elapsed
      --------------------------------------------------------------------------------
                boyer          -0.8%     -4.8%      0.06      0.07
               sphere          -0.7%     -2.5%      0.15      0.16
      --------------------------------------------------------------------------------
                  Min          -0.8%     -4.8%    -19.1%    -24.8%
                  Max          -0.5%     +0.0%     +3.4%   +127.1%
       Geometric Mean          -0.7%     -0.1%     -4.3%     -1.3%
      
      The +127% elapsed is a timing error; I re-ran the same binary and it's
      unchanged from the baseline.
      aff23274
  2. 11 Dec, 2009 1 commit
    • simonpj@microsoft.com's avatar
      Bottom extraction: float out bottoming expressions to top level · b84ba676
      simonpj@microsoft.com authored
        
      The idea is to float out bottoming expressions to top level,
      abstracting them over any variables they mention, if necessary.  This
      is good because it makes functions smaller (and more likely to
      inline), by keeping error code out of line. 
      
      See Note [Bottoming floats] in SetLevels.
      
      On the way, this fixes the HPC failures for cg059 and friends.
      
      I've been meaning to do this for some time.  See Maessen's paper 1999
      "Bottom extraction: factoring error handling out of functional
      programs" (unpublished I think).
      
      Here are the nofib results:
      
      
              Program           Size    Allocs   Runtime   Elapsed
      --------------------------------------------------------------------------------
                  Min          +0.1%     -7.8%    -14.4%    -32.5%
                  Max          +0.5%     +0.2%     +1.6%    +13.8%
       Geometric Mean          +0.4%     -0.2%     -4.9%     -6.7%
      
      Module sizes
              -1 s.d.                -----           -2.6%
              +1 s.d.                -----           +2.3%
              Average                -----           -0.2%
      
      Compile times:
              -1 s.d.                -----          -11.4%
              +1 s.d.                -----           +4.3%
              Average                -----           -3.8%
      
      I'm think program sizes have crept up because the base library
      is bigger -- module sizes in nofib decrease very slightly.  In turn
      I think that may be because the floating generates a call where
      there was no call before.  Anyway I think it's acceptable.
      
      
      The main changes are:
      
      * SetLevels floats out things that exprBotStrictness_maybe 
        identifies as bottom.  Make sure to pin on the right 
        strictness info to the newly created Ids, so that the
        info ends up in interface files.
      
        Since FloatOut is run twice, we have to be careful that we
        don't treat the function created by the first float-out as
        a candidate for the second; this is what worthFloating does.
      
        See SetLevels Note [Bottoming floats]
                      Note [Bottoming floats: eta expansion]
      
      * Be careful not to inline top-level bottoming functions; this 
        would just undo what the floating transformation achieves.
        See CoreUnfold Note [Do not inline top-level bottoming functions
       
        Ensuring this requires a bit of extra plumbing, but nothing drastic..
      
      * Similarly pre/postInlineUnconditionally should be 
        careful not to re-inline top-level bottoming things!
        See SimplUtils Note [Top-level botomming Ids]
                       Note [Top level and postInlineUnconditionally]
      b84ba676
  3. 02 Dec, 2009 1 commit
    • simonpj@microsoft.com's avatar
      More work on the simplifier's inlining strategies · c86161c5
      simonpj@microsoft.com authored
      This patch collects a small raft of related changes
      
      * Arrange that during 
           (a) rule matching and 
           (b) uses of exprIsConApp_maybe
        we "look through" unfoldings only if they are active
        in the phase. Doing this for (a) required a bit of 
        extra plumbing in the rule matching code, but I think
        it's worth it.
      
        One wrinkle is that even if inlining is off (in the 'gentle'
        phase of simplification) during rule matching we want to
        "look through" things with inlinings.  
         See SimplUtils.activeUnfInRule.
      
        This fixes a long-standing bug, where things that were
        supposed to be (say) NOINLINE, could still be poked into
        via exprIsConApp_maybe. 
      
      * In the above cases, also check for (non-rule) loop breakers; 
        we never look through these.  This fixes a bug that could make
        the simplifier diverge (and did for Roman).  
        Test = simplCore/should_compile/dfun-loop
      
      * Try harder not to choose a DFun as a loop breaker. This is 
        just a small adjustment in the OccurAnal scoring function
      
      * In the scoring function in OccurAnal, look at the InlineRule
        unfolding (if there is one) not the actual RHS, beause the
        former is what'll be inlined.  
      
      * Make the application of any function to dictionary arguments
        CONLIKE.  Thus (f d1 d2) is CONLIKE.  
        Encapsulated in CoreUtils.isExpandableApp
        Reason: see Note [Expandable overloadings] in CoreUtils
      
      * Make case expressions seem slightly smaller in CoreUnfold.
        This reverses an unexpected consequences of charging for
        alternatives.
      
      Refactorings
      ~~~~~~~~~~~~
      * Signficantly refactor the data type for Unfolding (again). 
        The result is much nicer.  
      
      * Add type synonym BasicTypes.CompilerPhase = Int
        and use it
      
      Many of the files touched by this patch are simply knock-on
      consequences of these two refactorings.
      c86161c5
  4. 19 Nov, 2009 3 commits
    • simonpj@microsoft.com's avatar
      Implement -fexpose-all-unfoldings, and fix a non-termination bug · 6a944ae7
      simonpj@microsoft.com authored
      The -fexpose-all-unfoldings flag arranges to put unfoldings for *everything*
      in the interface file.  Of course,  this makes the file a lot bigger, but
      it also makes it complete, and that's great for supercompilation; or indeed
      any whole-program work.
      
      Consequences:
        * Interface files need to record loop-breaker-hood.  (Previously,
          loop breakers were never exposed, so that info wasn't necessary.)
          Hence a small interface file format change. 
      
        * When inlining, must check loop-breaker-hood. (Previously, loop
          breakers didn't have an unfolding at all, so no need to check.)
      
        * Ditto in exprIsConApp_maybe.  Roman actually tripped this bug, 
          because a DFun, which had an unfolding, was also a loop breaker
      
        * TidyPgm.tidyIdInfo must be careful to preserve loop-breaker-hood
      
      So Id.idUnfolding checks for loop-breaker-hood and returns NoUnfolding
      if so. When you want the unfolding regardless of loop-breaker-hood, 
      use Id.realIdUnfolding.
      
      I have not documented the flag yet, because it's experimental.  Nor
      have I tested it thoroughly.  But with the flag off (the normal case)
      everything should work.
      6a944ae7
    • simonpj@microsoft.com's avatar
      Fix a nasty infelicity in the size computation of CoreUnfold · d21c80ea
      simonpj@microsoft.com authored
      The size computation was treating gigantic case expressions as
      practically free, which they really aren't.  It was exacerbated by
      recent decisions to charge 0 for naked variables and constructors, so
      the RHS of the case might look free too.  A good example was 
      Foreign.C.Error.errnoToIOError, which hsa lots of join points
      that were getting inlined way to vigorously, so we had:
      
        *** Simplifier Phase 2 [main]:
            Result size = 2983
        *** Core Linted result of Simplifier mode 2 [main], iteration 1 out of 4:
            Result size = 640327
        *** Core Linted result of Simplifier mode 2 [main], iteration 2 out of 4:
            Result size = 1659
      
      Notice that gigantic intermediate!
      
      This patch adds a small charge for each *alternative*.  Of course,
      that'll also mean that there's a bit less inling of things involving
      case expressions.
      d21c80ea
    • simonpj@microsoft.com's avatar
      Comments and white space only · 8a85f89b
      simonpj@microsoft.com authored
      8a85f89b
  5. 05 Nov, 2009 3 commits
  6. 04 Nov, 2009 1 commit
    • rl@cse.unsw.edu.au's avatar
      Consider variables with conlike unfoldings interesting · c01e472e
      rl@cse.unsw.edu.au authored
      In this expression:
      
        let x = f (g e1) in e2
      
      the simplifier will inline f if it thinks that (g e1) is an interesting
      argument. Until now, this was essentially the case if g was a data constructor
      - we'd inline f in the hope that it will inspect and hence eliminate the
      constructor application. This patch extends this mechanism to CONLIKE
      functions. We consider (g e1) interesting if g is CONLIKE and inline f in the
      hope that this will allow rewrite rules to match.
      c01e472e
  7. 30 Oct, 2009 2 commits
  8. 29 Oct, 2009 1 commit
    • simonpj@microsoft.com's avatar
      The Big INLINE Patch: totally reorganise way that INLINE pragmas work · 72462499
      simonpj@microsoft.com authored
      This patch has been a long time in gestation and has, as a
      result, accumulated some extra bits and bobs that are only
      loosely related.  I separated the bits that are easy to split
      off, but the rest comes as one big patch, I'm afraid.
      
      Note that:
       * It comes together with a patch to the 'base' library
       * Interface file formats change slightly, so you need to
         recompile all libraries
      
      The patch is mainly giant tidy-up, driven in part by the
      particular stresses of the Data Parallel Haskell project. I don't
      expect a big performance win for random programs.  Still, here are the
      nofib results, relative to the state of affairs without the patch
      
              Program           Size    Allocs   Runtime   Elapsed
      --------------------------------------------------------------------------------
                  Min         -12.7%    -14.5%    -17.5%    -17.8%
                  Max          +4.7%    +10.9%     +9.1%     +8.4%
       Geometric Mean          +0.9%     -0.1%     -5.6%     -7.3%
      
      The +10.9% allocation outlier is rewrite, which happens to have a
      very delicate optimisation opportunity involving an interaction
      of CSE and inlining (see nofib/Simon-nofib-notes). The fact that
      the 'before' case found the optimisation is somewhat accidental.
      Runtimes seem to go down, but I never kno wwhether to really trust
      this number.  Binary sizes wobble a bit, but nothing drastic.
      
      
      The Main Ideas are as follows.
      
      InlineRules
      ~~~~~~~~~~~
      When you say 
            {-# INLINE f #-}
            f x = <rhs>
      you intend that calls (f e) are replaced by <rhs>[e/x] So we
      should capture (\x.<rhs>) in the Unfolding of 'f', and never meddle
      with it.  Meanwhile, we can optimise <rhs> to our heart's content,
      leaving the original unfolding intact in Unfolding of 'f'.
      
      So the representation of an Unfolding has changed quite a bit
      (see CoreSyn).  An INLINE pragma gives rise to an InlineRule 
      unfolding.  
      
      Moreover, it's only used when 'f' is applied to the
      specified number of arguments; that is, the number of argument on 
      the LHS of the '=' sign in the original source definition. 
      For example, (.) is now defined in the libraries like this
         {-# INLINE (.) #-}
         (.) f g = \x -> f (g x)
      so that it'll inline when applied to two arguments. If 'x' appeared
      on the left, thus
         (.) f g x = f (g x)
      it'd only inline when applied to three arguments.  This slightly-experimental
      change was requested by Roman, but it seems to make sense.
      
      Other associated changes
      
      * Moving the deck chairs in DsBinds, which processes the INLINE pragmas
      
      * In the old system an INLINE pragma made the RHS look like
         (Note InlineMe <rhs>)
        The Note switched off optimisation in <rhs>.  But it was quite
        fragile in corner cases. The new system is more robust, I believe.
        In any case, the InlineMe note has disappeared 
      
      * The workerInfo of an Id has also been combined into its Unfolding,
        so it's no longer a separate field of the IdInfo.
      
      * Many changes in CoreUnfold, esp in callSiteInline, which is the critical
        function that decides which function to inline.  Lots of comments added!
      
      * exprIsConApp_maybe has moved to CoreUnfold, since it's so strongly
        associated with "does this expression unfold to a constructor application".
        It can now do some limited beta reduction too, which Roman found 
        was an important.
      
      Instance declarations
      ~~~~~~~~~~~~~~~~~~~~~
      It's always been tricky to get the dfuns generated from instance
      declarations to work out well.  This is particularly important in 
      the Data Parallel Haskell project, and I'm now on my fourth attempt,
      more or less.
      
      There is a detailed description in TcInstDcls, particularly in
      Note [How instance declarations are translated].   Roughly speaking
      we now generate a top-level helper function for every method definition
      in an instance declaration, so that the dfun takes a particularly
      stylised form:
        dfun a d1 d2 = MkD (op1 a d1 d2) (op2 a d1 d2) ...etc...
      
      In fact, it's *so* stylised that we never need to unfold a dfun.
      Instead ClassOps have a special rewrite rule that allows us to
      short-cut dictionary selection.  Suppose dfun :: Ord a -> Ord [a]
                                                  d :: Ord a
      Then   
          compare (dfun a d)  -->   compare_list a d 
      in one rewrite, without first inlining the 'compare' selector
      and the body of the dfun.
      
      To support this
      a) ClassOps have a BuiltInRule (see MkId.dictSelRule)
      b) DFuns have a special form of unfolding (CoreSyn.DFunUnfolding)
         which is exploited in CoreUnfold.exprIsConApp_maybe
      
      Implmenting all this required a root-and-branch rework of TcInstDcls
      and bits of TcClassDcl.
      
      
      Default methods
      ~~~~~~~~~~~~~~~
      If you give an INLINE pragma to a default method, it should be just
      as if you'd written out that code in each instance declaration, including
      the INLINE pragma.  I think that it now *is* so.  As a result, library
      code can be simpler; less duplication.
      
      
      The CONLIKE pragma
      ~~~~~~~~~~~~~~~~~~
      In the DPH project, Roman found cases where he had
      
         p n k = let x = replicate n k
                 in ...(f x)...(g x)....
      
         {-# RULE f (replicate x) = f_rep x #-}
      
      Normally the RULE would not fire, because doing so involves 
      (in effect) duplicating the redex (replicate n k).  A new
      experimental modifier to the INLINE pragma, {-# INLINE CONLIKE
      replicate #-}, allows you to tell GHC to be prepared to duplicate
      a call of this function if it allows a RULE to fire.
      
      See Note [CONLIKE pragma] in BasicTypes
      
      
      Join points
      ~~~~~~~~~~~
      See Note [Case binders and join points] in Simplify
      
      
      Other refactoring
      ~~~~~~~~~~~~~~~~~
      * I moved endPass from CoreLint to CoreMonad, with associated jigglings
      
      * Better pretty-printing of Core
      
      * The top-level RULES (ones that are not rules for locally-defined things)
        are now substituted on every simplifier iteration.  I'm not sure how
        we got away without doing this before.  This entails a bit more plumbing
        in SimplCore.
      
      * The necessary stuff to serialise and deserialise the new
        info across interface files.
      
      * Something about bottoming floats in SetLevels
            Note [Bottoming floats]
      
      * substUnfolding has moved from SimplEnv to CoreSubs, where it belongs
      
      
      --------------------------------------------------------------------------------
              Program           Size    Allocs   Runtime   Elapsed
      --------------------------------------------------------------------------------
                 anna          +2.4%     -0.5%      0.16      0.17
                 ansi          +2.6%     -0.1%      0.00      0.00
                 atom          -3.8%     -0.0%     -1.0%     -2.5%
               awards          +3.0%     +0.7%      0.00      0.00
               banner          +3.3%     -0.0%      0.00      0.00
           bernouilli          +2.7%     +0.0%     -4.6%     -6.9%
                boyer          +2.6%     +0.0%      0.06      0.07
               boyer2          +4.4%     +0.2%      0.01      0.01
                 bspt          +3.2%     +9.6%      0.02      0.02
            cacheprof          +1.4%     -1.0%    -12.2%    -13.6%
             calendar          +2.7%     -1.7%      0.00      0.00
             cichelli          +3.7%     -0.0%      0.13      0.14
              circsim          +3.3%     +0.0%     -2.3%     -9.9%
             clausify          +2.7%     +0.0%      0.05      0.06
        comp_lab_zift          +2.6%     -0.3%     -7.2%     -7.9%
             compress          +3.3%     +0.0%     -8.5%     -9.6%
            compress2          +3.6%     +0.0%    -15.1%    -17.8%
          constraints          +2.7%     -0.6%    -10.0%    -10.7%
         cryptarithm1          +4.5%     +0.0%     -4.7%     -5.7%
         cryptarithm2          +4.3%    -14.5%      0.02      0.02
                  cse          +4.4%     -0.0%      0.00      0.00
                eliza          +2.8%     -0.1%      0.00      0.00
                event          +2.6%     -0.0%     -4.9%     -4.4%
               exp3_8          +2.8%     +0.0%     -4.5%     -9.5%
               expert          +2.7%     +0.3%      0.00      0.00
                  fem          -2.0%     +0.6%      0.04      0.04
                  fft          -6.0%     +1.8%      0.05      0.06
                 fft2          -4.8%     +2.7%      0.13      0.14
             fibheaps          +2.6%     -0.6%      0.05      0.05
                 fish          +4.1%     +0.0%      0.03      0.04
                fluid          -2.1%     -0.2%      0.01      0.01
               fulsom          -4.8%     +9.2%     +9.1%     +8.4%
               gamteb          -7.1%     -1.3%      0.10      0.11
                  gcd          +2.7%     +0.0%      0.05      0.05
          gen_regexps          +3.9%     -0.0%      0.00      0.00
               genfft          +2.7%     -0.1%      0.05      0.06
                   gg          -2.7%     -0.1%      0.02      0.02
                 grep          +3.2%     -0.0%      0.00      0.00
               hidden          -0.5%     +0.0%    -11.9%    -13.3%
                  hpg          -3.0%     -1.8%     +0.0%     -2.4%
                  ida          +2.6%     -1.2%      0.17     -9.0%
                infer          +1.7%     -0.8%      0.08      0.09
              integer          +2.5%     -0.0%     -2.6%     -2.2%
            integrate          -5.0%     +0.0%     -1.3%     -2.9%
              knights          +4.3%     -1.5%      0.01      0.01
                 lcss          +2.5%     -0.1%     -7.5%     -9.4%
                 life          +4.2%     +0.0%     -3.1%     -3.3%
                 lift          +2.4%     -3.2%      0.00      0.00
            listcompr          +4.0%     -1.6%      0.16      0.17
             listcopy          +4.0%     -1.4%      0.17      0.18
             maillist          +4.1%     +0.1%      0.09      0.14
               mandel          +2.9%     +0.0%      0.11      0.12
              mandel2          +4.7%     +0.0%      0.01      0.01
              minimax          +3.8%     -0.0%      0.00      0.00
              mkhprog          +3.2%     -4.2%      0.00      0.00
           multiplier          +2.5%     -0.4%     +0.7%     -1.3%
             nucleic2          -9.3%     +0.0%      0.10      0.10
                 para          +2.9%     +0.1%     -0.7%     -1.2%
            paraffins         -10.4%     +0.0%      0.20     -1.9%
               parser          +3.1%     -0.0%      0.05      0.05
              parstof          +1.9%     -0.0%      0.00      0.01
                  pic          -2.8%     -0.8%      0.01      0.02
                power          +2.1%     +0.1%     -8.5%     -9.0%
               pretty         -12.7%     +0.1%      0.00      0.00
               primes          +2.8%     +0.0%      0.11      0.11
            primetest          +2.5%     -0.0%     -2.1%     -3.1%
               prolog          +3.2%     -7.2%      0.00      0.00
               puzzle          +4.1%     +0.0%     -3.5%     -8.0%
               queens          +2.8%     +0.0%      0.03      0.03
              reptile          +2.2%     -2.2%      0.02      0.02
              rewrite          +3.1%    +10.9%      0.03      0.03
                 rfib          -5.2%     +0.2%      0.03      0.03
                  rsa          +2.6%     +0.0%      0.05      0.06
                  scc          +4.6%     +0.4%      0.00      0.00
                sched          +2.7%     +0.1%      0.03      0.03
                  scs          -2.6%     -0.9%     -9.6%    -11.6%
               simple          -4.0%     +0.4%    -14.6%    -14.9%
                solid          -5.6%     -0.6%     -9.3%    -14.3%
              sorting          +3.8%     +0.0%      0.00      0.00
               sphere          -3.6%     +8.5%      0.15      0.16
               symalg          -1.3%     +0.2%      0.03      0.03
                  tak          +2.7%     +0.0%      0.02      0.02
            transform          +2.0%     -2.9%     -8.0%     -8.8%
             treejoin          +3.1%     +0.0%    -17.5%    -17.8%
            typecheck          +2.9%     -0.3%     -4.6%     -6.6%
              veritas          +3.9%     -0.3%      0.00      0.00
                 wang          -6.2%     +0.0%      0.18     -9.8%
            wave4main         -10.3%     +2.6%     -2.1%     -2.3%
         wheel-sieve1          +2.7%     -0.0%     +0.3%     -0.6%
         wheel-sieve2          +2.7%     +0.0%     -3.7%     -7.5%
                 x2n1          -4.1%     +0.1%      0.03      0.04
      --------------------------------------------------------------------------------
                  Min         -12.7%    -14.5%    -17.5%    -17.8%
                  Max          +4.7%    +10.9%     +9.1%     +8.4%
       Geometric Mean          +0.9%     -0.1%     -5.6%     -7.3%
      72462499
  9. 03 Apr, 2009 1 commit
    • simonpj@microsoft.com's avatar
      Adjust inlining heursitics · b71760aa
      simonpj@microsoft.com authored
      This patch is the result of a long series of nofib-based experiments
      to improve GHC's inlining heuristics.
      
      In the end, I'm not sure how worthwhile it all was: I only got a 
         1% decrease in code size
         1% decrease in allocation
      and I don't trust the runtime statistics enough to quote.
      
      Still, in doing all this I tidied up the code quite a bit, and 
      I understand it much better now, so I'm going to commit it.
      
      The main changes are in CoreUnfold, which has lots of new comments.
      Other changes:
      
        - litSize moves from Literal to CoreUnfold
        - interestingArg moves from SimplUtils to CoreUnfold
        - the default unfolding threshold (in StaticFlags) 
            reduces from 8 to 6 (since the size calculation 
            has changed a bit)
      
      b71760aa
  10. 18 Mar, 2009 1 commit
    • simonpj@microsoft.com's avatar
      Add the notion of "constructor-like" Ids for rule-matching · 4bc25e8c
      simonpj@microsoft.com authored
      This patch adds an optional CONLIKE modifier to INLINE/NOINLINE pragmas, 
         {-# NOINLINE CONLIKE [1] f #-}
      The effect is to allow applications of 'f' to be expanded in a potential
      rule match.  Example
        {-# RULE "r/f" forall v. r (f v) = f (v+1) #-}
      
      Consider the term
           let x = f v in ..x...x...(r x)...
      Normally the (r x) would not match the rule, because GHC would be scared
      about duplicating the redex (f v). However the CONLIKE modifier says to
      treat 'f' like a constructor in this situation, and "look through" the
      unfolding for x.  So (r x) fires, yielding (f (v+1)).
      
      The main changes are:
        - Syntax
      
        - The inlinePragInfo field of an IdInfo has a RuleMatchInfo
          component, which records whether or not the Id is CONLIKE.
          Of course, this needs to be serialised in interface files too.
      
        - The occurrence analyser (OccAnal) and simplifier (Simplify) treat
          CONLIKE thing like constructors, by ANF-ing them
      
        - New function coreUtils.exprIsExpandable is like exprIsCheap, but
          additionally spots applications of CONLIKE functions
      
        - A CoreUnfolding has a field that caches exprIsExpandable
      
        - The rule matcher consults this field.  See 
          Note [Expanding variables] in Rules.lhs.
      
      On the way I fixed a lurking variable bug in the way variables are
      expanded.  See Note [Do not expand locally-bound variables] in
      Rule.lhs.  I also did a bit of reformatting and refactoring in
      Rules.lhs, so the module has more lines changed than are really
      different.
      4bc25e8c
  11. 13 Jan, 2009 1 commit
  12. 02 Jan, 2009 1 commit
    • simonpj@microsoft.com's avatar
      Make record selectors into ordinary functions · 9ffadf21
      simonpj@microsoft.com authored
      This biggish patch addresses Trac #2670.  The main effect is to make
      record selectors into ordinary functions, whose unfoldings appear in
      interface files, in contrast to their previous existence as magic
      "implicit Ids".  This means that the usual machinery of optimisation,
      analysis, and inlining applies to them, which was failing before when
      the selector was somewhat complicated.  (Which it can be when
      strictness annotations, unboxing annotations, and GADTs are involved.)
      
      The change involves the following points
      
      * Changes in Var.lhs to the representation of Var.  Now a LocalId can
        have an IdDetails as well as a GlobalId.  In particular, the
        information that an Id is a record selector is kept in the
        IdDetails.  While compiling the current module, the record selector
        *must* be a LocalId, so that it participates properly in compilation
        (free variables etc).
      
        This led me to change the (hidden) representation of Var, so that there
        is now only one constructor for Id, not two.
      
      * The IdDetails is persisted into interface files, so that an
        importing module can see which Ids are records selectors.
      
      * In TcTyClDecls, we generate the record-selector bindings in renamed,
        but not typechecked form.  In this way, we can get the typechecker
        to add all the types and so on, which is jolly helpful especially
        when GADTs or type families are involved.  Just like derived
        instance declarations.
      
        This is the big new chunk of 180 lines of code (much of which is
        commentary).  A call to the same function, mkAuxBinds, is needed in
        TcInstDcls for associated types.
      
      * The typechecker therefore has to pin the correct IdDetails on to 
        the record selector, when it typechecks it.  There was a neat way
        to do this, by adding a new sort of signature to HsBinds.Sig, namely
        IdSig.  This contains an Id (with the correct Name, Type, and IdDetails);
        the type checker uses it as the binder for the final binding.  This
        worked out rather easily.
      
      * Record selectors are no longer "implicit ids", which entails changes to
           IfaceSyn.ifaceDeclSubBndrs
           HscTypes.implicitTyThings
           TidyPgm.getImplicitBinds
        (These three functions must agree.)
      
      * MkId.mkRecordSelectorId is deleted entirely, some 300+ lines (incl
        comments) of very error prone code.  Happy days.
      
      * A TyCon no longer contains the list of record selectors: 
        algTcSelIds is gone
      
      The renamer is unaffected, including the way that import and export of
      record selectors is handled.
      
      Other small things
      
      * IfaceSyn.ifaceDeclSubBndrs had a fragile test for whether a data
        constructor had a wrapper.  I've replaced that with an explicit flag
        in the interface file. More robust I hope.
      
      * I renamed isIdVar to isId, which touched a few otherwise-unrelated files.
      
      9ffadf21
  13. 16 Dec, 2008 1 commit
    • Simon Marlow's avatar
      Rollback INLINE patches · e79c9ce0
      Simon Marlow authored
      rolling back:
      
      Fri Dec  5 16:54:00 GMT 2008  simonpj@microsoft.com
        * Completely new treatment of INLINE pragmas (big patch)
        
        This is a major patch, which changes the way INLINE pragmas work.
        Although lots of files are touched, the net is only +21 lines of
        code -- and I bet that most of those are comments!
        
        HEADS UP: interface file format has changed, so you'll need to
        recompile everything.
        
        There is not much effect on overall performance for nofib, 
        probably because those programs don't make heavy use of INLINE pragmas.
        
                Program           Size    Allocs   Runtime   Elapsed
                    Min         -11.3%     -6.9%     -9.2%     -8.2%
                    Max          -0.1%     +4.6%     +7.5%     +8.9%
         Geometric Mean          -2.2%     -0.2%     -1.0%     -0.8%
        
        (The +4.6% for on allocs is cichelli; see other patch relating to
        -fpass-case-bndr-to-join-points.)
        
        The old INLINE system
        ~~~~~~~~~~~~~~~~~~~~~
        The old system worked like this. A function with an INLINE pragam
        got a right-hand side which looked like
             f = __inline_me__ (\xy. e)
        The __inline_me__ part was an InlineNote, and was treated specially
        in various ways.  Notably, the simplifier didn't inline inside an
        __inline_me__ note.  
        
        As a result, the code for f itself was pretty crappy. That matters
        if you say (map f xs), because then you execute the code for f,
        rather than inlining a copy at the call site.
        
        The new story: InlineRules
        ~~~~~~~~~~~~~~~~~~~~~~~~~~
        The new system removes the InlineMe Note altogether.  Instead there
        is a new constructor InlineRule in CoreSyn.Unfolding.  This is a 
        bit like a RULE, in that it remembers the template to be inlined inside
        the InlineRule.  No simplification or inlining is done on an InlineRule,
        just like RULEs.  
        
        An Id can have an InlineRule *or* a CoreUnfolding (since these are two
        constructors from Unfolding). The simplifier treats them differently:
        
          - An InlineRule is has the substitution applied (like RULES) but 
            is otherwise left undisturbed.
        
          - A CoreUnfolding is updated with the new RHS of the definition,
            on each iteration of the simplifier.
        
        An InlineRule fires regardless of size, but *only* when the function
        is applied to enough arguments.  The "arity" of the rule is specified
        (by the programmer) as the number of args on the LHS of the "=".  So
        it makes a difference whether you say
          	{-# INLINE f #-}
        	f x = \y -> e     or     f x y = e
        This is one of the big new features that InlineRule gives us, and it
        is one that Roman really wanted.
        
        In contrast, a CoreUnfolding can fire when it is applied to fewer
        args than than the function has lambdas, provided the result is small
        enough.
        
        
        Consequential stuff
        ~~~~~~~~~~~~~~~~~~~
        * A 'wrapper' no longer has a WrapperInfo in the IdInfo.  Instead,
          the InlineRule has a field identifying wrappers.
        
        * Of course, IfaceSyn and interface serialisation changes appropriately.
        
        * Making implication constraints inline nicely was a bit fiddly. In
          the end I added a var_inline field to HsBInd.VarBind, which is why
          this patch affects the type checker slightly
        
        * I made some changes to the way in which eta expansion happens in
          CorePrep, mainly to ensure that *arguments* that become let-bound
          are also eta-expanded.  I'm still not too happy with the clarity
          and robustness fo the result.
        
        * We now complain if the programmer gives an INLINE pragma for
          a recursive function (prevsiously we just ignored it).  Reason for
          change: we don't want an InlineRule on a LoopBreaker, because then
          we'd have to check for loop-breaker-hood at occurrence sites (which
          isn't currenlty done).  Some tests need changing as a result.
        
        This patch has been in my tree for quite a while, so there are
        probably some other minor changes.
        
      
          M ./compiler/basicTypes/Id.lhs -11
          M ./compiler/basicTypes/IdInfo.lhs -82
          M ./compiler/basicTypes/MkId.lhs -2 +2
          M ./compiler/coreSyn/CoreFVs.lhs -2 +25
          M ./compiler/coreSyn/CoreLint.lhs -5 +1
          M ./compiler/coreSyn/CorePrep.lhs -59 +53
          M ./compiler/coreSyn/CoreSubst.lhs -22 +31
          M ./compiler/coreSyn/CoreSyn.lhs -66 +92
          M ./compiler/coreSyn/CoreUnfold.lhs -112 +112
          M ./compiler/coreSyn/CoreUtils.lhs -185 +184
          M ./compiler/coreSyn/MkExternalCore.lhs -1
          M ./compiler/coreSyn/PprCore.lhs -4 +40
          M ./compiler/deSugar/DsBinds.lhs -70 +118
          M ./compiler/deSugar/DsForeign.lhs -2 +4
          M ./compiler/deSugar/DsMeta.hs -4 +3
          M ./compiler/hsSyn/HsBinds.lhs -3 +3
          M ./compiler/hsSyn/HsUtils.lhs -2 +7
          M ./compiler/iface/BinIface.hs -11 +25
          M ./compiler/iface/IfaceSyn.lhs -13 +21
          M ./compiler/iface/MkIface.lhs -24 +19
          M ./compiler/iface/TcIface.lhs -29 +23
          M ./compiler/main/TidyPgm.lhs -55 +49
          M ./compiler/parser/ParserCore.y -5 +6
          M ./compiler/simplCore/CSE.lhs -2 +1
          M ./compiler/simplCore/FloatIn.lhs -6 +1
          M ./compiler/simplCore/FloatOut.lhs -23
          M ./compiler/simplCore/OccurAnal.lhs -36 +5
          M ./compiler/simplCore/SetLevels.lhs -59 +54
          M ./compiler/simplCore/SimplCore.lhs -48 +52
          M ./compiler/simplCore/SimplEnv.lhs -26 +22
          M ./compiler/simplCore/SimplUtils.lhs -28 +4
          M ./compiler/simplCore/Simplify.lhs -91 +109
          M ./compiler/specialise/Specialise.lhs -15 +18
          M ./compiler/stranal/WorkWrap.lhs -14 +11
          M ./compiler/stranal/WwLib.lhs -2 +2
          M ./compiler/typecheck/Inst.lhs -1 +3
          M ./compiler/typecheck/TcBinds.lhs -17 +27
          M ./compiler/typecheck/TcClassDcl.lhs -1 +2
          M ./compiler/typecheck/TcExpr.lhs -4 +6
          M ./compiler/typecheck/TcForeign.lhs -1 +1
          M ./compiler/typecheck/TcGenDeriv.lhs -14 +13
          M ./compiler/typecheck/TcHsSyn.lhs -3 +2
          M ./compiler/typecheck/TcInstDcls.lhs -5 +4
          M ./compiler/typecheck/TcRnDriver.lhs -2 +11
          M ./compiler/typecheck/TcSimplify.lhs -10 +17
          M ./compiler/vectorise/VectType.hs +7
      
      Mon Dec  8 12:43:10 GMT 2008  simonpj@microsoft.com
        * White space only
      
          M ./compiler/simplCore/Simplify.lhs -2
      
      Mon Dec  8 12:48:40 GMT 2008  simonpj@microsoft.com
        * Move simpleOptExpr from CoreUnfold to CoreSubst
      
          M ./compiler/coreSyn/CoreSubst.lhs -1 +87
          M ./compiler/coreSyn/CoreUnfold.lhs -72 +1
      
      Mon Dec  8 17:30:18 GMT 2008  simonpj@microsoft.com
        * Use CoreSubst.simpleOptExpr in place of the ad-hoc simpleSubst (reduces code too)
      
          M ./compiler/deSugar/DsBinds.lhs -50 +16
      
      Tue Dec  9 17:03:02 GMT 2008  simonpj@microsoft.com
        * Fix Trac #2861: bogus eta expansion
        
        Urghlhl!  I "tided up" the treatment of the "state hack" in CoreUtils, but
        missed an unexpected interaction with the way that a bottoming function
        simply swallows excess arguments.  There's a long
             Note [State hack and bottoming functions]
        to explain (which accounts for most of the new lines of code).
        
      
          M ./compiler/coreSyn/CoreUtils.lhs -16 +53
      
      Mon Dec 15 10:02:21 GMT 2008  Simon Marlow <marlowsd@gmail.com>
        * Revert CorePrep part of "Completely new treatment of INLINE pragmas..."
        
        The original patch said:
        
        * I made some changes to the way in which eta expansion happens in
          CorePrep, mainly to ensure that *arguments* that become let-bound
          are also eta-expanded.  I'm still not too happy with the clarity
          and robustness fo the result.
          
        Unfortunately this change apparently broke some invariants that were
        relied on elsewhere, and in particular lead to panics when compiling
        with profiling on.
        
        Will re-investigate in the new year.
      
          M ./compiler/coreSyn/CorePrep.lhs -53 +58
          M ./configure.ac -1 +1
      
      Mon Dec 15 12:28:51 GMT 2008  Simon Marlow <marlowsd@gmail.com>
        * revert accidental change to configure.ac
      
          M ./configure.ac -1 +1
      e79c9ce0
  14. 08 Dec, 2008 1 commit
  15. 05 Dec, 2008 1 commit
    • simonpj@microsoft.com's avatar
      Completely new treatment of INLINE pragmas (big patch) · d95ce839
      simonpj@microsoft.com authored
      This is a major patch, which changes the way INLINE pragmas work.
      Although lots of files are touched, the net is only +21 lines of
      code -- and I bet that most of those are comments!
      
      HEADS UP: interface file format has changed, so you'll need to
      recompile everything.
      
      There is not much effect on overall performance for nofib, 
      probably because those programs don't make heavy use of INLINE pragmas.
      
              Program           Size    Allocs   Runtime   Elapsed
                  Min         -11.3%     -6.9%     -9.2%     -8.2%
                  Max          -0.1%     +4.6%     +7.5%     +8.9%
       Geometric Mean          -2.2%     -0.2%     -1.0%     -0.8%
      
      (The +4.6% for on allocs is cichelli; see other patch relating to
      -fpass-case-bndr-to-join-points.)
      
      The old INLINE system
      ~~~~~~~~~~~~~~~~~~~~~
      The old system worked like this. A function with an INLINE pragam
      got a right-hand side which looked like
           f = __inline_me__ (\xy. e)
      The __inline_me__ part was an InlineNote, and was treated specially
      in various ways.  Notably, the simplifier didn't inline inside an
      __inline_me__ note.  
      
      As a result, the code for f itself was pretty crappy. That matters
      if you say (map f xs), because then you execute the code for f,
      rather than inlining a copy at the call site.
      
      The new story: InlineRules
      ~~~~~~~~~~~~~~~~~~~~~~~~~~
      The new system removes the InlineMe Note altogether.  Instead there
      is a new constructor InlineRule in CoreSyn.Unfolding.  This is a 
      bit like a RULE, in that it remembers the template to be inlined inside
      the InlineRule.  No simplification or inlining is done on an InlineRule,
      just like RULEs.  
      
      An Id can have an InlineRule *or* a CoreUnfolding (since these are two
      constructors from Unfolding). The simplifier treats them differently:
      
        - An InlineRule is has the substitution applied (like RULES) but 
          is otherwise left undisturbed.
      
        - A CoreUnfolding is updated with the new RHS of the definition,
          on each iteration of the simplifier.
      
      An InlineRule fires regardless of size, but *only* when the function
      is applied to enough arguments.  The "arity" of the rule is specified
      (by the programmer) as the number of args on the LHS of the "=".  So
      it makes a difference whether you say
        	{-# INLINE f #-}
      	f x = \y -> e     or     f x y = e
      This is one of the big new features that InlineRule gives us, and it
      is one that Roman really wanted.
      
      In contrast, a CoreUnfolding can fire when it is applied to fewer
      args than than the function has lambdas, provided the result is small
      enough.
      
      
      Consequential stuff
      ~~~~~~~~~~~~~~~~~~~
      * A 'wrapper' no longer has a WrapperInfo in the IdInfo.  Instead,
        the InlineRule has a field identifying wrappers.
      
      * Of course, IfaceSyn and interface serialisation changes appropriately.
      
      * Making implication constraints inline nicely was a bit fiddly. In
        the end I added a var_inline field to HsBInd.VarBind, which is why
        this patch affects the type checker slightly
      
      * I made some changes to the way in which eta expansion happens in
        CorePrep, mainly to ensure that *arguments* that become let-bound
        are also eta-expanded.  I'm still not too happy with the clarity
        and robustness fo the result.
      
      * We now complain if the programmer gives an INLINE pragma for
        a recursive function (prevsiously we just ignored it).  Reason for
        change: we don't want an InlineRule on a LoopBreaker, because then
        we'd have to check for loop-breaker-hood at occurrence sites (which
        isn't currenlty done).  Some tests need changing as a result.
      
      This patch has been in my tree for quite a while, so there are
      probably some other minor changes.
      d95ce839
  16. 28 Oct, 2008 1 commit
    • simonpj@microsoft.com's avatar
      Fix Trac #2720: inlining and casts · c3fe0f36
      simonpj@microsoft.com authored
      The issue here is what happens when we have
      
      	(f |> co) x
      
      where f is itself marked INLINE.  We want callSiteInline to "see" 
      the fact that the function is applied, and hence have some incentive
      to inline.  I've done this by extending CoreUnfold.CallCtxt with 
      ValAppCtxt.  I think that should catch this case without messing up
      any of the others.
      c3fe0f36
  17. 02 Oct, 2008 1 commit
    • rl@cse.unsw.edu.au's avatar
      Prevent excessive inlining with DPH · 444c6250
      rl@cse.unsw.edu.au authored
      This adds a new flag -finline-if-enough-args which disables inlining for
      partially applied functions. It is automatically set by -Odph. This is a
      temporary hack and should remain undocumented.
      
      MERGE TO 6.10
      444c6250
  18. 14 Sep, 2008 1 commit
  19. 10 Sep, 2008 1 commit
    • simonpj@microsoft.com's avatar
      Fix Trac #2581: inlining of record selectors · 112ad197
      simonpj@microsoft.com authored
      Bryan discovered that a non-trivial record selector (non-trivial in 
      the sense that it has to reconstruct the result value because of
      UNPACK directives) weren't being inlined.  The reason was that the
      unfolding generated by MkId.mRecordSelId was never being optimised
      *at all*, and hence looked big, and hence wasn't inlined.
      
      (The out-of-line version *is* put into the code of the module
      and *is* optimised, which made this bug pretty puzzling.  But the
      unfolding inside the record-selector-Id itself, which is a GlobalId
      and hence does not get its inlining updated like LocalIds, was
      big and fat.)
      
      Solution: I wrote a very simple optimiser, CoreUnfold.simplOptExpr,
      which does enough optimisation to solve this particular problem.
      It's short, simple, and will be useful in other contexts.
      112ad197
  20. 09 Sep, 2008 1 commit
    • simonpj@microsoft.com's avatar
      Important performance wibble to callSiteInline (the n_vals_wanted > 0 thing) · e71d6d1f
      simonpj@microsoft.com authored
      See Note [Inlining in ArgCtxt].  This very small change gives quite a
      big performance win. Just showing the bigger ones:
      
              Program           Size    Allocs   Runtime
      --------------------------------------------------------------------------------
                 anna          -0.7%     -4.3%      0.15
             cichelli          -0.6%     -6.4%      0.15
               fulsom          -0.4%    -18.5%     -8.1%
                  gcd          -0.6%    -12.0%      0.06
              integer          -0.6%    -16.2%     -8.4%
                power          -0.7%    -19.3%     -4.8%
      --------------------------------------------------------------------------------
                  Min          -0.7%    -19.3%    -15.7%
                  Max          -0.1%     +0.1%     +5.7%
       Geometric Mean          -0.6%     -1.9%     -4.3%
      
      The original change was to improve a case that Roman found (see test
      eyeball/inline1) but that seems to work ok now anyway.
      
      e71d6d1f
  21. 12 Apr, 2008 1 commit
  22. 29 Mar, 2008 1 commit
  23. 07 Feb, 2008 1 commit
    • simonpj@microsoft.com's avatar
      Redo inlining patch, plus some tidying up · fa1c8a7e
      simonpj@microsoft.com authored
      This adds back in the patch 
        * UNDO: Be a little keener to inline
      
      It originally broke the compiler because it tickled a Cmm optimisation bug,
      now fixed.  
      
      In revisiting this I have also make inlining a bit cleverer, in response to
      more examples from Roman. In particular
      
        * CoreUnfold.CallCtxt is a data type that tells something about
          the context of a call.  The new feature is that if the context is
          the argument position of a function call, we record both 
      	- whether the function (or some higher up function) has rules
      	- what the argument discount in that position is
          Either of these make functions keener to inline, even if it's
          in a lazy position
      
        * There was conseqential tidying up on the data type of CallCont.
          In particular I got rid of the now-unused LetRhsFlag
      
      
      fa1c8a7e
  24. 01 Feb, 2008 1 commit
    • Simon Marlow's avatar
      UNDO: Be a little keener to inline · 2859b531
      Simon Marlow authored
      This patch caused at least the following test failures:
         1744(normal)
         ghci028(ghci)
         unicode001(normal)
      and additionally made the stage3 build fail.  
      
      A little more validation please!
      
      I didn't find the exact cause of the failure yet, but it appears that
      the Lexer is miscompiled in some strange way.  If any of {Encoding,
      StringBuffer, or Lexer} are compiled without -O, the problem goes
      away.
      2859b531
  25. 25 Jan, 2008 2 commits
  26. 17 Jan, 2008 1 commit
    • Isaac Dupree's avatar
      lots of portability changes (#1405) · 206b4dec
      Isaac Dupree authored
      re-recording to avoid new conflicts was too hard, so I just put it
      all in one big patch :-(  (besides, some of the changes depended on
      each other.)  Here are what the component patches were:
      
      Fri Dec 28 11:02:55 EST 2007  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * document BreakArray better
      
      Fri Dec 28 11:39:22 EST 2007  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * properly ifdef BreakArray for GHCI
      
      Fri Jan  4 13:50:41 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * change ifs on __GLASGOW_HASKELL__ to account for... (#1405)
        for it not being defined. I assume it being undefined implies
        a compiler with relatively modern libraries but without most
        unportable glasgow extensions.
      
      Fri Jan  4 14:21:21 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * MyEither-->EitherString to allow Haskell98 instance
      
      Fri Jan  4 16:13:29 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * re-portabilize Pretty, and corresponding changes
      
      Fri Jan  4 17:19:55 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * Augment FastTypes to be much more complete
      
      Fri Jan  4 20:14:19 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * use FastFunctions, cleanup FastString slightly
      
      Fri Jan  4 21:00:22 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * Massive de-"#", mostly Int# --> FastInt (#1405)
      
      Fri Jan  4 21:02:49 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * miscellaneous unnecessary-extension-removal
      
      Sat Jan  5 19:30:13 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
        * add FastFunctions
      206b4dec
  27. 04 Dec, 2007 1 commit
    • simonpj@microsoft.com's avatar
      Improve inlining for INLINE non-functions · 30c39066
      simonpj@microsoft.com authored
      	
      (No need to merge to 6.8, but no harm if a subsequent patch needs it.)
      
      The proximate cause for this patch is to improve the inlining for INLINE
      things that are not functions; this came up in the NDP project.  See
      Note [Lone variables] in CoreUnfold.
      
      This caused some refactoring that actually made things simpler.  In 
      particular, more of the inlining logic has moved from SimplUtils to 
      CoreUnfold, where it belongs.
      
      30c39066
  28. 04 Sep, 2007 1 commit
  29. 03 Sep, 2007 1 commit
  30. 01 Sep, 2007 1 commit
  31. 09 Feb, 2007 1 commit
    • simonpj@microsoft.com's avatar
      Major improvement to SpecConstr · cac2aca1
      simonpj@microsoft.com authored
      This patch improves the SpecConstr pass, by 
        a) making it work with join points
        b) making it generate specialisations transitively
      
      As part of it, SpecConstr now carries a substitution with it, which
      runs over the whole program as it goes.  This turned out to be 
      a big win; simplified the implementation quite a bit.
      
      I have *disabled* the specialisation on lambdas; it's pretty fragile,
      and sometimes generates more and more specialisations. Something to
      come back to, perhaps.
      
      I rejigged the flag-handling a bit.  Now the specification of passes
      in DynFlags is a bit nicer; see
      	- optLevelFlags top-level data structure
      	- runWhen function
      	- CoreDoPasses constructor
      
      There are now command-line flags
      	-fspec-constr
      	-fliberate-case
      	-fspec-threshold=N
      which do the obvious thing.  -O2 switches on both spec-constr and liberate-case.
      You can use -fno-liberate-case, -fno-spec-constr after -O2 to switch them off again.
      
      The spec-threshold applies to both these transformations; default value 200 for now.
      
      
      
      
      cac2aca1
  32. 11 Oct, 2006 1 commit
    • Simon Marlow's avatar
      Module header tidyup, phase 1 · 49c98d14
      Simon Marlow authored
      This patch is a start on removing import lists and generally tidying
      up the top of each module.  In addition to removing import lists:
      
         - Change DATA.IOREF -> Data.IORef etc.
         - Change List -> Data.List etc.
         - Remove $Id$
         - Update copyrights
         - Re-order imports to put non-GHC imports last
         - Remove some unused and duplicate imports
      49c98d14
  33. 05 Oct, 2006 2 commits
    • simonpj@microsoft.com's avatar
      Remove unused OccInfo (simplification) · b6cc5851
      simonpj@microsoft.com authored
      The substitution used to carry "fragile" OccInfo to call sites via the
      DoneId constructor of SimplEnv.SimplSR.  This was always a tricky thing 
      to do, and for some time I've been removing the need for it.
      
      Now at last I think we can nuke it altogether.  Hooray.
      
      I did a full nonfib run, and got zero perf changes.
      b6cc5851
    • simonpj@microsoft.com's avatar
      Take 2 on the recursive-rule fix · 805edf6e
      simonpj@microsoft.com authored
      This is another attempt to fix the interaction between recursion and
      RULES.  I just had it wrong before!  Now the significance of the
      flag on IAmALoopBreaker is given in BasicTypes
      
        | IAmALoopBreaker	-- Used by the occurrence analyser to mark loop-breakers
      			-- in a group of recursive definitions
      	!RulesOnly	-- True <=> This loop breaker mentions the other binders
      			--	    in its recursive group only in its RULES, not
      			--	    in its rhs
      			--  See OccurAnal Note [RulesOnly]
      805edf6e