[GHC] #7782: flag to run the demand analysis a second time

[GHC]

#7782: flag to run the demand analysis a second time
-----------------------------+----------------------------------------------
Reporter:  nfrisby           |          Owner:                        
    Type:  task              |         Status:  new                   
Priority:  normal            |      Component:  Compiler              
 Version:  7.7               |       Keywords:                        
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple      
 Failure:  None/Unknown      |      Blockedby:                        
Blocking:                    |        Related:  4941, 5302, 6087, 4962
-----------------------------+----------------------------------------------
 There are some tickets documenting runtime bugs that can be cleaned up by
 running the demand analyzer a second time at the end of the pipeline:
 #4941, #5302, #6087. #6070 ? Others?

 Here's the effects on nofib. Run time didn't seem to change as
 drastically.

 {{{
 Allocations

 -------------------------------------------------------------------------------
         Program                O2/O2     late-dmd/O2    late-dmd/late-dmd
 -------------------------------------------------------------------------------
    cryptarithm2             25078168           +0.0%           +8.0%
        nucleic2             98331744           +0.0%           +3.2%

        cichelli             80310632           +0.0%          -22.9%
           fasta            401159024           -9.1%           -9.1%
          fulsom            321427240           +0.0%           -2.6%
    k-nucleotide           4125102928           -0.0%           -4.8%
         knights              2037984           +0.0%           -3.7%
         mandel2              1041840           +0.0%          -21.4%
         parstof              3103208           +0.0%           -1.4%
 reverse-complem            155188304          -12.8%          -12.8%
          simple            226412800           -0.0%           -1.0%
 }}}

 Note that it improves a couple tests significantly just via changes in the
 base libraries.

 For cryptarithm2, see my comments on #4941. This might indicate that #4962
 should be re-opened.

 For nucleic2, in var_most_distant_atom, an inlined let grows numerous
 closures by a significant amount. I'm not sure where to lay the blame for
 this. Note however, that just making nucleic2's data types use strict
 !Float fields changes its allocation -72.4%, so maybe this "bad practice"
 corner case is a small issue.

 The main remaining task beyond the attached patch is to repair the
 treatment of wrapper's strictness signatures in .hi files. Because the
 second demand analysis might change a these signatures, the current
 compaction mechanism that .hi uses results in ill-formed Core. For the
 attached patch, I've just disabled that .hi compaction mechanism, but this
 just needlessly bloats .hi files.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7782>
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