[GHC] #13027: The let/app invariant, evaluated-ness, and reallyUnsafePtrEquality#

[GHC]

#13027: The let/app invariant, evaluated-ness, and reallyUnsafePtrEquality#
-------------------------------------+-------------------------------------
        Reporter:  erikd             |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Building GHC      |            Test Case:
  failed                             |  simplCore/should_compile/T13027
      Blocked By:                    |             Blocking:
 Related Tickets:  #11444            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"596dece7866006d699969f775fd97bd306aad85b/ghc" 596dece/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="596dece7866006d699969f775fd97bd306aad85b"
 Record evaluated-ness on workers and wrappers

 Summary:
 This patch is a refinement of the original commit (which
 was reverted):

   commit 6b976eb89fe72827f226506d16d3721ba4e28bab
   Date:   Fri Jan 13 08:56:53 2017 +0000
       Record evaluated-ness on workers and wrappers

 In Trac #13027, comment:20, I noticed that wrappers created after
 demand analysis weren't recording the evaluated-ness of strict
 constructor arguments.  In the ticket that led to a (debatable)
 Lint error but in general the more we know about evaluated-ness
 the better we can optimise.

 This commit adds that info
   * both in the worker (on args)
   * and in the wrapper (on CPR result patterns).
 See Note [Record evaluated-ness in worker/wrapper] in WwLib

 On the way I defined Id.setCaseBndrEvald, and used it to shorten
 the code in a few other places

 Then I added test T13077a to test the CPR aspect of this patch,
 but I found that Lint failed!

 Reason: simpleOptExpr was discarding evaluated-ness info on
 lambda binders because zapFragileIdInfo was discarding an
 Unfolding of (OtherCon _).  But actually that's a robust
 unfolding; there is no need to discard it. To fix this:

 * zapFragileIdInfo only zaps fragile unfoldings

 * Replace isClosedUnfolding with isFragileUnfolding (the latter
   is just the negation of the former, but the nomenclature is
   more consistent).  Better documentation too
        Note [Fragile unfoldings]

 * And Simplify.simplLamBndr can now look at isFragileUnfolding
   to decide whether to use the longer route of simplUnfolding.

 For some reason perf/compiler/T9233 improves in compile-time
 allocation by 10%.  Hooray

 Nofib: essentially no change:

 --------------------------------------------------------------------------------
         Program           Size    Allocs   Runtime   Elapsed  TotalMem
 --------------------------------------------------------------------------------
       cacheprof          +0.0%     -0.3%     +0.9%     +0.4%     +0.0%
 --------------------------------------------------------------------------------
             Min          +0.0%     -0.3%     -2.4%     -2.4%     +0.0%
             Max          +0.0%     +0.0%     +9.8%    +11.4%     +2.4%
  Geometric Mean          +0.0%     -0.0%     +1.1%     +1.0%     +0.0%
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13027#comment:36>
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