[GHC] #13221: OccurAnal fails to rediscover join points

[GHC]

#13221: OccurAnal fails to rediscover join points
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        Reporter:  lukemaurer        |                Owner:  lukemaurer
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * priority:  normal => high
 * milestone:  8.4.1 => 8.2.1


@@ -1,2 +1,15 @@
- Not clear why the warning from `OccurAnal` about rediscovering join points
- is ever firing. There's one circumstance I can think of, namely the
+ Ben writes: I've noticed that a new WARN in OccurAnal seems to be quite
+ loud. Validations now produce thousands of lines of the form,
+ {{{
+ WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
+   OccurAnal failed to rediscover join point(s): [$j_shTG]
+ WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
+   OccurAnal failed to rediscover join point(s): [$w$j_sl22]
+ WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
+   OccurAnal failed to rediscover join point(s): [$w$j_sl1W]
+ WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
+   OccurAnal failed to rediscover join point(s): [$w$j_sl1Q]
+ }}}
+
+ It is not clear why the warning from `OccurAnal` about rediscovering join
+ points is ever firing. There's one circumstance I can think of, namely the
@@ -6,2 +19,1 @@
- This isn't hard evidence of something wrong, but it indicates the
- occurrence analyzer may be missing something.
+ This isn't hard evidence of something wrong, but it is deeply suspicious.

New description:

 Ben writes: I've noticed that a new WARN in OccurAnal seems to be quite
 loud. Validations now produce thousands of lines of the form,
 {{{
 WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
   OccurAnal failed to rediscover join point(s): [$j_shTG]
 WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
   OccurAnal failed to rediscover join point(s): [$w$j_sl22]
 WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
   OccurAnal failed to rediscover join point(s): [$w$j_sl1W]
 WARNING: file compiler/simplCore/OccurAnal.hs, line 2633
   OccurAnal failed to rediscover join point(s): [$w$j_sl1Q]
 }}}

 It is not clear why the warning from `OccurAnal` about rediscovering join
 points is ever firing. There's one circumstance I can think of, namely the
 special typing rule allowing jumps from β-redexes, but the warning fires
 repeatedly and β-redexes don't survive the simplifier.

 This isn't hard evidence of something wrong, but it is deeply suspicious.

--

Comment:

 Let's at least investigate before releasing 8.2.  It's extremely fishy.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13221#comment:2>
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