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OccurAnal fails to rediscover join points

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.

Edited by Simon Peyton Jones
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