[GHC] #12562: GHC panic on rebuild (idInfo r_XsTP)
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Mon Oct 17 07:42:20 UTC 2016
#12562: GHC panic on rebuild (idInfo r_XsTP)
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Reporter: cocreature | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.0.1
Resolution: | Keywords:
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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Comment (by Simon Peyton Jones <simonpj@…>):
In [changeset:"692c8df03969ee6a0de5158f05907b16689945d0/ghc"
692c8df0/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="692c8df03969ee6a0de5158f05907b16689945d0"
Fix shadowing in mkWwBodies
This bug, exposed by Trac #12562 was very obscure, and has been
lurking for a long time. What happened was that, in the
worker/wrapper split
a tyvar binder for a worker function
accidentally shadowed an in-scope term variable
that was mentioned in the body of the function
It's jolly hard to provoke, so I have not even attempted to make
a test case. There's a Note [Freshen WW arguments] to explain.
Interestingly, fixing the bug (which meant fresher type variables)
revealed a second lurking bug: I'd failed to apply the substitution to
the coercion in the second last case of mkWWArgs, which introduces a
Cast.
}}}
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562#comment:13>
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