[GHC] #12562: GHC panic on rebuild (idInfo r_XsTP)

[GHC]

#12562: GHC panic on rebuild (idInfo r_XsTP)
-------------------------------------+-------------------------------------
           Reporter:  cocreature     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 First of all let me apologize for the terrible testcase. I tried to find a
 smaller one (and am still trying) but haven’t managed to do so. The good
 news is that at least for me it’s reproducible

 === Steps to reproduce ===

 {{{
 git clone 'git at github.com:bscarlet/llvm-general.git' -b llvm-3.8
 cd llvm-general
 cabal new-build llvm-general
 curl -s
 https://gist.githubusercontent.com/cocreature/c6807d7906756a2d58b8fe774141bfef/raw/2b70a8cc1a1aed7a44b418fba04e8df4818c1237/out.patch
 > out.patch
 git apply out.patch
 cabal new-build llvm-general
 }}}

 The patch just adds a newline somewhere to create a rebuild. I’ve seen
 this panic for completely different changes (all in this project) so I
 don’t think the change matters. I’ve also seen this panic with stack,
 cabal new-build and cabal build (using sandboxes).

 === Output ===

 {{{
 In order, the following will be built (use -v for more details):
 llvm-general-3.8.0.0
 Preprocessing library llvm-general-3.8.0.0...
 [84 of 92] Compiling LLVM.General.Internal.Module (
 src/LLVM/General/Internal/Module.hs, /home/moritz/tmp/llvm-general/dist-
 newstyle/build/llvm-general-3.8.0.0/build/LLVM/General/Internal/Module.o )
 [85 of 92] Compiling LLVM.General.Module ( src/LLVM/General/Module.hs,
 /home/moritz/tmp/llvm-general/dist-newstyle/build/llvm-
 general-3.8.0.0/build/LLVM/General/Module.o )
 [LLVM.General.Internal.Module changed]
 [89 of 92] Compiling LLVM.General.Internal.PassManager (
 src/LLVM/General/Internal/PassManager.hs, /home/moritz/tmp/llvm-general
 /dist-newstyle/build/llvm-
 general-3.8.0.0/build/LLVM/General/Internal/PassManager.o ) [TH]
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         idInfo r_XsTP

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 === Comments ===

 In this case this can be resolved by running cabal new-build again.
 However I’ve also had cases where this didn’t fix it and I had to blow
 away dist-newstyle. I haven’t yet managed to find a reproducible testcase
 for the latter. Matthew Pickering mentioned that he encountered this (or a
 similar) bug while building GHC. I tried core-lint but that didn’t help.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562>
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