[GHC] #13900: Core lint in BuildFlavour=perf-llvm

[GHC]

#13900: Core lint in BuildFlavour=perf-llvm
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 I found the following Core lint failure when compiling
 c9977385dca9536f18374242f713b1048a38dec5 with `BuildFlavour=perf-llvm`,
 {{{
 "inplace/bin/ghc-stage1" -hisuf dyn_hi -osuf  dyn_o -hcsuf dyn_hc -fPIC
 -dynamic  -O -H64m -fllvm -Wall       -hide-all-packages -i -ighc/.
 -ighc/stage2/build -Ighc/stage2/build -ighc/stage2/build/ghc/autogen
 -Ighc/stage2/build/ghc/autogen    -optP-DGHCI -optP-include
 -optPghc/stage2/build/ghc/autogen/cabal_macros.h -package-id base-4.10.0.0
 -package-id array-0.5.1.2 -package-id bytestring-0.10.8.2 -package-id
 directory-1.3.0.2 -package-id process-1.6.0.0 -package-id filepath-1.4.1.2
 -package-id ghc-boot-8.3 -package-id ghc-8.3 -package-id unix-2.7.2.2
 -package-id containers-0.5.10.2 -package-id deepseq-1.4.3.0 -package-id
 ghci-8.3 -package-id haskeline-0.7.4.0 -package-id time-1.8.0.1 -package-
 id transformers-0.5.2.0 -Wall -fno-warn-name-shadowing -XHaskell2010  -O2
 -dcore-lint -dcmm-lint -no-hs-main -threaded -no-user-package-db -rtsopts
 -Wnoncanonical-monad-instances  -odir ghc/stage2/build -hidir
 ghc/stage2/build -stubdir ghc/stage2/build    -c ghc/./GHCi/UI/Tags.hs -o
 ghc/stage2/build/GHCi/UI/Tags.dyn_o
 *** Core Lint errors : in result of Simplifier ***
 <no location info>: warning:
     [RHS of $wgo_XtpE :: [Name]
                          -> Session
                          -> State# RealWorld
                          -> (# State# RealWorld, [[TagInfo]] #)]
     Rule "SC:$wgo0": lhs type: (# State# RealWorld, [[TagInfo]] #)
                      rhs type: (# State# RealWorld, [Maybe TyThing] #)
 *** Offending Program ***
 (see attached)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13900>
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