[GHC] #11649: LLVM code generator produces mal-formed LLVM blocks

[GHC]

#11649: LLVM code generator produces mal-formed LLVM blocks
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc2
  (CodeGen)                          |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 This simpler testcase reproduces the issue on ARM,
 {{{#!hs
 {-# LANGUAGE NoImplicitPrelude #-}
 module Test where
 import GHC.Base

 data U1 p = U1

 instance Functor U1 where
     fmap f U1 = U1

 instance Applicative U1 where
     pure _ = U1
     U1 <*> U1 = U1

 instance Alternative U1 where
     empty = U1
     U1 <|> U1 = U1
 }}}

 {{{
 $ inplace/bin/ghc-stage1 Test.hs -O -fforce-recomp
 [1 of 1] Compiling Test             ( Test.hs, Test.o )
 Entry block to function must not have predecessors!
 label %cPR
 /home/ben/ghc/roots/llvm-3.7/bin/opt: /tmp/ghc26431_0/ghc_2.ll: error:
 input module is broken!
 `opt' failed in phase `LLVM Optimiser'. (Exit code: 1)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11649#comment:3>
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