Crash at -O2: Cannot read from uninitialized register

I did a quick x86_64 compile of all of Hackage today using HEAD, and GHC is crashing when compiling the utf8-string package.

[2 of 7] Compiling Codec.Binary.UTF8.Generic ( Codec/Binary/UTF8/Generic.hs, dist/dist-sandbox-4a6171fb/build/Codec/Binary/UTF8/Generic.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.7.20130915 for x86_64-unknown-linux):
        allocateRegsAndSpill: Cannot read from uninitialized register
    %vI_sa0l

To reproduce using utf8-string:

cabal get utf8-string
cd utf8-string*
ghc -XCPP -fforce-recomp -O2 --make -c Codec/Binary/UTF8/Generic.hs

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
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