ghc panic: RegAlloc.Liveness.computeLivenss

I have some code where ghc consistently panics with

  RegAlloc.Liveness.computeLivenss
    SCCs aren't in reverse dependent order
    bad blockId c1kek

The only reference I can find to that block in the dumped output is here:

     REC
        c1kej:
              movq $block{v c1keo}_info,(%rbp)
              movsd 7(%rbx),%vSSE_s1ivM
              movsd 15(%rbx),%vSSE_s1ivN
              movq 96(%rbp),%rbx
              movsd %vSSE_s1ivN,88(%rbp)
              movsd %vSSE_s1ivM,96(%rbp)
              testq $7,%rbx
              jne _c1keo
              jmp _c1kep
        c1kpo:
              movq $block{v c1kej}_info,(%rbp)
              movq %vI_s1it5,%rbx
              movq $0,120(%rbp)
              testq $7,%rbx
              jne _c1kej
              jmp _c1kek,

There doesn't appear to be any reference to c1kpo either.

Unfortunately I don't yet have a test case I can provide; I'll keep working on that. Building with -dcore-lint and -dcmm-lint don't show any extra errors.

This is with ghc-7.8.2 using NCG.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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