panic "hscCmmFile: no_mod" with `-v2 and above

Initailly found this on powerpc when debugging #11773, but it also happens on x86_64. The command line:

inplace/bin/ghc-stage1  -static  -H64m -O0  -Wall -v2  -Iincludes \
  -Iincludes/dist -Iincludes/dist-derivedconstants/header \
  -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build \
  -DCOMPILING_RTS -this-unit-id rts -optc-DNOSMP -dcmm-lint -i -irts \
  -irts/dist/build -irts/dist/build/autogen -Irts/dist/build \
  -Irts/dist/build/autogen -O2 -Wnoncanonical-monad-instances -c\
  rts/StgStartup.cmm -o rts/dist/build/StgStartup.o

panics with a message:

ghc-stage1: panic! (the 'impossible' happened)
  (GHC version 8.1.20160402 for powerpc-unknown-linux):
        hscCmmFile: no_mod

The only thing that was added to the command line that is different from the normal build command is the -v2.

This is caused by the code (in compiler/main/HscMain.hs):

    no_mod = panic "hscCmmFile: no_mod"

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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