Ticket #7159 (closed bug: invalid)
CoreToStg.coreToStgArgs fails when CoreToStg.coreToStg is called
Not much more to say than the title. It said Panic! (the 'impossible' happened), and to report it as a bug.
The file "typescript" in the attached tarball gives the version and all the information from "ghc --info", as well as a demonstration of the failure. The tarball also contains the program and test case that failed.