"tagToEnum# (0# ==# 1#) :: Bool" causes CASEFAIL in ghci

rwbarton@adjunction:~/dist/ghc/libraries/base/tests$ echo main | ~/dist/ghc/inplace/bin/ghc-stage2 -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db -rtsopts -fno-ghci-history --interactive -v0 -ignore-dot-ghci tup001d.hs 
<interactive>: internal error: interpretBCO: hit a CASEFAIL
    (GHC version 7.7.20130928 for x86_64_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted

This causes libraries/base test tup001 to fail in the same way with WAY=ghci, because the derived instance of Eq for enumeration-like types of more than 10 constructors does something like x == y = tagToEnum# (getTag x ==# getTag y).

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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CC	hvr
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