The bug is found when building conduit-1.2.4.2 package with '-O2 -g' options. The distilled sample looks like that:

{-# LANGUAGE BangPatterns #-}

module RewriteBug (bug) where

bug :: () -> ()
bug () = bug ()
{-# NOINLINE bug #-}

a2 :: ()
a2 = ()
{-# INLINE[1] a2 #-}

{-# RULES "bug a2" [0] bug a2 = () #-}

{-
 Crashes as:
   $ inplace/bin/ghc-stage2 -c -O1 -fforce-recomp RewriteBug.hs -g
    ghc-stage2: panic! (the 'impossible' happened)
      (GHC version 7.11.20150721 for x86_64-unknown-linux):
            Tick in rule ()
-}

My theory of sequence of actions is the following:

• rewrite rule gets read as-is by GHC (gentle phase)
• a2 INLINE changes LHS of rewrite rule (phase 1)
• when time comes to apply 'bug a2' rule GHC detects INLINE problem (phase 0)

In real code it happened across multiple files.

The bug is reproducible in both ghc-7.10.2-rc2 and today's HEAD.