[GHC] #10602: ghc panic: Template variable unbound in rewrite rule when compiling with -O2

[GHC]

#10602: ghc panic: Template variable unbound in rewrite rule when compiling with
-O2
-------------------------------------+-------------------------------------
        Reporter:  pacak             |                   Owner:  bgamari
            Type:  bug               |                  Status:  infoneeded
        Priority:  highest           |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.2-rc2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by thomie):

 Test still fails when `base` is compiled with -O2 (as it is in a perf or
 default/release build).

 {{{
 $ make TEST=T10602 TEST_HC=ghc-7.10.1.20150710
 ...
 =====> T10602(optasm) 92 of 92 [0, 0, 0]
 cd . &&  "/opt/ghc/7.10.2/bin/ghc-7.10.1.20150710" -c T10602.hs -fforce-
 recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db
 -rtsopts -fno-warn-tabs -fno-ghci-history  -O -fasm -O2 >
 T10602.comp.stderr 2>&1
 Compile failed (status 256) errors were:
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.10.1.20150710 for x86_64-unknown-linux):
         Template variable unbound in rewrite rule
   sg_s5zh
   [sc_s5zf, sc_s5zg, sg_s5zh, sg_s5zi]
   [sc_s5zf, sc_s5zg, sg_s5zh, sg_s5zi]
   [: @ a_a3fj sc_s5zf sc_s5zg]
   [: @ a_a3fj sc_s5zb sc_s5zc]
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10602#comment:15>
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