[GHC] #12396: Panic when specializing in another module

[GHC]

#12396: Panic when specializing in another module
-------------------------------------+-------------------------------------
           Reporter:  crockeea       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 In the attached example (which requires `criterion` and `deepseq`), when
 compiled with `ghc -O2 -funfolding-use-threshold1000 Main.hs`, I get the
 following error on `Main.hs`:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         StgCmmEnv: variable not found
   $d(%,%)_aaTF
   local binds for:
   $trModule
   $sfool
   $trModule1
   $trModule2
   $wlvl_rgY8
   lvl_rgY9
   lvl1_rgYa
   lvl3_rgYc
   lvl4_rgYd
   lvl5_rgYe
   lvl6_rgYf
   lvl7_rgYg
   lvl8_rgYh
   lvl9_rgYi
   lvl10_rgYj
   lvl11_rgYk
   lvl12_rgYl
   lvl13_rgYm
   lvl14_rgYn
   lvl15_rgYo
   lvl16_rgYp
   lvl17_rgYq
   lvl18_rgYr
   lvl19_rgYs
   lvl20_rgYt
   lvl21_rgYu
   lvl22_rgYv
   lvl23_rgYw
   lvl24_rgYx
   lvl25_rgYy
   lvl26_rgYz
   lvl27_rgYA
   lvl28_rgYB
   lvl29_rgYC
   lvl30_rgYD
   lvl31_rgYE
   lvl32_rgYF
   lvl33_rgYG
   lvl34_rgYH
   lvl35_rgYI
   lvl36_rgYJ
   lvl37_rgYK
   lvl38_rgYL
   lvl39_rgYM
   lvl40_rgYN
   lvl41_rgYO
   lvl42_rgYP
   lvl43_rgYQ
   lvl44_rgYR
   lvl45_rgYS
   lvl46_rgYT
   lvl47_rgYU
   lvl48_rgYV
   lvl49_rgYW
   lvl50_rgYX
   lvl51_rgYY
   lvl52_rgYZ
   lvl53_rgZ0
   lvl54_rgZ1
   lvl55_rgZ2
   lvl56_rgZ3
   lvl57_rgZ4
   lvl58_rgZ5
   lvl59_rgZ6
   lvl60_rgZ7
   lvl61_rgZ8
   lvl62_rgZ9
   lvl63_rgZa
   lvl64_rgZb
   lvl65_rgZc
   lvl66_rgZd
   ww1_rgZe
   ww2_rgZf
   ww3_rgZg
   ww4_rgZh
   pinfo_rgZi
   pinfo1_rgZj
   pinfo2_rgZk
   pinfo3_rgZl
   lvl67_rgZm
   lvl68_rgZn
   lvl69_rgZo
   $wgo12_rgZp
   eta_sh1k
   wild_sh1l
   v_sh1m
   sat_sh1n
 }}}

 I initially found this bug when I added a `SPECIALIZE` pragma for `fool`
 in `Main.hs`. However, I need `funfolding-use-threshold1000` and the
 constraint synonym `UCRTElt` in `Foo.hs` to trigger the bug.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12396>
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