"Simplifier ticks exhausted" compiling mutually recursive modules with GHC 8.

I encountered the "Simplifier ticks exhausted" error when compiling some code generated by hprotoc in GHC 8.0.1. It works with -O0, but fails with -O1. The code compiles successfully with GHC 7.10, but fails with 8.0.1.

Specifying a larger value for 'simpl-tick-factor' doesn't seem to help. The original code was generated by hprotoc, but a much simplified version is attached.

Here is the output with '-ddump-simpl-stats' enabled:

stack build cycle-test --ghc-options -ddump-simpl-stats
cycle-test-0.1.0.0: configure
Configuring cycle-test-0.1.0.0...
cycle-test-0.1.0.0: build
Preprocessing library cycle-test-0.1.0.0...
[1 of 4] Compiling Thing2[boot]     ( src/Thing2.hs-boot, .stack-work/dist/x86_64-osx/Cabal-1.24.0.0/build/Thing2.o-boot )
[2 of 4] Compiling Thing1           ( src/Thing1.hs, .stack-work/dist/x86_64-osx/Cabal-1.24.0.0/build/Thing1.o )
[3 of 4] Compiling Thing2           ( src/Thing2.hs, .stack-work/dist/x86_64-osx/Cabal-1.24.0.0/build/Thing2.o )
[4 of 4] Compiling Box              ( src/Box.hs, .stack-work/dist/x86_64-osx/Cabal-1.24.0.0/build/Box.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-apple-darwin):
	Simplifier ticks exhausted
  When trying UnfoldingDone $fxEqThing2
  To increase the limit, use -fsimpl-tick-factor=N (default 100)
  If you need to do this, let GHC HQ know, and what factor you needed
  Total ticks:     6442
  
  1681 PreInlineUnconditionally
    280 $dEq_a1AB
    280 ds_a1AC
    280 ds_i28z
    280 ds1_i28A
    279 ds_i29a
    279 ds1_i29b
    1 ds_a1As
    1 ds_d28r
    1 ds_d28s
  280 PostInlineUnconditionally 280 ds1_a1AD
  1120 UnfoldingDone
    280 $fEqMaybe_$c==
    280 $fEqThing1_$c==
    279 $fxEqThing2
    279 $fEqThing2_$c==
    1 $c==_a289
    1 not
  279 RuleFired 279 Class op ==
  2241 BetaReduction
    280 a_a1AA
    280 $dEq_a1AB
    280 ds_a1AC
    280 ds1_a1AD
    280 ds_i28z
    280 ds1_i28A
    279 ds_i29a
    279 ds1_i29b
    1 ds_a1As
    1 ds_d28r
    1 ds_d28s
  1 CaseOfCase 1 wild_a1At
  840 KnownBranch 840 wild_a1At

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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