panic! compiling Y combinator with optimizations

The following causes GHC 7.6.3, 7.8.3 and 7.10.1 (at least) to panic when compiling with optimizations:

module Y (y) where

newtype Rec a = Rec { out :: Rec a -> a}

k x = out x x

y f = (f . k) (Rec (f . k))

/tmp ««« ghc -O y.hs -fforce-recomp
[1 of 1] Compiling Y                ( y.hs, y.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.1 for x86_64-unknown-linux):
        Simplifier ticks exhausted
  When trying UnfoldingDone a_sof
  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
  To see detailed counts use -ddump-simpl-stats
  Total ticks: 5282

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Related
Blocking
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Operating system
Architecture

mentioned in issue #8168 (closed)

mentioned in issue #10105 (closed)

changed weight to 5

added Tbug Trac import labels

changed milestone to %⊥

changed weight to 0

Yes indeed: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/bugs.html

Alas I know of no good solution, but happily it doesn't seem to bite much (ever?) in real programs.

Simon

Trac metadata

Trac field	Value
Priority	normal → lowest

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
Related	- → #424 (closed)

added simplifier label

added Plow label