id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
2368,ASSERT failed! file coreSyn/CorePrep.lhs line 669,batterseapower,igloo,"This is exposed by running the testsuite on a stage2 compiler with -DDEBUG. The tests triggering it are:
 * simplCore/should_compile/simpl014

The affected context is:

{{{
etaExpandRhs :: CoreBndr -> CoreExpr -> UniqSM CoreExpr
etaExpandRhs bndr rhs = do
   	-- Eta expand to match the arity claimed by the binder
	-- Remember, CorePrep must not change arity
	--
	-- Eta expansion might not have happened already, 
	-- because it is done by the simplifier only when 
	-- there at least one lambda already.
	-- 
	-- NB1:we could refrain when the RHS is trivial (which can happen
	--     for exported things).  This would reduce the amount of code
	--     generated (a little) and make things a little words for
	--     code compiled without -O.  The case in point is data constructor
	--     wrappers.
	--
	-- NB2: we have to be careful that the result of etaExpand doesn't
	--    invalidate any of the assumptions that CorePrep is attempting
	--    to establish.  One possible cause is eta expanding inside of
	--    an SCC note - we're now careful in etaExpand to make sure the
	--    SCC is pushed inside any new lambdas that are generated.
	--
	-- NB3: It's important to do eta expansion, and *then* ANF-ising
	--		f = /\a -> g (h 3)	-- h has arity 2
	-- If we ANF first we get
	--		f = /\a -> let s = h 3 in g s
	-- and now eta expansion gives
	-- 		f = /\a -> \ y -> (let s = h 3 in g s) y
	-- which is horrible.
	-- Eta expanding first gives
	--		f = /\a -> \y -> let s = h 3 in g s y
	--
    us <- getUniquesM
    let eta_rhs = etaExpand arity us rhs (idType bndr)

    ASSERT2( manifestArity eta_rhs == arity, (ppr bndr <+> ppr arity <+> ppr (exprArity rhs)) 
					      $$ ppr rhs $$ ppr eta_rhs )
	-- Assertion checks that eta expansion was successful
      return eta_rhs
  where
	-- For a GlobalId, take the Arity from the Id.
	-- It was set in CoreTidy and must not change
	-- For all others, just expand at will
    arity | isGlobalId bndr = idArity bndr
	  | otherwise	    = exprArity rhs
}}}

The precise error is:
{{{
ghc-6.9.20080614: panic! (the 'impossible' happened)
  (GHC version 6.9.20080614 for i386-apple-darwin):
	ASSERT failed! file coreSyn/CorePrep.lhs line 669
main:ShouldCompile.runHandler{v r6G} [gid] 3 3
__inline_me ((\ (@ st{tv a73} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d})
                (w{v si9} [lid] :: main:ShouldCompile.M{tc r7}
                                     (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv]))
                (w1{v sia} [lid] :: main:ShouldCompile.IHandler{tc r8}
                                      st{tv a73} [tv])
                (eta{v sj4} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                       ghc-prim:GHC.Prim.RealWorld{(w) tc 31E})
                (eta1{v sjb} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                        ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}) ->
                main:ShouldCompile.$wrunHandler{v r2} [gid]
                  @ st{tv a73} [tv] w1{v sia} [lid] eta1{v sjb} [lid])
             `cast` (ghc-prim:GHC.Prim.trans{(w) tc 34y}
                       (forall st{tv a73} [tv].
                        main:ShouldCompile.M{tc r7}
                          (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                        -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                        -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                             ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                        -> ghc-prim:GHC.Prim.CoUnsafe{(w) tc 34K}
                             (ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                      ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                    base:GHC.Base.(){(w) tc 40} #))
                             (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                  ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                base:GHC.Base.(){(w) tc 40} #))
                       (forall st{tv a73} [tv].
                        main:ShouldCompile.M{tc r7}
                          (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                        -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                        -> ghc-prim:GHC.Prim.sym{(w) tc 34v}
                             ((base:GHC.IOBase.:CoIO{tc reo}) base:GHC.Base.(){(w) tc 40}))
                     :: <pred>forall st{tv a73} [tv].
                              main:ShouldCompile.M{tc r7}
                                (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                              -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                              -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                   ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                   ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                      ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                    base:GHC.Base.(){(w) tc 40} #)
                                ~
                              forall st{tv a73} [tv].
                              main:ShouldCompile.M{tc r7}
                                (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                              -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                              -> <nt>base:GHC.IOBase.IO{tc 32I} base:GHC.Base.(){(w) tc 40}))
__inline_me ((\ (@ st{tv a73} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d})
                (w{v si9} [lid] :: main:ShouldCompile.M{tc r7}
                                     (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv]))
                (w1{v sia} [lid] :: main:ShouldCompile.IHandler{tc r8}
                                      st{tv a73} [tv])
                (eta{v sj4} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                       ghc-prim:GHC.Prim.RealWorld{(w) tc 31E})
                (eta1{v sjb} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                        ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}) ->
                main:ShouldCompile.$wrunHandler{v r2} [gid]
                  @ st{tv a73} [tv] w1{v sia} [lid] eta1{v sjb} [lid])
             `cast` (ghc-prim:GHC.Prim.trans{(w) tc 34y}
                       (forall st{tv a73} [tv].
                        main:ShouldCompile.M{tc r7}
                          (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                        -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                        -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                             ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                        -> ghc-prim:GHC.Prim.CoUnsafe{(w) tc 34K}
                             (ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                      ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                    base:GHC.Base.(){(w) tc 40} #))
                             (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                  ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                base:GHC.Base.(){(w) tc 40} #))
                       (forall st{tv a73} [tv].
                        main:ShouldCompile.M{tc r7}
                          (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                        -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                        -> ghc-prim:GHC.Prim.sym{(w) tc 34v}
                             ((base:GHC.IOBase.:CoIO{tc reo}) base:GHC.Base.(){(w) tc 40}))
                     :: <pred>forall st{tv a73} [tv].
                              main:ShouldCompile.M{tc r7}
                                (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                              -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                              -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                   ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                   ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}
                              -> (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
                                      ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
                                    base:GHC.Base.(){(w) tc 40} #)
                                ~
                              forall st{tv a73} [tv].
                              main:ShouldCompile.M{tc r7}
                                (main:ShouldCompile.IHR{tc r6} st{tv a73} [tv])
                              -> main:ShouldCompile.IHandler{tc r8} st{tv a73} [tv]
                              -> <nt>base:GHC.IOBase.IO{tc 32I} base:GHC.Base.(){(w) tc 40}))
}}}

It appears to occur because the exprArity of the RHS (i.e. the value of arity variable above) is less than its manifest arity.",bug,closed,normal,6.10.2,Compiler,6.9,fixed,,,MacOS X,Unknown/Multiple,,Unknown,simplCore/should_compile/simpl014,,,