Eliminate redundant seq's (Trac #8900)
Eliminate redundant seq's (Trac #8900)

This patch makes the simplifier eliminate a redundant seq like
    case x of y -> ...y....
where y is used strictly.  GHC used to do this, but I made it less
aggressive in

   commit 28d9a03253e8fd613667526a170b684f2017d299 (Jan 2013)

However #8900 shows that doing so sometimes loses good
transformations; and the transformation is valid according to "A
semantics for imprecise exceptions".  So I'm restoring the old
behaviour.

See Note [Eliminating redundant seqs]

sdiehl/ghc,shlevy/ghc,snoyberg/ghc,oldmanmike/ghc,tibbe/ghc,christiaanb/ghc,fmthoma/ghc,elieux/ghc,wxwxwwxxx/ghc,lukexi/ghc,christiaanb/ghc,forked-upstream-packages-for-ghcjs/ghc,oldmanmike/ghc,lukexi/ghc,olsner/ghc,siddhanathan/ghc,bitemyapp/ghc,gridaphobe/ghc,ml9951/ghc,vikraman/ghc,forked-upstream-packages-for-ghcjs/ghc,frantisekfarka/ghc-dsi,forked-upstream-packages-for-ghcjs/ghc,ghc-android/ghc,nathyong/microghc-ghc,gridaphobe/ghc,ghc-android/ghc,TomMD/ghc,jstolarek/ghc,elieux/ghc,sdiehl/ghc,forked-upstream-packages-for-ghcjs/ghc,mcschroeder/ghc,nushio3/ghc,mettekou/ghc,ryantm/ghc,vTurbine/ghc,nkaretnikov/ghc,GaloisInc/halvm-ghc,acowley/ghc,lukexi/ghc,mettekou/ghc,gcampax/ghc,tjakway/ghcjvm,siddhanathan/ghc,mcschroeder/ghc,green-haskell/ghc,wxwxwwxxx/ghc,vikraman/ghc,olsner/ghc,spacekitteh/smcghc,forked-upstream-packages-for-ghcjs/ghc,TomMD/ghc,AlexanderPankiv/ghc,jstolarek/ghc,acowley/ghc,nkaretnikov/ghc,sgillespie/ghc,fmthoma/ghc,TomMD/ghc,vTurbine/ghc,vikraman/ghc,tibbe/ghc,green-haskell/ghc,acowley/ghc,anton-dessiatov/ghc,christiaanb/ghc,acowley/ghc,nushio3/ghc,tjakway/ghcjvm,nathyong/microghc-ghc,elieux/ghc,holzensp/ghc,TomMD/ghc,siddhanathan/ghc,da-x/ghc,green-haskell/ghc,sgillespie/ghc,mfine/ghc,christiaanb/ghc,TomMD/ghc,oldmanmike/ghc,holzensp/ghc,mettekou/ghc,anton-dessiatov/ghc,siddhanathan/ghc,snoyberg/ghc,siddhanathan/ghc,mettekou/ghc,ml9951/ghc,jstolarek/ghc,nkaretnikov/ghc,sgillespie/ghc,nkaretnikov/ghc,snoyberg/ghc,holzensp/ghc,christiaanb/ghc,tjakway/ghcjvm,da-x/ghc,ryantm/ghc,spacekitteh/smcghc,mfine/ghc,lukexi/ghc,nathyong/microghc-ghc,AlexanderPankiv/ghc,ghc-android/ghc,ezyang/ghc,nkaretnikov/ghc,AlexanderPankiv/ghc,forked-upstream-packages-for-ghcjs/ghc,gridaphobe/ghc,GaloisInc/halvm-ghc,urbanslug/ghc,nushio3/ghc,GaloisInc/halvm-ghc,mettekou/ghc,anton-dessiatov/ghc,elieux/ghc,ezyang/ghc,sdiehl/ghc,bitemyapp/ghc,ghc-android/ghc,vTurbine/ghc,holzensp/ghc,gcampax/ghc,gcampax/ghc,gcampax/ghc,bitemyapp/ghc,olsner/ghc,snoyberg/ghc,TomMD/ghc,fmthoma/ghc,gridaphobe/ghc,sgillespie/ghc,oldmanmike/ghc,vTurbine/ghc,tibbe/ghc,elieux/ghc,ryantm/ghc,ml9951/ghc,mcschroeder/ghc,nathyong/microghc-ghc,ezyang/ghc,sdiehl/ghc,nkaretnikov/ghc,TomMD/ghc,siddhanathan/ghc,fmthoma/ghc,AlexanderPankiv/ghc,spacekitteh/smcghc,tjakway/ghcjvm,tjakway/ghcjvm,elieux/ghc,ml9951/ghc,frantisekfarka/ghc-dsi,da-x/ghc,urbanslug/ghc,ml9951/ghc,urbanslug/ghc,shlevy/ghc,wxwxwwxxx/ghc,nushio3/ghc,elieux/ghc,christiaanb/ghc,frantisekfarka/ghc-dsi,jstolarek/ghc,fmthoma/ghc,gcampax/ghc,vTurbine/ghc,shlevy/ghc,mfine/ghc,gcampax/ghc,mcschroeder/ghc,shlevy/ghc,sgillespie/ghc,ezyang/ghc,acowley/ghc,da-x/ghc,mcschroeder/ghc,gridaphobe/ghc,snoyberg/ghc,nathyong/microghc-ghc,green-haskell/ghc,sdiehl/ghc,spacekitteh/smcghc,ghc-android/ghc,urbanslug/ghc,bitemyapp/ghc,ml9951/ghc,mfine/ghc,AlexanderPankiv/ghc,oldmanmike/ghc,tibbe/ghc,vikraman/ghc,ryantm/ghc,AlexanderPankiv/ghc,wxwxwwxxx/ghc,ml9951/ghc,mfine/ghc,nkaretnikov/ghc,tibbe/ghc,olsner/ghc,mettekou/ghc,wxwxwwxxx/ghc,GaloisInc/halvm-ghc,urbanslug/ghc,green-haskell/ghc,spacekitteh/smcghc,gcampax/ghc,nathyong/microghc-ghc,snoyberg/ghc,anton-dessiatov/ghc,sgillespie/ghc,oldmanmike/ghc,forked-upstream-packages-for-ghcjs/ghc,olsner/ghc,bitemyapp/ghc,anton-dessiatov/ghc,frantisekfarka/ghc-dsi,shlevy/ghc,sdiehl/ghc,ezyang/ghc,da-x/ghc,mcschroeder/ghc,shlevy/ghc,frantisekfarka/ghc-dsi,mettekou/ghc,christiaanb/ghc,nushio3/ghc,ryantm/ghc,urbanslug/ghc,nushio3/ghc,acowley/ghc,lukexi/ghc,anton-dessiatov/ghc,AlexanderPankiv/ghc,gridaphobe/ghc,GaloisInc/halvm-ghc,wxwxwwxxx/ghc,ghc-android/ghc,vTurbine/ghc,mcschroeder/ghc,nathyong/microghc-ghc,tjakway/ghcjvm,vikraman/ghc,fmthoma/ghc,jstolarek/ghc,anton-dessiatov/ghc,GaloisInc/halvm-ghc,olsner/ghc,mfine/ghc,sdiehl/ghc,ghc-android/ghc,vikraman/ghc,urbanslug/ghc,shlevy/ghc,holzensp/ghc,ezyang/ghc,mfine/ghc,da-x/ghc,vTurbine/ghc,da-x/ghc,snoyberg/ghc,siddhanathan/ghc,olsner/ghc,fmthoma/ghc,tjakway/ghcjvm,vikraman/ghc,GaloisInc/halvm-ghc,nushio3/ghc,ml9951/ghc,ezyang/ghc,wxwxwwxxx/ghc,acowley/ghc,oldmanmike/ghc,sgillespie/ghc,gridaphobe/ghc