I'm experimenting with making GHC a bit more aggressive about a) dropping case expressions if the result is unused Simplify.rebuildCase, CaseElim equation b) floating case expressions inwards FloatIn.fiExpr, AnnCase In both cases the new behaviour is gotten with a static (debug) flag -faggressive-primops. The extra "aggression" is to allow discarding and floating in for side-effecting operations. See the new, extensive Note [PrimOp can_fail and has_side_effects] and Note [Aggressive PrimOps] in PrimoOp. When discarding a case with unused binders, in the lifted-type case it's definitely ok if the scrutinee terminates; previously we were checking exprOkForSpeculation, which is significantly worse. There's a related change to CoreUtils/CoreArity, but I'll put that in the next commit.