+-- -Odph is equivalent to
+--
+-- -O2 optimise as much as possible
+-- -fno-method-sharing sharing specialisation defeats fusion
+-- sometimes
+-- -fdicts-cheap always inline dictionaries
+-- -fmax-simplifier-iterations20 this is necessary sometimes
+-- -fno-spec-constr-threshold run SpecConstr even for big loops
+--
+setDPHOpt :: DynFlags -> DynFlags
+setDPHOpt dflags = setOptLevel 2 (dflags { maxSimplIterations = 20
+ , specConstrThreshold = Nothing
+ })
+ `dopt_set` Opt_DictsCheap
+ `dopt_unset` Opt_MethodSharing
+
+
+