Profiling a simple scenario:

$ ~/Install/jdk9u20/bin/java -jar dist/nashorn.jar -Dnashorn.typeInfo.disabled=false --class-cache-size=0 --persistent-code-cache=false -scripting --log=time test/script/basic/compile-octane.js -- --iterations 5

...yields a few simple low-hanging fruits, here is one of them. Out of 320 seconds of run, 20 seconds is spent here:

19.750 jdk.nashorn.internal.ir.IdentNode.accept(jdk.nashorn.internal.ir.visitor.NodeVisitor)
19.750 jdk.nashorn.internal.codegen.ApplySpecialization$1.leaveIdentNode(jdk.nashorn.internal.ir.IdentNode)
19.140 java.lang.UnsupportedOperationException.<init>()
19.150 java.lang.RuntimeException.<init>()
19.150 java.lang.Exception.<init>()
19.150 java.lang.Throwable.<init>()
20.290 java.lang.Throwable.fillInStackTrace()

Please throw some different from UOE from ApplySpecialization$1.leaveIdentNode(), the exception with fillInStackTrace() overridden should be best. You may also consider throwing the pre-cached exception from the static field, if that is not messy for the Nashorn code.