STEP TO REPRODUCE THE PROBLE

class Y extends W {}
class W extends Z {}

class Z {
   static void m(Z z) {
       W w = (W)z;
   }
}

put all the classes in a single file (e.g. Test.java) and then execute the command:
javac Test.java -Xlint:all -XDverboseCompilePolicy

EXPECTED BEHAVIOUR

compilation passes with no warning

ACTUAL BEHAVIOR

the compiler generates a warning:

Test.java:6: warning: [cast] redundant cast to W
       W w = (W)z;
                   ^


It seems like Z's flow analysis is executed *after* Y's erasure - that is when Z itself has already been recursively erased.