IntelliJ IDEA highlights that initial assignment of 'y' is unnecessary.

y = Math.abs(x);

https://github.com/openjdk/jdk/blob/c9f8d0eff706d9ac59179afbb821367da09c9aae/src/java.base/share/classes/java/lang/FdLibm.java#L3008

After removing assignment code is still compiles. So it seems unnecessary.