The specific (3) warnings, as of time of writing.

jdk/src/jdk.crypto.ec/share/classes/sun/security/ec/XDHPublicKeyImpl.java:80: warning: [lossy-conversions] implicit cast from int to byte in compound assignment is possibly lossy
            u_arr[0] &= mask;
                        ^
jdk/src/jdk.crypto.ec/share/classes/sun/security/ec/ed/EdDSAOperations.java:259: warning: [lossy-conversions] implicit cast from int to byte in compound assignment is possibly lossy
            k[lastByteIndex - 1] |= 0x80;
                                    ^
jdk/src/jdk.crypto.ec/share/classes/sun/security/ec/ed/EdDSAOperations.java:281: warning: [lossy-conversions] implicit cast from int to byte in compound assignment is possibly lossy
        result[result.length - 1] |= (xLSB << 7);
                                     ^