The following test shows different results with the Interpreter and the C1/C2 compiler.

public class bug_fp32_fp16_conv {
   public static int POS_NAN = 0x7fc00000;
   public static int NEG_NAN = 0xffc00000;

   public static short GOLDEN = Float.floatToFloat16(Float.intBitsToFloat(NEG_NAN) + Float.intBitsToFloat(POS_NAN));

   public static short micro() {
       return Float.floatToFloat16(Float.intBitsToFloat(NEG_NAN) + Float.intBitsToFloat(POS_NAN));
   }

   public static void main(String [] args) {
       short [] res = new short[1024];
       for (int i = 0; i < 10000; i++) {
           for (int j = 0; j < 1024; j++) {
               res[j] = micro();
           }
       }

       for (int i = 0; i < 1024; i++) {
           if (GOLDEN != res[i]) {
               throw new AssertionError("FAIL " + " GOLDEN = " + GOLDEN + " != ACTUAL = " + res[i]);
           }
       }
       System.out.println("PASS");
   }
}

EMR>javac bug_fp32_fp16_conv.java
EMR>java -Xbatch -Xint -cp . bug_fp32_fp16_conv
PASS
EMR>
EMR>
EMR>java -Xbatch -XX:TieredStopAtLevel=3 -cp . bug_fp32_fp16_conv
Exception in thread "main" java.lang.AssertionError: FAIL GOLDEN = 32256 != ACTUAL = -512
        at bug_fp32_fp16_conv.main(bug_fp32_fp16_conv.java:25)

The problem can also be reproduced with JDK-21.